Science.gov

Sample records for absolute antenna calibration

  1. Absolute Antenna Calibration at the US National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Mader, G. L.; Bilich, A. L.

    2012-12-01

    Geodetic GNSS applications routinely demand millimeter precision and extremely high levels of accuracy. To achieve these accuracies, measurement and instrument biases at the centimeter to millimeter level must be understood. One of these biases is the antenna phase center, the apparent point of signal reception for a GNSS antenna. It has been well established that phase center patterns differ between antenna models and manufacturers; additional research suggests that the addition of a radome or the choice of antenna mount can significantly alter those a priori phase center patterns. For the more demanding GNSS positioning applications and especially in cases of mixed-antenna networks, it is all the more important to know antenna phase center variations as a function of both elevation and azimuth in the antenna reference frame and incorporate these models into analysis software. Determination of antenna phase center behavior is known as "antenna calibration". Since 1994, NGS has computed relative antenna calibrations for more than 350 antennas. In recent years, the geodetic community has moved to absolute calibrations - the IGS adopted absolute antenna phase center calibrations in 2006 for use in their orbit and clock products, and NGS's CORS group began using absolute antenna calibration upon the release of the new CORS coordinates in IGS08 epoch 2005.00 and NAD 83(2011,MA11,PA11) epoch 2010.00. Although NGS relative calibrations can be and have been converted to absolute, it is considered best practice to independently measure phase center characteristics in an absolute sense. Consequently, NGS has developed and operates an absolute calibration system. These absolute antenna calibrations accommodate the demand for greater accuracy and for 2-dimensional (elevation and azimuth) parameterization. NGS will continue to provide calibration values via the NGS web site www.ngs.noaa.gov/ANTCAL, and will publish calibrations in the ANTEX format as well as the legacy ANTINFO

  2. GNSS Absolute Antenna Calibration at the National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Mader, G. L.; Bilich, A. L.; Geoghegan, C.

    2011-12-01

    Geodetic GNSS applications routinely demand millimeter precision and extremely high levels of accuracy. To achieve these accuracies, measurement and instrument biases at the centimeter to millimeter level must be understood. One of these biases is the antenna phase center, the apparent point of signal reception for a GNSS antenna. It has been well established that phase center patterns differ between antenna models and manufacturers; additional research suggests that the addition of a radome or the choice of antenna mount can significantly alter those a priori phase center patterns. For the more demanding GNSS positioning applications and especially in cases of mixed-antenna networks, it is all the more important to know antenna phase center variations as a function of both elevation and azimuth in the antenna reference frame and incorporate these models into analysis software. To help meet the needs of the high-precision GNSS community, the National Geodetic Survey (NGS) now operates an absolute antenna calibration facility. Located in Corbin, Virginia, this facility uses field measurements and actual GNSS satellite signals to quantitatively determine the carrier phase advance/delay introduced by the antenna element. The NGS facility was built to serve traditional NGS constituents such as the surveying and geodesy communities, however calibration services are open and available to all GNSS users as the calibration schedule permits. All phase center patterns computed by this facility will be publicly available and disseminated in both the ANTEX and NGS formats. We describe the NGS calibration facility, and discuss the observation models and strategy currently used to generate NGS absolute calibrations. We demonstrate that NGS absolute phase center variation (PCV) patterns are consistent with published values determined by other absolute antenna calibration facilities, and compare absolute calibrations to the traditional NGS relative calibrations.

  3. Absolute GNSS Antenna Calibration at the National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Mader, G.; Bilich, A.; Geoghegan, C.

    2012-04-01

    Geodetic GNSS applications routinely demand millimeter precision and extremely high levels of accuracy. To achieve these accuracies, measurement and instrument biases at the centimeter to millimeter level must be understood. One of these biases is the antenna phase center, the apparent point of signal reception for a GNSS antenna. It has been well established that phase center patterns differ between antenna models and manufacturers; additional research suggests that the addition of a radome or the choice of antenna mount can significantly alter those a priori phase center patterns. For the more demanding GNSS positioning applications and especially in cases of mixed-antenna networks, it is all the more important to know antenna phase center variations as a function of both elevation and azimuth in the antenna reference frame and incorporate these models into analysis software. To help meet the needs of the high-precision GNSS community, the National Geodetic Survey (NGS) now operates an absolute antenna calibration facility. Located in Corbin, Virginia, this facility uses field measurements and actual GNSS satellite signals to quantitatively determine the carrier phase advance/delay introduced by the antenna element. The NGS facility was built to serve traditional NGS constituents such as the surveying and geodesy communities, however calibration services are open and available to all GNSS users as the calibration schedule permits. All phase center patterns computed by this facility will be publicly available and disseminated in both the ANTEX and NGS formats. We describe the NGS calibration facility, and discuss the observation models and strategy currently used to generate NGS absolute calibrations. We demonstrate that NGS absolute phase center variation (PCV) patterns are consistent with published values determined by other absolute antenna calibration facilities, and outline future planned refinements to the system.

  4. GNSS Absolute Antenna Calibration at the National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Bilich, A. L.; Mader, G. L.

    2009-12-01

    GNSS applications now routinely demand measurement and instrument biases at the centimeter to millimeter level in order to achieve the high precision and accuracy required for geodetic position solutions. One of these biases is the antenna phase center, the point of signal reception for a GNSS antenna. It has been well established that phase center patterns differ between antenna models and manufacturers; additional research suggests that the addition of a radome or the choice of antenna mount can significantly alter those a priori phase center patterns. As baseline lengths increase, or with antenna mixing, phase center effects on carrier phase data become more pronounced. To meet the needs of the high-precision GNSS community, the National Geodetic Survey (NGS) has constructed an absolute antenna calibration facility which uses field measurements and actual GNSS satellite signals to determine antenna phase center patterns. A pan/tilt motor changes the orientation of the antenna under test; signals are received at a wide range of angles, allowing computation of a robust phase center pattern. Ultimately, this facility will be used to measure antenna phase center variations of commonly-used geodetic GNSS antennas, as well as antennas submitted by users. The phase center patterns will be publicly available and disseminated in both the ANTEX and NGS formats. We provide information on the observation models and strategy currently used to generate NGS absolute calibrations, and propose some future refinements. We discuss the multipath mitigation strategy currently in use, and provide examples of antenna calibrations from the NGS facility. These examples are compared to the NGS relative calibrations as well as absolute calibrations generated by other organizations.

  5. On the Error Sources in Absolute Individual Antenna Calibrations

    NASA Astrophysics Data System (ADS)

    Aerts, Wim; Baire, Quentin; Bilich, Andria; Bruyninx, Carine; Legrand, Juliette

    2013-04-01

    field) multi path errors, both during calibration and later on at the station, absolute sub-millimeter positioning with GPS is not (yet) possible. References [1] G. Wübbena, M. Schmitz, G. Boettcher, C. Schumann, "Absolute GNSS Antenna Calibration with a Robot: Repeatability of Phase Variations, Calibration of GLONASS and Determination of Carrier-to-Noise Pattern", International GNSS Service: Analysis Center workshop, 8-12 May 2006, Darmstadt, Germany. [2] P. Zeimetz, H. Kuhlmann, "On the Accuracy of Absolute GNSS Antenna Calibration and the Conception of a New Anechoic Chamber", FIG Working Week 2008, 14-19 June 2008, Stockholm, Sweden. [3] P. Zeimetz, H. Kuhlmann, L. Wanninger, V. Frevert, S. Schön and K. Strauch, "Ringversuch 2009", 7th GNSS-Antennen-Workshop, 19-20 March 2009, Dresden, Germany.

  6. Relative vs Absolute Antenna Calibrations: How, when, and why do they differ? A Comparison of Antenna Calibration Catalogs

    NASA Astrophysics Data System (ADS)

    Mader, G. L.; Bilich, A. L.

    2013-12-01

    Since 1994, NGS has computed relative antenna calibrations for more than 350 antenna models used by NGS customers and geodetic networks worldwide. In a 'relative' calibration, the antenna under test is calibrated relative to a standard reference antenna, the AOA D/M_T chokering. The majority of NGS calibrations have been made publicly available at the web site www.ngs.noaa.gov/ANTCAL as well as via the NGS master calibrations file ant_info.003. In the mid-2000's, institutions in Germany began distributing 'absolute' antenna calibrations, where the antenna under test is calibrated independent of any reference antenna. These calibration methods also overcame some limitations of relative calibrations by going to lower elevation angles and capturing azimuthal variations. Soon thereafter (2008), the International GNSS Service (IGS) initiated a geodetic community movement away from relative calibrations and toward absolute calibrations as the defacto standard. The IGS now distributes a catalog of absolute calibrations taken from several institutions, distributed as the IGS master calibrations file igs08.atx. The competing methods and files have raised many questions about when it is or is not valid to process a geodetic network using a combination of relative and absolute calibrations, and if/when it is valid to combine the NGS and IGS catalogs. Therefore, in this study, we compare the NGS catalog of relative calibrations against the IGS catalog of absolute calibrations. As of the writing of this abstract, there are 77 antenna+radome combinations which are common to both the NGS relative and IGS absolute catalogs, spanning 16 years of testing (1997 to present). 50 different antenna models and 8 manufacturers are represented in the study sample. We apply the widely-accepted standard method for converting relative to absolute, then difference the calibrations. Various statistics describe the observed differences between phase center offset (PCO), phase center variation

  7. GNSS Absolute Antenna Calibration in the Field at the National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Mader, G.; Bilich, A.

    2008-12-01

    Geodetic GNSS applications now routinely demand millimeter precision and extremely high levels of accuracy. To achieve these accuracies, measurement and instrument biases at the centimeter to millimeter level must be understood. One of these biases is the antenna phase center, the point of signal reception for a GNSS antenna. It has been well established that phase center patterns differ between antenna models and manufacturers, and can be affected by the presence of a radome or other installation-specific factors. As GNSS geodesy increasingly moves toward real-time applications and high-rate or kinematic positioning, it is all the more important to have the most complete picture of antenna phase center variations possible, as a function of both elevation and azimuth. To meet the needs of the geodetic GNSS community, the National Geodetic Survey (NGS) has constructed an absolute antenna calibration facility. Located in Corbin, Virgina, adjacent to the NGS relative antenna calibration site, this facility uses field measurements and actual GNSS satellite signals to determine antenna phase center patterns. A pan/tilt motor changes the orientation of the antenna under test, so that signals are received and their phase center subsequently measured for a wide range of angles. The NGS phase center models are generated for all possible azimuths and over 90 to -30 degrees elevation angles; negative elevation angles are included to support studies where valid signals are received below the antenna's horizon. Ultimately, this facility will be used to measure antenna phase center variations of commonly-used geodetic GNSS antennas, as well as antennas submitted by users. The phase center patterns will be publicly available and disseminated in the ANTEX format. We present information on the current status of and future plans for the NGS antenna calibration facility. We outline the observation models and software used to generate absolute calibrations, and provide examples of

  8. First Results of Field Absolute Calibration of the GPS Receiver Antenna at Wuhan University.

    PubMed

    Hu, Zhigang; Zhao, Qile; Chen, Guo; Wang, Guangxing; Dai, Zhiqiang; Li, Tao

    2015-01-01

    GNSS receiver antenna phase center variations (PCVs), which arise from the non-spherical phase response of GNSS signals have to be well corrected for high-precision GNSS applications. Without using a precise antenna phase center correction (PCC) model, the estimated position of a station monument will lead to a bias of up to several centimeters. The Chinese large-scale research project "Crustal Movement Observation Network of China" (CMONOC), which requires high-precision positions in a comprehensive GPS observational network motived establishment of a set of absolute field calibrations of the GPS receiver antenna located at Wuhan University. In this paper the calibration facilities are firstly introduced and then the multipath elimination and PCV estimation strategies currently used are elaborated. The validation of estimated PCV values of test antenna are finally conducted, compared with the International GNSS Service (IGS) type values. Examples of TRM57971.00 NONE antenna calibrations from our calibration facility demonstrate that the derived PCVs and IGS type mean values agree at the 1 mm level. PMID:26580616

  9. First Results of Field Absolute Calibration of the GPS Receiver Antenna at Wuhan University

    PubMed Central

    Hu, Zhigang; Zhao, Qile; Chen, Guo; Wang, Guangxing; Dai, Zhiqiang; Li, Tao

    2015-01-01

    GNSS receiver antenna phase center variations (PCVs), which arise from the non-spherical phase response of GNSS signals have to be well corrected for high-precision GNSS applications. Without using a precise antenna phase center correction (PCC) model, the estimated position of a station monument will lead to a bias of up to several centimeters. The Chinese large-scale research project “Crustal Movement Observation Network of China” (CMONOC), which requires high-precision positions in a comprehensive GPS observational network motived establishment of a set of absolute field calibrations of the GPS receiver antenna located at Wuhan University. In this paper the calibration facilities are firstly introduced and then the multipath elimination and PCV estimation strategies currently used are elaborated. The validation of estimated PCV values of test antenna are finally conducted, compared with the International GNSS Service (IGS) type values. Examples of TRM57971.00 NONE antenna calibrations from our calibration facility demonstrate that the derived PCVs and IGS type mean values agree at the 1 mm level. PMID:26580616

  10. SAR antenna calibration techniques

    NASA Technical Reports Server (NTRS)

    Carver, K. R.; Newell, A. C.

    1978-01-01

    Calibration of SAR antennas requires a measurement of gain, elevation and azimuth pattern shape, boresight error, cross-polarization levels, and phase vs. angle and frequency. For spaceborne SAR antennas of SEASAT size operating at C-band or higher, some of these measurements can become extremely difficult using conventional far-field antenna test ranges. Near-field scanning techniques offer an alternative approach and for C-band or X-band SARs, give much improved accuracy and precision as compared to that obtainable with a far-field approach.

  11. Antenna Calibration and Measurement Equipment

    NASA Technical Reports Server (NTRS)

    Rochblatt, David J.; Cortes, Manuel Vazquez

    2012-01-01

    A document describes the Antenna Calibration & Measurement Equipment (ACME) system that will provide the Deep Space Network (DSN) with instrumentation enabling a trained RF engineer at each complex to perform antenna calibration measurements and to generate antenna calibration data. This data includes continuous-scan auto-bore-based data acquisition with all-sky data gathering in support of 4th order pointing model generation requirements. Other data includes antenna subreflector focus, system noise temperature and tipping curves, antenna efficiency, reports system linearity, and instrument calibration. The ACME system design is based on the on-the-fly (OTF) mapping technique and architecture. ACME has contributed to the improved RF performance of the DSN by approximately a factor of two. It improved the pointing performances of the DSN antennas and productivity of its personnel and calibration engineers.

  12. Absolute calibration in vivo measurement systems

    SciTech Connect

    Kruchten, D.A.; Hickman, D.P.

    1991-02-01

    Lawrence Livermore National Laboratory (LLNL) is currently investigating a new method for obtaining absolute calibration factors for radiation measurement systems used to measure internally deposited radionuclides in vivo. Absolute calibration of in vivo measurement systems will eliminate the need to generate a series of human surrogate structures (i.e., phantoms) for calibrating in vivo measurement systems. The absolute calibration of in vivo measurement systems utilizes magnetic resonance imaging (MRI) to define physiological structure, size, and composition. The MRI image provides a digitized representation of the physiological structure, which allows for any mathematical distribution of radionuclides within the body. Using Monte Carlo transport codes, the emission spectrum from the body is predicted. The in vivo measurement equipment is calibrated using the Monte Carlo code and adjusting for the intrinsic properties of the detection system. The calibration factors are verified using measurements of existing phantoms and previously obtained measurements of human volunteers. 8 refs.

  13. Absolute calibration of optical flats

    DOEpatents

    Sommargren, Gary E.

    2005-04-05

    The invention uses the phase shifting diffraction interferometer (PSDI) to provide a true point-by-point measurement of absolute flatness over the surface of optical flats. Beams exiting the fiber optics in a PSDI have perfect spherical wavefronts. The measurement beam is reflected from the optical flat and passed through an auxiliary optic to then be combined with the reference beam on a CCD. The combined beams include phase errors due to both the optic under test and the auxiliary optic. Standard phase extraction algorithms are used to calculate this combined phase error. The optical flat is then removed from the system and the measurement fiber is moved to recombine the two beams. The newly combined beams include only the phase errors due to the auxiliary optic. When the second phase measurement is subtracted from the first phase measurement, the absolute phase error of the optical flat is obtained.

  14. Absolute calibration of the Auger fluorescence detectors

    SciTech Connect

    Bauleo, P.; Brack, J.; Garrard, L.; Harton, J.; Knapik, R.; Meyhandan, R.; Rovero, A.C.; Tamashiro, A.; Warner, D.

    2005-07-01

    Absolute calibration of the Pierre Auger Observatory fluorescence detectors uses a light source at the telescope aperture. The technique accounts for the combined effects of all detector components in a single measurement. The calibrated 2.5 m diameter light source fills the aperture, providing uniform illumination to each pixel. The known flux from the light source and the response of the acquisition system give the required calibration for each pixel. In the lab, light source uniformity is studied using CCD images and the intensity is measured relative to NIST-calibrated photodiodes. Overall uncertainties are presently 12%, and are dominated by systematics.

  15. An SLF magnetic antenna calibration system

    NASA Astrophysics Data System (ADS)

    Shimin, Feng; Suihua, Zhou; Zhiyi, Chen; Hongxin, Zhang

    2014-05-01

    Calibrating the super low frequency (SLF) magnetic antenna in magnetic free space or an outdoor environment is difficult and complicated due to the large size calibration instruments and lots of measurement times. Aiming to calibrate the SLF magnetic antenna simply and efficiently, a calibration system comprised of a multi-frequency source, an AC constant-current source and a solenoid is proposed according to the characteristic of an SLF magnetic antenna. The static magnetic transfer coefficient of the designed solenoid is calibrated. The measurement of the frequency response characteristics suggests the transfer coefficient remains unchanged in the range of the SLF band and is unaffected by the magnetic antenna internally installed. The CORDIC algorithm implemented in an FPGA is realized to generate a linear evenly-spaced multi-frequency signal with equal energy at each frequency. An AC constant weak current source circuit is designed in order to avoid the impact on the magnetic induction intensity of a calibration system affected by impedance variation when frequency changing, linearity and the precision of the source are measured. The frequency characteristic of a magnetic antenna calibrated by the proposed calibration system agrees with the theoretical result and the standard Glass ring calibration result. The calibration precision satisfies the experimental requirement.

  16. Sentinel-2/MSI absolute calibration: first results

    NASA Astrophysics Data System (ADS)

    Lonjou, V.; Lachérade, S.; Fougnie, B.; Gamet, P.; Marcq, S.; Raynaud, J.-L.; Tremas, T.

    2015-10-01

    Sentinel-2 is an optical imaging mission devoted to the operational monitoring of land and coastal areas. It is developed in partnership between the European Commission and the European Space Agency. The Sentinel-2 mission is based on a satellites constellation deployed in polar sun-synchronous orbit. It will offer a unique combination of global coverage with a wide field of view (290km), a high revisit (5 days with two satellites), a high resolution (10m, 20m and 60m) and multi-spectral imagery (13 spectral bands in visible and shortwave infra-red domains). CNES is involved in the instrument commissioning in collaboration with ESA. This paper reviews all the techniques that will be used to insure an absolute calibration of the 13 spectral bands better than 5% (target 3%), and will present the first results if available. First, the nominal calibration technique, based on an on-board sun diffuser, is detailed. Then, we show how vicarious calibration methods based on acquisitions over natural targets (oceans, deserts, and Antarctica during winter) will be used to check and improve the accuracy of the absolute calibration coefficients. Finally, the verification scheme, exploiting photometer in-situ measurements over Lacrau plain, is described. A synthesis, including spectral coherence, inter-methods agreement and temporal evolution, will conclude the paper.

  17. Absolute calibration of TFTR helium proportional counters

    SciTech Connect

    Strachan, J.D.; Diesso, M.; Jassby, D.; Johnson, L.; McCauley, S.; Munsat, T.; Roquemore, A.L.; Barnes, C.W. |; Loughlin, M. |

    1995-06-01

    The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 msec and 50 msec depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments.

  18. Absolute Radiometric Calibration of KOMPSAT-3A

    NASA Astrophysics Data System (ADS)

    Ahn, H. Y.; Shin, D. Y.; Kim, J. S.; Seo, D. C.; Choi, C. U.

    2016-06-01

    This paper presents a vicarious radiometric calibration of the Korea Multi-Purpose Satellite-3A (KOMPSAT-3A) performed by the Korea Aerospace Research Institute (KARI) and the Pukyong National University Remote Sensing Group (PKNU RSG) in 2015.The primary stages of this study are summarized as follows: (1) A field campaign to determine radiometric calibrated target fields was undertaken in Mongolia and South Korea. Surface reflectance data obtained in the campaign were input to a radiative transfer code that predicted at-sensor radiance. Through this process, equations and parameters were derived for the KOMPSAT-3A sensor to enable the conversion of calibrated DN to physical units, such as at-sensor radiance or TOA reflectance. (2) To validate the absolute calibration coefficients for the KOMPSAT-3A sensor, we performed a radiometric validation with a comparison of KOMPSAT-3A and Landsat-8 TOA reflectance using one of the six PICS (Libya 4). Correlations between top-of-atmosphere (TOA) radiances and the spectral band responses of the KOMPSAT-3A sensors at the Zuunmod, Mongolia and Goheung, South Korea sites were significant for multispectral bands. The average difference in TOA reflectance between KOMPSAT-3A and Landsat-8 image over the Libya 4, Libya site in the red-green-blue (RGB) region was under 3%, whereas in the NIR band, the TOA reflectance of KOMPSAT-3A was lower than the that of Landsat-8 due to the difference in the band passes of two sensors. The KOMPSAT-3Aensor includes a band pass near 940 nm that can be strongly absorbed by water vapor and therefore displayed low reflectance. Toovercome this, we need to undertake a detailed analysis using rescale methods, such as the spectral bandwidth adjustment factor.

  19. Absolute calibration of ultraviolet filter photometry

    NASA Technical Reports Server (NTRS)

    Bless, R. C.; Fairchild, T.; Code, A. D.

    1972-01-01

    The essential features of the calibration procedure can be divided into three parts. First, the shape of the bandpass of each photometer was determined by measuring the transmissions of the individual optical components and also by measuring the response of the photometer as a whole. Secondly, each photometer was placed in the essentially-collimated synchrotron radiation bundle maintained at a constant intensity level, and the output signal was determined from about 100 points on the objective. Finally, two or three points on the objective were illuminated by synchrotron radiation at several different intensity levels covering the dynamic range of the photometers. The output signals were placed on an absolute basis by the electron counting technique described earlier.

  20. Absolute calibration of forces in optical tweezers

    NASA Astrophysics Data System (ADS)

    Dutra, R. S.; Viana, N. B.; Maia Neto, P. A.; Nussenzveig, H. M.

    2014-07-01

    Optical tweezers are highly versatile laser traps for neutral microparticles, with fundamental applications in physics and in single molecule cell biology. Force measurements are performed by converting the stiffness response to displacement of trapped transparent microspheres, employed as force transducers. Usually, calibration is indirect, by comparison with fluid drag forces. This can lead to discrepancies by sizable factors. Progress achieved in a program aiming at absolute calibration, conducted over the past 15 years, is briefly reviewed. Here we overcome its last major obstacle, a theoretical overestimation of the peak stiffness, within the most employed range for applications, and we perform experimental validation. The discrepancy is traced to the effect of primary aberrations of the optical system, which are now included in the theory. All required experimental parameters are readily accessible. Astigmatism, the dominant effect, is measured by analyzing reflected images of the focused laser spot, adapting frequently employed video microscopy techniques. Combined with interface spherical aberration, it reveals a previously unknown window of instability for trapping. Comparison with experimental data leads to an overall agreement within error bars, with no fitting, for a broad range of microsphere radii, from the Rayleigh regime to the ray optics one, for different polarizations and trapping heights, including all commonly employed parameter domains. Besides signaling full first-principles theoretical understanding of optical tweezers operation, the results may lead to improved instrument design and control over experiments, as well as to an extended domain of applicability, allowing reliable force measurements, in principle, from femtonewtons to nanonewtons.

  1. Technique for Radiometer and Antenna Array Calibration with Two Antenna Noise Diodes

    NASA Technical Reports Server (NTRS)

    Srinivasan, Karthik; Limaye, Ashutosh; Laymon, Charles; Meyer, Paul

    2011-01-01

    This paper presents a new technique to calibrate a microwave radiometer and phased array antenna system. This calibration technique uses a radiated noise source in addition to an injected noise sources for calibration. The plane of reference for this calibration technique is the face of the antenna and therefore can effectively calibration the gain fluctuations in the active phased array antennas. This paper gives the mathematical formulation for the technique and discusses the improvements brought by the method over the existing calibration techniques.

  2. Calibrating the absolute amplitude scale for air showers measured at LOFAR

    NASA Astrophysics Data System (ADS)

    Nelles, A.; Hörandel, J. R.; Karskens, T.; Krause, M.; Buitink, S.; Corstanje, A.; Enriquez, J. E.; Erdmann, M.; Falcke, H.; Haungs, A.; Hiller, R.; Huege, T.; Krause, R.; Link, K.; Norden, M. J.; Rachen, J. P.; Rossetto, L.; Schellart, P.; Scholten, O.; Schröder, F. G.; ter Veen, S.; Thoudam, S.; Trinh, T. N. G.; Weidenhaupt, K.; Wijnholds, S. J.; Anderson, J.; Bähren, L.; Bell, M. E.; Bentum, M. J.; Best, P.; Bonafede, A.; Bregman, J.; Brouw, W. N.; Brüggen, M.; Butcher, H. R.; Carbone, D.; Ciardi, B.; de Gasperin, F.; Duscha, S.; Eislöffel, J.; Fallows, R. A.; Frieswijk, W.; Garrett, M. A.; van Haarlem, M. P.; Heald, G.; Hoeft, M.; Horneffer, A.; Iacobelli, M.; Juette, E.; Karastergiou, A.; Kohler, J.; Kondratiev, V. I.; Kuniyoshi, M.; Kuper, G.; van Leeuwen, J.; Maat, P.; McFadden, R.; McKay-Bukowski, D.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A. G.; Reich, W.; Röttgering, H.; Schwarz, D.; Serylak, M.; Sluman, J.; Smirnov, O.; Tasse, C.; Toribio, M. C.; Vermeulen, R.; van Weeren, R. J.; Wijers, R. A. M. J.; Wucknitz, O.; Zarka, P.

    2015-11-01

    Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw-Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. We present three approaches that were used to check and improve the antenna model of LOFAR and to provide an absolute calibration of the whole system for air shower measurements. Two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the Galaxy, optimized for short data-sets. An accuracy of 19% in amplitude is reached. The absolute calibration is also compared to predictions from air shower simulations. These results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with LOFAR.

  3. Absolute radiometric calibration of advanced remote sensing systems

    NASA Technical Reports Server (NTRS)

    Slater, P. N.

    1982-01-01

    The distinction between the uses of relative and absolute spectroradiometric calibration of remote sensing systems is discussed. The advantages of detector-based absolute calibration are described, and the categories of relative and absolute system calibrations are listed. The limitations and problems associated with three common methods used for the absolute calibration of remote sensing systems are addressed. Two methods are proposed for the in-flight absolute calibration of advanced multispectral linear array systems. One makes use of a sun-illuminated panel in front of the sensor, the radiance of which is monitored by a spectrally flat pyroelectric radiometer. The other uses a large, uniform, high-radiance reference ground surface. The ground and atmospheric measurements required as input to a radiative transfer program to predict the radiance level at the entrance pupil of the orbital sensor are discussed, and the ground instrumentation is described.

  4. Absolute calibration of sniffer probes on Wendelstein 7-X.

    PubMed

    Moseev, D; Laqua, H P; Marsen, S; Stange, T; Braune, H; Erckmann, V; Gellert, F; Oosterbeek, J W

    2016-08-01

    Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m(2) per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m(2) per MW injected beam power is measured. PMID:27587121

  5. Absolute calibration of sniffer probes on Wendelstein 7-X

    NASA Astrophysics Data System (ADS)

    Moseev, D.; Laqua, H. P.; Marsen, S.; Stange, T.; Braune, H.; Erckmann, V.; Gellert, F.; Oosterbeek, J. W.

    2016-08-01

    Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m2 per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m2 per MW injected beam power is measured.

  6. A practical method for sensor absolute calibration.

    PubMed

    Meisenholder, G W

    1966-04-01

    This paper describes a method of performing sensor calibrations using an NBS standard of spectral irradiance. The method shown, among others, was used for calibration of the Mariner IV Canopus sensor. Agreement of inflight response to preflight calibrations performed by this technique has been found to be well within 10%. PMID:20048890

  7. System and method for calibrating a rotary absolute position sensor

    NASA Technical Reports Server (NTRS)

    Davis, Donald R. (Inventor); Permenter, Frank Noble (Inventor); Radford, Nicolaus A (Inventor)

    2012-01-01

    A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.

  8. Absolute sensitivity calibration of extreme ultraviolet photoresists

    SciTech Connect

    Jones, Juanita; Naulleau, Patrick P.; Gullikson, Eric M.; Aquila, Andrew; George, Simi; Niakoula, Dimitra

    2008-05-16

    One of the major challenges facing the commercialization of extreme ultraviolet (EUV) lithography remains simultaneously achieving resist sensitivity, line-edge roughness, and resolution requirement. Sensitivity is of particular concern owing to its direct impact on source power requirements. Most current EUV exposure tools have been calibrated against a resist standard with the actual calibration of the standard resist dating back to EUV exposures at Sandia National Laboratories in the mid 1990s. Here they report on an independent sensitivity calibration of two baseline resists from the SEMATECH Berkeley MET tool performed at the Advanced Light Source Calibrations and Standards beamline. The results show the baseline resists to be approximately 1.9 times faster than previously thought based on calibration against the long standing resist standard.

  9. Absolute flux density calibrations of radio sources: 2.3 GHz

    NASA Technical Reports Server (NTRS)

    Freiley, A. J.; Batelaan, P. D.; Bathker, D. A.

    1977-01-01

    A detailed description of a NASA/JPL Deep Space Network program to improve S-band gain calibrations of large aperture antennas is reported. The program is considered unique in at least three ways; first, absolute gain calibrations of high quality suppressed-sidelobe dual mode horns first provide a high accuracy foundation to the foundation to the program. Second, a very careful transfer calibration technique using an artificial far-field coherent-wave source was used to accurately obtain the gain of one large (26 m) aperture. Third, using the calibrated large aperture directly, the absolute flux density of five selected galactic and extragalactic natural radio sources was determined with an absolute accuracy better than 2 percent, now quoted at the familiar 1 sigma confidence level. The follow-on considerations to apply these results to an operational network of ground antennas are discussed. It is concluded that absolute gain accuracies within + or - 0.30 to 0.40 db are possible, depending primarily on the repeatability (scatter) in the field data from Deep Space Network user stations.

  10. Technique for Radiometer and Antenna Array Calibration - TRAAC

    NASA Technical Reports Server (NTRS)

    Meyer, Paul; Sims, William; Varnavas, Kosta; McCracken, Jeff; Srinivasan, Karthik; Limaye, Ashutosh; Laymon, Charles; Richeson. James

    2012-01-01

    Highly sensitive receivers are used to detect minute amounts of emitted electromagnetic energy. Calibration of these receivers is vital to the accuracy of the measurements. Traditional calibration techniques depend on calibration reference internal to the receivers as reference for the calibration of the observed electromagnetic energy. Such methods can only calibrate errors in measurement introduced by the receiver only. The disadvantage of these existing methods is that they cannot account for errors introduced by devices, such as antennas, used for capturing electromagnetic radiation. This severely limits the types of antennas that can be used to make measurements with a high degree of accuracy. Complex antenna systems, such as electronically steerable antennas (also known as phased arrays), while offering potentially significant advantages, suffer from a lack of a reliable and accurate calibration technique. The proximity of antenna elements in an array results in interaction between the electromagnetic fields radiated (or received) by the individual elements. This phenomenon is called mutual coupling. The new calibration method uses a known noise source as a calibration load to determine the instantaneous characteristics of the antenna. The noise source is emitted from one element of the antenna array and received by all the other elements due to mutual coupling. This received noise is used as a calibration standard to monitor the stability of the antenna electronics.

  11. Stitching interferometry: recent results and absolute calibration

    NASA Astrophysics Data System (ADS)

    Bray, Michael

    2004-02-01

    Stitching Interferometry is a method of analysing large optical components using a standard "small" interferometer. This result is obtained by taking multiple overlapping images of the large component, and numerically "stitching" these sub-apertures together. We have already reported the industrial use our Stitching Interferometry systems (Previous SPIE symposia), but experimental results had been lacking because this technique is still new, and users needed to get accustomed to it before producing reliable measurements. We now have more results. We will report user comments and show new, unpublished results. We will discuss sources of error, and show how some of these can be reduced to arbitrarily small values. These will be discussed in some detail. We conclude with a few graphical examples of absolute measurements performed by us.

  12. Absolute calibration technique for broadband ultrasonic transducers

    NASA Technical Reports Server (NTRS)

    Yost, William T. (Inventor); Cantrell, John H. (Inventor)

    1994-01-01

    Calibrating an ultrasonic transducer can be performed with a reduced number of calculations and testing. A wide-band pulser is connected to an ultrasonic transducer under test to generate ultrasonic waves in a liquid. A single frequency is transmitted to the electrostatic acoustic transducer (ESAT) and the voltage change produced is monitored. Then a broadband ultrasonic pulse is generated by the ultrasonic transducer and received by the ESAT. The output of the ESAT is amplified and input to a digitized oscilloscope for fast Fourier transform. The resulting plot is normalized with the monitored signal from the single frequency pulse. The plot is then corrected for characteristics of the membrane and diffraction effects. The transfer function of the final plot is determined. The transfer function gives the final sensitivity of the ultrasonic transducer as a function of frequency. The advantage of the system is the speed of calibrating the transducer by a reduced number of measurements and removal of the membrane and diffraction effects.

  13. Prelaunch absolute radiometric calibration of LANDSAT-4 protoflight Thematic Mapper

    NASA Technical Reports Server (NTRS)

    Barker, J. L.; Ball, D. L.; Leung, K. C.; Walker, J. A.

    1984-01-01

    Results are summarized and analyzed from several prelaunch tests with a 122 cm integrating sphere used as part of the absolute radiometric calibration experiments for the protoflight TM sensor carried on the LANDSAT-4 satellite. The calibration procedure is presented and the radiometric sensitivity of the TM is assessed. The internal calibrator and dynamic range after calibration are considered. Tables show dynamic range after ground processing, spectral radiance to digital number and digital number to spectral radiance values for TM bands 1, 2, 3, 4, 5, 7 and for channel 4 of band 6.

  14. In-flight absolute radiometric calibration of the thematic mapper

    NASA Technical Reports Server (NTRS)

    Castle, K. R.; Holm, R. G.; Kastner, C. J.; Palmer, J. M.; Slater, P. N.; Dinguirard, M.; Ezra, C. E.; Jackson, R. D.; Savage, R. K.

    1983-01-01

    The TM multispectral scanner system was calibrated in an absolute manner before launch. To determine the temporal changes of the absolute radiometric calibration of the entire system, spectroradiometric measurements of the ground and the atmosphere were made simultaneously with TM collections over White Sands, New Mexico. By entering the measured values in an atmospheric radiative transfer program, the radiance levels of the in four of the spectral bands of the TM were determined. Tables show values for the reflectance of snow at White Sands measured by a modular 8 channel radiometer, and values for exoatmospheric irradiance within the TM passbands, calculated for the Earth-Sun distance using a solar radiometer.

  15. Landsat-5 TM reflective-band absolute radiometric calibration

    USGS Publications Warehouse

    Chander, G.; Helder, D.L.; Markham, B.L.; Dewald, J.D.; Kaita, E.; Thome, K.J.; Micijevic, E.; Ruggles, T.A.

    2004-01-01

    The Landsat-5 Thematic Mapper (TM) sensor provides the longest running continuous dataset of moderate spatial resolution remote sensing imagery, dating back to its launch in March 1984. Historically, the radiometric calibration procedure for this imagery used the instrument's response to the Internal Calibrator (IC) on a scene-by-scene basis to determine the gain and offset of each detector. Due to observed degradations in the IC, a new procedure was implemented for U.S.-processed data in May 2003. This new calibration procedure is based on a lifetime radiometric calibration model for the instrument's reflective bands (1-5 and 7) and is derived, in part, from the IC response without the related degradation effects and is tied to the cross calibration with the Landsat-7 Enhanced Thematic Mapper Plus. Reflective-band absolute radiometric accuracy of the instrument tends to be on the order of 7% to 10%, based on a variety of calibration methods.

  16. Absolute irradiance of the Moon for on-orbit calibration

    USGS Publications Warehouse

    Stone, T.C.; Kieffer, H.H.

    2002-01-01

    The recognized need for on-orbit calibration of remote sensing imaging instruments drives the ROLO project effort to characterize the Moon for use as an absolute radiance source. For over 5 years the ground-based ROLO telescopes have acquired spatially-resolved lunar images in 23 VNIR (Moon diameter ???500 pixels) and 9 SWIR (???250 pixels) passbands at phase angles within ??90 degrees. A numerical model for lunar irradiance has been developed which fits hundreds of ROLO images in each band, corrected for atmospheric extinction and calibrated to absolute radiance, then integrated to irradiance. The band-coupled extinction algorithm uses absorption spectra of several gases and aerosols derived from MODTRAN to fit time-dependent component abundances to nightly observations of standard stars. The absolute radiance scale is based upon independent telescopic measurements of the star Vega. The fitting process yields uncertainties in lunar relative irradiance over small ranges of phase angle and the full range of lunar libration well under 0.5%. A larger source of uncertainty enters in the absolute solar spectral irradiance, especially in the SWIR, where solar models disagree by up to 6%. Results of ROLO model direct comparisons to spacecraft observations demonstrate the ability of the technique to track sensor responsivity drifts to sub-percent precision. Intercomparisons among instruments provide key insights into both calibration issues and the absolute scale for lunar irradiance.

  17. Lyman alpha SMM/UVSP absolute calibration and geocoronal correction

    NASA Technical Reports Server (NTRS)

    Fontenla, Juan M.; Reichmann, Edwin J.

    1987-01-01

    Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter (UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were analyzed and provide instrumental calibration details. Specific values of the instrument quantum efficiency, Lyman alpha absolute intensity, and correction for geocoronal absorption are presented.

  18. Absolute calibration of Landsat instruments using the moon.

    USGS Publications Warehouse

    Kieffer, H.H.; Wildey, R.L.

    1985-01-01

    A lunar observation by Landsat could provide improved radiometric and geometric calibration of both the Thematic Mapper and the Multispectral Scanner in terms of absolute radiometry, determination of the modulation transfer function, and sensitivity to scattered light. A pitch of the spacecraft would be required. -Authors

  19. Absolute charge calibration of scintillating screens for relativistic electron detection

    SciTech Connect

    Buck, A.; Popp, A.; Schmid, K.; Karsch, S.; Krausz, F.; Zeil, K.; Jochmann, A.; Kraft, S. D.; Sauerbrey, R.; Cowan, T.; Schramm, U.; Hidding, B.; Kudyakov, T.; Sears, C. M. S.; Veisz, L.; Pawelke, J.

    2010-03-15

    We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC/mm{sup 2}. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10-100 pC/mm{sup 2} was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference to simplify the transfer of a one-time absolute calibration to different experimental setups.

  20. Absolute charge calibration of scintillating screens for relativistic electron detection

    NASA Astrophysics Data System (ADS)

    Buck, A.; Zeil, K.; Popp, A.; Schmid, K.; Jochmann, A.; Kraft, S. D.; Hidding, B.; Kudyakov, T.; Sears, C. M. S.; Veisz, L.; Karsch, S.; Pawelke, J.; Sauerbrey, R.; Cowan, T.; Krausz, F.; Schramm, U.

    2010-03-01

    We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC/mm2. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10-100 pC/mm2 was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference to simplify the transfer of a one-time absolute calibration to different experimental setups.

  1. In-flight Absolute Radiometric Calibration of the Thematic Mapper

    NASA Technical Reports Server (NTRS)

    Castle, K. R.; Holm, R. G.; Kastner, C. J.; Palmer, J. M.; Slater, P. N.; Dinguirard, M.; Ezra, C. E.; Jackson, D.; Savage, R. K.

    1984-01-01

    The Thematic Mapper (TM) multispectral scanner system was placed into Earth orbit on July 16, 1982, as part of NASA's LANDSAT 4 payload. To determine temporal changes of the absolute radiometric calibration of the entire system in flight, spectroradiometric measurements of the ground and the atmosphere are made simultaneously with TM image acquisitions over the White Sands, New Mexico area. By entering the measured values into an atmospheric radiative transfer program, the radiance levels at the entrance pupil of the TM in four of the TM spectral bands are determined. These levels are compared to the output digital counts from the detectors that sampled the radiometrically measured ground area, thus providing an absolute radiometric calibration of the entire TM system utilizing those detectors. By reference to an adjacent, larger uniform area, the calibration is extended to all 16 detectors in each of the three bands.

  2. Absolute calibration for a broad range single shot electron spectrometer

    SciTech Connect

    Glinec, Y.; Faure, J.; Guemnie-Tafo, A.; Malka, V.; Monard, H.; Larbre, J. P.; De Waele, V.; Marignier, J. L.; Mostafavi, M.

    2006-10-15

    This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

  3. In-flight absolute radiometric calibration of the thematic mapper

    NASA Technical Reports Server (NTRS)

    Castle, K. R.; Holm, R. G.; Kastner, C. J.; Palmer, J. M.; Slater, P. N.; Dinguirard, M.; Ezra, C. E.; Jackson, R. D.; Savage, R. K.

    1984-01-01

    In order to determine temporal changes of the absolute radiometric calibration of the entire TM system in flight spectroradiometric measurements of the ground and the atmosphere were made simultaneously with TM image collections over the White Sands, New Mexico area. By entering the measured values in an atmospheric radiative transfer program, the radiance levels in four of the spectral bands of the TM were determined, band 1:0.45 to 0.52 micrometers, band 2:0.53 to 0.61 micrometers band 3:0.62 to 0.70 micrometers and 4:0.78 to 0.91 micrometers. These levels were compared to the output digital counts from the detectors that sampled the radiometrically measured ground area, thus providing an absolute radiometric calibration of the entire TM system utilizing those detectors.

  4. In-flight absolute radiometric calibration of the Thematic Mapper

    NASA Technical Reports Server (NTRS)

    Castle, K. R.; Holm, R. G.; Kastner, C. J.; Palmer, J. M.; Slater, P. N.; Dinguirard, M.; Ezra, C. E.; Jackson, R. D.; Savage, R. K.

    1984-01-01

    In order to determine temporal changes of the absolute radiometric calibration of the entire TM system in flight spectroradiometric measurements of the ground and the atmosphere were made simultaneously with TM image collections over the White Sands, NM area. By entering the measured values in an atmospheric radiative transfer program, the radiance levels in four of the spectral bands of the TM were determined, band 1: 0.45 to 0.52 micrometers, band 2: 0.53 to 0.61 micrometers, band 3: 0.62 to 0.70 micrometers, and 4: 0.78 to 0.91 micrometers. These levels were compared to the output digital counts from the detectors that sampled the radiometrically measured ground area, thus providing an absolute radiometric calibration of the entire TM system utilizing those detectors. Previously announced in STAR as N84-15633

  5. Absolute calibration for a broad range single shot electron spectrometer

    NASA Astrophysics Data System (ADS)

    Glinec, Y.; Faure, J.; Guemnie-Tafo, A.; Malka, V.; Monard, H.; Larbre, J. P.; De Waele, V.; Marignier, J. L.; Mostafavi, M.

    2006-10-01

    This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

  6. Landsat-7 ETM+ radiometric stability and absolute calibration

    USGS Publications Warehouse

    Markham, B.L.; Barker, J.L.; Barsi, J.A.; Kaita, E.; Thome, K.J.; Helder, D.L.; Palluconi, Frank Don; Schott, J.R.; Scaramuzza, P.

    2002-01-01

    Launched in April 1999, the Landsat-7 ETM+ instrument is in its fourth year of operation. The quality of the acquired calibrated imagery continues to be high, especially with respect to its three most important radiometric performance parameters: reflective band instrument stability to better than ??1%, reflective band absolute calibration to better than ??5%, and thermal band absolute calibration to better than ??0.6 K. The ETM+ instrument has been the most stable of any of the Landsat instruments, in both the reflective and thermal channels. To date, the best on-board calibration source for the reflective bands has been the Full Aperture Solar Calibrator, which has indicated changes of at most -1.8% to -2.0% (95% C.I.) change per year in the ETM+ gain (band 4). However, this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on ground observations, which bound the changes in gain in band 4 at -0.7% to +1.5%. Also, ETM+ stability is indicated by the monitoring of desert targets. These image-based results for four Saharan and Arabian sites, for a collection of 35 scenes over the three years since launch, bound the gain change at -0.7% to +0.5% in band 4. Thermal calibration from ground observations revealed an offset error of +0.31 W/m 2 sr um soon after launch. This offset was corrected within the U. S. ground processing system at EROS Data Center on 21-Dec-00, and since then, the band 6 on-board calibration has indicated changes of at most +0.02% to +0.04% (95% C.I.) per year. The latest ground observations have detected no remaining offset error with an RMS error of ??0.6 K. The stability and absolute calibration of the Landsat-7 ETM+ sensor make it an ideal candidate to be used as a reference source for radiometric cross-calibrating to other land remote sensing satellite systems.

  7. On-the-Fly Mapping for Calibrating Directional Antennas

    NASA Technical Reports Server (NTRS)

    Rochblatt, David; Richter, Paul; Withington, Philip

    2004-01-01

    An improved method of calibrating a large directional radio antenna of the type used in deep-space communication and radio astronomy has been developed. This method involves a raster-scanning-and-measurement technique denoted on-the-fly (OTF) mapping, applied in consideration of the results of a systematic analysis of the entire measurement procedure. Phenomena to which particular attention was paid in the analysis include (1) the noise characteristics of a total-power radiometer (TPR) that is used in the measurements and (2) tropospherically induced radiometer fluctuations. The method also involves the use of recently developed techniques for acquisition and reduction of data. In comparison with prior methods used to calibrate such antennas, this method yields an order-of-magnitude improvement in the precision of determinations of antenna aperture efficiency, and improvement by a factor of five or more in the precision of determination of pointing error and beam width. Prerequisite to a meaningful description of the present method is some background information concerning three aspects of the problem of calibrating an antenna of the type in question: In OTF mapping measurements in which a TPR is used, the desired data are the peak temperature corresponding to a radio source, the pointing offset when the antenna is commanded to point toward the source, and the shape of the main lobe of the antenna beam, all as functions of the antenna beam elevation and azimuth angles. These data enable one to calculate the (1) antenna aperture efficiency by comparing the measured peak temperature with that expected for a 100-percent-efficient antenna, (2) the mechanical pointing error resulting from small misalignments of various parts of the antenna structure, and (3) misalignments of the antenna subreflector and other mirrors. For practical reasons having to do with obtaining adequate angular resolution and all-sky coverage, it is necessary to perform azimuth and elevation scans

  8. Direct comparisons between absolute and relative geomagnetic paleointensities: Absolute calibration of a relative paleointensity stack

    NASA Astrophysics Data System (ADS)

    Mochizuki, N.; Yamamoto, Y.; Hatakeyama, T.; Shibuya, H.

    2013-12-01

    Absolute geomagnetic paleointensities (APIs) have been estimated from igneous rocks, while relative paleomagnetic intensities (RPIs) have been reported from sediment cores. These two datasets have been treated separately, as correlations between APIs and RPIs are difficult on account of age uncertainties. High-resolution RPI stacks have been constructed from globally distributed sediment cores with high sedimentation rates. Previous studies often assumed that the RPI stacks have a linear relationship with geomagnetic axial dipole moments, and calibrated the RPI values to API values. However, the assumption of a linear relationship between APIs and RPIs has not been evaluated. Also, a quantitative calibration method for the RPI is lacking. We present a procedure for directly comparing API and RPI stacks, thus allowing reliable calibrations of RPIs. Direct comparisons between APIs and RPIs were conducted with virtually no associated age errors using both tephrochronologic correlations and RPI minima. Using the stratigraphic positions of tephra layers in oxygen isotope stratigraphic records, we directly compared the RPIs and APIs reported from welded tuffs contemporaneously extruded with the tephra layers. In addition, RPI minima during geomagnetic reversals and excursions were compared with APIs corresponding to the reversals and excursions. The comparison of APIs and RPIs at these exact points allowed a reliable calibration of the RPI values. We applied this direct comparison procedure to the global RPI stack PISO-1500. For six independent calibration points, virtual axial dipole moments (VADMs) from the corresponding APIs and RPIs of the PISO-1500 stack showed a near-linear relationship. On the basis of the linear relationship, RPIs of the stack were successfully calibrated to the VADMs. The direct comparison procedure provides an absolute calibration method that will contribute to the recovery of temporal variations and distributions of geomagnetic axial dipole

  9. Updated Absolute Flux Calibration of the COS FUV Modes

    NASA Astrophysics Data System (ADS)

    Massa, D.; Ely, J.; Osten, R.; Penton, S.; Aloisi, A.; Bostroem, A.; Roman-Duval, J.; Proffitt, C.

    2014-03-01

    We present newly derived point source absolute flux calibrations for the COS FUV modes at both the original and second lifetime positions. The analysis includes observa- tions through the Primary Science Aperture (PSA) of the standard stars WD0308-565, GD71, WD1057+729 and WD0947+857 obtained as part of two calibration programs. Data were were obtained for all of the gratings at all of the original CENWAVE settings at both the original and second lifetime positions and for the G130M CENWAVE = 1222 at the second lifetime position. Data were also obtained with the FUVB segment for the G130M CENWAVE = 1055 and 1096 setting at the second lifetime position. We also present the derivation of L-flats that were used in processing the data and show that the internal consistency of the primary standards is 1%. The accuracy of the absolute flux calibrations over the UV are estimated to be 1-2% for the medium resolution gratings, and 2-3% over most of the wavelength range of the G140L grating, although the uncertainty can be as large as 5% or more at some G140L wavelengths. We note that these errors are all relative to the optical flux near the V band and small additional errors may be present due to inaccuracies in the V band calibration. In addition, these error estimates are for the time at which the flux calibration data were obtained; the accuracy of the flux calibration at other times can be affected by errors in the time dependent sensitivity (TDS) correction.

  10. Absolute Efficiency Calibration of a Beta-Gamma Detector

    SciTech Connect

    Cooper, Matthew W.; Ely, James H.; Haas, Derek A.; Hayes, James C.; McIntyre, Justin I.; Lidey, Lance S.; Schrom, Brian T.

    2013-04-10

    Abstract- Identification and quantification of nuclear events such as the Fukushima reactor failure and nuclear explosions rely heavily on the accurate measurement of radioxenon releases. One radioxenon detection method depends on detecting beta-gamma coincident events paired with a stable xenon measurement to determine the concentration of a plume. Like all measurements, the beta-gamma method relies on knowing the detection efficiency for each isotope measured. Several methods are commonly used to characterize the detection efficiency for a beta-gamma detector. The most common method is using a NIST certified sealed source to determine the efficiency. A second method determines the detection efficiencies relative to an already characterized detector. Finally, a potentially more accurate method is to use the expected sample to perform an absolute efficiency calibration; in the case of a beta-gamma detector, this relies on radioxenon gas samples. The complication of the first method is it focuses only on the gamma detectors and does not offer a solution for determining the beta efficiency. The second method listed is not similarly constrained, however it relies on another detector to have a well-known efficiency calibration. The final method using actual radioxenon samples to make an absolute efficiency determination is the most desirable, but until recently it was not possible to produce all four isotopically pure radioxenon. The production, by University of Texas (UT), of isotopically pure radioxenon has allowed the beta-gamma detectors to be calibrated using the absolute efficiency method. The first four radioxenon isotope calibration will be discussed is this paper.

  11. Absolute Timing Calibration of the USA Experiment Using Pulsar Observations

    NASA Astrophysics Data System (ADS)

    Ray, P. S.; Wood, K. S.; Wolff, M. T.; Lovellette, M. N.; Sheikh, S.; Moon, D.-S.; Eikenberry, S. S.; Roberts, M.; Lyne, A.; Jordon, C.; Bloom, E. D.; Tournear, D.; Saz Parkinson, P.; Reilly, K.

    2003-03-01

    We update the status of the absolute time calibration of the USA Experiment as determined by observations of X-ray emitting rotation-powered pulsars. The brightest such source is the Crab Pulsar and we have obtained observations of the Crab at radio, IR, optical, and X-ray wavelengths. We directly compare arrival time determinations for 2--10 keV X-ray observations made contemporaneously with the PCA on the Rossi X-ray Timing Explorer and the USA Experiment on ARGOS. These two X-ray measurements employ very different means of measuring time and satellite position and thus have different systematic error budgets. The comparison with other wavelengths requires additional steps such as dispersion measure corrections and a precise definition of the ``peak'' of the light curve since the light curve shape varies with observing wavelength. We will describe each of these effects and quantify the magnitude of the systematic error that each may contribute. We will also include time comparison results for other pulsars, such as PSR B1509-58 and PSR B1821-24. Once the absolute time calibrations are well understood, comparing absolute arrival times at multiple energies can provide clues to the magnetospheric structure and emission region geometry. Basic research on X-ray Astronomy at NRL is funded by NRL/ONR.

  12. Absolute magnitude calibration using trigonometric parallax - Incomplete, spectroscopic samples

    NASA Technical Reports Server (NTRS)

    Ratnatunga, Kavan U.; Casertano, Stefano

    1991-01-01

    A new numerical algorithm is used to calibrate the absolute magnitude of spectroscopically selected stars from their observed trigonometric parallax. This procedure, based on maximum-likelihood estimation, can retrieve unbiased estimates of the intrinsic absolute magnitude and its dispersion even from incomplete samples suffering from selection biases in apparent magnitude and color. It can also make full use of low accuracy and negative parallaxes and incorporate censorship on reported parallax values. Accurate error estimates are derived for each of the fitted parameters. The algorithm allows an a posteriori check of whether the fitted model gives a good representation of the observations. The procedure is described in general and applied to both real and simulated data.

  13. Absolute calibration of vacuum ultraviolet spectrograph system for plasma diagnostics

    SciTech Connect

    Yoshikawa, M.; Kubota, Y.; Kobayashi, T.; Saito, M.; Numada, N.; Nakashima, Y.; Cho, T.; Koguchi, H.; Yagi, Y.; Yamaguchi, N.

    2004-10-01

    A space- and time-resolving vacuum ultraviolet (VUV) spectrograph system has been applied to diagnose impurity ions behavior in plasmas produced in the tandem mirror GAMMA 10 and the reversed field pinch TPE-RX. We have carried out ray tracing calculations for obtaining the characteristics of the VUV spectrograph and calibration experiments to measure the absolute sensitivities of the VUV spectrograph system for the wavelength range from 100 to 1100 A. By changing the incident angle, 50.6 deg. -51.4 deg., to the spectrograph whose nominal incident angle is 51 deg., we can change the observing spectral range of the VUV spectrograph. In this article, we show the ray tracing calculation results and absolute sensitivities when the angle of incidence into the VUV spectrograph is changed, and the results of VUV spectroscopic measurement in both GAMMA 10 and TPE-RX plasmas.

  14. Flow rate calibration for absolute cell counting rationale and design.

    PubMed

    Walker, Clare; Barnett, David

    2006-05-01

    There is a need for absolute leukocyte enumeration in the clinical setting, and accurate, reliable (and affordable) technology to determine absolute leukocyte counts has been developed. Such technology includes single platform and dual platform approaches. Derivations of these counts commonly incorporate the addition of a known number of latex microsphere beads to a blood sample, although it has been suggested that the addition of beads to a sample may only be required to act as an internal quality control procedure for assessing the pipetting error. This unit provides the technical details for undertaking flow rate calibration that obviates the need to add reference beads to each sample. It is envisaged that this report will provide the basis for subsequent clinical evaluations of this novel approach. PMID:18770842

  15. Technique for Radiometer and Antenna Array Calibration with a Radiated Noise Diode

    NASA Technical Reports Server (NTRS)

    Srinivasan, Karthik; Limaye, Ashutosh; Laymon, Charles; Meyer, Paul

    2009-01-01

    This paper presents a new technique to calibrate a microwave radiometer and antenna array system. This calibration technique uses a radiated noise source in addition to two calibration sources internal to the radiometer. The method accurately calibrates antenna arrays with embedded active devices (such as amplifiers) which are used extensively in active phased array antennas.

  16. Stability of array spectroradiometers and their suitability for absolute calibrations

    NASA Astrophysics Data System (ADS)

    Nevas, Saulius; Teuber, Annette; Sperling, Armin; Lindemann, Matthias

    2012-04-01

    An investigation of the short- and long-term stability of various low-end and high-end array spectroradiometers is presented. Potentially weak points of array spectroradiometers with respect to their suitability for absolute calibrations are pointed out. The influence of ambient conditions on relevant instrumental characteristics and their temporal stability is discussed. It is shown that the temporal stability of some instruments can be significantly affected by high ambient humidity. Most important ambient temperature effects on instrument properties are also discussed.

  17. Modeling and calibration of BRAMS antenna systems

    NASA Astrophysics Data System (ADS)

    Martínez Picar, Antonio; Ranvier, Sylvain; Anciaux, Michel; Lamy, Hervé

    2014-02-01

    Because of the geometry associated with the forward-scatter method for observing meteors via radio, knowing the radiation pattern of the involved antennas is essential to obtain parameters of scientific interest such as the meteoroid flux density. In this paper results of simulations of the antennas belonging to the Belgian RAdio Meteor Stations network (BRAMS) that are directly managed by the Belgian Institute for Space Aeronomy (BISA) are presented, as well as plans for verifying their patterns using an Unmanned Aerial Vehicle (UAV).

  18. SPRED spectrograph upgrade: high resolution grating and improved absolute calibrations

    SciTech Connect

    Stratton, B.C.; Fonck, R.J.; Ida, K.; Jaehnig, K.P.; Ramsey, A.T.

    1986-05-01

    Two improvements to the SPRED multichannel VUV spectrographs used on the TFTR and PBX tokamaks have been made: (1) A new 2100-g/mm grating covering the 100 to 320 A region with 0.4 A resolution (FWHM) has been added to the existing 450 g/mm grating (100 to 1100 A with 2 A resolution), and (2) the TFTR SPRED has been absolutely calibrated using synchrotron radiation from the NBS SURF II facility, while the PBX system has been calibrated using conventional branching ratios along with line ratios from charge-exchange-recombination-excited lines. The availability of high resolution spectra in the 100 to 320 A range provides improved measurements of metallic ion emissions and, when the instrument views across a neutral beam as in PBX, allows carbon and oxygen densities to be measured via charge exchange recombination spectroscopy.

  19. Active radiometric calorimeter for absolute calibration of radioactive sources

    NASA Astrophysics Data System (ADS)

    Stump, K. E.; DeWerd, L. A.; Rudman, D. A.; Schima, S. A.

    2005-03-01

    This report describes the design and initial noise floor measurements of a radiometric calorimeter designed to measure therapeutic medical radioactive sources. The instrument demonstrates a noise floor of approximately 2 nW. This low noise floor is achieved by using high temperature superconducting (HTS) transition edge sensor (TES) thermometers in a temperature-control feedback loop. This feedback loop will be used to provide absolute source calibrations based upon the electrical substitution method. Other unique features of the calorimeter are (a) its ability to change sources for calibration without disrupting the vacuum of the instrument, and (b) the ability to measure the emitted power of a source in addition to the total contained source power.

  20. Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers

    NASA Astrophysics Data System (ADS)

    Nehls, S.; Hakenjos, A.; Arts, M. J.; Blümer, J.; Bozdog, H.; van Cappellen, W. A.; Falcke, H.; Haungs, A.; Horneffer, A.; Huege, T.; Isar, P. G.; Krömer, O.

    2008-05-01

    Radio pulses are emitted during the development of air showers, where air showers are generated by ultra-high energy cosmic rays entering the Earth's atmosphere. These nano-second short pulses are presently investigated by various experiments for the purpose of using them as a new detection technique for cosmic particles. For an array of 30 digital radio antennas (LOPES experiment) an absolute amplitude calibration of the radio antennas including the full electronic chain of the data acquisition system is performed, in order to estimate absolute values of the electric field strength for these short radio pulses. This is mandatory, because the measured radio signals in the MHz frequency range have to be compared with theoretical estimates and with predictions from Monte Carlo simulations to reconstruct features of the primary cosmic particle. A commercial reference radio emitter is used to estimate frequency dependent correction factors for each single antenna of the radio antenna array. The expected received power is related to the power recorded by the full electronic chain. Systematic uncertainties due to different environmental conditions and the described calibration procedure are of order 20%.

  1. Absolute radiometric calibration of Landsat using a pseudo invariant calibration site

    USGS Publications Warehouse

    Helder, D.; Thome, K.J.; Mishra, N.; Chander, G.; Xiong, Xiaoxiong; Angal, A.; Choi, Tae-young

    2013-01-01

    Pseudo invariant calibration sites (PICS) have been used for on-orbit radiometric trending of optical satellite systems for more than 15 years. This approach to vicarious calibration has demonstrated a high degree of reliability and repeatability at the level of 1-3% depending on the site, spectral channel, and imaging geometries. A variety of sensors have used this approach for trending because it is broadly applicable and easy to implement. Models to describe the surface reflectance properties, as well as the intervening atmosphere have also been developed to improve the precision of the method. However, one limiting factor of using PICS is that an absolute calibration capability has not yet been fully developed. Because of this, PICS are primarily limited to providing only long term trending information for individual sensors or cross-calibration opportunities between two sensors. This paper builds an argument that PICS can be used more extensively for absolute calibration. To illustrate this, a simple empirical model is developed for the well-known Libya 4 PICS based on observations by Terra MODIS and EO-1 Hyperion. The model is validated by comparing model predicted top-of-atmosphere reflectance values to actual measurements made by the Landsat ETM+ sensor reflective bands. Following this, an outline is presented to develop a more comprehensive and accurate PICS absolute calibration model that can be Système international d'unités (SI) traceable. These initial concepts suggest that absolute calibration using PICS is possible on a broad scale and can lead to improved on-orbit calibration capabilities for optical satellite sensors.

  2. Monochromator-Based Absolute Calibration of a Standard Radiation Thermometer

    NASA Astrophysics Data System (ADS)

    Mantilla, J. M.; Hernanz, M. L.; Campos, J.; Martín, M. J.; Pons, A.; del Campo, D.

    2014-04-01

    Centro Español de Metrología (CEM) is disseminating the International Temperature Scale (ITS-90), at high temperatures, by using the fixed points of Ag and Cu and a standard radiation thermometer. However, the future mise-en-pratique for the definition of the kelvin ( MeP-K) will include the dissemination of the kelvin by primary methods and by indirect approximations capable of exceptionally low uncertainties or increased reliability. Primary radiometry is, at present, able to achieve uncertainties competitive with the ITS-90 above the silver point with one of the possible techniques the calibration for radiance responsivity of an imaging radiometer (radiance method). In order to carry out this calibration, IO-CSIC (Spanish Designated Institute for luminous intensity and luminous flux) has collaborated with CEM, allowing traceability to its cryogenic radiometer. A monochromator integrating sphere-based spectral comparator facility has been used to calibrate one of the CEM standard radiation thermometers. The absolute calibrated standard radiation thermometer has been used to determine the temperatures of the fixed points of Cu, Co-C, Pt-C, and Re-C. The results obtained are 1357.80 K, 1597.10 K, 2011.66 K, and 2747.64 K, respectively, with uncertainties ranging from 0.4 K to 1.1 K.

  3. Absolute calibration of the fast-delivery SAR product processed at Tromso satellite station

    NASA Astrophysics Data System (ADS)

    Weydahl, Dan J.

    1994-12-01

    Tromso Satellite Station (TSS) is the Norwegian national receiving station for ERS-1 SAR data. The TSS Fast Delivery (FD) SAR processor was upgraded during spring 1994 so that the whole processing chain will now be performed in power rather than in voltage. This new FD SAR product from TSS needs absolute calibration, and a calibration constant is therefore estimated. First, a TSS Power-processed ERS-1 SAR image was used. This image covers the ESA transponders in Flevoland. The integration method was used to estimate the backscattered power from the 3 transponders. The Earth ellipsoid, local incidence angle, antenna pattern, range-spread loss, pixel size and RCS were also taken into account in the calculation. The result was a calibration constant of 53.51 dB. An other method is to compare the backscatter from an ESA processed PRI product and a TSS Power-processed FD product acquired at the same place and time. Areas were extracted from two such SAR images, and the pixel values averaged in power. The known calibration constant for the PRI product was used in the comparison of the image products. The calibration constant for the TSS FD product was then found to be 54.20 dB. This is close to the result from using the ESA transponders.

  4. Geodetic antenna calibration test in the Antarctic environment

    USGS Publications Warehouse

    Grejner-Brzezinska, A.; Vazquez, E.; Hothem, L.

    2006-01-01

    TransAntarctic Mountain DEFormation (TAMDEF) Monitoring Network is the NSF-sponsored OSU and USGS project, aimed at measuring crustal motion in the Transantarctic Mountains of Victoria Land using GPS carrier phase measurements. Station monumentation, antenna mounts, antenna types, and data processing strategies were optimized to achieve mm-level estimates for the rates of motion. These data contributes also to regional Antarctic frame definition. Significant amount of data collected over several years allow the investigation of unique aspects of GPS geodesy in Antarctica, to determine how the error spectrum compares to the mid-latitude regions, and to identify the optimum measurement and data processing schemes for Antarctic conditions, in order to test the predicted rates of motion (mm-level w.r.t. time). The data collection for the TAMDEF project was initiated in 1996. The primary antenna used has been the Ashtech L1/L2 Dorne Margolin (D/M) choke ring. A few occupations involved the use of a Trimble D/M choke ring. The data were processed using the antenna calibration data available from the National Geodetic Survey (NGS). The recent developments in new antenna designs that are lighter in weight and lower in cost are being considered as a possible alternative to the bulkier and more expensive D/M choke ring design. In November 2003, in situ testing of three alternative models of L1/L2 antennas was conducted at a site located in the vicinity of McMurdo Station, Antarctica (S77.87, E166.56). The antenna models used in this test were: Ashtech D/M choke ring, Trimble D/M choke ring, Trimble Zephyr, and the NovAtel GPS-702. Two stations, spaced within 30 meters, were used in the test. Both had the characteristics similar to the stations of the TAMDEF network, i.e., the UNAVCO fixed-height, force-centered level mounts with a constant antenna offset were used, ensuring extreme stability of the antenna/ mount/pin set up. During each of the four 3-day test data collection

  5. The Absolute Calibration of the HiRes Detectors

    NASA Astrophysics Data System (ADS)

    Matthews, J. N.; Thomas, S. B.; HiRes Collaboration

    2003-07-01

    The HiRes experiment studies ultra high energy cosmic rays using the air fluorescence technique. The experiment uses large mirrors that collect the fluorescence light and fo cus it onto arrays of photomultiplier tubes (PMTs). The PMTs measure the intensity and time of arrival of the collected light. Our primary system for in situ calibration of the PMTs uses a high stability (<1%) portable light source. This source is transferred from the lab to the field where it is employed as a standard candle to calibrate the 64 detectors (>16,000 PMTs). To determine the absolute response it is necessary to understand the absolute light output of this source. We have measured the source irradiance using a hybrid photo dio de system, two NIST calibrated photo-dio des, and by observing the photo electron statistics of the PMTs. 2. Introduction The goal of the High Resolution Fly's Eye (HiRes) project is to study cosmic rays at the highest energies. An ultra high energy cosmic ray entering the earth's atmosphere collides with atmospheric nuclei triggering the development of an Extensive Air Shower (EAS). The EAS emits fluorescence light as it develops. HiRes uses the air fluorescence signal to measure properties of the primary cosmic ray particle. The fundamental detector elements in HiRes are photomultiplier tubes (PMTs). The light from an EAS is collected by large mirrors and fo cused into cameras each consisting of 256 PMTs [1]. Routine monitoring and calibration of the PMTs and associated electronics are crucial to the proper interpretation of the data. The primary system for in situ calibration of the PMTs involves the use of a high stability portable xenon flash lamp. The Roving Xenon Flasher (RXF) offers several advantages. The pulse-to-pulse variation in intensity is very small ˜0.3% and the stability over a night is better than 2%. The emission spectrum of the RXF is sufficiently broad to allow calibration over a wide range of wavelengths. It is also readily transported

  6. Antenna calibration models in height determinations in ASG-EUPOS' POZGEO-D service - a case study

    NASA Astrophysics Data System (ADS)

    Dawidowicz, Karol

    2012-12-01

    GNSS observations in a network of permanent stations are a complex systems which offer both post-processing and corrections sent in real-time. In Poland such a system, known as the Polish Active Geodetic Network (ASG-EUPOS), has been in operation since June 2008. The GNSS development forces also continuous modernization of ASG-EUPOS (e.g.: GPS/GLONASS receivers mounting, ASG+ project) which aims to improve the accuracy of position determination. One of the factors limiting the accuracy (especially the vertical component) is antenna phase center variations (PCV) problem. PCV problem is resolved using the antenna calibration process. As a result, antenna phase center corrections models (PCC) are created. So far three methods have been developed to determine GNSS antenna PCV. For this reason and because of some problems in introducing of absolute models at present we can speak of three models of receiver antennas PCV (so called: relative, absolute converted and absolute). The aim of this paper was to study the height differences caused by using different calibration models in GNSS observation processing done in the ASG-EUPOS POZGEO-D service. The analysis was done using 3 days of GNSS data, collected with four different receivers and antennas, divided by one hour observation sessions. The results of the calculations show that switching between PCV models may have a visible effect on height determination, particularly in high accuracy applications.

  7. On the absolute calibration of SO2 cameras

    NASA Astrophysics Data System (ADS)

    Lübcke, P.; Bobrowski, N.; Illing, S.; Kern, C.; Alvarez Nieves, J. M.; Vogel, L.; Zielcke, J.; Delgado Granados, H.; Platt, U.

    2012-09-01

    Sulphur dioxide emission flux measurements are an important tool for volcanic monitoring and eruption risk assessment. The SO2 camera technique remotely measures volcanic emissions by analysing the ultraviolet absorption of SO2 in a narrow spectral window between 305 nm and 320 nm using solar radiation scattered in the atmosphere. The SO2 absorption is selectively detected by mounting band-pass interference filters in front of a two-dimensional, UV-sensitive CCD detector. While this approach is simple and delivers valuable insights into the two-dimensional SO2 distribution, absolute calibration has proven to be difficult. An accurate calibration of the SO2 camera (i.e., conversion from optical density to SO2 column density, CD) is crucial to obtain correct SO2 CDs and flux measurements that are comparable to other measurement techniques and can be used for volcanological applications. The most common approach for calibrating SO2 camera measurements is based on inserting quartz cells (cuvettes) containing known amounts of SO2 into the light path. It has been found, however, that reflections from the windows of the calibration cell can considerably affect the signal measured by the camera. Another possibility for calibration relies on performing simultaneous measurements in a small area of the camera's field-of-view (FOV) by a narrow-field-of-view Differential Optical Absorption Spectroscopy (NFOV-DOAS) system. This procedure combines the very good spatial and temporal resolution of the SO2 camera technique with the more accurate column densities obtainable from DOAS measurements. This work investigates the uncertainty of results gained through the two commonly used, but quite different calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO2 camera, a NFOV-DOAS system and an Imaging DOAS (IDOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective

  8. Absolute IGS antenna phase center model igs08.atx: status and potential improvements

    NASA Astrophysics Data System (ADS)

    Schmid, R.; Dach, R.; Collilieux, X.; Jäggi, A.; Schmitz, M.; Dilssner, F.

    2016-04-01

    On 17 April 2011, all analysis centers (ACs) of the International GNSS Service (IGS) adopted the reference frame realization IGS08 and the corresponding absolute antenna phase center model igs08.atx for their routine analyses. The latter consists of an updated set of receiver and satellite antenna phase center offsets and variations (PCOs and PCVs). An update of the model was necessary due to the difference of about 1 ppb in the terrestrial scale between two consecutive realizations of the International Terrestrial Reference Frame (ITRF2008 vs. ITRF2005), as that parameter is highly correlated with the GNSS satellite antenna PCO components in the radial direction.

  9. Absolute Calibration of Optical Satellite Sensors Using Libya 4 Pseudo Invariant Calibration Site

    NASA Technical Reports Server (NTRS)

    Mishra, Nischal; Helder, Dennis; Angal, Amit; Choi, Jason; Xiong, Xiaoxiong

    2014-01-01

    The objective of this paper is to report the improvements in an empirical absolute calibration model developed at South Dakota State University using Libya 4 (+28.55 deg, +23.39 deg) pseudo invariant calibration site (PICS). The approach was based on use of the Terra MODIS as the radiometer to develop an absolute calibration model for the spectral channels covered by this instrument from visible to shortwave infrared. Earth Observing One (EO-1) Hyperion, with a spectral resolution of 10 nm, was used to extend the model to cover visible and near-infrared regions. A simple Bidirectional Reflectance Distribution function (BRDF) model was generated using Terra Moderate Resolution Imaging Spectroradiometer (MODIS) observations over Libya 4 and the resulting model was validated with nadir data acquired from satellite sensors such as Aqua MODIS and Landsat 7 (L7) Enhanced Thematic Mapper (ETM+). The improvements in the absolute calibration model to account for the BRDF due to off-nadir measurements and annual variations in the atmosphere are summarized. BRDF models due to off-nadir viewing angles have been derived using the measurements from EO-1 Hyperion. In addition to L7 ETM+, measurements from other sensors such as Aqua MODIS, UK-2 Disaster Monitoring Constellation (DMC), ENVISAT Medium Resolution Imaging Spectrometer (MERIS) and Operational Land Imager (OLI) onboard Landsat 8 (L8), which was launched in February 2013, were employed to validate the model. These satellite sensors differ in terms of the width of their spectral bandpasses, overpass time, off-nadir-viewing capabilities, spatial resolution and temporal revisit time, etc. The results demonstrate that the proposed empirical calibration model has accuracy of the order of 3% with an uncertainty of about 2% for the sensors used in the study.

  10. Documentation for the machine-readable version of the Absolute Calibration of Stellar Spectrophotometry

    NASA Technical Reports Server (NTRS)

    Warren, W. H., Jr.

    1982-01-01

    The machine-readable data file of The Absolute Calibration of Stellar Spectrophotometry as distributed by the Astronomical Data Center is described. The data file contains the absolute fluxes for 16 stars published in Tables 1 and 2 of Johnson (1980). The absolute calibrations were accomplished by combining the 13-color photometry calibrations of Johnson and Mitchell (1975) with spectra obtained with a Michelson spectrophotometer and covering the wavelength range 4000 to 10300 A (Johnson 1977). The agreement between this absolute calibration and another recent one based upon data for a Lyr and 109 Vir by Tug, White and Lockwood (1977) is shown by Johnson (1980) to be quite good.

  11. Differences between GPS receiver antenna calibration models and influence on geodetic positioning

    NASA Astrophysics Data System (ADS)

    Baire, Q.; Bruyninx, C.; Pottiaux, E.; Legrand, J.; Aerts, W.

    2012-12-01

    Since April 2011, the igs08.atx antenna calibration model is used in the routine IGS (International GNSS Service) data analysis. The model includes mean robot calibrations to correct for the offset and phase center variations of the GNSS receiver antennas. These so-called "type" calibrations are means of the individual calibrations available for a specific antenna/radome combination. The aim of this study is to quantify the offset on the computed station positions when using different receiver antenna calibration models in the analysis. First, type calibrations are compared to individual receiver antenna calibrations. We analyze the observations of the 43 EUREF Permanent Network (EPN) stations equipped with individually calibrated receiver antenna over the period covering 2003 to 2010 using the Precise Point Positioning (PPP) technique. The difference between individual and type calibrations has a larger impact on the vertical component: the position offsets reach 4 mm in the horizontal components and 10 mm in the vertical component. In a second step, the effect of different individual calibration models of the same antenna on the positioning is assessed. For that purpose, data from several GNSS stations equipped with an antenna which has been individually calibrated at two calibration agencies are used. Those agencies are GEO++, performing robot calibrations, and University of Bonn, performing anechoic chamber calibrations, both recognized by the IGS. Initial results show that the position offsets induced by different calibration methods can reach 3 mm in the horizontal components and 7 mm in the vertical component.

  12. Modelling and measurement of the absolute level of power radiated by antenna integrated THz UTC photodiodes.

    PubMed

    Natrella, Michele; Liu, Chin-Pang; Graham, Chris; van Dijk, Frederic; Liu, Huiyun; Renaud, Cyril C; Seeds, Alwyn J

    2016-05-30

    We determine the output impedance of uni-travelling carrier (UTC) photodiodes at frequencies up to 400 GHz by performing, for the first time, 3D full-wave modelling of detailed UTC photodiode structures. In addition, we demonstrate the importance of the UTC impedance evaluation, by using it in the prediction of the absolute power radiated by an antenna integrated UTC, over a broad frequency range and confirming the predictions by experimental measurements up to 185 GHz. This is done by means of 3D full-wave modelling and is only possible since the source (UTC) to antenna impedance match is properly taken into account. We also show that, when the UTC-to-antenna coupling efficiency is modelled using the classical junction-capacitance/series-resistance concept, calculated and measured levels of absolute radiated power are in substantial disagreement, and the maximum radiated power is overestimated by a factor of almost 7 dB. The ability to calculate the absolute emitted power correctly enables the radiated power to be maximised through optimisation of the UTC-to-antenna impedance match. PMID:27410104

  13. Methods to calibrate the absolute receive sensitivity of single-element, focused transducers

    PubMed Central

    Rich, Kyle T.; Mast, T. Douglas

    2015-01-01

    Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812

  14. Methods to calibrate the absolute receive sensitivity of single-element, focused transducers.

    PubMed

    Rich, Kyle T; Mast, T Douglas

    2015-09-01

    Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812

  15. Impact of different individual GNSS receiver antenna calibration models on geodetic positioning

    NASA Astrophysics Data System (ADS)

    Baire, Q.; Pottiaux, E.; Bruyninx, C.; Defraigne, P.; Aerts, W.; Legrand, J.; Bergeot, N.; Chevalier, J. M.

    2012-04-01

    Since April 2011, the igs08.atx antenna calibration model is used in the routine IGS (International GNSS Service) data analysis. The model includes mean robot calibrations to correct for the offset and phase center variations of the GNSS receiver antennas. These so-called "type" calibrations are means of the individual calibrations available for a specific antenna/radome combination. The GNSS data analysis performed within the EUREF Permanent Network (EPN) aims at being as consistent as possible with the IGS analysis. This also applies to the receiver antenna calibrations. However, when available, individual antenna calibrations are used within the EPN analysis instead of the "type" calibration. When these individual calibrations are unavailable, then the EPN analysis falls back to (type) calibrations identical as the ones used within the IGS (igs08.atx). The aim of this study is to evaluate the significance of the offset caused by using different receiver antenna calibration models on the station position. Using the PPP (Precise Point Positioning) technique, we first investigate the differences in positioning obtained when switching between individual antenna calibrations and type calibrations. We analyze the observations of the 43 EPN stations equipped with receiver antenna individually calibrated over the period covering from 2003 to 2010 and we show that these differences can reach up to 4 mm in horizontal and 10 mm in vertical. Secondly, we study the accuracy of the individual calibrations models and we evaluate the effect of different sets of individual calibrations on the positioning. For that purpose, we use the data from 6 GNSS stations equipped with an antenna which has been individually calibrated at two calibration facilities recognized by the IGS: GEO++ and Bonn institute.

  16. [In-flight absolute radiometric calibration of UAV multispectral sensor].

    PubMed

    Chen, Wei; Yan, Lei; Gou, Zhi-Yang; Zhao, Hong-Ying; Liu, Da-Ping; Duan, Yi-Ni

    2012-12-01

    Based on the data of the scientific experiment in Urad Front Banner for UAV Remote Sensing Load Calibration Field project, with the help of 6 hyperspectral radiometric targets with good Lambertian property, the wide-view multispectral camera in UAV was calibrated adopting reflectance-based method. The result reveals that for green, red and infrared channel, whose images were successfully captured, the linear correlation coefficients between the DN and radiance are all larger than 99%. In final analysis, the comprehensive error is no more than 6%. The calibration results demonstrate that the hyperspectral targets equipped by the calibration field are well suitable for air-borne multispectral load in-flight calibration. The calibration result is reliable and could be used in the retrieval of geophysical parameters. PMID:23427528

  17. Absolute spectral radiance responsivity calibration of sun photometers

    SciTech Connect

    Xu Qiuyun; Zheng Xiaobing; Zhang Wei; Wang Xianhua; Li Jianjun; Li Xin; Li Zhengqiang

    2010-03-15

    Sun photometers are designed to measure direct solar irradiance and diffused sky radiance for the purpose of atmospheric parameters characterization. A sun photometer is usually calibrated by using a lamp-illuminated integrating sphere source for its band-averaged radiance responsivity, which normally has an uncertainty of 3%-5% at present. Considering the calibration coefficients may also change with time, a regular high precision calibration is important to maintain data quality. In this paper, a tunable-laser-based facility for spectral radiance responsivity calibration has been developed at the Key Laboratory of Optical Calibration and Characterization, Chinese Academy of Sciences. A reference standard radiance radiometer, calibrated against cryogenic radiometer, is used to determine the radiance from a laser-illuminated integrating sphere source. Spectral radiance responsivity of CIMEL CE318-2 sun photometer is calibrated using this new calibration system with a combined standard uncertainty of about 0.8%. As a validation, the derived band-averaged radiance responsivity are compared to that from a Goddard Space Flight Center lamp-based sphere calibration and good agreements (difference <1.4%) are found from 675 to 1020 nm bands.

  18. On the absolute calibration of SO2 cameras

    USGS Publications Warehouse

    Lübcke, Peter; Bobrowski, Nicole; Illing, Sebastian; Kern, Christoph; Alvarez Nieves, Jose Manuel; Vogel, Leif; Zielcke, Johannes; Delgados Granados, Hugo; Platt, Ulrich

    2013-01-01

    This work investigates the uncertainty of results gained through the two commonly used, but quite different, calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO2 camera, a NFOVDOAS system and an Imaging DOAS (I-DOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective results are compared with measurements from an I-DOAS to verify the calibration curve over the spatial extent of the image. The results show that calibration cells, while working fine in some cases, can lead to an overestimation of the SO2 CD by up to 60% compared with CDs from the DOAS measurements. Besides these errors of calibration, radiative transfer effects (e.g. light dilution, multiple scattering) can significantly influence the results of both instrument types. The measurements presented in this work were taken at Popocatepetl, Mexico, between 1 March 2011 and 4 March 2011. Average SO2 emission rates between 4.00 and 14.34 kg s−1 were observed.

  19. Quantum Efficient Detectors for Use in Absolute Calibration

    NASA Technical Reports Server (NTRS)

    Faust, Jessica; Eastwood, Michael; Pavri, Betina; Raney, James

    1998-01-01

    The trap or quantum efficient detector has a quantum efficiency of greater than 0.98 for the region from 450 to 900 nm. The region of flattest response is from 600 to 900 nm. The QED consists of three windowless Hamamatsu silicon detectors. The QED was mounted below AVIRIS to monitor the Spectralon panel for changes in radiance during radiometric calibration. The next step is to permanently mount the detector to AVIRIS and monitor the overall radiance of scenes along with calibration.

  20. The absolute radiometric calibration of the advanced very high resolution radiometer

    NASA Technical Reports Server (NTRS)

    Slater, P. N.; Teillet, P. M.; Ding, Y.

    1988-01-01

    The need for independent, redundant absolute radiometric calibration methods is discussed with reference to the Thematic Mapper. Uncertainty requirements for absolute calibration of between 0.5 and 4 percent are defined based on the accuracy of reflectance retrievals at an agricultural site. It is shown that even very approximate atmospheric corrections can reduce the error in reflectance retrieval to 0.02 over the reflectance range 0 to 0.4.

  1. Simple and accurate empirical absolute volume calibration of a multi-sensor fringe projection system

    NASA Astrophysics Data System (ADS)

    Gdeisat, Munther; Qudeisat, Mohammad; AlSa`d, Mohammed; Burton, David; Lilley, Francis; Ammous, Marwan M. M.

    2016-05-01

    This paper suggests a novel absolute empirical calibration method for a multi-sensor fringe projection system. The optical setup of the projector-camera sensor can be arbitrary. The term absolute calibration here means that the centre of the three dimensional coordinates in the resultant calibrated volume coincides with a preset centre to the three-dimensional real-world coordinate system. The use of a zero-phase fringe marking spot is proposed to increase depth calibration accuracy, where the spot centre is determined with sub-pixel accuracy. Also, a new method is proposed for transversal calibration. Depth and transversal calibration methods have been tested using both single sensor and three-sensor fringe projection systems. The standard deviation of the error produced by this system is 0.25 mm. The calibrated volume produced by this method is 400 mm×400 mm×140 mm.

  2. On the precision of absolute sensitivity calibration and specifics of spectroscopic quantities interpretation in tokamaks.

    PubMed

    Naydenkova, D I; Weinzettl, V; Stockel, J; Matějíček, J

    2014-12-01

    Typical situations, which can be met during the process of absolute calibration, are shown in the case of a visible light observation system for the COMPASS tokamak. Technical issues and experimental limitations of absolute measurements connected with tokamak operation are discussed. PMID:25607972

  3. Confidence-Accuracy Calibration in Absolute and Relative Face Recognition Judgments

    ERIC Educational Resources Information Center

    Weber, Nathan; Brewer, Neil

    2004-01-01

    Confidence-accuracy (CA) calibration was examined for absolute and relative face recognition judgments as well as for recognition judgments from groups of stimuli presented simultaneously or sequentially (i.e., simultaneous or sequential mini-lineups). When the effect of difficulty was controlled, absolute and relative judgments produced…

  4. On the absolute calibration of SO2 cameras

    NASA Astrophysics Data System (ADS)

    Lübcke, P.; Bobrowski, N.; Illing, S.; Kern, C.; Alvarez Nieves, J. M.; Vogel, L.; Zielcke, J.; Delgado Granados, H.; Platt, U.

    2013-03-01

    Sulphur dioxide emission rate measurements are an important tool for volcanic monitoring and eruption risk assessment. The SO2 camera technique remotely measures volcanic emissions by analysing the ultraviolet absorption of SO2 in a narrow spectral window between 300 and 320 nm using solar radiation scattered in the atmosphere. The SO2 absorption is selectively detected by mounting band-pass interference filters in front of a two-dimensional, UV-sensitive CCD detector. One important step for correct SO2 emission rate measurements that can be compared with other measurement techniques is a correct calibration. This requires conversion from the measured optical density to the desired SO2 column density (CD). The conversion factor is most commonly determined by inserting quartz cells (cuvettes) with known amounts of SO2 into the light path. Another calibration method uses an additional narrow field-of-view Differential Optical Absorption Spectroscopy system (NFOV-DOAS), which measures the column density simultaneously in a small area of the camera's field-of-view. This procedure combines the very good spatial and temporal resolution of the SO2 camera technique with the more accurate column densities obtainable from DOAS measurements. This work investigates the uncertainty of results gained through the two commonly used, but quite different, calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO2 camera, a NFOV-DOAS system and an Imaging DOAS (I-DOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective results are compared with measurements from an I-DOAS to verify the calibration curve over the spatial extent of the image. The results show that calibration cells, while working fine in some cases, can lead to an overestimation of the SO2 CD by up to 60% compared with CDs from the DOAS measurements. Besides these errors of calibration, radiative transfer

  5. Calibration of positional consistency between mechanical shaft and electronic boresight for radar antenna

    NASA Astrophysics Data System (ADS)

    Jiang, Li; Wang, Dong-wei; Liu, Yong; Chen, Xiao-hui; Liu, Yue-dong

    2015-02-01

    By fixing a glass cubic prism facing an antenna, the positional relation between the coordinates of the cubic prism and the mechanical shaft was measured in a lab for the antenna, and the positional relation between the coordinates of the cubic prism and the wave was measured in a microwave anechoic chamber. The positional relation between the antenna and the wave was used to calibrate the positional consistency between the mechanical shaft and the electronic boresight. The calibration uncertainty was calibrated by analyzing the measurement data collected in the lab and the microwave anechoic chamber. Experimental results indicated that the proposed method could be used to calibrate the positional consistency between the antenna and the electronic boresight of a radar system, and the calibration results are within the accuracy limits for radar antennas.

  6. Absolute calibration of the RADSCAT scatterometer using precision spheres

    NASA Technical Reports Server (NTRS)

    Grantham, W. L.; Schroeder, L. C.; Mitchell, J. L.

    1976-01-01

    Tests using precision sphere targets suspended from balloons were conducted to calibrate the received-power/transmitted-power tatio of the RADSCAT scatterometer. Comparisons were made of these measured results with theoretical return from spheres. The RADSCAT scatterometer measurements at 13.9 GHz should be corrected by -2.4 dB, and those at 9.3 GHz, by -4.3 dB. The techniques described should be generally applicable to calibration of scatterometers where measurement precision is of prime importance. Inferred from the magnitude of these RADSCAT corrections was the present state of technology in building precision scatterometers.

  7. Verification of Absolute Calibration of Quantum Efficiency for LSST CCDs

    NASA Astrophysics Data System (ADS)

    Coles, Rebecca; Chiang, James; Cinabro, David; Gilbertson, Woodrow; Haupt, justine; Kotov, Ivan; Neal, Homer; Nomerotski, Andrei; O'Connor, Paul; Stubbs, Christopher; Takacs, Peter

    2016-01-01

    We describe a system to measure the Quantum Efficiency in the wavelength range of 300nm to 1100nm of 40x40 mm n-channel CCD sensors for the construction of the 3.2 gigapixel LSST focal plane. The technique uses a series of instruments to create a very uniform flux of photons of controllable intensity in the wavelength range of interest across the face of the sensor. This allows the absolute Quantum Efficiency to be measured with an accuracy in the 1% range. This system will be part of a production facility at Brookhaven National Lab for the basic components of the LSST camera.

  8. Calibration Methods for Air Coupled Antennas - COST Action TU1208

    NASA Astrophysics Data System (ADS)

    Marecos, Vânia; Solla, Mercedes; Fontul, Simona; Pajewski, Lara

    2016-04-01

    This work focuses on the comparison of different methods for calibrating air coupled antennas: Coring, Surface Reflection Method (SRM) and Common Mid-Point (CMP) through the analysis of GPR data collected in a test site with different pavement solutions. Research activities have been carried out during a Short Term Scientific Mission (STSM) funded by the COST (European Cooperation in Science and Technology) Action TU1208 "Civil Engineering Applications of Ground Penetrating Radar" in December 2015. The use of GPR in transport infrastructures represents one of the most significant advances for obtaining continuous data along the road, with the advantage of operation at traffic speed and being a non-destructive technique. Its main application has been the evaluation of layer thickness. For the determination of layer thickness, it is necessary to know the velocity of the signal, which depends on the dielectric constant of the material, and the two-way travel time of the reflected signal that is recorded by the GPR system. The calculation of the dielectric value of the materials can be done using different approaches such as: using fixed values based on experience, laboratory determination of dielectric values, applying the SRM, performing back calculation from ground truth references such as cores and test pits, or using the CMP method. The problem with using ground truth is that it is time consuming, labour intensive and intrusive to traffic, in addition, a drill core is not necessarily representative of the whole surveyed area. Regarding the surface reflection technique, one of the problems is that it only measures the dielectric value from the layer surface and not from the whole layer. Recent works already started to address some of these challenges proposing new approaches for GPR layer thickness measurements using multiple antennas to calculate the average dielectric value of the asphalt layer, taking advantage of significant hardware improvements in GPR

  9. First Absolutely Calibrated Localized Measurements of Ion Velocity in the MST in Locked and Rotating Plasmas

    NASA Astrophysics Data System (ADS)

    Baltzer, M.; Craig, D.; den Hartog, D. J.; Nornberg, M. D.; Munaretto, S.

    2015-11-01

    An Ion Doppler Spectrometer (IDS) is used on MST for high time-resolution passive and active measurements of impurity ion emission. Absolutely calibrated measurements of flow are difficult because the spectrometer records data within 0.3 nm of the C+5 line of interest, and commercial calibration lamps do not produce lines in this narrow range . A novel optical system was designed to absolutely calibrate the IDS. The device uses an UV LED to produce a broad emission curve in the desired region. A Fabry-Perot etalon filters this light, cutting transmittance peaks into the pattern of the LED emission. An optical train of fused silica lenses focuses the light into the IDS with f/4. A holographic diffuser blurs the light cone to increase homogeneity. Using this light source, the absolute Doppler shift of ion emissions can be measured in MST plasmas. In combination with charge exchange recombination spectroscopy, localized ion velocities can now be measured. Previously, a time-averaged measurement along the chord bisecting the poloidal plane was used to calibrate the IDS; the quality of these central chord calibrations can be characterized with our absolute calibration. Calibration errors may also be quantified and minimized by optimizing the curve-fitting process. Preliminary measurements of toroidal velocity in locked and rotating plasmas will be shown. This work has been supported by the US DOE.

  10. A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Steinmetz, T.; Holzwarth, R.; Kentischer, T.; Schmidt, W.

    2012-10-01

    A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut für Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.

  11. Precise calibration of a GNSS antenna array for adaptive beamforming applications.

    PubMed

    Daneshmand, Saeed; Sokhandan, Negin; Zaeri-Amirani, Mohammad; Lachapelle, Gérard

    2014-01-01

    The use of global navigation satellite system (GNSS) antenna arrays for applications such as interference counter-measure, attitude determination and signal-to-noise ratio (SNR) enhancement is attracting significant attention. However, precise antenna array calibration remains a major challenge. This paper proposes a new method for calibrating a GNSS antenna array using live signals and an inertial measurement unit (IMU). Moreover, a second method that employs the calibration results for the estimation of steering vectors is also proposed. These two methods are applied to the receiver in two modes, namely calibration and operation. In the calibration mode, a two-stage optimization for precise calibration is used; in the first stage, constant uncertainties are estimated while in the second stage, the dependency of each antenna element gain and phase patterns to the received signal direction of arrival (DOA) is considered for refined calibration. In the operation mode, a low-complexity iterative and fast-converging method is applied to estimate the satellite signal steering vectors using the calibration results. This makes the technique suitable for real-time applications employing a precisely calibrated antenna array. The proposed calibration method is applied to GPS signals to verify its applicability and assess its performance. Furthermore, the data set is used to evaluate the proposed iterative method in the receiver operation mode for two different applications, namely attitude determination and SNR enhancement. PMID:24887043

  12. Precise Calibration of a GNSS Antenna Array for Adaptive Beamforming Applications

    PubMed Central

    Daneshmand, Saeed; Sokhandan, Negin; Zaeri-Amirani, Mohammad; Lachapelle, Gérard

    2014-01-01

    The use of global navigation satellite system (GNSS) antenna arrays for applications such as interference counter-measure, attitude determination and signal-to-noise ratio (SNR) enhancement is attracting significant attention. However, precise antenna array calibration remains a major challenge. This paper proposes a new method for calibrating a GNSS antenna array using live signals and an inertial measurement unit (IMU). Moreover, a second method that employs the calibration results for the estimation of steering vectors is also proposed. These two methods are applied to the receiver in two modes, namely calibration and operation. In the calibration mode, a two-stage optimization for precise calibration is used; in the first stage, constant uncertainties are estimated while in the second stage, the dependency of each antenna element gain and phase patterns to the received signal direction of arrival (DOA) is considered for refined calibration. In the operation mode, a low-complexity iterative and fast-converging method is applied to estimate the satellite signal steering vectors using the calibration results. This makes the technique suitable for real-time applications employing a precisely calibrated antenna array. The proposed calibration method is applied to GPS signals to verify its applicability and assess its performance. Furthermore, the data set is used to evaluate the proposed iterative method in the receiver operation mode for two different applications, namely attitude determination and SNR enhancement. PMID:24887043

  13. SMOV Absolute Flux Calibration of the COS FUV Modes

    NASA Astrophysics Data System (ADS)

    Massa, Derck; Keyes, Charles; Penton, Steve; Bohlin, Ralph; Froning, Cynthia

    2010-01-01

    Point source sensitivity curves are determined for the COS FUV gratings: G140L, G130M and G160M. Observations through the Primary Science Aperture (PSA) were obtained of the standard star LDS749b for all central wavelength settings of all the gratings. In addition, PSA observations of the standard stars WD1057+729 and GD71 were obtained at selected settings. Further, observations of the standard star GD71 were also obtained at selected settings through the Bright Object Aperture (BOA), in order to characterize its transmission and, hence, the COS sensitivity using the BOA. The accuracy of the calibration is estimated to be 5%. Issues limiting the current accuracy and approaches to address them are discussed.

  14. Z-corrections for DSN 70-meter antenna ranging calibration

    NASA Technical Reports Server (NTRS)

    Cha, A. G.

    1987-01-01

    The Z-corrections of the DSN 70 m dual-shaped reflector antennas are documented. These corrections to the group delay time measured by the translator are required before the 70 m antennas can be used for ranging.

  15. Calibration of the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

    NASA Technical Reports Server (NTRS)

    Thome, Kurtis; Barnes, Robert; Baize, Rosemary; O'Connell, Joseph; Hair, Jason

    2010-01-01

    The Climate Absolute Radiance and Refractivity Observatory (CLARREO) plans to observe climate change trends over decadal time scales to determine the accuracy of climate projections. The project relies on spaceborne earth observations of SI-traceable variables sensitive to key decadal change parameters. The mission includes a reflected solar instrument retrieving at-sensor reflectance over the 320 to 2300 nm spectral range with 500-m spatial resolution and 100-km swath. Reflectance is obtained from the ratio of measurements of the earth s surface to those while viewing the sun relying on a calibration approach that retrieves reflectance with uncertainties less than 0.3%. The calibration is predicated on heritage hardware, reduction of sensor complexity, adherence to detector-based calibration standards, and an ability to simulate in the laboratory on-orbit sources in both size and brightness to provide the basis of a transfer to orbit of the laboratory calibration including a link to absolute solar irradiance measurements.

  16. Absolute wavelength calibration of pulsed lasers by use of machine vision.

    PubMed

    Nayuki, T; Fujii, T; Nemoto, K

    2001-04-01

    We developed a new absolute wavelength calibration system that uses machine vision for measurement of low-repetition-rate, short-pulse-duration (10-Hz, 5-ns) tunable lasers. Weak fluorescence from an iodine cell was measured by use of machine vision as a spatially gated integrator, and a pulsed dye-laser wavelength was calibrated with an accuracy of +/-0.005 nm , which is precise enough for differential absorption lidar application. PMID:18040341

  17. Absolute intensity calibration of the 32-channel heterodyne radiometer on experimental advanced superconducting tokamak

    SciTech Connect

    Liu, X.; Zhao, H. L.; Liu, Y. Li, E. Z.; Han, X.; Ti, A.; Hu, L. Q.; Zhang, X. D.; Domier, C. W.; Luhmann, N. C.

    2014-09-15

    This paper presents the results of the in situ absolute intensity calibration for the 32-channel heterodyne radiometer on the experimental advanced superconducting tokamak. The hot/cold load method is adopted, and the coherent averaging technique is employed to improve the signal to noise ratio. Measured spectra and electron temperature profiles are compared with those from an independent calibrated Michelson interferometer, and there is a relatively good agreement between the results from the two different systems.

  18. Absolute intensity calibration of the 32-channel heterodyne radiometer on experimental advanced superconducting tokamak.

    PubMed

    Liu, X; Zhao, H L; Liu, Y; Li, E Z; Han, X; Domier, C W; Luhmann, N C; Ti, A; Hu, L Q; Zhang, X D

    2014-09-01

    This paper presents the results of the in situ absolute intensity calibration for the 32-channel heterodyne radiometer on the experimental advanced superconducting tokamak. The hot/cold load method is adopted, and the coherent averaging technique is employed to improve the signal to noise ratio. Measured spectra and electron temperature profiles are compared with those from an independent calibrated Michelson interferometer, and there is a relatively good agreement between the results from the two different systems. PMID:25273727

  19. Flying Boresight for Advanced Testing and Calibration of Tracking Antennas and Flight Path Simulations

    NASA Astrophysics Data System (ADS)

    Hafner, D.

    2015-09-01

    The application of ground-based boresight sources for calibration and testing of tracking antennas usually entails various difficulties, mostly due to unwanted ground effects. To avoid this problem, DLR MORABA developed a small, lightweight, frequency-adjustable S-band boresight source, mounted on a small remote-controlled multirotor aircraft. Highly accurate GPS-supported, position and altitude control functions allow both, very steady positioning of the aircraft in mid-air, and precise waypoint-based, semi-autonomous flights. In contrast to fixed near-ground boresight sources this flying setup enables to avoid obstructions in the Fresnel zone between source and antenna. Further, it minimizes ground reflections and other multipath effects which can affect antenna calibration. In addition, the large operating range of a flying boresight simplifies measurements in the far field of the antenna and permits undisturbed antenna pattern tests. A unique application is the realistic simulation of sophisticated flight paths, including overhead tracking and demanding trajectories of fast objects such as sounding rockets. Likewise, dynamic tracking tests are feasible which provide crucial information about the antenna pedestal performance — particularly at high elevations — and reveal weaknesses in the autotrack control loop of tracking antenna systems. During acceptance tests of MORABA's new tracking antennas, a manned aircraft was never used, since the Flying Boresight surpassed all expectations regarding usability, efficiency, and precision. Hence, it became an integral part of MORABA's standard antenna setup and calibration procedures.

  20. Artifact correction and absolute radiometric calibration techniques employed in the Landsat 7 image assessment system

    USGS Publications Warehouse

    Boncyk, Wayne C.; Markham, Brian L.; Barker, John L.; Helder, Dennis

    1996-01-01

    The Landsat-7 Image Assessment System (IAS), part of the Landsat-7 Ground System, will calibrate and evaluate the radiometric and geometric performance of the Enhanced Thematic Mapper Plus (ETM +) instrument. The IAS incorporates new instrument radiometric artifact correction and absolute radiometric calibration techniques which overcome some limitations to calibration accuracy inherent in historical calibration methods. Knowledge of ETM + instrument characteristics gleaned from analysis of archival Thematic Mapper in-flight data and from ETM + prelaunch tests allow the determination and quantification of the sources of instrument artifacts. This a priori knowledge will be utilized in IAS algorithms designed to minimize the effects of the noise sources before calibration, in both ETM + image and calibration data.

  1. Electron cyclotron emission measurements on JET: Michelson interferometer, new absolute calibration, and determination of electron temperature.

    PubMed

    Schmuck, S; Fessey, J; Gerbaud, T; Alper, B; Beurskens, M N A; de la Luna, E; Sirinelli, A; Zerbini, M

    2012-12-01

    At the fusion experiment JET, a Michelson interferometer is used to measure the spectrum of the electron cyclotron emission in the spectral range 70-500 GHz. The interferometer is absolutely calibrated using the hot/cold technique and, in consequence, the spatial profile of the plasma electron temperature is determined from the measurements. The current state of the interferometer hardware, the calibration setup, and the analysis technique for calibration and plasma operation are described. A new, full-system, absolute calibration employing continuous data acquisition has been performed recently and the calibration method and results are presented. The noise level in the measurement is very low and as a result the electron cyclotron emission spectrum and thus the spatial profile of the electron temperature are determined to within ±5% and in the most relevant region to within ±2%. The new calibration shows that the absolute response of the system has decreased by about 15% compared to that measured previously and possible reasons for this change are presented. Temperature profiles measured with the Michelson interferometer are compared with profiles measured independently using Thomson scattering diagnostics, which have also been recently refurbished and recalibrated, and agreement within experimental uncertainties is obtained. PMID:23282107

  2. Glassy Carbon as an Absolute Intensity Calibration Standard for Small-Angle Scattering

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Ilavsky, Jan; Long, Gabrielle G.; Quintana, John P. G.; Allen, Andrew J.; Jemian, Pete R.

    2010-05-01

    Absolute calibration of small-angle scattering (SAS) intensity data (measured in terms of the differential scattering cross section per unit sample volume per unit solid angle) is essential for many important aspects of quantitative SAS analysis, such as obtaining the number density, volume fraction, and specific surface area of the scatterers. It also enables scattering data from different instruments (light, X-ray, or neutron scattering) to be combined, and it can even be useful to detect the existence of artifacts in the experimental data. Different primary or secondary calibration methods are available. In the latter case, absolute intensity calibration requires a stable artifact with the necessary scattering profile. Glassy carbon has sometimes been selected as this intensity calibration standard. Here we review the spatial homogeneity and temporal stability of one type of commercially available glassy carbon that is being used as an intensity calibration standard at a number of SAS facilities. We demonstrate that glassy carbon is sufficiently homogeneous and stable during routine use to be relied upon as a suitable standard for absolute intensity calibration of SAS data.

  3. Glassy carbon as an absolute intensity calibration standard for small-angle scattering.

    SciTech Connect

    Zhang, F.; Ilavsky, J.; Long, G.; Allen, A.; Quintana, J.; Jemian, P.; NIST

    2010-05-01

    Absolute calibration of small-angle scattering (SAS) intensity data (measured in terms of the differential scattering cross section per unit sample volume per unit solid angle) is essential for many important aspects of quantitative SAS analysis, such as obtaining the number density, volume fraction, and specific surface area of the scatterers. It also enables scattering data from different instruments (light, X-ray, or neutron scattering) to be combined, and it can even be useful to detect the existence of artifacts in the experimental data. Different primary or secondary calibration methods are available. In the latter case, absolute intensity calibration requires a stable artifact with the necessary scattering profile. Glassy carbon has sometimes been selected as this intensity calibration standard. Here we review the spatial homogeneity and temporal stability of one type of commercially available glassy carbon that is being used as an intensity calibration standard at a number of SAS facilities. We demonstrate that glassy carbon is sufficiently homogeneous and stable during routine use to be relied upon as a suitable standard for absolute intensity calibration of SAS data.

  4. Image plate characterization and absolute calibration to low kilo-electron-volt electrons

    SciTech Connect

    Busold, S.; Philipp, K.; Otten, A.; Roth, M.

    2014-11-15

    We report on the characterization of an image plate and its absolute calibration to electrons in the low keV energy range (1–30 keV). In our case, an Agfa MD4.0 without protection layer was used in combination with a Fuji FLA7000 scanner. The calibration data are compared to other published data and a consistent picture of the sensitivity of image plates to electrons is obtained, which suggests a validity of the obtained calibration up to 100 keV.

  5. Variations in in-flight absolute radiometric calibration. [satellite remote sensors

    NASA Technical Reports Server (NTRS)

    Slater, Philip N.

    1986-01-01

    Variations in the in-flight absolute radiometric calibration of the Coastal Zone Color Scanner and the Thematic Mapper (TM) are reviewed. At short wavelengths, the sensors show a gradual reduction in response, while in the mid-IR the TM shows oscillatory variations. One set of measurements made at White Sands, New Mexico shows anomalous results in TM bands 2 and 4. The results of a reflectance-based and a radiance-based calibration method at White Sands are described. An analysis of the radiance-based method shows the value of such measurements from helicopter altitudes for calibration.

  6. Possibility of absolute calibration of analog detectors by using parametric downconversion: a systematic study

    SciTech Connect

    Brida, Giorgio; Genovese, Marco; Ruo-Berchera, Ivano; Chekhova, Maria; Penin, Alexander

    2006-10-15

    Prompted by the need for various studies ranging from quantum information to foundations of quantum mechanics, we systematically study the possibility of the absolute calibration of analog photodetectors based on the properties of parametric amplifiers. Our results show that such a method can be effectively developed with interesting possible applications in metrology.

  7. [Research on absolute calibration of sun channel of sun photometer using laser raster scanning method].

    PubMed

    Xu, Wen-Bin; Li, Jian-Jun; Zheng, Xiao-Bing

    2013-01-01

    In the present paper, a new calibration method of absolute spectral irradiance responsivity of sun channel of sun photometer was developed. A tunable laser was used as source and a standard tranfer detector, calibrated against cryogenic absolute radiometer, was used to measure laser beam power. By raster scanning of a single collimated laser beam to generate the uniform irradiance field at the plane of effective aperture stop of sun photometer, the absolute irradiance responsivity of center wavelength of the 870 nm unpolarized sun channels of sun photometer was obtained accurately. The relative spectral irradiance responsivity of corresponding channel was obtained by using lamp-monochromator system and then used to acquire the absolute spectral irradiance responsivity in the laboratory. On the basis of the above results, the top-of-the-atmosphere responsive constant V0 was obtained by integration with extraterrestrial solar spectral irradiance data. Comparing the calibration result with that from GSFC, NASA in 2009, the difference is only 3.75%. In the last, the uncertainties of calibration were evaluated and reached to 2.06%. The principle feasibility of the new method was validated. PMID:23586268

  8. A new determination of the Geneva photometric passbands and their absolute calibration

    NASA Astrophysics Data System (ADS)

    Rufener, F.; Nicolet, B.

    The consensus regarding the absolute calibrations of the spectra of alpha Lyr and subdwarfs provoked a revision of the calibration of the Geneva photometric system passbands. The alterations made to the earlier version by Rufener and Maeder (1971) are smaller than plus or minus -5 percent. The new response functions are presented in tabular form for an equiphotonic flux. An absolute spectrophotometric adjustment allows to obtain for each entry of the Geneva catalog (28,000 stars) a corresponding spectrophotometric description in SI units. The definition and the means of computing the necessary quasi-isophotal frequencies or wavelengths are given. The coherence of the Geneva catalog with several sets of absolute spectrophotometric data is examined. A correction for the entire Gunn and Stryker (1983) catalog is proposed.

  9. Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulations

    NASA Astrophysics Data System (ADS)

    Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hiller, R.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Nehls, S.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schoo, S.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

    2016-02-01

    LOPES was a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency comb with defined amplitudes. Recently, we obtained improved reference values by the manufacturer of the reference source, which significantly changed the absolute calibration of LOPES. We reanalyzed previously published LOPES measurements, studying the impact of the changed calibration. The main effect is an overall decrease of the LOPES amplitude scale by a factor of 2.6 ± 0.2, affecting all previously published values for measurements of the electric-field strength. This results in a major change in the conclusion of the paper 'Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations' published by Apel et al. (2013) : With the revised calibration, LOPES measurements now are compatible with CoREAS simulations, but in tension with REAS 3.11 simulations. Since CoREAS is the latest version of the simulation code incorporating the current state of knowledge on the radio emission of air showers, this new result indicates that the absolute amplitude prediction of current simulations now is in agreement with experimental data.

  10. Absolute radiometric calibration of the RapidEye multispectral imager using the reflectance-based vicarious calibration method

    NASA Astrophysics Data System (ADS)

    Naughton, Denis; Brunn, Andreas; Czapla-Myers, Jeff; Douglass, Scott; Thiele, Michael; Weichelt, Horst; Oxfort, Michael

    2011-01-01

    RapidEye AG is a commercial provider of geospatial information products and customized solutions derived from Earth observation image data. The source of the data is the RapidEye constellation consisting of five low-earth-orbit imaging satellites. We describe the rationale, methods, and results of a reflectance-based vicarious calibration campaign that was conducted between April 2009 and May 2010 at Railroad Valley Playa and Ivanpah Playa to determine the on-orbit radiometric accuracy of the RapidEye sensor. In situ surface spectral reflectance measurements of known ground targets and an assessment of the atmospheric conditions above the sites were taken during spacecraft overpasses. The ground data are used as input to a radiative transfer code to compute a band-specific top-of-atmosphere spectral radiance. A comparison of these predicted values based on absolute physical data to the measured at-sensor spectral radiance provide the absolute calibration of the sensor. Initial assessments show that the RapidEye sensor response is within 8% of the predicted values. Outcomes from this campaign are then used to update the calibration parameters in the ground segment processing system. Subsequent verification events confirmed that the measured RapidEye response improved to within 4% of the predictions based on the vicarious calibration method.

  11. Gain calibration of a horn antenna using pattern integration

    NASA Technical Reports Server (NTRS)

    Ludwig, A. C.; Hardy, J.; Norman, R.

    1972-01-01

    Gain measurement of a horn antenna using three different techniques is discussed. The methods include a two-antenna insertion loss measurement, a pattern integration method, and a near-field measurement method. The application of the pattern integration method is considered, as well as the evaluation of the near-field gain correction factors for the horn, which are determined by a method based directly on measured data. This method involves a spherical wave expansion of the experimental radiation pattern of the specific antenna being tested, rather than evaluation of an assumed analytical model. The spherical wave expansion is also compared to experimental near-field pattern data.

  12. Rapid, absolute calibration of x-ray filters employed by laser-produced plasma diagnostics.

    PubMed

    Brown, G V; Beiersdorfer, P; Emig, J; Frankel, M; Gu, M F; Heeter, R F; Magee, E; Thorn, D B; Widmann, K; Kelley, R L; Kilbourne, C A; Porter, F S

    2008-10-01

    The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are detected using the high resolution EBIT Calorimeter Spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the x-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated x-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed. PMID:19044471

  13. Rapid, absolute calibration of x-ray filters employed by laser-produced plasma diagnostics

    SciTech Connect

    Brown, G. V.; Beiersdorfer, P.; Emig, J.; Frankel, M.; Gu, M. F.; Heeter, R. F.; Magee, E.; Thorn, D. B.; Widmann, K.; Kelley, R. L.; Kilbourne, C. A.; Porter, F. S.

    2008-10-15

    The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are detected using the high resolution EBIT Calorimeter Spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the x-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated x-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed.

  14. Rapid, Absolute Calibration of X-ray Filters Employed By Laser-Produced Plasma Diagnostics

    SciTech Connect

    Brown, G V; Beiersdorfer, P; Emig, J; Frankel, M; Gu, M F; Heeter, R F; Magee, E; Thorn, D B; Widmann, K; . Kelley, R L; Kilbourne, C A; Porter, F S

    2008-05-11

    The electron beam ion trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of X-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen X-ray energies. X-rays are detected using the high-resolution EBIT calorimeter spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the X-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated X-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed.

  15. A liquid-helium-cooled absolute reference cold load for long-wavelength radiometric calibration

    NASA Technical Reports Server (NTRS)

    Bensadoun, Marc; Witebsky, Chris; Smoot, George; De Amici, Giovanni; Kogut, AL; Levin, Steve

    1992-01-01

    Design, radiometric and thermal performance, and operation of a large diameter (78 cm) liquid-helium-cooled blackbody absolute reference cold load (CL) for the calibration of microwave radiometers is described. CL provides an absolute calibration near the liquid-helium (LHe) boiling point, with total uncertainty in the radiometric temperature of less than 30 mK over the 2.5-23 cm wavelength operating range. CL was used at several wavelengths at the South Pole, Antarctica and the White Mountain Research Center, California. Results show that, for the instruments operated at 20-, 12-, 7.9-, and 4.0 cm wavelength at the South Pole, the total corrections to the LHe boiling-point temperature (about 3.8 K) were 48 +/-23, 18 +/-10, 10 +/-18, and 15 +/-mK.

  16. A Liquid-Helium-Cooled Absolute Reference Cold Load forLong-Wavelength Radiometric Calibration

    SciTech Connect

    Bensadoun, M.; Witebsky, C.; Smoot, George F.; De Amici,Giovanni; Kogut, A.; Levin, S.

    1990-05-01

    We describe a large (78-cm) diameter liquid-helium-cooled black-body absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid helium (LHe) boiling point, accurate to better than 30 mK for wavelengths from 2.5 to 25 cm (12-1.2 GHz). The emission (from non-LHe temperature parts of the cold load) and reflection are small and well determined. Total corrections to the LHe boiling point temperature are {le} 50 mK over the operating range. This cold load has been used at several wavelengths at the South Pole and at the White Mountain Research Station. In operation, the average LHe loss rate was {le} 4.4 l/hr. Design considerations, radiometric and thermal performance and operational aspects are discussed. A comparison with other LHe-cooled reference loads including the predecessor of this cold load is given.

  17. DSN 70-meter antenna X- and S-band calibration. Part 1: Gain measurements

    NASA Technical Reports Server (NTRS)

    Richter, P. H.; Slobin, S. D.

    1989-01-01

    Aperture efficiency measurements made during 1988 on the three 70-m stations (DSS-14, DSS-43, and DSS-63) at X-band (8420 MHz) and S-band (2295 MHz) have been analyzed and reduced to yield best estimates of antenna gain versus elevation. The analysis has been carried out by fitting the gain data to a theoretical expression based on the Ruze formula. Newly derived flux density and source-size correction factors for the natural radio calibration sources used in the measurements have been used in the reduction of the data. Peak gains measured at the three stations were 74.18 (plus or minus 0.10) dBi at X-band, and 63.34 (plus or minus 0.03) dBi at S-band, with corresponding peak aperture efficiencies of 0.687 (plus or minus 0.015) and 0.762 (plus or minus 0.006), respectively. The values quoted assume no atmosphere is present, and the estimated absolute accuracy of the gain measurements is approximately plus or minus 0.2 dB at X-band and plus or minus 0.1 dB at S-band (1-sigma values).

  18. The absolute radiometric calibration of the advanced very high resolution radiometer

    NASA Technical Reports Server (NTRS)

    Slater, P. N.; Teillet, P. M.; Ding, Y.

    1988-01-01

    An increasing number of remote sensing investigations require radiometrically calibrated imagery from NOAA Advanced Very High Resolution Radiation (AVHRR) sensors. Although a prelaunch calibration is done for these sensors, there is no capability for monitoring any changes in the in-flight absolute calibration for the visible and near infrared spectral channels. Hence, the possibility of using the reflectance-based method developed at White Sands for in-orbit calibration of LANDSAT Thematic Mapper (TM) and SPOT Haute Resolution Visible (HVR) data to calibrate the AVHRR sensor was investigated. Three diffrent approaches were considered: Method 1 - ground and atmospheric measurements and reference to another calibrated satellite sensor; Method 2 - ground and atmospheric measurements with no reference to another sensor; and Method 3 - no ground and atmospheric measurements but reference to another satellite sensor. The purpose is to describe an investigation on the use of Method 2 to calibrate NOAA-9 AVHRR channels 1 and 2 with the help of ground and atmospheric measurements at Rogers (dry) Lake, Edwards Air Force Base (EAFB) in the Mojave desert of California.

  19. Absolute calibration of photon-number-resolving detectors with an analog output using twin beams

    NASA Astrophysics Data System (ADS)

    Peřina, Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria

    2014-01-01

    A method for absolute calibration of a photon-number resolving detector producing analog signals as the output is developed using a twin beam. The method gives both analog-to-digital conversion parameters and quantum detection efficiency for the photon fields. Characteristics of the used twin beam are also obtained. A simplified variant of the method applicable to fields with high signal to noise ratios and suitable for more intense twin beams is suggested.

  20. Absolute calibration of a charge-coupled device camera with twin beams

    SciTech Connect

    Meda, A.; Ruo-Berchera, I. Degiovanni, I. P.; Brida, G.; Rastello, M. L.; Genovese, M.

    2014-09-08

    We report on the absolute calibration of a Charge-Coupled Device (CCD) camera by exploiting quantum correlation. This method exploits a certain number of spatial pairwise quantum correlated modes produced by spontaneous parametric-down-conversion. We develop a measurement model accounting for all the uncertainty contributions, and we reach the relative uncertainty of 0.3% in low photon flux regime. This represents a significant step forward for the characterization of (scientific) CCDs used in mesoscopic light regime.

  1. A New Approach For Absolute Temperature Calibration: Application to the CLARREO Mission

    NASA Astrophysics Data System (ADS)

    Best, F. A.; Adler, D. P.; Ellington, S. D.; Thielman, D. J.; Revercomb, H. E.; Anderson, J. G.

    2007-12-01

    A novel scheme to provide on-orbit absolute calibration of blackbody temperature sensors (on-demand) has been demonstrated using a copy of the engineering model version of a space flight hardware blackbody design (GIFTS). The scheme uses the phase change signature of reference materials to assign an absolute temperatures scale to the blackbody sensors over a large temperature range. Uncertainties of better than 0.020 K have been demonstrated over the temperature range from 234 to 303 K. Thermal modeling has been conducted to optimize the design, and to show that accuracies comparable to those measured in the laboratory should be obtainable in the less-controlled on-orbit temperature environment. The implementation if this scheme is very attractive due to its simplicity and relatively low mass. In addition, all aspects of the electronics (control and temperature readout) needed to support this scheme have been developed and demonstrated in the as-delivered GIFTS Engineering Model blackbody calibration system developed by the University of Wisconsin. NASA's anticipated plan for a mission dedicated to Climate (CLARREO) will hinge upon the ability to fly absolute standards that can provide the basis to meet stringent requirements on measurement accuracy. For example, instrumentation designed to measure spectrally resolved infrared radiances will require high-emissivity calibration blackbodies having absolute temperature uncertainties of better than 0.020 K (3 sigma). The novel blackbody temperature calibration scheme described here is very well suited for the CLARREO mission because if its low mass, high accuracy, and ease of implementation into a demonstrated flight blackbody design.

  2. Absolute calibration of photon-number-resolving detectors with an analog output using twin beams

    SciTech Connect

    Peřina, Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria

    2014-01-27

    A method for absolute calibration of a photon-number resolving detector producing analog signals as the output is developed using a twin beam. The method gives both analog-to-digital conversion parameters and quantum detection efficiency for the photon fields. Characteristics of the used twin beam are also obtained. A simplified variant of the method applicable to fields with high signal to noise ratios and suitable for more intense twin beams is suggested.

  3. On-orbit absolute temperature calibration using multiple phase change materials: overview of recent technology advancements

    NASA Astrophysics Data System (ADS)

    Best, Fred A.; Adler, Douglas P.; Pettersen, Claire; Revercomb, Henry E.; Perepezko, John H.

    2010-11-01

    NASA's anticipated plan for a mission dedicated to Climate (CLARREO) will hinge upon the ability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed to measure spectrally resolved infrared radiances will require high-emissivity calibration blackbodies that have absolute temperature uncertainties of better than 0.045K (3 sigma). A novel scheme to provide absolute calibration of temperature sensors onorbit, that uses the transient melt signatures from multiple phase change materials, has been demonstrated in the laboratory at the University of Wisconsin and is now undergoing technology advancement under NASA Instrument Incubator Program funding. Using small quantities of phase change material (less than half of a percent of the mass of the cavity), melt temperature accuracies of better than 10 mK have been demonstrated for mercury, water, and gallium (providing calibration from 233K to 303K). Refinements currently underway focus on ensuring that the melt materials in their sealed confinement housings perform as expected in the thermal and microgravity environment of a multi-year spaceflight mission. Thermal soak and cycling tests are underway to demonstrate that there is no dissolution from the housings into the melt materials that could alter melt temperature, and that there is no liquid metal embrittlement of the housings from the metal melt materials. In addition, NASA funding has been recently secured to conduct a demonstration of this scheme in the microgravity environment of the International Space Station.

  4. Characterization and Calibration of the 12-m Antenna in Warkworth, New Zealand

    NASA Technical Reports Server (NTRS)

    Gulyaev, Sergei; Natusch, Tim; Wilson, David

    2010-01-01

    The New Zealand 12-m antenna is scheduled to start participating in regular IVS VLBI sessions from the middle of 2010. Characterization procedures and results of calibration of the New Zealand 12- m radio telescope are presented, including the main reflector surface accuracy measurement, pointing model creation, and the system equivalent flux density (SEFD) determination in both S and X bands. Important issues of network connectivity, co-located geodetic systems, and the use of the antenna in education are also discussed.

  5. Absolute calibration of a hydrogen discharge lamp in the vacuum ultraviolet

    NASA Technical Reports Server (NTRS)

    Nealy, J. E.

    1975-01-01

    A low-pressure hydrogen discharge lamp was calibrated for radiant intensity in the vacuum ultraviolet spectral region on an absolute basis and was employed as a laboratory standard source in spectrograph calibrations. This calibration was accomplished through the use of a standard photodiode detector obtained from the National Bureau of Standards together with onsite measurements of spectral properties of optical components used. The stability of the light source for use in the calibration of vacuum ultraviolet spectrographs and optical systems was investigated and found to be amenable to laboratory applications. The lamp was studied for a range of operating parameters; the results indicate that with appropriate peripheral instrumentation, the light source can be used as a secondary laboratory standard source when operated under preset controlled conditions. Absolute intensity measurements were recorded for the wavelengths 127.7, 158.0, 177.5, and 195.0 nm for a time period of over 1 month, and the measurements were found to be repeatable to within 11 percent.

  6. New apparatus for calibrations in the range of 2 kPa absolute pressure

    NASA Astrophysics Data System (ADS)

    Woo, S. Y.; Choi, I. M.

    2005-12-01

    Capacitance diaphragm gauges (CDGs) are precise electromechanical pressure sensors in which the displacement of a stretched thin metal diaphragm is detected by the measurement of a capacitance. These are very accurate gauges, and are frequently used as transfer gauges. To calibrate such accurate low-pressure gauges, precise mercury manometers have been used. However, complexity, concern about mercury vapour, and cost of mercury manometers have made it difficult to use these manometers in many industrial calibration laboratories. As a substitute, gas-operated piston gauges can be used for the calibration of such low-pressure gauges. However, the minimum pressure that is necessary to balance the tare weight, which generally corresponds to a pressure of several kilopascals, is a major obstacle. To reduce this minimum operating pressure, we adopted a variable bell-jar pressure method. To realize this method effectively, we developed a new mass-handling device that makes it possible to add or remove weights up to 200 g easily, with a resolution of 10 g, without breaking the vacuum during the calibration. This calibration system can be used to measure pressures from 100 Pa to 2 kPa in the absolute mode. In this paper, we also present the calibration results for two types of CDGs with full-scale ranges of 1330 Pa and 1000 Pa, respectively.

  7. A new method for the absolute radiance calibration for UV-vis measurements of scattered sunlight

    NASA Astrophysics Data System (ADS)

    Wagner, T.; Beirle, S.; Dörner, S.; Penning de Vries, M.; Remmers, J.; Rozanov, A.; Shaiganfar, R.

    2015-10-01

    Absolute radiometric calibrations are important for measurements of the atmospheric spectral radiance. Such measurements can be used to determine actinic fluxes, the properties of aerosols and clouds, and the shortwave energy budget. Conventional calibration methods in the laboratory are based on calibrated light sources and reflectors and are expensive, time consuming and subject to relatively large uncertainties. Also, the calibrated instruments might change during transport from the laboratory to the measurement sites. Here we present a new calibration method for UV-vis instruments that measure the spectrally resolved sky radiance, for example zenith sky differential optical absorption spectroscopy (DOAS) instruments or multi-axis (MAX)-DOAS instruments. Our method is based on the comparison of the solar zenith angle dependence of the measured zenith sky radiance with radiative transfer simulations. For the application of our method, clear-sky measurements during periods with almost constant aerosol optical depth are needed. The radiative transfer simulations have to take polarisation into account. We show that the calibration results are almost independent from the knowledge of the aerosol optical properties and surface albedo, which causes a rather small uncertainty of about < 7 %. For wavelengths below about 330 nm it is essential that the ozone column density during the measurements be constant and known.

  8. Absolute photometric calibration of detectors to 0.3 mmag using amplitude-stabilized lasers and a helium-cooled absolute radiometer

    NASA Technical Reports Server (NTRS)

    Miller, Peter J.

    1988-01-01

    Laser sources whose intensity is determined with a cryogenic electrical substitution radiometer are described. Detectors are then calibrated against this known flux, with an overall error of 0.028 percent (0.3 mmag). Ongoing research has produced laser intensity stabilizers with flicker and drift of less than 0.01 percent. Recently, the useful wavelength limit of these stabilizers have been extended to 1.65 microns by using a new modular technology and InGaAs detector systems. Data from Si photodiode calibration using the method of Zalewski and Geist are compared against an absolute cavity radiometer calibration as an internal check on the calibration system.

  9. Simple method for absolute calibration of geophones, seismometers, and other inertial vibration sensors

    SciTech Connect

    Kann, Frank van; Winterflood, John

    2005-03-01

    A simple but powerful method is presented for calibrating geophones, seismometers, and other inertial vibration sensors, including passive accelerometers. The method requires no cumbersome or expensive fixtures such as shaker platforms and can be performed using a standard instrument commonly available in the field. An absolute calibration is obtained using the reciprocity property of the device, based on the standard mathematical model for such inertial sensors. It requires only simple electrical measurement of the impedance of the sensor as a function of frequency to determine the parameters of the model and hence the sensitivity function. The method is particularly convenient if one of these parameters, namely the suspended mass is known. In this case, no additional mechanical apparatus is required and only a single set of impedance measurements yields the desired calibration function. Moreover, this measurement can be made with the device in situ. However, the novel and most powerful aspect of the method is its ability to accurately determine the effective suspended mass. For this, the impedance measurement is made with the device hanging from a simple spring or flexible cord (depending on the orientation of its sensitive axis). To complete the calibration, the device is weighed to determine its total mass. All the required calibration parameters, including the suspended mass, are then determined from a least-squares fit to the impedance as a function of frequency. A demonstration using both a 4.5 Hz geophone and a 1 Hz seismometer shows that the method can yield accurate absolute calibrations with an error of 0.1% or better, assuming no a priori knowledge of any parameters.

  10. On-Orbit Absolute Temperature Calibration for CLARREO Using Multiple Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Best, F. A.; Adler, D. P.; Ellington, S. D.; Thielman, D. J.; Revercomb, H. E.; Perepezko, J. H.

    2008-12-01

    NASA's anticipated plan for a mission dedicated to Climate (CLARREO) will hinge upon the ability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed to measure spectrally resolved infrared radiances will require high-emissivity calibration blackbodies that have absolute temperature uncertainties of better than 0.045K (3 sigma). A novel scheme to provide absolute calibration of temperature sensors, suitable for CLARREO on-orbit operation, has been demonstrated in the laboratory at the University of Wisconsin, and is now undergoing refinement under NASA Instrument Incubator Program funding. In this scheme, small quantities of reference materials (mercury, water, and gallium - to date) are imbedded into the blackbody cavity wall, in a manner similar to the temperature sensors to be calibrated. As the blackbody cavity is slowly heated through a reference material melt temperature, the transient temperature signature of the imbedded thermistor sensors provides a very accurate indication of the melt temperature. Using small quantities of phase change material (less than half of a percent of the mass of the cavity), melt temperature accuracies of better than 10 mK have been demonstrated for mercury, water, and gallium (providing calibration from 233K to 303K). The flight implementation of this new scheme will involve special considerations for packaging the phase change materials to ensure long-term compatibility with the containment system, and design features that help ensure that the on-orbit melt behavior in a microgravity environment is unchanged from pre-flight full gravitational conditions under which the system is characterized.

  11. On-Orbit Absolute Temperature Calibration Using Multiple Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Best, F. A.; Adler, D. P.; Pettersen, C.; Revercomb, H. E.; Perepezko, J. H.

    2009-12-01

    NASA’s anticipated plan for a mission dedicated to Climate (CLARREO) will hinge upon the ability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed to measure spectrally resolved infrared radiances will require high-emissivity calibration blackbodies that have absolute temperature uncertainties of better than 0.045K (3 sigma). A novel scheme to provide absolute calibration of temperature sensors, suitable for CLARREO on-orbit operation, has been demonstrated in the laboratory at the University of Wisconsin, and is now undergoing refinement under NASA Instrument Incubator Program funding. In this scheme, small quantities of reference materials (mercury, water, and gallium) are imbedded into the blackbody cavity wall, in a manner similar to the temperature sensors to be calibrated. As the blackbody cavity is slowly heated through the melt point of each reference material, the transient temperature signature from the imbedded thermistor sensors provides a very accurate indication of the melt temperature. Using small quantities of phase change material (less than half of a percent of the mass of the cavity), melt temperature accuracies of better than 10 mK have been demonstrated for mercury, water, and gallium (providing calibration from 233K to 303K). Refinements currently underway focus on ensuring that the melt materials in their sealed confinement housings perform as expected in the thermal and microgravity environment of a multi-year spaceflight mission. Thermal soak and cycling tests are underway to demonstrate that there is no dissolution from the housings into the melt materials that could alter melt temperature, and that there is no liquid metal embrittlement of the housings from the metal melt materials. In addition, NASA funding has been recently secured to conduct a demonstration of this scheme in the microgravity environment of the International Space Station.

  12. Multispectral Photometry of the Moon and Absolute Calibration of the Clementine UV/Vis Camera

    NASA Astrophysics Data System (ADS)

    Hillier, John K.; Buratti, Bonnie J.; Hill, Kathryn

    1999-10-01

    We present a multispectral photometric study of the Moon between solar phase angles of 0 and 85°. Using Clementine images obtained between 0.4 and 1.0 μm, we produce a comprehensive study of the lunar surface containing the following results: (1) empirical photometric functions for the spectral range and viewing and illumination geometries mentioned, (2) photometric modeling that derives the physical properties of the upper regolith and includes a detailed study of the causes for the lunar opposition surge, (3) an absolute calibration of the Clementine UV/Vis camera. The calibration procedure given on the Clementine calibration web site produces reflectances relative to a halon standard and further appear significantly higher than those seen in groundbased observations. By comparing Clementine observations with prior groundbased observations of 15 sites on the Moon we have determined a good absolute calibration of the Clementine UV/Vis camera. A correction factor of 0.532 has been determined to convert the web site (www.planetary.brown.edu/clementine/calibration.html) reflectances to absolute values. From the calibrated data, we calculate empirical phase functions useful for performing photometric corrections to observations of the Moon between solar phase angles of 0 and 85° and in the spectral range 0.4 to 1.0μm. Finally, the calibrated data is used to fit a version of Hapke's photometric model modified to incorporate a new formulation, developed in this paper, of the lunar opposition surge which includes coherent backscatter. Recent studies of the lunar opposition effect have yielded contradictory results as to the mechanism responsible: shadow hiding, coherent backscatter, or both. We find that most of the surge can be explained by shadow hiding with a halfwidth of ˜8°. However, for the brightest regions (the highlands at 0.75-1.0μm) a small additional narrow component (halfwidth of <2°) of total amplitude ˜1/6 to 1/4 that of the shadow hiding surge is

  13. PREMOS Absolute Radiometer Calibration and Implications to on-orbit Measurements of the Total Solar Irradiance

    NASA Astrophysics Data System (ADS)

    Fehlmann, A.; Kopp, G.; Schmutz, W. K.; Winkler, R.; Finsterle, W.; Fox, N.

    2011-12-01

    On orbit measurements starting in the late 1970's, have revealed the 11 year cycle of the Total Solar Irradiance (TSI). However, the absolute results from individual experiments differ although all instrument teams claim to measure an absolute value. Especially the data from the TIM/SORCE experiment confused the community as it measures 0.3 % lower than the other instruments, e.g. VIRGO/SOHO by PMOD/WRC, which clearly exceeds the uncertainty stated for the absolute characterization of the experiments. The PREMOS package on the PICARD platform launched in June 2010 is the latest space experiment by PMOD/WRC measuring the TSI. We have put great effort in the calibration and characterization of this instrument in order to resolve the inter-instrument differences. We performed calibrations at the National Physical Laboratory (NPL) in London and the Laboratory for Atmospheric and Space Physics (LASP) in Boulder against national SI standards for radiant power using a laser beam with a diameter being smaller than the aperture of the instrument. These measurements together with the World Radiometric Reference (WRR) calibration in Davos allowed to compare the WRR and the SI radiant power scale. We found that the WRR lies 0.18 % above the SI radiant power scale which explains a part of the VIRGO-TIM difference. The Total solar irradiance Radiometer Facility (TRF) at the LASP allows to generate a beam that over fills the apertures of our instruments, giving the presently best available representation of solar irradiance in a laboratory. These irradiance calibrations revealed a stray light contribution between 0.09 and 0.3 % to the measurements which had been underestimated in the characterization of our instruments. Using the irradiance calibrations, we found that the WRR lies 0.32 % above the TRF scale which in turn explains the full VIRGO-TIM difference. The first light PREMOS measurements in space confirmed our findings. If we use the WRR calibration, PREMOS yields a TSI

  14. Method to calibrate the absolute energy scale of air showers with ultrahigh energy photons.

    PubMed

    Homola, Piotr; Risse, Markus

    2014-04-18

    Calibrating the absolute energy scale of air showers initiated by ultrahigh energy (UHE) cosmic rays is an important experimental issue. Currently, the corresponding systematic uncertainty amounts to 14%-21% using the fluorescence technique. Here, we describe a new, independent method which can be applied if ultrahigh energy photons are observed. While such photon-initiated showers have not yet been identified, the capabilities of present and future cosmic-ray detectors may allow their discovery. The method makes use of the geomagnetic conversion of UHE photons (preshower effect), which significantly affects the subsequent longitudinal shower development. The conversion probability depends on photon energy and can be calculated accurately by QED. The comparison of the observed fraction of converted photon events to the expected one allows the determination of the absolute energy scale of the observed photon air showers and, thus, an energy calibration of the air shower experiment. We provide details of the method and estimate the accuracy that can be reached as a function of the number of observed photon showers. Already a very small number of UHE photons may help to test and fix the absolute energy scale. PMID:24785024

  15. Absolute Calibration of Si iRMs used for Si Paleo-nutrient proxies

    NASA Astrophysics Data System (ADS)

    Vocke, Robert; Rabb, Savelas

    2016-04-01

    The Avogadro Project is an ongoing international effort, coordinated by the International Bureau of Weights and Measures (BIPM) and the International Avogadro Coordination (IAC) to redefine the SI unit mole in terms of the Avogadro constant and the SI unit kg in terms of the Planck constant. One of the outgrowths of this effort has been the development of a novel, precise and highly accurate method to measure calibrated (absolute) isotopic ratios that are traceable to the SI (Vocke et al., 2014 Metrologia 51, 361, Azuma et al., 2015 Metrologia 52 360). This approach has also been able to produce absolute Si isotope ratio data with lower levels of uncertainty when compared to the traditional "Atomic Weights" method of absolute isotope ratio measurement. Silicon isotope variations (reported as delta(Si30)and delta(Si29)) in silicic acid dissolved in ocean waters, in biogenic silica and in diatoms are extremely informative paleo-nutrient proxies. The utility and comparability of such measurements however depends on calibration with artifact isotopic Reference Materials (iRMs). We will be reporting new measurements on the iRMs NBS-28 (RM 8546 - Silica Sand), Diatomite, Big Batch and SRM 990 using the Avogadro measurement approach, comparing them with prior assessments of these iRMs.

  16. Precision evaluation of calibration factor of a superconducting gravimeter using an absolute gravimeter

    NASA Astrophysics Data System (ADS)

    Feng, Jin-yang; Wu, Shu-qing; Li, Chun-jian; Su, Duo-wu; Xu, Jin-yi; Yu, Mei

    2016-01-01

    The precision of the calibration factor of a superconducting gravimeter (SG) using an absolute gravimeter (AG) is analyzed based on linear least square fitting and error propagation theory and factors affecting the accuracy are discussed. It can improve the accuracy to choose the observation period of solid tide as a significant change or increase the calibration time. Simulation is carried out based on synthetic gravity tides calculated with T-soft at observed site from Aug. 14th to Sept. 2nd in 2014. The result indicates that the highest precision using half a day's observation data is below 0.28% and the precision exponentially increases with the increase of peak-to-peak gravity change. The comparison of results obtained from the same observation time indicated that using properly selected observation data has more beneficial on the improvement of precision. Finally, the calibration experiment of the SG iGrav-012 is introduced and the calibration factor is determined for the first time using AG FG5X-249. With 2.5 days' data properly selected from solid tide period with large tidal amplitude, the determined calibration factor of iGrav-012 is (-92.54423+/-0.13616) μGal/V (1μGal=10-8m/s2), with the relative accuracy of about 0.15%.

  17. In-progress absolute radiometric inflight calibration of the LANDSAT-4 sensors

    NASA Technical Reports Server (NTRS)

    Castle, K.; Dinguirard, M.; Ezra, C. E.; Holm, R. G.; Jackson, R. J.; Kastner, C. J.; Palmer, J. M.; Savage, R.; Slater, P. N.

    1983-01-01

    An approach is described for providing periodic inflight absolute radiometric calibrations of the LANDSAT-4 sensors by reference to selected, instrumented ground areas. Results of some early ground measurements and computer simulations are presented. Selection of a suitable ground reference site, accurate measurement of the spectral reflectance of the selected area, determination of atmospheric characteristics during the morning of the sensor overpass, reduction of the measured data and their use in an appropriate atmospheric radiative transfer program, and comparison of the radiance level data with the digital counts of for the images of the selected areas are discussed. Preliminary measurements of gypsum are being made as an aid in defining the characteristics of field equipment to be constructed and calibrated for use over the White Sands Missile Range.

  18. An imaging technique for detection and absolute calibration of scintillation light

    SciTech Connect

    Pappalardo, Alfio; Cosentino, Luigi; Finocchiaro, Paolo

    2010-03-15

    Triggered by the need of a detection system to be used in experiments of nuclear fusion in laser-generated plasmas, we developed an imaging technique for the measurement and calibration of the scintillation light yield of scintillating materials. As in such experiments, all the reaction products are generated in an ultrashort time frame, the event-by-event data acquisition scheme is not feasible. As an alternative to the emulsion technique (or the equivalent CR39 sheets) we propose a scintillating screen readout by means of a high performance charge coupled device camera. Even though it is not strictly required in the particular application, this technique allows the absolute calibration of the scintillation light yield.

  19. Absolute Current Calibrations of 1muA CW Electron Beam

    SciTech Connect

    A. Freyberger, M.E. Bevins, A.R. Day, P. Degtiarenko, A. Saha, S. Slachtouski, R. Gilman

    2005-06-06

    The future experimental program at Jefferson Lab requires an absolute current calibration of a 1{mu}A CW electron beam to better than 1% accuracy. This paper presents the mechanical and electrical design of a Tungsten calorimeter that is being constructed to provide an accurate measurement of the deposited energy. The energy is determined by measuring the change in temperature after beam exposure. Knowledge of the beam energy then yields number of electrons stopped by the calorimeter during the exposure. Simulations show that the energy losses due to electromagnetic and hadronic losses are the dominant uncertainty. Details of the precision thermometry and calibration, mechanical design, thermal simulations and GEANT simulations will be presented.

  20. Absolute Current Calibration of 1$\\mu$A CW Electron Beam

    SciTech Connect

    Arne Freyberger; Mike Bevins; Anthony Day; Arunava Saha; Stephanie Slachtouski; Ronald Gilman; Pavel Degtiarenko

    2005-06-01

    The future experimental program at Jefferson Lab requires an absolute current calibration of a 1 {mu}A CW electron beam to better than 1% accuracy. This paper presents the mechanical and electrical design of a Tungsten calorimeter that is being constructed to provide an accurate measurement of the deposited energy. The energy is determined by measuring the change in temperature after beam exposure. Knowledge of the beam energy then yields number of electrons stopped by the calorimeter during the exposure. Simulations show that the energy lost due to electromagnetic and hadronic particle losses are the dominant uncertainty. Details of the precision thermometry and calibration, mechanical design, thermal simulations and simulations will be presented.

  1. [In-flight absolute radiometric calibration of UAV hyperspectral camera and its validation analysis].

    PubMed

    Gou, Zhi-yang; Yan, Lei; Chen, Wei; Jing, Xin; Yin, Zhong-yi; Duan, Yi-ni

    2012-02-01

    With the data in Urad Front Banner, Inner Mongolia on November 14th, 2010, hyper-spectral camera on UAV was calibrated adopting reflectance-based method. During the in-flight absolute radiometric calibration, 6 hyper-spectral radiometric gray-scale targets were arranged in the validation field. These targets' reflectances are 4.5%, 20%, 30%, 40%, 50% and 60% separately. To validate the calibration result, four extra hyper-spectral targets with sharp-edge spectrum were arranged to simulate the reflection and absorption peaks in natural objectives. With these peaks, the apparent radiance calculated by radiation transfer model and that calculated through calibration coefficients are much different. The result shows that in the first 15 bands (blue bands), errors are somewhat huge due to the noises of equipment. In the rest bands with quite even spectrum, the errors are small, most of which are less than 10%. For those bands with sharp changes in spectral curves, the errors are quite considerable, varying from 10% to 25%. PMID:22512184

  2. The absolute radiometric calibration of the advanced very high resolution radiometer

    NASA Technical Reports Server (NTRS)

    Slater, P. N.; Teillet, P. M.; Mao, Y.

    1987-01-01

    The early results of an absolute radiometric calibration of the NOAA-9 AVHRR sensor indicate significant degradations in the response of bands 1 and 2 compared to prelaunch values. The results are currently in the process of being verified and it may be that refinements of the methodology will be in order as additional data sets are analyzed. The LANDSAT TM calibration used in this approach is known to be very precise and the Herman radiative transfer code, supplemented by the 5-S code for gaseous transmission, is reliable as well. The extent to which other steps in the analysis procedure give rise to uncertainties in the results is currently under investigation. Particular attention is being given to the geometric matching of the AVHRR and TM imagery, as well as to the spectral redistribution procedure. By taking advantage of a reasonably precise calibration of TM imagery acquired on the same day as the AVHRR data at White Sands, a promising approach to the in-orbit calibration of AVHRR sensors is being developed. Current efforts involve primarily the examination of additional test cases and the investigation of possible simplifications in the procedure through judicious use of atmospheric models.

  3. Absolute calibration of TFTR neutron detectors for D-T plasma operation

    SciTech Connect

    Jassby, D.L.; Johnson, L.C.; Roquemore, A.L.; Strachan, J.D.; Johnson, D.W.; Medley, S.S.; Young, K.M.; Barnes, C.W.

    1995-03-01

    The two most sensitive TFTR fission-chamber detectors were absolutely calibrated in situ by a D-T neutron generator ({approximately}5 {times} 10{sup 7} n/s) rotated once around the torus in each direction, with data taken at about 45 positions. The combined uncertainty for determining fusion neutron rates, including the uncertainty in the total neutron generator output ({plus_minus}9%), counting statistics, the effect of coil coolant, detector stability, cross-calibration to the current mode or log Campbell mode and to other fission chambers, and plasma position variation, is about {plus_minus}13%. The NE-451 (ZnS) scintillators and {sup 4}He proportional counters that view the plasma in up to 10 collimated sightlines were calibrated by scanning. the neutron generator radially and toroidally in the horizontal midplane across the flight tubes of 7 cm diameter. Spatial integration of the detector responses using the calibrated signal per unit chord-integrated neutron emission gives the global neutron source strength with an overall uncertainty of {plus_minus}14% for the scintillators and {plus_minus}15% for the {sup 4}He counters.

  4. Landsat-7 ETM+ on-orbit reflective-band radiometric stability and absolute calibration

    USGS Publications Warehouse

    Markham, B.L.; Thome, K.J.; Barsi, J.A.; Kaita, E.; Helder, Dennis L.; Barker, J. L.; Scaramuzza, Pat

    2004-01-01

    Launched in April 1999, the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument is in its sixth year of operation. The ETM+ instrument has been the most stable of any of the Landsat instruments. To date, the best onboard calibration source for the reflective bands has been the Full Aperture Solar Calibrator, a solar-diffuser-based system, which has indicated changes of between 1% to 2% per year in the ETM+ gain for bands 1-4 and 8 and less than 0.5%/year for bands 5 and 7. However, most of this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on vicarious calibrations and observations of "invariant sites", hyperarid sites of the Sahara and Arabia. Weighted average slopes determined from these datasets suggest changes of 0.0% to 0.4% per year for bands 1-4 and 8 and 0.4% to 0.5% per year for bands 5 and 7. Absolute calibration of the reflective bands of the ETM+ is consistent with vicarious observations and other sensors generally at the 5% level, though there appear to be some systematic differences.

  5. Absolute calibration method for nanosecond-resolved, time-streaked, fiber optic light collection, spectroscopy systems

    SciTech Connect

    Johnston, Mark D.; Oliver, Bryan V.; Droemer, Darryl W.; Frogget, Brent; Crain, Marlon D.; Maron, Yitzhak

    2012-08-15

    This paper describes a convenient and accurate method to calibrate fast (<1 ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such systems are inherently difficult to calibrate due to the lack of sufficiently intense, calibrated light sources. Such a system is used to collect spectral data on plasmas generated in electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA) at Sandia National Laboratories. On RITS, plasma light is collected through a small diameter (200 {mu}m) optical fiber and recorded on a fast streak camera at the output of a 1 meter Czerny-Turner monochromator. For this paper, a 300 W xenon short arc lamp (Oriel Model 6258) was used as the calibration source. Since the radiance of the xenon arc varies from cathode to anode, just the area around the tip of the cathode ('hotspot') was imaged onto the fiber, to produce the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power was measured using 10 nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The shape of the spectrum is determined by the collective response of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of the spectral curve to the measured bandpass filter curve at each wavelength produces a correction factor (Q) curve. This curve is then applied to the experimental data and the resultant spectra are given in absolute intensity units (photons/sec/cm{sup 2}/steradian/nm). Error analysis shows this method to be accurate to within +/- 20%, which represents a high level of accuracy for this type of measurement.

  6. Absolute calibration method for nanosecond-resolved, time-streaked, fiber optic light collection, spectroscopy systems

    NASA Astrophysics Data System (ADS)

    Johnston, Mark D.; Oliver, Bryan V.; Droemer, Darryl W.; Frogget, Brent; Crain, Marlon D.; Maron, Yitzhak

    2012-08-01

    This paper describes a convenient and accurate method to calibrate fast (<1 ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such systems are inherently difficult to calibrate due to the lack of sufficiently intense, calibrated light sources. Such a system is used to collect spectral data on plasmas generated in electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA) at Sandia National Laboratories. On RITS, plasma light is collected through a small diameter (200 μm) optical fiber and recorded on a fast streak camera at the output of a 1 meter Czerny-Turner monochromator. For this paper, a 300 W xenon short arc lamp (Oriel Model 6258) was used as the calibration source. Since the radiance of the xenon arc varies from cathode to anode, just the area around the tip of the cathode ("hotspot") was imaged onto the fiber, to produce the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power was measured using 10 nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The shape of the spectrum is determined by the collective response of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of the spectral curve to the measured bandpass filter curve at each wavelength produces a correction factor (Q) curve. This curve is then applied to the experimental data and the resultant spectra are given in absolute intensity units (photons/sec/cm2/steradian/nm). Error analysis shows this method to be accurate to within +/- 20%, which represents a high level of accuracy for this type of measurement.

  7. Absolute Calibration of the Radio Astronomy Flux Density Scale at 22 to 43 GHz Using Planck

    NASA Astrophysics Data System (ADS)

    Partridge, B.; López-Caniego, M.; Perley, R. A.; Stevens, J.; Butler, B. J.; Rocha, G.; Walter, B.; Zacchei, A.

    2016-04-01

    The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite’s annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus, Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1%–2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 2%–3% ± 1.0% below Planck values with an uncertainty of +/- 1.0%; at 43 GHz, the discrepancy increases to 5%–6% ± 1.4% for both ATCA and the VLA.

  8. Field Measurement of Sand Dune Bidirectional Reflectance Characteristics for Absolute Radiometric Calibration of Optical Remote Sensing Data.

    NASA Astrophysics Data System (ADS)

    Coburn, C. A.; Logie, G.; Beaver, J.; Helder, D.

    2015-12-01

    The use of Pseudo Invariant Calibration Sites (PICS) for establishing the radiometric trending of optical remote sensing systems has a long history of successful implementation. Past studies have shown that the PICS method is useful for evaluating the trend of sensors over time or cross-calibration of sensors but was not considered until recently for deriving absolute calibration. Current interest in using this approach to establish absolute radiometric calibration stems from recent research that indicates that with empirically derived models of the surface properties and careful atmospheric characterisation Top of Atmosphere (TOA) reflectance values can be predicted and used for absolute sensor radiometric calibration. Critical to the continued development of this approach is the accurate characterization of the Bidirectional Reflectance Distribution Function (BRDF) of PICS sites. This paper presents the field data collected by a high-performance portable goniometer system in order to develop a BRDF model for the Algodones Dunes in California. These BRDF data are part of a larger study that is seeking to evaluate and quantify all aspects of this dune system (from regional effects to the micro scale optical properties of the sand) in order to provide an absolute radiometric calibration PICS. This paper presents the results of a dense temporal measurement sequence (several measurements per hour with high angular resolution), to yield detailed information on the nature of the surface reflectance properties. The BRDF data were collected covering typical view geometry of space borne sensors and will be used to close the loop on the calibration to create an absolute calibration target for optical satellite absolute radiometric calibration.

  9. Ka-Band Monopulse Antenna Pointing Calibration Using Wideband Radio Sources

    NASA Astrophysics Data System (ADS)

    Buu, C.; Calvo, J.; Cheng, T.-H.; Vazquez, M.

    2010-08-01

    A new method of performing a system end-to-end monopulse antenna calibration using widely available wideband astronomical radio sources is presented as an alternative to the current method of using a spacecraft signal. Current monopulse calibration requires a spacecraft carrier signal to measure amplitude and phase differences in the monopulse feed and low-noise amplifiers (LNAs). The alternative method presented here will allow the ground station to perform monopulse calibrations during maintenance periods instead of spacecraft track time, and provide an end-to-end system check-out capability without requiring a spacecraft signal. In this article, we give an overview of the current calibration approach, describe a new method for calibrating with radio sources, and present results from field testing of this new method.

  10. The absolute radiometric calibration of Terra imaging sensors: MODIS, MISR, and ASTER

    NASA Astrophysics Data System (ADS)

    Czapla-Myers, Jeffrey; Thome, Kurtis; Anderson, Nikolaus; Biggar, Stuart

    2014-10-01

    The Terra spacecraft contains five Earth-observation instruments, three of which are multispectral imaging sensors that complement each other in spectral and spatial coverage. The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 channels ranging from 0.4-14.4 μm, with spatial resolutions of 250, 500, and 1000 m. The Multi-angle Imaging SpectroRadiometer (MISR) uses individual imaging sensors to view the earth at nine discreet angles. Each radiometer has four channels in the visible and near infrared (VNIR), and the nadir-viewing camera has a spatial resolution of 275 m. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was designed with fourteen bands ranging from 0.5-11.6 μm. It is the high-resolution sensor on Terra, with a spatial resolution of 15 m in the VNIR, and 30 m in the shortwave infrared (SWIR). This work describes the vicarious techniques used to perform the absolute radiometric calibration of MODIS, MISR, and ASTER in the solar-reflective region (0.4-2.5 μm). It includes the reflectance-based approach, which uses ground-based personnel to make in situ measurements during the time of overpass. It also includes more recent results that were obtained using the University of Arizona's automated Radiometric Calibration Test Site (RadCaTS) at Railroad Valley, Nevada. In addition to the absolute radiometric calibration of Terra sensors, RadCaTS is used to perform the cross comparison of MODIS, MISR, and ASTER with Landsat 7 ETM+ and Landsat 8 OLI.

  11. Self-calibration of Antenna Errors Using Focal Plane Arrays

    NASA Astrophysics Data System (ADS)

    Napier, P. J.; Cornwell, T. J.

    The thery of focal-plane correlation is reviewed and applied to the problem of the self-calibration and self-correction of a radio telescope with errors in its reflecting surface. Curves are presented which allow the estimation of focal-plane array size and integration time needed for telescopes with varying amounts of error. It is suggested that the technique may have application to the problem of the construction of large telescopes in space.

  12. Absolute calibration method for laser megajoule neutron yield measurement by activation diagnostics.

    PubMed

    Landoas, Olivier; Glebov, Vladimir Yu; Rossé, Bertrand; Briat, Michelle; Disdier, Laurent; Sangster, Thomas C; Duffy, Tim; Marmouget, Jean Gabriel; Varignon, Cyril; Ledoux, Xavier; Caillaud, Tony; Thfoin, Isabelle; Bourgade, Jean-Luc

    2011-07-01

    The laser megajoule (LMJ) and the National Ignition Facility (NIF) plan to demonstrate thermonuclear ignition using inertial confinement fusion (ICF). The neutron yield is one of the most important parameters to characterize ICF experiment performance. For decades, the activation diagnostic was chosen as a reference at ICF facilities and is now planned to be the first nuclear diagnostic on LMJ, measuring both 2.45 MeV and 14.1 MeV neutron yields. Challenges for the activation diagnostic development are absolute calibration, accuracy, range requirement, and harsh environment. At this time, copper and zirconium material are identified for 14.1 MeV neutron yield measurement and indium material for 2.45 MeV neutrons. A series of calibrations were performed at Commissariat à l'Energie Atomique (CEA) on a Van de Graff facility to determine activation diagnostics efficiencies and to compare them with results from calculations. The CEA copper activation diagnostic was tested on the OMEGA facility during DT implosion. Experiments showed that CEA and Laboratory for Laser Energetics (LLE) diagnostics agree to better than 1% on the neutron yield measurement, with an independent calibration for each system. Also, experimental sensitivities are in good agreement with simulations and allow us to scale activation diagnostics for the LMJ measurement range. PMID:21806179

  13. ScaRaB: first results of absolute and cross calibration

    NASA Astrophysics Data System (ADS)

    Trémas, Thierry L.; Aznay, Ouahid; Chomette, Olivier

    2015-10-01

    ScaRaB (SCAnner for RAdiation Budget) is the name of three radiometers whose two first flight models have been launched in 1994 and 1997. The instruments were mounted on-board Russian satellites, METEOR and RESURS. On October 12th 2011, a last model has been launched from the Indian site of Sriharikota. ScaRaB is a passenger of MEGHA-TROPIQUES, an Indo-French joint Satellite Mission for studying the water cycle and energy exchanges in the tropics. ScaRaB is composed of four parallel and independent channels. Channel-2 and channel-3 are considered as the main ones. Channel-1 is dedicated to measure solar radiance (0.5 to 0.7 μm) while channel-4 (10 to 13 μm) is an infrared window. The absolute calibration of ScaRab is assured by internal calibration sources (black bodies and a lamp for channel-1). However, during the commissioning phase, the lamp used for the absolute calibration of channel-1 revealed to be inaccurate. We propose here an alternative calibration method based on terrestrial targets. Due to the spectral range of channel-1, only calibration over desert sites (temporal monitoring) and clouds (cross band) is suitable. Desert sites have been widely used for sensor calibration since they have a stable spectral response over time. Because of their high reflectances, the atmospheric effect on the upward radiance is relatively minimal. In addition, they are spatially uniform. Their temporal instability without atmospheric correction has been determined to be less than 1-2% over a year. Very-high-altitude (10 km) bright clouds are good validation targets in the visible and near-infrared spectra because of their high spectrally consistent reflectance. If the clouds are very high, there is no need to correct aerosol scattering and water vapor absorption as both aerosol and water vapor are distributed near the surface. Only Rayleigh scattering and ozone absorption need to be considered. This method has been found to give a 4% uncertainty. Radiometric cross

  14. Extension of the absolute flux density scale to 22.285 GHz. [radio astronomy

    NASA Technical Reports Server (NTRS)

    Janssen, M. A.; Golden, L. M.; Welch, W. J.

    1974-01-01

    Extending the absolute flux density scale at microwave wavelengths, the absolute flux densities at 22.285 GHz of several standard sources were determined using the absolute calibrations of the 6.1 meter antenna of the Hat Creek Observatory. Interpolation formulas for each nonthermal standard source have been derived by combining these data with those determined at lower frequencies. The suitability of employing the standard sources for calibrating other antennas is discussed.

  15. Absolute calibration of an EMCCD camera by quantum correlation, linking photon counting to the analog regime.

    PubMed

    Avella, A; Ruo-Berchera, I; Degiovanni, I P; Brida, G; Genovese, M

    2016-04-15

    We show how the same setup and procedure, exploiting spatially multimode quantum correlations, allows the absolute calibration of an electron-multiplying charge-coupled (EMCCD) camera from the analog regime down to the single-photon-counting level, just by adjusting the brightness of the quantum source. At the single-photon level, an EMCCD can be operated as an on-off detector, where quantum efficiency depends on the discriminating threshold. We develop a simple model to explain the connection of the two different regimes demonstrating that the efficiency estimated in the analog (bright) regime allows us to accurately predict the detector behavior in the photocounting regime and vice versa. This work establishes a bridge between two regions of the optical measurements that up to now have been based on completely different standards, detectors, and measurement techniques. PMID:27082359

  16. Absolute Density Calibration Cell for Laser Induced Fluorescence Erosion Rate Measurements

    NASA Technical Reports Server (NTRS)

    Domonkos, Matthew T.; Stevens, Richard E.

    2001-01-01

    Flight qualification of ion thrusters typically requires testing on the order of 10,000 hours. Extensive knowledge of wear mechanisms and rates is necessary to establish design confidence prior to long duration tests. Consequently, real-time erosion rate measurements offer the potential both to reduce development costs and to enhance knowledge of the dependency of component wear on operating conditions. Several previous studies have used laser-induced fluorescence (LIF) to measure real-time, in situ erosion rates of ion thruster accelerator grids. Those studies provided only relative measurements of the erosion rate. In the present investigation, a molybdenum tube was resistively heated such that the evaporation rate yielded densities within the tube on the order of those expected from accelerator grid erosion. This work examines the suitability of the density cell as an absolute calibration source for LIF measurements, and the intrinsic error was evaluated.

  17. Comb-calibrated frequency-modulated continuous-wave ladar for absolute distance measurements.

    PubMed

    Baumann, Esther; Giorgetta, Fabrizio R; Coddington, Ian; Sinclair, Laura C; Knabe, Kevin; Swann, William C; Newbury, Nathan R

    2013-06-15

    We demonstrate a comb-calibrated frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) system for absolute distance measurements. The FMCW ladar uses a compact external cavity laser that is swept quasi-sinusoidally over 1 THz at a 1 kHz rate. The system simultaneously records the heterodyne FMCW ladar signal and the instantaneous laser frequency at sweep rates up to 3400 THz/s, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the ladar signal against the instantaneous laser frequency yields the range to the target with 1 ms update rates, bandwidth-limited 130 μm resolution and a ~100 nm accuracy that is directly linked to the counted repetition rate of the comb. The precision is <100 nm at the 1 ms update rate and reaches ~6 nm for a 100 ms average. PMID:23938965

  18. Pantomime-Grasping: Advance Knowledge of Haptic Feedback Availability Supports an Absolute Visuo-Haptic Calibration

    PubMed Central

    Davarpanah Jazi, Shirin; Heath, Matthew

    2016-01-01

    An emerging issue in movement neurosciences is whether haptic feedback influences the nature of the information supporting a simulated grasping response (i.e., pantomime-grasping). In particular, recent work by our group contrasted pantomime-grasping responses performed with (i.e., PH+ trials) and without (i.e., PH− trials) terminal haptic feedback in separate blocks of trials. Results showed that PH− trials were mediated via relative visual information. In contrast, PH+ trials showed evidence of an absolute visuo-haptic calibration—a finding attributed to an error signal derived from a comparison between expected and actual haptic feedback (i.e., an internal forward model). The present study examined whether advanced knowledge of haptic feedback availability influences the aforementioned calibration process. To that end, PH− and PH+ trials were completed in separate blocks (i.e., the feedback schedule used in our group’s previous study) and a block wherein PH− and PH+ trials were randomly interleaved on a trial-by-trial basis (i.e., random feedback schedule). In other words, the random feedback schedule precluded participants from predicting whether haptic feedback would be available at the movement goal location. We computed just-noticeable-difference (JND) values to determine whether responses adhered to, or violated, the relative psychophysical principles of Weber’s law. Results for the blocked feedback schedule replicated our group’s previous work, whereas in the random feedback schedule PH− and PH+ trials were supported via relative visual information. Accordingly, we propose that a priori knowledge of haptic feedback is necessary to support an absolute visuo-haptic calibration. Moreover, our results demonstrate that the presence and expectancy of haptic feedback is an important consideration in contrasting the behavioral and neural properties of natural and simulated grasping. PMID:27199718

  19. Initial pointing calibrations for the DSS 13 34-meter beam-waveguide antenna

    NASA Technical Reports Server (NTRS)

    Alvarez, L. S.

    1991-01-01

    The beam pointing of the Deep Space Station (DSS) 13 beam-waveguide antenna at the Goldstone Venus site was calibrated during the postconstruction performance testing period from Jul. 1990 through Jan. 1991. The pointing calibrations were based on errors measured on radio sources at both the Cassegrain and centerline beam-waveguide focal points. The blind pointing performance goal of 5.0 mdeg, 3-sigma at Ka-band (32 GHz) was demonstrated to be met for low (less than 10 mph) wind conditions.

  20. Absolute calibration accuracy of L4 TM and L5 TM sensor image pairs

    USGS Publications Warehouse

    Chander, G.; Micijevic, E.

    2006-01-01

    The Landsat suite of satellites has collected the longest continuous archive of multispectral data of any land-observing space program. From the Landsat program's inception in 1972 to the present, the Earth science user community has benefited from a historical record of remotely sensed data. However, little attention has been paid to ensuring that the data are calibrated and comparable from mission to mission, Launched in 1982 and 1984 respectively, the Landsat 4 (L4) and Landsat 5 (L5) Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The approach involves comparing image statistics derived from large common areas observed eight days apart by the two sensors. The average percent differences in reflectance estimates obtained from the L4 TM agree with those from the L5 TM to within 15 percent. Additional work to characterize the absolute differences between the two sensors over the entire mission is in progress.

  1. Absolute energy calibration for relativistic electron beams with pointing instability from a laser-plasma accelerator

    SciTech Connect

    Cha, H. J.; Choi, I. W.; Kim, H. T.; Kim, I J.; Nam, K. H.; Jeong, T. M.; Lee, J.

    2012-06-15

    The pointing instability of energetic electron beams generated from a laser-driven accelerator can cause a serious error in measuring the electron spectrum with a magnetic spectrometer. In order to determine a correct electron spectrum, the pointing angle of an electron beam incident on the spectrometer should be exactly defined. Here, we present a method for absolutely calibrating the electron spectrum by monitoring the pointing angle using a scintillating screen installed in front of a permanent dipole magnet. The ambiguous electron energy due to the pointing instability is corrected by the numerical and analytical calculations based on the relativistic equation of electron motion. It is also possible to estimate the energy spread of the electron beam and determine the energy resolution of the spectrometer using the beam divergence angle that is simultaneously measured on the screen. The calibration method with direct measurement of the spatial profile of an incident electron beam has a simple experimental layout and presents the full range of spatial and spectral information of the electron beams with energies of multi-hundred MeV level, despite the limited energy resolution of the simple electron spectrometer.

  2. A dedicated pistonphone for absolute calibration of infrasound sensors at very low frequencies

    NASA Astrophysics Data System (ADS)

    He, Wen; He, Longbiao; Zhang, Fan; Rong, Zuochao; Jia, Shushi

    2016-02-01

    Aimed at the absolute calibration of infrasound sensors at very low frequencies, an upgraded and improved infrasonic pistonphone has been developed. The pistonphone was designed such that a very narrow clearance between the piston and its guide was realized based on an automatically-centered clearance-sealing structure, and a large volume rigid-walled chamber was also adopted, which improved the leakage time-constant of the chamber. A composite feedback control system was applied to the electromagnetic vibrator to control the precise motion of the piston. Performance tests and uncertainty analysis show that the leakage time-constant is so large, and the distortion of the sound pressure is so small, that the pistonphone can be used as a standard infrasound source in the frequency range from 0.001 Hz to 20 Hz. The low frequency property of the pistonphone has been verified through calibrating low frequency microphones. Comparison tests with the reciprocity method have shown that the pressure sensitivities from the pistonphone are not only reliable at common frequencies but also have smaller uncertainties at low frequencies.

  3. Absolute calibration of Saral/altiKa on Lake Issykkul from GPS field

    NASA Astrophysics Data System (ADS)

    Crétaux, Jean-Francois; Calmant, Stephane; Romanovsky, Vladimir; Bonnefond, Pascal; Tashbaeva, Saadat; Berge-Nguyen, Muriel; Maisongrande, Philippe

    2015-04-01

    Within the framework of Jason-2 mission, a Cal-Val project including continental waters (Rivers and lakes) had been setup in 2007. It includes installation of permanent site (meteo station, limnigraphs, GPS reference point) and regular field campaign for the whole lifetime of the satellite. The lake Issykkul in Kyrgyzstan has been chosen as site dedicated to lakes following a preliminary project in 2004 on this lake. It is funded by CNES. Over the last decade more and more scientific studies were using satellite altimetry to monitor inland waters. However, same as for ocean studies, linking time series from different missions require to accurately monitoring the biases and drifts for each parameter contributing to the final estimate of the reflector height. Moreover there is clear evidence that the calibration of satellite altimetry over ocean does not apply to inland seas (e.g., corrections, retracking, geographical effects). Regional Cal/Val sites supply invaluable data to formally establish the error budget of altimetry over continental water bodies, in addition to the global mission biases and drift monitoring. Moreover the variety of calibration sites for altimetry had to be enlarged in order to have more global distribution and more robust assessment of the altimetry system, and to check if specific conditions lead to different estimation of absolute bias of the instruments. Calibration over lakes surfaces for example has interesting characteristics with respect to ocean surface: wave and ocean tides are generally low, and to summarize, dynamic variability is much smaller than in the oceanic domain. CAL/VAL activities on the oceanic domain have a long history and protocols are well established. CAL/VAL activities on lakes are much recent but in turn they address other problems such as the performance of the various tracking/retracking algorithms and more globally assess the quality of the geophysical corrections. This is achievable when measurements of

  4. Towards better GNSS observations at the new IGS reference station BRUX: multipath mitigation and individual antenna calibration

    NASA Astrophysics Data System (ADS)

    Aerts, W.; Baire, Q.; Bruyninx, C.; Legrand, J.; Pottiaux, E.

    2012-12-01

    A new multi-GNSS IGS reference station, BRUX, has been installed at Brussels. It replaces the former IGS reference station BRUS, which had to be dismantled because of construction works. The antenna of BRUX is sited on top of a telescope dome. Although this might be an unfortunate choice from an electromagnetic point of view, the siting is very convenient for other reasons. Being close to the time lab hosting the atomic clocks, the cable length is within acceptable and affordable limits, both for cost and signal loss reasons. Moreover, the site offers open sky view, which can indeed be expected from a former telescope siting. The dome is entirely metal, hence shielding of the dome was required in order to mitigate multipath propagation. This was achieved using a metal shield topped with RF absorbing material and respecting a certain antenna-to-absorber spacing in order not to alter the antenna phase center offset (PCO) and variations (PCVs) too much. This would otherwise render the individual calibration of the antenna, in an anechoic chamber in the case of BRUX, invalid. But even taking all precautions, the PCO and PCVs of the calibration do not exactly equal those after installation. Moreover, different calibrations, in an anechoic chamber and by an outdoor robot, of the same antenna have shown to result in PCO and PCVs that differ up to several mm at certain azimuths and elevations. A test set-up with 6 such redundantly calibrated GNSS antennas revealed that the calibration differences can reach 8 mm on the ionosphere-free frequency, which amplifies the calibration differences by a factor three compared to L1 and L2 only. The use of different receiver antenna calibration models can impact position at almost the centimeter level. In an attempt to align the historical time series for BRUS with the (future) data for BRUX, the tie between the new station BRUX and the old IGS station BRUS was determined using terrestrial measurements as well as GPS. In the case of

  5. Development of Absolute Calibration of the Phase Contrast Imaging Diagnostic and Experimental Tests in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tsujii, N.; Porkolab, M.; Edlund, E. M.; Lin, L.

    2007-11-01

    The Phase Contrast Imaging (PCI) system in Alcator C-Mod is used to measure density perturbations from MHD modes, turbulence and RF waves. Recently, an absolutely calibrated system has been installed. This system consists of a set of transducers which cover frequency from 30 kHz to 200 kHz, and wavenumber from 5.5 cm-1 to 36.6 cm-1. The amplitude and phase of the transducer wavefronts are measured using a calibrated microphone. We will present the system design and modeling of this calibration system. Initial results, including a comparison with experimental measurements will also be discussed, if available.

  6. A BAYESIAN METHOD FOR CALCULATING REAL-TIME QUANTITATIVE PCR CALIBRATION CURVES USING ABSOLUTE PLASMID DNA STANDARDS

    EPA Science Inventory

    In real-time quantitative PCR studies using absolute plasmid DNA standards, a calibration curve is developed to estimate an unknown DNA concentration. However, potential differences in the amplification performance of plasmid DNA compared to genomic DNA standards are often ignore...

  7. Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra

    NASA Astrophysics Data System (ADS)

    Cohen, Martin; Walker, Russell G.; Carter, Brian; Hammersley, Peter; Kidger, Mark; Noguchi, Kunio

    1999-04-01

    We start from our six absolutely calibrated continuous stellar spectra from 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These were constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory, and the IRAS Low Resolution Spectrometer, and all have a common calibration pedigree. From these we spawn 422 calibrated ``spectral templates'' for stars with spectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. We normalize each template by photometry for the individual stars using published and/or newly secured near- and mid-infrared photometry obtained through fully characterized, absolutely calibrated, combinations of filter passband, detector radiance response, and mean terrestrial atmospheric transmission. These templates continue our ongoing effort to provide an all-sky network of absolutely calibrated, spectrally continuous, stellar standards for general infrared usage, all with a common, traceable calibration heritage. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors, particularly low- to moderate-resolution spectrometers. We analyze the statistics of probable uncertainties, in the normalization of these templates to actual photometry, that quantify the confidence with which we can assert that these templates truly represent the individual stars. Each calibrated template provides an angular diameter for that star. These radiometric angular diameters compare very favorably with those directly observed across the range from 1.6 to 21 mas.

  8. Test Plan for a Calibration Demonstration System for the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

    NASA Technical Reports Server (NTRS)

    Thome, Kurtis; McCorkel, Joel; Hair, Jason; McAndrew, Brendan; Daw, Adrian; Jennings, Donald; Rabin, Douglas

    2012-01-01

    The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe high-accuracy, long-term climate change trends and to use decadal change observations as the most critical method to determine the accuracy of climate change. One of the major objectives of CLARREO is to advance the accuracy of SI traceable absolute calibration at infrared and reflected solar wavelengths. This advance is required to reach the on-orbit absolute accuracy required to allow climate change observations to survive data gaps while remaining sufficiently accurate to observe climate change to within the uncertainty of the limit of natural variability. While these capabilities exist at NIST in the laboratory, there is a need to demonstrate that it can move successfully from NIST to NASA and/or instrument vendor capabilities for future spaceborne instruments. The current work describes the test plan for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches , alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The end result of efforts with the SOLARIS CDS will be an SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climate-quality data collections. The CLARREO mission addresses the need to observe high-accuracy, long-term climate change trends and advance the accuracy of SI traceable absolute calibration. The current work describes the test plan for the SOLARIS which is the calibration demonstration

  9. A comparison of absolute calibrations of a radiation thermometer based on a monochromator and a tunable source

    NASA Astrophysics Data System (ADS)

    Keawprasert, T.; Anhalt, K.; Taubert, D. R.; Sperling, A.; Schuster, M.; Nevas, S.

    2013-09-01

    An LP3 radiation thermometer was absolutely calibrated at a newly developed monochromator-based set-up and the TUneable Lasers in Photometry (TULIP) facility of PTB in the wavelength range from 400 nm to 1100 nm. At both facilities, the spectral radiation of the respective sources irradiates an integrating sphere, thus generating uniform radiance across its precision aperture. The spectral irradiance of the integrating sphere is determined via an effective area of a precision aperture and a Si trap detector, traceable to the primary cryogenic radiometer of PTB. Due to the limited output power from the monochromator, the absolute calibration was performed with the measurement uncertainty of 0.17 % (k = 1), while the respective uncertainty at the TULIP facility is 0.14 %. Calibration results obtained by the two facilities were compared in terms of spectral radiance responsivity, effective wavelength and integral responsivity. It was found that the measurement results in integral responsivity at the both facilities are in agreement within the expanded uncertainty (k = 2). To verify the calibration accuracy, the absolutely calibrated radiation thermometer was used to measure the thermodynamic freezing temperatures of the PTB gold fixed-point blackbody.

  10. A comparison of absolute calibrations of a radiation thermometer based on a monochromator and a tunable source

    SciTech Connect

    Keawprasert, T.; Anhalt, K.; Taubert, D. R.; Sperling, A.; Schuster, M.; Nevas, S.

    2013-09-11

    An LP3 radiation thermometer was absolutely calibrated at a newly developed monochromator-based set-up and the TUneable Lasers in Photometry (TULIP) facility of PTB in the wavelength range from 400 nm to 1100 nm. At both facilities, the spectral radiation of the respective sources irradiates an integrating sphere, thus generating uniform radiance across its precision aperture. The spectral irradiance of the integrating sphere is determined via an effective area of a precision aperture and a Si trap detector, traceable to the primary cryogenic radiometer of PTB. Due to the limited output power from the monochromator, the absolute calibration was performed with the measurement uncertainty of 0.17 % (k= 1), while the respective uncertainty at the TULIP facility is 0.14 %. Calibration results obtained by the two facilities were compared in terms of spectral radiance responsivity, effective wavelength and integral responsivity. It was found that the measurement results in integral responsivity at the both facilities are in agreement within the expanded uncertainty (k= 2). To verify the calibration accuracy, the absolutely calibrated radiation thermometer was used to measure the thermodynamic freezing temperatures of the PTB gold fixed-point blackbody.

  11. A White Dwarf-Based Investigation of the IRAC Photometric Absolute Calibration

    NASA Astrophysics Data System (ADS)

    Holberg, Jay; Bergeron, Pierre

    2006-05-01

    We propose a SPITZER Archive Program to use the extensive set of DA (pure hydrogen) white dwarfs in the SPITZER Science Archive to: 1) perform an independent investigation of the absolute calibration of the IRAC bands, 2) to evaluated the claim (Kilic et al. 2005) that cool white dwarfs possess unexplained flux deficits in the IRAC 4.5 micron and 8 micron channels, and 3) to systematically investigate the effects of Collisionally Induced Opacities and other opacity sources in cool white dwarfs. Our proposed data set consists primarily of the large set of those DA white dwarfs which have been observed with IRAC, AND which possess spectroscopically determined temperatures and gravities. These stars are placed on the HST photometric scale, with its well defined links to Vega, to optical fluxes, and to the 2MASS Near-IR bands. Model atmosphere fluxes, precisely matching the optical and 2MASS photometry and optical spectroscopy, are used to predict the corresponding IRAC fluxes. This procedure is demonstrated for a set of published IRAC observations.

  12. Absolute reactivity calibration of accelerator-driven systems after RACE-T experiments

    SciTech Connect

    Jammes, C. C.; Geslot, B.

    2006-07-01

    The RACE-T experiments that were held in november 2005 in the ENEA-Casaccia research center near Rome allowed us to improve our knowledge of the experimental techniques for absolute reactivity calibration at either startup or shutdown phases of accelerator-driven systems. Various experimental techniques for assessing a subcritical level were inter-compared through three different subcritical configurations SC0, SC2 and SC3, about -0.5, -3 and -6 dollars, respectively. The area-ratio method based of the use of a pulsed neutron source appears as the most performing. When the reactivity estimate is expressed in dollar unit, the uncertainties obtained with the area-ratio method were less than 1% for any subcritical configuration. The sensitivity to measurement location was about slightly more than 1% and always less than 4%. Finally, it is noteworthy that the source jerk technique using a transient caused by the pulsed neutron source shutdown provides results in good agreement with those obtained from the area-ratio technique. (authors)

  13. Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

    NASA Astrophysics Data System (ADS)

    Bohlin, Ralph C.; Gordon, Karl D.; Tremblay, P.-E.

    2014-08-01

    The measurement of precise absolute fluxes for stellar sources has been pursued with increased vigor since the discovery of dark energy and the realization that its detailed understanding requires accurate spectral energy distributions (SEDs) of redshifted Ia supernovae in the rest frame. The flux distributions of spectrophotometric standard stars were initially derived from the comparison of stars to laboratory sources of known flux but are now mostly based on calculated model atmospheres. For example, pure hydrogen white dwarf (WD) models provide the basis for the HST CALSPEC archive of flux standards. The basic equations for quantitative spectrophotometry and photometry are explained in detail. Several historical lab-based flux calibrations are reviewed; and the SEDs of stars in the major online astronomical databases are compared to the CALSPEC reference standard spectrophotometry. There is good evidence that relative fluxes from the visible to the near-IR wavelength of ~2.5 μm are currently accurate to 1% for the primary reference standards, and new comparisons with lab flux standards show promise for improving that precision.

  14. Error budget for a calibration demonstration system for the reflected solar instrument for the climate absolute radiance and refractivity observatory

    NASA Astrophysics Data System (ADS)

    Thome, Kurtis; McCorkel, Joel; McAndrew, Brendan

    2013-09-01

    A goal of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is to observe highaccuracy, long-term climate change trends over decadal time scales. The key to such a goal is to improving the accuracy of SI traceable absolute calibration across infrared and reflected solar wavelengths allowing climate change to be separated from the limit of natural variability. The advances required to reach on-orbit absolute accuracy to allow climate change observations to survive data gaps exist at NIST in the laboratory, but still need demonstration that the advances can move successfully from to NASA and/or instrument vendor capabilities for spaceborne instruments. The current work describes the radiometric calibration error budget for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The resulting SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climatequality data collections is given. Key components in the error budget are geometry differences between the solar and earth views, knowledge of attenuator behavior when viewing the sun, and sensor behavior such as detector linearity and noise behavior. Methods for demonstrating this error budget are also presented.

  15. Error Budget for a Calibration Demonstration System for the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

    NASA Technical Reports Server (NTRS)

    Thome, Kurtis; McCorkel, Joel; McAndrew, Brendan

    2013-01-01

    A goal of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is to observe highaccuracy, long-term climate change trends over decadal time scales. The key to such a goal is to improving the accuracy of SI traceable absolute calibration across infrared and reflected solar wavelengths allowing climate change to be separated from the limit of natural variability. The advances required to reach on-orbit absolute accuracy to allow climate change observations to survive data gaps exist at NIST in the laboratory, but still need demonstration that the advances can move successfully from to NASA and/or instrument vendor capabilities for spaceborne instruments. The current work describes the radiometric calibration error budget for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The resulting SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climatequality data collections is given. Key components in the error budget are geometry differences between the solar and earth views, knowledge of attenuator behavior when viewing the sun, and sensor behavior such as detector linearity and noise behavior. Methods for demonstrating this error budget are also presented.

  16. Radiometric absolute noise-temperature measurement system features improved accuracy and calibration ease

    NASA Technical Reports Server (NTRS)

    Brown, W.; Ewen, H.; Haroules, G.

    1970-01-01

    Radiometric receiver system, which measures noise temperatures in degrees Kelvin, does not require cryogenic noise sources for routine operation. It eliminates radiometer calibration errors associated with RF attenuation measurements. Calibrated noise source is required only for laboratory adjustment and calibration.

  17. An Analysis of the Effect on the Data Processing of Korea GPS Network by the Absolute Phase Center Variations of GPS Antenna

    NASA Astrophysics Data System (ADS)

    Baek, Jeongho; Lim, Hyung-Chul; Jo, Jung Hyun; Cho, Sungki; Cho, Jung-Ho

    2006-12-01

    The International GNSS Service (IGS) has prepared for a transition from the relative phase center variation (PCV) to the absolute PCV, because the terrestrial scale problem of the absolute PCV was resolved by estimating the PCV of the GPS satellites. Thus, the GPS data will be processed by using the absolute PCV which will be an IGS standard model in the near future. It is necessary to compare and analyze the results between the relative PCV and the absolute PCV for the establishment of the reliable processing strategy. This research analyzes the effect caused by the absolute PCV via the GPS network data processing. First, the four IGS stations, Daejeon, Suwon, Beijing and Wuhan, are selected to make longer baselines than 1000 km, and processed by using the relative PCV and the absolute PCV to examine the effect of the antenna raydome. Beijing and Wuhan stations of which the length of baselines are longer than 1000 km show the average difference of 1.33 cm in the vertical! component, and 2.97 cm when the antenna raydomes are considered. Second, the 7 permanent GPS stations among the total 9 stations, operated by Korea Astronomy and Space Science Institute, are processed by applying the relative PCV and the absolute PCV, and their results are compared and analyzed. An insignificant effect of the absolute PCV is shown in Korea regional network with the average difference of 0.12 cm in the vertical component.

  18. Improved Strategies and Optimization of Calibration Models for Real-time PCR Absolute Quantification

    EPA Science Inventory

    Real-time PCR absolute quantification applications rely on the use of standard curves to make estimates of DNA target concentrations in unknown samples. Traditional absolute quantification approaches dictate that a standard curve must accompany each experimental run. However, t...

  19. A TECHNIQUE FOR PRIMARY BEAM CALIBRATION OF DRIFT-SCANNING, WIDE-FIELD ANTENNA ELEMENTS

    SciTech Connect

    Pober, Jonathan C.; Parsons, Aaron R.; Jacobs, Daniel C.; Aguirre, James E.; Moore, David F.; Bradley, Richard F.; Parashare, Chaitali R.; Carilli, Chris L.; Gugliucci, Nicole E.

    2012-02-15

    We present a new technique for calibrating the primary beam of a wide-field, drift-scanning antenna element. Drift-scan observing is not compatible with standard beam calibration routines, and the situation is further complicated by difficult-to-parameterize beam shapes and, at low frequencies, the sparsity of accurate source spectra to use as calibrators. We overcome these challenges by building up an interrelated network of source 'crossing points'-locations where the primary beam is sampled by multiple sources. Using the single assumption that a beam has 180 Degree-Sign rotational symmetry, we can achieve significant beam coverage with only a few tens of sources. The resulting network of crossing points allows us to solve for both a beam model and source flux densities referenced to a single calibrator source, circumventing the need for a large sample of well-characterized calibrators. We illustrate the method with actual and simulated observations from the Precision Array for Probing the Epoch of Reionization.

  20. Absolute Dating of Desert Varnish Using Portable X-Ray Fluorescence: Calibration and Testing

    NASA Astrophysics Data System (ADS)

    Pingitore, N. E.; Lytle, F. W.; Rowley, P. D.; Ferris, D. E.

    2004-12-01

    Desert varnish, also called rock varnish, is a thin biogenic layer of Mn-oxides, Fe-oxides, and clays that coats rock surfaces in arid and semi-arid regions. The mass of these metals in the varnish registers cumulative biologic activity over time and presents a possible dating mechanism, subject to appropriate assumptions and restrictions. We have used a portable x-ray fluorescence (PXRF) unit to measure Mn and Fe in numerous desert varnishes, both in the field and laboratory; the anticipated relationship between age and mass emerges from these data. Our attempts to refine the PXRF technique for absolute dating of desert varnish are confounded by the limited number of "dated" varnishes available to calibrate and test the method. Although there is no current method to directly ascertain the age of desert varnish, our search for "dated" varnishes has yielded three suitable types of test materials: (1) The ages of young basalt flows dated by various K/Ar radiometric techniques represent the maximum age of varnish developed on those surfaces. Such rocks are useful in the time range of perhaps 250,000 to 10,000 years; surface spalling with loss of varnish presents an upper time limit and difficulty in dating Holocene basalts presents a lower limit. Basalt flows typically provide horizontal surfaces that are ideal for PXRF measurements because, as a biogenic process, varnish development even at a single site varies with solar orientation. (2) Petroglyphs are the rock art that native peoples produced by pecking away varnish to expose fresh rock. This process restarts varnish development and the pecked surface gradually repatinates over time. At some locales, certain figures, symbols, and stylistic elements can be associated with an archaeological culture of known antiquity and duration, thus providing an age range for such glyphs. In the desert Southwest and Great Basin of the United States, appropriate glyphs are known from the present to at least 7000 years BP. Many of

  1. Absolute radiometric calibration of Als intensity data: effects on accuracy and target classification.

    PubMed

    Kaasalainen, Sanna; Pyysalo, Ulla; Krooks, Anssi; Vain, Ants; Kukko, Antero; Hyyppä, Juha; Kaasalainen, Mikko

    2011-01-01

    Radiometric calibration of airborne laser scanning (ALS) intensity data aims at retrieving a value related to the target scattering properties, which is independent on the instrument or flight parameters. The aim of a calibration procedure is also to be able to compare results from different flights and instruments, but practical applications are sparsely available, and the performance of calibration methods for this purpose needs to be further assessed. We have studied the radiometric calibration with data from three separate flights and two different instruments using external calibration targets. We find that the intensity data from different flights and instruments can be compared to each other only after a radiometric calibration process using separate calibration targets carefully selected for each flight. The calibration is also necessary for target classification purposes, such as separating vegetation from sand using intensity data from different flights. The classification results are meaningful only for calibrated intensity data. PMID:22346660

  2. Absolute Radiometric Calibration of ALS Intensity Data: Effects on Accuracy and Target Classification

    PubMed Central

    Kaasalainen, Sanna; Pyysalo, Ulla; Krooks, Anssi; Vain, Ants; Kukko, Antero; Hyyppä, Juha; Kaasalainen, Mikko

    2011-01-01

    Radiometric calibration of airborne laser scanning (ALS) intensity data aims at retrieving a value related to the target scattering properties, which is independent on the instrument or flight parameters. The aim of a calibration procedure is also to be able to compare results from different flights and instruments, but practical applications are sparsely available, and the performance of calibration methods for this purpose needs to be further assessed. We have studied the radiometric calibration with data from three separate flights and two different instruments using external calibration targets. We find that the intensity data from different flights and instruments can be compared to each other only after a radiometric calibration process using separate calibration targets carefully selected for each flight. The calibration is also necessary for target classification purposes, such as separating vegetation from sand using intensity data from different flights. The classification results are meaningful only for calibrated intensity data. PMID:22346660

  3. Exploring a Black Body Source as an Absolute Radiometric Calibration Standard and Comparison with a NIST Traced Lamp Standard

    NASA Technical Reports Server (NTRS)

    Green, Robert O.; Chrien, Thomas; Sarture, Chuck

    2001-01-01

    Radiometric calibration of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) is required for the scientific research and application objectives pursued with the spectroscopic measurements. Specifically calibration is required for: inter-comparison of AVIRIS data measured at different locations and at different times; analysis of AVIRIS data with data measured by other instruments; and analysis of AVIRIS data in conjunction with computer models. The primary effect of radiometric calibration is conversion of AVIRIS instrument response values (digitized numbers, or DN) to units of absolute radiance. For example, a figure shows the instrument response spectrum measured by AVIRIS over a portion of Rogers Dry Lake, California, and another figure shows the same spectrum calibrated to radiance. Only the calibrated spectrum may be quantitatively analyzed for science research and application objectives. Since the initial development of the AVIRIS instrument-radiometric calibration has been based upon a 1000-W irradiance lamp with a calibration traced to the National Institute of Standards and Technology (NIST). There are several advantages to this irradiance-lamp calibration approach. First, the considerable effort of NIST backs up the calibration. Second, by changing the distance to the lamp, the output can closely span the radiance levels measured by AVIRIS. Third, this type of standard is widely used. Fourth, these calibrated lamps are comparatively inexpensive. Conversely, there are several disadvantages to this approach as well. First, the lamp is not a primary standard. Second, the lamp output characteristics may change in an unknown manner through time. Third, it is difficult to assess, constrain, or improve the calibration uncertainty delivered with the lamp. In an attempt to explore the effect and potentially address some of these disadvantages a set of analyses and measurements comparing an irradiance lamp with a black-body source have been completed

  4. Reprocessing of GPS observations: influence of calibration models of antenna/radome combinations on permanent GPS station coordinates

    NASA Astrophysics Data System (ADS)

    Ishchenko, Marina

    2012-05-01

    Observations of the GPS satellites at permanent stations located in Ukraine and in the Eastern Europe were reprocessed at the GPS Analysis Center of the Main Astronomical Observatory with Bernese GPS Software ver. 5.0. The effect of influence of relative and absolute phase center variations of antenna/radome combinations to determination coordinates of permanent GPS stations are considered.

  5. Absolute Calibration of Image Plate for electrons at energy between 100 keV and 4 MeV

    SciTech Connect

    Chen, H; Back, N L; Eder, D C; Ping, Y; Song, P M; Throop, A

    2007-12-10

    The authors measured the absolute response of image plate (Fuji BAS SR2040) for electrons at energies between 100 keV to 4 MeV using an electron spectrometer. The electron source was produced from a short pulse laser irradiated on the solid density targets. This paper presents the calibration results of image plate Photon Stimulated Luminescence PSL per electrons at this energy range. The Monte Carlo radiation transport code MCNPX results are also presented for three representative incident angles onto the image plates and corresponding electron energies depositions at these angles. These provide a complete set of tools that allows extraction of the absolute calibration to other spectrometer setting at this electron energy range.

  6. Measurement of Antenna Bore-Sight Gain

    NASA Technical Reports Server (NTRS)

    Fortinberry, Jarrod; Shumpert, Thomas

    2016-01-01

    The absolute or free-field gain of a simple antenna can be approximated using standard antenna theory formulae or for a more accurate prediction, numerical methods may be employed to solve for antenna parameters including gain. Both of these methods will result in relatively reasonable estimates but in practice antenna gain is usually verified and documented via measurements and calibration. In this paper, a relatively simple and low-cost, yet effective means of determining the bore-sight free-field gain of a VHF/UHF antenna is proposed by using the Brewster angle relationship.

  7. Auxiliary instruments for the absolute calibration of the ASTRI SST-2M prototype for the Cherenkov Telescope Array

    NASA Astrophysics Data System (ADS)

    Maccarone, Maria C.; Segreto, Alberto; Catalano, Osvaldo; La Rosa, Giovanni; Russo, Francesco; Sottile, Giuseppe; Gargano, Carmelo; Biondo, Benedetto; Fiorini, Mauro; Incorvaia, Salvatore; Toso, Giorgio

    2014-08-01

    ASTRI SST-2M is the end-to-end prototype telescope under development by the Italian National Institute of Astrophysics, INAF, proposed for the investigation of the highest-energy gamma-ray band in the framework of the Cherenkov Telescope Array, CTA. The ASTRI SST-2M prototype will be installed in Italy at the INAF station located at Serra La Nave on Mount Etna during Fall 2014. The calibration and scientific validation phase will start soon after. The calibration of a Cherenkov telescope includes several items and tools. The ASTRI SST- 2M camera is equipped with an internal fiber illumination system that allows to perform the relative calibration through monitoring of gain and efficiency variations of each pixel. The absolute calibration of the overall system, including optics, will take advantage from auxiliary instrumentation, namely UVscope and UVSiPM, two small-aperture multi-pixels photon detectors NIST calibrated in lab. During commissioning phase, to measure the main features of ASTRI SST-2M, as its overall spectral response, the main telescope and the auxiliary UVscope-UVSiPM will be illuminated simultaneously by a spatially uniform flux generated by a ground-based light source, named Illuminator, placed at a distance of few hundreds meters. Periodically, during clear nights, the flux profiles of a reference star tracked simultaneously by ASTRI SST-2M and UVscope-UVSiPM will allow to evaluate the total atmospheric attenuation and the absolute calibration constant of the ASTRI SST-2M prototype. In this contribution we describe the auxiliary UVscope-UVSiPM and Illuminator sub-system together with an overview of the end-to-end calibration procedure foreseen for the ASTRI SST-2M telescope prototype.

  8. Absolute Radiometric Calibration of Narrow-Swath Imaging Sensors with Reference to Non-Coincident Wide-Swath Sensors

    NASA Technical Reports Server (NTRS)

    McCorkel, Joel; Thome, Kurtis; Lockwood, Ronald

    2012-01-01

    An inter-calibration method is developed to provide absolute radiometric calibration of narrow-swath imaging sensors with reference to non-coincident wide-swath sensors. The method predicts at-sensor radiance using non-coincident imagery from the reference sensor and knowledge of spectral reflectance of the test site. The imagery of the reference sensor is restricted to acquisitions that provide similar view and solar illumination geometry to reduce uncertainties due to directional reflectance effects. Spectral reflectance of the test site is found with a simple iterative radiative transfer method using radiance values of a well-understood wide-swath sensor and spectral shape information based on historical ground-based measurements. At-sensor radiance is calculated for the narrow-swath sensor using this spectral reflectance and atmospheric parameters that are also based on historical in situ measurements. Results of the inter-calibration method show agreement on the 2 5 percent level in most spectral regions with the vicarious calibration technique relying on coincident ground-based measurements referred to as the reflectance-based approach. While the variability of the inter-calibration method based on non-coincident image pairs is significantly larger, results are consistent with techniques relying on in situ measurements. The method is also insensitive to spectral differences between the sensors by transferring to surface spectral reflectance prior to prediction of at-sensor radiance. The utility of this inter-calibration method is made clear by its flexibility to utilize image pairings with acquisition dates differing in excess of 30 days allowing frequent absolute calibration comparisons between wide- and narrow-swath sensors.

  9. Determining the importance of model calibration for forecasting absolute/relative changes in streamflow from LULC and climate changes

    USGS Publications Warehouse

    Niraula, Rewati; Meixner, Thomas; Norman, Laura M.

    2015-01-01

    Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Assessing the impact of LULC and climate changes on streamflow is typically done with a calibrated and validated watershed model. However, there is a debate on the degree of calibration required. The objective of this study was to quantify the variation in estimated relative and absolute changes in streamflow associated with LULC and climate changes with different calibration approaches. The Soil and Water Assessment Tool (SWAT) was applied in an uncalibrated (UC), single outlet calibrated (OC), and spatially-calibrated (SC) mode to compare the relative and absolute changes in streamflow at 14 gaging stations within the Santa Cruz River Watershed in southern Arizona, USA. For this purpose, the effect of 3 LULC, 3 precipitation (P), and 3 temperature (T) scenarios were tested individually. For the validation period, Percent Bias (PBIAS) values were >100% with the UC model for all gages, the values were between 0% and 100% with the OC model and within 20% with the SC model. Changes in streamflow predicted with the UC and OC models were compared with those of the SC model. This approach implicitly assumes that the SC model is “ideal”. Results indicated that the magnitude of both absolute and relative changes in streamflow due to LULC predicted with the UC and OC results were different than those of the SC model. The magnitude of absolute changes predicted with the UC and SC models due to climate change (both P and T) were also significantly different, but were not different for OC and SC models. Results clearly indicated that relative changes due to climate change predicted with the UC and OC were not significantly different than that predicted with the SC models. This result suggests that it is important to calibrate the model spatially to analyze the effect of LULC change but not as important for analyzing the relative change in streamflow due to climate change. This

  10. Absolute calibration of optical power for PDT: report of AAPM TG140.

    PubMed

    Zhu, Timothy C; Bonnerup, Chris; Colussi, Valdir C; Dowell, Marla L; Finlay, Jarod C; Lilge, Lothar; Slowey, Thomas W; Sibata, Claudio

    2013-08-01

    This report is primarily concerned with methods for optical calibration of laser power for continuous wave (CW) light sources, predominantly used in photodynamic therapy (PDT). Light power calibration is very important for PDT, however, no clear standard has been established for the calibration procedure nor the requirements of power meters suitable for optical power calibration. The purposes of the report are to provide guidance for establishing calibration procedures for thermopile type power meters and establish calibration uncertainties for most commercially available detectors and readout assemblies. The authors have also provided a review of the use of various power meters for CW and pulsed optical sources, and provided recommended temporal frequencies for optical power meter calibrations and guidance for routine quality assurance procedure. PMID:23927297

  11. Telescope Spectrophotometric and Absolute Flux Calibration, and National Security Applications, Using a Turntable Laser on a Satellite

    NASA Astrophysics Data System (ADS)

    Albert, J.; Burgett, W.; Rhodes, J.

    We propose a tunable laser-based satellite-mounted spectrophotometric and absolute flux calibration system, to be utilized by ground- and space-based telescopes. As uncertainties on the photometry, due to imperfect knowledge of both telescope optics and the atmosphere, will in the near future begin to dominate the uncertainties on fundamental cosmological parameters such as WL (Omega_Lambda) and w in measurements from SNIa, weak gravitational lensing, and baryon oscillations, a method for reducing such uncertainties is needed. We propose to improve spectrophotometric calibration, currently obtained using standard stars, by placing a tunable laser and a wide-angle light source on a satellite by early next decade (perhaps included in the upgrade to the GPS satellite network) to improve absolute flux calibration to 0.1% and relative spectrophotometric calibration to better than 0.001% across the visible and near-infrared spectrum. As well as fundamental astrophysical applications, the system proposed here potentially has broad utility for defense and national security applications such as ground target illumination and space communication. For further details please see http://www.arxiv.org/abs/astro-ph/0604339.

  12. A new method for the absolute radiance calibration for UV/vis measurements of scattered sun light

    NASA Astrophysics Data System (ADS)

    Wagner, T.; Beirle, S.; Dörner, S.; Penning de Vries, M.; Remmers, J.; Rozanov, A.; Shaiganfar, R.

    2015-05-01

    Absolute radiometric calibrations are important for measurements of the atmospheric spectral radiance. Such measurements can be used to determine actinic fluxes, the properties of aerosols and clouds and the short wave energy budget. Conventional calibration methods in the laboratory are based on calibrated light sources and reflectors and are expensive, time consuming and subject to relatively large uncertainties. Also, the calibrated instruments might change during transport from the laboratory to the measurement sites. Here we present a new calibration method for UV/vis instruments that measure the spectrally resolved sky radiance, like for example zenith sky Differential Optical Absorption Spectroscopy (DOAS-) instruments or Multi-AXis (MAX-) DOAS instruments. Our method is based on the comparison of the solar zenith angle dependence of the measured zenith sky radiance with radiative transfer simulations. For the application of our method clear sky measurements during periods with almost constant aerosol optical depth are needed. The radiative transfer simulations have to take polarisation into account. We show that the calibration results are almost independent from the knowledge of the aerosol optical properties and surface albedo, which causes a rather small uncertainty of about <7%. For wavelengths below about 330 nm it is essential that the ozone column density during the measurements is constant and known.

  13. Absolute intensity calibration of the Wendelstein 7-X high efficiency extreme ultraviolet overview spectrometer system

    NASA Astrophysics Data System (ADS)

    Greiche, Albert; Biel, Wolfgang; Marchuk, Oleksandr; Burhenn, Rainer

    2008-09-01

    The new high effiency extreme ultraviolet overview spectrometer (HEXOS) system for the stellarator Wendelstein 7-X is now mounted for testing and adjustment at the tokamak experiment for technology oriented research (TEXTOR). One part of the testing phase was the intensity calibration of the two double spectrometers which in total cover a spectral range from 2.5 to 160.0 nm with overlap. This work presents the current intensity calibration curves for HEXOS and describes the method of calibration. The calibration was implemented with calibrated lines of a hollow cathode light source and the branching ratio technique. The hollow cathode light source provides calibrated lines from 16 up to 147 nm. We could extend the calibrated region in the spectrometers down to 2.8 nm by using the branching line pairs emitted by an uncalibrated pinch extreme ultraviolet light source as well as emission lines from boron and carbon in TEXTOR plasmas. In total HEXOS is calibrated from 2.8 up to 147 nm, which covers most of the observable wavelength region. The approximate density of carbon in the range of the minor radius from 18 to 35 cm in a TEXTOR plasma determined by simulating calibrated vacuum ultraviolet emission lines with a transport code was 5.5×1017 m-3 which corresponds to a local carbon concentration of 2%.

  14. Calibration of Gimbaled Platforms: The Solar Dynamics Observatory High Gain Antennas

    NASA Technical Reports Server (NTRS)

    Hashmall, Joseph A.

    2006-01-01

    Simple parameterization of gimbaled platform pointing produces a complete set of 13 calibration parameters-9 misalignment angles, 2 scale factors and 2 biases. By modifying the parameter representation, redundancy can be eliminated and a minimum set of 9 independent parameters defined. These consist of 5 misalignment angles, 2 scale factors, and 2 biases. Of these, only 4 misalignment angles and 2 biases are significant for the Solar Dynamics Observatory (SDO) High Gain Antennas (HGAs). An algorithm to determine these parameters after launch has been developed and tested with simulated SDO data. The algorithm consists of a direct minimization of the root-sum-square of the differences between expected power and measured power. The results show that sufficient parameter accuracy can be attained even when time-dependent thermal distortions are present, if measurements from a pattern of intentional offset pointing positions is included.

  15. Absolute calibration of photostimulable image plate detectors used as (0.5-20 MeV) high-energy proton detectors.

    PubMed

    Mancić, A; Fuchs, J; Antici, P; Gaillard, S A; Audebert, P

    2008-07-01

    In this paper, the absolute calibration of photostimulable image plates (IPs) used as proton detectors is presented. The calibration is performed in a wide range of proton energies (0.5-20 MeV) by exposing simultaneously the IP and calibrated detectors (radiochromic films and solid state detector CR39) to a source of broadband laser-accelerated protons, which are spectrally resolved. The final result is a calibration curve that enables retrieving the proton number from the IP signal. PMID:18681694

  16. ABSOLUTE FLUX CALIBRATION OF THE IRAC INSTRUMENT ON THE SPITZER SPACE TELESCOPE USING HUBBLE SPACE TELESCOPE FLUX STANDARDS

    SciTech Connect

    Bohlin, R. C.; Gordon, K. D.; Deustua, S.; Ferguson, H. C.; Flanagan, K.; Kalirai, J.; Meixner, M.; Rieke, G. H.; Engelbracht, C.; Su, K. Y. L.; Ardila, D.; Tremblay, P.-E.

    2011-05-15

    The absolute flux calibration of the James Webb Space Telescope (JWST) will be based on a set of stars observed by the Hubble and Spitzer Space Telescopes. In order to cross-calibrate the two facilities, several A, G, and white dwarf stars are observed with both Spitzer and Hubble and are the prototypes for a set of JWST calibration standards. The flux calibration constants for the four Spitzer IRAC bands 1-4 are derived from these stars and are 2.3%, 1.9%, 2.0%, and 0.5% lower than the official cold-mission IRAC calibration of Reach et al., i.e., in agreement within their estimated errors of {approx}2%. The causes of these differences lie primarily in the IRAC data reduction and secondarily in the spectral energy distributions of our standard stars. The independent IRAC 8 {mu}m band-4 fluxes of Rieke et al. are about 1.5% {+-} 2% higher than those of Reach et al. and are also in agreement with our 8 {mu}m result.

  17. Comparison of absolute gain photometric calibration between Planck/HFI and Herschel/SPIRE at 545 and 857 GHz

    NASA Astrophysics Data System (ADS)

    Bertincourt, B.; Lagache, G.; Martin, P. G.; Schulz, B.; Conversi, L.; Dassas, K.; Maurin, L.; Abergel, A.; Beelen, A.; Bernard, J.-P.; Crill, B. P.; Dole, H.; Eales, S.; Gudmundsson, J. E.; Lellouch, E.; Moreno, R.; Perdereau, O.

    2016-04-01

    We compare the absolute gain photometric calibration of the Planck/HFI and Herschel/SPIRE instruments on diffuse emission. The absolute calibration of HFI and SPIRE each relies on planet flux measurements and comparison with theoretical far-infrared emission models of planetary atmospheres. We measure the photometric cross calibration between the instruments at two overlapping bands, 545 GHz/500 μm and 857 GHz/350 μm. The SPIRE maps used have been processed in the Herschel Interactive Processing Environment (Version 12) and the HFI data are from the 2015 Public Data Release 2. For our study we used 15 large fields observed with SPIRE, which cover a total of about 120 deg2. We have selected these fields carefully to provide high signal-to-noise ratio, avoid residual systematics in the SPIRE maps, and span a wide range of surface brightness. The HFI maps are bandpass-corrected to match the emission observed by the SPIRE bandpasses. The SPIRE maps are convolved to match the HFI beam and put on a common pixel grid. We measure the cross-calibration relative gain between the instruments using two methods in each field, pixel-to-pixel correlation and angular power spectrum measurements. The SPIRE/HFI relative gains are 1.047 (±0.0069) and 1.003 (±0.0080) at 545 and 857 GHz, respectively, indicating very good agreement between the instruments. These relative gains deviate from unity by much less than the uncertainty of the absolute extended emission calibration, which is about 6.4% and 9.5% for HFI and SPIRE, respectively, but the deviations are comparable to the values 1.4% and 5.5% for HFI and SPIRE if the uncertainty from models of the common calibrator can be discounted. Of the 5.5% uncertainty for SPIRE, 4% arises from the uncertainty of the effective beam solid angle, which impacts the adopted SPIRE point source to extended source unit conversion factor, highlighting that as a focus for refinement.

  18. Landsat-7 ETM+ On-Orbit Reflective-Band Radiometric Stability and Absolute Calibration

    NASA Technical Reports Server (NTRS)

    Markham, Brian L.; Thome, Kurtis J.; Barsi, Julia A.; Kaita, Ed; Helder, Dennis L.; Barker, John L.

    2003-01-01

    The Landsat-7 spacecraft carries the Enhanced Thematic Mapper Plus (ETM+) instrument. This instrument images the Earth land surface in eight parts of the electromagnetic spectrum, termed spectral bands. These spectral images are used to monitor changes in the land surface, so a consistent relationship, i.e., calibration, between the image data and the Earth surface brightness, is required. The ETM+ has several on- board calibration devices that are used to monitor this calibration. The best on-board calibration source employs a flat white painted reference panel and has indicated changes of between 0.5% to 2% per year in the ETM+ response, depending on the spectral band. However, most of these changes are believed to be caused by changes in the reference panel, as opposed to changes in the instrument's sensitivity. This belief is based partially on on-orbit calibrations using instrumented ground sites and observations of "invariant sites", hyper-arid sites of the Sahara and Arabia. Changes determined from these data sets indicate are 0.1% - 0.6% per year. Tests and comparisons to other sensors also indicate that the uncertainty of the calibration is at the 5% level.

  19. Absolute calibration of OH density in a nanosecond pulsed plasma filament in atmospheric pressure He-H2O: comparison of independent calibration methods

    NASA Astrophysics Data System (ADS)

    Verreycken, T.; van der Horst, R. M.; Sadeghi, N.; Bruggeman, P. J.

    2013-11-01

    The absolute density of OH radicals generated in a nanosecond pulsed filamentary discharge in atmospheric pressure He +0.84% H2O is measured independently by UV absorption and laser induced fluorescence (LIF) calibrated with Rayleigh scattering. For the calibration of LIF with Rayleigh scattering, two LIF models, with six levels and four levels, are studied to investigate the influence of the rotational and vibrational energy transfers. In addition, a chemical model is used to deduce the OH density in the afterglow from the relative LIF intensity as function of time. The different models show good correspondence and by comparing these different methods, the accuracy and the effect of assumptions on the obtained OH density are discussed in detail. This analysis includes an analysis of the sensitivity to parameters used in the LIF models.

  20. Absolute calibration of a variable attenuator using few-photon pulses.

    PubMed

    Levine, Zachary H; Glebov, Boris L; Pintar, Adam L; Migdall, Alan L

    2015-06-15

    We demonstrate the ability to calibrate a variable optical attenuator directly at the few-photon level using a superconducting Transition Edge Sensor (TES). Because of the inherent linearity of photon-number resolving detection, no external calibrations are required, even for the energy of the laser pulses, which ranged from means of 0.15 to 18 photons per pulse at the detector. To verify this method, calibrations were compared to an independent conventional calibration made at much higher photon fluxes using analog detectors. In all cases, the attenuations estimated by the two methods agree within their uncertainties.Our few-photon measurement determined attenuations using the Poisson-Influenced K-Means Algorithm (PIKA) to extract mean numbers of photons per pulse along with the uncertainties of these means. The robustness of the method is highlighted by the agreement of the two calibrations even in the presence of significant drifts in the optical power over the course of the experiment.Work of the United States Government. Not subject to copyright. PMID:26193610

  1. The absolute radiometric calibration of the advanced very high resolution radiometer

    NASA Technical Reports Server (NTRS)

    Slater, P. N.; Teillet, P. M.; Ding, Y.

    1989-01-01

    The measurement conditions are described for an intensive field campaign at White Sands Missile Range for the calibration of the AVHRRs on NOAA-9, NOAA-10 and NOAA-11, LANDSAT-4 TM and SPOT. Three different methods for calibration of AVHRRs by reference to a ground surface site are reported, and results from these methods are compared. Significant degradations in NOAA-9 and NOAA-10 AVHRR responsivities occurred since prelaunch calibrations were completed. As of February 1988, degradations in NOAA-9 AVHRR responsivities were on the order of 37 percent in channel and 41 percent in channel 2, and for the NOAA-10 AVHRR these degradations were 42 and 59 percent in channels 1 and 2, respectively.

  2. Absolute calibration of the Gamma Knife{sup ®} Perfexion™ and delivered dose verification using EPR/alanine dosimetry

    SciTech Connect

    Hornbeck, Amaury E-mail: tristan.garcia@cea.fr; Garcia, Tristan E-mail: tristan.garcia@cea.fr; Cuttat, Marguerite; Jenny, Catherine

    2014-06-15

    Purpose: Elekta Leksell Gamma Knife{sup ®} (LGK) is a radiotherapy beam machine whose features are not compliant with the international calibration protocols for radiotherapy. In this scope, the Laboratoire National Henri Becquerel and the Pitié-Salpêtrière Hospital decided to conceive a new LKG dose calibration method and to compare it with the currently used one. Furthermore, the accuracy of the dose delivered by the LGK machine was checked using an “end-to-end” test. This study also aims to compare doses delivered by the two latest software versions of the Gammaplan treatment planning system (TPS). Methods: The dosimetric method chosen is the electron paramagnetic resonance (EPR) of alanine. Dose rate (calibration) verification was done without TPS using a spherical phantom. Absolute calibration was done with factors calculated by Monte Carlo simulation (MCNP-X). For “end-to-end” test, irradiations in an anthropomorphic head phantom, close to real treatment conditions, are done using the TPS in order to verify the delivered dose. Results: The comparison of the currently used calibration method with the new one revealed a deviation of +0.8% between the dose rates measured by ion chamber and EPR/alanine. For simple fields configuration (less than 16 mm diameter), the “end-to-end” tests showed out average deviations of −1.7% and −0.9% between the measured dose and the calculated dose by Gammaplan v9 and v10, respectively. Conclusions: This paper shows there is a good agreement between the new calibration method and the currently used one. There is also a good agreement between the calculated and delivered doses especially for Gammaplan v10.

  3. The Importance of Post-Launch, On-Orbit Absolute Radiometric Calibration for Remote Sensing Applications

    NASA Astrophysics Data System (ADS)

    Kuester, M. A.

    2015-12-01

    Remote sensing is a powerful tool for monitoring changes on the surface of the Earth at a local or global scale. The use of data sets from different sensors across many platforms, or even a single sensor over time, can bring a wealth of information when exploring anthropogenic changes to the environment. For example, variations in crop yield and health for a specific region can be detected by observing changes in the spectral signature of the particular species under study. However, changes in the atmosphere, sun illumination and viewing geometries during image capture can result in inconsistent image data, hindering automated information extraction. Additionally, an incorrect spectral radiometric calibration will lead to false or misleading results. It is therefore critical that the data being used are normalized and calibrated on a regular basis to ensure that physically derived variables are as close to truth as is possible. Although most earth observing sensors are well-calibrated in a laboratory prior to launch, a change in the radiometric response of the system is inevitable due to thermal, mechanical or electrical effects caused during the rigors of launch or by the space environment itself. Outgassing and exposure to ultra-violet radiation will also have an effect on the sensor's filter responses. Pre-launch lamps and other laboratory calibration systems can also fall short in representing the actual output of the Sun. A presentation of the differences in the results of some example cases (e.g. geology, agriculture) derived for science variables using pre- and post-launch calibration will be presented using DigitalGlobe's WorldView-3 super spectral sensor, with bands in the visible and near infrared, as well as in the shortwave infrared. Important defects caused by an incomplete (i.e. pre-launch only) calibration will be discussed using validation data where available. In addition, the benefits of using a well-validated surface reflectance product will be

  4. Absolute calibration method for fast-streaked, fiber optic light collection, spectroscopy systems.

    SciTech Connect

    Johnston, Mark D.; Frogget, Brent; Oliver, Bryan Velten; Maron, Yitzhak; Droemer, Darryl W.; Crain, Marlon D.

    2010-04-01

    This report outlines a convenient method to calibrate fast (<1ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such a system is used to collect spectral data on plasmas generated in the A-K gap of electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA). On RITS, light is collected through a small diameter (200 micron) optical fiber and recorded on a fast streak camera at the output of 1 meter Czerny-Turner monochromator (F/7 optics). To calibrate such a system, it is necessary to efficiently couple light from a spectral lamp into a 200 micron diameter fiber, split it into its spectral components, with 10 Angstroms or less resolution, and record it on a streak camera with 1ns or less temporal resolution.

  5. Absolute Sea Level Monitoring and Altimeter Calibration At Gavdos, Crete, Greece

    NASA Astrophysics Data System (ADS)

    Pavlis, E. C.; Gavdos Team

    We present the mean sea level (MSL) monitoring aspect of the altimeter calibration fa- cility under deployment on western Crete and the isle of Gavdos. The Eastern Mediter- ranean area is one of great interest for its intense tectonic activity as well as for its regional oceanography. Recent observations have convincingly demonstrated the im- portance of that area for the regional meteorological and climatological changes. Tide- gauge monitoring with GPS has gained importance lately since tectonics contaminate the inferred sea level variations, and a global network of tide-gauges with long his- torical records can be used as satellite altimeter calibration sites for current and fu- ture missions (e.g. TOPEX/POSEIDON, GFO, JASON-1, ENVISAT, etc.). This is at present a common IOC-GLOSS-IGS effort, already underway (TIGA). Crete hosts two of the oldest tide-gauges in the regional network and our project will further ex- pand it to the south of the island with a new site on the isle of Gavdos, the southernmost European parcel of land. One component of our "GAVDOS" project is the repeated occupation of two already in existence tide-gauge sites at Souda Bay and Heraklion, and their tie to the new facility. We show here initial results from positioning of these sites and some of the available tidal records. Gavdos is situated under a ground-track crossing point of the present T/P and JASON-1 orbits. It is an ideal calibration site if the tectonic motions are monitored precisely and continuously. Our plans include the deployment of additional instrumentation at this site: GPS and DORIS beacons for positioning, transponders for direct calibration, water vapor radiometers, GPS-loaded buoys, airborne surveys with gravimeters and laser profiling lidars, etc., to ensure the best possible and most reliable results.

  6. First preliminary results for the absolute calibration of the Chinese HY-2 altimetric mission using the CRS1 calibration facilities in West Crete, Greece

    NASA Astrophysics Data System (ADS)

    Mertikas, Stelios P.; Zhou, Xinghua; Qiao, Fangli; Daskalakis, Antonis; Lin, Mingsen; Peng, Hailong; Tziavos, Ilias N.; Vergos, George; Tripolitsiotis, Achilleas; Frantzis, Xenophon

    2016-01-01

    In this work, absolute calibration of the Chinese HY-2 satellite altimetry mission is carried out, employing Pass No. 280 and the calibration facility, CRS1, located in the Southwest end of the island of Crete, Greece. Satellite Pass No. 280 is descending and follows a ground track almost parallel to the west coast of Crete. It comes close to the coast, at a distance of about 9 km from the CRS1 calibration site, and finally goes away south of Crete. The HY-2 sensor geophysical data records (S-GDR) have been incorporated into the calibration procedures and processing has taken place for cycles No. 54-62, at 20 Hz data rate. Some peculiarities in the HY-2 satellite altimeter data, as delivered and depicted in the I-GDR and S-GDR data, have also been noticed. All calibration results have been determined using a regional, precise and detailed geoid, along with a good knowledge of local ocean circulation and site characteristics and a well-defined sea-surface calibration methodology. The first preliminary results for the HY-2 altimeter calibration have shown that the initial cycles, up to No. 51, display an erratic behavior. After those cycles, the altimeter range bias values seem to be stable and reach a value of B = -45.6 cm ± 4.4 cm, when applying the net instrument corrections as provided in the GDR. If the relativistic effects of the satellite clocks are properly applied for the net instrument corrections, then the altimeter range bias goes down to B = -27 cm ± 3 cm. Also, preliminary cross-over analysis with the SARAL/AliKa and Jason-2 satellites show a bias of B = -23 cm, and B = -28.5 cm, respectively. The performance of the HY-2 on-board radiometer has also been examined in terms of the wet troposphere corrections and shows a mean difference of -1 cm ± 0.1 cm with respect to in-situ GNSS-derived corrections. Finally, the ionosphere path corrections of the HY-2 satellite show a difference of +1 cm ± 1.1 cm, when compared against the GNSS-derived ionosphere

  7. A calibration-independent laser-induced incandescence technique for soot measurement by detecting absolute light intensity.

    PubMed

    Snelling, David R; Smallwood, Gregory J; Liu, Fengshan; Gülder, Omer L; Bachalo, William D

    2005-11-01

    Laser-induced incandescence (LII) has proved to be a useful diagnostic tool for spatially and temporally resolved measurement of particulate (soot) volume fraction and primary particle size in a wide range of applications, such as steady flames, flickering flames, and Diesel engine exhausts. We present a novel LII technique for the determination of soot volume fraction by measuring the absolute incandescence intensity, avoiding the need for ex situ calibration that typically uses a source of particles with known soot volume fraction. The technique developed in this study further extends the capabilities of existing LII for making practical quantitative measurements of soot. The spectral sensitivity of the detection system is determined by calibrating with an extended source of known radiance, and this sensitivity is then used to interpret the measured LII signals. Although it requires knowledge of the soot temperature, either from a numerical model of soot particle heating or experimentally determined by detecting LII signals at two different wavelengths, this technique offers a calibration-independent procedure for measuring soot volume fraction. Application of this technique to soot concentration measurements is demonstrated in a laminar diffusion flame. PMID:16270566

  8. In-progress Absolute Radiometric Inflight Calibration of the LANDSAT-4 Sensors. [New Mexico

    NASA Technical Reports Server (NTRS)

    Castle, K. R.; Dinguirard, M.; Ezra, C. E.; Holm, R. G.; Jackson, R. D.; Kastner, C. J.; Palmer, J. M.; Savage, R.; Slater, P. N.

    1985-01-01

    Using selected instrumented areas at White Sands Missile Range, New Mexico as reference, radiometric calibration is to be effected on the sensors of LANDSAT 4, particularly the thematic mapper. Optical measurements made during a TM overpass are discussed. The radiances of selected large ground areas are measured in the spectral bandpasses of the TM; the total optical thickness of the atmosphere is measured in nine narrow spectral intervals. Ground truth in the form of reflectances collected for the alkalai flat region of gypsum and for the snow at White Sands is described.

  9. Validation of short-pulse-laser-based measurement setup for absolute spectral irradiance responsivity calibration.

    PubMed

    Schuster, Michaela; Nevas, Saulius; Sperling, Armin

    2014-05-01

    This paper describes the validation process of mode-locked lasers in the "tunable lasers in photometry" (TULIP) setup at Physikalisch-Technische Bundesanstalt (PTB) regarding spectral irradiance responsivity calibrations. Validation has been carried out in the visible spectral range, 400-700 nm, with two different photometer heads and in the long wavelength range, 690-780 nm, with a filtered radiometer. A comparison of the results against those from two different validated measurement setups has been carried out for validation. For the visible spectral range, the comparison is conducted against the data obtained from a lamp-based monochromator setup for spectral irradiance responsivity calibrations and against the photometric values (integral quantity) measured at the photometric bench setup of PTB. For the long wavelength range, comparisons against results from two different lamp-based monochromator measurement setups were made. Additionally, the effect of different radiation bandwidths on interference oscillations has been determined for a filter radiometer without a diffuser. A procedure for the determination of the optimum bandwidth of the setup for the respective measurement device is presented. PMID:24921865

  10. SU-E-J-85: Leave-One-Out Perturbation (LOOP) Fitting Algorithm for Absolute Dose Film Calibration

    SciTech Connect

    Chu, A; Ahmad, M; Chen, Z; Nath, R

    2014-06-01

    Purpose: To introduce an outliers-recognition fitting routine for film dosimetry. It cannot only be flexible with any linear and non-linear regression but also can provide information for the minimal number of sampling points, critical sampling distributions and evaluating analytical functions for absolute film-dose calibration. Methods: The technique, leave-one-out (LOO) cross validation, is often used for statistical analyses on model performance. We used LOO analyses with perturbed bootstrap fitting called leave-one-out perturbation (LOOP) for film-dose calibration . Given a threshold, the LOO process detects unfit points (“outliers”) compared to other cohorts, and a bootstrap fitting process follows to seek any possibilities of using perturbations for further improvement. After that outliers were reconfirmed by a traditional t-test statistics and eliminated, then another LOOP feedback resulted in the final. An over-sampled film-dose- calibration dataset was collected as a reference (dose range: 0-800cGy), and various simulated conditions for outliers and sampling distributions were derived from the reference. Comparisons over the various conditions were made, and the performance of fitting functions, polynomial and rational functions, were evaluated. Results: (1) LOOP can prove its sensitive outlier-recognition by its statistical correlation to an exceptional better goodness-of-fit as outliers being left-out. (2) With sufficient statistical information, the LOOP can correct outliers under some low-sampling conditions that other “robust fits”, e.g. Least Absolute Residuals, cannot. (3) Complete cross-validated analyses of LOOP indicate that the function of rational type demonstrates a much superior performance compared to the polynomial. Even with 5 data points including one outlier, using LOOP with rational function can restore more than a 95% value back to its reference values, while the polynomial fitting completely failed under the same conditions

  11. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

    NASA Astrophysics Data System (ADS)

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-01

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.20, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

  12. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata.

    PubMed

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-01

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.2(0), respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result. PMID:23464200

  13. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

    SciTech Connect

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-15

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and {+-}0.2{sup 0}, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ('Dee' voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

  14. Calibration and absolute normalization procedure of a new Deep Inelastic Neutron Scattering spectrometer

    NASA Astrophysics Data System (ADS)

    Rodríguez Palomino, L. A.; Blostein, J. J.; Dawidowski, J.

    2011-08-01

    We describe the calibration process of a new Deep Inelastic Neutron Scattering (DINS) spectrometer, recently implemented at the Bariloche Electron LINAC (Argentina), consisting in the determination of the incident neutron spectrum, dead-time and electronic delay of the data acquisition line, and detector bank efficiency. For this purpose, samples of lead, polyethylene and graphite of different sizes were employed. Their measured spectra were corrected by multiple scattering, attenuation and detector efficiency effects, by means of an ad hoc Monte Carlo code. We show that the corrected spectra are correctly scaled with respect to the scattering power of the tested materials within a 2% of experimental error, thus allowing us to define an experimental constant that links the arbitrary experimental scale (number of recorded counts per monitor counts) with the involved cross-sections. The present work also serves to analyze the existence of possible sources of systematic errors.

  15. An absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz. Observations and data reduction

    NASA Astrophysics Data System (ADS)

    Wolleben, M.; Landecker, T. L.; Reich, W.; Wielebinski, R.

    2006-03-01

    A new polarization survey of the northern sky at 1.41 GHz is presented. The observations were carried out using the 25.6 m telescope at the Dominion Radio Astrophysical Observatory in Canada, with an angular resolution of 36 arcmin. The data are corrected for ground radiation to obtain Stokes U and Q maps on a well-established intensity scale tied to absolute determinations of zero levels, containing emission structures of large angular extent, with an rms noise of 12 mK. Survey observations were carried out by drift scanning the sky between -29° and +90° declination. The fully sampled drift scans, observed in steps of 0.25° to ˜ 2.5° in declination, result in a northern sky coverage of 41.7% of full Nyquist sampling. The survey surpasses by a factor of 200 the coverage, and by a factor of 5 the sensitivity, of the Leiden/Dwingeloo polarization survey that was until now the most complete large-scale survey. The temperature scale is tied to the Effelsberg scale. Absolute zero-temperature levels are taken from the Leiden/Dwingeloo survey after rescaling those data by the factor of 0.94. The paper describes the observations, data processing, and calibration steps. The data are publicly available at http://www.mpifr-bonn.mpg.de/div/konti/26msurvey or http://www.drao.nrc.ca/26msurvey.

  16. Comparison of Using Relative and Absolute PCV Corrections in Short Baseline GNSS Observation Processing

    NASA Astrophysics Data System (ADS)

    Dawidowicz, Karol

    2011-01-01

    GNSS antenna phase center variations (PCV) are defined as shifts in positions depending on the observed elevation angle and azimuth to the satellite. When identical antennae are used in relative measurement the phase center variations will cancel out, particularly over short baselines. When different antennae are used, even on short baselines, ignoring these phase center variations can lead to serious (up to 10 cm) vertical errors. The only way to avoid these errors, when mixing different antenna types, is by applying antenna phase center variation models in processing. Till the 6th November 2006, the International GNSS Service used relative phase center models for GNSS antenna receivers. Then absolute calibration models, developed by the company "Geo++", started to be used. These models involved significant differences on the scale of GNSS networks compared to the VLBI and SLR measurements. The differences were due to the lack of the GNSS satellite antenna calibration models. When this problem was sufficiently resolved, the IGS decided to switch from relative to absolute models for both satellites and receivers. This decision caused significant variations to the results of the GNSS network solutions. The aim of this paper is to study the height differences in short baseline GNSS observations processing when different calibration models are used. The analysis was done using GNSS data collected at short baselines moved with different receiver antennas. The results of calculations show, that switching from relative to absolute receiver antenna PCV models has a significant effect on GNSS network solutions, particularly in high accuracy applications.

  17. Antennae

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Atlas Image mosaic, covering 7' x 7' on the sky of the interacting galaxies NGC 4038 and NGC 4039, better known as the Antennae, or Ring Tail galaxies. The two galaxies are engaged in a tug-of-war as they collide. The mutual gravitation between them is working to distort each spiral galaxy's appearance as the two merge. The interaction is evidently impetus for an intense burst of new star formation, as can be seen from the many infrared-bright knots and bright galactic nuclei. Compare the 2MASS view of this system with that obtained by the Hubble Space Telescope in the optical. Many of the same features are seen, although 2MASS is able to peer through much of the dust seen in the galaxies' disks. The galaxy light looks smoother. Also, in the near-infrared the bright knots of star formation are likely highlighted by the light of massive red supergiant stars. The much more extended 'tidal tails,' which give the Antennae their name, are quite faint in the 2MASS image mosaic.

  18. Absolute brightness temperature measurements at 2.1-mm wavelength

    NASA Technical Reports Server (NTRS)

    Ulich, B. L.

    1974-01-01

    Absolute measurements of the brightness temperatures of the Sun, new Moon, Venus, Mars, Jupiter, Saturn, and Uranus, and of the flux density of DR21 at 2.1-mm wavelength are reported. Relative measurements at 3.5-mm wavelength are also preented which resolve the absolute calibration discrepancy between The University of Texas 16-ft radio telescope and the Aerospace Corporation 15-ft antenna. The use of the bright planets and DR21 as absolute calibration sources at millimeter wavelengths is discussed in the light of recent observations.

  19. In-flight calibration of the experimental Absolute Scalar Magnetometer vector mode on board the Swarm satellites

    NASA Astrophysics Data System (ADS)

    Leger, J. M.; Jager, T.; Bertrand, F.; Cattin, V.; Fratter, I.; Brocco, L.; Vigneron, P.; Lalanne, X.; Hulot, G.

    2014-12-01

    While the role of the ASM is to provide absolute measurements of the magnetic field's strength for the in-flight calibration of the Vector Fluxgate Magnetometer, it can also deliver simultaneously vector measurements with no impact on its scalar performance. Since these scalar and vector measurements are both perfectly synchronous and spatially coherent, their comparison can be directly used to assess the ASM performances at instrument level with no need to correct for the various magnetic perturbations generated by the satellites. This presentation will detail the ASM vector calibration process, with an emphasis on its susceptibility to the ASM operational conditions (primarily the sensor temperature and attitude, but also sun exposition parameters). The evolution of the instrument's performances during the first year of the Swarm mission will then be discussed, with a particular interest in the long term scalar residuals behaviour. These results will be analyzed to demonstrate both the noise performances of the ASM scalar and vector measurements and their excellent long term stability.

  20. A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

    SciTech Connect

    Waugh, C. J.; Rosenberg, M. J.; Zylstra, A. B.; Frenje, J. A.; Seguin, F. H.; Petrasso, R. D.; Glebov, V. Yu.; Sangster, T. C.; Stoeckl, C.

    2015-05-27

    Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.

  1. A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

    DOE PAGESBeta

    Waugh, C. J.; Rosenberg, M. J.; Zylstra, A. B.; Frenje, J. A.; Seguin, F. H.; Petrasso, R. D.; Glebov, V. Yu.; Sangster, T. C.; Stoeckl, C.

    2015-05-27

    Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition,more » comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.« less

  2. A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

    SciTech Connect

    Waugh, C. J. Zylstra, A. B.; Frenje, J. A.; Séguin, F. H.; Petrasso, R. D.; Rosenberg, M. J.; Glebov, V. Yu.; Sangster, T. C.; Stoeckl, C.

    2015-05-15

    Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.

  3. A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors.

    PubMed

    Waugh, C J; Rosenberg, M J; Zylstra, A B; Frenje, J A; Séguin, F H; Petrasso, R D; Glebov, V Yu; Sangster, T C; Stoeckl, C

    2015-05-01

    Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule. PMID:26026524

  4. A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

    NASA Astrophysics Data System (ADS)

    Waugh, C. J.; Rosenberg, M. J.; Zylstra, A. B.; Frenje, J. A.; Séguin, F. H.; Petrasso, R. D.; Glebov, V. Yu.; Sangster, T. C.; Stoeckl, C.

    2015-05-01

    Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.

  5. Absolute sensitivity calibration of vacuum and extreme ultraviolet spectrometer systems and Z(eff) measurement based on bremsstrahlung continuum in HL-2A tokamak.

    PubMed

    Zhou, Hangyu; Cui, Zhengying; Morita, Shigeru; Fu, Bingzhong; Goto, Motoshi; Sun, Ping; Dong, Chunfeng; Gao, Yadong; Xu, Yuan; Lu, Ping; Yang, Qingwei; Duan, Xuru

    2012-10-01

    A grazing-incidence flat-field extreme ultraviolet (EUV) spectrometer has been newly developed in HL-2A tokamak. Typical spectral lines are observed from intrinsic impurities of carbon, oxygen, iron, and extrinsic impurity of helium in the wavelength range of 20 Å-500 Å. Bremsstrahlung continuum is measured at different electron densities of HL-2A discharges to calibrate absolute sensitivity of the EUV spectrometer system and to measure effective ionic charge, Z(eff). The sensitivity of a vacuum ultraviolet (VUV) spectrometer system is also absolutely calibrated in overlapped wavelength range of 300 Å-500 Å by comparing the intensity between VUV and EUV line emissions. PMID:23126850

  6. Absolute sensitivity calibration of vacuum and extreme ultraviolet spectrometer systems and Z{sub eff} measurement based on bremsstrahlung continuum in HL-2A tokamak

    SciTech Connect

    Zhou Hangyu; Cui Zhengying; Fu Bingzhong; Sun Ping; Gao Yadong; Xu Yuan; Lu Ping; Yang Qingwei; Duan Xuru; Morita, Shigeru; Goto, Motoshi; Dong Chunfeng

    2012-10-15

    A grazing-incidence flat-field extreme ultraviolet (EUV) spectrometer has been newly developed in HL-2A tokamak. Typical spectral lines are observed from intrinsic impurities of carbon, oxygen, iron, and extrinsic impurity of helium in the wavelength range of 20 A-500 A. Bremsstrahlung continuum is measured at different electron densities of HL-2A discharges to calibrate absolute sensitivity of the EUV spectrometer system and to measure effective ionic charge, Z{sub eff}. The sensitivity of a vacuum ultraviolet (VUV) spectrometer system is also absolutely calibrated in overlapped wavelength range of 300 A-500 A by comparing the intensity between VUV and EUV line emissions.

  7. Absolute calibration of the Jenoptik CHM15k-x ceilometer and its applicability for quantitative aerosol monitoring

    NASA Astrophysics Data System (ADS)

    Geiß, Alexander; Wiegner, Matthias

    2014-05-01

    The knowledge of the spatiotemporal distribution of atmospheric aerosols and its optical characterization is essential for the understanding of the radiation budget, air quality, and climate. For this purpose, lidar is an excellent system as it is an active remote sensing technique. As multi-wavelength research lidars with depolarization channels are quite complex and cost-expensive, increasing attention is paid to so-called ceilometers. They are simple one-wavelength backscatter lidars with low pulse energy for eye-safe operation. As maintenance costs are low and continuous and unattended measurements can be performed, they are suitable for long-term aerosol monitoring in a network. However, the signal-to-noise ratio is low, and the signals are not calibrated. The only optical property that can be derived from a ceilometer is the particle backscatter coefficient, but even this quantity requires a calibration of the signals. With four years of measurements from a Jenoptik ceilometer CHM15k-x, we developed two methods for an absolute calibration on this system. This advantage of our approach is that only a few days with favorable meteorological conditions are required where Rayleigh-calibration and comparison with our research lidar is possible to estimate the lidar constant. This method enables us to derive the particle backscatter coefficient at 1064 nm, and we retrieved for the first time profiles in near real-time within an accuracy of 10 %. If an appropriate lidar ratio is assumed the aerosol optical depth of e.g. the mixing layer can be determined with an accuracy depending on the accuracy of the lidar ratio estimate. Even for 'simple' applications, e.g. assessment of the mixing layer height, cloud detection, detection of elevated aerosol layers, the particle backscatter coefficient has significant advantages over the measured (uncalibrated) attenuated backscatter. The possibility of continuous operation under nearly any meteorological condition with temporal

  8. (18)F primary standard at ENEA-INMRI by three absolute techniques and calibration of a well-type IG11 ionization chamber.

    PubMed

    Capogni, Marco; Carconi, Pierluigi; De Felice, Pierino; Fazio, Aldo

    2016-03-01

    A new (18)F primary standardization carried out at ENEA-INMRI by three different absolute techniques, i.e. 4πγNaI(Tl)γ high-efficiency counting, TDCR and 4πβ(LS)-γ[NaI(Tl)] coincidence counting method, allowed the calibration of a fixed well-reentrant IG11 ionization chamber (IC), with an uncertainty lower than 1%, and to check the calibration factor of a portable well-type IC NPL-CRC model, previously calibrated. By the new standard the ENEA-INMRI was linked to the BIPM International Reference System (SIR) through the BIPM SIR Transfer Instrument (SIRTI). PMID:26774395

  9. Continuous absolute g monitoring of the mobile LNE-SYRTE Cold Atom Gravimeter - a new tool to calibrate superconducting gravimeters -

    NASA Astrophysics Data System (ADS)

    Merlet, Sébastien; Gillot, Pierre; Cheng, Bing; Pereira Dos Santos, Franck

    2016-04-01

    Atom interferometry allows for the realization of a new generation of instruments for inertial sensing based on laser cooled atoms. We have developed an absolute gravimeter (CAG) based on this technic, which can perform continuous gravity measurements at a high cycling rate. This instrument, operating since summer 2009, is the new metrological french standard for gravimetry. The CAG has been designed to be movable, so as to participate to international comparisons and on field measurements. It took part to several comparisons since ICAG'09 and operated in both urban environments and low noise underground facilities. The atom gravimeter operates with a high cycling rate of 3 Hz. Its sensitivity is predominantly limited by ground vibration noise which is rejected thanks to isolation platforms and correlation with other sensors, such as broadband accelerometers or sismometers. These developments allow us to perform continuous gravity measurements, no matter what the sismic conditions are and even in the worst cases such as during earthquakes. At best, a sensitivity of 5.6 μGal at 1 s measurement time has been demonstrated. The long term stability averages down to 0.1 μGal for long term measurements. Presently, the measurement accuracy is 4 μGal, which we plan to reduce to 1 μGal or below. I will present the instrument, the principle of the gravity acceleration measurement and its performances. I will focus on continuous gravity measurements performed over several years and compared with our superconducting gravimeter iGrav signal. This comparison allows us to calibrate the iGrav scale factor and follow its evolution. Especially, we demonstrate that, thanks to the CAG very high cycling rate, a single day gravity measurement allows to calibrate the iGrav scaling factor with a relative uncertainty as good as 4.10-4.

  10. DAQ Software Contributions, Absolute Scale Energy Calibration and Background Evaluation for the NOvA Experiment at Fermilab

    SciTech Connect

    Flumerfelt, Eric Lewis

    2015-08-01

    The NOvA (NuMI Off-axis ve [nu_e] Appearance) Experiment is a long-baseline accelerator neutrino experiment currently in its second year of operations. NOvA uses the Neutrinos from the Main Injector (NuMI) beam at Fermilab, and there are two main off-axis detectors: a Near Detector at Fermilab and a Far Detector 810 km away at Ash River, MN. The work reported herein is in support of the NOvA Experiment, through contributions to the development of data acquisition software, providing an accurate, absolute-scale energy calibration for electromagnetic showers in NOvA detector elements, crucial to the primary electron neutrino search, and through an initial evaluation of the cosmic background rate in the NOvA Far Detector, which is situated on the surface without significant overburden. Additional support work for the NOvA Experiment is also detailed, including DAQ Server Administration duties and a study of NOvA’s sensitivity to neutrino oscillations into a “sterile” state.

  11. Absolutely calibrated radio polarimetry of the inner Galaxy at 2.3 and 4.8 GHz

    NASA Astrophysics Data System (ADS)

    Sun, X. H.; Gaensler, B. M.; Carretti, E.; Purcell, C. R.; Staveley-Smith, L.; Bernardi, G.; Haverkorn, M.

    2014-01-01

    We present high-sensitivity and absolutely calibrated images of diffuse radio polarization at a resolution of about 10 arcmin covering the range 10° < l < 34° and |b| < 5° at 2.3 GHz from the S-band Polarization All Sky Survey and at 4.8 GHz from the Sino-German λ6 cm polarization survey of the Galactic plane. Strong depolarization near the Galactic plane is seen at 2.3 GHz, which correlates with strong Hα emission. We ascribe the depolarization to spatial Faraday rotation measure fluctuations of about 65 rad m-2 on scales smaller than 6-9 pc. We argue that most (about 90 per cent) of the polarized emission seen at 4.8 GHz originates from a distance of 3-4 kpc in the Scutum arm and that the random magnetic field dominates the regular field there. A branch extending from the North Polar Spur towards lower latitudes can be identified from the polarization image at 4.8 GHz but only partly from the polarization image at 2.3 GHz, implying that the branch is at a distance larger than 2-3 kpc. We show that comparison of structure functions of complex polarized intensity with those of polarized intensity can indicate whether the observed polarized structures are intrinsic or caused by Faraday screens. The probability distribution function of gradients from the polarization images at 2.3 GHz indicates that the turbulence in the warm ionized medium is transonic.

  12. A non-invasive diffuse reflectance calibration-free method for absolute determination of exogenous biochemicals concentration in biological tissues

    NASA Astrophysics Data System (ADS)

    Lappa, Alexander V.; Kulikovskiy, Artem N.; Busarov, Oleg G.

    2014-03-01

    The paper presents a new method for distant non-destructive determination of concentration of light absorbing admixtures in turbid media. In particular, it is intended for non-invasive in vivo control of accumulation in patient tissues of various biochemicals introduced to the patients for chemotherapy, photodynamic therapy or diagnostics. It is require that the admixture absorption spectrum should have a clearly marked peak in the wavelength region where the pure medium one varies regularly. Fluorescence of admixtures is not required. The method uses the local diffuse reflectance spectroscopy with optical fiber probe including one emitting and two reading There are several features in the method: the value to be determined is absolute concentration of admixtures; the method needs no calibration measurements on phantoms; it needs no reference measurements on sample with zero admixture concentration; it uses a two parametric kinetic light propagation model and original algorithms to resolve direct and inverse tasks of radiation transport theory. Experimental testing passed with tissue equivalent phantoms and different admixtures, including a chlorine photosensitizer, showed accuracy under 10% in all cases.

  13. SAR calibration: A technology review

    NASA Technical Reports Server (NTRS)

    Larson, R. W.; Politis, D. T.; Shuchman, R. A.

    1983-01-01

    Various potential applications of amplitude-calibrated SAR systems are briefly described, along with an estimate of calibration performance requirements. A review of the basic SAR calibration problem is given. For background purposes and to establish consistent definition of terms, various conventional SAR performance parameters are reviewed along with three additional parameters which are directly related to calibrated SAR systems. Techniques for calibrating a SAR are described. Included in the results presented are: calibration philosophy and procedures; review of the calibration signal generator technology development with results describing both the development of instrumentation and internal calibration measurements for two SAR systems; summary of analysis and measurements required to determine optimum retroreflector design and configuration for use as a reference for the absolute calibration of a SAR system; and summary of techniques for in-flight measurements of SAR antenna response.

  14. The efficiency calibration of the DSS-24 34-meter beam-waveguide antenna

    NASA Technical Reports Server (NTRS)

    Alvarez, L. S.; Britcliffe, M. J.; Franco, M. M.; Stewart, S. R.; Jackson, H. J.

    1995-01-01

    Microwave performance testing of the new Deep Space Station (DSS)-24 34-m-diameter antenna was carried out during the summer of 1994. Efficiency measurements were made at the 8.45 GHz (X-band) and 32-GHz (ka-band) frequencies both at the antenna Cassegrian (f1) and beam-waveguide (f3) focal points. In addition, the antenna f3 efficiencies were measured on the DSS-24 operational 2.295-GHz (S-band) and 8.45-Ghz feeds. This article presents the efficiency determinations as a function of elevation angle along with a corresponding error analysis of the measurements. Peak measured gains and efficiencies are tabulated for all frequencies.

  15. First calibration results and antenna placement studies of the RPW ANT instrument on Solar Orbiter

    NASA Astrophysics Data System (ADS)

    Sampl, M.; Oswald, T. H.; Rucker, H. O.; Plettemeier, D.; Maksimovic, M.; Macher, W.

    2010-12-01

    We report our analyses of the Radio and Plasma Wave Analyzer (RPW ANT) onboard the Solar Orbiter spacecraft with a focus on the high-frequency electric antennas. The aim of the Solar Orbiter mission is to determine in-situ properties and dynamics of solarwind plasma, electric and magnetic fields in the near-Sun heliosphere. The mission is planned to be launched in 2017 with a spacecraft trajectory of, for the first time, partial co-rotation with the Sun, providing a full suite of in-situ and remote sensing instruments from as close as 0.25 AU. The RPW ANT high-frequency electric sensors, consist of three cylindrical antennas mounted on appendant booms extruded from the central body of the spacecraft. Due to the parasitic effects of the conducting spacecraft body and solar panels the true antenna properties (effective axes and length; capacitances) do not coincide with their physical representations. In order to analyze the antenna system we applied a numerical method. The current distribution on the spacecraft body and the effective length vector was calculated, by solving the underlying field equations using electromagnetic codes. In the applied method the spacecraft is modelled as a patch-grid. The numerical analysis of the reception properties, including several placement options of these antennas, is presented. Since the Solar Orbiter spacecraft body and antennas are not yet finally specified, the results can be used to evaluate the performance of the proposed sensors. In particular, goniopolarimetry techniques like polarization analysis, direction finding and ray tracing depend crucially on the effective axes and the therefore the corresponding data analysis significantly improves. Software model (patch-grid) of the Solar Orbiter spacecraft

  16. Absolute calibration of soft x-ray detectors (photocathodes, XUV photodiodes, thinned CCD, ...) with the synchrotron radiation of SUPER ACO at the LURE, Orsay

    NASA Astrophysics Data System (ADS)

    Reverdin, C.; Troussel, P.; Bourgade, J. L.; Le Guern, F.; Mens, A.; Schirmann, D.; Dalmasso, J. M.; Gontier, D.; Mazataud, D.

    1994-10-01

    To interpret the experimental results in laser matter interaction experiments, the absolute spectral response of soft x-ray detectors is often needed. For this purpose CEL-V uses calibration lines of synchrotron radiation of SUPER-ACO at the LURE. The energy of output photons can be selected from 50 eV to 1000 eV. The output photon flux is absolutely calibrated with a bolometer or a soft x-ray photodiode. Then we measure the response of the studied detector installed at the same location. Measurements of quantum efficiencies of photocathodes (Al and CsI on Al) and of the response of a thinned CCD are presented versus photon energy.

  17. Consistency of L4 TM absolute calibration with respect to the L5 TM sensor based on near-simultaneous image acquisition

    USGS Publications Warehouse

    Chander, G.; Helder, D.L.; Malla, R.; Micijevic, E.; Mettler, C.J.

    2007-01-01

    The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the backbone of an extensive archive. Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic ranges, as previously defined. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria. The cross-calibration approach involved comparing image statistics derived from large common areas observed eight days apart by the two sensors. This paper summarizes the average percent differences in reflectance estimates obtained between the

  18. Performance Demonstration of Miniature Phase Transition Cells in Microgravity as a Validation for their use in the Absolute Calibration of Temperature Sensors On-Orbit

    NASA Astrophysics Data System (ADS)

    Pettersen, C.; Adler, D. P.; Best, F. A.; Aguilar, D. M.; Perepezko, J. H.

    2011-12-01

    The next generation of infrared remote sensing missions, including the climate benchmark missions, will require better absolute measurement accuracy than now available, and will most certainly rely on the emerging capability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed to measure spectrally resolved infrared radiances with an absolute brightness temperature error of better than 0.1 K will require high-emissivity (>0.999) calibration blackbodies requiring absolute temperature uncertainties of better than 0.045K (k=3). Key elements of an On-Orbit Absolute Radiance Standard (OARS) meeting these stringent requirements have been demonstrated in the laboratory at the University of Wisconsin and are undergoing further refinement under the NASA Instrument Incubator Program (IIP). In particular, the OARS has embedded thermistors that can be periodically calibrated on-orbit using the melt signatures of small quantities (<0.5g) of three reference materials - mercury, water, and gallium (providing calibration from 233K to 303K). One of the many tests to determine the readiness of this technology for on-orbit application is a demonstration of performance in microgravity. We present the details of a demonstration experiment to be conducted on the International Space Station later this year. The demonstration will use the configuration of the phase transition cells developed under our NASA IIP that has been tested extensively in the laboratory under simulated mission life cycle scenarios - these included vibration, thermal soaks, and deep cycling. The planned microgravity demonstration will compare melt signatures obtained pre-flight on the ground with those obtained on the ISS for three phase change materials (water, gallium-tin, and gallium). With a successful demonstration experiment the phase transition cells in a microgravity environment will have cleared the last hurdle before being ready for

  19. Absolute Radiometric Calibration of the GÖKTÜRK-2 Satellite Sensor Using Tuz GÖLÜ (landnet Site) from Ndvi Perspective

    NASA Astrophysics Data System (ADS)

    Sakarya, Ufuk; Hakkı Demirhan, İsmail; Seda Deveci, Hüsne; Teke, Mustafa; Demirkesen, Can; Küpçü, Ramazan; Feray Öztoprak, A.; Efendioğlu, Mehmet; Fehmi Şimşek, F.; Berke, Erdinç; Zübeyde Gürbüz, Sevgi

    2016-06-01

    TÜBİTAK UZAY has conducted a research study on the use of space-based satellite resources for several aspects of agriculture. Especially, there are two precision agriculture related projects: HASSAS (Widespread application of sustainable precision agriculture practices in Southeastern Anatolia Project Region (GAP) Project) and AKTAR (Smart Agriculture Feasibility Project). The HASSAS project aims to study development of precision agriculture practice in GAP region. Multi-spectral satellite imagery and aerial hyperspectral data along with ground measurements was collected to analyze data in an information system. AKTAR aims to develop models for irrigation, fertilization and spectral signatures of crops in Inner Anatolia. By the end of the project precision agriculture practices to control irrigation, fertilization, pesticide and estimation of crop yield will be developed. Analyzing the phenology of crops using NDVI is critical for the projects. For this reason, absolute radiometric calibration of the Red and NIR bands in space-based satellite sensors is an important issue. The Göktürk-2 satellite is an earth observation satellite which was designed and built in Turkey and was launched in 2012. The Göktürk-2 satellite sensor has a resolution 2.5 meters in panchromatic and 5 meters in R/G/B/NIR bands. The absolute radiometric calibration of the Göktürk-2 satellite sensor was performed via the ground-based measurements - spectra-radiometer, sun photometer, and meteorological station- in Tuz Gölü cal/val site in 2015. In this paper, the first ground-based absolute radiometric calibration results of the Göktürk-2 satellite sensor using Tuz Gölü is demonstrated. The absolute radiometric calibration results of this paper are compared with the published cross-calibration results of the Göktürk-2 satellite sensor utilizing Landsat 8 imagery. According to the experimental comparison results, the Göktürk-2 satellite sensor coefficients for red and NIR bands

  20. Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp

    NASA Astrophysics Data System (ADS)

    Fat'yanov, O. V.; Asimow, P. D.

    2015-10-01

    We describe an accurate and precise calibration procedure for multichannel optical pyrometers such as the 6-channel, 3-ns temporal resolution instrument used in the Caltech experimental geophysics laboratory. We begin with a review of calibration sources for shock temperatures in the 3000-30 000 K range. High-power, coiled tungsten halogen standards of spectral irradiance appear to be the only practical alternative to NIST-traceable tungsten ribbon lamps, which are no longer available with large enough calibrated area. However, non-uniform radiance complicates the use of such coiled lamps for reliable and reproducible calibration of pyrometers that employ imaging or relay optics. Careful analysis of documented methods of shock pyrometer calibration to coiled irradiance standard lamps shows that only one technique, not directly applicable in our case, is free of major radiometric errors. We provide a detailed description of the modified Caltech pyrometer instrument and a procedure for its absolute spectral radiance calibration, accurate to ±5%. We employ a designated central area of a 0.7× demagnified image of a coiled-coil tungsten halogen lamp filament, cross-calibrated against a NIST-traceable tungsten ribbon lamp. We give the results of the cross-calibration along with descriptions of the optical arrangement, data acquisition, and processing. We describe a procedure to characterize the difference between the static and dynamic response of amplified photodetectors, allowing time-dependent photodiode correction factors for spectral radiance histories from shock experiments. We validate correct operation of the modified Caltech pyrometer with actual shock temperature experiments on single-crystal NaCl and MgO and obtain very good agreement with the literature data for these substances. We conclude with a summary of the most essential requirements for error-free calibration of a fiber-optic shock-temperature pyrometer using a high-power coiled tungsten halogen

  1. Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp.

    PubMed

    Fat'yanov, O V; Asimow, P D

    2015-10-01

    We describe an accurate and precise calibration procedure for multichannel optical pyrometers such as the 6-channel, 3-ns temporal resolution instrument used in the Caltech experimental geophysics laboratory. We begin with a review of calibration sources for shock temperatures in the 3000-30,000 K range. High-power, coiled tungsten halogen standards of spectral irradiance appear to be the only practical alternative to NIST-traceable tungsten ribbon lamps, which are no longer available with large enough calibrated area. However, non-uniform radiance complicates the use of such coiled lamps for reliable and reproducible calibration of pyrometers that employ imaging or relay optics. Careful analysis of documented methods of shock pyrometer calibration to coiled irradiance standard lamps shows that only one technique, not directly applicable in our case, is free of major radiometric errors. We provide a detailed description of the modified Caltech pyrometer instrument and a procedure for its absolute spectral radiance calibration, accurate to ±5%. We employ a designated central area of a 0.7× demagnified image of a coiled-coil tungsten halogen lamp filament, cross-calibrated against a NIST-traceable tungsten ribbon lamp. We give the results of the cross-calibration along with descriptions of the optical arrangement, data acquisition, and processing. We describe a procedure to characterize the difference between the static and dynamic response of amplified photodetectors, allowing time-dependent photodiode correction factors for spectral radiance histories from shock experiments. We validate correct operation of the modified Caltech pyrometer with actual shock temperature experiments on single-crystal NaCl and MgO and obtain very good agreement with the literature data for these substances. We conclude with a summary of the most essential requirements for error-free calibration of a fiber-optic shock-temperature pyrometer using a high-power coiled tungsten halogen

  2. Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp

    SciTech Connect

    Fat’yanov, O. V. Asimow, P. D.

    2015-10-15

    We describe an accurate and precise calibration procedure for multichannel optical pyrometers such as the 6-channel, 3-ns temporal resolution instrument used in the Caltech experimental geophysics laboratory. We begin with a review of calibration sources for shock temperatures in the 3000-30 000 K range. High-power, coiled tungsten halogen standards of spectral irradiance appear to be the only practical alternative to NIST-traceable tungsten ribbon lamps, which are no longer available with large enough calibrated area. However, non-uniform radiance complicates the use of such coiled lamps for reliable and reproducible calibration of pyrometers that employ imaging or relay optics. Careful analysis of documented methods of shock pyrometer calibration to coiled irradiance standard lamps shows that only one technique, not directly applicable in our case, is free of major radiometric errors. We provide a detailed description of the modified Caltech pyrometer instrument and a procedure for its absolute spectral radiance calibration, accurate to ±5%. We employ a designated central area of a 0.7× demagnified image of a coiled-coil tungsten halogen lamp filament, cross-calibrated against a NIST-traceable tungsten ribbon lamp. We give the results of the cross-calibration along with descriptions of the optical arrangement, data acquisition, and processing. We describe a procedure to characterize the difference between the static and dynamic response of amplified photodetectors, allowing time-dependent photodiode correction factors for spectral radiance histories from shock experiments. We validate correct operation of the modified Caltech pyrometer with actual shock temperature experiments on single-crystal NaCl and MgO and obtain very good agreement with the literature data for these substances. We conclude with a summary of the most essential requirements for error-free calibration of a fiber-optic shock-temperature pyrometer using a high-power coiled tungsten halogen

  3. DSS 14 antenna calibrations for GSSR/VLA Saturn radar experiments

    NASA Technical Reports Server (NTRS)

    Guiar, C. N.; Riggs, R. L.; Stevens, R.; Wert, M.

    1988-01-01

    The DSS 14 pointing and gain were calibrated to support X-band bistatic radar observations of Saturn's rings. The observations used the Goldstone Solar System Radar and the National Radio Astronomy Observatory's Very Large Array (VLA) in Socorro, New Mexico. The pointing calibrations were based on conscan offset data collected during Voyager 1 and 2 support passes. The conscan data show angle-of-arrival sensing with no bias and 0.3 mdeg 1-sigma error. Using the calibrations, demonstrated blind pointing performance on Saturn was less than 3 mdeg 1-sigma error. Meteorological observations at the site were used to reduce elevation errors caused by atmospheric refraction. The techniques used corrected about one-third of the error-poorer than expected performance.

  4. Absolute calibration of the Agfa Structurix series films at energies between 2.7 and 6.2 keVa)

    NASA Astrophysics Data System (ADS)

    Lanier, N. E.; Cowan, J. S.

    2014-11-01

    Although photo-emulsion technology is many decades old, x-ray film still remains a key asset for diagnosing hydrodynamic features in High-Energy Density (HED) experiments. For decades, the preferred option had been Kodak's direct exposure film. After its discontinuance in 2004, the push to find alternatives began. In many situations, the Agfa Structurix series offers the most favorable substitute, but being new to the HED community, its characterization was lacking. To remedy this, recent experiments, conducted at Brookhaven's National Synchrotron Light Source, provide absolute, monochromatic calibration data for the Agfa Structurix series films at K-shell backlighter energies between 2.7 and 6.2 keV. Absolute response curves are presented for Agfa D8, D7, D4, D4sc, D3, and D2. Moreover, the transmission of each film type is also measured.

  5. Absolute Calibration of Kodak Biomax-MS Film Response to X Rays in the 1.5- to 8-keV Energy Range

    SciTech Connect

    Marshall, F.J.; Knauer, J.P.; Anderson, D.; Schmitt, B.L.

    2006-09-28

    The absolute response of Kodak Biomax-MS film to x rays in the range from 1.5- to 8-keV has been measured using a laboratory e-beam generated x-ray source. The measurements were taken at specific line energies by using Bragg diffraction to produce monochromatic beams of x rays. Multiple exposures were taken on Biomax MS film up to levels exceeding optical densities of 2 as measured by a microdensitometer. The absolute beam intensity for each exposure was measured with a Si(Li) detector. Additional response measurements were taken with Kodak direct exposure film (DEF) so as to compare the results of this technique to previously published calibrations.

  6. Absolute calibration of the intramolecular site preference of 15N fractionation in tropospheric N2O by FT-IR spectroscopy.

    PubMed

    Griffith, David W T; Parkes, Stephen D; Haverd, Vanessa; Paton-Walsh, Clare; Wilson, Stephen R

    2009-03-15

    Nitrous oxide (N(2)O) plays important roles in atmospheric chemistry both as a greenhouse gas and in stratospheric ozone depletion. Isotopic measurements of N(2)O have provided an invaluable insight into understanding its atmospheric sources and sinks. The preference for (15)N fractionation between the central and terminal positions (the "site preference") is particularly valuable because it depends principally on the processes involved in N(2)O production or consumption, rather than the (15)N content of the substrate from which it is formed. Despite the value of measurements of the site preference, there is no internationally recognized standard reference material of accurately known and accepted site preference, and there has been some lack of agreement in published studies aimed at providing such a standard. Previous work has been based on isotope ratio mass spectrometry (IRMS); in this work we provide an absolute calibration for the intramolecular site preference of (15)N fractionation of working standard gases used in our laboratory by a completely independent technique--high-resolution Fourier transform infrared (FT-IR) spectroscopy. By reference to this absolute calibration, we determine the site preference for 25 samples of tropospheric N(2)O collected under clean air conditions to be 19.8 per thousand +/- 2.1 per thousand. This result is in agreement with that based on the earlier absolute calibration of Toyoda and Yoshida (Toyoda , S. , and Yoshida , N. Anal. Chem. 1999 , 71, 4711-4718 ) who found an average tropospheric site preference of 18.7 per thousand +/- 2.2 per thousand. We now recommend an interlaboratory exchange of working standard N(2)O gases as the next step to providing an international reference standard. PMID:19231842

  7. Performance Demonstration of Miniature Phase Transition Cells in Microgravity as a Validation for their use in the Absolute Calibration of Temperature Sensors On-Orbit

    NASA Astrophysics Data System (ADS)

    Pettersen, C.; Best, F. A.; Adler, D. P.; Aguilar, D. M.; Perepezko, J. H.

    2012-12-01

    The next generation of infrared remote sensing missions, including the climate benchmark missions, will require better absolute measurement accuracy than now available, and will most certainly rely on the emerging capability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed to measure spectrally resolved infrared radiances with an absolute brightness temperature error of better than 0.1 K will require high-emissivity (>0.999) calibration blackbodies requiring absolute temperature uncertainties of better than 0.045K (k=3). Key elements of an On-Orbit Absolute Radiance Standard (OARS) meeting these stringent requirements have been demonstrated in the laboratory at the University of Wisconsin and were further refined under the NASA Instrument Incubator Program (IIP). In particular, the OARS has imbedded thermistors that can be periodically calibrated on-orbit using the melt signatures of small quantities (<0.5g) of three reference materials - mercury, water, and gallium, providing calibration from 233K to 303K. One of the many tests to determine the readiness of this technology for on-orbit application is a demonstration of performance in microgravity to be conducted on the International Space Station (ISS). This demonstration will make use of an Experiment Support Package developed by Utah State Space Dynamics Laboratory to continuously run melt cycles on miniature phase change cells containing gallium, a gallium-tin eutectic, and water. The phase change cells will be mounted in a small aluminum block along with a thermistor temperature sensor. A thermoelectric cooler will be used to change the temperature of the block. The demonstration will use the configuration of the phase transition cells developed under our NASA IIP that has been tested extensively in the laboratory under simulated mission life cycle scenarios - these included vibration, thermal soaks, and deep cycling. Melt signatures

  8. Update to the Cosmic Origins Spectrograph FUV Calibration: Improved Characterization Below 1150 Angstroms and Improved Absolute Flux Calibration at all Wavelengths

    NASA Astrophysics Data System (ADS)

    Sonnentrucker, Paule; Bostroem, K. A.; Ely, J.; Debes, J. H.; DiFelice, A.; Hernandez, S.; Hodge, P. E.; Lindsay, K.; Lockwood, S. A.; Massa, D.; Oliveira, C. M.; Roman-Duval, J.; Penton, S. V.; Proffitt, C. R.; Taylor, J. M.

    2014-01-01

    As of Cycle 20, the three COS/FUV "Blue Mode" wavelength settings at G130M/1055, 1096 and 1222, have become available as regular observing modes. We provide updates on the wavelength and flux calibration of these new Blue Mode settings, which allow medium-resolution spectroscopy down to 900A with effective areas comparable to those of FUSE. We discuss also recent improvements to the COS/FUV flux and flat-field calibrations and present the most recent time-dependent sensitivity trends of the FUV and NUV channels.

  9. Characteristics of wire antennas onboard Akebono satellite

    NASA Astrophysics Data System (ADS)

    Higashi, R.; Imachi, T.; Yagitani, S.; Nagano, I.; Kimura, I.

    2004-12-01

    Characteristics of a wire antenna used for the electric field observation in the magnetized space plasma could be different from those in free space because of the plasma sheath surrounding the antenna. We need to know the antenna characteristics (antenna impedance and effective length) in the magnetized plasma to calibrate the observed data and obtain the absolute intensity of the electric field. In our previous antenna study, we have estimated the effective length from the ratio of the open voltage induced at the antenna terminal and the electric field theoretically calculated from Maxwell's equations using the observed plasma density and geomagnetic field. We have estimated the effective lengths of antennas onboard the GEOTAIL and Akebono satellites. The two types of wire antennas onboard the GEOTAIL are nearly equal to the effective length in free space. However, we see their fluctuations depending on the angle between the antenna and the sunward direction which varies with the satellite spin. The effective lengths of the two wire antennas onboard the Akebono satellite are also nearly equal to those in free space. Again, we see a small variation depending on the angle between the antenna and the geomagnetic field. The impedance of the antennas onboard GEOTAIL has been measured by Tsutsui et al.[1997] by using the calibration function onboard GEOTAIL. They have found that the impedance depends mainly on the ambient electron density and the satellite spin. The impedance onboard Akebono has been measured by Hashimoto et al.[1991], where the results also depends on the electron density and the satellite spin. For the GEOTAIL case, the dependence of the effective length and the impedance measurement on the satellite spin is caused by the fluctuation of the photoelectron emissions from the satellite body and the antenna surfaces. On the other hand, for the Akebono case, the photoelectrons do not play an important role because the spin axis of Akebono always points to

  10. Development of an absolute method for efficiency calibration of a coaxial HPGe detector for large volume sources

    NASA Astrophysics Data System (ADS)

    Ortiz-Ramírez, Pablo C.

    2015-09-01

    In this work an absolute method for the determination of the full energy peak efficiency of a gamma spectroscopy system for voluminous sources is presented. The method was tested for a high-resolution coaxial HPGe detector and cylindrical homogeneous volume source. The volume source is represented by a set of point sources filling its volume. We found that the absolute efficiency of a volume source can be determined as the average over its volume of the absolute efficiency of each point source. Experimentally, we measure the intrinsic efficiency as a function upon source-detector position. Then, considering the solid angle and the attenuations of the gamma rays emitted to the detector by each point source, considered as embedded in the source matrix, the absolute efficiency for each point source inside of the volume was determined. The factor associate with the solid angle and the self-attenuation of photons in the sample was deduced from first principles without any mathematical approximation. The method was tested by determining the specific activity of 137Cs in cylindrical homogeneous sources, using IAEA reference materials with specific activities between 14.2 Bq/kg and 9640 Bq/kg at the moment of the experimentation. The results obtained shown a good agreement with the expected values. The relative difference was less than 7% in most of the cases. The main advantage of this method is that it does not require of the use of expensive and hard to produce standard materials. In addition it does not require of matrix effect corrections, which are the main cause of error in this type of measurements, and it is easy to implement in any nuclear physics laboratory.

  11. The influence of the ionizer geometry on the absolute density calibration of reactive neutral species in a molecular beam mass spectrometry.

    PubMed

    Krähling, Tobias; Ellerweg, Dirk; Benedikt, Jan

    2012-04-01

    Molecular beam mass spectrometry is a powerful diagnostic technique, which can be used for the measurement of absolute number densities of reactive species in non-equilibrium reactive plasmas. However, the calibration of absolute number densities is susceptible to systematic errors. Critical issues are the proper design of the sampling system and the correction of the background signal. Here we discuss the effect of reflections of particles from the molecular beam in an ionizer, formation of additional background particle density in the ionizer, and its effect on the density calibration of reactive particle densities. A Monte Carlo simulation of particle trajectories in the ionizer is used to estimate the detection probability of a beam particle after the collision with the ionizer wall. The simulation shows that as much as two-third of the signal can be due to scattered particles in the commercially available mass spectrometers. This effect leads to systematic underestimation of densities of reactive particles, which are reactive at the surface and, therefore, do not have any background density. A simple change in the ionizer geometry is suggested, which can significantly reduce this problem. PMID:22559583

  12. The influence of the ionizer geometry on the absolute density calibration of reactive neutral species in a molecular beam mass spectrometry

    SciTech Connect

    Kraehling, Tobias; Ellerweg, Dirk; Benedikt, Jan

    2012-04-15

    Molecular beam mass spectrometry is a powerful diagnostic technique, which can be used for the measurement of absolute number densities of reactive species in non-equilibrium reactive plasmas. However, the calibration of absolute number densities is susceptible to systematic errors. Critical issues are the proper design of the sampling system and the correction of the background signal. Here we discuss the effect of reflections of particles from the molecular beam in an ionizer, formation of additional background particle density in the ionizer, and its effect on the density calibration of reactive particle densities. A Monte Carlo simulation of particle trajectories in the ionizer is used to estimate the detection probability of a beam particle after the collision with the ionizer wall. The simulation shows that as much as two-third of the signal can be due to scattered particles in the commercially available mass spectrometers. This effect leads to systematic underestimation of densities of reactive particles, which are reactive at the surface and, therefore, do not have any background density. A simple change in the ionizer geometry is suggested, which can significantly reduce this problem.

  13. Absolute calibration of Kodak Biomax-MS film response to x rays in the 1.5- to 8-keV energy range

    SciTech Connect

    Marshall, F. J.; Knauer, J. P.; Anderson, D.; Schmitt, B. L

    2006-10-15

    The absolute response of Kodak Biomax-MS film to x rays in the range from 1.5- to 8-keV has been measured using a laboratory electron-beam generated x-ray source. The measurements were taken at specific line energies by using Bragg diffraction to produce monochromatic beams of x rays. Multiple exposures were taken on Biomax MS film up to levels exceeding optical densities of 2 as measured by a microdensitometer. The absolute beam intensity for each exposure was measured with a Si(Li) detector. Additional response measurements were taken with Kodak direct exposure film (DEF) so as to compare the results of this technique to previously published calibrations. The Biomax-MS results have been fitted to a semiempirical mathematical model (Knauer et al., these proceedings). Users of the model can infer absolute fluences from observed exposure levels at either interpolated or extrapolated energies. To summarize the results: Biomax MS has comparable sensitivity to DEF film below 3 keV but has reduced sensitivity above 3 keV ({approx}50%). The lower exposure results from thinner emulsion layers, designed for use with phosphor screens. The ease with which Biomax-MS can be used in place of DEF (same format film, same developing process, and comparable sensitivity) makes it a good replacement.

  14. Absolutely calibrated vacuum ultraviolet spectra in the 150-250-nm range from plasmas generated by the NIKE KrF laser

    NASA Astrophysics Data System (ADS)

    Seely, J. F.; Feldman, Uri; Holland, G. E.; Weaver, J. L.; Mostovych, A. N.; Obenschain, S. P.; Schmitt, A. J.; Lehmberg, R.; Kjornarattanawanich, Benjawan; Back, C. A.

    2005-06-01

    High-resolution vacuum ultraviolet (VUV) spectra were recorded from plasmas generated by the NIKE KrF laser for the purpose of observing emission from the two-plasmon decay instability (TPDI) at 2/3 the NIKE wavelength (165nm). The targets were irradiated by up to 43 overlapping beams with intensity up to ≈1014W/cm2 and with beam smoothing by induced spatial incoherence (ISI). The targets consisted of planar foils of CH, BN, Al, Si, S, Ti, Pd, and Au. Titanium-doped silica aerogels in Pyrex cylinders were also irradiated. The spectra of the target elements were observed from charge states ranging from the neutral atoms to five times ionized. The spectrometer was absolutely calibrated using synchrotron radiation, and absolute VUV plasma emission intensities were determined. Emission from the TPDI at 165-nm wavelength was not observed from any of the irradiated targets. An upper bound on the possible TPDI emission was less than 4×10-8 the incident NIKE laser energy. The NIKE laser radiation backscattered from the silica aerogel targets at 248nm was typically 6×10-6 the incident NIKE laser energy, and the spectral broadening corresponded to the 1-THz bandwidth of the ISI smoothing. The spectra from the moderately charged plasma ions (up to five times ionized), spectral linewidths, absolute continuum emission level, and slope of the continuum were consistent with plasma temperatures in the 100-300-eV range.

  15. Absolute calibration of Kodak Biomax-MS film response to x rays in the 1.5- to 8-keV energy range

    NASA Astrophysics Data System (ADS)

    Marshall, F. J.; Knauer, J. P.; Anderson, D.; Schmitt, B. L.

    2006-10-01

    The absolute response of Kodak Biomax-MS film to x rays in the range from 1.5- to 8-keV has been measured using a laboratory electron-beam generated x-ray source. The measurements were taken at specific line energies by using Bragg diffraction to produce monochromatic beams of x rays. Multiple exposures were taken on Biomax MS film up to levels exceeding optical densities of 2 as measured by a microdensitometer. The absolute beam intensity for each exposure was measured with a Si (Li) detector. Additional response measurements were taken with Kodak direct exposure film (DEF) so as to compare the results of this technique to previously published calibrations. The Biomax-MS results have been fitted to a semiempirical mathematical model (Knauer et al., these proceedings). Users of the model can infer absolute fluences from observed exposure levels at either interpolated or extrapolated energies. To summarize the results: Biomax MS has comparable sensitivity to DEF film below 3keV but has reduced sensitivity above 3keV (˜50%). The lower exposure results from thinner emulsion layers, designed for use with phosphor screens. The ease with which Biomax-MS can be used in place of DEF (same format film, same developing process, and comparable sensitivity) makes it a good replacement.

  16. An absolute calibration method of an ethyl alcohol biosensor based on wavelength-modulated differential photothermal radiometry

    SciTech Connect

    Liu, Yi Jun; Mandelis, Andreas; Guo, Xinxin

    2015-11-15

    In this work, laser-based wavelength-modulated differential photothermal radiometry (WM-DPTR) is applied to develop a non-invasive in-vehicle alcohol biosensor. WM-DPTR features unprecedented ethanol-specificity and sensitivity by suppressing baseline variations through a differential measurement near the peak and baseline of the mid-infrared ethanol absorption spectrum. Biosensor signal calibration curves are obtained from WM-DPTR theory and from measurements in human blood serum and ethanol solutions diffused from skin. The results demonstrate that the WM-DPTR-based calibrated alcohol biosensor can achieve high precision and accuracy for the ethanol concentration range of 0-100 mg/dl. The high-performance alcohol biosensor can be incorporated into ignition interlocks that could be fitted as a universal accessory in vehicles in an effort to reduce incidents of drinking and driving.

  17. An absolute calibration method of an ethyl alcohol biosensor based on wavelength-modulated differential photothermal radiometry.

    PubMed

    Liu, Yi Jun; Mandelis, Andreas; Guo, Xinxin

    2015-11-01

    In this work, laser-based wavelength-modulated differential photothermal radiometry (WM-DPTR) is applied to develop a non-invasive in-vehicle alcohol biosensor. WM-DPTR features unprecedented ethanol-specificity and sensitivity by suppressing baseline variations through a differential measurement near the peak and baseline of the mid-infrared ethanol absorption spectrum. Biosensor signal calibration curves are obtained from WM-DPTR theory and from measurements in human blood serum and ethanol solutions diffused from skin. The results demonstrate that the WM-DPTR-based calibrated alcohol biosensor can achieve high precision and accuracy for the ethanol concentration range of 0-100 mg/dl. The high-performance alcohol biosensor can be incorporated into ignition interlocks that could be fitted as a universal accessory in vehicles in an effort to reduce incidents of drinking and driving. PMID:26628164

  18. An absolute calibration method of an ethyl alcohol biosensor based on wavelength-modulated differential photothermal radiometry

    NASA Astrophysics Data System (ADS)

    Liu, Yi Jun; Mandelis, Andreas; Guo, Xinxin

    2015-11-01

    In this work, laser-based wavelength-modulated differential photothermal radiometry (WM-DPTR) is applied to develop a non-invasive in-vehicle alcohol biosensor. WM-DPTR features unprecedented ethanol-specificity and sensitivity by suppressing baseline variations through a differential measurement near the peak and baseline of the mid-infrared ethanol absorption spectrum. Biosensor signal calibration curves are obtained from WM-DPTR theory and from measurements in human blood serum and ethanol solutions diffused from skin. The results demonstrate that the WM-DPTR-based calibrated alcohol biosensor can achieve high precision and accuracy for the ethanol concentration range of 0-100 mg/dl. The high-performance alcohol biosensor can be incorporated into ignition interlocks that could be fitted as a universal accessory in vehicles in an effort to reduce incidents of drinking and driving.

  19. Precision absolute frequency laser spectroscopy of argon II in parallel and antiparallel geometry using a frequency comb for calibration

    NASA Astrophysics Data System (ADS)

    Lioubimov, Vladimir

    A collinear fast ion beam laser apparatus was constructed and tested. It will be used on-line to the SLOW RI radioactive beam facility in RIKEN (Japan) and as in the present experiment for precision absolute frequency measurements of astrophysically important reference lines. In the current work we conducted absolute measurements of spectral lines of Ar+ ions using parallel and antiparallel geometries. To provide a reference for the laser wavelength iodine saturation spectroscopy was used. The precision of this reference was enhanced by simultaneously observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. When performing collinear and anticollinear measurements simultaneously for the laser induced fluorescence, the exact relativistic formula for the transition frequency n0=ncoll˙n anticoll can be applied. In this geometry ion source instabilities due to pressure and anode voltage fluctuation are minimized. The procedure of fluorescence lineshapes fitting is discussed and the errors in the measurements are estimated. The result is n0 = 485, 573, 619.7 +/- 0.3MHz corresponding to Dnn = 6 x 10-10 and is an improvement of two orders of magnitude over the NIST published value.

  20. Absorption by ground-state lead atoms of the 283. 3-nm resonant line from a lead hollow cathode lamp. An absolute number density calibration

    SciTech Connect

    Simons, J.W. ); Oldenborg, R.C.; Baughcum, S.L. )

    1989-10-19

    An accurate absolute number density calibration curve for absorption by gaseous lead atoms of the 283.3-nm resonant line from a typical lead hollow cathode lamp is reported. This calibration shows the usual curvature in the Beer-Lambert plot for atomic absorption at moderate to high absorbances that is commonly attributed to self-absorption leading to line reversal in the source and/or preferential absorption at the line center when the absorber temperature is not much greater than the source Doppler temperature. A theoretical calculation utilizing a Doppler-limited Fourier transform spectrum of the 283.3-nm emission from the lamp and a tabulated value of the absorption cross section and accounting for the isotopic and nuclear hyperfine components in both the emission and absorption due to naturally occurring lead quantitatively reproduces the experimental calibration curve without any parameter adjustments. It is found that the curvature in the Beer-Lambert plot has more to do with the fact that the absorbing and emitting atoms are a mixture of isotopes giving several isotopic and nuclear hyperfine transitions at slightly different frequencies than it does with preferential absorption at line centers.

  1. The CARMA Paired Antenna Calibration System: Atmospheric Phase Correction for Millimeter Wave Interferometry and Its Application to Mapping the Ultraluminous Galaxy Arp 193

    NASA Astrophysics Data System (ADS)

    Zauderer, B. Ashley; Bolatto, Alberto D.; Vogel, Stuart N.; Carpenter, John M.; Peréz, Laura M.; Lamb, James W.; Woody, David P.; Bock, Douglas C.-J.; Carlstrom, John E.; Culverhouse, Thomas L.; Curley, Roger; Leitch, Erik M.; Plambeck, Richard L.; Pound, Marc W.; Marrone, Daniel P.; Muchovej, Stephen J.; Mundy, Lee G.; Teng, Stacy H.; Teuben, Peter J.; Volgenau, Nikolaus H.; Wright, Melvyn C. H.; Wu, Dalton

    2016-01-01

    Phase fluctuations introduced by the atmosphere are the main limiting factor in attaining diffraction limited performance in extended interferometric arrays at millimeter and submillimeter wavelengths. We report the results of C-PACS, the Combined Array for Research in Millimeter-Wave Astronomy Paired Antenna Calibration System. We present a systematic study of several hundred test observations taken during the 2009–2010 winter observing season where we utilize CARMA's eight 3.5 m antennas to monitor an atmospheric calibrator while simultaneously acquiring science observations with 6.1 and 10.4 m antennas on baselines ranging from a few hundred meters to ∼2 km. We find that C-PACS is systematically successful at improving coherence on long baselines under a variety of atmospheric conditions. We find that the angular separation between the atmospheric calibrator and target source is the most important consideration, with consistently successful phase correction at CARMA requiring a suitable calibrator located ≲6° away from the science target. We show that cloud cover does not affect the success of C-PACS. We demonstrate C-PACS in typical use by applying it to the observations of the nearby very luminous infrared galaxy Arp 193 in 12CO(2-1) at a linear resolution of ≈70 pc (0.″12 × 0.″18), 3 times better than previously published molecular maps of this galaxy. We resolve the molecular disk rotation kinematics and the molecular gas distribution and measure the gas surface densities and masses on 90 pc scales. We find that molecular gas constitutes ∼30% of the dynamical mass in the inner 700 pc of this object with a surface density ∼104 M⊙ pc‑2 we compare these properties to those of the starburst region of NGC 253.

  2. The CARMA Paired Antenna Calibration System: Atmospheric Phase Correction for Millimeter Wave Interferometry and Its Application to Mapping the Ultraluminous Galaxy Arp 193

    NASA Astrophysics Data System (ADS)

    Zauderer, B. Ashley; Bolatto, Alberto D.; Vogel, Stuart N.; Carpenter, John M.; Peréz, Laura M.; Lamb, James W.; Woody, David P.; Bock, Douglas C.-J.; Carlstrom, John E.; Culverhouse, Thomas L.; Curley, Roger; Leitch, Erik M.; Plambeck, Richard L.; Pound, Marc W.; Marrone, Daniel P.; Muchovej, Stephen J.; Mundy, Lee G.; Teng, Stacy H.; Teuben, Peter J.; Volgenau, Nikolaus H.; Wright, Melvyn C. H.; Wu, Dalton

    2016-01-01

    Phase fluctuations introduced by the atmosphere are the main limiting factor in attaining diffraction limited performance in extended interferometric arrays at millimeter and submillimeter wavelengths. We report the results of C-PACS, the Combined Array for Research in Millimeter-Wave Astronomy Paired Antenna Calibration System. We present a systematic study of several hundred test observations taken during the 2009-2010 winter observing season where we utilize CARMA's eight 3.5 m antennas to monitor an atmospheric calibrator while simultaneously acquiring science observations with 6.1 and 10.4 m antennas on baselines ranging from a few hundred meters to ˜2 km. We find that C-PACS is systematically successful at improving coherence on long baselines under a variety of atmospheric conditions. We find that the angular separation between the atmospheric calibrator and target source is the most important consideration, with consistently successful phase correction at CARMA requiring a suitable calibrator located ≲6° away from the science target. We show that cloud cover does not affect the success of C-PACS. We demonstrate C-PACS in typical use by applying it to the observations of the nearby very luminous infrared galaxy Arp 193 in 12CO(2-1) at a linear resolution of ≈70 pc (0.″12 × 0.″18), 3 times better than previously published molecular maps of this galaxy. We resolve the molecular disk rotation kinematics and the molecular gas distribution and measure the gas surface densities and masses on 90 pc scales. We find that molecular gas constitutes ˜30% of the dynamical mass in the inner 700 pc of this object with a surface density ˜104 M⊙ pc-2 we compare these properties to those of the starburst region of NGC 253.

  3. Absolute radiant power measurement for the Au M lines of laser-plasma using a calibrated broadband soft X-ray spectrometer with flat-spectral response

    SciTech Connect

    Troussel, Ph.; Villette, B.; Oudot, G.; Tassin, V.; Bridou, F.; Delmotte, F.; Krumrey, M.

    2014-01-15

    CEA implemented an absolutely calibrated broadband soft X-ray spectrometer called DMX on the Omega laser facility at the Laboratory for Laser Energetics (LLE) in 1999 to measure radiant power and spectral distribution of the radiation of the Au plasma. The DMX spectrometer is composed of 20 channels covering the spectral range from 50 eV to 20 keV. The channels for energies below 1.5 keV combine a mirror and a filter with a coaxial photo-emissive detector. For the channels above 5 keV the photoemissive detector is replaced by a conductive detector. The intermediate energy channels (1.5 keV < photon energy < 5 keV) use only a filter and a coaxial detector. A further improvement of DMX consists in flat-response X-ray channels for a precise absolute measurement of the photon flux in the photon energy range from 0.1 keV to 6 keV. Such channels are equipped with a filter, a Multilayer Mirror (MLM), and a coaxial detector. We present as an example the development of channel for the gold M emission lines in the photon energy range from 2 keV to 4 keV which has been successfully used on the OMEGA laser facility. The results of the radiant power measurements with the new MLM channel and with the usual channel composed of a thin titanium filter and a coaxial detector (without mirror) are compared. All elements of the channel have been calibrated in the laboratory of the Physikalisch-Technische Bundesanstalt, Germany's National Metrology Institute, at the synchrotron radiation facility BESSY II in Berlin using dedicated well established and validated methods.

  4. Absolute radiant power measurement for the Au M lines of laser-plasma using a calibrated broadband soft X-ray spectrometer with flat-spectral response.

    PubMed

    Troussel, Ph; Villette, B; Emprin, B; Oudot, G; Tassin, V; Bridou, F; Delmotte, F; Krumrey, M

    2014-01-01

    CEA implemented an absolutely calibrated broadband soft X-ray spectrometer called DMX on the Omega laser facility at the Laboratory for Laser Energetics (LLE) in 1999 to measure radiant power and spectral distribution of the radiation of the Au plasma. The DMX spectrometer is composed of 20 channels covering the spectral range from 50 eV to 20 keV. The channels for energies below 1.5 keV combine a mirror and a filter with a coaxial photo-emissive detector. For the channels above 5 keV the photoemissive detector is replaced by a conductive detector. The intermediate energy channels (1.5 keV < photon energy < 5 keV) use only a filter and a coaxial detector. A further improvement of DMX consists in flat-response X-ray channels for a precise absolute measurement of the photon flux in the photon energy range from 0.1 keV to 6 keV. Such channels are equipped with a filter, a Multilayer Mirror (MLM), and a coaxial detector. We present as an example the development of channel for the gold M emission lines in the photon energy range from 2 keV to 4 keV which has been successfully used on the OMEGA laser facility. The results of the radiant power measurements with the new MLM channel and with the usual channel composed of a thin titanium filter and a coaxial detector (without mirror) are compared. All elements of the channel have been calibrated in the laboratory of the Physikalisch-Technische Bundesanstalt, Germany's National Metrology Institute, at the synchrotron radiation facility BESSY II in Berlin using dedicated well established and validated methods. PMID:24517761

  5. Radio metric errors due to mismatch and offset between a DSN antenna beam and the beam of a troposphere calibration instrument

    NASA Technical Reports Server (NTRS)

    Linfield, R. P.; Wilcox, J. Z.

    1993-01-01

    Two components of the error of a troposphere calibration measurement were quantified by theoretical calculations. The first component is a beam mismatch error, which occurs when the calibration instrument senses a conical volume different from the cylindrical volume sampled by a Deep Space Network (DSN) antenna. The second component is a beam offset error, which occurs if the calibration instrument is not mounted on the axis of the DSN antenna. These two error sources were calculated for both delay (e.g., VLBI) and delay rate (e.g., Doppler) measurements. The beam mismatch error for both delay and delay rate drops rapidly as the beamwidth of the troposphere calibration instrument (e.g., a water vapor radiometer or an infrared Fourier transform spectrometer) is reduced. At a 10-deg elevation angle, the instantaneous beam mismatch error is 1.0 mm for a 6-deg beamwidth and 0.09 mm for a 0.5-deg beam (these are the full angular widths of a circular beam with uniform gain out to a sharp cutoff). Time averaging for 60-100 sec will reduce these errors by factors of 1.2-2.2. At a 20-deg elevation angle, the lower limit for current Doppler observations, the beam-mismatch delay rate error is an Allan standard deviation over 100 sec of 1.1 x 10(exp -14) with a 4-deg beam and 1.3 x 10(exp -l5) for a 0.5-deg beam. A 50-m beam offset would result in a fairly modest (compared to other expected error sources) delay error (less than or equal to 0.3 mm for 60-sec integrations at any elevation angle is greater than or equal to 6 deg). However, the same offset would cause a large error in delay rate measurements (e.g., an Allan standard deviation of 1.2 x 10(exp -14) over 100 sec at a 20-deg elevation angle), which would dominate over other known error sources if the beamwidth is 2 deg or smaller. An on-axis location is essential for accurate troposphere calibration of delay rate measurements. A half-power beamwidth (for a beam with a tapered gain profile) of 1.2 deg or smaller is

  6. Absolute brightness temperature measurements at 3.5-mm wavelength. [of sun, Venus, Jupiter and Saturn

    NASA Technical Reports Server (NTRS)

    Ulich, B. L.; Rhodes, P. J.; Davis, J. H.; Hollis, J. M.

    1980-01-01

    Careful observations have been made at 86.1 GHz to derive the absolute brightness temperatures of the sun (7914 + or - 192 K), Venus (357.5 + or - 13.1 K), Jupiter (179.4 + or - 4.7 K), and Saturn (153.4 + or - 4.8 K) with a standard error of about three percent. This is a significant improvement in accuracy over previous results at millimeter wavelengths. A stable transmitter and novel superheterodyne receiver were constructed and used to determine the effective collecting area of the Millimeter Wave Observatory (MWO) 4.9-m antenna relative to a previously calibrated standard gain horn. The thermal scale was set by calibrating the radiometer with carefully constructed and tested hot and cold loads. The brightness temperatures may be used to establish an absolute calibration scale and to determine the antenna aperture and beam efficiencies of other radio telescopes at 3.5-mm wavelength.

  7. Relative and Absolute Calibration of a Multihead Camera System with Oblique and Nadir Looking Cameras for a Uas

    NASA Astrophysics Data System (ADS)

    Niemeyer, F.; Schima, R.; Grenzdörffer, G.

    2013-08-01

    Numerous unmanned aerial systems (UAS) are currently flooding the market. For the most diverse applications UAVs are special designed and used. Micro and mini UAS (maximum take-off weight up to 5 kg) are of particular interest, because legal restrictions are still manageable but also the payload capacities are sufficient for many imaging sensors. Currently a camera system with four oblique and one nadir looking cameras is under development at the Chair for Geodesy and Geoinformatics. The so-called "Four Vision" camera system was successfully built and tested in the air. A MD4-1000 UAS from microdrones is used as a carrier system. Light weight industrial cameras are used and controlled by a central computer. For further photogrammetric image processing, each individual camera, as well as all the cameras together have to be calibrated. This paper focuses on the determination of the relative orientation between the cameras with the „Australis" software and will give an overview of the results and experiences of test flights.

  8. Galactic model parameters of cataclysmic variables: Results from a new absolute magnitude calibration with 2MASS and WISE

    NASA Astrophysics Data System (ADS)

    Özdönmez, A.; Ak, T.; Bilir, S.

    2015-01-01

    In order to determine the spatial distribution, Galactic model parameters and luminosity function of cataclysmic variables (CVs), a J-band magnitude limited sample of 263 CVs has been established using a newly constructed period-luminosity-colours (PLCs) relation which includes J,Ks and W1-band magnitudes in 2MASS and WISE photometries, and the orbital periods of the systems. This CV sample is assumed to be homogeneous regarding to distances as the new PLCs relation is calibrated with new or re-measured trigonometric parallaxes. Our analysis shows that the scaleheight of CVs is increasing towards shorter periods, although selection effects for the periods shorter than 2.25 h dramatically decrease the scaleheight: the scaleheight of the systems increases from 192 pc to 326 pc as the orbital period decreases from 12 to 2.25 h. The z-distribution of all CVs in the sample is well fitted by an exponential function with a scaleheight of 213-10+11 pc. However, we suggest that the scaleheight of CVs in the Solar vicinity should be ∼300 pc and that the scaleheights derived using the sech2 function should be also considered in the population synthesis models. The space density of CVs in the Solar vicinity is found 5.58(1.35)×10-6 pc-3 which is in the range of previously derived space densities and not in agreement with the predictions of the population models. The analysis based on the comparisons of the luminosity function of white dwarfs with the luminosity function of CVs in this study show that the best fits are obtained by dividing the luminosity functions of white dwarfs by a factor of 350-450.

  9. Easy Absolute Values? Absolutely

    ERIC Educational Resources Information Center

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

    The authors teach a problem-solving course for preservice middle-grades education majors that includes concepts dealing with absolute-value computations, equations, and inequalities. Many of these students like mathematics and plan to teach it, so they are adept at symbolic manipulations. Getting them to think differently about a concept that they…

  10. Calibration

    NASA Astrophysics Data System (ADS)

    Kunze, Hans-Joachim

    Commercial spectrographic systems are usually supplied with some wave-length calibration, but it is essential that the experimenter performs his own calibration for reliable measurements. A number of sources emitting well-known emission lines are available, and the best values of their wavelengths may be taken from data banks accessible on the internet. Data have been critically evaluated for many decades by the National Institute of Standards and Technology (NIST) of the USA [13], see also p. 3. Special data bases have been established by the astronomy and fusion communities (Appendix B).

  11. SkyProbe: Real-Time Precision Monitoring in the Optical of the Absolute Atmospheric Absorption on the Telescope Science and Calibration Fields

    NASA Astrophysics Data System (ADS)

    Cuillandre, J.-C.; Magnier, E.; Sabin, D.; Mahoney, B.

    2016-05-01

    Mauna Kea is known for its pristine seeing conditions but sky transparency can be an issue for science operations since at least 25% of the observable (i.e. open dome) nights are not photometric, an effect mostly due to high-altitude cirrus. Since 2001, the original single channel SkyProbe mounted in parallel on the Canada-France-Hawaii Telescope (CFHT) has gathered one V-band exposure every minute during each observing night using a small CCD camera offering a very wide field of view (35 sq. deg.) encompassing the region pointed by the telescope for science operations, and exposures long enough (40 seconds) to capture at least 100 stars of Hipparcos' Tycho catalog at high galactic latitudes (and up to 600 stars at low galactic latitudes). The measurement of the true atmospheric absorption is achieved within 2%, a key advantage over all-sky direct thermal infrared imaging detection of clouds. The absolute measurement of the true atmospheric absorption by clouds and particulates affecting the data being gathered by the telescope's main science instrument has proven crucial for decision making in the CFHT queued service observing (QSO) representing today all of the telescope time. Also, science exposures taken in non-photometric conditions are automatically registered for a new observation at a later date at 1/10th of the original exposure time in photometric conditions to ensure a proper final absolute photometric calibration. Photometric standards are observed only when conditions are reported as being perfectly stable by SkyProbe. The more recent dual color system (simultaneous B & V bands) will offer a better characterization of the sky properties above Mauna Kea and should enable a better detection of the thinnest cirrus (absorption down to 0.01 mag., or 1%).

  12. Aquarius L-Band Radiometers Calibration Using Cold Sky Observations

    NASA Technical Reports Server (NTRS)

    Dinnat, Emmanuel P.; Le Vine, David M.; Piepmeier, Jeffrey R.; Brown, Shannon T.; Hong, Liang

    2015-01-01

    An important element in the calibration plan for the Aquarius radiometers is to look at the cold sky. This involves rotating the satellite 180 degrees from its nominal Earth viewing configuration to point the main beams at the celestial sky. At L-band, the cold sky provides a stable, well-characterized scene to be used as a calibration reference. This paper describes the cold sky calibration for Aquarius and how it is used as part of the absolute calibration. Cold sky observations helped establish the radiometer bias, by correcting for an error in the spillover lobe of the antenna pattern, and monitor the long-term radiometer drift.

  13. Absolute number density calibration of the absorption by ground-state lead atoms of the 283. 3-nm resonance line from a high-intensity lead hollow cathode lamp and the calculated effect of argon pressures

    SciTech Connect

    Simons, J.W.; McClean, R.E. ); Oldenborg, R.C. )

    1991-03-21

    The absolute number density calibration for the absorption by ground-state lead atoms of the 283.3-nm resonance line from a high-intensity lead hollow cathode lamp (Photron superlamp) is determined and found to be the same as that of a standard hollow cathode lamp. Comparisons of the calibrations to theoretical calculations are found to be quite satisfactory. The effects of argon pressures in the absorption cell on the calibration are examined theoretically by using a simple Lorentzian broadening and shifting model. These calculations show the expected reduction in sensitivity and increasing linearity of Beer-Lambert plots with increasing argon pressure.

  14. MARBLE (Multiple Antenna Radio-interferometry for Baseline Length Evaluation): Development of a Compact VLBI System for Calibrating GNSS and Electronic Distance Measurement Devices

    NASA Astrophysics Data System (ADS)

    Ichikawa, R.; Ishii, A.; Takiguchi, H.; Kimura, M.; Sekido, M.; Takefuji, K.; Ujihara, H.; Hanado, Y.; Koyama, Y.; Kondo, T.; Kurihara, S.; Kokado, K.; Kawabata, R.; Nozawa, K.; Mukai, Y.; Kuroda, J.; Ishihara, M.; Matsuzaka, S.

    2012-12-01

    We are developing a compact VLBI system with a 1.6-m diameter aperture dish in order to provide reference baseline lengths for calibration. The reference baselines are used to validate surveying instruments such as GPS and EDM and is maintained by the Geospatial Information Authority of Japan (GSI). The compact VLBI system will be installed at both ends of the reference baseline. Since the system is not sensitive enough to detect fringes between the two small dishes, we have designed a new observation concept including one large dish station. We can detect two group delays between each compact VLBI system and the large dish station based on conventional VLBI measurement. A group delay between the two compact dishes can be indirectly calculated using a simple equation. We named the idea "Multiple Antenna Radio-interferometry for Baseline Length Evaluation", or MARBLE system. The compact VLBI system is easy transportable and consists of the compact dish, a new wide-band front-end system, azimuth and elevation drive units, an IF down-converter unit, an antenna control unit (ACU), a counterweight, and a monument pillar. Each drive unit is equipped with a zero-backlash harmonic drive gearing component. A monument pillar is designed to mount typical geodetic GNSS antennas easily and an offset between the GNSS antenna reference point. The location of the azimuth-elevation crossing point of the VLBI system is precisely determined with an uncertainty of less than 0.2 mm. We have carried out seven geodetic VLBI experiments on the Kashima-Tsukuba baseline (about 54 km) using the two prototypes of the compact VLBI system between December 2009 and December 2010. The average baseline length and repeatability of the experiments is 54184874.0 ± 2.4 mm. The results are well consistent with those obtained by GPS measurements. In addition, we are now planning to use the compact VLBI system for precise time and frequency comparison between separated locations.

  15. Absolute calibration and atmospheric versus mineralogic origin of absorption features in 2.0 to 2.5 micron Mars spectra obtained during 1993

    NASA Technical Reports Server (NTRS)

    Bell, James F., III; Pollack, James B.; Geballe, Thomas R.; Cruikshank, Dale P.; Freedman, Richard

    1994-01-01

    We obtained new high resolution reflectance spectra of Mars during the 1993 opposition from Mauna Kea Observatory using the UKIRT CGS4 spectrometer. Fifty spectra of 1600-2000 km surface regions and a number of standard star spectra were obtained in the 2.04 to 2.44 micron wavelength region on 4 February 1993 UT. Near-simultaneous observations of bright standard stars were used to perform terrestrial atmospheric corrections and an absolute flux calibration. Using the known magnitude of the stars and assuming blackbody continuum behavior, the flux from Mars could be derived. A radiative transfer model and the HITRAN spectral line data base were used to compute atmospheric transmission spectra for Mars and the Earth in order to simulate the contributions of these atmospheres to our observed data. Also, we examined the ATMOS solar spectrum in the near-IR to try to identify absorption features in the spectrum of the Sun that could be misinterpreted as Mars features. Eleven absorption features were detected in our Mars spectra. Our data provide no conclusive identification of the mineralogy responsible for the absorption features we detected. However, examination of terrestrial spectral libraries and previous high spectral resolution mineral studies indicates that the most likely origin of these features is either CO3(sup 2-), HCO3(-), or HSO4(-) anions in framework silicates or possibly (Fe, Mg)-OH bonds in sheet silicates.

  16. Determination of Delta m(d) and absolute calibration of flavor taggers for the Delta m(s) analysis, in fully reconstructed decays at the CDF experiment

    SciTech Connect

    Gomez, Jonatan Piedra

    2005-07-01

    The new trigger processor, the Silicon Vertex Tracking (SVT), has dramatically improved the B physics capabilities of the upgraded CDF II Detector; for the first time in a hadron collider, the SVT has enabled the access to non-lepton-triggered B meson decays. Within the new available range of decay modes, the B{sub s}{sup 0} {yields} D{sub s}{sup -}{pi}{sup +} signature is of paramount importance in the measurement of the {Delta}m{sub s} mixing frequency. The analysis reported here is a step towards the measurement of this frequency; two where our goals: carrying out the absolute calibration of the opposite side flavor taggers, used in the {Delta}m{sub s} measurement; and measuring the B{sub d}{sup 0} mixing frequency in a B {yields} D{pi} sample, establishing the feasibility of the mixing measurement in this sample whose decay-length is strongly biased by the selective SVT trigger. We analyze a total integrated luminosity of 355 pb{sup -1} collected with the CDF II Detector. By triggering on muons, using the conventional di-muon trigger; or displaced tracks, using the SVT trigger, we gather a sample rich in bottom and charm mesons.

  17. Calibration of a cylindrical RF capacitance probe. [for ionospheric plasma effects on Radio Astronomy Explorer 1 antenna

    NASA Technical Reports Server (NTRS)

    Mosier, S. R.; Kaiser, M. L.

    1975-01-01

    Ambient electron concentrations derived from observations with the Radio Astronomy Explorer 1 antenna capacitance probe have been compared with upper hybrid resonance measurements from the same spacecraft. From this comparison an empirical correction factor for the capacitance probe measurements has been derived. The differences between the two types of measurements is attributed to sheath effects.

  18. Multibeam antenna study, phase 1

    NASA Technical Reports Server (NTRS)

    Bellamy, J. L.

    1972-01-01

    A multibeam antenna concept was developed for providing spot beam coverage of the contiguous 48 states. The selection of a suitable antenna concept for the multibeam application and an experimental evaluation of the antenna concept selected are described. The final analysis indicates that the preferred concept is a dual-antenna, circular artificial dielectric lens. A description of the analytical methods is provided, as well as a discussion of the absolute requirements placed on the antenna concepts. Finally, a comparative analysis of reflector antenna off-axis beam performance is presented.

  19. Phase center modeling for LEO GPS receiver antennas and its impact on precise orbit determination

    NASA Astrophysics Data System (ADS)

    Jäggi, Adrian; Dach, R.; Montenbruck, O.; Hugentobler, U.; Bock, H.; Beutler, G.

    2009-12-01

    Most satellites in a low-Earth orbit (LEO) with demanding requirements on precise orbit determination (POD) are equipped with on-board receivers to collect the observations from Global Navigation Satellite systems (GNSS), such as the Global Positioning System (GPS). Limiting factors for LEO POD are nowadays mainly encountered with the modeling of the carrier phase observations, where a precise knowledge of the phase center location of the GNSS antennas is a prerequisite for high-precision orbit analyses. Since 5 November 2006 (GPS week 1400), absolute instead of relative values for the phase center location of GNSS receiver and transmitter antennas are adopted in the processing standards of the International GNSS Service (IGS). The absolute phase center modeling is based on robot calibrations for a number of terrestrial receiver antennas, whereas compatible antenna models were subsequently derived for the remaining terrestrial receiver antennas by conversion (from relative corrections), and for the GNSS transmitter antennas by estimation. However, consistent receiver antenna models for space missions such as GRACE and TerraSAR-X, which are equipped with non-geodetic receiver antennas, are only available since a short time from robot calibrations. We use GPS data of the aforementioned LEOs of the year 2007 together with the absolute antenna modeling to assess the presently achieved accuracy from state-of-the-art reduced-dynamic LEO POD strategies for absolute and relative navigation. Near-field multipath and cross-talk with active GPS occultation antennas turn out to be important and significant sources for systematic carrier phase measurement errors that are encountered in the actual spacecraft environments. We assess different methodologies for the in-flight determination of empirical phase pattern corrections for LEO receiver antennas and discuss their impact on POD. By means of independent K-band measurements, we show that zero-difference GRACE orbits can be

  20. Absolute and relative quantification and calibration for sectioning fluorescence microscopy using standardized uniform fluorescent layers and SIPchart-based correction procedures

    NASA Astrophysics Data System (ADS)

    Zwier, J. M.; Oomen, L.; Brocks, L.; Jalink, K.; Brakenhoff, G. J.

    2007-02-01

    The total or integrated fluorescence intensity of a through-focus series of a thin standardized uniform fluorescent or calibration layer is shown to be suitable for image intensity correction and calibration in sectioning microscopy. This integrated intensity can be derived from the earlier introduced SectionedImagingProperty or SIPcharts, derived from the 3D layer datasets. By correcting the 3D image of an object with the 3D image of the standardized uniform fluorescent layer obtained under identical conditions one is able to express the object fluorescence in units fluorescence of the calibration layer. With object fluorescence intensities in fluorescence layer unit's or FLU's the object image intensities becomes independent of microscope system and imaging conditions. A direct result is that the often-appreciable lateral intensity variations present in confocal microscopy are eliminated (shading correction). Of more general value is that images obtained with different objectives, magnifications or from different microscope systems can be quantitatively related to each other. The effectiveness of shading correction and relating images obtained under various microscope conditions is demonstrated on images of standard fluorocent beads. Expressing the object fluorescence in FLU units seems to be a promising approach for general quantification of sectioning imaging enabling cross-correlation of imaging results over time and between imaging systems.

  1. Absolute vicarious calibration of Landsat-8 OLI and Resourcesat-2 AWiFS sensors over Rann of Kutch site in Gujarat

    NASA Astrophysics Data System (ADS)

    Sharma, Shweta; Sridhar, V. N.; Prajapati, R. P.; Rao, K. M.; Mathur, A. K.

    2016-05-01

    In this work, vicarious calibration coefficients for all the four bands (green, red, NIR and SWIR) of Resourcesat-2 AWiFS sensor for four dates during Dec 2013-Nov 2014 and for seven bands (blue, green, red, NIR, SWIR1, SWIR2 and PAN) of OLI sensor onboard Landsat-8 for six dates during Dec 2013-Feb 2015 were estimated using field measured reflectance and measured atmospheric parameters during sensor image acquisition over Rann of Kutch site in Gujarat. The top of atmosphere (TOA) at-satellite radiances for all the bands were simulated using 6S radiative transfer code with field measured reflectance, synchronous atmospheric measurements and respective sensor's spectral response functions as an input. These predicted spectral radiances were compared with the radiances from the respective sensor's image in the respective band over the calibration site. Cross-calibration between the sensors AWiFS and OLI was also attempted using near-simultaneous same day image acquisition. Effect of spectral band adjustment factor was also studied with OLI sensor taken as reference sensor. Results show that the variation in average estimated radiance ratio for the AWiFS sensor was found to be within 10% for all the bands, whereas, for OLI sensor, the variation was found to be within 6% for all the bands except green and SWIR2 for which the variation was 8% and 11% respectively higher than the 5% uncertainty of the OLI sensor specification for TOA spectral radiance. At the 1σ level, red, NIR, SWIR1 and Panchromatic bands of OLI sensor showed close agreement between sensor-measured and vicarious TOA radiance resulting no change in calibration coefficient and hence indicating no sensor degradation. Two sets of near-simultaneous SBAFs were derived from respective ground measured target reflectance profiles and applied to the AWiFS and it was observed that overall, SBAF compensation provides a significant improvement in sensor agreement. The reduction in the difference between AWiFS and

  2. Absolute Zero

    NASA Astrophysics Data System (ADS)

    Donnelly, Russell J.; Sheibley, D.; Belloni, M.; Stamper-Kurn, D.; Vinen, W. F.

    2006-12-01

    Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book “Absolute Zero and the Conquest of Cold” by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

  3. Absolute Energy Calibration of X-ray TESs with 0.04 eV Uncertainty at 6.4 keV in a Hadron-Beam Environment

    NASA Astrophysics Data System (ADS)

    Tatsuno, H.; Doriese, W. B.; Bennett, D. A.; Curceanu, C.; Fowler, J. W.; Gard, J.; Gustafsson, F. P.; Hashimoto, T.; Hayano, R. S.; Hays-Wehle, J. P.; Hilton, G. C.; Iliescu, M.; Ishimoto, S.; Itahashi, K.; Iwasaki, M.; Kuwabara, K.; Ma, Y.; Marton, J.; Noda, H.; O'Neil, G. C.; Okada, S.; Outa, H.; Reintsema, C. D.; Sato, M.; Schmidt, D. R.; Shi, H.; Suzuki, K.; Suzuki, T.; Uhlig, J.; Ullom, J. N.; Widmann, E.; Yamada, S.; Zmeskal, J.; Swetz, D. S.

    2016-01-01

    A performance evaluation of superconducting transition-edge sensors (TESs) in the environment of a pion beam line at a particle accelerator is presented. Averaged across the 209 functioning sensors in the array, the achieved energy resolution is 5.2 eV FWHM at Co K_{α } (6.9 keV) when the pion beam is off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of ± 0.04 eV is demonstrated for Fe K_{α } (6.4 keV) with in-situ energy calibration obtained from other nearby known X-ray lines. To achieve this small uncertainty, it is essential to consider the non-Gaussian energy response of the TESs and thermal cross-talk pile-up effects due to charged particle hits in the silicon substrate of the TES array.

  4. Absolute Energy Calibration of X-ray TESs with 0.04 eV Uncertainty at 6.4 keV in a Hadron-Beam Environment

    NASA Astrophysics Data System (ADS)

    Tatsuno, H.; Doriese, W. B.; Bennett, D. A.; Curceanu, C.; Fowler, J. W.; Gard, J.; Gustafsson, F. P.; Hashimoto, T.; Hayano, R. S.; Hays-Wehle, J. P.; Hilton, G. C.; Iliescu, M.; Ishimoto, S.; Itahashi, K.; Iwasaki, M.; Kuwabara, K.; Ma, Y.; Marton, J.; Noda, H.; O'Neil, G. C.; Okada, S.; Outa, H.; Reintsema, C. D.; Sato, M.; Schmidt, D. R.; Shi, H.; Suzuki, K.; Suzuki, T.; Uhlig, J.; Ullom, J. N.; Widmann, E.; Yamada, S.; Zmeskal, J.; Swetz, D. S.

    2016-08-01

    A performance evaluation of superconducting transition-edge sensors (TESs) in the environment of a pion beam line at a particle accelerator is presented. Averaged across the 209 functioning sensors in the array, the achieved energy resolution is 5.2 eV FWHM at Co K_{α } (6.9 keV) when the pion beam is off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of ± 0.04 eV is demonstrated for Fe K_{α } (6.4 keV) with in-situ energy calibration obtained from other nearby known X-ray lines. To achieve this small uncertainty, it is essential to consider the non-Gaussian energy response of the TESs and thermal cross-talk pile-up effects due to charged particle hits in the silicon substrate of the TES array.

  5. Aircraft antennas/conformal antennas missile antennas

    NASA Astrophysics Data System (ADS)

    Solbach, Klaus

    1987-04-01

    Three major areas of airborne microwave antennas are examined. The basic system environment for missile telemetry/telecommand and fuze functions is sketched and the basic antenna design together with practical examples are discussed. The principle requirements of modern nose radar flat plate antennas are shown to result from missile/aircraft system requirements. Basic principles of slotted waveguide antenna arrays are sketched and practical antenna designs are discussed. The present early warning system designs are sketched to point out requirements and performance of practical radar warning and jamming antennas (broadband spiral antennas and horn radiators). With respect to newer developments in the ECM scenario, some demonstrated and proposed antenna systems (lens fed arrays, phased array, active array) are discussed.

  6. Calibration of diffuse correlation spectroscopy with a time-resolved near-infrared technique to yield absolute cerebral blood flow measurements.

    PubMed

    Diop, Mamadou; Verdecchia, Kyle; Lee, Ting-Yim; St Lawrence, Keith

    2011-07-01

    A primary focus of neurointensive care is the prevention of secondary brain injury, mainly caused by ischemia. A noninvasive bedside technique for continuous monitoring of cerebral blood flow (CBF) could improve patient management by detecting ischemia before brain injury occurs. A promising technique for this purpose is diffuse correlation spectroscopy (DCS) since it can continuously monitor relative perfusion changes in deep tissue. In this study, DCS was combined with a time-resolved near-infrared technique (TR-NIR) that can directly measure CBF using indocyanine green as a flow tracer. With this combination, the TR-NIR technique can be used to convert DCS data into absolute CBF measurements. The agreement between the two techniques was assessed by concurrent measurements of CBF changes in piglets. A strong correlation between CBF changes measured by TR-NIR and changes in the scaled diffusion coefficient measured by DCS was observed (R(2) = 0.93) with a slope of 1.05 ± 0.06 and an intercept of 6.4 ± 4.3% (mean ± standard error). PMID:21750781

  7. Absolute calibration of a photodiode array with the use of the synchrotron radiation in the range of 1-10 keV

    NASA Astrophysics Data System (ADS)

    Beck, L.; Bizeuil, C.; Soullie, G.

    1995-02-01

    The silicon photodiode array Hamamatsu S3901 series (1024, 25 μm pixel) were primarily developed for the visible-UV spectral range, mainly for photon wavelengths between 200 and 1100 nm. By utilizing it without a quartz window, it is demonstrated that this sensor can be used for x rays, especially in the 1-10 keV range. Experimental measurements of the absolute detection efficiency of the photodiode array between 1.5 and 12 keV are presented. The experiments were performed on an x-ray tube-excited secondary targets and on the SB3 beamline at the Super ACO storage ring (LURE-Orsay). The measured spectral efficiency is compared with the results of a simple model calculation based on the data given in the Hamamatsu note. The simulation is in good agreement with the experimental data for a silicon active depth of 6 μm and a silicon dioxide passivation layer of 5 μm. The linearity is better than 1% and the spatial resolution is estimated to be 120 μm.

  8. Calibration of diffuse correlation spectroscopy with a time-resolved near-infrared technique to yield absolute cerebral blood flow measurements

    PubMed Central

    Diop, Mamadou; Verdecchia, Kyle; Lee, Ting-Yim; St Lawrence, Keith

    2011-01-01

    A primary focus of neurointensive care is the prevention of secondary brain injury, mainly caused by ischemia. A noninvasive bedside technique for continuous monitoring of cerebral blood flow (CBF) could improve patient management by detecting ischemia before brain injury occurs. A promising technique for this purpose is diffuse correlation spectroscopy (DCS) since it can continuously monitor relative perfusion changes in deep tissue. In this study, DCS was combined with a time-resolved near-infrared technique (TR-NIR) that can directly measure CBF using indocyanine green as a flow tracer. With this combination, the TR-NIR technique can be used to convert DCS data into absolute CBF measurements. The agreement between the two techniques was assessed by concurrent measurements of CBF changes in piglets. A strong correlation between CBF changes measured by TR-NIR and changes in the scaled diffusion coefficient measured by DCS was observed (R2 = 0.93) with a slope of 1.05 ± 0.06 and an intercept of 6.4 ± 4.3% (mean ± standard error). PMID:21750781

  9. Development of a calibration workstation for SIR-C

    NASA Technical Reports Server (NTRS)

    Madsen, S. N.; Dubois, P.; Freeman, A.; Norikane, L.; Shaffer, S.; Shimada, J.

    1991-01-01

    The paper describes the status of a comprehensive synthetic aperture radar (SAR) software package developed specifically to aid the calibration of a multifrequency and multipolarization radar like the Shuttle Imaging Radar, SIR-C. The primary data types processed are engineering telemetry, point targets (corner reflectors and polarimetric active radar calibrators), distributed targets (clutter), tone-generators, and ground receivers. The parameters derived to aid the calibration of the production processor include measurements of relative radiometric channel to channel imbalance, absolute calibration constants, antenna pattern corrections, noise levels, polarimetric cross-talk, and geometric offsets. The software reports standard performance measurements such as resolution, peak and integrated sidelobes, radiometric response accuracy, and geometrical distortions such as scale errors, position bias and standard deviation, and image skew. Furthermore, the inclusion of software to allow updates of the shuttle-state vector (position and velocity) is considered.

  10. Development of a calibration workstation for SIR-C

    NASA Astrophysics Data System (ADS)

    Madsen, S. N.; Dubois, P.; Freeman, A.; Norikane, L.; Shaffer, S.; Shimada, J.

    The paper describes the status of a comprehensive synthetic aperture radar (SAR) software package developed specifically to aid the calibration of a multifrequency and multipolarization radar like the Shuttle Imaging Radar, SIR-C. The primary data types processed are engineering telemetry, point targets (corner reflectors and polarimetric active radar calibrators), distributed targets (clutter), tone-generators, and ground receivers. The parameters derived to aid the calibration of the production processor include measurements of relative radiometric channel to channel imbalance, absolute calibration constants, antenna pattern corrections, noise levels, polarimetric cross-talk, and geometric offsets. The software reports standard performance measurements such as resolution, peak and integrated sidelobes, radiometric response accuracy, and geometrical distortions such as scale errors, position bias and standard deviation, and image skew. Furthermore, the inclusion of software to allow updates of the shuttle-state vector (position and velocity) is considered.

  11. Absolute Summ

    NASA Astrophysics Data System (ADS)

    Phillips, Alfred, Jr.

    Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al., human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. .

  12. Extension of the GPS satellite antenna patterns to nadir angles beyond 14°

    NASA Astrophysics Data System (ADS)

    Jaeggi, A.; Dilssner, F.; Schmid, R.; Dach, R.; Springer, T.; Bock, H.; Steigenberger, P.; Andres, Y.; Enderle, W.

    2012-04-01

    The absolute phase center model igs08.atx adopted by the International GNSS Service (IGS) in 2011 is based on robot calibrations for more than 200 terrestrial GNSS receiver antennas and consistent correction values for the GNSS transmitter antennas estimated from tracking data of the global IGS ground network. As the calibration of the satellite antennas is solely based on terrestrial measurements, the estimation of their phase patterns is limited to a nadir angle of 14°. This is not sufficient for the analysis of spaceborne GPS data collected by low Earth orbiting (LEO) satellites that record - depending on the missions' orbital altitude - observations at nadir angles of up to 17°. We use GPS tracking data from the LEO missions Jason-1/2, MetOp-A, GRACE, and GOCE to extend the IGS satellite antenna patterns to nadir angles beyond 14° using different processing strategies and GNSS software packages (BERNESE, NAPEOS). In order to achieve estimates that are consistent with the PCVs currently used within the IGS, GPS satellite orbits and clocks are fixed to reprocessed solutions obtained by adopting the IGS conventional values from igs08.atx. Due to significant near-field multipath effects arising in the LEO spacecraft environment, it is necessary to solve for GPS (nadir-dependent only) and LEO (azimuth- and elevation-dependent) antenna patterns simultaneously. We compare and combine the results obtained with both software packages and derive the PCV extension proposed for igs08.atx.

  13. Interactions of the IGS reprocessing and the IGS antenna phase center model (Invited)

    NASA Astrophysics Data System (ADS)

    Schmid, R.; Steigenberger, P.; Dach, R.; Schmitz, M.; Dilssner, F.; Hugentobler, U.

    2009-12-01

    Since November 2006 an absolute phase center correction model for GNSS satellite and receiver antennas has been used within the International GNSS Service (IGS). This model, called igs05.atx, comprises consistent phase center offset (PCO) and variation (PCV) values given in ANTEX format. Generally, these correction values have not been changed in the meantime.For most of the receiver antenna types dominating the IGS network, absolute robot calibrations provided by Geo++ GmbH are available. Those comprise azimuth- and zenith-dependent PCVs down to the horizon. For the remaining antenna types converted field calibrations from the National Geodetic Survey are applied that are purely zenith-dependent. The impact of radomes is taken into account, if calibration results are available. So far, igs05.atx only contains calibrations for the GPS frequencies.The GPS satellite antenna corrections contained in igs05.atx were estimated by Deutsches GeoForschungsZentrum and by TUM by reprocessing more than ten years of IGS data. The corresponding GLONASS corrections were provided by the Center for Orbit Determination in Europe (CODE) after processing more than one year of data. Although azimuth-dependent PCVs are present, the igs05.atx model is limited to block-specific purely nadir-dependent PCVs. In contrast, satellite-specific z-offsets are given.At the time the satellite antenna corrections were estimated, the solutions could only be aligned to IGb00, the IGS realization of ITRF2000, that was based on relative receiver antenna corrections. Moreover, the impact of radomes had to be ignored, as calibration results were not available. So, the IGS reprocessing campaign is an excellent possibility to improve the consistency between both satellite and receiver antenna corrections and the terrestrial reference frame.Several analysis centers (ACs) of the IGS provide z-offset estimates within their weekly SINEX files. By back-solving those files with selected station coordinates fixed

  14. Mechanisms of the Rosetta high gain antenna

    NASA Astrophysics Data System (ADS)

    Pereira, Carlos

    2001-09-01

    This paper describes the antenna pointing mechanism (APM) and the hold down and release mechanism (HRM) used in the high gain antenna of the ROSETTA mission. The hold down and release mechanism consists of three units which compensate the tolerance mismatch between antenna and spacecraft through incorporation of potting rings. Given that the activation mode is pyrotechnic, release shock is a major concern and is minimised through integration of shock absorbers which allow stroking of the separation nuts. The antenna pointing mechanism is a dual drive (azimuth over elevation) unit which allows controlled rotation of the antenna. The drive units incorporate spring loaded end stops to prevent the antenna from hitting the spacecraft, and optical encoders which register the absolute position of the antenna. The pointing and the hold down mechanisms of the ROSETTA antenna are fully qualified and will withstand the high launch loads of the Ariane-5 and the environmental demands of deep space operation.

  15. FOREGROUND MODEL AND ANTENNA CALIBRATION ERRORS IN THE MEASUREMENT OF THE SKY-AVERAGED λ21 cm SIGNAL AT z∼ 20

    SciTech Connect

    Bernardi, G.; McQuinn, M.; Greenhill, L. J.

    2015-01-20

    The most promising near-term observable of the cosmic dark age prior to widespread reionization (z ∼ 15-200) is the sky-averaged λ21 cm background arising from hydrogen in the intergalactic medium. Though an individual antenna could in principle detect the line signature, data analysis must separate foregrounds that are orders of magnitude brighter than the λ21 cm background (but that are anticipated to vary monotonically and gradually with frequency, e.g., they are considered {sup s}pectrally smooth{sup )}. Using more physically motivated models for foregrounds than in previous studies, we show that the intrinsic spectral smoothness of the foregrounds is likely not a concern, and that data analysis for an ideal antenna should be able to detect the λ21 cm signal after subtracting a ∼fifth-order polynomial in log ν. However, we find that the foreground signal is corrupted by the angular and frequency-dependent response of a real antenna. The frequency dependence complicates modeling of foregrounds commonly based on the assumption of spectral smoothness. Our calculations focus on the Large-aperture Experiment to detect the Dark Age, which combines both radiometric and interferometric measurements. We show that statistical uncertainty remaining after fitting antenna gain patterns to interferometric measurements is not anticipated to compromise extraction of the λ21 cm signal for a range of cosmological models after fitting a seventh-order polynomial to radiometric data. Our results generalize to most efforts to measure the sky-averaged spectrum.

  16. Foreground Model and Antenna Calibration Errors in the Measurement of the Sky-averaged λ21 cm Signal at z~ 20

    NASA Astrophysics Data System (ADS)

    Bernardi, G.; McQuinn, M.; Greenhill, L. J.

    2015-01-01

    The most promising near-term observable of the cosmic dark age prior to widespread reionization (z ~ 15-200) is the sky-averaged λ21 cm background arising from hydrogen in the intergalactic medium. Though an individual antenna could in principle detect the line signature, data analysis must separate foregrounds that are orders of magnitude brighter than the λ21 cm background (but that are anticipated to vary monotonically and gradually with frequency, e.g., they are considered "spectrally smooth"). Using more physically motivated models for foregrounds than in previous studies, we show that the intrinsic spectral smoothness of the foregrounds is likely not a concern, and that data analysis for an ideal antenna should be able to detect the λ21 cm signal after subtracting a ~fifth-order polynomial in log ν. However, we find that the foreground signal is corrupted by the angular and frequency-dependent response of a real antenna. The frequency dependence complicates modeling of foregrounds commonly based on the assumption of spectral smoothness. Our calculations focus on the Large-aperture Experiment to detect the Dark Age, which combines both radiometric and interferometric measurements. We show that statistical uncertainty remaining after fitting antenna gain patterns to interferometric measurements is not anticipated to compromise extraction of the λ21 cm signal for a range of cosmological models after fitting a seventh-order polynomial to radiometric data. Our results generalize to most efforts to measure the sky-averaged spectrum.

  17. Mapping with MAV: Experimental Study on the Contribution of Absolute and Relative Aerial Position Control

    NASA Astrophysics Data System (ADS)

    Skaloud, J.; Rehak, M.; Lichti, D.

    2014-03-01

    This study highlights the benefit of precise aerial position control in the context of mapping using frame-based imagery taken by small UAVs. We execute several flights with a custom Micro Aerial Vehicle (MAV) octocopter over a small calibration field equipped with 90 signalized targets and 25 ground control points. The octocopter carries a consumer grade RGB camera, modified to insure precise GPS time stamping of each exposure, as well as a multi-frequency/constellation GNSS receiver. The GNSS antenna and camera are rigidly mounted together on a one-axis gimbal that allows control of the obliquity of the captured imagery. The presented experiments focus on including absolute and relative aerial control. We confirm practically that both approaches are very effective: the absolute control allows omission of ground control points while the relative requires only a minimum number of control points. Indeed, the latter method represents an attractive alternative in the context of MAVs for two reasons. First, the procedure is somewhat simplified (e.g. the lever-arm between the camera perspective and antenna phase centers does not need to be determined) and, second, its principle allows employing a single-frequency antenna and carrier-phase GNSS receiver. This reduces the cost of the system as well as the payload, which in turn increases the flying time.

  18. Deployable antenna

    NASA Technical Reports Server (NTRS)

    Fink, Patrick W. (Inventor); Dobbins, Justin A. (Inventor); Lin, Greg Y. (Inventor); Chu, Andrew W. (Inventor); Scully, Robert C. (Inventor)

    2006-01-01

    A deployable antenna and method for using wherein the deployable antenna comprises a collapsible membrane having at least one radiating element for transmitting electromagnetic waves, receiving electromagnetic waves, or both.

  19. Investigations on the Influence of Antenna Near-field Effects and Satellite Obstruction on the Uncertainty of GNSS-based Distance Measurements

    NASA Astrophysics Data System (ADS)

    Zimmermann, Florian; Eling, Christian; Kuhlmann, Heiner

    2016-03-01

    Antenna near-field effects are one of the accuracy limiting factors on GNSS-based distance measurements. In order to analyse these influences, a measurement campaign at an EDM calibration baseline site with optimum GNSS conditions was performed. To vary the distance between the antenna mount and the absolutely calibrated antennas, spacers with different lengths were used. Due to the comparison of the resulting GNSS-based distance measurements to a reference solution, the influences of the antenna near-field could be analyzed. The standard deviations of the differences to the reference solution, i. e., 0.31 mm for the distance and 0.46 mm for the height component, indicate that equal spacer and antenna combinations at both stations lead to a very high accuracy level. In contrast, different spacer and antenna combinations decrease the accuracy level. Thus, an identical set-up at both antenna stations and the usage of individually calibrated antennas minimize the near-field effects during the double-differencing process. Hence, these aspects can be identified as a prerequisite for highly accurate GNSS-measurements. In addition to near-field effects, the influence of satellite obstructions is investigated. Four realistic shadowing scenarios are numerically simulated on the basis of the observations, which were collected in the optimum surrounding of the EDM calibration baseline site. The comparison to nominal values indicates that a shadowing leads only to a slight decreasing of the accuracy. Consequently, there is a strong suspicion that multipath effects and signal distortions seem to have a greater influence on the accuracy of GNSS-based distance measurements than the satellite constellation.

  20. User Antennas

    NASA Technical Reports Server (NTRS)

    Jamnejad, Vahraz; Cramer, Paul

    1990-01-01

    The following subject areas are covered: (1) impact of frequency change of user and spacecraft antenna gain and size; (2) basic personal terminal antennas (impact of 20/30 GHz frequency separation; parametric studies - gain, size, weight; gain and figure of merit (G/T); design data for selected antenna concepts; critical technologies and development goals; and recommendations); and (3) user antenna radiation safety concerns.

  1. Impact of individual Receiver Antenna Code Phase Variation on the Ambiguity Resolution

    NASA Astrophysics Data System (ADS)

    Kersten, T.; Schoen, S.

    2013-12-01

    The Institut für Erdmessung (IfE) is an official IGS antenna calibration institution, calibrating carrier-phase center variations (PCV) for receiver antennas routinely in the field, using the actual GNSS satellite signals in space. Current research activities are focussed on the antenna code-phase calibration with the Hannover Concept of absolute antenna calibration. Besides PCV, the receiving antenna introduces systematic effects, currently known as Group Delay Variations (GDV), i.e. azimuth and elevation dependent code-phase delays. These delays can be determined by precisely rotating and tilting the antenna under test. Forming imedifferenced single differences with respect to a near (ca. 8m) fixed reference station, the GDV can be separated from further systematic effects like tropospheric delays, which are reduced far below the code observation noise level. Depending on the antenna design, suitable for specific applications, different magnitudes and features of GDV has been determined at IfE. In previous papers the authors could elaborate that GDV are antenna specific and they systematically affect the code observation up to 1.8m as well as the obtained coordinates, (Kersten and Schön, 2013). The impact depends on the corresponding magnitude of the GDV pattern. In several studies, improvements were obtained for static code based single point positioning (SPP) as well as for code based differential positioning when applying GDV corrections. This contribution discusses the current investigations at IfE on GDV within combined code and carrier phase processing strategies. The study of the GDV impact on the Melbourne-Wübbena linear combination (MW-LC) which is widely used for cycle slip detection and ambiguity resolution is of special interest, since due to the linear combination GDV effects on both code phases are amplified. We detect systematic effects and significant trends in the MW-LC time series due to receiver antenna specific GDV with an amount of up to 0

  2. The 238U/235U isotope ratio of the Earth and the solar system: Constrains from a gravimetrically calibrated U double spike and implications for absolute Pb-Pb ages

    NASA Astrophysics Data System (ADS)

    Weyer, Stefan; Noordmann, Janine; Brennecka, Greg; Richter, Stephan

    2010-05-01

    The ratio of 238U and 235U, the two primordial U isotopes, has been assumed to be constant on Earth and in the solar system. The commonly accepted value for the 238U/235U ratio, which has been used in Pb-Pb dating for the last ~ 30 years, was 137.88. Within the last few years, it has been shown that 1) there are considerable U isotope variations (~1.3‰) within terrestrial material produced by isotope fractionation during chemical reactions [1-3] and 2) there are even larger isotope variations (at least 3.5‰) in calcium-aluminum-rich inclusions (CAIs) in meoteorites that define the currently accepted age of the solar system [4]. These findings are dramatic for geochronology, as a known 238U/235U is a requirement for Pb-Pb dating, the most precise dating technique for absolute ages. As 238U/235U variations can greatly affect the reported absolute Pb-Pb age, understanding and accurately measuring variation of the 238U/235U ratio in various materials is critical, With these new findings, the questions also arises of "How well do we know the average U isotope composition of the Earth and the solar system?" and "How accurate can absolute Pb-Pb ages be?" Our results using a gravimetrically calibrated 233U/236U double spike IRMM 3636 [5] indicate that the U standard NBL 950a, which was commonly used to define the excepted "natural" 238U/235U isotope ratio, has a slightly lower 238U/235U of 137.836 ± 0.024. This value is indistinguishable from the U isotope compositions for NBL 960 and NBL112A, which have been determined by several laboratories, also using the newly calibrated U double spike IRMM 3636 [6]. These findings provide new implications about the average U isotope composition of the Earth and the solar system. Basalts display a very tight range of U isotope variations (~0.25-0.32‰ relative to SRM 950a). Their U isotope composition is also very similar to that of chondrites [4], which however appear to show a slightly larger spread. Accepting terrestrial

  3. Reconfigurable antenna pattern verification

    NASA Technical Reports Server (NTRS)

    Drexler, Jerome P. (Inventor); Becker, Robert C. (Inventor); Meyers, David W. (Inventor); Muldoon, Kelly P. (Inventor)

    2013-01-01

    A method of verifying programmable antenna configurations is disclosed. The method comprises selecting a desired antenna configuration from a plurality of antenna configuration patterns, with the selected antenna configuration forming at least one reconfigurable antenna from reconfigurable antenna array elements. The method validates the formation of the selected antenna configuration to determine antenna performance of the at least one reconfigurable antenna.

  4. On Adequate Comparisons of Antenna Phase Center Variations

    NASA Astrophysics Data System (ADS)

    Schoen, S.; Kersten, T.

    2013-12-01

    One important part for ensuring the high quality of the International GNSS Service's (IGS) products is the collection and publication of receiver - and satellite antenna phase center variations (PCV). The PCV are crucial for global and regional networks, since they introduce a global scale factor of up to 16ppb or changes in the height component with an amount of up to 10cm, respectively. Furthermore, antenna phase center variations are also important for precise orbit determination, navigation and positioning of mobile platforms, like e.g. the GOCE and GRACE gravity missions, or for the accurate Precise Point Positioning (PPP) processing. Using the EUREF Permanent Network (EPN), Baire et al. (2012) showed that individual PCV values have a significant impact on the geodetic positioning. The statements are further supported by studies of Steigenberger et al. (2013) where the impact of PCV for local-ties are analysed. Currently, there are five calibration institutions including the Institut für Erdmessung (IfE) contributing to the IGS PCV file. Different approaches like field calibrations and anechoic chamber measurements are in use. Additionally, the computation and parameterization of the PCV are completely different within the methods. Therefore, every new approach has to pass a benchmark test in order to ensure that variations of PCV values of an identical antenna obtained from different methods are as consistent as possible. Since the number of approaches to obtain these PCV values rises with the number of calibration institutions, there is the necessity for an adequate comparison concept, taking into account not only the numerical values but also stochastic information and computational issues of the determined PCVs. This is of special importance, since the majority of calibrated receiver antennas published by the IGS origin from absolute field calibrations based on the Hannover Concept, Wübbena et al. (2000). In this contribution, a concept for the adequate

  5. Active antenna

    NASA Astrophysics Data System (ADS)

    Sutton, John F.

    1994-05-01

    An antenna, which may be a search coil, is connected to an operational amplifier circuit which provides negative impedances, each of which is in the order of magnitude of the positive impedances which characterize the antenna. The antenna is connected to the inverting input of the operational amplifier; a resistor is connected between the inverting input and the output of the operational amplifier; a capacitor-resistor network, in parallel, is connected between the output and the noninverting input of the operational amplifier; and a resistor is connected from the noninverting input and the circuit common. While this circuit provides a negative resistance and a negative inductance, in series, which appear, looking into the noninverting input of the operational amplifier, in parallel with the antenna, these negative impedances appear in a series loop with the antenna positive impedances, so as to algebraically add. This circuit is tuned by varying the various circuit components so that the negative impedances are very close, but somewhat less, in magnitude, to the antenna impedances. The result is to increase the sensitivity of the antenna by lowering its effective impedance. This, in turn, increases the effective area of the antenna, which may be broadband.

  6. Active antenna

    NASA Technical Reports Server (NTRS)

    Sutton, John F. (Inventor)

    1994-01-01

    An antenna, which may be a search coil, is connected to an operational amplifier circuit which provides negative impedances, each of which is in the order of magnitude of the positive impedances which characterize the antenna. The antenna is connected to the inverting input of the operational amplifier; a resistor is connected between the inverting input and the output of the operational amplifier; a capacitor-resistor network, in parallel, is connected between the output and the noninverting input of the operational amplifier; and a resistor is connected from the noninverting input and the circuit common. While this circuit provides a negative resistance and a negative inductance, in series, which appear, looking into the noninverting input of the operational amplifier, in parallel with the antenna, these negative impedances appear in a series loop with the antenna positive impedances, so as to algebraically add. This circuit is tuned by varying the various circuit components so that the negative impedances are very close, but somewhat less, in magnitude, to the antenna impedances. The result is to increase the sensitivity of the antenna by lowering its effective impedance. This, in turn, increases the effective area of the antenna, which may be broadband.

  7. Calibration validation for the GEOS-3 altimeter

    NASA Technical Reports Server (NTRS)

    Martin, C. F.; Kolenkiewicz, R.

    1980-01-01

    The absolute bias calibration for the GEOS-3 intensive mode altimeter was measured using two satellite passes whose groundtracks were within 1 km of the Bermuda laser station. The Bermuda laser tracked on the two passes, and was supported by two other NASA lasers on one pass and by the NASA Spacecraft Tracking and Data Network on the other pass. For each pass, the altimeter data around Bermuda was smoothed and extrapolated to the point closest to overhead at the laser site. After correcting for tide heights and sea state effects, the two passes give calibration biases which are in agreement to within 26 cm and have a weighted mean of -5.69 + or - 0.16m for correcting altimeter measurements to the center-of-mass of the spacecraft (i.e., including the antenna tracking point correction). It was found impossible to reconcile the two calibration passes, as well as a set of altimeter crossovers in the middle of the GEOS-3 calibration area, without allowing for a data time tag error. On the bias of a selected set of four crossovers, and an assessment of probable sources of timing error, it was concluded that one interpulse period (10.24 msec) should be added to the data time tags.

  8. Air shower measurements with the LOPES radio antenna array

    NASA Astrophysics Data System (ADS)

    Lopes Collaboration; Haungs, A.; Apel, W. D.; Arteaga, J. C.; Asch, T.; Auffenberg, J.; Badea, F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Kolotaev, Y.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Łuczak, P.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Stümpert, M.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Walkowiak, W.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.; LOPES Collaboration

    2009-06-01

    LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from extensive air showers. Since radio waves suffer very little attenuation, radio measurements allow the detection of very distant or highly inclined showers. These waves can be recorded day and night, and provide a bolometric measure of the leptonic shower component. LOPES is designed as a digital radio interferometer using high bandwidths and fast data processing and profits from the reconstructed air shower observables of KASCADE-Grande. The LOPES antennas are absolutely amplitude calibrated allowing to reconstruct the electric field strength which can be compared with predictions from detailed Monte-Carlo simulations. We report about the analysis of correlations present in the radio signals measured by the LOPES 30 antenna array. Additionally, LOPES operates antennas of a different type (LOPESSTAR) which are optimized for an application at the Pierre Auger Observatory. Status, recent results of the data analysis and further perspectives of LOPES and the possible large scale application of this new detection technique are discussed.

  9. A new polarimetric active radar calibrator and calibration technique

    NASA Astrophysics Data System (ADS)

    Tang, Jianguo; Xu, Xiaojian

    2015-10-01

    Polarimetric active radar calibrator (PARC) is one of the most important calibrators with high radar cross section (RCS) for polarimetry measurement. In this paper, a new double-antenna polarimetric active radar calibrator (DPARC) is proposed, which consists of two rotatable antennas with wideband electromagnetic polarization filters (EMPF) to achieve lower cross-polarization for transmission and reception. With two antennas which are rotatable around the radar line of sight (LOS), the DPARC provides a variety of standard polarimetric scattering matrices (PSM) through the rotation combination of receiving and transmitting polarization, which are useful for polarimatric calibration in different applications. In addition, a technique based on Fourier analysis is proposed for calibration processing. Numerical simulation results are presented to demonstrate the superior performance of the proposed DPARC and processing technique.

  10. Teaching Absolute Value Meaningfully

    ERIC Educational Resources Information Center

    Wade, Angela

    2012-01-01

    What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

  11. Notch Antennas

    NASA Technical Reports Server (NTRS)

    Lee, Richard Q.

    2004-01-01

    Notch antennas, also known as the tapered slot antenna (TSA), have been the topics of research for decades. TSA has demonstrated multi-octave bandwidth, moderate gain (7 to 10 dB), and symmetric E- and H- plane beam patterns and can be used for many different applications. This chapter summarizes the research activities on notch antennas over the past decade with emphasis on their most recent advances and applications. This chapter begins with some discussions on the designs of single TSA; then follows with detailed discussions of issues associated with TSA designs and performance characteristics. To conclude the chapter, some recent developments in TSA arrays and their applications are highlighted.

  12. Phase calibration generator

    NASA Technical Reports Server (NTRS)

    Sigman, E. H.

    1988-01-01

    A phase calibration system was developed for the Deep Space Stations to generate reference microwave comb tones which are mixed in with signals received by the antenna. These reference tones are used to remove drifts of the station's receiving system from the detected data. This phase calibration system includes a cable stabilizer which transfers a 20 MHz reference signal from the control room to the antenna cone. The cable stabilizer compensates for delay changes in the long cable which connects its control room subassembly to its antenna cone subassembly in such a way that the 20 MHz is transferred to the cone with no significant degradation of the hydrogen maser atomic clock stability. The 20 MHz reference is used by the comb generator and is also available for use as a reference for receiver LO's in the cone.

  13. Calibration of the Geosar Dual Frequency Interferometric SAR

    NASA Technical Reports Server (NTRS)

    Chapine, Elaine

    1999-01-01

    GeoSAR is an airborne, interferometric Synthetic Aperture Radar (INSAR) system for terrain mapping, currently under development by a consortium including NASA's Jet Propulsion Laboratory (JPL), Calgis, Inc., and the California Department of Conservation (CalDOC) with funding provided by the Topographic Engineering Center (TEC) of the U.S. Army Corps of Engineers and the Defense Advanced Research Projects Agency (DARPA). The radar simultaneously maps swaths on both sides of the aircraft at two frequencies, X-Band and P-Band. For the P-Band system, data is collected for two across track interferometric baselines and at the crossed polarization. The aircraft position and attitude are measured using two Honeywell Embedded GPS Inertial Navigation Units (EGI) and an Ashtech Z12 GPS receiver. The mechanical orientation and position of the antennas are actively measured using a Laser Baseline Metrology System (LBMS). In the GeoSAR motion measurement software, these data are optimally combined with data from a nearby ground station using Ashtech PNAV software to produce the position, orientation, and baseline information are used to process the dual frequency radar data. Proper calibration of the GeoSAR system is essential to obtaining digital elevation models (DEMS) with the required sub-meter level planimetric and vertical accuracies. Calibration begins with the determination of the yaw and pitch biases for the two EGI units. Common range delays are determined for each mode, along with differential time and phase delays between channels. Because the antennas are measured by the LBMS, baseline calibration consists primarily of measuring a constant offset between mechanical center and the electrical phase center of the antennas. A phase screen, an offset to the interferometric phase difference which is a function of absolute phase, is applied to the interferometric data to compensate for multipath and leakage. Calibration parameters are calculated for each of the ten

  14. Spacecraft Antennas

    NASA Technical Reports Server (NTRS)

    Jamnejad, Vahraz; Manshadi, Farzin; Rahmat-Samii, Yahya; Cramer, Paul

    1990-01-01

    Some of the various categories of issues that must be considered in the selection and design of spacecraft antennas for a Personal Access Satellite System (PASS) are addressed, and parametric studies for some of the antenna concepts to help the system designer in making the most appropriate antenna choice with regards to weight, size, and complexity, etc. are provided. The question of appropriate polarization for the spacecraft as well as for the User Terminal Antenna required particular attention and was studied in some depth. Circular polarization seems to be the favored outcome of this study. Another problem that has generally been a complicating factor in designing the multiple beam reflector antennas, is the type of feeds (single vs. multiple element and overlapping vs. non-overlapping clusters) needed for generating the beams. This choice is dependent on certain system design factors, such as the required frequency reuse, acceptable interbeam isolation, antenna efficiency, number of beams scanned, and beam-forming network (BFN) complexity. This issue is partially addressed, but is not completely resolved. Indications are that it may be possible to use relatively simple non-overlapping clusters of only a few elements, unless a large frequency reuse and very stringent isolation levels are required.

  15. Precise Measurement of the Absolute Fluorescence Yield

    NASA Astrophysics Data System (ADS)

    Ave, M.; Bohacova, M.; Daumiller, K.; Di Carlo, P.; di Giulio, C.; San Luis, P. Facal; Gonzales, D.; Hojvat, C.; Hörandel, J. R.; Hrabovsky, M.; Iarlori, M.; Keilhauer, B.; Klages, H.; Kleifges, M.; Kuehn, F.; Monasor, M.; Nozka, L.; Palatka, M.; Petrera, S.; Privitera, P.; Ridky, J.; Rizi, V.; D'Orfeuil, B. Rouille; Salamida, F.; Schovanek, P.; Smida, R.; Spinka, H.; Ulrich, A.; Verzi, V.; Williams, C.

    2011-09-01

    We present preliminary results of the absolute yield of fluorescence emission in atmospheric gases. Measurements were performed at the Fermilab Test Beam Facility with a variety of beam particles and gases. Absolute calibration of the fluorescence yield to 5% level was achieved by comparison with two known light sources--the Cherenkov light emitted by the beam particles, and a calibrated nitrogen laser. The uncertainty of the energy scale of current Ultra-High Energy Cosmic Rays experiments will be significantly improved by the AIRFLY measurement.

  16. Eosinophil count - absolute

    MedlinePlus

    Eosinophils; Absolute eosinophil count ... the white blood cell count to give the absolute eosinophil count. ... than 500 cells per microliter (cells/mcL). Normal value ranges may vary slightly among different laboratories. Talk ...

  17. Antenna theory and design

    NASA Astrophysics Data System (ADS)

    Stutzman, W. L.; Thiele, G. A.

    Antenna fundamentals and definitions are examined, taking into account electromagnetic fundamentals, the solution of Maxwell's equations for radiation problems, the ideal dipole, the radiation pattern, directivity and gain, reciprocity and antenna pattern measurements, antenna impedance and radiation efficiency, antenna polarization, antennas in communication links and radar, and the receiving properties of antennas. Some simple radiating systems are considered along with arrays, line sources, wire antennas, broadband antennas, moment methods, and aperture antennas. High-frequency methods and aspects of antenna synthesis are discussed, giving attention to geometrical optics, physical optics, wedge diffraction theory, the ray-fixed coordinate system, the cylindrical parabolic antenna, and linear array methods.

  18. Calibrating coastal GNSS-R instrumentation

    NASA Astrophysics Data System (ADS)

    Löfgren, Johan; Haas, Rüdiger; Hobiger, Thomas

    2015-04-01

    Since 2011, a GNSS-R (Global Navigation Satellite System - Reflectometry) instrument for local sea level observations is operated at the Onsala Space Observatory (Löfgren et al., 2011). The Onsala Space Observatory is the Swedish geodetic fundamental station, located at the Swedish West Coast, and contributes to the Global Geodetic Observing System (GGOS) by a variety of geodetic and geophysical observations. The Onsala GNSS-R instrumentation consists of two GNSS antennas that are mounted back-to-back on a bar at the coastline extending over the open sea in southward direction. One of the antennas is upward oriented and receives the direct satellite signals, while the other antenna is downward oriented and receives the satellite signals that reflect off the sea surface. The antennas are connected to a commercial GNSS receiver each and data are recorded with sampling rate of up to 20 Hz. Satellite signals of several GNSS are received and are analysed with various different analysis strategies to provide sea level results with different temporal resolution and precision (Larson et al., 2013; Löfgren and Haas, 2014). Since the instrumentation uses GNSS signals, it is possible to derive both local sea level, i.e. relative to the coast, and absolute sea level, i.e. relative to the geocentre as realised by the GNSS. The bar carrying the two antennas can be placed in 10 different vertical positions covering a height difference of 2.5 m between the highest and lowest position. We present results from a calibration campaign of the Onsala GNSS-R instrumentation performed in 2014. During this several weeks long campaign the antennas were placed at different vertical positions for several days at each position. The recorded data are analysed with the different analysis strategies, and the results are compared to the results derived from the co-located tide gauge equipment. References - Löfgren J, Haas R, Scherneck H-G (2011). Three months of local sea-level derived from

  19. Phased Array Radiometer Calibration Using a Radiated Noise Source

    NASA Technical Reports Server (NTRS)

    Srinivasan, Karthik; Limaye, Ashutoch S.; Laymon, Charles A.; Meyer, Paul J.

    2010-01-01

    Electronic beam steering capability of phased array antenna systems offer significant advantages when used in real aperture imaging radiometers. The sensitivity of such systems is limited by the ability to accurately calibrate variations in the antenna circuit characteristics. Passive antenna systems, which require mechanical rotation to scan the beam, have stable characteristics and the noise figure of the antenna can be characterized with knowledge of its physical temperature [1],[2]. Phased array antenna systems provide the ability to electronically steer the beam in any desired direction. Such antennas make use of active components (amplifiers, phase shifters) to provide electronic scanning capability while maintaining a low antenna noise figure. The gain fluctuations in the active components can be significant, resulting in substantial calibration difficulties [3]. In this paper, we introduce two novel calibration techniques that provide an end-to-end calibration of a real-aperture, phased array radiometer system. Empirical data will be shown to illustrate the performance of both methods.

  20. The Science of Calibration

    NASA Astrophysics Data System (ADS)

    Kent, S. M.

    2016-05-01

    This paper presents a broad overview of the many issues involved in calibrating astronomical data, covering the full electromagnetic spectrum from radio waves to gamma rays, and considering both ground-based and space-based missions. These issues include the science drivers for absolute and relative calibration, the physics behind calibration and the mechanisms used to transfer it from the laboratory to an astronomical source, the need for networks of calibrated astronomical standards, and some of the challenges faced by large surveys and missions.

  1. Remote Cloud Sensing Intensive Observation Period (RCS-IOP) millimeter-wave radar calibration and data intercomparison

    SciTech Connect

    Sekelsky, S.M.; Firda, J.M.; McIntosh, R.E.

    1996-04-01

    During April 1994, the University of Massachusetts (UMass) and the Pennsylvania State University (Penn State) fielded two millimeter-wave atmospheric radars in the Atmospheric Radiation Measurement Remote Cloud Sensing Intensive Operation Period (RCS-IOP) experiment. The UMass Cloud Profiling Radar System (CPRS) operates simultaneously at 33.12 GHz and 94.92 GHz through a single antenna. The Penn State radar operates at 93.95 GHz and has separate transmitting and receiving antennas. The two systems were separated by approximately 75 meters and simultaneously observed a variety of cloud types at verticle incidence over the course of the experiment. This abstract presents some initial results from our calibration efforts. An absolute calibration of the UMass radar was made from radar measurements of a trihedral corner reflector, which has a known radar cross-section. A relative calibration of between the Penn State and UMass radars is made from the statistical comparison of zenith pointing measurements of low altitude liquid clouds. Attenuation is removed with the aid of radiosonde data, and the difference in the calibration between the UMass and Penn State radars is determined by comparing the ratio of 94-GHz and 95-GHz reflectivity values to a model that accounts for parallax effects of the two antennas used in the Penn State system.

  2. Summary of KOMPSAT-5 Calibration and Validation

    NASA Astrophysics Data System (ADS)

    Yang, D.; Jeong, H.; Lee, S.; Kim, B.

    2013-12-01

    Korean Multi-Purpose Satellite 5 (KOMPSAT-5), equipped with high resolution X-band (9.66 GHz) Synthetic Aperture Radar (SAR), is planning to be launched on August 22, 2013. With the satellite's primary mission objective being providing Geographical Information System (GIS), Ocean monitoring and Land management, and Disaster and ENvironment monitoring (GOLDEN), it is expected that its applications for scientific research on geographical processes will be extensive. In order to meet its mission objective, the KOMPSAT-5 will provide three different kinds of SAR imaging modes; High Resolution Mode (1 m resolution, 5 km swath), Standard Mode (3 m resolution, 30 km swath), and Wide Swath Mode (20 m resolution, 100 km swath). The KOMPSAT-5 will be operated in a 550 km sun-synchronous, dawn- dusk orbit with a 28-day ground repeat cycle providing valuable image information on Earth surface day-or-night and even in bad weather condition. After successful launch of the satellite, it will go through Launch and Early Operation (LEOP) and In-Orbit Testing (IOT) period about for 6 months to carry out various tests on satellite bus and payload systems. The satellite bus system will be tested during the first 3 weeks after the launch focusing on the Attitude and Orbit Control Subsystem (AOCS) and Integrated GPS Occultation Receiver (IGOR) calibration. With the completion of bus system test, the SAR payload system will be calibrated during initial In-Flight check period (11 weeks) by the joint effort of Thales Alenia Space Italy (TAS-I) and Korea Aerospace Research Institute (KARI). The pointing and relative calibration will be carried out during this period by analyzing the doppler frequency and antenna beam pattern of reflected microwave signal from selected regions with uniform backscattering coefficients (e.g. Amazon rainforest). A dedicated SAR calibration, called primary calibration, will be allocated at the end of LEOP for 12 weeks to perform thorough calibration activities

  3. Breadboard Signal Processor for Arraying DSN Antennas

    NASA Technical Reports Server (NTRS)

    Jongeling, Andre; Sigman, Elliott; Chandra, Kumar; Trinh, Joseph; Soriano, Melissa; Navarro, Robert; Rogstad, Stephen; Goodhart, Charles; Proctor, Robert; Jourdan, Michael; Rayhrer, Benno

    2008-01-01

    A recently developed breadboard version of an advanced signal processor for arraying many antennas in NASA s Deep Space Network (DSN) can accept inputs in a 500-MHz-wide frequency band from six antennas. The next breadboard version is expected to accept inputs from 16 antennas, and a following developed version is expected to be designed according to an architecture that will be scalable to accept inputs from as many as 400 antennas. These and similar signal processors could also be used for combining multiple wide-band signals in non-DSN applications, including very-long-baseline interferometry and telecommunications. This signal processor performs functions of a wide-band FX correlator and a beam-forming signal combiner. [The term "FX" signifies that the digital samples of two given signals are fast Fourier transformed (F), then the fast Fourier transforms of the two signals are multiplied (X) prior to accumulation.] In this processor, the signals from the various antennas are broken up into channels in the frequency domain (see figure). In each frequency channel, the data from each antenna are correlated against the data from each other antenna; this is done for all antenna baselines (that is, for all antenna pairs). The results of the correlations are used to obtain calibration data to align the antenna signals in both phase and delay. Data from the various antenna frequency channels are also combined and calibration corrections are applied. The frequency-domain data thus combined are then synthesized back to the time domain for passing on to a telemetry receiver

  4. DIRECTIONAL ANTENNA

    DOEpatents

    Bittner, B.J.

    1958-05-20

    A high-frequency directional antenna of the 360 d scaring type is described. The antenna has for its desirable features the reduction in both size and complexity of the mechanism for rotating the antenna through its scanning movement. These advantages result from the rotation of only the driven element, the reflector remaining stationary. The particular antenna structure comprises a refiector formed by a plurality of metallic slats arranged in the configuration of an annular cage having the shape of a zone of revolution. The slats are parallel to each other and are disposed at an angle of 45 d to the axis of the cage. A directional radiator is disposed inside the cage at an angle of 45 d to the axis of the cage in the same direction as the reflecting slats which it faces. As the radiator is rotated, the electromagnetic wave is reflected from the slats facing the radiator and thereafter passes through the cage on the opposite side, since these slats are not parallel with the E vector of the wave.

  5. Simultaneous relative and absolute orientation of point clouds with "TLS radomes"

    NASA Astrophysics Data System (ADS)

    Glira, Philipp; Briese, Christian; Kamp, Nicole; Pfeifer, Norbert

    2013-04-01

    For the georeferencing of point clouds acquired by a terrestrial laser scanner (TLS) targets with known coordinates (control points) can be used. The determination of the target positions in a global coordinate frame with a total station and/or with GNSS can be very time-consuming. For multi-temporal comparison of TLS data these targets can be permanently installed on the measurement site. In permanent changing environments (e.g. high-moutain proglacial environments) this is not possible due to the movement of the targets. Furthermore, the integration of the TLS data with other data sources (e.g. airborne laser scanning data) has to be considered. For that aim the georeferencing of TLS measurements in a global coordinate frame has to be established. This work describes a new method for the simultaneous relative orientiation (registration) and absolute orientation (georeferencing) of point clouds by using spheres with a GNSS antenna inside. These spheres are thus used as GNSS antenna radomes. Consequently they are called within this work "TLS radomes". The simultaneous measurement with at least three GNSS antennas during the TLS data acquisition leads to long measurement times, i.e. high position accuracy and subsequently a very accurate realization of the datum. The presented TLS radomes consist of two hemispheres of polyethene enclosing the GNSS antenna. The GNSS antenna is mounted on an antenna rod, which can be enhanced by a prism and/or a reflective cylinder. For a modified optical reflectivity several coatings were tested. The one causing the smallest deformations, the smallest noise, and with the highest reflectivity was chosen. The whole construction can be mounted on a tripod. The TLS radomes are suitable for a wide range of different TLS sensors (i.e. independent of the ranging principle and the manufacturers). For the simultaneous relative and absolute orientation of the point clouds the centers of the radomes are used as identical points. With TLS these

  6. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2012-05-15

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  7. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2010-07-13

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  8. Improving HST Pointing & Absolute Astrometry

    NASA Astrophysics Data System (ADS)

    Lallo, Matthew; Nelan, E.; Kimmer, E.; Cox, C.; Casertano, S.

    2007-05-01

    Accurate absolute astrometry is becoming increasingly important in an era of multi-mission archives and virtual observatories. Hubble Space Telescope's (HST's) Guidestar Catalog II (GSC2) has reduced coordinate error to around 0.25 arcsecond, a factor 2 or more compared with GSC1. With this reduced catalog error, special attention must be given to calibrate and maintain the Fine Guidance Sensors (FGSs) and Science Instruments (SIs) alignments in HST to a level well below this in order to ensure that the accuracy of science product's astrometry keywords and target positioning are limited only by the catalog errors. After HST Servicing Mission 4, such calibrations' improvement in "blind" pointing accuracy will allow for more efficient COS acquisitions. Multiple SIs and FGSs each have their own footprints in the spatially shared HST focal plane. It is the small changes over time in primarily the whole-body positions & orientations of these instruments & guiders relative to one another that is addressed by this work. We describe the HST Cycle 15 program CAL/OTA 11021 which, along with future variants of it, determines and maintains positions and orientations of the SIs and FGSs to better than 50 milli- arcseconds and 0.04 to 0.004 degrees of roll, putting errors associated with the alignment sufficiently below GSC2 errors. We present recent alignment results and assess their errors, illustrate trends, and describe where and how the observer sees benefit from these calibrations when using HST.

  9. Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination

    SciTech Connect

    Scheller, Maik; Baaske, Kai; Koch, Martin

    2010-04-12

    We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2pi uncertainty known from conventional photomixing systems while preserving a high spatial resolution.

  10. Quantitative spectroscopy on individual wire, slot, bow-tie, rectangular, and square-shaped optical antennas.

    PubMed

    Husnik, Martin; Niegemann, Jens; Busch, Kurt; Wegener, Martin

    2013-11-15

    By using a recently introduced approach combining a focus-modulation technique with a common-path interferometer, we measure quantitatively the extinction, scattering, and absorption cross-section spectra of individual optical antennas. The experimental results on thin-wire antennas, slot antennas, bow-tie antennas, rectangular antennas, and square-shaped antennas resonating at around 1.4 μm wavelength are discussed. We find increased resonant scattering cross sections for the latter four antennas compared to the thin-wire antenna, both in absolute terms and relative to the absorption cross section. The square-shaped antenna's resonant extinction cross section approaches the limit of a coherent point dipole. However, the ratio of the resonant extinction cross section to the geometrical cross section of 38 is largest for the simple thin-wire antenna. PMID:24322083

  11. Calibration of the TOPEX altimeter using a GPS buoy

    NASA Technical Reports Server (NTRS)

    Born, G. H.; Parke, Michael E.; Axelrad, P.; Gold, K. L.; Johnson, James; Key, K.; Kubitschek, Daniel G.; Christensen, Edward J.

    1994-01-01

    The use of a spar buoy equipped with a Global Positioning System (GPS) antenna to calibrate the height measurement of the TOPEX radar altimeter is described. In order to determine the height of the GPS antenna phase center above the ocean surface, the buoy was also equipped with instrumentation to measure the instantaneous location of the waterline, and tilt of the bouy from vertical. The experiment was conducted off the California coast near the Texaco offshore oil platform, Harvest, during cycle 34 of the TOPEX/POSEIDON observational period. GPS solutions were computed for the bouy position using two different software packages, K&RS and GIPSY-OASIS II. These solutions were combined with estimates of the waterline location on the bouy to yield the height of the ocean surface. The ocean surface height in an absolute coordinate system combined with knowledge of the spacecraft height from tracking data provides a computed altimeter range measurement. By comparing this computed value to the actual altimeter measurement, the altimeter bias can be calibrated. The altimeter height bias obtained with the buoy using K&RS was -14.6 +/- 4 cm, while with GIPSY-OASIS II it was -13.1 +/- 4 cm. These are 0.1 cm and 1.6 cm different from the -14.7 +/- 4 cm result obtained for this flight overflight with the tide gauge instruments located on Platform Harvest.

  12. Astigmatism in reflector antennas.

    NASA Technical Reports Server (NTRS)

    Cogdell, J. R.; Davis, J. H.

    1973-01-01

    Astigmatic phase error in large parabolic reflector antennas is discussed. A procedure for focusing an antenna and diagnosing the presence and degree of astigmatism is described. Theoretical analysis is conducted to determine the nature of this error in such antennas.

  13. Extending the GPS satellite antenna patterns of the IGS to nadir angles beyond 14° using LEO data

    NASA Astrophysics Data System (ADS)

    Dach, R.; Jaeggi, A.; Bock, H.; Beutler, G.; Montenbruck, O.; Schmid, R.

    2010-12-01

    The absolute phase center model adopted by the International GNSS Service (IGS) in 2006 is based on robot calibrations for a number of terrestrial GNSS receiver antennas and consistent correction values for the GNSS transmitter antennas estimated from data of the global IGS tracking network. As the calibration of the satellite antennas is solely based on terrestrial measurements, the estimation of their phase patterns is limited to a nadir angle of 14°. This is not sufficient for the analysis of spaceborne GPS data collected by low Earth orbiting (LEO) satellites that record observations at nadir angles of up to 17°. Moreover, phase center variation (PCV) estimates for nadir angles close to 14° derived from terrestrial measurements might be affected by uncertainties in the troposphere modeling. This drawback could also be overcome by the use of LEO data. We use GPS tracking data from several LEO missions to extend the IGS satellite antenna patterns to nadir angles beyond 14°. In order to achieve estimates that are consistent with the PCVs currently used within the IGS, GPS and LEO orbits are fixed to solutions obtained by adopting the IGS conventional values. Due to significant near-field multipath effects in the LEO spacecraft environment, it is necessary to solve for GPS (nadir-dependent only) and LEO (azimuth- and elevation-dependent) antenna patterns simultaneously. We analyze the separability of these parameters and discuss appropriate constraints. We assess the contribution of different LEO missions to a combined solution and analyze the impact of LEO orbit modeling errors.

  14. Absolute biological needs.

    PubMed

    McLeod, Stephen

    2014-07-01

    Absolute needs (as against instrumental needs) are independent of the ends, goals and purposes of personal agents. Against the view that the only needs are instrumental needs, David Wiggins and Garrett Thomson have defended absolute needs on the grounds that the verb 'need' has instrumental and absolute senses. While remaining neutral about it, this article does not adopt that approach. Instead, it suggests that there are absolute biological needs. The absolute nature of these needs is defended by appeal to: their objectivity (as against mind-dependence); the universality of the phenomenon of needing across the plant and animal kingdoms; the impossibility that biological needs depend wholly upon the exercise of the abilities characteristic of personal agency; the contention that the possession of biological needs is prior to the possession of the abilities characteristic of personal agency. Finally, three philosophical usages of 'normative' are distinguished. On two of these, to describe a phenomenon or claim as 'normative' is to describe it as value-dependent. A description of a phenomenon or claim as 'normative' in the third sense does not entail such value-dependency, though it leaves open the possibility that value depends upon the phenomenon or upon the truth of the claim. It is argued that while survival needs (or claims about them) may well be normative in this third sense, they are normative in neither of the first two. Thus, the idea of absolute need is not inherently normative in either of the first two senses. PMID:23586876

  15. Adaptive antennas

    NASA Astrophysics Data System (ADS)

    Barton, P.

    1987-04-01

    The basic principles of adaptive antennas are outlined in terms of the Wiener-Hopf expression for maximizing signal to noise ratio in an arbitrary noise environment; the analogy with generalized matched filter theory provides a useful aid to understanding. For many applications, there is insufficient information to achieve the above solution and thus non-optimum constrained null steering algorithms are also described, together with a summary of methods for preventing wanted signals being nulled by the adaptive system. The three generic approaches to adaptive weight control are discussed; correlation steepest descent, weight perturbation and direct solutions based on sample matrix conversion. The tradeoffs between hardware complexity and performance in terms of null depth and convergence rate are outlined. The sidelobe cancellor technique is described. Performance variation with jammer power and angular distribution is summarized and the key performance limitations identified. The configuration and performance characteristics of both multiple beam and phase scan array antennas are covered, with a brief discussion of performance factors.

  16. Instrument calibration architecture of Radar Imaging Satellite (RISAT-1)

    NASA Astrophysics Data System (ADS)

    Misra, T.; Bhan, R.; Putrevu, D.; Mehrotra, P.; Nandy, P. S.; Shukla, S. D.; Rao, C. V. N.; Dave, D. B.; Desai, N. M.

    2016-05-01

    Radar Imaging Satellite (RISAT-1) payload system is configured to perform self-calibration of transmit and receive paths before and after imaging sessions through a special instrument calibration technique. Instrument calibration architecture of RISAT-1 supported ground verification and validation of payload including active array antenna. During on-ground validation of 126 beams of active array antenna which needed precise calibration of boresight pointing, a unique method called "collimation coefficient error estimation" was utilized. This method of antenna calibration was supported by special hardware and software calibration architecture of RISAT-1. This paper concentrates on RISAT-1 hardware and software architecture which supports in-orbit and on-ground instrument calibration. Efforts are also put here to highlight use of special calibration scheme of RISAT-1 instrument to evaluate system response during ground verification and validation.

  17. Mid-infrared absolute spectral responsivity scale based on an absolute cryogenic radiometer and an optical parametric oscillator laser

    NASA Astrophysics Data System (ADS)

    Zhao, Kun; Shi, Xueshun; Chen, Haidong; Liu, Yulong; Liu, Changming; Chen, Kunfeng; Li, Ligong; Gan, Haiyong; Ma, Chong

    2016-06-01

    We are reporting on a laser-based absolute spectral responsivity scale in the mid-infrared spectral range. By using a mid-infrared tunable optical parametric oscillator as the laser source, the absolute responsivity scale has been established by calibrating thin-film thermopile detectors against an absolute cryogenic radiometer. The thin-film thermopile detectors can be then used as transfer standard detectors. The extended uncertainty of the absolute spectral responsivity measurement has been analyzed to be 0.58%–0.68% (k  =  2).

  18. Computer controlled antenna system

    NASA Technical Reports Server (NTRS)

    Raumann, N. A.

    1972-01-01

    The application of small computers using digital techniques for operating the servo and control system of large antennas is discussed. The advantages of the system are described. The techniques were evaluated with a forty foot antenna and the Sigma V computer. Programs have been completed which drive the antenna directly without the need for a servo amplifier, antenna position programmer or a scan generator.

  19. Antenna radome sample test report

    NASA Astrophysics Data System (ADS)

    Baker, Leonard H.; Bratton, Thomas D.

    1991-01-01

    The antenna radome sample test conducted at the Federal Aviation Administration (FAA) Technical Center by the Secondary Surveillance Systems Branch, ACN-220 is documented. The test configuration consisted of the antenna radome sample centered between the Discrete Address Beacon System's (DABS) antenna and its remote Calibration Performance Monitor Equipment (CPME). The Range and Azimuth Accuracy (RAA) diagnostic program was used to determine changes in DABS performance. There were two test objectives. The first test objective was to determine if existing FAA en route radar antenna radomes would distort the signal characteristics detected by a beacon monopulse processor system. The second test objective was to determine whether this test configuration could be used to test radome samples supplied by prospective contractors in the en route radome replacement program. The RAA diagnostic program could not determine if the radome sample depicted changes in the DABS performance. It is recommended that this test procedure be abandoned due to inconclusive test results. The prospective radome manufacturers should provide the FAA with sufficient test data to confirm that it meets the requirements of the radome procurement specification.

  20. ARISE antenna

    NASA Astrophysics Data System (ADS)

    Chmielewski, Arthur B.; Noca, Muriel; Ulvestad, James

    2000-03-01

    Supermassive black holes are among the most spectacular objects in the Universe, and are laboratories for physics in extreme conditions. Understanding the physics of massive black holes and related phenomena is a primary goal of the ARISE mission. The scientific goals of the mission are described in detail on the ARISE web site http://arise.ipl.nasa.gov and in the ARISE Science Goals document. The following paper, as the title suggests, is not intended to be a comprehensive description of ARISE, but deals only with one aspect of the ARISE mission-the inflatable antenna which is the key element of the ARISE spacecraft. This spacecraft,due to the extensive reliance on inflatables, may be considered as the first generation Gossamer spacecraft

  1. Control of phased-array antennas

    NASA Astrophysics Data System (ADS)

    Samoilenko, V. I.; Shishov, Iu. A.

    Principles and algorithms for the control of phased arrays are described. Particular consideration is given to algorithms for the control of phase distribution, adaptive arrays, beam-steerable arrays, the design of phase shifters, the compensation of beam-pointing errors, and the calibration of high-gain antenna pointing.

  2. The absolute path command

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it canmore » provide the absolute path to a relative directory from the current working directory.« less

  3. The absolute path command

    SciTech Connect

    Moody, A.

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it can provide the absolute path to a relative directory from the current working directory.

  4. Automatic compensation of antenna beam roll-off in SAR images.

    SciTech Connect

    Doerry, Armin Walter

    2006-04-01

    The effects of a non-uniform antenna beam are sometimes visible in Synthetic Aperture Radar (SAR) images. This might be due to near-range operation, wide scenes, or inadequate antenna pointing accuracy. The effects can be mitigated in the SAR image by fitting very a simple model to the illumination profile and compensating the pixel brightness accordingly, in an automated fashion. This is accomplished without a detailed antenna pattern calibration, and allows for drift in the antenna beam alignments.

  5. A reconfigurable plasma antenna

    SciTech Connect

    Kumar, Rajneesh; Bora, Dhiraj

    2010-03-15

    An experiment aimed at investigating the antenna properties of different plasma structures of a plasma column as a reconfigurable plasma antenna, is reported. A 30 cm long plasma column is excited by surface wave, which acts as a plasma antenna. By changing the operating parameters, e.g., working pressure, drive frequency, input power, radius of glass tube, length of plasma column, and argon gas, single plasma antenna (plasma column) can be transformed to multiple small antenna elements (plasma blobs). It is also reported that number, length, and separation between two antenna elements can be controlled by operating parameters. Moreover, experiments are also carried out to study current profile, potential profile, conductivity profile, phase relations, radiation power patterns, etc. of the antenna elements. The effect on directivity with the number of antenna elements is also studied. Findings of the study indicate that entire structure of antenna elements can be treated as a phased array broadside vertical plasma antenna, which produces more directive radiation pattern than the single plasma antenna as well as physical properties and directivity of such antenna can be controlled by operating parameters. The study reveals the advantages of a plasma antenna over the conventional antenna in the sense that different antennas can be formed by tuning the operating parameters.

  6. Strategy for the absolute neutron emission measurement on ITER

    SciTech Connect

    Sasao, M.; Bertalot, L.; Ishikawa, M.; Popovichev, S.

    2010-10-15

    Accuracy of 10% is demanded to the absolute fusion measurement on ITER. To achieve this accuracy, a functional combination of several types of neutron measurement subsystem, cross calibration among them, and in situ calibration are needed. Neutron transport calculation shows the suitable calibration source is a DT/DD neutron generator of source strength higher than 10{sup 10} n/s (neutron/second) for DT and 10{sup 8} n/s for DD. It will take eight weeks at the minimum with this source to calibrate flux monitors, profile monitors, and the activation system.

  7. Precision standoff guidance antenna accuracy evaluation

    NASA Astrophysics Data System (ADS)

    Irons, F. H.; Landesberg, M. M.

    1981-02-01

    This report presents a summary of work done to determine the inherent angular accuracy achievable with the guidance and control precision standoff guidance antenna. The antenna is a critical element in the anti-jam single station guidance program since its characteristics can limit the intrinsic location guidance accuracy. It was important to determine the extent to which high ratio beamsplitting results could be achieved repeatedly and what issues were involved with calibrating the antenna. The antenna accuracy has been found to be on the order of 0.006 deg. through the use of a straightforward lookup table concept. This corresponds to a cross range error of 21 m at a range of 200 km. This figure includes both pointing errors and off-axis estimation errors. It was found that the antenna off-boresight calibration is adequately represented by a straight line for each position plus a lookup table for pointing errors relative to broadside. In the event recalibration is required, it was found that only 1% of the model would need to be corrected.

  8. Radiation calibration targets

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Several prominent features of Mars Pathfinder and surrounding terrain are seen in this image, taken by the Imager for Mars Pathfinder on July 4 (Sol 1), the spacecraft's first day on the Red Planet. Portions of a lander petal are at the lower part of the image. At the left, the mechanism for the high-gain antenna can be seen. The dark area along the right side of the image represents a portion of the low-gain antenna. The radiation calibration target is at the right. The calibration target is made up of a number of materials with well-characterized colors. The known colors of the calibration targets allow scientists to determine the true colors of the rocks and soils of Mars. Three bull's-eye rings provide a wide range of brightness for the camera, similar to a photographer's grayscale chart. In the middle of the bull's-eye is a 5-inch tall post that casts a shadow, which is distorted in this image due to its location with respect to the lander camera.

    A large rock is located at the near center of the image. Smaller rocks and areas of soil are strewn across the Martian terrain up to the horizon line.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C.

  9. Absolute dosimetry for extreme-ultraviolet lithography

    NASA Astrophysics Data System (ADS)

    Berger, Kurt W.; Campiotti, Richard H.

    2000-06-01

    The accurate measurement of an exposure dose reaching the wafer on an extreme ultraviolet (EUV) lithographic system has been a technical challenge directly applicable to the evaluation of candidate EUV resist materials and calculating lithography system throughputs. We have developed a dose monitoring sensor system that can directly measure EUV intensities at the wafer plane of a prototype EUV lithographic system. This sensor system, located on the wafer stage adjacent to the electrostatic chuck used to grip wafers, operates by translating the sensor into the aerial image, typically illuminating an 'open' (unpatterned) area on the reticle. The absolute signal strength can be related to energy density at the wafer, and thus used to determine resist sensitivity, and the signal as a function of position can be used to determine illumination uniformity at the wafer plane. Spectral filtering to enhance the detection of 13.4 nm radiation was incorporated into the sensor. Other critical design parameters include the packaging and amplification technologies required to place this device into the space and vacuum constraints of a EUV lithography environment. We describe two approaches used to determine the absolute calibration of this sensor. The first conventional approach requires separate characterization of each element of the sensor. A second novel approach uses x-ray emission from a mildly radioactive iron source to calibrate the absolute response of the entire sensor system (detector and electronics) in a single measurement.

  10. The LED calibration system of the SPHERE-2 detector

    NASA Astrophysics Data System (ADS)

    Antonov, R. A.; Bonvech, E. A.; Chernov, D. V.; Podgrudkov, D. A.; Roganova, T. M.

    2016-04-01

    An absolute calibration method for the PMT mosaic used in the SPHERE-2 experiment is presented. The method is based on the relative calibration of all PMTs in the mosaic to a single stable PMT, incorporated in it, during each measurement event and subsequent absolute calibration of that single PMT using a known stable light source. The results of the SPHERE-2 detector PMTs calibration are presented and are discussed.

  11. JPL antenna technology development

    NASA Technical Reports Server (NTRS)

    Freeland, R. E.

    1982-01-01

    Systems-level technology for evolving cost-effective, STS compatible antennas that will be automatically deployed in orbit to perform a variety of missions in the 1985 to 2000 time period is discussed. For large space-based antenna systems, the LSST program has selected deployable antennas for development. The maturity of this class of antenna, demonstrated by the success of smaller size apertures, provides a potential capability for satisfying a significant number of near-term, space-based applications. The offset wrap-rib concept development is the basis of the JPL LSST antenna technology development program. Supporting technology to the antenna concept development include analytical performance prediction, the capability for measuring and evaluating mechanical antenna performance in the intended service environment, and the development of candidate system-level configurations for potential applications utilizing the offset wrap-rib antenna concept.

  12. Prototype microprocessor controller. [for STDN antennas

    NASA Technical Reports Server (NTRS)

    Zarur, J.; Kraeuter, R.

    1980-01-01

    A microcomputer controller for STDN antennas was developed. The microcomputer technology reduces the system's physical size by the implementation in firmware of functions. The reduction in the number of components increases system reliability and similar benefit is derived when a graphic video display is substituted for several control and indicator panels. A substantial reduction in the number of cables, connectors, and mechanical switches is achieved. The microcomputer based system is programmed to perform calibration and diagnostics, to update the satellite orbital vector, and to communicate with other network systems. The design is applicable to antennas and lasers.

  13. Photometer calibration error using extended standard sources

    NASA Technical Reports Server (NTRS)

    Torr, M. R.; Hays, P. B.; Kennedy, B. C.; Torr, D. G.

    1976-01-01

    As part of a project to compare measurements of the night airglow made by the visible airglow experiment on the Atmospheric Explorer-C satellite, the standard light sources of several airglow observatories were compared with the standard source used in the absolute calibration of the satellite photometer. In the course of the comparison, it has been found that serious calibration errors (up to a factor of two) can arise when a calibration source with a reflecting surface is placed close to an interference filter. For reliable absolute calibration, the source should be located at a distance of at least five filter radii from the interference filter.

  14. Antenna and radome loss measurements for MFMR and PMIS with appendix on MFMR/PMIS computer programs

    NASA Technical Reports Server (NTRS)

    Carver, K. R.; Cooper, W. K.

    1975-01-01

    The NMSU/PSL radiometer antenna calibration facility is described, and the antenna and radome loss measurements made on the passive microwave imaging system and the multifrequency microwave radiometer are summarized. Antenna/radome data reduction techniques, estimation of sky brightness temperatures, and bucket performance tests are presented along with radiometer computer programs.

  15. Calibration and Validation of Third Stokes Parameter Measurements of SMOS Zero-Baseline Radiometers

    NASA Astrophysics Data System (ADS)

    Chae, C.; Kainulainen, J.; Colliander, A.

    2012-12-01

    SMOS (Soil Moisture Ocean Salinity) zero-baseline radiometers provide absolute brightness temperature reference for SMOS images. Thus, accurate calibration of the zero-baseline radiometers is of great importance for the quality of SMOS data. The primary utility of the third Stokes parameter at L-band is to estimate the Faraday rotation caused by the Earth's ionosphere which affects the balance of vertical and horizontal brightness temperatures. In this presentation a calibration and validation approach to improve the accuracy of the of the third Stokes parameter measurement of the SMOS zero-baselines is described. The approach relies on modeling of the third Stokes parameter over non-uniform scenes (e.g. sea-land boundaries) over antenna Field of View (FOV) to establish reference scenes for calibration. The basis of the method is the fact that the non-uniform scenes which are asymmetrical about the along-track direction within the FOV invoke the third Stokes parameter as a result of the integration over the antenna pattern. The FOV of the zero-baselines is very large and therefore this effect is significant (on the order of 10 K). The surface brightness temperature for vertical and horizontal polarization is acquired from the SMOS images instead of surface emission models to initiate the model with as realistic brightness temperature distribution as possible. These measurements can be used since the critical information for the calibration approach is the geometric distribution of the brightness temperature within the FOV instead of the very accurate knowledge of the brightness temperature magnitude (i.e. features in the measurement of vertical and horizontal polarization will not propagate back to reference). Three additional sources which contribute to the modeling of the third Stokes parameter are studied. First, the knowledge of the antenna pattern shape over the non-uniform scenes; second, the unpolarized atmospheric attenuation and upwelling brightness

  16. Antenna development at DARPA

    NASA Astrophysics Data System (ADS)

    Corey, Larry; Jaska, Esko

    2004-09-01

    This paper reviews recent and ongoing antenna technology and systems development in the Special Projects Office of the Defense Advanced Research Projects Agency (DARPA/SPO). These programs fall into two categories: development and application of antenna component technologies and development of transportable phased-array radar antennas. These development programs are presented in a chronological order.

  17. Space-communications antennas

    NASA Astrophysics Data System (ADS)

    Kozyrev, Nikolai D.

    This textbook examines the design principles, requirements, and technical characteristics of earth-station and space-station antennas. Methods for realizing high gain and low noise temperature are examined along with ways to enhance antenna performance. Particular attention is given to the antenna-feed sections of earth stations.

  18. Coherently combining antennas

    NASA Technical Reports Server (NTRS)

    Dybdal, Robert B. (Inventor); Curry, Samuel J. (Inventor)

    2009-01-01

    An apparatus includes antenna elements configured to receive a signal including pseudo-random code, and electronics configured to use the pseudo-random code to determine time delays of signals incident upon the antenna elements and to compensate the signals to coherently combine the antenna elements.

  19. Electronic Absolute Cartesian Autocollimator

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.

    2006-01-01

    An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the

  20. Testing the quasi-absolute method in photon activation analysis

    SciTech Connect

    Sun, Z. J.; Wells, D.; Starovoitova, V.; Segebade, C.

    2013-04-19

    In photon activation analysis (PAA), relative methods are widely used because of their accuracy and precision. Absolute methods, which are conducted without any assistance from calibration materials, are seldom applied for the difficulty in obtaining photon flux in measurements. This research is an attempt to perform a new absolute approach in PAA - quasi-absolute method - by retrieving photon flux in the sample through Monte Carlo simulation. With simulated photon flux and database of experimental cross sections, it is possible to calculate the concentration of target elements in the sample directly. The QA/QC procedures to solidify the research are discussed in detail. Our results show that the accuracy of the method for certain elements is close to a useful level in practice. Furthermore, the future results from the quasi-absolute method can also serve as a validation technique for experimental data on cross sections. The quasi-absolute method looks promising.

  1. ABSOLUTE POLARIMETRY AT RHIC.

    SciTech Connect

    OKADA; BRAVAR, A.; BUNCE, G.; GILL, R.; HUANG, H.; MAKDISI, Y.; NASS, A.; WOOD, J.; ZELENSKI, Z.; ET AL.

    2007-09-10

    Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy Of {Delta}P{sub beam}/P{sub beam} < 5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {Delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of AN in the CNI region (four-momentum transfer squared 0.001 < -t < 0.032 (GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

  2. Automatic beamline calibration procedures

    SciTech Connect

    Corbett, W.J.; Lee, M.J.; Zambre, Y.

    1992-03-01

    Recent experience with the SLC and SPEAR accelerators have led to a well-defined set of procedures for calibration of the beamline model using the orbit fitting program, RESOLVE. Difference orbit analysis is used to calibrate quadrupole strengths, BPM sensitivities, corrector strengths, focusing effects from insertion devices, and to determine the source of dispersion and coupling errors. Absolute orbit analysis is used to locate quadrupole misalignments, BPM offsets, or beam loss. For light source applications, the photon beam source coordinates can be found. The result is an accurate model of the accelerator which can be used for machine control. In this paper, automatable beamline calibration procedures are outlined and illustrated with recent examples. 5 refs.

  3. Characterization of the DARA solar absolute radiometer

    NASA Astrophysics Data System (ADS)

    Finsterle, W.; Suter, M.; Fehlmann, A.; Kopp, G.

    2011-12-01

    The Davos Absolute Radiometer (DARA) prototype is an Electrical Substitution Radiometer (ESR) which has been developed as a successor of the PMO6 type on future space missions and ground based TSI measurements. The DARA implements an improved thermal design of the cavity detector and heat sink assembly to minimize air-vacuum differences and to maximize thermal symmetry of measuring and compensating cavity. The DARA also employs an inverted viewing geometry to reduce internal stray light. We will report on the characterization and calibration experiments which were carried out at PMOD/WRC and LASP (TRF).

  4. Uplink Array Calibration via Far-Field Power Maximization

    NASA Technical Reports Server (NTRS)

    Vilnrotter, V.; Mukai, R.; Lee, D.

    2006-01-01

    Uplink antenna arrays have the potential to greatly increase the Deep Space Network s high-data-rate uplink capabilities as well as useful range, and to provide additional uplink signal power during critical spacecraft emergencies. While techniques for calibrating an array of receive antennas have been addressed previously, proven concepts for uplink array calibration have yet to be demonstrated. This article describes a method of utilizing the Moon as a natural far-field reflector for calibrating a phased array of uplink antennas. Using this calibration technique, the radio frequency carriers transmitted by each antenna of the array are optimally phased to ensure that the uplink power received by the spacecraft is maximized.

  5. Swarm's Absolute Scalar Magnetometer metrological performances

    NASA Astrophysics Data System (ADS)

    Leger, J.; Fratter, I.; Bertrand, F.; Jager, T.; Morales, S.

    2012-12-01

    The Absolute Scalar Magnetometer (ASM) has been developed for the ESA Earth Observation Swarm mission, planned for launch in November 2012. As its Overhauser magnetometers forerunners flown on Oersted and Champ satellites, it will deliver high resolution scalar measurements for the in-flight calibration of the Vector Field Magnetometer manufactured by the Danish Technical University. Latest results of the ground tests carried out to fully characterize all parameters that may affect its accuracy, both at instrument and satellite level, will be presented. In addition to its baseline function, the ASM can be operated either at a much higher sampling rate (burst mode at 250 Hz) or in a dual mode where it also delivers vector field measurements as a by-product. The calibration procedure and the relevant vector performances will be discussed.

  6. JPL antenna technology development

    NASA Technical Reports Server (NTRS)

    Freeland, R. E.

    1981-01-01

    Plans for evaluating, designing, fabricating, transporting and deploying cost effective and STS compatible offset wrap rib antennas up to 300 meters in diameter for mobile communications, Earth resources observation, and for the orbiting VLBI are reviewed. The JPL surface measurement system, intended for large mesh deployable antenna applications will be demonstrated and validated as part of the antenna ground based demonstration program. Results of the offset wrap rib deployable antenna technology development will include: (1) high confidence structural designs for antennas up to 100 meters in diameter; (2) high confidence estimates of functional performance and fabrication cost for a wide range of antenna sizes (up to 300 meters in diameter); (3) risk assessment for fabricating the large size antennas; and (4) 55 meter diameter flight quality hardware that can be cost effectively completed toto accommodate a flight experiment and/or application.

  7. L-Band Transmit/Receive Module for Phase-Stable Array Antennas

    NASA Technical Reports Server (NTRS)

    Andricos, Constantine; Edelstein, Wendy; Krimskiy, Vladimir

    2008-01-01

    Interferometric synthetic aperture radar (InSAR) has been shown to provide very sensitive measurements of surface deformation and displacement on the order of 1 cm. Future systematic measurements of surface deformation will require this capability over very large areas (300 km) from space. To achieve these required accuracies, these spaceborne sensors must exhibit low temporal decorrelation and be temporally stable systems. An L-band (24-cmwavelength) InSAR instrument using an electronically steerable radar antenna is suited to meet these needs. In order to achieve the 1-cm displacement accuracy, the phased array antenna requires phase-stable transmit/receive (T/R) modules. The T/R module operates at L-band (1.24 GHz) and has less than 1- deg absolute phase stability and less than 0.1-dB absolute amplitude stability over temperature. The T/R module is also high power (30 W) and power efficient (60-percent overall efficiency). The design is currently implemented using discrete components and surface mount technology. The basic T/R module architecture is augmented with a calibration loop to compensate for temperature variations, component variations, and path loss variations as a function of beam settings. The calibration circuit consists of an amplitude and phase detector, and other control circuitry, to compare the measured gain and phase to a reference signal and uses this signal to control a precision analog phase shifter and analog attenuator. An architecture was developed to allow for the module to be bidirectional, to operate in both transmit and receive mode. The architecture also includes a power detector used to maintain a transmitter power output constant within 0.1 dB. The use of a simple, stable, low-cost, and high-accuracy gain and phase detector made by Analog Devices (AD8302), combined with a very-high efficiency T/R module, is novel. While a self-calibrating T/R module capability has been sought for years, a practical and cost-effective solution has

  8. Antenna Controller Replacement Software

    NASA Technical Reports Server (NTRS)

    Chao, Roger Y.; Morgan, Scott C.; Strain, Martha M.; Rockwell, Stephen T.; Shimizu, Kenneth J.; Tehrani, Barzia J.; Kwok, Jaclyn H.; Tuazon-Wong, Michelle; Valtier, Henry; Nalbandi, Reza; Wert, Michael; Leung, Patrick

    2010-01-01

    The Antenna Controller Replacement (ACR) software accurately points and monitors the Deep Space Network (DSN) 70-m and 34-m high-efficiency (HEF) ground-based antennas that are used to track primarily spacecraft and, periodically, celestial targets. To track a spacecraft, or other targets, the antenna must be accurately pointed at the spacecraft, which can be very far away with very weak signals. ACR s conical scanning capability collects the signal in a circular pattern around the target, calculates the location of the strongest signal, and adjusts the antenna pointing to point directly at the spacecraft. A real-time, closed-loop servo control algorithm performed every 0.02 second allows accurate positioning of the antenna in order to track these distant spacecraft. Additionally, this advanced servo control algorithm provides better antenna pointing performance in windy conditions. The ACR software provides high-level commands that provide a very easy user interface for the DSN operator. The operator only needs to enter two commands to start the antenna and subreflector, and Master Equatorial tracking. The most accurate antenna pointing is accomplished by aligning the antenna to the Master Equatorial, which because of its small size and sheltered location, has the most stable pointing. The antenna has hundreds of digital and analog monitor points. The ACR software provides compact displays to summarize the status of the antenna, subreflector, and the Master Equatorial. The ACR software has two major functions. First, it performs all of the steps required to accurately point the antenna (and subreflector and Master Equatorial) at the spacecraft (or celestial target). This involves controlling the antenna/ subreflector/Master-Equatorial hardware, initiating and monitoring the correct sequence of operations, calculating the position of the spacecraft relative to the antenna, executing the real-time servo control algorithm to maintain the correct position, and

  9. Implants as absolute anchorage.

    PubMed

    Rungcharassaeng, Kitichai; Kan, Joseph Y K; Caruso, Joseph M

    2005-11-01

    Anchorage control is essential for successful orthodontic treatment. Each tooth has its own anchorage potential as well as propensity to move when force is applied. When teeth are used as anchorage, the untoward movements of the anchoring units may result in the prolonged treatment time, and unpredictable or less-than-ideal outcome. To maximize tooth-related anchorage, techniques such as differential torque, placing roots into the cortex of the bone, the use of various intraoral devices and/or extraoral appliances have been implemented. Implants, as they are in direct contact with bone, do not possess a periodontal ligament. As a result, they do not move when orthodontic/orthopedic force is applied, and therefore can be used as "absolute anchorage." This article describes different types of implants that have been used as orthodontic anchorage. Their clinical applications and limitations are also discussed. PMID:16463910

  10. Absolute Equilibrium Entropy

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1997-01-01

    The entropy associated with absolute equilibrium ensemble theories of ideal, homogeneous, fluid and magneto-fluid turbulence is discussed and the three-dimensional fluid case is examined in detail. A sigma-function is defined, whose minimum value with respect to global parameters is the entropy. A comparison is made between the use of global functions sigma and phase functions H (associated with the development of various H-theorems of ideal turbulence). It is shown that the two approaches are complimentary though conceptually different: H-theorems show that an isolated system tends to equilibrium while sigma-functions allow the demonstration that entropy never decreases when two previously isolated systems are combined. This provides a more complete picture of entropy in the statistical mechanics of ideal fluids.

  11. Antenna testing for the Inmarsat 2 ground control system

    NASA Astrophysics Data System (ADS)

    Ashton, C.

    1992-02-01

    This article describes how the antennas of the Inmarsat 2 TT&C and IOT ground stations were tested and calibrated. It explains the main test methods used, giving the theory behind the tests and indicates some of the practical difficulties encountered during testing. Techniques described include the use of radio stars, boresight antennas and satellite verification testing using Intelsat and Inmarsat satellites. Parameters tested include gain, G/T (figure of merit), sidelobe patterns, cross polar discrimination and isolation.

  12. Real-Time Estimation Of Aiming Error Of Spinning Antenna

    NASA Technical Reports Server (NTRS)

    Dolinsky, Shlomo

    1992-01-01

    Spinning-spacecraft dynamics and amplitude variations in communications links studied from received-signal fluctuations. Mathematical model and associated analysis procedure provide real-time estimates of aiming error of remote rotating transmitting antenna radiating constant power in narrow, pencillike beam from spinning platform, and current amplitude of received signal. Estimates useful in analyzing and enhancing calibration of communication system, and in analyzing complicated dynamic effects in spinning platform and antenna-aiming mechanism.

  13. Synthesis of a large communications aperture using small antennas

    NASA Technical Reports Server (NTRS)

    Resch, George M.; Cwik, T. W.; Jamnejad, V.; Logan, R. T.; Miller, R. B.; Rogstad, Dave H.

    1994-01-01

    In this report we compare the cost of an array of small antennas to that of a single large antenna assuming both the array and single large antenna have equal performance and availability. The single large antenna is taken to be one of the 70-m antennas of the Deep Space Network. The cost of the array is estimated as a function of the array element diameter for three different values of system noise temperature corresponding to three different packaging schemes for the first amplifier. Array elements are taken to be fully steerable paraboloids and their cost estimates were obtained from commercial vendors. Array loss mechanisms and calibration problems are discussed. For array elements in the range 3 - 35 m there is no minimum in the cost versus diameter curve for the three system temperatures that were studied.

  14. Techniques of absolute low energy x-ray calibration

    SciTech Connect

    Day, R.H.

    1986-01-01

    Recent advances in pulsed plasma research, materials science, and astrophysics have required many new diagnostic instruments for use in the low energy x-ray regime. The characterization of these instruments has provided a challenge to instrument designers and provided the momentum to improve x-ray sources and dosimetry techniques. In this paper, the present state-of-the-art in low energy x-ray characterization techniques is reviewed. A summary is given of low energy x-ray generator technology and dosimetry techniques including a discussion of thin window proportional counters and ionization chambers. A review is included of the widely used x-ray data bases and a sample of ultrasoft x-ray measuring procedures, chopped x-ray source generators, phase sensitive detection of ultralow currents, and angular divergence measurements.

  15. Improved cavity-type absolute total-radiation radiometer

    NASA Technical Reports Server (NTRS)

    Kendall, J. M., Sr.; Plamondon, J. A., Jr.

    1967-01-01

    Conical cavity-type absolute radiometer measures the intensity of radiant energy to an accuracy of one to two percent in a vacuum of ten to the minus fifth torr or lower. There is a uniform response over the ultraviolet, visible, and infrared range, and it requires no calibration or comparison with a radiation standard.

  16. LOFAR Facet Calibration

    NASA Astrophysics Data System (ADS)

    van Weeren, R. J.; Williams, W. L.; Hardcastle, M. J.; Shimwell, T. W.; Rafferty, D. A.; Sabater, J.; Heald, G.; Sridhar, S. S.; Dijkema, T. J.; Brunetti, G.; Brüggen, M.; Andrade-Santos, F.; Ogrean, G. A.; Röttgering, H. J. A.; Dawson, W. A.; Forman, W. R.; de Gasperin, F.; Jones, C.; Miley, G. K.; Rudnick, L.; Sarazin, C. L.; Bonafede, A.; Best, P. N.; Bîrzan, L.; Cassano, R.; Chyży, K. T.; Croston, J. H.; Ensslin, T.; Ferrari, C.; Hoeft, M.; Horellou, C.; Jarvis, M. J.; Kraft, R. P.; Mevius, M.; Intema, H. T.; Murray, S. S.; Orrú, E.; Pizzo, R.; Simionescu, A.; Stroe, A.; van der Tol, S.; White, G. J.

    2016-03-01

    LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At the same time LOFAR also provides excellent short baseline coverage to map diffuse extended emission. However, producing high-quality deep images is challenging due to the presence of direction-dependent calibration errors, caused by imperfect knowledge of the station beam shapes and the ionosphere. Furthermore, the large data volume and presence of station clock errors present additional difficulties. In this paper we present a new calibration scheme, which we name facet calibration, to obtain deep high-resolution LOFAR High Band Antenna images using the Dutch part of the array. This scheme solves and corrects the direction-dependent errors in a number of facets that cover the observed field of view. Facet calibration provides close to thermal noise limited images for a typical 8 hr observing run at ∼ 5\\prime\\prime resolution, meeting the specifications of the LOFAR Tier-1 northern survey.

  17. Absolute Spectrophotometry of 237 Open Cluster Stars

    NASA Astrophysics Data System (ADS)

    Clampitt, L.; Burstein, D.

    1994-12-01

    We present absolute spectrophotometry of 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M 39. The observations were taken using the Wampler single-channel scanner (Wampler 1966) on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. 21 bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwiths ranging from 32Angstroms to 64 Angstroms. Data are standardized to the Hayes--Latham (1975) system. Our measurements are compared to filter colors on the Johnson BV, Stromgren ubvy, and Geneva U V B_1 B_2 V_1 G systems, as well as to spectrophotometry of a few stars published by Gunn, Stryker & Tinsley and in the Spectrophotometric Standards Catalog (Adelman; as distributed by the NSSDC). Both internal and external comparisons to the filter systems indicate a formal statistical accuracy per bandpass of 0.01 to 0.02 mag, with apparent larger ( ~ 0.03 mag) differences in absolute calibration between this data set and existing spectrophotometry. These data will comprise part of the spectrophotometry that will be used to calibrate the Beijing-Arizona-Taipei-Connecticut Color Survey of the Sky (see separate paper by Burstein et al. at this meeting).

  18. Method for calibration of plutonium NDA

    SciTech Connect

    Lemming, J.F.; Campbell, A.R.; Rodenburg, W.W.

    1980-01-01

    Calibration materials characterized by calorimetric assay can be a practical alternative to synthetic standards for the calibration of plutonium nondestructive assay. Calorimetric assay is an effective measurement system for the characterization because: it can give an absolute assay from first principles when the isotopic composition is known, it is insensitive to most matrix effects, and its traceability to international measurement systems has been demonstrated.

  19. Absolute cavity pyrgeometer

    DOEpatents

    Reda, Ibrahim

    2013-10-29

    Implementations of the present disclosure involve an apparatus and method to measure the long-wave irradiance of the atmosphere or long-wave source. The apparatus may involve a thermopile, a concentrator and temperature controller. The incoming long-wave irradiance may be reflected from the concentrator to a thermopile receiver located at the bottom of the concentrator to receive the reflected long-wave irradiance. In addition, the thermopile may be thermally connected to a temperature controller to control the device temperature. Through use of the apparatus, the long-wave irradiance of the atmosphere may be calculated from several measurements provided by the apparatus. In addition, the apparatus may provide an international standard of pyrgeometers' calibration that is traceable back to the International System of Units (SI) rather than to a blackbody atmospheric simulator.

  20. A True Metasurface Antenna

    PubMed Central

    Badawe, Mohamed El; Almoneef, Thamer S.; Ramahi, Omar M.

    2016-01-01

    We present a true metasurface antenna based on electrically-small resonators. The resonators are placed on a flat surface and connected to one feed point using corporate feed. Unlike conventional array antennas where the distance between adjacent antennas is half wavelength to reduce mutual coupling between adjacent antennas, here the distance between the radiating elements is electrically very small to affect good impedance matching of each resonator to its feed. A metasurface antenna measuring 1.2λ × 1.2λ and designed to operate at 3 GHz achieved a gain of 12 dBi. A prototype was fabricated and tested showing good agreement between numerical simulations and experimental results. Through numerical simulation, we show that the metasurface antenna has the ability to provide beam steering by phasing all the resonators appropriately. PMID:26759177

  1. A True Metasurface Antenna.

    PubMed

    El Badawe, Mohamed; Almoneef, Thamer S; Ramahi, Omar M

    2016-01-01

    We present a true metasurface antenna based on electrically-small resonators. The resonators are placed on a flat surface and connected to one feed point using corporate feed. Unlike conventional array antennas where the distance between adjacent antennas is half wavelength to reduce mutual coupling between adjacent antennas, here the distance between the radiating elements is electrically very small to affect good impedance matching of each resonator to its feed. A metasurface antenna measuring 1.2λ × 1.2λ and designed to operate at 3 GHz achieved a gain of 12 dBi. A prototype was fabricated and tested showing good agreement between numerical simulations and experimental results. Through numerical simulation, we show that the metasurface antenna has the ability to provide beam steering by phasing all the resonators appropriately. PMID:26759177

  2. A True Metasurface Antenna

    NASA Astrophysics Data System (ADS)

    Badawe, Mohamed El; Almoneef, Thamer S.; Ramahi, Omar M.

    2016-01-01

    We present a true metasurface antenna based on electrically-small resonators. The resonators are placed on a flat surface and connected to one feed point using corporate feed. Unlike conventional array antennas where the distance between adjacent antennas is half wavelength to reduce mutual coupling between adjacent antennas, here the distance between the radiating elements is electrically very small to affect good impedance matching of each resonator to its feed. A metasurface antenna measuring 1.2λ × 1.2λ and designed to operate at 3 GHz achieved a gain of 12 dBi. A prototype was fabricated and tested showing good agreement between numerical simulations and experimental results. Through numerical simulation, we show that the metasurface antenna has the ability to provide beam steering by phasing all the resonators appropriately.

  3. STIS Calibration Pipeline

    NASA Astrophysics Data System (ADS)

    Hulbert, S.; Hodge, P.; Lindler, D.; Shaw, R.; Goudfrooij, P.; Katsanis, R.; Keener, S.; McGrath, M.; Bohlin, R.; Baum, S.

    1997-05-01

    Routine calibration of STIS observations in the HST data pipeline is performed by the CALSTIS task. CALSTIS can: subtract the over-scan region and a bias image from CCD observations; remove cosmic ray features from CCD observations; correct global nonlinearities for MAMA observations; subtract a dark image; and, apply flat field corrections. In the case of spectral data, CALSTIS can also: assign a wavelength to each pixel; apply a heliocentric correction to the wavelengths; convert counts to absolute flux; process the automatically generated spectral calibration lamp observations to improve the wavelength solution; rectify two-dimensional (longslit) spectra; subtract interorder and sky background; and, extract one-dimensional spectra. CALSTIS differs in significant ways from the current HST calibration tasks. The new code is written in ANSI C and makes use of a new C interface to IRAF. The input data, reference data, and output calibrated data are all in FITS format, using IMAGE or BINTABLE extensions. Error estimates are computed and include contributions from the reference images. The entire calibration can be performed by one task, but many steps can also be performed individually.

  4. Absolute neutrino mass measurements

    NASA Astrophysics Data System (ADS)

    Wolf, Joachim

    2011-10-01

    The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2β) searches, single β-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy. Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium β-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope (137Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R&D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2β decay and single β-decay.

  5. Absolute neutrino mass measurements

    SciTech Connect

    Wolf, Joachim

    2011-10-06

    The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2{beta}) searches, single {beta}-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy.Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium {beta}-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope ({sup 137}Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R and D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2{beta} decay and single {beta}-decay.

  6. Phased array antenna control

    NASA Technical Reports Server (NTRS)

    Doland, G. D. (Inventor)

    1978-01-01

    Several new and useful improvements in steering and control of phased array antennas having a small number of elements, typically on the order of 5 to 17 elements are provided. Among the improvements are increasing the number of beam steering positions, reducing the possibility of phase transients in signals received or transmitted with the antennas, and increasing control and testing capacity with respect to the antennas.

  7. Tunable circular patch antennas

    NASA Astrophysics Data System (ADS)

    Lan, G.-L.; Sengupta, D. L.

    1985-10-01

    A method to control the resonant or operating frequencies of circular patch antennas has been investigated experimentally and theoretically. It consists of the placement of passive metallic or tuning posts at approximate locations within the input region of the antenna. Comparison of measured and analytical results seems to establish the validity of a theoretical model proposed to determine the input performance of such circular patch antennas.

  8. Precise frequency calibration using television video carriers

    NASA Technical Reports Server (NTRS)

    Burkhardt, Edward E.

    1990-01-01

    The availability of inexpensive and quick precise frequency calibration methods is limited. VLF and GPS do offer precise calibration. However, antenna placement, cost of equipment, and calibration time place many restrictions on the user. The USNO maintained line-10 television Time of Coincidence (TOC) of station WTTG, channel 5, Washington, DC requires a frequency stable video carrier. This video carrier, 77.24 MHz is controlled by the same cesium beam standard controlling the TOC of line-10. Excellent frequency comparisons against this video carrier have been accomplished at 95 miles (153 km). With stable propagation and a three foot wire antenna, a part in 10(exp 9) can be determined in a few minutes. Inexpensive field equipment with a synthesized 1 kHz offset from the video carrier offers parts in 10(exp 11) calibrations in a few minutes using an oscilloscope as a phase comparator.

  9. Turnstile slot antenna

    NASA Technical Reports Server (NTRS)

    Munson, R. E. (Inventor)

    1974-01-01

    A turnstile slot antenna is disclosed, the antenna being for and integral with a spacecraft having a substantially cylindrical body portion. The antenna comprises a circumferential slot about the periphery of the spacecraft body portion with an annular wave guide cavity defining a radial transmission line disposed within the spacecraft body portion behind and in communication with the circumferential slot. Feed stubs and associated transmission apparatus are provided to excite the annular cavity in quadrature phase such that an omnidirectional, circularly polarized, rotating radiation pattern is generated. The antenna of the instant invention has utility both as a transmitting and receiving device, and ensures continuous telemetry and command coverage with the spacecraft.

  10. Antennas for diverse requirements

    NASA Astrophysics Data System (ADS)

    Boukamp, Joachim

    An account is given of a major German aerospace manufacturer's state-of-the-art methods for development, design, construction, testing and certification of a wide variety of civilian and military communications and radar antennas. Attention is given to reflector antennas for very large aperture/wavelength ratios, slotted waveguide arrays in which the radiating aperture is synthesized by guided structures, and both microstrip arrays and active arrays, for the creation of very large area antennas. Antenna tests and measurements are conducted in an anechoic chamber.

  11. The single antenna interferometer

    SciTech Connect

    Fitch, J.P.

    1990-01-15

    Air and space borne platforms using synthetic aperture radars (SAR) have made interferometric measurements by using either two physical antennas mounted on one air-frame or two passes of one antenna over a scene. In this paper, a new interferometric technique using one pass of a single-antenna SAR system is proposed and demonstrated on data collected by the NASA-JPL AirSAR. Remotely sensed L-band microwave data are used to show the sensitivity of this technique to ocean surface features as well as a baseline for comparison with work by others using two-antenna systems. 7 refs., 3 figs.

  12. MASTER TELEVISION ANTENNA SYSTEM.

    ERIC Educational Resources Information Center

    Rhode Island State Dept. of Education, Providence.

    SPECIFICATIONS FOR THE FURNISHING AND INSTALLATION OF TELEVISION MASTER ANTENNA SYSTEMS FOR SECONDARY AND ELEMENTARY SCHOOLS ARE GIVEN. CONTRACTOR REQUIREMENTS, EQUIPMENT, PERFORMANCE STANDARDS, AND FUNCTIONS ARE DESCRIBED. (MS)

  13. Cellular Reflectarray Antenna

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.

    2010-01-01

    The cellular reflectarray antenna is intended to replace conventional parabolic reflectors that must be physically aligned with a particular satellite in geostationary orbit. These arrays are designed for specified geographical locations, defined by latitude and longitude, each called a "cell." A particular cell occupies nominally 1,500 square miles (3,885 sq. km), but this varies according to latitude and longitude. The cellular reflectarray antenna designed for a particular cell is simply positioned to align with magnetic North, and the antenna surface is level (parallel to the ground). A given cellular reflectarray antenna will not operate in any other cell.

  14. MSU Antenna Pattern Data

    NASA Technical Reports Server (NTRS)

    Mo, Tsan; Kleespies, Thomas J.; Green, J. Philip

    2000-01-01

    The Microwave Sounding Unit (MSU) antenna pattern data for nine MSU Flight Models (FMs) have been successfully rescued from 22-year old 7-track and 9-track magnetic tapes and cartridges. These antenna pattern data were unpacked into user-friendly ASCII format, and are potentially useful for making antenna pattern corrections to MSU antenna temperatures in retrieving the true brightness temperatures. We also properly interpreted the contents of the data and show how to convert the measured antenna signal amplitude in volts into relative antenna power in dB with proper normalization. It is found that the data are of high quality with a 60-dB drop in the co-polarized antenna patterns from the central peak value to its side-lobe regions at scan angles beyond 30 deg. The unpacked antenna pattern data produced in this study provide a useful database for data users to correct the antenna side-lobe contribution to MSU measurements. All of the data are available to the scientific community on a single CD-ROM.

  15. Recent results for plasma antennas

    SciTech Connect

    Alexeff, Igor; Anderson, Ted; Farshi, Esmaeil; Karnam, Naresh; Pulasani, Nanditha Reddy

    2008-05-15

    Plasma antennas are just as effective as metal antennas. They can transmit, receive, and reflect radio waves just as well as metal antennas. In addition, plasma generated noise does not appear to be a problem.

  16. 1987 calibration of the TFTR neutron spectrometers

    SciTech Connect

    Barnes, C.W.; Strachan, J.D.; Princeton Univ., NJ . Plasma Physics Lab.)

    1989-12-01

    The {sup 3}He neutron spectrometer used for measuring ion temperatures and the NE213 proton recoil spectrometer used for triton burnup measurements were absolutely calibrated with DT and DD neutron generators placed inside the TFTR vacuum vessel. The details of the detector response and calibration are presented. Comparisons are made to the neutron source strengths measured from other calibrated systems. 23 refs., 19 figs., 6 tabs.

  17. Redetermining CEBAF's Absolute Energy

    NASA Astrophysics Data System (ADS)

    Su, Tong; Jlab Marathon Collaboration

    2015-04-01

    With the upgrade of the Jefferson Lab accelerator (CEBAF) from 6 GeV max energy to 12 GeV, all the dipole magnets in the machine were refurbished. Most of them were switched from open c-shaped to closed h-shaped by adding extra iron. With these upgraded magnets, the energy calibration of the accelerator needed to be redetermined. We will show how an extra external dipole, which is run in series with those in the machine, helps us cross check the current in the magnets as well as precisely map out the integral field for any machine setting. Using knowledge of the relative performance of the dipoles as well as the bend angle into the Hall, has allowed us to already determine a 4th pass 7 GeV beam to better than 7 MeV. In the future, we will use g-2 spin precession as a second independent energy determination. This work is supported by Kent State University, NSF Grant PHY-1405814, and DOE Contract DE-AC05-06OR23177 (JLab).

  18. Calibration of Envisat radar altimeter over Lake Issykkul

    NASA Astrophysics Data System (ADS)

    Crétaux, J.-F.; Bergé-Nguyen, M.; Calmant, S.; Romanovski, V. V.; Meyssignac, B.; Perosanz, F.; Tashbaeva, S.; Arsen, A.; Fund, F.; Martignago, N.; Bonnefond, P.; Laurain, O.; Morrow, R.; Maisongrande, P.

    2013-04-01

    This study presents the results of calibration/validation (C/V) of Envisat satellite radar altimeter over Lake Issykkul located in Kyrgyzstan, which was chosen as a dedicated radar altimetry C/V site in 2004. The objectives are to estimate the absolute altimeter bias of Envisat and its orbit based on cross-over analysis with TOPEX/Poseidon (T/P), Jason-1 and Jason-2 over the ocean. We have used a new method of GPS data processing in a kinematic mode, developed at the Groupe de Recherche de Geodesie Spatiale (GRGS), which allows us to calculate the position of the GPS antenna without needing a GPS reference station. The C/V is conducted using various equipments: a local GPS network, a moving GPS antenna along the satellites tracks over Lake Issykkul, In Situ level gauges and weather stations. The absolute bias obtained for Envisat from field campaigns conducted in 2009 and 2010 is between 62.1 and 63.4 ± 3.7 cm, using the Ice-1 retracking algorithm, and between 46.9 and 51.2 cm with the ocean retracking algorithm. These results differ by about 10 cm from previous studies, principally due to improvement of the C/V procedure. Apart from the new algorithm for GPS data processing and the orbit error reduction, more attention has been paid to the GPS antenna height calculation, and we have reduced the errors induced by seiche over Lake Issykkul. This has been assured using cruise data along the Envisat satellite track at the exact date of the pass of the satellite for the two campaigns. The calculation of the Envisat radar altimeter bias with respect to the GPS levelling is essential to allow the continuity of multi-mission data on the same orbit, with the expected launch of SARAL/Altika mission in 2012. Implications for hydrology in particular, will be to produce long term homogeneous and reliable time series of lake levels worldwide.

  19. Scanning means for Cassegrainian antenna

    NASA Technical Reports Server (NTRS)

    Giandomenico, A.; Rusch, W. V. T.

    1967-01-01

    Mechanical antenna beam switching device detects weak signals over atmospheric and equipment noise sources in microwave antennas. It periodically nutates the paraboloidal subdish in a Cassegrainian reflector system.

  20. Absolute Identification by Relative Judgment

    ERIC Educational Resources Information Center

    Stewart, Neil; Brown, Gordon D. A.; Chater, Nick

    2005-01-01

    In unidimensional absolute identification tasks, participants identify stimuli that vary along a single dimension. Performance is surprisingly poor compared with discrimination of the same stimuli. Existing models assume that identification is achieved using long-term representations of absolute magnitudes. The authors propose an alternative…

  1. Be Resolute about Absolute Value

    ERIC Educational Resources Information Center

    Kidd, Margaret L.

    2007-01-01

    This article explores how conceptualization of absolute value can start long before it is introduced. The manner in which absolute value is introduced to students in middle school has far-reaching consequences for their future mathematical understanding. It begins to lay the foundation for students' understanding of algebra, which can change…

  2. mm-wave antenna

    NASA Astrophysics Data System (ADS)

    Muhs, H. P.

    1985-07-01

    The present low profile seeker front end's slotted waveguide antenna was primarily developed to investigate the feasibility of the application of standard manufacturing techniques to mm-wave hardware. A dual plane monopulse comparator was constructed to mate with the antenna via integrated packaging techniques. The comparator was fabricated by CAD/CAM milling operations.

  3. Airborne antenna pattern calculations

    NASA Technical Reports Server (NTRS)

    Bagherian, A. B.; Mielke, R. R.

    1983-01-01

    Use of calculation program START and modeling program P 3D to produce radiation patterns of antennas mounted on a space station is discussed. Basic components of two space stations in the early design stage are simulated and radiation patterns for antennas mounted on the modules are presented.

  4. Experiments with Dipole Antennas

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2009-01-01

    Employment of a data-acquisition system for data collection and calculations makes experiments with antennas more convenient and less time consuming. The determined directional patterns of the dipole antennas of different lengths are in reasonable agreement with theory. The enhancement of the signal by using a reflector is demonstrated, and a…

  5. Milestones in Broadcasting: Antennas.

    ERIC Educational Resources Information Center

    Media in Education and Development, 1985

    1985-01-01

    Briefly describes the development of antennas in the prebroadcast era (elevated antenna, selectivity to prevent interference between stations, birth of diplex, directional properties, support structures), as well as technological developments used in long-, medium-, and short-wave broadcasting, VHF/FM and television broadcasting, and satellite…

  6. Deformations in VLBI antennas

    NASA Technical Reports Server (NTRS)

    Clark, T. A.; Thomsen, P.

    1988-01-01

    A study is presented of deformations in antennas with the emphasis on their influence on VLBI measurements. The GIFTS structural analysis program has been used to model the VLBI antenna in Fairbanks (Alaska). The report identifies key deformations and studies the effect of gravity, wind, and temperature. Estimates of expected deformations are given.

  7. Calibration of X-Ray Observatories

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; L'Dell, Stephen L.

    2011-01-01

    Accurate calibration of x-ray observatories has proved an elusive goal. Inaccuracies and inconsistencies amongst on-ground measurements, differences between on-ground and in-space performance, in-space performance changes, and the absence of cosmic calibration standards whose physics we truly understand have precluded absolute calibration better than several percent and relative spectral calibration better than a few percent. The philosophy "the model is the calibration" relies upon a complete high-fidelity model of performance and an accurate verification and calibration of this model. As high-resolution x-ray spectroscopy begins to play a more important role in astrophysics, additional issues in accurately calibrating at high spectral resolution become more evident. Here we review the challenges of accurately calibrating the absolute and relative response of x-ray observatories. On-ground x-ray testing by itself is unlikely to achieve a high-accuracy calibration of in-space performance, especially when the performance changes with time. Nonetheless, it remains an essential tool in verifying functionality and in characterizing and verifying the performance model. In the absence of verified cosmic calibration sources, we also discuss the notion of an artificial, in-space x-ray calibration standard. 6th

  8. Parabolic torus transreflector antenna

    NASA Astrophysics Data System (ADS)

    Diaz, L. M.; Smith, M. S.

    1984-12-01

    The possible scan rate of conventional radar antennas using parabolic dishes is limited to about 60 rev/min. This limitation is related to mechanical rotation requirements. Many radar applications require high data renewal rates, including short-range defense systems and systems for reduction of sea clutter. Faster scan rates can be obtained by using phased arrays and electronic scanning. However, the use of the required equipment introduces considerable complexity and cost. The present investigation is concerned with a novel form of antenna permitting high scan rates, taking into account a parabolic torus transreflector antenna. The feed horn illuminates one side of the radome with polarization parallel to the wires, which therefore reflect the radiation like a dish antenna. In the antenna considered, rotation of the beam is effected by mechanical rotation of the horn feed only, and this provides the potential for high scanning rates.

  9. GPS antenna designs

    NASA Technical Reports Server (NTRS)

    Laube, Samuel J. P.

    1987-01-01

    Application of the current GPS NAVSTAR system to civilian service requires that a right hand, circularly polarized, -160 dBW spread spectrum signal be received from an orbiting satellite, where the antenna environment is also moving. This presents a design challenge when inexpensive antennas are desired. The intent of this survey is to provide information on the antennas mentioned and to construct and test prototypes to determine whether the choice made by the industry, the quadrifilar helix, is the best. The helix antenna is currently the low cost standard for GPS. Prototype versions were constructed using 12 gauge wire and subminiature coaxial hardline. The constructed antennas were tested using a signal generator and a reference turnstile. A spectrum analyzer was used to measure the level of the received signal.

  10. GPS antenna designs

    NASA Astrophysics Data System (ADS)

    Laube, Samuel J. P.

    1987-05-01

    Application of the current GPS NAVSTAR system to civilian service requires that a right hand, circularly polarized, -160 dBW spread spectrum signal be received from an orbiting satellite, where the antenna environment is also moving. This presents a design challenge when inexpensive antennas are desired. The intent of this survey is to provide information on the antennas mentioned and to construct and test prototypes to determine whether the choice made by the industry, the quadrifilar helix, is the best. The helix antenna is currently the low cost standard for GPS. Prototype versions were constructed using 12 gauge wire and subminiature coaxial hardline. The constructed antennas were tested using a signal generator and a reference turnstile. A spectrum analyzer was used to measure the level of the received signal.

  11. Antenna unit and radio base station therewith

    DOEpatents

    Kuwahara, Mikio; Doi, Nobukazu; Suzuki, Toshiro; Ishida, Yuji; Inoue, Takashi; Niida, Sumaru

    2007-04-10

    Phase and amplitude deviations, which are generated, for example, by cables connecting an array antenna of a CDMA base station and the base station, are calibrated in the baseband. The base station comprises: an antenna apparatus 1; couplers 2; an RF unit 3 that converts a receive signal to a baseband signal, converts a transmit signal to a radio frequency, and performs power control; an A/D converter 4 for converting a receive signal to a digital signal; a receive beam form unit 6 that multiplies the receive signal by semi-fixed weight; a despreader 7 for this signal input; a time-space demodulator 8 for demodulating user data; a despreader 9 for probe signal; a space modulator 14 for user data; a spreader 13 for user signal; a channel combiner 12; a Tx calibrater 11 for controlling calibration of a signal; a D/A converter 10; a unit 16 for calculation of correlation matrix for generating a probe signal used for controlling an Rx calibration system and a TX calibration system; a spreader 17 for probe signal; a power control unit 18; a D/A converter 19; an RF unit 20 for probe signal; an A/D converter 21 for signal from the couplers 2; and a despreader 22.

  12. Autonomous omnidirectional spacecraft antenna system

    NASA Technical Reports Server (NTRS)

    Taylor, T. H.

    1983-01-01

    The development of a low gain Electronically Switchable Spherical Array Antenna is discussed. This antenna provides roughly 7 dBic gain for receive/transmit operation between user satellites and the Tracking and Data Relay Satellite System. When used as a pair, the antenna provides spherical coverage. The antenna was tested in its primary operating modes: directed beam, retrodirective, and Omnidirectional.

  13. RF MEMS Based Reconfigurable Antennas

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.

    2004-01-01

    The presentation will first of all address the advantages of RF MEMS circuit in antenna applications and also the need for electronically reconfigurable antennas. Next, discuss some of the recent examples of RF MEMS based reconfigurable microstrip antennas. Finally, conclude the talk with a summary of MEMS antenna performance.

  14. Antenna Technologies for NASA Applications

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.

    2006-01-01

    This presentation addresses the efforts being performed at GRC to develop antenna technology in support of NASA s Exploration Vision. In particular, the presentation discusses the communications architecture asset-specific data services, as well as wide area coverage, high gain, low mass deployable antennas. Phased array antennas as well as electrically small, lightweight, low power, multifunctional antennas will be also discussed.

  15. Antenna Technologies for NASA Applications

    NASA Technical Reports Server (NTRS)

    Miranda, Felix

    2007-01-01

    This presentation addresses the efforts being performed at GRC to develop antenna technology in support of NASA s Exploration Vision. In particular, the presentation discusses the communications architecture asset-specific data services, as well as wide area coverage, high gain, low mass deployable antennas. Phased array antennas as well as electrically small, lightweight, low power, multifunctional antennas will be also discussed.

  16. MAGSAT: Vector magnetometer absolute sensor alignment determination

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.

    1981-01-01

    A procedure is described for accurately determining the absolute alignment of the magnetic axes of a triaxial magnetometer sensor with respect to an external, fixed, reference coordinate system. The method does not require that the magnetic field vector orientation, as generated by a triaxial calibration coil system, be known to better than a few degrees from its true position, and minimizes the number of positions through which a sensor assembly must be rotated to obtain a solution. Computer simulations show that accuracies of better than 0.4 seconds of arc can be achieved under typical test conditions associated with existing magnetic test facilities. The basic approach is similar in nature to that presented by McPherron and Snare (1978) except that only three sensor positions are required and the system of equations to be solved is considerably simplified. Applications of the method to the case of the MAGSAT Vector Magnetometer are presented and the problems encountered discussed.

  17. X-Antenna: A graphical interface for antenna analysis codes

    NASA Technical Reports Server (NTRS)

    Goldstein, B. L.; Newman, E. H.; Shamansky, H. T.

    1995-01-01

    This report serves as the user's manual for the X-Antenna code. X-Antenna is intended to simplify the analysis of antennas by giving the user graphical interfaces in which to enter all relevant antenna and analysis code data. Essentially, X-Antenna creates a Motif interface to the user's antenna analysis codes. A command-file allows new antennas and codes to be added to the application. The menu system and graphical interface screens are created dynamically to conform to the data in the command-file. Antenna data can be saved and retrieved from disk. X-Antenna checks all antenna and code values to ensure they are of the correct type, writes an output file, and runs the appropriate antenna analysis code. Volumetric pattern data may be viewed in 3D space with an external viewer run directly from the application. Currently, X-Antenna includes analysis codes for thin wire antennas (dipoles, loops, and helices), rectangular microstrip antennas, and thin slot antennas.

  18. Directional pattern measurement of the BRAMS beacon antenna system

    NASA Astrophysics Data System (ADS)

    Martínez Picar, A.; Marqué, C.; Anciaux, M.; Lamy, H.

    2015-01-01

    The typical methods for measuring antenna characteristics are mostly based on the use of remote transmitters or receivers. For antennas used in radio communications, calibrations are usually done on an antenna test stand using transmitters with known power output. In order to minimize the ground effects while performing measurements, it is necessary to place the transmitter or receiver high above ground with the aid of aircrafts. It is, however, necessary to determine precisely the coordinates of the airborne devices as well as to maintain high stability. This used to be excessively difficult to carry out, but recent advances in Unmanned Aerial Vehicle (UAV) technologies have brought a feasible option. In this paper, the results of using a low-cost system for measuring the directional pattern of BRAMS beacon antenna system based on an UAV are presented.

  19. Satellite Antenna Systems

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Through the Technology Affiliates Program at the Jet Propulsion Laboratory, the ACTS antenna system was transferred from experimental testing status to commercial development with KVH Industries, Inc. The ACTS design enables mobile satellite antennas to remain pointed at the satellite, regardless of the motion or vibration on which it is mounted. KVH's first product based on the ACTS design is a land-mobile satellite antenna system that will enable direct broadcast satellite television aboard moving trucks, recreational vehicles, trains, and buses. Future products could include use in broadcasting, emergency medical and military vehicles.

  20. Deep space antennas

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    Three 26-m tracking antennas operated by the NASA Deep Space Network at Goldstone, Calif.; Madrid, Spain; and near Canberra, Australia, will cease operations on Dec. 1, 1981. The stations will continue to operate 64-m and 34-m deep space tracking antennas. Ending operation of the 26-m antennas will cause a reduction of about 30%; of the Deep Space Network tracking and data acquisition capability. This means less support for NASA planetary spacecraft. Currently, the Deep Space Network is supporting Voyagers 1 and 2, Helios 1, the Mars Viking 1 Lander and Pioneers 6 through 12.

  1. Analysis and applications of a general boresight algorithm for the DSS-13 beam waveguide antenna

    NASA Technical Reports Server (NTRS)

    Alvarez, L. S.

    1992-01-01

    A general antenna beam boresight algorithm is presented. Equations for axial pointing error, peak received signal level, and antenna half-power beamwidth are given. A pointing error variance equation is derived that illustrates the dependence of the measurement estimation performance on the various algorithm inputs, including RF signal level uncertainty. Plots showing pointing error uncertainty as function of algorithm inputs are presented. Insight gained from the performance analysis is discussed in terms of its application to the areas of antenna controller and receiver interfacing, pointing error compensation, and antenna calibrations. Current and planned applications of the boresight algorithm, including its role in the upcoming Ka-band downlink experiment (KABLE), are highlighted.

  2. Characterization of the RPW Electric Antenna System aboard Solar Orbiter

    NASA Astrophysics Data System (ADS)

    Plettemeier, D.; Rucker, H. O.; Oswald, T.; Sampl, M.; Fischer, G.; Macher, W.; Maksimovic, M.

    2009-12-01

    the antenna system is performed in a frequency range from 100 kHz up to 20 MHz. One-side heating of the antenna rods caused by solar radiation will lead to a significant antenna bending. This will influence the effective antenna vectors and has to be taken into account for the calibration process, especially if the bending will cause asymmetries in the antenna system. A detailed study of radiation coupling effects caused for instance by solar panels and high gain communication antenna (HGA) has been performed. The orientation of solar panels and HGA as well as the bending of the antenna elements has a significant influence on the instrument calibration. The analysis of different combinations of the three foot point voltages points out the instrument capabilities in polarization sensitive direction finding. The results of the computer simulations together with model scaled measurements will be used to evaluate the influence of the spacecraft on the antenna system reception properties and may be used for a re-evaluation of the structure and position of antennas and instruments on board Solar Orbiter

  3. Qualification of UHF Antenna for Extreme Martian Thermal Environments

    NASA Technical Reports Server (NTRS)

    Ramesham, Rajeshuni; Amaro, Luis R.; Brown, Paula R.; Usiskin, Robert

    2013-01-01

    The purpose of this development was to validate the use of the external Rover Ultra High Frequency (RUHF) antenna for space under extreme thermal environments to be encountered during the surface operations of the Mars Science Laboratory (MSL) mission. The antenna must survive all ground operations plus the nominal 670 Martian sol mission that includes summer and winter seasons of the Mars thermal environment.The qualification effort was to verify that the RUHF antenna design and its bonding and packaging processes are adequate to survive the harsh environmental conditions. The RUHF is a quadrifilar helix antenna mounted on the MSL Curiosity rover deck. The main components of the RUHF antenna are the helix structure, feed cables, and hybrid coupler, and the high-power termination load. In the case of MSL rover externally mounted hardware, not only are the expected thermal cycle depths severe, but there are temperature offsets between the Mars summer and winter seasons. The total number of temperature cycles needed to be split into two regimes of summer cycles and winter cycles. The qualification test was designed to demonstrate a survival life of three times more than all expected ground testing, plus a nominal 670 Martian sol missions. Baseline RF tests and a visual inspection were performed prior to the start of the qualification test. Functional RF tests were performed intermittently during chamber breaks over the course of the qualification test. For the RF return loss measurements, the antenna was tested in a controlled environment outside the thermal chamber with a vector network analyzer that was calibrated over the antenna s operational frequency range. A total of 2,010 thermal cycles were performed. Visual inspection showed a dulling of the solder material. This change will not affect the performance of the antenna. No other changes were observed. RF tests were performed on the RUHF helix antenna, hybrid, and load after the 2,010 qualification cycles test

  4. Rheometry and numerical simulations of antennas onboard the Resonance spacecraft

    NASA Astrophysics Data System (ADS)

    Sampl, M.; Macher, W.; Gruber, Ch.; Oswald, Th.; Rucker, H. O.

    2009-04-01

    We report on the calibration effort for the monopole antennas onboard the Resonance spacecraft which will be launched in the middle of the next decade. The Resonance mission is dedicated to the study of the wave-particle interactions and plasma dynamics in the inner magnetosphere and the auroral region. It is intended to fly four spacecrafts on specific trajectories, so that on parts of the orbits the four spacecraft fly along the same field line (precisely speaking in the same flux tube) of the geomagnetic field. Time and space correlated measurements are planned which will reveal new insights into processes propagating along the field lines and phenomena which span large parts of the flux tubes. The calibration is performed for four boom antennas and four cylindrical sensors at the boom tips. These antennas are devised for the measurement of electric fields and plasma parameters. We apply two methods for the antenna analysis: First, electrolytic tank measurements (rheometry), which is a method to determine the effective length vectors of electrically short antennas (in this context up to about 1MHz); second, numerical computer simulations which enable us to study also the transition to higher frequencies. The accuracy of the applied methods is about 1 degree for directions of effective axes and some percent for effective lengths and capacitances. With both methods we determined the following antenna parameters which are most relevant in the present context: The effective length vectors (comprising effective axes and effective lengths), and the antenna capacitance matrix. For that purpose the whole antenna-spacecraft system is treated as an 8-port antenna. For the first time this kind of analysis is performed for a spaceborne antenna system consisting of boom monopoles and cylindrical tip antennas. The results show that the effective antenna lengths do not coincide with the physical ones but are tilted away from the solar panels by several degrees. The numerical

  5. NASA technology for large space antennas

    NASA Technical Reports Server (NTRS)

    Russell, R. A.; Campbell, T. G.; Freeland, R. E.

    1980-01-01

    Some leading concepts for deployable antennas are described and an assessment of the state of the art in deployable antennas is presented. The advanced sunflower precision antenna, the radial rib antenna and the maypole (hoop/column) antenna, the wrap rib antenna and the parabolic erectable truss antenna are covered. In addition, a discussion on the technology development program for two deployable antenna concepts that are responsive to the antenna mission requirements as defined in the NASA mission model is presented.

  6. Achieving Climate Change Absolute Accuracy in Orbit

    NASA Technical Reports Server (NTRS)

    Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C. O.; Bantges, R.; Best, F.; Bowman, K.; Brindley, H.; Butler, J. J.; Collins, W.; Dykema, J. A.; Doelling, D. R.; Feldman, D. R.; Fox, N.; Huang, X.; Holz, R.; Huang, Y.; Jennings, D.; Jin, Z.; Johnson, D. G.; Jucks, K.; Kato, S.; Kratz, D. P.; Liu, X.; Lukashin, C.; Mannucci, A. J.; Phojanamongkolkij, N.; Roithmayr, C. M.; Sandford, S.; Taylor, P. C.; Xiong, X.

    2013-01-01

    The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Système Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5-50 micron), the spectrum of solar radiation reflected by the Earth and its atmosphere (320-2300 nm), and radio occultation refractivity from which accurate temperature profiles are derived. The mission has the ability to provide new spectral fingerprints of climate change, as well as to provide the first orbiting radiometer with accuracy sufficient to serve as the reference transfer standard for other space sensors, in essence serving as a "NIST [National Institute of Standards and Technology] in orbit." CLARREO will greatly improve the accuracy and relevance of a wide range of space-borne instruments for decadal climate change. Finally, CLARREO has developed new metrics and methods for determining the accuracy requirements of climate observations for a wide range of climate variables and uncertainty sources. These methods should be useful for improving our understanding of observing requirements for most climate change observations.

  7. Ultraviolet photometry from the Orbiting Astronomical Observatory. XXI - Absolute energy distribution of stars in the ultraviolet

    NASA Technical Reports Server (NTRS)

    Bless, R. C.; Code, A. D.; Fairchild, E. T.

    1976-01-01

    The absolute energy distribution in the ultraviolet is given for the stars alpha Vir, eta UMa, and alpha Leo. The calibration is based on absolute heterochromatic photometry between 2920 and 1370 A carried out with an Aerobee sounding rocket. The fundamental radiation standard is the synchrotron radiation from 240-MeV electrons in a certain synchrotron storage ring. On the basis of the sounding-rocket calibration, the preliminary OAO-2 spectrometer calibration has been revised; the fluxes for the three program stars are tabulated in energy per second per square centimeter per unit wavelength interval.

  8. Electrically driven optical antennas

    NASA Astrophysics Data System (ADS)

    Kern, Johannes; Kullock, René; Prangsma, Jord; Emmerling, Monika; Kamp, Martin; Hecht, Bert

    2015-09-01

    Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.

  9. Antenna pattern study

    NASA Technical Reports Server (NTRS)

    Harper, Warren

    1988-01-01

    Prediction of antenna radiation patterns has long been an important function in the design of command, communication, and tracking systems for rocket vehicles and spacecraft. An acceptable degree of assurance that a radio link will provide the required quality of data or certainty of correct command execution must be acquired by some means if the system is to be certified as reliable. Two methods have been used to perform this function: (1) Theoretical analysis, based on the known properties of basic antenna element types and their behavior in the presence of conductive structures of simple shape, and (2) Measurement of the patterns on scale models of the spacecraft or rocket vehicle on which the antenna is located. Both of these methods are ordinarily employed in the antenna design process.

  10. Rotary antenna attenuator

    NASA Technical Reports Server (NTRS)

    Dickinson, R. M.; Hardy, J. C.

    1969-01-01

    Radio frequency attenuator, having negligible insertion loss at minimum attenuation, can be used for making precise antenna gain measurements. It is small in size compared to a rotary-vane attenuator.

  11. CIRCULAR CAVITY SLOT ANTENNA

    DOEpatents

    Kerley, P.L.

    1959-01-01

    A small-size antenna having a doughnut-shaped field pattern and which can act both as an antenna and a resonant circuit is described. The antenna is of the slotted type and comprises a resonant cavity with a center hole. A circular slot is provided in one wall of the cavity concentric with the hole and a radio frequency source is connected across the slot. The pattern and loading of the antenna are adjusted by varying the position and shape of a center element slidably disposed within the hole and projecting from the slotted side of the resonant cavity. The disclosed structure may also be used to propagate the oscillator signal down a transniission line by replacing the center element with one leg of the transmission line in a spaced relation from the walls of the cavity.

  12. Coaxial phased array antenna

    NASA Astrophysics Data System (ADS)

    Ellis, H., Jr.

    1980-08-01

    A coaxial antenna array for communicating circularly polarized electromagnetic radiation is disclosed. A pair of open ended antenna cavities is coaxially constructed and operates by excitation of linear radiation elements arranged within each of the cavities. A pair of crossed dipole radiation devices is centered within the inner cavity and operated by means of a phase shifting network circuit to transmit as well as receive circularly polarized radiation. Four monopole radiation devices are symmetrically arranged to operate in the outer cavity in phase quadrature by means of the phase shifting network circuit to both transmit and receive circularly polarized electromagnetic radiation. Combined operation of the two antenna cavities with a 180 deg phase differential between the fields related to the two antenna cavities provides a broad beam, relatively wide frequency bandwidth communication capability. Particular embodiments disclosed feature a generally square cavity array as well as a circular cavity array.

  13. Coaxial phased array antenna

    NASA Technical Reports Server (NTRS)

    Ellis, H., Jr. (Inventor)

    1980-01-01

    A coaxial antenna array for communicating circularly polarized electromagnetic radiation is disclosed. A pair of open ended antenna cavities is coaxially constructed and operates by excitation of linear radiation elements arranged within each of the cavities. A pair of crossed dipole radiation devices is centered within the inner cavity and operated by means of a phase shifting network circuit to transmit as well as receive circularly polarized radiation. Four monopole radiation devices are symmetrically arranged to operate in the outer cavity in phase quadrature by means of the phase shifting network circuit to both transmit and receive circularly polarized electromagnetic radiation. Combined operation of the two antenna cavities with a 180 deg phase differential between the fields related to the two antenna cavities provides a broad beam, relatively wide frequency bandwidth communication capability. Particular embodiments disclosed feature a generally square cavity array as well as a circular cavity array.

  14. Microwave antenna holography

    NASA Technical Reports Server (NTRS)

    Rochblatt, David J.; Seidel, Boris L.

    1992-01-01

    This microwave holography technique utilizes the Fourier transform relation between the complex far field radiation pattern of an antenna and the complex aperture field distribution. Resulting aperture phase and amplitude distribution data can be used to precisely characterize various crucial performance parameters, including panel alignment, panel shaping, subreflector position, antenna aperture illumination, directivity at various frequencies, and gravity deformation effects. The methodology of data processing presented here was successfully applied to the Deep Space Network (DSN) 34-m beam waveguide antennas. The antenna performance was improved at all operating frequencies by reducing the main reflector mechanical surface rms error to 0.43 mm. At Ka-band (32 GHz), the estimated improvement is 4.1 dB, resulting in an aperture efficiency of 52 percent. The performance improvement was verified by efficiency measurements and additional holographic measurements.

  15. Dielectric Covered Planar Antennas

    NASA Technical Reports Server (NTRS)

    Llombart Juan, Nuria (Inventor); Lee, Choonsup (Inventor); Chattopadhyay, Goutam (Inventor); Gill, John J. (Inventor); Skalare, Anders J. (Inventor); Siegel, Peter H. (Inventor)

    2014-01-01

    An antenna element suitable for integrated arrays at terahertz frequencies is disclosed. The antenna element comprises an extended spherical (e.g. hemispherical) semiconductor lens, e.g. silicon, antenna fed by a leaky wave waveguide feed. The extended spherical lens comprises a substantially spherical lens adjacent a substantially planar lens extension. A couple of TE/TM leaky wave modes are excited in a resonant cavity formed between a ground plane and the substantially planar lens extension by a waveguide block coupled to the ground plane. Due to these modes, the primary feed radiates inside the lens with a directive pattern that illuminates a small sector of the lens. The antenna structure is compatible with known semiconductor fabrication technology and enables production of large format imaging arrays.

  16. Anemometer calibrator

    NASA Technical Reports Server (NTRS)

    Bate, T.; Calkins, D. E.; Price, P.; Veikins, O.

    1971-01-01

    Calibrator generates accurate flow velocities over wide range of gas pressure, temperature, and composition. Both pressure and flow velocity can be maintained within 0.25 percent. Instrument is essentially closed loop hydraulic system containing positive displacement drive.

  17. Polarized Antenna Splitting Functions

    SciTech Connect

    Larkoski, Andrew J.; Peskin, Michael E.; /SLAC

    2009-10-17

    We consider parton showers based on radiation from QCD dipoles or 'antennae'. These showers are built from 2 {yields} 3 parton splitting processes. The question then arises of what functions replace the Altarelli-Parisi splitting functions in this approach. We give a detailed answer to this question, applicable to antenna showers in which partons carry definite helicity, and to both initial- and final-state emissions.

  18. Intelsat VI antenna system

    NASA Astrophysics Data System (ADS)

    Caulfield, M. F.; Lane, S. O.; Taormina, F. A.

    The antenna system design of a series of five new communications satellites known as Intelsat VI is described in detail. Each satellite will utilize 50 transponders operating in the C and K band portions of the frequency spectrum. The transponders are interconnectible using either static switch matrices or a network which provides satellite switched time division multiple access capability. The antenna coverages, characteristics, and special design features are shown and discussed.

  19. MLS airborne antenna research

    NASA Technical Reports Server (NTRS)

    Yu, C. L.; Burnside, W. D.

    1975-01-01

    The geometrical theory of diffraction was used to analyze the elevation plane pattern of on-aircraft antennas. The radiation patterns for basic elements (infinitesimal dipole, circumferential and axial slot) mounted on fuselage of various aircrafts with or without radome included were calculated and compared well with experimental results. Error phase plots were also presented. The effects of radiation patterns and error phase plots on the polarization selection for the MLS airborne antenna are discussed.

  20. Large Deployable Reflectarray Antenna

    NASA Technical Reports Server (NTRS)

    Fang, Houfei; Huang, John; Lou, Michael

    2006-01-01

    A report discusses a 7-meter-diameter reflectarray antenna that has been conceived in a continuing effort to develop large reflectarray antennas to be deployed in outer space. Major underlying concepts were reported in three prior NASA Tech Briefs articles: "Inflatable Reflectarray Antennas" (NPO-20433), Vol. 23, No. 10 (October 1999), page 50; "Tape-Spring Reinforcements for Inflatable Structural Tubes" (NPO-20615), Vol. 24, No. 7 (July 2000), page 58; and "Self-Inflatable/Self-Rigidizable Reflectarray Antenna" (NPO-30662), Vol. 28, No. 1 (January 2004), page 61. Like previous antennas in the series, the antenna now proposed would include a reflectarray membrane stretched flat on a frame of multiple inflatable booms. The membrane and booms would be rolled up and folded for compact stowage during transport. Deployment in outer space would be effected by inflating the booms to unroll and then to unfold the membrane, thereby stretching the membrane out flat to its full size. The membrane would achieve the flatness for a Ka-band application. The report gives considerable emphasis to designing the booms to rigidify themselves upon deployment: for this purpose, the booms could be made as spring-tape-reinforced aluminum laminate tubes like those described in two of the cited prior articles.

  1. Antenna engineering handbook /2nd edition/

    NASA Astrophysics Data System (ADS)

    Johnson, R. C.; Jasik, H.

    Essential principles, methods, and data for solving a wide range of problems in antenna design and application are presented. The basic concepts and fundamentals of antennas are reviewed, followed by a discussion of arrays of discrete elements. Then all primary types of antennas currently in use are considered, providing concise descriptions of operating principles, design methods, and performance data. Small antennas, microstrip antennas, frequency-scan antennas, conformal and low-profile arrays, adaptive antennas, and phased arrays are covered. The major applications of antennas and the design methods peculiar to those applications are discussed in detail. The employment of antennas to meet the requirements of today's complex electronic systems is emphasized, including earth station antennas, satellite antennas, seeker antennas, microwave-relay antennas, tracking antennas, radiometer antennas, and ECM and ESM antennas. Finally, significant topics related to antenna engineering, such as transmission lines and waveguides, radomes, microwave propagation, and impedance matching and broadbanding, are addressed.

  2. Inflight calibration of AVIRIS in 1992 and 1993

    NASA Technical Reports Server (NTRS)

    Green, Robert O.; Conel, James E.; Helmlinger, Mark; Vandenbosch, Jeannette; Chovit, Chris; Chrien, Tom

    1993-01-01

    In order to pursue the quantitative research objective of AVIRIS, the spectral, radiometric characteristic of the sensor must be known at the time of flight data acquisition. AVIRIS is rigorously calibrated in the laboratory. In addition, three times each year these characteristics of AVIRIS are validated through an inflight calibration experiment. Absolute radiometric calibration and signal-to-noise results are present for the inflight calibration experiment orchestrated in 1992 and 1993.

  3. An atlas of selected calibrated stellar spectra

    NASA Technical Reports Server (NTRS)

    Walker, Russell G.; Cohen, Martin

    1992-01-01

    Five hundred and fifty six stars in the IRAS PSC-2 that are suitable for stellar radiometric standards and are brighter than 1 Jy at 25 microns were identified. In addition, 123 stars that meet all of our criteria for calibration standards, but which lack a luminosity class were identified. An approach to absolute stellar calibration of broadband infrared filters based upon new models of Vega and Sirius due to Kurucz (1992) is presented. A general technique used to assemble continuous wide-band calibrated infrared spectra is described and an absolutely calibrated 1-35 micron spectrum of alpha(Tau) is constructed and the method using new and carefully designed observations is independently validated. The absolute calibration of the IRAS Low Resolution Spectrometer (LRS) database is investigated by comparing the observed spectrum of alpha(Tau) with that assumed in the original LRS calibration scheme. Neglect of the SiO fundamental band in alpha(Tau) has led to the presence of a specious 'emission' feature in all LRS spectra near 8.5 microns, and to an incorrect spectral slope between 8 and 12 microns. Finally, some of the properties of asteroids that effect their utility as calibration objects for the middle and far infrared region are examined. A technique to determine, from IRAS multiwaveband observations, the basic physical parameters needed by various asteroid thermal models that minimize the number of assumptions required is developed.

  4. VLF/LF transmitting antennas

    NASA Astrophysics Data System (ADS)

    Belrose, John S.

    1993-05-01

    Very Low Frequency (VLF) transmitting antenna design is a specialized field of engineering that requires the combined skill of radio, civil, and mechanical engineers. The antenna systems used for this band (15-30 kHz) are enormous structures. Vertical radiators with very extensive top-loading (non-radiating top-hats) are necessary because the electrical height of practical towers is small. For tower heights of 300-450 meters (1000-1500 feet) the electrical heights are only fifteen to forty-five one thousandths of a wavelength. This presentation discusses the following topics: antenna design concepts, antenna fundamentals, tools for antenna modeling, a mini-study of conventional antennas, multiple tuned antenna systems, and a comparison between performance (measured and predicted) for multiple tuned antennas vs. single tuned antennas.

  5. Reducing Antenna Mechanical Noise in Precision Doppler Tracking

    NASA Astrophysics Data System (ADS)

    Armstrong, J. W.; Estabrook, F. B.; Asmar, S. W.; Iess, L.; Tortora, P.

    2006-05-01

    Precision Doppler tracking of deep-space probes is central to spacecraft navigation and many radio science investigations. The most sensitive Doppler observations to date have been taken using the NASA/JPL Deep Space Network (DSN) antenna DSS 25, a 34-m-diameter beam-waveguide station especially instrumented with simultaneous X-band (approximately 8.4-GHz) and Ka-band (approximately 32-GHz) links and tropospheric scintillation calibration equipment, tracking the Cassini spacecraft. These Cassini observations achieved Doppler fractional frequency stability (Doppler frequency fluctuation divided by center frequency, Delta f / f_o ) of approximately 3 x 10^-15 at tau = 1000 s integration. In those very-high-sensitivity tracks, the leading disturbance was antenna mechanical noise: time-dependent unmodeled physical motion of the ground antenna's phase center caused by antenna sag as the elevation angle changed, unmodeled subreflector motion, wind loading, bulk motion of the antenna as it rolled over irregularities in the supporting azimuth ring, differential thermal expansion of the structure, etc. This noise has seemed irreducible at reasonable cost, since it is unclear how to build a practical, large, moving, steel structure having mechanical stability significantly better than that of current tracking stations. Here we show how the mechanical noise of a large tracking antenna can effectively be removed when two-way Doppler tracking data from an existing DSN antenna are suitably combined with simultaneous tracking data using an ancillary (smaller and stiffer) antenna. Using our method, the mechanical noise in the final Doppler observable can be reduced, substantially, to that of the stiffer antenna.

  6. A detailed comparison of antenna impedance measurements on ASDEX Upgrade with the ion cyclotron range of frequencies antenna code TOPICA

    NASA Astrophysics Data System (ADS)

    Stepanov, I.; Noterdaeme, J.-M.; Bobkov, V.; Faugel, H.; Coster, D.; Milanesio, D.; Maggiora, R.; Siegl, G.; Bilato, R.; Brambilla, M.; Verdoolaege, G.; Braun, F.; Fünfgelder, H.; D'Inca, R.; Suttrop, W.; Kallenbach, A.; Schweinzer, J.; Wolfrum, E.; Fischer, R.; Mlynek, A.; Nikolaeva, V.; Guimarais, L.; the ASDEX Upgrade Team

    2015-09-01

    New antenna diagnostics on the ASDEX Upgrade, in the form of voltage and current probe pairs on the feeding lines of each ion cyclotron range of frequencies antenna, close to the input ports, have made it possible to study in detail the behavior of the ASDEX Upgrade two-strap antenna under changing loading conditions, and compare these measurements with the results of simulations using the TOPICA code. The present work extends previous studies by using the input impedance (more precisely, the complex voltage reflection coefficient Γ ) on each antenna port for comparison, instead of the more commonly used loading resistance or coupled power. The electron density profiles used for the simulation were reconstructed from the deuterium-carbon-nitrogen interferometer and lithium beam emission spectroscopy measurements, edge-localized mode-synchronized and averaged over time intervals from 10 to 200 ms depending on the case; 112 cases were compared from seven ASDEX Upgrade discharges with widely different plasma parameters and two operating frequencies (30 and 36.5 MHz). Very good agreement in \\vert Γ\\vert was found with the measurements on antenna 3 (<3% averaged over a shot), and good agreement was found with antennas 1 and 2 (<10%) the code reproduced the correct trend in loading resistance {{R}\\text{L}} in a significant majority of cases, although the discrepancies in the absolute values were rather high (up to  ˜50%) due to high reflection. Sources of discrepancy are discussed.

  7. Modeling of compact loop antennas

    SciTech Connect

    Baity, F.W.

    1987-01-01

    A general compact loop antenna model which treats all elements of the antenna as lossy transmission lines has been developed. In addition to capacitively-tuned resonant double loop (RDL) antennas the model treats stub-tuned resonant double loop antennas. Calculations using the model have been compared with measurements on full-scale mockups of resonant double loop antennas for ATF and TFTR in order to refine the transmission line parameters. Results from the model are presented for RDL antenna designs for ATF, TFTR, Tore Supra, and for the Compact Ignition Tokamak (CIT).

  8. Modeling of compact loop antennas

    NASA Astrophysics Data System (ADS)

    Baity, F. W.

    A general compact loop antenna model which treats all elements of the antenna as lossy transmission lines has been developed. In addition to capacitively-tuned resonant double loop (RDL) antennas the model treats stub-tuned resonant double loop antennas. Calculations using the model have been compared with measurements on full-scale mockups of resonant double loop antennas for ATF and TFTR in order to refine the transmission line parameters. Results from the model are presented for RDL antenna designs for ATF, TFTR, Tore Supra, and for the Compact Ignition Tokamak (CIT).

  9. Modeling of compact loop antennas

    NASA Astrophysics Data System (ADS)

    Baity, F. W.

    1987-09-01

    A general compact loop antenna model which treats all elements of the antenna as lossy transmission lines has been developed. In addition to capacitively tuned resonant double loop (RDL) antennas, the model treats sub-tuned RDL antennas. Calculations using the model have been compared with measurements on full-scale mock-ups of RDL antennas for ATF and TFTR in order to refine the transmission line parameters. Results from the model are presented for RDL antenna designs for ATF, TFTR, Tore Supra, and the Compact Ignition Tokamak (CIT).

  10. On-Wafer Characterization of Millimeter-Wave Antennas for Wireless Applications

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Lee, Richard Q.

    1998-01-01

    The paper demonstrates a de-embedding technique and a direct on-substrate measurement technique for fast and inexpensive characterization of miniature antennas for wireless applications at millimeter-wave frequencies. The technique is demonstrated by measurements on a tapered slot antenna (TSA). The measured results at Ka-Band frequencies include input impedance, mutual coupling between two TSAs and absolute gain of TSA.

  11. CONSCAN implementation for Antenna Control Assembly

    NASA Technical Reports Server (NTRS)

    Ohlson, J. E.; Abichandani, K. P.

    1982-01-01

    The specifics of the CONSCAN, including calibration, signal cleanup, and system protection are presented. The CONSCAN was previously recommended for implementation in the antenna control assembly. Equations for programming the algorithms are provided. The described treatment is designed to lead to developing K-band. The recommended techniques to be employed in conjunction with CONSCAN are summarized: (1) for initial acquisition, employ stepped spiral search; (2) employ continued and incessant testing of signals to verify: in-lock, reasonable in level, and within limits; (3) use FFT for signal processing if feasible, as it provides more tests and insight into existence of glitches and spurious content of the input signal level.

  12. The PREMOS/PICARD instrument calibration

    NASA Astrophysics Data System (ADS)

    Schmutz, Werner; Fehlmann, André; Hülsen, Gregor; Meindl, Peter; Winkler, Rainer; Thuillier, Gérard; Blattner, Peter; Buisson, François; Egorova, Tatiana; Finsterle, Wolfgang; Fox, Nigel; Gröbner, Julian; Hochedez, Jean-François; Koller, Silvio; Meftah, Mustapha; Meisonnier, Mireille; Nyeki, Stephan; Pfiffner, Daniel; Roth, Hansjörg; Rozanov, Eugene; Spescha, Marcel; Wehrli, Christoph; Werner, Lutz; Wyss, Jules U.

    2009-08-01

    PREMOS is a space experiment scheduled to fly on the French solar mission PICARD. The experiment comprises filter radiometers and absolute radiometers to measure the spectral and total solar irradiance. The aim of PREMOS is to contribute to the long term monitoring of the total solar irradiance, to use irradiance observations for 'nowcasting' the state of the terrestrial middle atmosphere and to provide long term sensitivity calibration for the solar imaging instrument SODISM on PICARD. In this paper we describe the calibration of the instruments. The filter radiometer channels in the visible and near IR were characterized at PMOD/WRC and the UV channels were calibrated at PTB Berlin. The absolute radiometers were compared with the World Radiometric Reference at PMOD/WRC and a power calibration relative to a primary cryogenic radiometer standard was performed in vacuum and air at NPL.

  13. Adaptive antenna design considerations for satellite communication antennas

    NASA Astrophysics Data System (ADS)

    Mayhan, J. T.

    1983-02-01

    The present investigation is concerned with some general considerations inherent in designing an adaptive antenna system for use on a geosynchronous satellite illuminating the earth field of view. The problem has been addressed from the viewpoint of the system designer who has to determine the required antenna characteristics and the antenna aperture size. Concerning the choice of the antenna type, it usually has to be decided whether to use a phased array (PA) or a multiple-beam antenna (MBA). Attention is given to nulling resolution and MBA/PA configuration, taking into account the phased array and multiple-beam antennas. The choice of which antenna type to use depends on the nulling bandwidth, the number of weighted channels in the adaptive processor, and the overall coverage area to be served by the antenna system.

  14. Antenna cab interior showing equipment rack and fiberglass antenna panels, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Antenna cab interior showing equipment rack and fiberglass antenna panels, looking southeast. - Western Union Telegraph Company, Jennerstown Relay, Laurel Summit Road off U.S. 30, Laughlintown, Westmoreland County, PA

  15. Antenna cab interior showing equipment rack and fiberglass antenna panels, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Antenna cab interior showing equipment rack and fiberglass antenna panels, looking west. - Western Union Telegraph Company, Jennerstown Relay, Laurel Summit Road off U.S. 30, Laughlintown, Westmoreland County, PA

  16. Antenna cab interior showing waveguide from external parabolic antenna (later ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Antenna cab interior showing waveguide from external parabolic antenna (later addition), looking north. - Western Union Telegraph Company, Jennerstown Relay, Laurel Summit Road off U.S. 30, Laughlintown, Westmoreland County, PA

  17. View of Antenna #1 (foreground), and Antenna #2 surface doors. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of Antenna #1 (foreground), and Antenna #2 surface doors. Image looking northeast - Titan One Missile Complex 2A, .3 miles west of 129 Road and 1.5 miles north of County Line Road, Aurora, Adams County, CO

  18. A Intercomparison of Interferometric Meteor Radar Calibration Techniques

    NASA Astrophysics Data System (ADS)

    Kang, C.; Palo, S.

    Interferometric techniques are commonly used in all-sky meteor radar systems to determine the meteors position in the sky Before correctly conducting the task of estimating the direction-of-arrival DOA of the meteors effective and reliable calibrating the phases of the system is required Although different methods have been reported there is no satisfactory technique published This study thoroughly discusses the current and prospective calibration techniques Generally speaking phase calibration is implemented by measuring the phase difference between the receivers for a signal produced by a source with known locations Next the phase offsets can be estimated by comparing the measured phase difference with the expected phase difference between the antenna pairs Use of a low elevation ground antenna was reported by Valentic 1997 as the calibration source to estimate the receiver s phase offsets The advantage of this method is that the antennas can be mounted easily moved to a range of azimuths Measurements from these positions can thus be averaged to increase the accuracy of the estimated phase offsets However the angle estimation error at low elevation angles is larger than at high elevation angles which will degrade the performance of the calibration technique Unmanned vehicle UAV because of the low cost and operating flexibility received more concerns recently and is under development for autonomous antenna calibration Pisano et al 2005 This approach requires a robust navigation system in addition to GPS for system

  19. Satellite dual antenna pointing system

    NASA Technical Reports Server (NTRS)

    Keigler, John E. (Inventor); Hartshorne, Frank A. (Inventor)

    1986-01-01

    A satellite antenna pointing system for separately pointing separated transmit and receive high gain antenna systems includes means for separately and sequentially applying a beacon signal to the transmit and receive antenna systems and a broad beam width antenna which has a coverage area greater than the overall coverage region of the spot beam antenna systems. The system includes ground stations located at or near the periphery of the overall coverage region adapted to receive these beacon signals. At a central control station these beacon signals are compared to provide first signals proportional to the ratio of said beacon signals received from said transmit antenna system and said broad beam width antenna and second signals proportional to the ratio of said beacon signals received from said satellite receive antenna system and said broad beam width antenna. The central station generates from said first signals transmit antenna control signals which are sent to the satellite to control the orientation of said transmit antenna system. Likewise, the central control station generates from the second signals receiver antenna control signals which are applied to the satellite to control the orientation of the satellite receive antenna system.

  20. Image Calibration

    NASA Technical Reports Server (NTRS)

    Peay, Christopher S.; Palacios, David M.

    2011-01-01

    Calibrate_Image calibrates images obtained from focal plane arrays so that the output image more accurately represents the observed scene. The function takes as input a degraded image along with a flat field image and a dark frame image produced by the focal plane array and outputs a corrected image. The three most prominent sources of image degradation are corrected for: dark current accumulation, gain non-uniformity across the focal plane array, and hot and/or dead pixels in the array. In the corrected output image the dark current is subtracted, the gain variation is equalized, and values for hot and dead pixels are estimated, using bicubic interpolation techniques.

  1. Industrial Plasma Antennas

    NASA Astrophysics Data System (ADS)

    Alexeff, Igor

    2007-11-01

    This presentation summarizes an extensive program on plasma antennas. Plasma antennas are just as effective as metal antennas. In addition, they can transmit, receive and reflect lower frequency signals while being transparent to higher frequency signals. When de-energized, they electrically disappear. Plasma noise does not appear to be a problem. New technology that has been developed include a method of operating at high plasma density at minimal power consumption, a novel technique of noise reduction, and a method of opening a plasma window in a plasma microwave barrier on a time scale of microseconds rather than the usual time scale of milliseconds due to plasma decay. We are at present testing an intelligent plasma antenna in which a plasma ``window'' in a circular plasma barrier surrounding an antenna rotates azimuthally, seeking a radio transmitter. When located, a computer locks onto the transmitter. When the transmitter is de-energized, the plasma window recommences scanning. Commercial interest is strong, with invited papers being presented for 4 years in succession at the SMi Stealth Conference in London, UK, an operating model on permanent exhibition at the Booze-Allen headquarters in Alexandria, VA, and strong interest from Lockheed-Martin. In collaboration with Ted Anderson, Haleakala R&D Corp.; Esmaeil Farshi, Fred Dyer, Jeffrey Peck, Eric Pradeep, Nanditha Pulasani, and Naresh Karnam, University of Tennessee.

  2. Imaging antenna arrays

    NASA Technical Reports Server (NTRS)

    Rutledge, D. B.; Muha, M. S.

    1982-01-01

    Many millimeter and far-infrared imaging systems are limited in sensitivity and speed because they depend on a single scanned element. Because of recent advances in planar detectors such as Schottky diodes, superconducting tunnel junctions, and microbolometers, an attractive approach to this problem is a planar antenna array with integrated detectors. A planar line antenna array and optical system for imaging has been developed. The significant advances are a 'reverse-microscope' optical configuration and a modified bow-tie antenna design. In the 'reverse-microscope' configuration, a lens is attached to the bottom of the substrate containing the antennas. Imaging is done through the substrate. This configuration eliminates the troublesome effects of substrate surface waves. The substrate lens has only a single refracting surface, making possible a virtually aplanatic system, with little spherical aberration or coma. The array is characterized by an optical transfer function that is easily measured. An array with 19 dB crosstalk levels between adjacent antennas has been tested and it was found that the array captured 50 percent of the available power. This imaging system was diffraction limited.

  3. Aperture excited dielectric antennas

    NASA Technical Reports Server (NTRS)

    Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

    1974-01-01

    The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

  4. Electrochemically Programmable Plasmonic Antennas.

    PubMed

    Dong, Shi; Zhang, Kai; Yu, Zhiping; Fan, Jonathan A

    2016-07-26

    Plasmonic antennas are building blocks in advanced nano-optical systems due to their ability to tailor optical response based on their geometry. We propose an electrochemical approach to program the optical properties of dipole antennas in a scalable, fast, and energy-efficient manner. These antennas comprise two arms, one serving as an anode and the other a cathode, separated by a solid electrolyte. As a voltage is applied between the antenna arms, a conductive filament either grows or dissolves within the electrolyte, modifying the antenna load. We probe the dynamics of stochastic filament formation and their effects on plasmonic mode programming using a combination of three-dimensional optical and electronic simulations. In particular, we identify device operation regimes in which the charge-transfer plasmon mode can be programmed to be "on" or "off." We also identify, unexpectedly, a strong correlation between DC filament resistance and charge-transfer plasmon mode frequency that is insensitive to the detailed filament morphology. We envision that the scalability of our electrochemical platform can generalize to large-area reconfigurable metamaterials and metasurfaces for on-chip and free-space applications. PMID:27328022

  5. Cup Cylindrical Waveguide Antenna

    NASA Technical Reports Server (NTRS)

    Acosta, Roberto J.; Darby, William G.; Kory, Carol L.; Lambert, Kevin M.; Breen, Daniel P.

    2008-01-01

    The cup cylindrical waveguide antenna (CCWA) is a short backfire microwave antenna capable of simultaneously supporting the transmission or reception of two distinct signals having opposite circular polarizations. Short backfire antennas are widely used in mobile/satellite communications, tracking, telemetry, and wireless local area networks because of their compactness and excellent radiation characteristics. A typical prior short backfire antenna contains a half-wavelength dipole excitation element for linear polarization or crossed half-wavelength dipole elements for circular polarization. In order to achieve simultaneous dual circular polarization, it would be necessary to integrate, into the antenna feed structure, a network of hybrid components, which would introduce significant losses. The CCWA embodies an alternate approach that entails relatively low losses and affords the additional advantage of compactness. The CCWA includes a circular cylindrical cup, a circular disk subreflector, and a circular waveguide that serves as the excitation element. The components that make it possible to obtain simultaneous dual circular polarization are integrated into the circular waveguide. These components are a sixpost polarizer and an orthomode transducer (OMT) with two orthogonal coaxial ports. The overall length of the OMT and polarizer (for the nominal middle design frequency of 2.25 GHz) is about 11 in. (approximately equal to 28 cm), whereas the length of a commercially available OMT and polarizer for the same frequency is about 32 in. (approximately equal to 81 cm).

  6. VERITAS Distant Laser Calibration and Atmospheric Monitoring

    SciTech Connect

    Hui, C. M.

    2008-12-24

    As a calibrated laser pulse propagates through the atmosphere, the intensity of the Rayleigh scattered light arriving at the VERITAS telescopes can be calculated precisely. This allows for absolute calibration of imaging atmospheric Cherenkov telescopes (IACT) to be simple and straightforward. In these proceedings, we present the comparison between laser data and simulation to estimate the light collection efficiencies of the VERITAS telescopes, and the analysis of multiple laser data sets taken in different months for atmospheric monitoring purpose.

  7. Biogeographic calibrations for the molecular clock

    PubMed Central

    Ho, Simon Y. W.; Tong, K. Jun; Foster, Charles S. P.; Ritchie, Andrew M.; Lo, Nathan; Crisp, Michael D.

    2015-01-01

    Molecular estimates of evolutionary timescales have an important role in a range of biological studies. Such estimates can be made using methods based on molecular clocks, including models that are able to account for rate variation across lineages. All clock models share a dependence on calibrations, which enable estimates to be given in absolute time units. There are many available methods for incorporating fossil calibrations, but geological and climatic data can also provide useful calibrations for molecular clocks. However, a number of strong assumptions need to be made when using these biogeographic calibrations, leading to wide variation in their reliability and precision. In this review, we describe the nature of biogeographic calibrations and the assumptions that they involve. We present an overview of the different geological and climatic events that can provide informative calibrations, and explain how such temporal information can be incorporated into dating analyses. PMID:26333662

  8. Calibration Monitor for Dark Energy Experiments

    SciTech Connect

    Kaiser, M. E.

    2009-11-23

    The goal of this program was to design, build, test, and characterize a flight qualified calibration source and monitor for a Dark Energy related experiment: ACCESS - 'Absolute Color Calibration Experiment for Standard Stars'. This calibration source, the On-board Calibration Monitor (OCM), is a key component of our ACCESS spectrophotometric calibration program. The OCM will be flown as part of the ACCESS sub-orbital rocket payload in addition to monitoring instrument sensitivity on the ground. The objective of the OCM is to minimize systematic errors associated with any potential changes in the ACCESS instrument sensitivity. Importantly, the OCM will be used to monitor instrument sensitivity immediately after astronomical observations while the instrument payload is parachuting to the ground. Through monitoring, we can detect, track, characterize, and thus correct for any changes in instrument senstivity over the proposed 5-year duration of the assembled and calibrated instrument.

  9. Absolute luminosity measurements with the LHCb detector at the LHC

    NASA Astrophysics Data System (ADS)

    LHCb Collaboration

    2012-01-01

    Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic ``van der Meer scan'' method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overal precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.

  10. View north of the antenna array, note the communications antenna ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View north of the antenna array, note the communications antenna in the middleground - Over-the-Horizon Backscatter Radar Network, Christmas Valley Radar Site Transmit Sector Four Antenna Array, On unnamed road west of Lost Forest Road, Christmas Valley, Lake County, OR

  11. View of antenna tunnel end. Right to Antenna Silo #1, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of antenna tunnel end. Right to Antenna Silo #1, left to Antenna Silo #2 - Titan One Missile Complex 2A, .3 miles west of 129 Road and 1.5 miles north of County Line Road, Aurora, Adams County, CO

  12. Electron-Photon Coincidence Calibration Of Photon Detectors

    NASA Technical Reports Server (NTRS)

    Srivastava, Santosh K.

    1988-01-01

    Absolute and relative detector efficiencies measured. Apparatus uses coincidence-counting techniques to measure efficiency of ultraviolet or vacuum ultraviolet detector at very low radiation intensity. Crossed electron and atomic beams generate photons used to calibrate photon detector. Pulses from electron counter and photon detector(s) processed by standard coincidence-counting techniques. Used to calibrate other detectors or make absolute measurements of incident photon fluxes.

  13. An Alpha-Gamma Counter for Absolute Neutron Flux Measurement

    NASA Astrophysics Data System (ADS)

    Yue, A.; Greene, G.; Dewey, M.; Gilliam, D.; Nico, J.; Laptev, A.

    2012-03-01

    An alpha-gamma counter was used to measure the absolute neutron flux of a monochromatic cold neutron beam to sub-0.1,% precision. Simultaneously, the counter was used to calibrate a thin neutron flux monitor based on neutron absorption on ^6Li to the same precision. This monitor was used in the most precise beam-based measurement of the neutron lifetime, where the limiting systematic effect was the uncertainty in the neutron counting efficiency (0.3,%). The counter uses a thick target of ^10B-enriched boron carbide to completely absorb the beam. The rate of absorbed neutrons is determined by counting 478 keV gamma rays from neutron capture on ^10B with calibrated high-purity germanium detectors. The calibration results and the implications for the neutron lifetime will be discussed.

  14. Flight calibration assessment of HiRAP accelerometer data

    NASA Technical Reports Server (NTRS)

    Blanchard, Robert C.; Larman, Kevin T.; Moast, Christina D.

    1993-01-01

    A flight derived method of calibrating the High Resolution Accelerometer Package (HiRAP) flight data has been developed and is discussed for Shuttle Orbiter missions STS-35 and STS-40. These two mission data sets have been analyzed using ground calibration factors and flight derived calibration factors. This flight technique evolved early in the flight program when it was recognized that ground calibration factors are insufficient to determine absolute low-acceleration levels. The application of flight calibration factors to the data sets from these missions produced calibrated acceleration levels within an accuracy of less than +/- 1.5 microgravity of zero during a time in the flight when the acceleration level was known to be less than 1.0 microgravity. This analysis further confirms the theory that flight calibrations are required in order to obtain the absolute measurement of low-frequency, low-acceleration flight signals.

  15. Absolute transition probabilities of phosphorus.

    NASA Technical Reports Server (NTRS)

    Miller, M. H.; Roig, R. A.; Bengtson, R. D.

    1971-01-01

    Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

  16. Hemispheric ultra-wideband antenna.

    SciTech Connect

    Brocato, Robert Wesley

    2006-04-01

    This report begins with a review of reduced size ultra-wideband (UWB) antennas and the peculiar problems that arise when building a UWB antenna. It then gives a description of a new type of UWB antenna that resolves these problems. This antenna, dubbed the hemispheric conical antenna, is similar to a conventional conical antenna in that it uses the same inverted conical conductor over a ground plane, but it also uses a hemispheric dielectric fill in between the conductive cone and the ground plane. The dielectric material creates a fundamentally new antenna which is reduced in size and much more rugged than a standard UWB conical antenna. The creation of finite-difference time domain (FDTD) software tools in spherical coordinates, as described in SAND2004-6577, enabled this technological advance.

  17. Dual polarization flat plate antenna

    NASA Astrophysics Data System (ADS)

    Kelly, Kenneth C.

    Rectangular waveguides with radiating slots are used in groups to form planar array microwave antennas with large apertures and small depth. Such flat plate antennas are widely used on spacecraft and aircraft. Typically, flat plate antennas provide fixed linear polarization. The present paper describes a new flat plate antenna which produces two coincident beams that are distinguished by their orthogonal linear polarizations. The antenna has two ports, one for each of the coicident beams. Completely external to the antenna, connecting a simple network to those terminal ports enables the antenna to provide right circular polarization from one port and left from the other. A different external network enables the antenna to have arbitrarily adjustable polarizations.

  18. A radio telescope for the calibration of radio sources at 32 gigahertz

    NASA Astrophysics Data System (ADS)

    Gatti, M. S.; Stewart, S. R.; Bowen, J. G.; Paulsen, E. B.

    1994-08-01

    A 1.5-m-diameter radio telescope has been designed, developed, and assembled to directly measure the flux density of radio sources in the 32-GHz (Ka-band) frequency band. The main goal of the design and development was to provide a system that could yield the greatest absolute accuracy yet possible with such a system. The accuracy of the measurements have a heritage that is traceable to the National Institute of Standards and Technology. At the present time, the absolute accuracy of flux density measurements provided by this telescope system, during Venus observations at nearly closest approach to Earth, is plus or minus 5 percent, with an associated precision of plus or minus 2 percent. Combining a cooled high-electron mobility transistor low-noise amplifier, twin-beam Dicke switching antenna, and accurate positioning system resulted in a state-of-the-art system at 32 GHz. This article describes the design and performance of the system as it was delivered to the Owens Valley Radio Observatory to support direct calibrations of the strongest radio sources at Ka-band.

  19. A radio telescope for the calibration of radio sources at 32 gigahertz

    NASA Technical Reports Server (NTRS)

    Gatti, M. S.; Stewart, S. R.; Bowen, J. G.; Paulsen, E. B.

    1994-01-01

    A 1.5-m-diameter radio telescope has been designed, developed, and assembled to directly measure the flux density of radio sources in the 32-GHz (Ka-band) frequency band. The main goal of the design and development was to provide a system that could yield the greatest absolute accuracy yet possible with such a system. The accuracy of the measurements have a heritage that is traceable to the National Institute of Standards and Technology. At the present time, the absolute accuracy of flux density measurements provided by this telescope system, during Venus observations at nearly closest approach to Earth, is plus or minus 5 percent, with an associated precision of plus or minus 2 percent. Combining a cooled high-electron mobility transistor low-noise amplifier, twin-beam Dicke switching antenna, and accurate positioning system resulted in a state-of-the-art system at 32 GHz. This article describes the design and performance of the system as it was delivered to the Owens Valley Radio Observatory to support direct calibrations of the strongest radio sources at Ka-band.

  20. Standard Dataset of Brightness Temperature Resampled by Antenna Pattern Matching for Microwave Radiometer AMSR2 on GCOM-W1 Satellite

    NASA Astrophysics Data System (ADS)

    Maeda, Takashi; Imaoka, Keiji

    2014-05-01

    The operation of the Advanced Microwave Scanning Radiometer for Earth-Observation System (AMSR-E) loaded on Aqua satellite stopped in October, 2011 after more than 9-years observation. But after that, the successor of AMSR-E (AMSR2) was developed and loaded on GCOM-W1 (Global Change Observation Mission 1st - Water) satellite. GCOM-W1 satellite was successfully launched in May, 2012. AMSR2 is a microwave radiometer almost similar to AMSR-E, but some important improvements are made (i.e., expansion of its main reflector's size, addition of 7.3-GHz channel to detect radio frequency interferences at 6.9 GHz). GCOM-W1 satellite is deployed into a sun-synchronous sub-recurrent orbit, and AMSR2 observes microwave powers emitted from anywhere on the Earth almost twice a day, daytime in an ascending track and nighttime in a descending track. When we use a satellite-borne microwave radiometer data that have a main reflector shared by plural feed horns, there is an inevitable problem, the differences of footprints' sizes among frequencies. In case of AMSR2, the smallest footprint's size of 89 GHz (3 × 5 km2) has just one percent of the broadest one of 6.9 GHz (35 × 62 km2). Under the circumstance, when brightness temperatures (Tb values) of plural frequencies are obtained from the same geolocation, it is difficult to compare them one another because their observation areas are absolutely different. The concept to solve this problem is simple: actually, after a satellite-borne microwave radiometer observed on the Earth's surface, footprints which give brightness temperatures of each frequency densely distribute on it with overlaps at several-kilometer intervals (i.e., 5 km as for 89 GHz and 10 km as for other frequencies in AMSR2). The footprint is an antenna pattern projected to the Earth's surface. The antenna pattern's shape is generally like a 2-dimensional Gaussian distribution. The center of the antenna pattern has strong sensitivity, and its circumjacent part has weak

  1. Calibration strategies for the Cherenkov Telescope Array

    NASA Astrophysics Data System (ADS)

    Gaug, Markus; Berge, David; Daniel, Michael; Doro, Michele; Förster, Andreas; Hofmann, Werner; Maccarone, Maria C.; Parsons, Dan; de los Reyes Lopez, Raquel; van Eldik, Christopher

    2014-08-01

    The Central Calibration Facilities workpackage of the Cherenkov Telescope Array (CTA) observatory for very high energy gamma ray astronomy defines the overall calibration strategy of the array, develops dedicated hardware and software for the overall array calibration and coordinates the calibration efforts of the different telescopes. The latter include LED-based light pulsers, and various methods and instruments to achieve a calibration of the overall optical throughput. On the array level, methods for the inter-telescope calibration and the absolute calibration of the entire observatory are being developed. Additionally, the atmosphere above the telescopes, used as a calorimeter, will be monitored constantly with state-of-the-art instruments to obtain a full molecular and aerosol profile up to the stratosphere. The aim is to provide a maximal uncertainty of 10% on the reconstructed energy-scale, obtained through various independent methods. Different types of LIDAR in combination with all-sky-cameras will provide the observatory with an online, intelligent scheduling system, which, if the sky is partially covered by clouds, gives preference to sources observable under good atmospheric conditions. Wide-field optical telescopes and Raman Lidars will provide online information about the height-resolved atmospheric extinction, throughout the field-of-view of the cameras, allowing for the correction of the reconstructed energy of each gamma-ray event. The aim is to maximize the duty cycle of the observatory, in terms of usable data, while reducing the dead time introduced by calibration activities to an absolute minimum.

  2. Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

    NASA Astrophysics Data System (ADS)

    Salhi, Mohammed Adnan; Kazemipour, Alireza; Gentille, Gennaro; Spirito, Marco; Kleine-Ostmann, Thomas; Schrader, Thorsten

    2016-04-01

    We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003™ substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.

  3. Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

    NASA Astrophysics Data System (ADS)

    Salhi, Mohammed Adnan; Kazemipour, Alireza; Gentille, Gennaro; Spirito, Marco; Kleine-Ostmann, Thomas; Schrader, Thorsten

    2016-09-01

    We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003™ substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.

  4. Microstrip antenna technology

    NASA Astrophysics Data System (ADS)

    Carver, K. R.; Mink, J. W.

    1981-01-01

    A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques. Available substrate materials are reviewed along with the relation between dielectric constant tolerance and resonant frequency of microstrip patches. Several theoretical analysis techniques are summarized, including transmission-line and modal-expansion (cavity) techniques as well as numerical methods such as the method of moments and finite-element techniques. Practical procedures are given for both standard rectangular and circular patches, as well as variations on those designs including circularly polarized microstrip patches. The quality, bandwidth, and efficiency factors of typical patch designs are discussed. Microstrip dipole and conformal antennas are summarized. Finally, critical needs for further research and development for this antenna are identified.

  5. The ACTS multibeam antenna

    NASA Astrophysics Data System (ADS)

    Regier, Frank A.

    1992-06-01

    The Advanced Communications Technology Satellite (ACTS) to be launched in 1993 is briefly introduced. Its multibeam antenna, consisting of electrically similar 30 GHz receive and 20 GHz transmit offset Cassegrain systems, both utilizing orthogonal polarizations, is described. Dual polarization is achieved by using one feed assembly for each polarization in conjunction with nested front and back subreflectors, the gridded front subreflector acting as a window for one polarization and a reflector for the other. The antennas produce spot beams with approximately 0.3 degree beamwidth and gains of approximately 50 dbi. High surface accuracy and high edge taper produce low sidelobe levels and high cross-polarization isolation. A brief description is given of several Ka-band components fabricated for ACTS. These include multiflare antenna feedhorns, beam-forming networks utilizing latching ferrite waveguide switches, a 30 GHz HEMT low-noise amplifier and a 20 GHz TWT power amplifier.

  6. The ACTS multibeam antenna

    NASA Technical Reports Server (NTRS)

    Regier, Frank A.

    1992-01-01

    The Advanced Communications Technology Satellite (ACTS) to be launched in 1993 is briefly introduced. Its multibeam antenna, consisting of electrically similar 30 GHz receive and 20 GHz transmit offset Cassegrain systems, both utilizing orthogonal polarizations, is described. Dual polarization is achieved by using one feed assembly for each polarization in conjunction with nested front and back subreflectors, the gridded front subreflector acting as a window for one polarization and a reflector for the other. The antennas produce spot beams with approximately 0.3 degree beamwidth and gains of approximately 50 dbi. High surface accuracy and high edge taper produce low sidelobe levels and high cross-polarization isolation. A brief description is given of several Ka-band components fabricated for ACTS. These include multiflare antenna feedhorns, beam-forming networks utilizing latching ferrite waveguide switches, a 30 GHz HEMT low-noise amplifier and a 20 GHz TWT power amplifier.

  7. Launching large antennas

    NASA Astrophysics Data System (ADS)

    Brandli, H. W.

    1983-09-01

    Large antennas will provide communication to rural and remote areas in times of need. This is seen as facilitating the work of law enforcement agencies. All mobile radio communications will enjoy advantages in distances covered and information relayed owing to the large number of beams possible from super radio transmitters in space. If the antennas are placed in low-earth orbit, advantages will be realized in the remote sensing of the earth's resources. It is pointed out that with umbrella or bicyclelike antennas turned outward toward space, the universe could be scouted for signals from intelligent life. Various concepts that have been put forward by U.S. companies are described. These include the radial rib, wrap rib, and parabolic erectable truss designs. Others are the mesh hoop column collapsable umbrella made of gold and molybdenum and the maypole design.

  8. Dielectric coated wire antennas

    NASA Technical Reports Server (NTRS)

    Richmond, J. H.; Newman, E. H.

    1976-01-01

    An electrically thin dielectric insulating shell on an antenna composed of electrically thin circular cylindrical wires is examined. A moment method solution is obtained, and the insulating shell is modeled by equivalent volume polarization currents. These polarization currents are related in a simple manner to the surface charge density on the wire antenna. In this way the insulating shell causes no new unknowns to be introduced, and the size of the impedance matrix is the same as for the uninsulated wires. The insulation is accounted for entirely through a modification of the symmetric impedance matrix. This modification influences the current distribution, impedance, efficiency, field patterns, and scattering properties. The theory is compared with measurement for dielectric coated antennas in air.

  9. Far-field patterns of spaceborne antennas from plane-polar near-field measurements

    NASA Technical Reports Server (NTRS)

    Rahmat-Samii, Y.; Gatti, M. S.

    1985-01-01

    Certain unique features of a recently constructed plane-polar near-field measurement facility for determining the far-field patterns of large and fragile spaceborne antennas are described. In this facility, the horizontally positioned antenna rotates about its axis while the measuring probe is advanced incrementally in a fixed radial direction. The near-field measured data is then processed using a Jacobi-Bessel expansion to obtain the antenna far fields. A summary of the measurement and computational steps is given. Comparisons between the outdoor far-field measurements and the constructed far-field patterns from the near-field measured data are provided for different antenna sizes and frequencies. Application of the substitution method for the absolute gain measurement is discussed. In particular, results are shown for the 4.8-m mesh-deployable high-gain antenna of the Galileo spacecraft which has the mission of orbiting Jupiter in 1988.

  10. Ionospheric effects to antenna impedance

    NASA Technical Reports Server (NTRS)

    Bethke, K. H.

    1986-01-01

    The reciprocity between high power satellite antennas and the surrounding plasma are examined. The relevant plasma states for antenna impedance calculations are presented and plasma models, and hydrodynamic and kinetic theory, are discussed. A theory from which a variation in antenna impedance with regard to the radiated power can be calculated for a frequency range well above the plasma resonance frequency is give. The theory can include photo and secondary emission effects in antenna impedance calculations.

  11. Galileo satellite antenna modeling

    NASA Astrophysics Data System (ADS)

    Steigenberger, Peter; Dach, Rolf; Prange, Lars; Montenbruck, Oliver

    2015-04-01

    The space segment of the European satellite navigation system Galileo currently consists of six satellites. Four of them belong to the first generation of In-Orbit Validation (IOV) satellites whereas the other two are Full Operational Capability (FOC) satellites. High-precision geodetic applications require detailed knowledge about the actual phase center of the satellite and receiver antenna. The deviation of this actual phase center from a well-defined reference point is described by phase center offsets (PCOs) and phase center variations (PCVs). Unfortunately, no public information is available about the Galileo satellite antenna PCOs and PCVs, neither for the IOV, nor the FOC satellites. Therefore, conventional values for the IOV satellite antenna PCOs have been adopted for the Multi-GNSS experiment (MGEX) of the International GNSS Service (IGS). The effect of the PCVs is currently neglected and no PCOs for the FOC satellites are available yet. To overcome this deficiency in GNSS observation modeling, satellite antenna PCOs and PCVs are estimated for the Galileo IOV satellites based on global GNSS tracking data of the MGEX network and additional stations of the legacy IGS network. Two completely independent solutions are computed with the Bernese and Napeos software packages. The PCO and PCV values of the individual satellites are analyzed and the availability of two different solutions allows for an accuracy assessment. The FOC satellites are built by a different manufacturer and are also equipped with another type of antenna panel compared to the IOV satellites. Signal transmission of the first FOC satellite has started in December 2014 and activation of the second satellite is expected for early 2015. Based on the available observations PCO estimates and, optionally PCVs of the FOC satellites will be presented as well. Finally, the impact of the new antenna model on the precision and accuracy of the Galileo orbit determination is analyzed.

  12. Satellite communication antenna technology

    NASA Technical Reports Server (NTRS)

    Mittra, R. (Editor); Imbriale, W. A. (Editor); Maanders, E. J. (Editor)

    1983-01-01

    A general overview of current technology in the field of communication satellite antennas is presented. Among the topics discussed are: the design of multiple beam systems; frequency reuse; and polarization control of antenna measurements. Consideration is also given to: contour beam synthesis; dual shaped reflector synthesis; beam shaping; and offset reflector design. The applications of the above technologies to present and future generations of communications satellites is considered, with emphasis given to such systems as: the Intelsats; the Defense Satellite Communications System, (DSCS-III); Satellite Business System (SBS), and Comstar.

  13. Furlable spacecraft antenna development

    NASA Technical Reports Server (NTRS)

    Oliver, R. E.; Wilson, A. H.

    1972-01-01

    The development of large furlable spacecraft antennas using conical main reflectors is described. Two basic antenna configurations which utilize conical main reflectors have been conceived and are under development. In the conical-Gregorian configuration each ray experiences two reflections in traveling from the feed center to the aperture plane. In the Quadreflex (four reflection) configuration, each ray experiences four reflections, one at each of two subreflector surfaces and two at the main conical reflector surface. The RF gain measurements obtained from 6-ft and 30-in. models of the conical-Gregorian and Quadreflex concepts respectively were sufficiently encouraging to warrant further development of the concepts.

  14. Collapsible high gain antenna

    NASA Technical Reports Server (NTRS)

    Cribb, H. E. (Inventor)

    1973-01-01

    A lightweight small high gain antenna which is capable of being packaged in a collapsed form and automatically expanded when in use is described. The antenna includes a cylindrical housing having a rod with a piston adjacent to one end extending through it. Attached to the outer end of the rod in a normally collapsed state is a helical wire coil. When the gas producing means is activated the piston and rod are shifted outwardly to expand the wire coil. A latch is provided for holding the helical coil in the expanded position.

  15. Spaced antenna drift

    NASA Technical Reports Server (NTRS)

    Royrvik, O.

    1983-01-01

    It has been suggested that the spaced antenna drift (SAD) technique could be successfully used by VHF radars and that it would be superior to a Doppler-beam-swinging (DBS) technique because it would take advantage of the aspect sensitivity of the scattered signal, and might also benefit from returns from single meteors. It appears, however, that the technique suffers from several limitations. On the basis of one SAD experiment performed at the very large Jicamarca radar, it is concluded that the SAD technique can be compared in accuracy to the DBS technique only if small antenna dimensions are used.

  16. DSN Microwave Antenna Holography

    NASA Technical Reports Server (NTRS)

    Rochblatt, D. J.; Seidel, B. L.

    1984-01-01

    The DSN microwave antenna holography project will obtain three-dimensional pictures of the large DSN antenna surfaces. These pictures must be of suffi icient resolution to allow adjustment of the reflector panels to an rms surface of 0.5 mm (0.25 mm, goal). The major parameters and equations needed to define a holographic measurement system are outlined and then the proof of concept demonstration measurement that was made at DSS-43 (Australia) that resulted in contour maps with spatial resolution of 7 m in the aperture plane and resolution orthogonal to the aperture plane of 0.7 mm was discussed.

  17. A century of antenna development

    NASA Astrophysics Data System (ADS)

    Olver, A. D.

    The paper describes a century of antenna development as part of a century of radio communications. This historical review examines, chronologically, the pre-Hertz period, Hertz antennas, the microwave optics period, the Marconi era, short waves, theoretical design before and after computers, and radar. Consideration is also given to mobile antennas, microwave comunications, radio astronomy, and satellite comunications.

  18. The JPL mechanically steered antenna

    NASA Technical Reports Server (NTRS)

    Berner, Jeff B.; Bell, David J.

    1988-01-01

    The Jet Propulsion Laboratory has designed and developed a mechanically steered antenna for tracking satellites in a mobile environment. This antenna was used to track an L-band beacon on the MARISAT satellite. A description of the antenna and the results of the satellite experiment are given.

  19. Characterization of Fricke-gel layers for absolute dose measurements in radiotherapy

    SciTech Connect

    Gambarini, G.; Carrara, M.; Rrushi, B.; Guilizzoni, R.; Borroni, M.; Tomatis, S.; Pirola, L.; Battistoni, G.

    2011-07-01

    Fricke-gel layer dosimeters (FGLDs) have shown promising features for attaining absolute measurements of the spatial distribution of the absorbed dose in radiotherapy. Good precision of results (within 3%) is achieved by means of calibration of each single dosimeter before measurement. The calibration is performed irradiating the dosimeter at a uniform and precisely known dose, in order to get a calibration matrix that must be used, with pixel-to-pixel manipulation, to obtain the dose image. A study of the trend in time of dosimeter response after one or more exposures was carried out and calibration protocols were suitably established and verified. (authors)

  20. Optomechanics for absolute rotation detection

    NASA Astrophysics Data System (ADS)

    Davuluri, Sankar

    2016-07-01

    In this article, we present an application of optomechanical cavity for the absolute rotation detection. The optomechanical cavity is arranged in a Michelson interferometer in such a way that the classical centrifugal force due to rotation changes the length of the optomechanical cavity. The change in the cavity length induces a shift in the frequency of the cavity mode. The phase shift corresponding to the frequency shift in the cavity mode is measured at the interferometer output to estimate the angular velocity of absolute rotation. We derived an analytic expression to estimate the minimum detectable rotation rate in our scheme for a given optomechanical cavity. Temperature dependence of the rotation detection sensitivity is studied.