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1

HF radar ionospheric clutter  

NASA Astrophysics Data System (ADS)

The characteristics of HF radar echoes reflected from ionization irregularities aligned along the lines of force of the Earth's magnetic field are presented. Utilizing experimental radar-ionospheric clutter data acquired at frequencies between HF and UHF, an analysis is made of the amplitude, the cross-sectional area and the angular extent statistics of HF field-aligned echoes. The Doppler frequency variation, the frequency of occurrence and the diurnal and seasonal variation of HF ionospheric backscatter echoes and their correlation with solar-geophysical conditions are also discussed.

Millman, G. H.

1982-08-01

2

Prospects for tsunami detection and characterisation with HF skywave radar  

Microsoft Academic Search

The Indian Ocean tsunami of Boxing Day, 2004, stimulated interest in the potential of HF radar to provide early warning of such threats. Almost all of the resulting activity focussed on HF surface wave radar (HFSWR), and in at least one case, deployment of a dedicated HFSWR tsunami warning system has eventuated. Yet, while the efficacy of HFSWR in this

Stuart Anderson

2008-01-01

3

Application of HF radar currents to oil spill modelling  

Microsoft Academic Search

In this work, the benefits of high-frequency (HF) radar currents for oil spill modeling and trajectory analysis of floating objects are analyzed. The HF radar performance is evaluated by means of comparison between a drifter buoy trajectory and the one simulated using a Lagrangian trajectory model. A methodology to optimize the transport model performance and to calculate the search area

Ana J. Abascal; Sonia Castanedo; Raul Medina; Inigo J. Losada; Enrique Alvarez-Fanjul

2009-01-01

4

Progress in the interpretation of HF sea echo - HF radar as a remote sensing tool  

NASA Astrophysics Data System (ADS)

When HF radar systems are used for surveillance or tracking of ships or aircraft the strong signal from the ocean surface is termed clutter since it obscures the required signals. Over 30 years ago it was recognized that this sea 'clutter' had characteristics that could be related to the ocean wave spectrum and the idea of using HF radar for remote sensing was born. This paper describes recent work on the inversion of the Doppler spectrum of HF radar echoes from the ocean surface to provide measurements of the ocean wave directional spectrum.

Wyatt, L. R.

1990-04-01

5

Directional wave spectrum measurement with multistatic HF surface wave radar  

Microsoft Academic Search

HF surface wave radars (HFSWR) measure sea surface currents and current profiles via the Doppler shift of the discrete (first-order scattering) line structure in the radar Doppler spectrum. They can also exploit the higher-order scattering contributions to the Doppler spectrum which yield information on the sea surface directional spectrum in the gravity wave band. Most HFSWR systems operate in a

S. J. Anderson

2000-01-01

6

Investigations with SECAR - a bistatic HF surface wave radar  

Microsoft Academic Search

This paper describes a bistatic HF surface wave radar, designated SECAR, which was deployed near Darwin, Australia, and used to conduct a variety of scientific investigations related to radar design, siting and target detection, as well as providing a test-bed for evaluating the operational utility of HFSWR as an element of a national surveillance network. The scientific results are significant

S. J. Anderson; P. J. Edwards; P. Marrone; Y. I. Abramovich

2003-01-01

7

Ionospheric Clutter Suppression in HF Surface Wave Radar  

Microsoft Academic Search

The ionospheric clutter has been proved to be one of the dominant clutters degrading the performance of the HF surface-wave radar (HFSWR) severely, so suppressing the ionospheric clutter is a vital part of radar signal processing sequence. In this paper, the spatial characteristics of the ionospheric clutter in a planar array are analyzed, then a new orthogonal projection method with

M. Wu; B. Y. Wen; H. Zhou

2009-01-01

8

The case for bistatic HF surface wave radar  

Microsoft Academic Search

This paper examines some of the issues associated with implementation of HF surface wave radars (HFSWR) in bistatic and monostatic configurations. Most HFSWRs deployed in the field are pseudo-monostatic although they may not be optimum for all deployments. Radar transmitter spectral characteristics, detection performance based on received signal strength and site selection criteria are considered in this paper for both

P. Marrone; P. Edwards

2008-01-01

9

Ionospheric Clutter Suppression in HF Surface Wave Radar OSMAR  

Microsoft Academic Search

Experimental trials conducted from 2003 to 2005 in east China sea demonstrated that HF surface wave radar (HFSWR) OSMAR (ocean state monitor and analysis radar) could be strongly affected by scattering from ionospheric structures and irregularities. A large database acquired during those trials has been used in detailed investigations of the phenomenology of this ionospheric clutter, leading to the development

Wan Xianrong; Xiong Xinlong; Ke Hengyu

2006-01-01

10

Adaptive radio frequency interference mitigation for HF surface wave radar  

Microsoft Academic Search

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HF-SWR) which adopts\\u000a the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the\\u000a positive frequency and negative frequency, and the negative frequency range cells contain only the interference information.\\u000a Based on the above characteristics, we introduce and

Wan Xian-rong; Ke Heng-yu; Cheng Feng

2005-01-01

11

KONRAD: Wide band digital HF receiver  

NASA Astrophysics Data System (ADS)

Electronic support measures (ESM) and spread spectrum techniques, i.e. direct sequence (DS) or frequency hopping (FH), in the HF band require a high dynamic range as well as a large instantaneous bandwidth in the receiver. This report describes an experimental digital receiver utilizing digitally implemented quadrature splitting and baseband translation. It is shown that the use of digital quadrature splitting improves the image rejection and that oversampling and digital filtering improves the dynamic range. The receiver is built of standard components which give a beneficial cost/performance ratio. The focus is on the analog hardware of the experimental digital receiver named KONRAD. The report also serves as the manual for this receiver.

Oscarsson, F.

1994-01-01

12

On the accuracy of HF radar surface current measurements: Intercomparisons with ship-based sensors  

Microsoft Academic Search

High-frequency (HF) radar systems can provide periodic, two-dimensional, vector current estimates over an area approaching 1000 km . As the use of these HF systems has gained wider acceptance, a number of attempts have been made to estimate the accuracy of such systems. However, comparisons of HF radar current estimates with in situ sensors are difficult to interpret since HF

R. D. Chapman; L. K. Shay; H. C. Graber; J. B. Edson; A. Karachintsev; C. L. Trump; D. B. Ross

1997-01-01

13

HF surface wave radar operation in adverse conditions  

Microsoft Academic Search

For the past 12 years the Canadian Department of National Defence and Raytheon Canada Limited have collaborated on a cost-shared programme to develop an Integrated Maritime Surveillance (IMS) system based on HF Surface Wave Radar (HFSWR). The primary objective behind the programme was to demonstrate the capability of HFSWR to continuously detect and track surface targets (ships and icebergs) as

Anthony M. Ponsford; Reza M. Dizaji; R. McKerracher

2003-01-01

14

Correlation based novel detection scheme for HF Surface Wave Radar  

Microsoft Academic Search

The challenge in HF Surface Wave Radar (SWR) lies in the detection of a target signal in the background of a strong sea clutter. A novel detection scheme is proposed which assumes that for a given Range Doppler (RD) cell in absence of a target, the normalized second order sea clutter power along the azimuth cells will be correlated over

A. Gupta; Th. Fickenscher

2011-01-01

15

Beamformer evaluation of low power coastal HF surface wave radar  

Microsoft Academic Search

Owing to large operational range and relatively low cost of operation coastal HF Surface Wave Radar has witnessed an increased interest in monitoring coastal territories. Using a well established sea clutter model this paper evaluates the state of art beamformer (Hamming) employed by such coastal systems. Evaluation parameters are degradation during beam scanning and target azimuth resolution in high sea

Anshu Gupta; Thomas Fickenscher

2011-01-01

16

Ship detection and tracking using HF surface wave radar  

Microsoft Academic Search

The Canadian Department of National Defence (DND) conducted a joint trial involving multiple sensors in the detection and tracking of ships in the Grand Banks of Canada in March 2000, including the HF surface wave radar (HFSWR) system at Cape Race, Newfoundland. One objective of the trial was to evaluate the detection and tracking capabilities of the HFSWR system. Three

H. Leong; C. Helleur; M. Rey

2002-01-01

17

Hard threshold correlation detector for mobile HF Surface Wave Radar  

Microsoft Academic Search

Mobile HF Surface Wave Radar (SWR) can be realized by an offshore distributed receiver array structure which communicates to the central processing unit at the base station via a wireless link. State of the art detectors demand a sophisticated signal processing which can only be done at base station hence making it imperative to transmit raw data form receiver to

Anshu Gupta; Th. Fickenscher

2012-01-01

18

Adaptive radio frequency interference mitigation for HF surface wave radar  

Microsoft Academic Search

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HFSWR) which adopt the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the positive and negative frequency, and that the negative frequency range cells contain only the interference information. Based on the above characteristics, we introduce and

Wan Xianrong; Wen Biyang; Ke Hengyu

2004-01-01

19

Iceberg tracking using HF surface wave radar  

Microsoft Academic Search

An iceberg surveillance experiment involving multiple sensors was carried out in a one-week period between April and May, 1995. Several Canadian and U.S. Agencies and members of industry participated The Canadian Department of National Defence, in collaboration with industry provided high-frequency surface-wave radar (HFSWR) sensors, while the Canadian and U.S. Coast Guards collected surface and aerial ground-truth data. The experiment

H. C. Chan; T. W. Davies; P. Hall

1997-01-01

20

Customizable Digital Receivers for Radar  

NASA Technical Reports Server (NTRS)

Compact, highly customizable digital receivers are being developed for the system described in 'Radar Interferometer for Topographic Mapping of Glaciers and Ice Sheets' (NPO-43962), NASA Tech Briefs, Vol. 31, No. 7 (August 2007), page 72. The receivers are required to operate in unison, sampling radar returns received by the antenna elements in a digital beam-forming (DBF) mode. The design of these receivers could also be adapted to commercial radar systems. At the time of reporting the information for this article, there were no commercially available digital receivers capable of satisfying all of the operational requirements and compact enough to be mounted directly on the antenna elements. A provided figure depicts the overall system of which the digital receivers are parts. Each digital receiver includes an analog-to-digital converter (ADC), a demultiplexer (DMUX), and a field-programmable gate array (FPGA). The ADC effects 10-bit band-pass sampling of input signals having frequencies up to 3.5 GHz. The input samples are demultiplexed at a user-selectable rate of 1:2 or 1:4, then buffered in part of the FPGA that functions as a first-in/first-out (FIFO) memory. Another part of the FPGA serves as a controller for the ADC, DMUX, and FIFO memory and as an interface between (1) the rest of the receiver and (2) a front-panel data port (FPDP) bus, which is an industry-standard parallel data bus that has a high data-rate capability and multichannel configuration suitable for DBF. Still other parts of the FPGA in each receiver perform signal-processing functions. The digital receivers can be configured to operate in a stand-alone mode, or in a multichannel mode as needed for DBF. The customizability of the receiver makes it applicable to a broad range of system architectures. The capability for operation of receivers in either a stand-alone or a DBF mode enables the use of the receivers in an unprecedentedly wide variety of radar systems.

Moller, Delwyn; Heavey, Brandon; Sadowy, Gregory

2008-01-01

21

HF Surface Wave Radar Tests at the Eastern China Sea  

Microsoft Academic Search

The HF surface wave radar system OSMAR2000 adopts Frequency Modulated Interrupted Continuous Waveform (FMICW) and its 120m-antenna array is transmitting\\/receiving co-used. MUSIC and MVM are applied to obtain sea echo's direction of arrival (DOA) when extracting currents information. Verification tests of OSMAR2000 ocean surface dynamics detection against in-situ measurements had been accomplished on Oct. 23~29, 2000. Ship detection test was

Xiong Bin Wu; Feng Cheng; Shi Cai Wu; Zi Jie Yang; Biyang Wen; Zhen Hua Shi; Jiansheng Tian; Hengyu Ke; Huotao Gao

2005-01-01

22

Non-stationary interference cancellation in HF surface wave radar  

Microsoft Academic Search

High frequency (HF) interference in surface wave over-the-horizon (OTH) radars typically exhibits a time-varying or non-stationary spatial structure. Adaptive beamformers that update the spatial filtering weight vector within the coherent processing interval (CPI) are likely to suppress such interference most effectively, but the intra-CPI antenna pattern fluctuations result in temporal de-correlation of the clutter which severely degrades sub-clutter visibility after

G. A. Fabrizio; A. B. Gershman; Mike D. Turley

2003-01-01

23

HF surface wave radar management techniques applied to surface craft detection  

Microsoft Academic Search

HF radar is a unique land or ship based sensor which provides over the horizon (OTH) target detection. In the absence of microwave ducting, which is not a reliable environmental feature, HF radar operating in the 3-30 MHz band offers the primary method of obtaining target returns from beyond the conventional radar horizon. Two alternative approaches are employed utilising different

D. G. Money; David J. Emery; Trevor M. Blake; Colin F. Clutterbuck; Stephen J. Ablett

2000-01-01

24

HF Surface Wave Radar Tests at the Eastern China Sea  

NASA Astrophysics Data System (ADS)

The HF surface wave radar system OSMAR2000 adopts Frequency Modulated Interrupted Continuous Waveform (FMICW) and its 120m-antenna array is transmitting/receiving co-used. MUSIC and MVM are applied to obtain sea echo's direction of arrival (DOA) when extracting currents information. Verification tests of OSMAR2000 ocean surface dynamics detection against in-situ measurements had been accomplished on Oct. 23~29, 2000. Ship detection test was carried out on Dec.24, 2001. It shows that OSMAR2000 is capable of detecting 1000 tons ships with a wide beam out to 70 km. This paper introduces the radar system and the applied DOA estimation methods in the first, and then presents ship detection results and some sea state measurement results of surface currents and waves. The results indicate the validity of the developed radar system and the effectiveness of the applied signal processing methods.

Wu, Xiong Bin; Cheng, Feng; Wu, Shi Cai; Yang, Zi Jie; Wen, Biyang; Shi, Zhen Hua; Tian, Jiansheng; Ke, Hengyu; Gao, Huotao

2005-01-01

25

New antenna layout for a SuperDARN HF radar  

NASA Astrophysics Data System (ADS)

A new antenna layout for a Super Dual Auroral Radar Network (SuperDARN) HF radar has been developed. The new layout utilizes two auxiliary arrays; one behind and one in front of the main array, rather than the single auxiliary array that existing radars use. The rear auxiliary array consists of three antennas providing beam-steering capability while the front auxiliary array consists of a single antenna. This layout is expected to greatly improve the calculation of elevation angle of arrival. Simulations presented show the advantages and disadvantages of using twin-terminated folded dipole (TTFD) antennas and log-periodic dipole arrays in standard and modified SuperDARN array configurations. TTFD antennas are shown to have superior front-to-back ratio and beam-steering capability but suffer from shadowing effects due to the presence of corner reflectors. Impedance-matching techniques used in SuperDARN radars are discussed, and the results of a new matching method, exhibiting a superior voltage standing-wave ratio over the SuperDARN frequency band, are presented. Shadowing of the main array by the front auxiliary array is investigated, and it is shown that the impact of the front array on the main array gain pattern is significantly less for the case of a single front antenna than for a four-antenna front array. Radar phase calibration techniques are discussed, and it is proposed that the additional single-antenna front array be used for system-wide radar phase calibration. An algorithm for the determination of elevation angle of arrival using the new layout is also given.

Custovic, Edhem; McDonald, Andrew J.; Whittington, James; Elton, Darrell; Kane, Thomas A.; Devlin, John C.

2013-11-01

26

Large-scale imaging of high-latitude convection with Super Dual Auroral Radar Network HF radar observations  

Microsoft Academic Search

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E x B drift of ionospheric plasma over extended regions of the high- latitude ionosphere. With the recent augmentation of the northern hemisphere component to six radars, a sizable fraction of the entire convection zone (approximately one-third) can be imaged nearly instantaneously (-2 min). To

J. M. Ruohoniemi; K. B. Baker

1998-01-01

27

Assimilation of HF radar data into the SWAN wave model  

NASA Astrophysics Data System (ADS)

Data assimilation is a method used for optimally combining information to improve forecasting and model parameters. Three data assimilation algorithms are investigated and used for assimilating HF radar data into the SWAN wave model. The schemes under consideration are the Ensemble Kalman Filter, Ensemble Optimal Interpolation and a Three-Dimensional Variational scheme. Two approaches for updating the ocean wave spectrum are considered which consist of describing the spectrum using integral wave parameters of the whole spectrum and wave parameters within various frequency bands. The results show improvement in the wave parameters at the buoy location for the 3DVAR and ENS-OI scheme. The EnKF only shows good performance in one of the considered runs which leads to a conclusion that the methods used for calculating the errors for the EnKF scheme need further analysis.

Siddons, L. A.; Wyatt, L. R.; Wolf, J.

2009-05-01

28

Measuring rms Wave Height and the Scalar Ocean Wave Spectrum With HF Skywave Radar  

Microsoft Academic Search

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high-frequency (HF) skywave radar-measured sea-echo Doppler spectra. Whereas low-power surface- wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection.

Joseph W. Maresca; T. M. Georges

1980-01-01

29

Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study  

Microsoft Academic Search

The dynamics of the cusp region and post- noon sector for an interval of predominantly IMF By, Bz < 0 nT are studied with the CUTLASS Finland coherent HF radar, a meridian-scanning photometer located at Ny Alesund, Svalbard, and a meridional network of magnetometers. The scanning mode of the radar is such that one beam is sampled every 14 s,

S. E. Milan; M. Lester; S. W. H. Cowley; J. Moen; P. E. Sandholt; C. J. Owen

1999-01-01

30

Improved detection and suppression of external interference in HF Surface Wave Radar  

Microsoft Academic Search

This paper presents a propagation-attenuation-model-based method to detect the ranges where ionospherically distorted signals in HF Surface Wave Radar (HFSWR) may become dominant. While the method can be used to detect the presence of both ionospheric clutter and skywave interference, this paper focuses on the detection of skywave interference only. The radar data in the detected ranges where skywave interference

Hank Leong

2011-01-01

31

HF surface wave radar for oceanography - a review of activities in Germany  

Microsoft Academic Search

The remote sensing group of the University of Hamburg is working in the field of HF radar since 1980. For the start three CODAR systems have been purchased from NOAA\\/ERL (developed by D. Barrick's NOAA group). Based on 16 years of experience a new system called WEllen RAdar (WERA) has been designed at the University of Hamburg in 1996. The

Klaus-Werner Gurgel; Heinz-Hennann Essen; Thomas Schlick

2003-01-01

32

Some aspects of design and environmental management in HF surface wave radar  

Microsoft Academic Search

With the current emphasis on the surveillance of coastal waters, particularly for economic exclusion zone (EEZ) applications, there has been an increased interest in the capability of HF surface wave radar (HFSWR) to detect targets beyond the conventional radar horizon. The surface wave mode is generated where a vertically polarised high frequency electromagnetic wave is launched over a saline water

D. J. Emery; D. G. Money; H. W. Mainwaring

2002-01-01

33

Inversion of swell frequency from a 1-year HF radar dataset collected in Brittany (France)  

NASA Astrophysics Data System (ADS)

This article presents long period ocean wave (swell) frequencies inverted from a 13-month dataset of high-frequency (HF) phased array radars and an assessment of these estimates by comparison with WAVEWATCH III model data. The method of swell frequency inversion from high-frequency radar sea echo Doppler spectra is described. Radar data were collected from a two-site HF Wellen Radar (WERA) radar system on the west coast of Brittany (France) operating at 12 MHz. A standard beam-forming processing technique has been used to obtain Doppler spectra of processed radar cells. Swell frequencies are obtained from the frequencies of particular spectral peaks of the second-order continuum in hourly averaged Doppler spectra. The data coverage of effective Doppler spectra considered for swell frequency estimates shows the influence of islands and shallow water effects. Swell estimates from both radar stations are in good agreement. The comparison of radar-derived results to WAVEWATCH III (WW3) estimates shows that radar measurements agree quite well with model results. The bias and standard deviation between two estimates are very small for swells with frequency less than 0.09 Hz (period >11 s), whereas radar estimates are generally lower than model estimates for shorter swells, along with higher standard deviation. Statistical analysis suggests that radar measurement uncertainty explains most of the difference between radar and model estimates. For each swell event, time series of frequency exhibits a quasi-linear frequency increase which is associated with the dispersive property of wave phase velocity. The use of swell frequency estimates from both radars on common radar cells only slightly increases the accuracy of swell frequency measurement.

Wang, Weili; Forget, Philippe; Guan, Changlong

2014-10-01

34

Inversion of swell frequency from a 1-year HF radar dataset collected in Brittany (France)  

NASA Astrophysics Data System (ADS)

This article presents long period ocean wave (swell) frequencies inverted from a 13-month dataset of high-frequency (HF) phased array radars and an assessment of these estimates by comparison with WAVEWATCH III model data. The method of swell frequency inversion from high-frequency radar sea echo Doppler spectra is described. Radar data were collected from a two-site HF Wellen Radar (WERA) radar system on the west coast of Brittany (France) operating at 12 MHz. A standard beam-forming processing technique has been used to obtain Doppler spectra of processed radar cells. Swell frequencies are obtained from the frequencies of particular spectral peaks of the second-order continuum in hourly averaged Doppler spectra. The data coverage of effective Doppler spectra considered for swell frequency estimates shows the influence of islands and shallow water effects. Swell estimates from both radar stations are in good agreement. The comparison of radar-derived results to WAVEWATCH III (WW3) estimates shows that radar measurements agree quite well with model results. The bias and standard deviation between two estimates are very small for swells with frequency less than 0.09 Hz (period >11 s), whereas radar estimates are generally lower than model estimates for shorter swells, along with higher standard deviation. Statistical analysis suggests that radar measurement uncertainty explains most of the difference between radar and model estimates. For each swell event, time series of frequency exhibits a quasi-linear frequency increase which is associated with the dispersive property of wave phase velocity. The use of swell frequency estimates from both radars on common radar cells only slightly increases the accuracy of swell frequency measurement.

Wang, Weili; Forget, Philippe; Guan, Changlong

2014-08-01

35

Preliminary analysis of HF auroral backscatter data observed using Verona Ava linear array radar  

NASA Astrophysics Data System (ADS)

HF auroral backscatter recordings were made using the Verona Ava linear array radar (VALAR) during 1990. The authors present an example of initial results from the analysis of HF data collected during September 1990. The range-azimuth distribution and Doppler characteristics of 2F ground backscatter from the sub-auroral and the auroral F-region were identified and characterized using amplitude-range-azimuth maps and amplitude-range-Doppler maps.

Choi, D. S.; Weijers, B.; Norris, R. J.; Myers, N. B.

36

Ionospheric effect of HF surface wave over-the-horizon radar  

NASA Astrophysics Data System (ADS)

The use of HF surface wave radar as an effective method for inspecting the environment of the ocean in the beyond-the-horizon area has been developing in recent years. However, because the radiating beam of the transmitting antenna is of a certain width and its electromagnetic radiating power propagates not only along the sea surface but also to the upper space, as a result, after interacting with the ionosphere or a scattering object on its path, the backscattered signal then returns to the radar along the radiative path. Thus, if we analyze the echo signal received by the radar, we can obtain some information about the ionosphere. This paper presents a method of sensing the ionosphere using HF ground wave radar, which can give information about the altitude of the ionosphere, Doppler, meteor showers, etc.

Gao, Huotao; Li, Geyang; Li, Yongxu; Yang, Zijie; Wu, Xiongbin

2006-12-01

37

Sporadic-E ionospheric clutter suppression in HF surface-wave radar  

Microsoft Academic Search

The unwanted radar echoes from the ionosphere are collectively called ionospheric clutter. It has proved to be the greatest impediment to achieving consistently good performance in long-range detection of surface vessels and sea state monitoring for HF surface wave radar (HFSWR). Ionospheric clutter can mask target\\/sea echoes having similar Doppler shifts. Main characteristics of sporadic-E ionospheric clutter (Es-layer clutter) are

Wan Xianrong; Cheng Feng; Ke Hengyu

2005-01-01

38

The effects of reduced bandwidth on HF surface wave radar performance in ship detection  

Microsoft Academic Search

Bandwidth reduction not only degrades the range resolution of a radar, but may also reduce the maximum detection range. In the clutter-dominated region, the target signal-to-clutter-plus-interference-and-noise power ratio (SCINR) is reduced by the same factor as the bandwidth, but in the external-interference-and-noise-dominated region, the SCINR is unchanged. A dataset from a monostatic pulse HF surface wave radar (HFSWR) operating between

Hank Leong

2009-01-01

39

Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study  

Microsoft Academic Search

The dynamics of the cusp region and post-noon sector for an interval of predominantly IMF By, Bz < 0 nT are studied with the CUTLASS Finland coherent HF radar, a meridian-scanning photometer located at Ny Ålesund, Svalbard, and a meridional network of magnetometers. The scanning mode of the radar is such that one beam is sampled every 14 s, and

S. E. Milan; M. Lester; S. W. H. Cowley; J. Moen; P. E. Sandholt; C. J. Owen

1999-01-01

40

Estimation of the sea surface radar cross section at HF from second order Doppler spectrum characteristics  

Microsoft Academic Search

A technique is developed for estimating the radar cross section of the sea surface at HF (2-30 MHz) from two simple measurements made of the radar Doppler spectrum. These are: the ratio of approach\\/recede Bragg line energy, and the ratio of strongest Bragg line amplitude to average value amplitude of second-order backscatter at zero Doppler frequency. A nomograph is given,

D. B. Trizna

1982-01-01

41

Optimization of boundary conditions of a North Western Mediterranean coastal zone using HF radar measurements  

NASA Astrophysics Data System (ADS)

Correction of open boundary conditions (OBC) is attempted to improve surface velocity fields by assimilating HF radar velocities in a North Western Mediterranean (NWM) coastal model nested in a large scale operational model (Mercator Ocean system PSY2) providing IC (Initial Conditions) and OBC. A method based on HF radar velocities assimilation using an Ensemble Kalman Filter (EnKF) to derive the optimal wind forcing had already been validated. The objective of this work is to implement this method to the OBC correction. An ensemble simulation of the NWM sea model is carried out under different OBC to estimate model error covariance and covariance between surface currents and OBC. We evaluate the ability to correct the baroclinic oceanic forcings and to improve the surface current using a distant HF radar system. First, the method is assessed using twin experiments and a NWM sea model based on a Regional Ocean Model System (ROMS) configuration at 1/12°. Next, the method is applied to a high resolution (1/64°) NEMO-based model using a HF radar system operating in the Cote d'Azur. The method evaluation is done in both the eulerian and the lagrangian framework, based on a comprehensive data set (surface radial currents, surface drifter trajectories) obtained during the TOSCA (MedProgram) campaign. TOSCA project intends to optimize the response to marine accidents (oil spill, search and rescue) in Mediterranean sea, and the radar data assimilation may represent a great advantage to describe with more accuracy surface currents. Keywords : HF radar, data assimilation, ensemble simulation, surface meso-scale process, North Western Mediterranean sea, coastal modelling.

Marmain, Julien; Molcard, Anne; Forget, Philippe; Barth, Alexander

2013-04-01

42

EMC study of a shipboard HF surface wave radar  

Microsoft Academic Search

This paper presents the results of a feasibility study of a high frequency surface wave radar (HFSWR) on a navy ship. The electromagnetic compatibility (EMC) and transmit antenna design issues are addressed

S. T. Li; L. B. Koyama; R. J. Dinger

1995-01-01

43

Interpolation of the Radial Velocity Data from Coastal HF Radars.  

National Technical Information Service (NTIS)

In recent years, monitoring nearshore surface currents became an important application of the high-frequency radar (HFR) technology. The Doppler shifts of backscattered radio signals from surface waves provide the surface velocity component in the directi...

A. Sentchev, M. Yaremchuk

2013-01-01

44

Ionospheric effect of HF surface wave over-the-horizon radar  

Microsoft Academic Search

The use of HF surface wave radar as an effective method for inspecting the environment of the ocean in the beyond-the-horizon area has been developing in recent years. However, because the radiating beam of the transmitting antenna is of a certain width and its electromagnetic radiating power propagates not only along the sea surface but also to the upper space,

Huotao Gao; Geyang Li; Yongxu Li; Zijie Yang; Xiongbin Wu

2006-01-01

45

The effects of sea clutter on the performance of HF Surface Wave Radar in ship detection  

Microsoft Academic Search

This paper presents a study of the effects of sea clutter on the performance of HF surface wave radar (HFSWR), operating in the band between 3 and 5 MHz, in the detection of two classes of ships: large freighters with gross registered tonnage (GRT) in the order of several tens of thousands of tons and small vessels with a GRT

Hank Leong; A. Ponsford

2008-01-01

46

Cancellation of Es layer clutter in a HF Surface Wave Radar using auxiliary horizontal Dipole antennas  

Microsoft Academic Search

This paper presents the results of a preliminary study of an adaptive system using horizontal antennas for the cancellation of Es layer clutter in HF surface wave radar (HFSWR). Four horizontal dipoles, configured as two separate crosses, were added to a HFSWR system that normally uses vertically polarized antennas (VPAs). The data received from the horizontal antennas were correlated with

Long Zhao

2009-01-01

47

Adaptive suppression of skywave interference in HF surface wave radar using auxiliary horizontal dipole antennas  

Microsoft Academic Search

This paper presents the results of a study to evaluate the effectiveness of an adaptive technique using horizontal dipoles to suppress the skywave interference in HF surface wave radar (HFSWR). Four auxiliary horizontal dipole antennas, configured in the form of two separate crosses, are used to form an adaptive system with the vertically polarized antennas (VPA) of a HFSWR system.

Hank W. H. Leong

1999-01-01

48

Using HF Surface Wave Radar and the Ship Automatic Identification System (AIS) to Monitor Coastal Vessels  

Microsoft Academic Search

We compare the ship detection capabilities of the automatic identification system AIS (installed on some ships) and coastal, surface wave HF radars, showing how to use both systems together to enhance ship detection performance in coastal regions. Practical reasons to want better real-time awareness of the location, velocity and type of vessels along coasts include vessel safety, protection of the

John F. Vesecky; Kenneth E. Laws; Jeffery D. Paduan

2009-01-01

49

Spatial temporal and frequency methods to mitigate interference in HF surface wave radar  

Microsoft Academic Search

In this paper, the spatial, temporal and frequency techniques to suppress interference in HF surface wave radar are presented. By exploiting the characteristics of the co-channel interference and deliberately selecting the secondary data, the proposed methods can effectively suppress both stationary and non-stationary interference. For most practical applications, the proposed interference suppression techniques can be combined to improve the interference

Su Hong-tao; An Zhi-juan; Bao Zheng; Zhang Shou-hong

2006-01-01

50

Wind farm impacts on HF radar current and wave measurements in Liverpool Bay  

Microsoft Academic Search

HF radar systems are increasingly used as components of coastal monitoring systems but the accuracy of the measurements can be compromised if there are other significant non-wave targets (e.g. ships or wind turbines) in the field of view. Liverpool Bay, on the North West coast of England and Wales, is an area of significant wind farm development and is also

L. R. Wyatt; A. M. Robinson; M. J. Howarth

2011-01-01

51

Ocean wave directional spectra estimation from an HF ocean radar with a single antenna array: Observation  

Microsoft Academic Search

A method of estimating ocean wave directional spectra using a]high-frequency (HF) radar with a single antenna array was applied to actual ocean data. This method incorporates the wave energy balance equation and the continuity equation of wind vectors into the inversion method to solve the integral equation which relates a Doppler spectrum to wave spectra. This method uses dynamic extrapolation

Yukiharu Hisaki

2005-01-01

52

Verication of the Second-Order HF Bistatic Radar Cross Section of \\\\Patch Scatter\\  

Microsoft Academic Search

The verication of the second-order cross section on a surface patch remote from the transmitter and receiver is presented. In order to verify the result, two proofs are used: (1)the complete form of the bistatic HF radar cross section in backscattering case is equvielent with monstatic equation; (2)the bistatic coupling coecience can be shown to reduce to the monostatic result

Weimin Huang; Eric Gill; John Walsh

53

First in-situ measurements of HF radar echoing targets J. Moen,1,2  

E-print Network

traversed a cusp electron density structure created by ongoing soft precipitation. 10-m scale irregularities of decameter scale irregularities in the electron plasma associated with HF radar backscatter. The main mission- lute density measurements, ICI-2 has provided the first documentation in terms of absolute electron

Bergen, Universitetet i

54

APQ-102 imaging radar digital image quality study  

NASA Technical Reports Server (NTRS)

A modified APQ-102 sidelooking radar collected synthetic aperture radar (SAR) data which was digitized and recorded on wideband magnetic tape. These tapes were then ground processed into computer compatible tapes (CCT's). The CCT's may then be processed into high resolution radar images by software on the CYBER computer.

Griffin, C. R.; Estes, J. M.

1982-01-01

55

Surface current and wave validation of a nested regional HF radar Network in the Mid-Atlantic Bight  

Microsoft Academic Search

The National High Frequency Surface Current Mapping Radar Network is being developed as a backbone system within the Integrated Ocean Observing System (IOOS). Of the core variables recognized in the IOOS Development Plan, two can be measured by high frequency radar (HFR): ocean surface currents and ocean surface waves. Rutgers University operates a nested multi-frequency network of HF radar systems

J. Kohut; H. Roarty; S. Licthenwalner; S. Glenn; D. Barrick; B. Lipa; A. Allen

2008-01-01

56

Ionospheric Cusp Polar Cap phenomena of particular relevance for generation of HF radar backscatter targets (Invited)  

NASA Astrophysics Data System (ADS)

High density polar cap patches are associated with enhanced backscatter power observed by the SuperDARN HF radars. How decametre scale HF radar echoing targets form is still a matter of debate. The Gradient Drift Instability (GDI) is usually regarded as the dominant mode for generating HF backscatter irregularities in the F-region cusp ionosphere. However, observations by EISCAT Svalbard Radar indicate that reversed flow events (RFEs), 100-200 km wide flow channels opposing the background convection, occur up to 40% of the time near the cusp inflow region. Here we present the first documentation of the RFE phenomenon by SuperDARN. When the RFE flow disturbance expands in longitude there is an immediate response in enhanced level of backscatter power, to within the one minute resolution of the radar. This gives experimental support to the new idea that the Kelvin-Helmholtz Instability (KHI) forms 0.1-10 km seed structures on which other instabilities like the GDI can operate more efficiently. However, high-resolution in-situ measurements by sounding rockets are really needed to reliably evaluate the relative importance of various plasma instability modes. The first results from the ICI-2 sounding rocket launched from Svalbard 5 December 2008 will be presented. The payload was equipped with Langmuir probes, AC and DC electric field experiment, plasma wave experiment, particle spectrometers for electrons (10 eV-10keV & >30keV) and ions (>30 keV). It intersected 3 regions of HF backscatter during its 10 min flight reaching an apogee of 330 km. With University of Oslo’s novel multi-Needle Langmuir probe experiment we performed absolute electron density measurements of decametre scale HF backscatter targets. Each HF backscatter region was associated with an inverted V precipitation region which opens for current driven instabilities.

Moen, J.

2009-12-01

57

Improved statistical prediction of surface currents based on historic HF-radar observations  

NASA Astrophysics Data System (ADS)

Accurate short-term prediction of surface currents can improve the efficiency of search-and-rescue operations, oil-spill response, and marine operations. We developed a linear statistical model for predicting surface currents (up to 48 h in the future) based on a short time history of past HF-radar observations (past 48 h) and an optional forecast of surface winds. Our model used empirical orthogonal functions (EOFs) to capture spatial correlations in the HF-radar data and used a linear autoregression model to predict the temporal dynamics of the EOF coefficients. We tested the developed statistical model using historical observations of surface currents in Monterey Bay, California. The predicted particle trajectories separated from particles advected with HF-radar data at a rate of 4.4 km/day. The developed model was more accurate than an existing statistical model (drifter separation of 5.5 km/day) and a circulation model (drifter separation of 8.9 km/day). When the wind forecast was not available, the accuracy of our model degraded slightly (drifter separation of 4.9 km/day), but was still better than existing models. We found that the minimal length of the HF-radar data required to train an accurate statistical model was between 1 and 2 years, depending on the accuracy desired. Our evaluation showed that the developed model is accurate, is easier to implement and maintain than existing statistical and circulation models, and can be relocated to other coastal systems of similar complexity that have a sufficient history of HF-radar observations.

Frolov, Sergey; Paduan, Jeffrey; Cook, Michael; Bellingham, James

2012-07-01

58

A Multi-frequency Beam-forming HF Radar for Tsunami Detection  

NASA Astrophysics Data System (ADS)

We discuss a new multi-frequency beam-forming HF radar design for robust detection and tracking of tsunami waves from 200 km distances, providing continuous coverage of the tsunami wave pattern after it impinges on the continental shelf. The method works by mapping ocean currents at long range using traditional HF radar method of radial Bragg line Doppler shift measurements. The tsunami is detected by anomalous spatial patterns of higher than normal Bragg-line shifts due to the large orbital wave of the series of tsunami wave crests as they impinge on the continental shelf. An approach using beam forming of 16 or 32 antenna elements provides an update every five minutes or less, while Direction-of-Arrival method systems using just a few antenna elements inherently require of the order of 30 to 60 minutes for a reliable current map. The multi-frequency radar provides a more robust capability than the single frequency HF radar for at least two reasons. First, because the HF channel user spectrum suffers diurnal variability in channel occupancy due to the ionosphere changing with time of day, low frequencies can become contaminated with user noise, so that maximum range for reliable detection not achieved. Under this condition, one would rely on quiet higher HF frequencies that lie above the Maximum Usable Frequency (MUF) for ionospheric reflection propagation. Alternatively, for daylight operation when low frequency utilization can be used to minimize surface wave propagation loss, the sea state might not be sufficiently active to allow long range coverage needed for reliable detection, due to the lack of ocean wave spectral energy at the Bragg-resonant wave frequency. Thus, single- frequency radars, operating in the 4-6 MHz range to minimize propagation losses to achieve long-range coverage, would suffer due to low wind conditions. The multi-frequency HF radar discussed here allows one to dynamically choose the optimum frequency from a set of 8 to 16, as allowed by local radio frequency allocation authorities, assuming just a single frequency is used at a time. Alternatively, one may choose four to eight frequencies operating simultaneously, to allow the clearest channel and best signal strength channel for enhanced processing. We will discuss the tradeoffs on multiple frequency use versus single optimum frequency use, both using a multi-frequency radar capability. Results of preliminary testing of a prototype system at Duck, NC will also be presented.

Trizna, D. B.

2007-05-01

59

Sea Wind Power Energy Evaluation by HF Radar System  

Microsoft Academic Search

This paper presents a remote sensing method for wind energy measurement and evaluation on sea surface, which can be used for the investigation of wind farm. It provides a valid proof for building wind plants or monitoring wind farms on the sea surface. The wind speed and direction can be derived from radar echo spectrum as well as wind profile,

Wei Shen; Biyang Wen

2009-01-01

60

Digital image transformation and rectification of spacecraft and radar images  

USGS Publications Warehouse

Digital image transformation and rectification can be described in three categories: (1) digital rectification of spacecraft pictures on workable stereoplotters; (2) digital correction of radar image geometry; and (3) digital reconstruction of shaded relief maps and perspective views including stereograms. Digital rectification can make high-oblique pictures workable on stereoplotters that would otherwise not accommodate such extreme tilt angles. It also enables panoramic line-scan geometry to be used to compile contour maps with photogrammetric plotters. Rectifications were digitally processed on both Viking Orbiter and Lander pictures of Mars as well as radar images taken by various radar systems. By merging digital terrain data with image data, perspective and three-dimensional views of Olympus Mons and Tithonium Chasma, also of Mars, are reconstructed through digital image processing. ?? 1985.

Wu, S. S. C.

1985-01-01

61

Observations of the broadening and coherence of MF\\/lower HF surface-radar ocean echoes  

Microsoft Academic Search

Known broadening mechanisms for the first-order Bragg peaks in high-frequency (HF: 3-30 MHz) and very-high-frequency (VHF: 30-300 MHz) Doppler spectra of radar echoes from the sea surface are summarized. Observations of medium-frequency (MF: 0.3-3 MHz)\\/lower HF sea echoes were made with a surface-wave phased-antenna array transmitting Gaussian pulses of width ≈40 and 70 ?s at frequencies 1.98, 3.84, and 5.80

Murray L. Parkinson

1997-01-01

62

Measuring rms wave height and the scalar ocean wave spectrum with HF skywave radar  

NASA Astrophysics Data System (ADS)

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high-frequency (HF) skywave radar-measured sea-echo Doppler spectra. Whereas low-power surface-wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection. To demonstrate this capability, we used the Wide Aperture Research Faculty (WARF) HF skywave radar to measure Pacific Ocean sea backscatter near NOAA data buoy EB 20 during the passage of an at mospheric cold front. The height of the wind-generated waves measured at the buoy doubled within a 6-h period. Two new analysis techniques were used to derive rms wave height and the scalar ocean wave frequency spectrum from radar echoes. Estimates of rms wave height were made east and west of the front by using a power-law relation that was derived from theoretical simulations of the sea-echo Doppler spectrum for a wide range of wave conditions. Two of the rms wave height estimates were compared with the estimates made at EB 20 at two different times and are in agreement to within 7 and 17%, respectively. Scalar wave spectrum and rms wave height estimates were made by matching a theoretical Doppler spectrum derived in terms of a five-parameter model of the wind-wave spectrum to the measured Doppler spectrum. The radar and buoy estimates of the rms wave height agree within 7%. Agreement between the WARF-derived and buoy-derived rms wave height and wave spectra is within the combined experimental error of the buoy and the radar measurements.

Maresca, Joseph W.; Georges, T. M.

1980-05-01

63

Measurement of ocean wave height and direction by means of HF radar: An empirical approach  

NASA Astrophysics Data System (ADS)

High-frequency (HF) radar has been used for 20 years for remote sensing of ocean surface currents and ocean waves. Backscattered Doppler spectra contain two discrete lines, whose frequencies (Bragg frequency) determine the current speed, and four continuous side bands enabling inversion techniques to be used for retrieving ocean wave spectra. Recently, a new HF radar has been developed at the University of Hamburg (Germany). Data of a 34-day experiment reveal a high correlation between the standard deviation of the Bragg frequencies and the significant wave height weighted by an azimuthal function. Applying empirical regression curves it is possible to determine the significant wave height and the mean wave direction from intersecting beams of two radar stations. Compared to inversion techniques, the new method is applicable to data with a lower signal-to-noise ratio, i.e. it allows larger ranges. Two radar sites are required for current measurements. The optimum distance between two 30 MHz radars is about 20 km and, with the new method, needs not be reduced for the purpose of simultaneous wave measurements.

Essen, H.-H.; Gurgel, K.-W.; Schlick, T.

1999-12-01

64

Dependence of HF surface wave radar sea clutter on sea state  

Microsoft Academic Search

An empirical relationship between the power of the second-order sea clutter in HF surface wave radar (HFSWR) and the average ocean wave height is derived from the data measured from a trial using the HFSWR at Cape Race, Newfoundland and a TriAxys wave buoy. The power of the second-order sea clutter between Bragg lines, measured at the radio frequency of

H. Leong

2002-01-01

65

Adaptive interference cancellation synthesized SMI and eigenspace-based method for HF surface wave radar  

Microsoft Academic Search

High frequency (HF) interference typically exhibits a time-varying or non-stationary spatial structure for the propagation through ionosphere. Adaptive interference cancellation methods are known to degrade in this case. In this paper, a new approach that effectively suppresses the non-stationary interference without degrading target visibility is presented for high frequency surface wave radar (HFSWR) circumstance. The proposed method synthesizes the sample

Li Lei; Li gaopeng; Liu Yuan; Xu Rongqing

2005-01-01

66

Robust adaptive beamforming for HF surface wave over-the-horizon radar  

Microsoft Academic Search

Adaptive beamforming is used to enhance the detection of target echoes received by high frequency (HF) surface wave (HFSW) over-the-horizon (OTH) radars in the presence of spatially structured interference. External interference from natural and man-made sources typically masks the entire range-Doppler search space and is characterized by a spatial covariance matrix that is time-varying or nonstationary over the coherent processing

GIUSEPPE A. FABRIZIO; ALEX B. GERSHMAN; MIKE D. TURLEY

2004-01-01

67

Statistical patterns of high-latitude convection obtained from Goose Bay HF radar observations  

Microsoft Academic Search

We have derived patterns that describe the statistical interplanetary magnetic field (IMF) dependencies of ionospheric convection in the high-latitude region of the northern hemisphere. The observations of plasma motion were made with the HF coherent backscatter radar located at Goose Bay, Labrador, over the period September 1987 to June 1993. The area covered by the measurements extended poleward of 65øA

J. M. Ruohoniemi; R. A. Greenwald

1996-01-01

68

Trajectory prediction using HF radar surface currents: Monte Carlo simulations of prediction uncertainties  

Microsoft Academic Search

An important aspect of particle trajectory modeling in the ocean is the assessment of the uncertainty in the final particle position. Monte Carlo particle trajectory simulations using surface currents derived from standard-range and long-range CODAR HF radar systems were performed using random-walk and random-flight models of the unresolved velocities. Velocity statistics for these models were derived from the covariance functions

David S. Ullman; James O'Donnell; Josh Kohut; Todd Fake; Arthur Allen

2006-01-01

69

The second-order monostatic HF radar cross section incorporating antenna barge motion  

Microsoft Academic Search

The second-order HF radar ocean cross section is derived for the case of the transmitting and receiving antenna undergoing platform (i.e. barge) motion. The derivation for electromagnetic patch scatter begins with a general expression for the bistatically received second-order electric field. Based on an assumption that the ocean surface can be described as a Fourier series with coefficients being zero-mean

John Walsh; Weimin Huang; Eric Gill

2009-01-01

70

Low-cost, panelized digital array radar antennas  

Microsoft Academic Search

The design challenges associated with the development of the antenna array for a highly-integrated, low-cost, panelized radar system have been presented, and the methodology for the development of a digital array radar (DAR) antenna panel has been detailed. Now that a solution for the maximization of scan range in in the DAR antenna panel has been identified, the next step

C. Fulton; W. Chappell

2008-01-01

71

An estimation and verification of vessel radar-cross-sections for HF surface wave radar  

Microsoft Academic Search

The radar cross sections (RCS) of both small and large ships for High Frequency Surface Wave Radar (HFSWR) were studied by using Numerical Electromagnetics Code and by using measurements from a HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicate that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo-container vessels (?36000 ton) have comparable

Harold Wilson; Hank Leong

2003-01-01

72

Surface current patterns in the Ibiza Channel with the use of High Frequency (HF) Radar system  

NASA Astrophysics Data System (ADS)

The Ibiza Channel located between the East Coast of the Iberian Peninsula, and the West Coast of Ibiza, at the Balearic Islands, is a well-known biodiversity hot spot. This area is relevant due to the interaction of water masses coming from the Atlantic Ocean - ascending through the Iberian Peninsula coast - with the older Atlantic waters descending from the Gulf of Lion. In 2012, the installation of Coastal HF Radar in the area provides valuable information for the study of the surface transport along the channel. The Coastal HF Radar operates since June 2012, and provides hourly surface current maps with a spatial resolution of approximately 3 km and a range reaching up to 70 km offshore. The instrument forms part of a monitoring multi-platform system, which is completed with satellite-derived data, gliders, modelling and fixed and lagrangian buoys. All HF Radar data are processed with standard quality control methods. Drifter velocity obtained from lagrangian buoys for two oceanographic campaigns, satellite-derived data and currentmeter data from a fixed buoy in the Ibiza Channel are used to validate the HF Radar data. All surface current data are used to perform a spectrum analysis in order to show the physical processes, at the main temporal periods. The contribution of the different temporal scales to the total Kinetic Energy has been analysed for the first time at different seasonal intervals. This served to evaluate the energetic importance of the different components of the surface currents. The inertial currents have a lower contribution to the total KE during winter, compared with the summer period. Besides, the spatial distribution of the inertial component to the total KE varies seasonally, and according to the bathymetry of the area. The low-pass (sub-inertial) filtered HF Radar currents show a predominant northern current during the summer months in the channel, and a mean southern current during the winter period. These results are discussed and related with the external forcing, and bathymetry distribution, according to coastal or open ocean data.

Lana, Arancha; Fernández, Vicente; Troupin, Charles; Pascual, Ananda; Orfila, Alejandro; Tintoré, Joaquín

2014-05-01

73

A comparison of sidelobe cancellation techniques using auxiliary horizontal and vertical antennas in HF surface wave radar  

Microsoft Academic Search

Sidelobe cancellation techniques are evaluated here using auxiliary horizontal and vertical antennas in a HF surface wave radar (HFSWR). The objective is to compare the pros and cons of using horizontal dipoles or vertical monopoles as auxiliary antennas in HFSWR. A radar experiment was carried out to facilitate this comparison. Four horizontal dipoles, configured in the form of two separate

Hank W. H. Leong

2000-01-01

74

A MIMO technique for enhanced clutter selectivity in a multiple scattering environment: Application to HF surface wave radar  

Microsoft Academic Search

The significance of multiple scattering processes whereby unwanted Doppler-spread energy can contaminate HFSWR remote sensing measurements has recently been reported. In this paper we present the results of quantitative calculations of the extent of the contamination, and then outline a solution based on the adoption of MIMO radar concepts which have been applied successfully in HF skywave radars.

S. J. Anderson; W. C. Anderson

2010-01-01

75

HF radar detection of infrasonic waves generated in the ionosphere by the 28 March1 2005 Sumatra earthquake2  

E-print Network

1 HF radar detection of infrasonic waves generated in the ionosphere by the 28 March1 2005 Sumatra-the-horizon (OTH) radar NOSTRADAMUS after the very strong5 earthquake (M=8.6) that occurred in Sumatra on March 28

Boyer, Edmond

76

Evaluation of the attenuation provided by a radar absorbing material (RAM) coating on an HF wire rope antenna  

Microsoft Academic Search

A shipboard electromagnetic interference (EMI) problem is considered. The use of radar absorbent material (RAM) to reduce unintentional X-band (8-12 GHz) radar reflections from HF wire rope antennas is analyzed. An exact series solution for a lossy-coated circular cylinder was developed and used to determine the effectiveness of the various RAM coatings

Griffin K. Gothard; Broun Hall

1991-01-01

77

An airborne digital processor for radar scatterometer data  

E-print Network

AN AIRBORNE DIGITAL PROCESSOR FOR RADAR SCATTEROMETER DATA A Thesis by DAVID STEVEN YEADON Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 1977... Major Subject: Electrical Engineering AN AIRBORNE DIGITAL PROCESSOR FOR RADAR SCATTEROMETER DATA A Thesis by DAVID STEVEN YEADON Approved as to style and content by: (Chairman o Committee) Head of epartment) ( (Member ) (Member) August 1977...

Yeadon, David Steven

2012-06-07

78

Tornado identification from analyses of digital radar data  

E-print Network

TORNADO IDENTIFICATION FROM ANALYSES OF DIGITAL RADAR DATA A Thesis by DONALD NAYNE PITTMAN Submitted to the Graduate College of Texas ASM Onion nsity in Partial fulfillment of the requirement for the d=gr e of MASTFR OF SCIENCE December... 1976 Major Subject: Meteorology TORNADO IDENTIFICATION FROM ANALYSES OF DIGITAL RADAR DATA A Thesis by DONALD WAYNE PITTMAN Approved as to sty1e and content by: , Chair, an of Committe C! (Head of Department M"mber Member December 19. 6...

Pittman, Donald Wayne

2012-06-07

79

The AN\\/TPQ-39\\/V\\/ Digital Instrumentation Radar  

Microsoft Academic Search

The AN\\/TPQ-39(V) Digital Instrumentation Radar (DIR) is a modern versatile radar which meets many of the short-range requirements of test ranges. It is a transportable instrument designed for flexibility, low cost, and moderate accuracy. It makes use of a general-purpose digital computer with the objective of minimizing hardware and maximizing reliability and flexibility. The system was designed to accept a

L. E. Kitchens; D. N. Thomson

1974-01-01

80

A Technique to Separate Ground and Ionospheric HF Radar Backscatter for Ionospheric Remote Sensing  

NASA Astrophysics Data System (ADS)

The use of High Frequency (HF) radar for ionospheric remote sensing has recently proliferated, as in the case of the growing Super Dual Auroral Radar Network (SuperDARN). However, because of the complexity of ionospheric propagation modes and the fact that individual echoes of ground and ionospheric scatter origin may have similar spectral characteristics, it is often impossible to determine whether an echo is a legitimate ionospheric scatter echo or a spurious ground scatter echo. We have developed a technique that utilizes the statistical distribution of spectral parameters and range and elevation angle of arrival data of ground and ionospheric echoes to identify the origin of an echo with a high degree of confidence. For the two radar stations specifically presented here, the confidence of identification of an echo's origin is 90%. We use data from the Kapuskasing and Saskatoon HF radars for 12 days throughout the year of 2001 and examine the joint distribution of backscatter line-of-sight velocity v and spectral width w. We observe that for v >/= 100 m/s, which is presumably ionospheric scatter, the distribution of line-of-sight velocity decreases exponentially with v for a given value of spectral width. The e-folding velocity is 450 m/s. We extrapolate this distribution to smaller v to obtain the joint distribution of velocity and width in ionospheric scatter, which we subtract from the total distribution to obtain the distribution of velocity and width in ground scatter. These distributions, when normalized, intersect along the line v[m/s] = 60 m/s - 0.4w[m/s]. This line represents the separatrix between ground scatter and ionospheric scatter for these stations. To validate this separatrix, we investigate the distribution of the reflection heights calculated from echo range and elevation angle of arrival data. The distribution of reflection heights for presumed ionospheric and ground scatter are distinctly different and are consistent with the presumed identification. Finally, the separatrix provides a 90% confidence of identification of a particular echo as of ground scatter or ionospheric scatter origin based on the overlap between the respective distributions of spectral parameters. This result is robust, being independent of radar station and season. While the particular values of the separatrix parameters and confidence level may vary for other HF radar stations based on local ionospheric and surface conditions, the technique should be generally applicable.

Blanchard, G.; Sundeen, S.; Baker, K.

2005-12-01

81

The Response of Surface Currents to Wind Investigated by HF Ocean Surface Radar  

NASA Astrophysics Data System (ADS)

The momentum transfer from air to sea generates surface currents through both the wind shear stress and the Stokes drift induced by waves, corresponding to the two components in the surface current response to wind. Stokes drift depends on the sea state which is influenced by the fetch and the duration for wave development. This study focuses on the response of sea surface currents to wind under different fetch conditions using surface current data over a 30-day duration measured by HF (30MHz) ocean surface radar near the entrance to Port Phillip Bay in Victoria, Australia. Results suggest that the ratio of current speed to wind speed is larger under the long fetch condition and the angle between surface current vector and wind vector is smaller, suggesting the increasing significance of Stokes drift with fetch as the sea develops. Surface current data under different fetch conditions is analysed with an integration of Ekman theory and Stokes mass transport theory, which decomposes the currents into two components, i.e. Stokes drift and currents generated by wind stress. The analysed magnitude of Stokes drift agrees well with results derived from the empirical wave growth function. Results suggest that Stokes drift dominates the total currents in the mature sea state under the long fetch condition, whereas currents generated by wind shear stress is as important as Stokes drift under the short fetch condition when the sea is not well developed. As both the magnitude and the direction dependency of Stokes drift on wind are different from those of wind-generated currents, fetch plays a significant role in the total response of surface current to wind as it determines the sea state and therefore the contribution of Stokes drift in the total current. These results provide observational evidence that currents measured by HF ocean surface radar include Stokes drift, and therefore demonstrate the potential of HF radar measurement in providing insights into the mechanisms of the momentum transfer from air to sea.

Mao, Y.; Heron, M.

2010-12-01

82

The Long Wavelength Array (LWA): A Large HF/VHF Array for Solar Physics, Ionospheric Science, and Solar Radar  

NASA Astrophysics Data System (ADS)

The Long Wavelength Array (LWA), currently under construction in New Mexico, will be an imaging HF/VHF interferometer providing a new approach for studying the Sun-Earth environment from the surface of the sun to the Earth’s ionosphere. The LWA will be a powerful tool for solar physics and space weather investigations, through its ability to characterize a diverse range of low-frequency, solar-related emissions, thereby increasing our understanding of particle acceleration and shocks in the solar atmosphere along with their impact on the Sun-Earth environment. As a passive receiver the LWA will directly detect Coronal Mass Ejections (CMEs) in emission, and indirectly through the scattering of cosmic background sources as they propagate towards Earth. If coupled with a suitable transmitter, the LWA would be an excellent receiver for solar radar, potentially demonstrating accurate geomagnetic storm prediction from the Earth’s surface. Both radar and passive receiving techniques could monitor the Sun-Earth environment during daytime as a compliment to nighttime space weather remote sensing techniques. The LWA will also naturally provide a measure of small-scale spatial and temporal ionospheric structure, a pre-requisite for accurate calibration and imaging of solar and space weather phenomena. As a sensitive monitor of differences in total electron content (TEC) through the ionosphere, the LWA will provide an unprecedented characterization of ionospheric turbulence and waves, capable of testing predictions of global ionospheric models with an aim towards improving their accuracy through input to physics-based models. As a fully digital, multi-beaming instrument, the LWA can monitor the Sun daily with a dedicated solar beam, while simultaneously pursuing ionospheric and astrophysics science programs both day and night. In this paper we present an overview of the LWA, currently under construction in New Mexico, and discuss the scientific goals of the project in the areas of solar, ionospheric, and solar radar applications.

Kassim, N.; White, S.; Rodriquez, P.; Hartman, J.; Hicks, B.; Lazio, J.; Stewart, K.; Craig, J.; Taylor, G.; Cormier, C.; Romero, V.; Jenet, F.

2010-09-01

83

Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake  

NASA Astrophysics Data System (ADS)

Giant ionospheric disturbances induced by the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) on 11 March 2011 are studied by using data from the SuperDARN Hokkaido HF radar and GPS receiver network (GEONET) in Japan. The HF radar observations revealed strong disturbances to the north of Hokkaido that propagated northward at velocities of 6.7-1.8 km/s triggered by northward-propagating seismic surface waves. An induction magnetometer in Hokkaido recorded part of the seismic wave propagation from the epicenter. After the passage of the 6.7-1.8 km/s waves the radar observed northward-propagating disturbances (343-136 m/s) due to atmospheric gravity waves (AGW) perhaps excited near the epicenter. Interestingly, the radar first detected peculiar disturbances with periods of about 2-4 min caused by the acoustic resonance. GEONET, which covers the area on the south of the radar field of view, provided total electron content (TEC) data. Comparisons between radar and TEC observations indicate the following: (1) 6.7-1.8 km/s waves observed with the radar do not always have counterparts in TEC. (2) Acoustic waves of 1.3-0.7 km/s identified in TEC are not observed with the radar. (3) Disturbances caused by both AGW and acoustic resonance are simultaneously discernible in both TEC and radar data.

Ogawa, T.; Nishitani, N.; Tsugawa, T.; Shiokawa, K.

2012-12-01

84

HF radar signatures of the cusp and low-latitude boundary layer  

SciTech Connect

Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environment Modeling (GEM) program. It is therefore important to establish clear intercalibrations between different ground-based instruments and satellites in order to clearly place the ground-based observations in context with the corresponding in situ satellite measurements. HF-radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis. In this paper the authors report on an intercalibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labador, and Halley Station, Antarctica, and the Defense Meterological Satellite Program (DMSP) satellites. The DMSP satellite data are used to provide clear identifications of the ionospheric cusp and the low-latitude boundary layer (LLBL). The radar data for eight cusp events and eight LLBL events have been examined in order to determine a radar signature of these ionospheric regions. This intercalibration indicates that the cusp is always characterized by wide, complex Doppler power spectra, whereas the LLBL is usually found to have spectra dominated by a single component. The distribution of spectral widths in the cusp is of a generally Gaussian form with a peak at about 220 m/s. The distribution of spectral widths in the LLBL is more like an exponential distribution, with the peak of the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to those observed in the cusp. 49 refs., 26 figs., 2 tabs.

Baker, K.B.; Greenwald, R.A.; Newell, P.T. [Johns Hopkins Univ., Laurel, MD (United States)] [and others] [Johns Hopkins Univ., Laurel, MD (United States); and others

1995-05-01

85

Methods for the extraction of long-period ocean wave parameters from narrow beam HF radar sea echo  

Microsoft Academic Search

This paper describes inversion methods for HF radar sea echo Doppler spectra, giving parameters of the ocean wave spectrum in the important long-wavelength region. Radar spectra exhibiting very narrow spikes in the higher-order structure adjacent to the first-order lines are indicative of ocean wave components with a single dominant wavelength. In the simplest method of interpretation these components are assumed

Belinda Lipa; Donald Barrick

1980-01-01

86

Thunderstorm characteristics displayed with three-dimensional digital radar data and digital goes infrared data  

E-print Network

. S. , Texas A&M University Chairman of Advisory Committee: Dr. Aylmer H. Thompson Three-dimensional (3-D) digital 10-cm radar data and digital GOES infrared ( IR) data for a 3-h period during a Southeast Texas squall line were examined. The radar... for 0300 GMT . . . . . . . . . . . . . . . . . . 65 Schematic time cross-section through an Oklahoma squall line . . . . . . . . . . . . . . . . . . . . . . . . . 67 29 Hodograph of pre-squall environment 69 30 PVAZ2 map for Scan 5NW, 0115 GMT, and IR...

McAnelly, Ray Lewis

2012-06-07

87

Estimation of the sea surface radar cross section at HF from second order Doppler spectrum characteristics  

NASA Astrophysics Data System (ADS)

A technique is developed for estimating the radar cross section of the sea surface at HF (2-30 MHz) from two simple measurements made of the radar Doppler spectrum. These are: the ratio of approach/recede Bragg line energy, and the ratio of strongest Bragg line amplitude to average value amplitude of second-order backscatter at zero Doppler frequency. A nomograph is given, based on a theoretical model of second-order scatter developed by the author, which then allows one to determine the number of decibels the Bragg ocean spectral component is down from the classical Phillips asymptotic value, used here only for a reference. Comparison is made with some surface wave data for three different cases in which buoy data are available for comparison with multi-frequency radar data collected simultaneously at two different look angles. An example is also shown where such a calculation can be used to estimate the cross section of a target return existing within the same Doppler spectrum. Limitations of the technique are also discussed.

Trizna, D. B.

1982-05-01

88

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects  

NASA Astrophysics Data System (ADS)

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

Watkins, Brenton; Fallen, Christopher; Secan, James

89

74. Transmitter building no. 102, view of radar digital test ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

74. Transmitter building no. 102, view of radar digital test and maintenance cabinet area control panel and date storage system showing ampex tape storage devices. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

90

Gigabit Networking: Digitized Radar Data Transfer and Beyond  

E-print Network

data transfer is one such real-time application that will tap the Next Generation Internet technology reality, desktop video, CAD/CAM design, and satellite image transfer. Gigabit- networking technologyGigabit Networking: Digitized Radar Data Transfer and Beyond Sangeetha L. Bangolae, Anura P

Jayasumana, Anura P.

91

HF Radar Performance in a Low-Energy Environment: CODAR SeaSonde Experience on the West Florida Shelf*  

E-print Network

are discussed, with the findings that both the low-energy sea state and the unfavorable surface wave directionsHF Radar Performance in a Low-Energy Environment: CODAR SeaSonde Experience on the West Florida performance on this low-energy (currents and waves) continental shelf is evaluated with respect to data

92

The potential of bistatic HF surface wave radar system for the surveillance of water-entry area along coastline  

Microsoft Academic Search

A bistatic\\/monostatic HF surface wave radar (HFSWR) experiment was conducted using both the transmit and receive systems of the HFSWR at Cape Race, Newfoundland and the receive system of the HFSWR at Cape Bonavista, Newfoundland. While the HFSWR at Cape Race operated in the monostatic mode, the transmitter at Cape Race and the receiver at Cape Bonavista were synchronized via

H. Leong

2006-01-01

93

On the Use of HF Surface Wave Radar in Congested Waters: Influence of Masking Effect on Detection of Small Ships  

Microsoft Academic Search

In this paper, we assess the capability of a high-frequency surface wave radar (HFSWR) to detect a small fast boat moving behind a ship, the dimensions of which are comparable to the wavelength. We show that, in the HF-band, the scattered field in the shadow region of the large ship is significant enough to induce strong coupling between the two

Rgis Guinvarc'h; Marc Lesturgie; Rémi Durand; Anil Cheraly

2006-01-01

94

History, present status, and future directions of HF surface-wave radars in the U.S  

Microsoft Academic Search

HF surface-wave radars (HFSWRs) offer two distinct advantages when used over the sea: with vertical polarization, they see beyond the horizon, and the interaction of their signals with ocean waves is simple and well understood. As a result, many HFSWR research test programs were conducted in the U.S., beginning 35 years ago. This author was fortunate to have been immersed

D. Barrick

2003-01-01

95

A relaxation method for integral inversion applied to HF radar measurement of the ocean wave directional spectrum  

Microsoft Academic Search

The Chahine-Twomey relaxation method for inversion of the atmospheric radiative transfer equation is extended to provide an inverse solution to Barrick's equation describing second order scatter of high frequency (HF) radio waves from the ocean surface. The success of the method is demonstrated here using synthesised radar Doppler spectra obtained by solving the direct problem with wave buoy directional spectrum

LUCY R. WYATT

1990-01-01

96

The Long Wavelength Array (LWA): A Large HF/VHF Array for Solar Physics, Ionospheric Science, and Solar Radar  

E-print Network

The Long Wavelength Array (LWA): A Large HF/VHF Array for Solar Physics, Ionospheric Science, and Solar Radar A Ground-Based Instrument Paper for the 2010 NRC Decadal Survey of Solar and Space Consortium #12;Executive Summary The Long Wavelength Array (LWA), currently under construction in New

Ellingson, Steven W.

97

Traveling convection vortices as seen by the SuperDARN HF radars  

NASA Astrophysics Data System (ADS)

Two impulsive traveling convection vortex (TCV) events observed simultaneously by ground based magnetometers and the SuperDARN HF radars in the prenoon sector were studied. In both cases, disturbances traveled westward at speeds of 4-6 km/s. Convection patterns derived from magnetometer measurements and radar observations were overall in reasonable agreement; observed differences at some points might be caused by both the nonuniform ionospheric conductivity distribution and difference in the integration time of the radar and magnetometer data. For one event, the convection patterns obtained from magnetometer data and SuperDARN radar measurements were relatively simple; they can be interpreted as a result of the westward motion of a convection vortex system associated with a pair of field-aligned currents separated in azimuthal direction. This TCV event was associated with relatively low Pc5 pulsation activity, contrary to the second TCV event that was accompanied by a train of Pc5 magnetic pulsations of large amplitude. Convection patterns for the second event were complicated. A simple scenario for the interpretation of the generation of TCVs and Pc5 pulsations is suggested. A sudden impulse in the solar wind dynamic pressure produces disturbances on several boundaries of magnetospheric plasma: on the magnetopause, the LLBL inner edge, and the plasma sheet inner edge. These boundaries are elastic so that surface waves can propagate along them. The high-latitude wave is responsible mainly for TCVs, whereas the low-latitude waves may be responsible for excitation of Pc5 field line resonance pulsations. The scenario explains important features of both TCV events and Pc5 pulsations: both phenomena appear simultaneously and show westward (eastward) propagation, but the TCVs are observed at latitudes close to the LLBL inner edge, whereas the Pc5 pulsations occur at lower latitudes, close to the inner boundary of the plasma sheet.

Lyatsky, W. B.; Sofko, G. J.; Kustov, A. V.; André, D.; Hughes, W. J.; Murr, D.

1999-02-01

98

Spatial and temporal behavior of ULF pulsations observed by the Goose Bay HF radar  

NASA Technical Reports Server (NTRS)

Techniques which allow the instantaneous amplitude and phase to be determined as functions of geomagnetic lattitude, longitude, and time are employed to carry out a detailed analysis of HF radar data of a ULF pulsation event in the postmidnight sector on January 11, 1989. Field line resonances with several different frequencies occur simultaneously at different latitudes. These can be associated with cavity mode frequencies of 1.3 mHz, 1.9 mHz, 2.7 mGz, and 3.3 mHz. These frequencies are constant to better than 10 percent over a local time period of nearly 4 hr. The field-aligned currents driven by the resonances can be as large as 5 micro-A/sq m at ionospheric heights. The data support a picture of modes driven by solar wind impulses.

Walker, A. D. M.; Ruohoniemi, J. M.; Baker, K. B.; Greenwald, R. A.; Samson, J. C.

1992-01-01

99

Radar shadow detection in synthetic aperture radar images using digital elevation model and projections  

NASA Astrophysics Data System (ADS)

Synthetic aperture radar (SAR) images are currently widely used in target recognition tasks. In this work, we propose an automatic approach for radar shadow detection and extraction from SAR images utilizing geometric projections along with the digital elevation model (DEM), which corresponds to the given georeferenced SAR image. First, the DEM is rotated into the radar geometry, so that each row would match that of a radar line of sight. Next, we extract the shadow regions by processing row by row until the image is covered fully. We test the proposed shadow detection approach on different DEMs and simulated one-dimensional signals and two-dimensional hills and valleys modeled by various variance-based Gaussian functions. Experimental results indicate that the proposed algorithm produces good results in detecting shadows in SAR images with high resolution.

Prasath, V. B. Surya; Haddad, Oussama

2014-01-01

100

Ionospheric factors affecting the performance of HF sky-wave sea-state radars  

NASA Astrophysics Data System (ADS)

This paper contains an assessment, partly theoretical and partly based on observations, of the impact of various ionospheric factors on the usefulness of the HF sky-wave sea-state radar technique. The points discussed include the following: (1) The ionospheric propagation modes available will not permit all parts of the ocean which it is desired to investigate to be illuminiated at all times in such a way that good-quality Doppler spectra are obtained. Es-mode propagation generally results in good-quality Doppler spectra from which information about the sea waves can be inferred, but F-mode propagation yields poor spectra which can only be used to deduce the surface wind direction. (2) Doppler shifts associated with vertical ionospheric motions give spectral contamination which limits the amount of information that can be derived. Spectral contamination also arises under conditions of multi-mode propagation and when high- and low-angle rays are present. (3) Lack of knowledge of the height of reflection of the sky-wave signals means that the area of ocean probed cannot be located accurately. (4) The azimuthal spreading (arising because of the antenna beam width) and range spreading (caused by ionospheric tilts and corrugations and associated with the finite radar pulse width) both result in Doppler contamination of the returned signals.

Bradley, P. A.; Bramley, E. N.; Gibson, A. J.; King, J. W.

1983-08-01

101

Surface transport in the Northeastern Adriatic Sea from FSLE analysis of HF radar measurements  

NASA Astrophysics Data System (ADS)

This study focuses on the surface transport in the Northeastern Adriatic Sea and the related hydrodynamic connectivity with the Gulf of Trieste (GoT) under calm or typical wind conditions: Bora (from the NE) and Sirocco (from the SE). The surface transport in the area has been investigated by evaluating the Finite-Size Lyapunov Exponents (FSLE) on the current field measured by the High Frequency (HF) coastal radar network. FSLE allow us to estimate Lagrangian Coherent Structures (LCSs), which provide information on the transport patterns associated with the flow and identify regions characterized by different dynamics. This work includes the development and set-up of the FSLE algorithm applied for the first time to the specific Adriatic area considered. The FSLE analysis during calm wind reveals an attractive LCS crossing the GoT entrance, marking the convergence between the Northern Adriatic and the outflowing gulf waters. During Bora episodes this attractive LCS is displaced westward with respect to the calm wind case, indicating that Bora drives an extended coherent outflow from the GoT. On the other hand, Sirocco wind piles up the water along the northern end of the basin. In this area an attractive LCS is found, extending mainly in the SW-NE direction. The sirocco-induced inflow of Adriatic waters in the GoT is mainly driven along its northern (Italian) side, as evidenced by the orientation of the LCS. Under Sirocco condition, as in the Bora case, there is no barrier in front of the gulf. No relevant LCSs are observed in the southern radar coverage area except for Bora cases, when a repulsive LCS develops in front of the Istrian coast separating water masses to the North and the South of it.

Berta, Maristella; Ursella, Laura; Nencioli, Francesco; Doglioli, Andrea M.; Petrenko, Anne A.; Cosoli, Simone

2014-04-01

102

Detecting upwelling along the central coast of California during an El Niño year using HF-radar  

Microsoft Academic Search

Surface currents in the vicinity of Granite Canyon, California (36°25.9?N, 121°55.0?W), were measured hourly using HF-radar in 1990–1992. The 1990 data revealed the M2 and S2 semi-diurnal tidal constituents. These high frequency components were removed from 6-month records taken during part of the upwelling season of 1991 and 1992. Daily and weekly variations in current speed and direction were generally

Yehoshua Shkedy; Daniel Fernandez; Calvin Teague; John Vesecky; Jonathan Roughgarden

1995-01-01

103

A Cascaded Approach for Correcting Ionospheric Contamination with Large Amplitude in HF Skywave Radars  

PubMed Central

Ionospheric phase perturbation with large amplitude causes broadening sea clutter's Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA) is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR); such a cascade correction method has a good effect. PMID:24578656

Wei, Yinsheng; Guo, Rujiang; Xu, Rongqing; Tang, Xiudong

2014-01-01

104

Hokkaido HF radar signatures of periodically reoccurring nighttime medium-scale traveling ionospheric disturbances detected at short ranges  

NASA Astrophysics Data System (ADS)

Super Dual Auroral Radar Network Hokkaido HF radar often detects periodically reoccurring E region echoing regions propagating toward or away from it. In this work, we consider 117 of such events identified for 2008-2012. These are shown to occur at nighttime, preferentially during summer, although significant number for events was found for winter. Statistics for the local time of occurrence, magnitude of the speed and polarity of progressions, and temporal and spatial periodicities are presented. We show that the power of echoes is linearly related to their Doppler velocity which makes it possible to identify the events on both power and Doppler velocity plots. Other peculiar characteristics of echoes are discussed. The onset of events is associated with gravity waves propagation through the radar field of view.

Koustov, A. V.; Yakymenko, K. N.; Nishitani, N.; Ponomarenko, P. V.

2014-02-01

105

The effects of space and time resolution on the quality of sea echo Doppler spectra measured with HF sky wave radar  

Microsoft Academic Search

Measurements using the SRI Wide-Aperture Research Facility (WARF) HF sky wave radar show that the radar's azimuthal beamwidth and integration time play important roles in determining the quality of sky wave (ionospherically propagated) sea echo Doppler spectra. Using as a quality index the equivalent width of a portion of the Doppler spectrum in the vicinity of the stronger Bragg line,

T. M. Georges; J. W. Maresca

1979-01-01

106

Development of a digital receiver for range imaging atmospheric radar  

NASA Astrophysics Data System (ADS)

In this paper, we describe a new digital receiver developed for a 1.3-GHz range imaging atmospheric radar. The digital receiver comprises a general-purpose software-defined radio receiver referred to as the Universal Software Radio Peripheral 2 (USRP2) and a commercial personal computer (PC). The receiver is designed to collect received signals at an intermediate frequency (IF) of 130 MHz with a sample rate of 10 MS s-1. The USRP2 digitizes IF received signals, produces IQ time series, and then transfers the IQ time series to the PC through Gigabit Ethernet. The PC receives the IQ time series, performs range sampling, carries out filtering in the range direction, decodes the phase-modulated received signals, integrates the received signals in time, and finally saves the processed data to the hard disk drive (HDD). Because only sequential data transfer from the USRP2 to the PC is available, the range sampling is triggered by transmitted pulses leaked to the receiver. For range imaging, the digital receiver performs real-time signal processing for each of the time series collected at different frequencies. Further, the receiver is able to decode phase-modulated oversampled signals. Because the program code for real-time signal processing is written in a popular programming language (C++) and widely used libraries, the signal processing is easy to implement, reconfigure, and reuse. From radar experiments using a 1-?s subpulse width and 1-MHz frequency span (i.e., 2-MHz frequency bandwidth), we demonstrate that range imaging in combination with oversampling, which was implemented for the first time by the digital receiver, is able to resolve the fine-scale structure of turbulence with a vertical scale as small as 100 m or finer.

Yamamoto, Masayuki K.; Fujita, Toshiyuki; Abdul Aziz, Noor Hafizah Binti; Gan, Tong; Hashiguchi, Hiroyuki; Yu, Tian-You; Yamamoto, Mamoru

2014-10-01

107

Digital meteorological radar data compared with digital infrared data from a geostationary meteorological satellite  

E-print Network

of meteorological data and the proliferation of interactive systems The citations on the following pages follow the style of the J 1 f A~li d M~tl designed to display and compare fields of satellite, digital radar, and conventional surface and upper-air data... on TIROS 9 imagery, shipborne and shore- based radar data, and surface and upper-air data. Yonder Haar (1969) employed data from the geostationary satel- lites ATS 1 (Applications Technology Satellite 1) and ATS 3 in a study of reflected radiance...

Henderson, Rodney Stuart

2012-06-07

108

Nonlinear inversion of the integral equation to estimate ocean wave spectra from HF radar  

NASA Astrophysics Data System (ADS)

Since all ocean wave components contribute to the second-order scattering of a high-frequency radio wave by the sea surface, it is theoretically possible to estimate the ocean wave spectrum from first- and second-order scattering in the Doppler spectrum measured with an HF ocean radar. To extract the wave spectral information, however, it is necessary to solve a nonlinear integral equation. This paper describes in detail how to solve the nonlinear integral equation without linearization or approximation. We show that the problem of solving the nonlinear integral equation can be converted into a nonlinear optimization problem. An algorithm to find the optimal solution is described. Examples of the algorithm applied to simulated data and measured data are shown. The wave frequency spectrum can be estimated even if the Doppler spectrum is available in only a single direction. In this case, however, the solution of the two-dimensional wavenumber spectrum tends to converge to a spectrum that is symmetrical to the beam direction. Even if the wave spectrum is dominant in a single direction, the solution may give two peaks in the wavenumber spectrum. One of them is the true peak and the other is the mirror image of it with respect to the beam direction. This ambiguity can be avoided by using Doppler spectra measured in at least two different directions. Although there is still some room for improvement in the practical application of this method, it can be applied to estimate the wave directional spectrum up to a rather high frequency, or Bragg frequency.

Hisaki, Yukiharu

1996-01-01

109

Wave and current measurements obtained using the WERA and Pisces HF radar systems and Seaview  

E-print Network

an overview of ground-based wave measuring radar. I would like to com- ment on both of these. Current from Neptune Radar Ltd) from two sites and compared with the UK Met Office depth-averaged storm- surge

Wyatt, Lucy

110

Data association of monostatic-bistatic composite HF radar network under ionospheric interference  

Microsoft Academic Search

High frequency surface wave radar (HFSWR) is superior to detect and track beyond-the-horizon targets but susceptible to the ionosphere interference because of the specific wavelength. Seeking out the real target points from plenty of false ones is an obsessional problem for data association. This is commendably solved by establishing a new radar system, the monostatic-bistatic composite radar network, and providing

Zong Hua; Quan Taifan; Ma Yinging; Zong Chengge

2008-01-01

111

Full digital High Frequency Surface Wave Radar: French trials in the biscay bay  

Microsoft Academic Search

Assessment of actual detection capabilities obtained with high frequency surface wave radar (HFSWR) is a key issue for the global surveillance of the exclusive economic zone (EEZ). ONERA (The French Aerospace Lab) has just finished a ten month trial cycle of its new full digital HFSWR system. This system uses digital signal generation, digital receivers, high computational power workstations and

M. Menelle; G. Auffray; F. Jangal

2008-01-01

112

Suppression of power line harmonic interference in HF surface-wave radar  

Microsoft Academic Search

Experimental data of the Cape Bonavista High-Frequency Surface-Wave Radar (HFSWR) Facility was contaminated by power line harmonics. The harmonics modulate the radar signal (mainly sea clutter) and replicate it into the Doppler spectrum. The spectral replicas distort the noise and sea clutter statistics in the signal. It is necessary to suppress them before the statistics can be obtained. A new

Hank Leong

1992-01-01

113

The HF surface wave radar WERA. Part I: Statistical analysis of recorded data  

Microsoft Academic Search

Surface wave (SW) over-the-horizon (OTH) radars are not only widely used for ocean remote sensing, but they can also be exploited in integrated maritime surveillance systems. This paper represents the first part of the description of the statistical and spectral analysis performed on sea backscattered signals recorded by the oceanographic WEllen RAdar (WERA) system. Data were collected on May 13th

Salvatore Maresca; Maria Greco; Fulvio Gini; R. Grasso; S. Coraluppi; N. Thomas

2010-01-01

114

Low speed target detection with short CIT in HF surface wave radar  

Microsoft Academic Search

High frequency surface wave radar can detect targets beyond the horizon. It needs long coherent integration time (CIT) to detect low speed targets, such as ships, in the environment with sea clutter. In order to improve the efficiency of the radar system, and avoid the Doppler broadening caused by long CIT, it is necessary to shorten coherent integration time. Modern

Shang Shang; Zhang Ning

2010-01-01

115

Ionospheric and auroral clutter models for HF surface wave and over-the-horizon radar systems  

NASA Astrophysics Data System (ADS)

The detection performance of high frequency surface wave radar (HFSWR) and high frequency over-the-horizon radar (OTHR) systems is heavily influenced by the presence of radar clutter. In HFSWR systems, the clutter has its origins in vertical-incidence ionospheric reflections, whereas in OTHR systems, the origin is Bragg backscatter from plasma structures in the auroral zone. This paper models the spreading of the radar clutter signal in the Doppler and angle-of-arrival domains that arises from forward-scattering effects as the radar pulse propagates through regions of ionospheric plasma irregularities. The models use a geometric optics approach to determine the power spectrum of the radar signal phase. This power spectrum is then used to simulate three-dimensional space-time-range radar data cubes. The accuracy of the models is tested by comparing the simulated data to measured data cubes. As an application, the data are then used to evaluate the performance of the newly developed fast fully adaptive (FFA) space-time adaptive processing (STAP) scheme to improve the extraction of target echoes from a clutter background.

Ravan, M.; Riddolls, R. J.; Adve, R. S.

2012-01-01

116

Multidimensional Waveform Encoding: A New Digital Beamforming Technique for Synthetic Aperture Radar Remote Sensing  

Microsoft Academic Search

This paper introduces the innovative concept of multidimensional waveform encoding for spaceborne synthetic aperture radar (SAR). The combination of this technique with digital beamforming on receive enables a new generation of SAR systems with improved performance and flexible imaging capabilities. Examples are high-resolution wide-swath radar imaging with compact antennas, enhanced sensitivity for applications like alongtrack interferometry and moving object indication,

Gerhard Krieger; Nicolas Gebert; Alberto Moreira

2008-01-01

117

Opening and closing of sea ice leads: Digital measurements from synthetic aperture radar  

Microsoft Academic Search

The coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques. An algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar (SAR) digital images. The pair of images is classified into leads and ice, correcting for variation in

M. Fily; D. A. Rothrock

1990-01-01

118

HF shipborne over-the-horizon surface wave radar background clutter statistics  

Microsoft Academic Search

Sea clutter statistics are very important in designing target detection algorithms in both shore-based SWR (surface wave radar) and shipborne SWR. The sea clutter statistical characteristics in shore-based SWR have been discussed (see Barrick, D.E. and Bsnider, J., IEEE Trans. on Antennas and Propagation, p.19-28, 1997), but the statistics of sea echo in shipborne SWR radar have not been reported.

Zhong Zhang; Yeshu Yuan; Xiande Meng

2001-01-01

119

A system trade model for the monitoring of coastal vessels using HF surface wave radar and ship automatic identification systems (AIS)  

Microsoft Academic Search

Coastal nations have an interest in maritime domain awareness for applications in national security, coastal conservancy, fishery and stewardship of the exclusive economic zones (EEZs) along their coastlines. Using our previously developed HF radar and AIS ship detection models we find signal to noise ratio (SNR) as a function of range, including ducted propagation for the AIS radio signals. We

John F. Vesecky; Kenneth E. Laws; Jeffery D. Paduan

2010-01-01

120

Analysis of post-sunset F-region vertical plasma drifts during Counter Electrojet days using multi frequency HF Doppler Radar  

NASA Astrophysics Data System (ADS)

In this paper, through a case study, an attempt has been made to bring out the relationship between post noon E-region electric field and post sunset F-region vertical plasma drift on quiet time Counter Electrojet (CEJ) days. Study carried out using the data from a multi frequency HF Doppler Radar and Digital Ionosonde located over Trivandrum (8.5° N; 77° E; 0.5° N dip lat.) a geomagnetic dip equatorial station in India during quite time CEJ days of the years 2004 and 2006, revealed some interesting aspects of the E region electrodynamics and post sunset F region electrodynamics. It has been observed that, in contrast to the normal electrojet (EEJ) days, the Pre-Reversal Enhancement (PRE) is either weakened or inhibited on CEJ days and the field reversal takes place much earlier than that on a normal day. It is suggested that even after the effects of the field reversal ceases to show up in the ground magnetic data, the reversed field may persist and shows up as a decrease in the PRE experienced by the F-region. In other words, the study indicates that the EEJ associated electrodynamics have a significant role in controlling the PRE.

Simi, K. G.; Vineeth, C.; Pant, T. K.

2014-08-01

121

Comparative analyses for the prediction of streamflow from small watershed by use of digitized radar data  

E-print Network

compared to rainfall values estimated from 0-deg and tilt, digital-radar data for April 26 and 27, 1972. . 83 xi LIST OF TABLES (CONTINfJED) Table Page Comparison of observed surface runoff and that computed by using the NWS API program with ARS... from 0-deg radar data between 2000-2100 CST, May 31, 1971 79 xiv LIST OF FIGURES (CONTINUED) Figure Page 25. Isohytal map (in inches) for rainfall estimated from tilt, digital-radar between 2000-2100 CST, May 31, 1971 80 26. Surface weather map...

Braatz, Dean Thomas

2012-06-07

122

Development of a ground signal processor for digital synthetic array radar data  

NASA Technical Reports Server (NTRS)

A modified APQ-102 sidelooking array radar (SLAR) in a B-57 aircraft test bed is used, with other optical and infrared sensors, in remote sensing of Earth surface features for various users at NASA Johnson Space Center. The video from the radar is normally recorded on photographic film and subsequently processed photographically into high resolution radar images. Using a high speed sampling (digitizing) system, the two receiver channels of cross-and co-polarized video are recorded on wideband magnetic tape along with radar and platform parameters. These data are subsequently reformatted and processed into digital synthetic aperture radar images with the image data available on magnetic tape for subsequent analysis by investigators. The system design and results obtained are described.

Griffin, C. R.; Estes, J. M.

1981-01-01

123

Phase instability of ionospheric propagation and its influence on HF Doppler radar remote sensing  

NASA Astrophysics Data System (ADS)

Theoretical and experimental progress toward operational use of decametric radar in an ionospherically propagated mode to obtain sea state and surface wind data is reviewed. Estimates are made of the expected Doppler radar contamination from data gained during the JASIN experiment involving one hop CW transmissions into the sporadic E layer. Shipboard propagation and receiving were found to yield data accurate to the degree of sea surface roughness. Further tests during the MARSEN trials, which featured a 5 MHz for multihop F-mode propagation from the emitter 700 km to an area where the sea truth was known, and then on to a land platform. A one-hop mode displayed a Doppler spread of 10 dB at the 0.05-0.1 Hz. Theoretical consideration of the problem indicated radar sea-echo spectra Doppler spreads of 0.1 Hz rms, acceptable for deducing wave-height spectra. Statistical analyses with a larger data base is recommended.

Shearman, E. D. R.; Theodoridis, S.; Sandham, W. A.; Bradley, P. A.

124

Significance of short-scale irregularities for radar diagnostics of HF-driven Langmuir turbulence in the ionosphere  

NASA Astrophysics Data System (ADS)

In experiments where ground-based VHF/UHF radars are used to diagnose Langmuir turbulence driven by powerful HF waves transmitted from the ground into the ionosphere, there has been a severe observability aspect: The excited Langmuir wave vector spectrum must contain a component satisfying the actual radar Bragg condition. In order to explain earlier observations, in particular those made by the Arecibo facility, it was proposed long ago that the actual wave number spectra were widened by refraction in small-scale irregularities, or ducts. This mechanism of improved observability is discussed in a broad approach in this paper. The main contribution is a mathematical derivation of the theory of parametric decay instability in the presence of magnetic-field-aligned ducts. This implies that the decay is into discrete duct modes. The threshold is slightly higher and the growth rate is slightly lower than for a corresponding homogeneous medium. Moreover, this tendency is more pronounced for the higher duct modes, which are those that may satisfy conditions for observability. The mathematical derivation is based on the driven and damped Zakharov model with ducts included. The model is run numerically, confirming the approximate decay instability theory and demonstrating improved observability. The numerics also demonstrate higher Langmuir energy density inside the ducts than outside.

Mjølhus, E.; Helmersen, E.; DuBois, D. F.

2001-09-01

125

Towards HF metamaterials  

Microsoft Academic Search

Surface waves are a key point for high frequency radars. Our global objective is to improve or avoid their excitation depending on whether we operate surface wave radars or sky wave radars. This paper deals with suppression of surface wave for high frequency sky wave radar. We aim to develop periodic sub-wavelength structures like metamatrial ones. Indeed, considering HF wavelength,

Florent Jangal; Luca Petrillo; Muriel Darces

2009-01-01

126

The HF surface wave radar WERA. Part II: Spectral analysis of recorded data  

Microsoft Academic Search

This paper covers the second part of the analysis of data recorded by the surface wave (SW) over-the-horizon (OTH) WEllen RAdar (WERA). Data were collected by two WERA systems, on May 13th 2008, during the NURC experiment in the Bay of Brest, France. The principal aim of this work is to provide an accurate characterization of the spectral components of

Salvatore Maresca; Maria Greco; Fulvio Gini; R. Grasso; S. Coraluppi; N. Thomas

2010-01-01

127

Super-resolution processing for HF surface wave radar based on pre-whitened MUSIC  

Microsoft Academic Search

Owing to the decametric wavelength, the angular resolution of high-frequency surface wave radar (HFSWR) is usually coarse, especially when dimensions of antenna arrays are restricted such as in shipborne HFSWR applications. In this paper, the relative strength of atmospheric noise and sea clutter that will heavily degrade the capabilities of HFSWR in target detection and resolution are calculated, then a

Junhao Xie; Yeshu Yuan; Yongtan Liu

1998-01-01

128

Range sidelobes suppression for HF surface wave radar with discontinuous spectra  

Microsoft Academic Search

In order to improve the anti-interference performance, the high-frequency surface wave radar uses several discontinuous clear frequency bands for transmission. Spectral discontinuity causes high range sidelobes which influence detecting and identifying the targets. A novel modified CLEAN algorithm is proposed to remove the sidelobes interferences of the equivalent matched processing result of the received signals. The simulation results show that

Wang Qin; Yang Zijie; Wan Xianrong; Xiong Junzhi

2008-01-01

129

A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network  

NASA Astrophysics Data System (ADS)

In order to address the need for surface trajectory forecasts following deployment of coastal HF radar systems during emergency-response situations (e.g., search and rescue, oil spill), a short-term predictive system (STPS) based on only a few hours data background is presented. First, open-modal analysis (OMA) coefficients are fitted to 1-D surface currents from all available radar stations at each time interval. OMA has the effect of applying a spatial low-pass filter to the data, fills gaps, and can extend coverage to areas where radial vectors are available from a single radar only. Then, a set of temporal modes is fitted to the time series of OMA coefficients, typically over a short 12-h trailing period. These modes include tidal and inertial harmonics, as well as constant and linear trends. This temporal model is the STPS basis for producing up to a 12-h current vector forecast from which a trajectory forecast can be derived. We show results of this method applied to data gathered during the September 2010 rapid-response demonstration in northern Norway. Forecasted coefficients, currents, and trajectories are compared with the same measured quantities, and statistics of skill are assessed employing 16 24-h data sets. Forecasted and measured kinetic variances of the OMA coefficients typically agreed to within 10-15%. In one case where errors were larger, strong wind changes are suspected and examined as the cause. Sudden wind variability is not included properly within the STPS attack we presently employ and will be a subject for future improvement.

Barrick, Donald; Fernandez, Vicente; Ferrer, Maria I.; Whelan, Chad; Breivik, Øyvind

2012-05-01

130

Detection of heavy convective precipitation using rapid interval digital radar and satellite data  

NASA Technical Reports Server (NTRS)

A study was carried out to investigate the evolution of thunderstorms with short-interval (5 min) geosynchronous digital satellite data and with digital radar data (12 min interval) in order to determine the potential and limitations of using the satellite data to detect regions of heavy convective precipitation. Initial results indicate that satellite-based estimates of thunderstorm updraft intensity are related to storm precipitation rate as indicated in the digital radar data. The conclusions give support to the effort to use satellite data for detection of heavy convective precipitation, but emphasize the need for high time resolution (5 min) data.

Negri, A. J.; Adler, R. F.

1980-01-01

131

Measuring surface wind direction by monostatic HF ground-wave radar at the eastern China Sea  

Microsoft Academic Search

The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived

Weimin Huang; Eric Gill; Shicai Wu; Biyang Wen; Zijie Yang; Jiechang Hou

2004-01-01

132

Mesoscale and submesoscale zoo observed with HF radar in Monterey Bay  

Microsoft Academic Search

Shore-based high-frequency Doppler radar observations collected in Monterey Bay between 1999 and 2001 are utilized for the reconstruction of high-resolution surface currents: mesoscale and submesoscale ageostrophic spiral eddies, eddy dipoles, eddy tripoles and multi-eddy systems with lifetimes about 4-12 hours (sub-inertial periods). Our analysis demonstrates topography nature of all these eddies because of rectification of tides in the submarine canyon

L. M. Ivanov; O. V. Melnichenko

2004-01-01

133

Doppler spectral characteristics of high latitude ionospheric irregularities: Effect on HF radars  

Microsoft Academic Search

This report considers the Doppler spectral properties of radar signals scattered from high latitude E and F-region ionospheric irregularities. Although the exact mechanism for the production of F-region irregularities is not yet known, it appears that the Doppler shift from these as well as from E-region irregularities is determined by the ionospheric electric field via the E X B\\/B-squared drift

R. A. Greenwald

1981-01-01

134

Digital transmission techniques for a long haul HF link: DSSS versus OFDM  

NASA Astrophysics Data System (ADS)

This paper presents two digital transmission techniques for long haul ionospheric links. Since 2003 we have studied the HF link between the Antarctic Spanish Base, Juan Carlos I, and Spain; and we have described the link in terms of availability, signal-to-noise ratio, and delay and Doppler power profile. Based on these previous studies we have developed a test bed to investigate two digital transmission techniques, i.e., Direct-Sequence Spread Spectrum (DSSS) and Orthogonal Frequency Division Multiplexing (OFDM), which can provide a low power, low-rate ionospheric data link from Antarctica. Symbol length, bandwidth, and constellation are some of the features that are analyzed in this work. Data gathered from the link throughout the 2010/2011 and 2011/2012 Antarctic surveys show that the spread spectrum techniques can be used to transmit data at low rate when the channel forecast is poor, but when the channel forecast is good multicarrier techniques can be used to transmit sporadic bursts of data at higher rate.

Bergadà, P.; Alsina-Pagès, R. M.; Pijoan, J. L.; Salvador, M.; Regué, J. R.; Badia, D.; Graells, S.

2014-07-01

135

Digital beamforming developments for the joint NASA\\/Air Force Space Based Radar  

Microsoft Academic Search

The Space Based Radar (SBR) program includes a joint technology demonstration between NASA and the Air Force to design a low-earth orbiting, 2×50 m L-band (1.26 GHz) radar system for Earth science and intelligence-related observations. A key subsystem aboard SBR is the electronically-steerable digital beamformer (DBF) network that interfaces between 32 smaller subantenna panels in the array and the on-board

Mark A. Fischman; Charles Le

2004-01-01

136

Assessing the fidelity of surface currents from a coastal ocean model and HF radar using drifting buoys in the Middle Atlantic Bight  

NASA Astrophysics Data System (ADS)

The rapid expansion of urbanization along the world's coastal areas requires a more comprehensive and accurate understanding of the coastal ocean. Over the past several decades, numerical ocean circulation models have tried to provide such insight, based on our developing understanding of physical ocean processes. The systematic establishment of coastal ocean observation systems adopting cutting-edge technology, such as high frequency (HF) radar, satellite sensing, and gliders, has put such ocean model predictions to the test, by providing comprehensive observational datasets for the validation of numerical model forecasts. The New York Harbor Observing and Prediction System (NYHOPS) is a comprehensive system for understanding coastal ocean processes on the continental shelf waters of New York and New Jersey. To increase confidence in the system's ocean circulation predictions in that area, a detailed validation exercise was carried out using HF radar and Lagrangian drifter-derived surface currents from three drifters obtained between March and October 2010. During that period, the root mean square (RMS) differences of both the east-west and north-south currents between NYHOPS and HF radar were approximately 15 cm s-1. Harmonic analysis of NYHOPS and HF radar surface currents shows similar tidal ellipse parameters for the dominant M2 tide, with a mean difference of 2.4 cm s-1 in the semi-major axis and 1.4 cm s-1 in the semi-minor axis and 3° in orientation and 10° in phase. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. RMS errors when compared to currents derived along the trajectory of the three drifters were approximately 10 cm s-1. Overall, the analysis suggests that NYHOPS and HF radar had similar skill in estimating the currents over the continental shelf waters of the Middle Atlantic Bight during this time period. An ensemble-based set of particle tracking simulations using one drifter which was tracked for 11 days showed that the ensemble mean separation generally increases with time in a linear fashion. The separation distance is not dominated by high frequency or short spatial scale wavelengths suggesting that both the NYHOPS and HF radar currents are representing tidal and inertial time scales correctly and resolving some of the smaller scale eddies. The growing ensemble mean separation distance is dominated by errors in the mean flow causing the drifters to slowly diverge from their observed positions. The separation distance for both HF radar and NYHOPS stays below 30 km after 5 days, and the two technologies have similar tracking skill at the 95 % level. For comparison, the ensemble mean distance of a drifter from its initial release location (persistence assumption) is estimated to be greater than 70 km in 5 days.

Kuang, Liang; Blumberg, Alan F.; Georgas, Nickitas

2012-08-01

137

Measurements of drift velocity of artificial small-scale field-aligned irregularities using multi-position HF radars  

NASA Astrophysics Data System (ADS)

In report the results of multi-position radar measurements of Doppler frequency shift DFS scattered signals by artificial small-scale field-aligned irregularities FAI are presented In measurements two pairs of bistatic configurations HF radars have been used Kaliningrad 54 7 r N 20 6 r E -- SURA 56 1 r N 46 1 r E - IZMIRAN 55 3 r N 37 2 r E path 1 and RVI 55 8 r N 38 3 r E - SURA - Rostov-Don 47 2 r N 39 6 r E path 2 Such geometry of paths has allowed to determine the value and direction of drift velocity of FAI in a plane orthogonal to magnetic field Observations were carried out in March 2005 in the evening hours from 16 00 to 19 00 UT On the first path the probing transmitter operated at frequency 9300 kHz in a pulse mode tau 100 mu s F rep 25 Hz on the second path as the probing transmitter was used the RVI station of precise times which operated at frequency 14996 kHz in continuous carrier mode The heating facility SURA operated in a mode 5 min -- radiation and 5 min - pause on pump wave frequency f p close to critical frequency of F-layer f p le f o F2 According to results of spectral measurements in an operating time of heating facility on both paths scattered signals from artificial small-scale field-aligned irregularities were observed On the basis of DFS measurements of the scattered signal SS we have calculated value V and direction azimuth A of the irregularities drift velocity It is obtained that during moderate disturbance period magnetic

Uryadov, V. P.; Frolov, V. L.; Vertogradov, G. G.; Vertogradov, V. G.; Kim, V. Yu.; Panchenko, V. A.; Polimatidi, V. P.; Ivanov, V. P.

138

Doppler spectral characteristics of high latitude ionospheric irregularities: Effect on HF radars  

NASA Astrophysics Data System (ADS)

This report considers the Doppler spectral properties of radar signals scattered from high latitude E and F-region ionospheric irregularities. Although the exact mechanism for the production of F-region irregularities is not yet known, it appears that the Doppler shift from these as well as from E-region irregularities is determined by the ionospheric electric field via the E X B/B-squared drift velocity. The width of the backscattered spectra is determined by the viewing angle of the radar relative to the E X B/B-squared drift direction as well as the drift magnitude. Assuming an electrical potential distribution over the Earth's high latitude regions, it has been possible to predict the diurnal variability of the Doppler velocity and width associated with high latitude irregularities. Although some of these predictions agree with previous observations, considerably more knowledge is required of the high latitude potential distribution and its temporal variability. Finally, a novel new technique is proposed whereby through cross spectral analysis the detrimental effects of clutter due to ionospheric irregularities may be eliminated.

Greenwald, R. A.

1981-05-01

139

Variability in the air-sea interaction patterns and time-scales within the Southeastern Bay of Biscay, as observed by HF radar data  

NASA Astrophysics Data System (ADS)

Two high frequency (HF) radar stations were installed on the Southeastern Bay of Biscay in 2009, providing high spatial and temporal resolution and large spatial coverage currents for the first time in the area. This has enabled to determine quantitatively the air-sea interaction patterns and time-scales for the period 2009-2010. The analysis was conducted by using the Barnett-Preisendorfer approach to canonical correlation analysis (CCA) of reanalysis surface winds and HF radar-derived currents. The results reveal that the CCA yields two canonical patterns. The first wind-current interaction pattern corresponds to the classical Ekman drift at sea surface, whilst the second describes an anticyclonic/cyclonic surface circulation. The results obtained demonstrate that the local winds play an important role in driving the upper water circulation. The wind-current interaction time-scales are mainly related to diurnal breezes and synoptic variability. In particular, the breezes force diurnal currents in the continental shelf and slope of the Southeastern Bay. It is concluded that the breezes may force diurnal currents over considerably wider areas than that covered by the HF radar, considering that the northern and southern continental shelves of the Bay exhibit stronger diurnal than annual wind amplitudes.

Fontán, A.; Esnaola, G.; Sáenz, J.; González, M.

2012-08-01

140

Variability in the air-sea interaction patterns and timescales within the south-eastern Bay of Biscay, as observed by HF radar data  

NASA Astrophysics Data System (ADS)

Two high-frequency (HF) radar stations were installed on the coast of the south-eastern Bay of Biscay in 2009, providing high spatial and temporal resolution and large spatial coverage of currents in the area for the first time. This has made it possible to quantitatively assess the air-sea interaction patterns and timescales for the period 2009-2010. The analysis was conducted using the Barnett-Preisendorfer approach to canonical correlation analysis (CCA) of reanalysis surface winds and HF radar-derived surface currents. The CCA yields two canonical patterns: the first wind-current interaction pattern corresponds to the classical Ekman drift at the sea surface, whilst the second describes an anticyclonic/cyclonic surface circulation. The results obtained demonstrate that local winds play an important role in driving the upper water circulation. The wind-current interaction timescales are mainly related to diurnal breezes and synoptic variability. In particular, the breezes force diurnal currents in waters of the continental shelf and slope of the south-eastern Bay. It is concluded that the breezes may force diurnal currents over considerably wider areas than that covered by the HF radar, considering that the northern and southern continental shelves of the Bay exhibit stronger diurnal than annual wind amplitudes.

Fontán, A.; Esnaola, G.; Sáenz, J.; González, M.

2013-04-01

141

HF radar detection of infrasonic waves generated in the ionosphere by the 28 March 2005 Sumatra earthquake  

NASA Astrophysics Data System (ADS)

Surface waves generated by earthquakes create atmospheric waves detectable in the ionosphere using radio waves techniques: i.e., HF Doppler sounding, GPS and altimeter TEC measurements, as well as radar measurements. We present observations performed with the over-the-horizon (OTH) radar NOSTRADAMUS after the very strong earthquake (M=8.6) that occurred in Sumatra on March 28, 2005. An original method based on the analysis of the RTD (Range-Time-Doppler) image is suggested to identify the multi-chromatic ionospheric signature of the Rayleigh wave. The proposed method presents the advantage to preserve the information on the range variation and time evolution, and provides comprehensive results, as well as easy identification of the waves. In essence, a Burg algorithm of order 1 is proposed to compute the Doppler shift of the radar signal, resulting in sensitivity as good as obtained with higher orders. The multi-chromatic observation of the ionospheric signature of Rayleigh wave allows to extrapolate information coherent with the dispersion curve of Rayleigh waves, that is, we observe two components of the Rayleigh waves with estimated group velocities of 3.8 km/s and 3.6 km/s associated to 28 mHz (T~36 s) and 6.1 mHz (T~164 s) waves, respectively. Spectral analysis of the RTD image reveals anyway the presence of several oscillations at frequencies between 3 and 8 mHz clearly associated to the transfer of energy from the solid-Earth to the atmosphere, and nominally described by the normal modes theory for a complete planet with atmosphere. Oscillations at frequencies larger than 8 mHz are also observed in the spectrum but with smaller amplitudes. Particular attention is pointed out to normal modes 0S29 and 0S37 which are strongly involved in the coupling process. As the proposed method is frequency free, it could be used not only for detection of ionospheric perturbations induced by earthquakes, but also by other natural phenomena as well as volcanic explosions and particularly tsunamis, for future oceanic monitoring and tsunami warning systems.

Bourdillon, Alain; Occhipinti, Giovanni; Molinié, Jean-Philippe; Rannou, Véronique

2014-03-01

142

An assessment of shuttle radar topography mission digital elevation data for studies of volcano morphology  

E-print Network

An assessment of shuttle radar topography mission digital elevation data for studies of volcano's volcanoes. Although these data were acquired with a nominal spatial resolution of 30 m, such data are only available for volcanoes located within the U.S.A. and its Territories. For the overwhelming majority

Wright, Robert

143

An advanced digital signal processor for the HRR polarimetric MMW active guidance radar  

Microsoft Academic Search

Polarimetric CFAR detection procedures are first outlined. An advanced digital signal processor used for MMW polarimetric HRR active precision guiding radar is configured that involves a preamplifier and filter, a spectral analyzer and a DSP-based polarimetric detector\\/discriminator to seek and track ground targets in surface clutter. A fuzzy relative optimal state (FROS) of a processor is conceptualized concerning the compromise

Yong Rin; Benchao Sie; Lui Yongtan

1993-01-01

144

Design and implementation of a digital impulse generator for a 24GHz UWB radar  

NASA Astrophysics Data System (ADS)

In this paper, we design and implement a digital impulse generator using a DCM block and an OSERDES block for a 24GHz UWB impulse-Doppler radar. The Federal Communications Commission (FCC) has confirmed the spectrum from 22 to 29GHz for UWB radar with a limit power of -41.3dBm/MHz. UWB signal possesses an absolute bandwidth larger than 500MHz or a relative bandwidth up to 20%. The vehicle radar is the key technology with the inherent advantage detected the distance and the velocity regardless of weather. Radar has a role to measure the distance and the velocity of long-distance vehicle. But, the radar with 1m resolution is difficult to satisfy the detection performance in the blind spot zone because the blind spot zone needs high resolution. So, UWB impulse-Doppler radar with 30cm resolution is suitable for the blind spot zone. The designed impulse generator has a 2ns pulse width and 100us PRI. We perform simulations through Xilinx ISE; experiments use a spectrum analyzer and a digital oscilloscope. For UWB radar, we use an AD9779 DAC module with a 1Gsps maximum sampling rate. For equipment, we use a TDS5104B oscilloscope of Tektronix with 3dB bandwidth at 1GHz for the analysis of the time domain and an E4448A spectrum analyzer of Agilent with a 50GHz spectrum for the analysis of the frequency domain. The results of the digital impulse measurement show a 2ns pulse width in the time domain, a 500MHz bandwidth, and a 10KHz spectrum peak in the frequency domain.

Kim, Sang-Dong; Lee, Jong-Hun

2011-06-01

145

A novel digital receiver concept for ISRO's future remote sensing radars  

NASA Astrophysics Data System (ADS)

Technology development related to digital, antenna and RF subsystems for Microwave Radar Sensors like Synthetic Aperture Radar, Scatterometer, Altimeter and Radiometer is one of the major activities under ISRO's microwave remote sensing programme, since 1980s. These technologies are now being gainfully utilized for building ISRO's operational Earth Observation missions involving microwave sensors like Radar Imaging Satellite, RISAT SAR, Oceansat-2 Scatterometer, Megha-Tropiques, MADRAS and Airborne SAR for Disaster Management, DMSAR. Concurrently, advanced technology developments in these fields are underway to meet the major technological challenges of building ISRO's proposed advanced microwave missions like ultra-high resolution SAR's, Synthetic Aperture Radiometer (SARAD), Milli-meter and sub-millimeter wave sounders and SAR Constellations for Disaster management as well as Interferometric, Polarmetric and polarmetric interferometry applications. Also, these hardware are being designed with core radar electronics concept, in which the same RF and digital hardware sub-units / modules will be utilized to build different microwave radar sensors. One of the major and common requirements for all these active and passive microwave sensors is the moderate to highspeed data acquisition and signal processing system. Traditionally, the Data acquisition units for all these radar sensors are implemented as stand-alone units, following the radar receivers. For ISRO's C-band airborne SAR (ASAR) and RISAT high resolution SAR, we have designed and developed High Speed 8-bit ADC based I/Q Digitisers, operating at 30.814 MHz and 250 MHz sampling rates, respectively. With the increasing demand of wide bandwidth and ultra-high resolution in imaging and non-imaging radar systems, the technology trend worldwide is towards a digital receiver, involving bandpass or IF sampling, thus eliminating the need for RF down converters and analog IQ demodulators. In order to evolve a generic configuration for all the microwave sensors, we have initiated design and development of a generic L-band digital receiver, consisting of receiver elements (LNA, digital attenuator and Bandpass filter) followed by Analog-to-Digital Converter. The digitised data can then be output in parallel or serial format. Additionally, a digital signal processor performing tasks like data compression, convolution or correlation and formatting can also be integrated with this generic digital receiver. The front end of the receiver is wide-band, catering to bandwidths of upto 2 GHz while the digitisation rates are also of the order of 1-2 GHz. It is proposed to standardize the design and use this generic receiver for front end data acquisition of all the future microwave sensors. It will meet the digitisation requirements of 500 MHz to 1 GHz for ultra-high resolution (0.25-0.5 meter) SAR as well as direct sampling of the signal around 1.4GHz for L-band Synthetic Aperture Radiometer. After initial prototyping using discrete receiver elements and ultra-high speed 8-bit ADC, it will be taken up as a custom ASIC or multi-chip module consisting of RF MMIC's and a mixed signal ADC ASIC. These designs will be fabricated using InP, GaAs or SiGe process technologies at competent foundries like GATEC, SCL, Infineon/Germany, X-Fab/Germany and Ommic-Philips/France. This novel digital receiver will offer several advantages like flexibility, stability, reduced RF hardware and miniaturisation. This paper describes the ultra-high speed design requirements, configuration details and target specifications and salient features of this generic L-band digital receiver for ISRO's future spaceborne and airborne radar missions. It also addresses the associated signal integrity, EMI/EMC and thermal issues.

Desai, Nilesh; Vachhani, J. G.; Soin, Sumit; Agrawal, Rinku; Rao, C. V. N.; Gujraty, Virendra; Rana, Surindersingh

2006-12-01

146

Digitized dual wavelength radar data from a Texas thunderstorm  

E-print Network

for 1800Z on 15 April 1977 ~ 23 Surface synoptic conditions for 2100Z on 15 April 1977, ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 24 5 Radar summary for 2135Z 15 April 1977. . . , , 25 6 ~ Progression of three bands of thunderstorm cells with time... data from the spring of 1972 to determine the relationship between severe storm events and hoth 0-deg tilt indicators and VIL He considered storms with a 0-deg tilt reflectivity maximum of at least 10 mm /m (41 dBZ) and a VIL 4 1 6 3 1 The Bi ER...

Radlein, Robin Ann

2012-06-07

147

On the spatiotemporal evolution of the ionospheric backscatter during magnetically disturbed periods as observed by the TIGER Bruny Island HF radar  

NASA Astrophysics Data System (ADS)

The Superposed Epoch Analysis (SEA) method is used to examine a 4-year database (2000-2003) of the TIGER Bruny Island radar (MLON=226.78°E, MLAT=55.06°S) measurements to determine typical patterns of the spatiotemporal evolution of ionospheric backscatter during geomagnetically disturbed periods. SEA is performed separately for three disturbance categories: short-, medium-, and long-duration magnetic disturbances, based on the Dst index variation. Prior to SEA, the diurnal, seasonal, and solar cycle effects have been accounted for by subtracting the nominal quiet-time values. It is found that the occurrence of ionospheric HF backscatter exhibited strongest enhancements near t=0 h between 65°S and 70°S MLAT (range of 800-2500 km) during short-duration magnetic disturbance. In contrast, a reduction in echo occurrence first occurred near t=0 h at higher ranges (r?2500 km) and expanded equatorwards during the recovery phase of the magnetic disturbances. This reduction in occurrence became progressively stronger and prolonged for medium- and long-duration magnetic disturbances. These categories also showed clear enhancements in the E-region backscatter (r<765 km) commencing from t=0 h. These observations can be explained by three main factors: (1) an enhancement in the E-region densities due to high-energy particle precipitation during magnetically disturbed periods causing the HF radar waves to refract from smaller altitudes and closer ranges, (2) a variability in the F-region densities associated with magnetic disturbances also affecting the propagation of the HF radar waves, and (3) a short-lived strong enhancement in growth rate of decametre-scale ionospheric irregularities when IMF turned southwards causing the highest echo occurrence near t=0 h during SEA.

Kumar, V. V.; Makarevich, R. A.; Kane, T. A.; Ye, H.; Devlin, J. C.; Dyson, P. L.

2011-08-01

148

MAS2-8 radar and digital control unit  

NASA Technical Reports Server (NTRS)

The design of the MAS 2-8 (2 to 8 GHz microwave-active spectrometer), a ground-based sensor system, is presented. A major modification in 1974 to the MAS 2-8, that of a control subsystem to automate the data-taking operation, is the prime focus. The digital control unit automatically changes all system parameters except FM rate and records the return signal on paper tape. The overall system operation and a detailed discussion of the design and operation of the digital control unit are presented.

Oberg, J. M.; Ulaby, F. T.

1974-01-01

149

Estimating Lagrangian transport blending drifters with HF radar data and models: Results from the TOSCA experiment in the Ligurian Current (North Western Mediterranean Sea)  

NASA Astrophysics Data System (ADS)

Lagrangian transport estimates are investigated using results from HF radar, model and drifter data during a dedicated experiment in the Ligurian Current in the Toulon area (North Western Mediterranean Sea). Uncertainty estimates on particle position, D(t), are computed and compared to absolute dispersion, D0(t), that provides an indication of the uncertainty in case of zero prior knowledge. In agreement with previous studies, radar results show that D(t)?1/2D0(t) (i.e. ?6 km after 24 h). Model results are less reliable, as it can be expected in highly nonlinear coastal flows without local data assimilation. The central result of this paper is that when drifters are promptly deployed in an area of interest, their data can be used to significantly improve transport estimates using the Lagrangian blending algorithm LAVA with velocity fields from models or radar. Uncertainty can be reduced to ?1/6D0(t), (i.e. ?2 km after 24 h) for both radar and model, implying a much reduced search range in case of operational applications. The method is also found to have some forecasting skills with uncertainty ?1/2D0(t) during the first ?6 h. Sensitivity tests provide indications on relevant time and space scales of predictability and provide suggestions for appropriate drifter sampling strategies.

Berta, Maristella; Bellomo, Lucio; Magaldi, Marcello G.; Griffa, Annalisa; Molcard, Anne; Marmain, Julien; Borghini, Mireno; Taillandier, Vincent

2014-11-01

150

Automatic modulation classification of digital modulations in presence of HF noise  

NASA Astrophysics Data System (ADS)

Designing an automatic modulation classifier (AMC) for high frequency (HF) band is a research challenge. This is due to the recent observation that noise distribution in HF band is changing over time. Existing AMCs are often designed for one type of noise distribution, e.g., additive white Gaussian noise. This means their performance is severely compromised in the presence of HF noise. Therefore, an AMC capable of mitigating the time-varying nature of HF noise is required. This article presents a robust AMC method for the classification of FSK, PSK, OQPSK, QAM, and amplitude-phase shift keying modulations in presence of HF noise using feature-based methods. Here, extracted features are insensitive to symbol synchronization and carrier frequency and phase offsets. The proposed AMC method is simple to implement as it uses decision-tree approach with pre-computed thresholds for signal classification. In addition, it is capable to classify type and order of modulation in both Gaussian and non-Gaussian environments.

Alharbi, Hazza; Mobien, Shoaib; Alshebeili, Saleh; Alturki, Fahd

2012-12-01

151

Temporal variability in intensity-height profiles of a severe storm using digital radar data  

E-print Network

of the real potential of the digital radar will be presented for a thunderstorm system observed on April 26, 1969, that produced a confirmed tornado and rains of considerable intensity at 1700 CST at Ninnekah, Oklahoma. Between 1600 CST and 1700 CST, two... was investigated also. In particular, techniques were formulated that explain partially the explosive development associ- ated with the tornado occurrence. Convergence of several of the satellite cells into the main cell may have been a contributing factor...

Canipe, Yates Julio

2012-06-07

152

A digital system to produce imagery from SAR data. [Synthetic Aperture Radar  

NASA Technical Reports Server (NTRS)

This paper describes a digital processing algorithm and its associated system design for producing images from Synthetic Aperture Radar (SAR) data. The proposed system uses the Fast Fourier Transform (FFT) approach to perform the two-dimensional correlation process. The range migration problem, which is often a major obstacle to efficient processing, can be alleviated by approximating the locus of echoes from a point target by several linear segments. SAR data corresponding to each segment is correlated separately, and the results are coherently summed to produce full-resolution images. This processing approach exhibits greatly improved computation efficiency relative to conventional digital processing methods.

Wu, C.

1976-01-01

153

Comparison of the X-TRACK altimetry estimated currents with moored ADCP and HF radar observations on the West Florida Shelf  

NASA Astrophysics Data System (ADS)

The performance of coastal altimetry over a wide continental shelf is assessed using multiple-year ocean current observations by moored Acoustic Doppler Current Profilers (ADCP) and high-frequency (HF) radar on the West Florida Shelf. Across-track, surface geostrophic velocity anomalies, derived from the X-TRACK along-track sea level anomalies are compared with the near surface current vector components from moored ADCP observations at mid shelf. The altimeter-derived velocity anomalies are also directly compared with the HF radar surface current vector radial components that are aligned perpendicular to the satellite track. Preliminary results indicate the potential usefulness of the along-track altimetry data in contributing to descriptions of the surface circulation on the West Florida Shelf and the challenges of such applications. On subtidal time scales, the root-mean-square difference (rmsd) between the estimated and the observed near surface velocity component anomalies is 8-11 cm/s, which is about the same magnitude as the standard deviations of the velocity components themselves. Adding a wind-driven Ekman velocity component generally helps to reduce the rmsd values.

Liu, Yonggang; Weisberg, Robert H.; Vignudelli, Stefano; Roblou, Laurent; Merz, Clifford R.

2012-10-01

154

Complementary code and digital filtering for detection of weak VHF radar signals from the mesoscale. [SOUSY-VHF radar, Harz Mountains, Germany  

NASA Technical Reports Server (NTRS)

The SOUSY-VHF-Radar operates at a frequency of 53.5 MHz in a valley in the Harz mountains, Germany, 90 km from Hanover. The radar controller, which is programmed by a 16-bit computer holds 1024 program steps in core and controls, via 8 channels, the whole radar system: in particular the master oscillator, the transmitter, the transmit-receive-switch, the receiver, the analog to digital converter, and the hardware adder. The high-sensitivity receiver has a dynamic range of 70 dB and a video bandwidth of 1 MHz. Phase coding schemes are applied, in particular for investigations at mesospheric heights, in order to carry out measurements with the maximum duty cycle and the maximum height resolution. The computer takes the data from the adder to store it in magnetic tape or disc. The radar controller is programmed by the computer using simple FORTRAN IV statements. After the program has been loaded and the computer has started the radar controller, it runs automatically, stopping at the program end. In case of errors or failures occurring during the radar operation, the radar controller is shut off caused either by a safety circuit or by a power failure circuit or by a parity check system.

Schmidt, G.; Ruster, R.; Czechowsky, P.

1983-01-01

155

The Long Wavelength Array (LWA): A Large HF/VHF Array for Solar Physics, Ionospheric Science, and Solar Radar  

E-print Network

, and Solar Radar Namir E. Kassim Naval Research Laboratory, Washington, DC 20375 Stephen M. White AFRL, Kirtland AFB, Albuquerque, NM 87117 Paul Rodriguez Consultant, Washington, DC 20375 Jacob M. Hartman, Brian

Ellingson, Steven W.

156

Applications of high-frequency radar  

NASA Astrophysics Data System (ADS)

Efforts to extend radar range by an order of magnitude with use of the ionosphere as a virtual mirror started after the end of World War II. A number of HF radar programs were pursued, with long-range nuclear burst and missile launch detection demonstrated by 1956. Successful east coast radar aircraft detect and track tests extending across the Atlantic were conducted by 1961. The major obstacles to success, the large target-to-clutter ratio and low signal-to-noise ratio, were overcome with matched filter Doppler processing. To search the areas that a 2000 nautical mile (3700 km) radar can reach, very complex and high dynamic range processing is required. The spectacular advances in digital processing technology have made truly wide-area surveillance possible. Use of the surface attached wave over the oceans can enable HF radar to obtain modest extension of range beyond the horizon. The decameter wavelengths used by both skywave and surface wave radars require large physical antenna apertures, but they have unique capabilities for air and surface targets, many of which are of resonant scattering dimensions. Resonant scattering from the ocean permits sea state and direction estimation. Military and commercial applications of HF radar are in their infancy.

Headrick, J. M.; Thomason, J. F.

1998-07-01

157

Digital processing of orbital radar data to enhance geologic structure - Examples from the Canadian Shield  

NASA Technical Reports Server (NTRS)

Various digital enhancement techniques for SAR are compared using SIR-B and Seasat images of the Canadian Shield. The three best methods for enhancing geological structure were found to be: (1) a simple linear contrast stretch; (2) a mean or median low-pass filter to reduce speckle prior to edge enhancement or a K nearest-neighbor average to cosmetically reduce speckle; and (3) a modification of the Moore-Waltz (1983) technique. Three look directions were coregistered and several means of data display were investigated as means of compensating for radar azimuth biasing.

Masuoka, Penny M.; Harris, Jeff; Lowman, Paul D., Jr.; Blodget, Herbert W.

1988-01-01

158

Applications of digital radar in the analysis of severe local storms  

E-print Network

(& V (Co-Chairman of Committee) k. )&7 I). *v 'e(C' & ~. (Head of Department) (Member) ( ember) August 1973 ABSTRACT Applications of Digital Radar in the Analysis of Severe Local Storms (August 1973) John E. Vogel, B. S. , Texas A&M University... 2A 15 15 I* I! 51 I I 11 15 15 15 15 I I Ie I II le 13 15 te I I I OKLANOMA CLTY N S SL NORMAN 0 I m mi Fig. 16. 50, 000-ft CAZN for 2350 CST on April 29, 1970. Isopleths of reflectivity in dbZ. 33 level. Fig. 10, the 20, 000-ft CAZM...

Vogel, John Everett

2012-06-07

159

47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.  

Code of Federal Regulations, 2010 CFR

...HFBC bands. Among several possible “simulcast” modes are those having a combination of analog and digital...amplitude modulation (QAM) with orthogonal frequency division multiplexing (OFDM) shall be used. 64-QAM is feasible...

2010-10-01

160

Modern Radar Techniques for Geophysical Applications: Two Examples  

NASA Technical Reports Server (NTRS)

The last decade of the evolution of radar was heavily influenced by the rapid increase in the information processing capabilities. Advances in solid state radio HF devices, digital technology, computing architectures and software offered the designers to develop very efficient radars. In designing modern radars the emphasis goes towards the simplification of the system hardware, reduction of overall power, which is compensated by coding and real time signal processing techniques. Radars are commonly employed in geophysical radio soundings like probing the ionosphere; stratosphere-mesosphere measurement, weather forecast, GPR and radio-glaciology etc. In the laboratorio di Geofisica Ambientale of the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy, we developed two pulse compression radars. The first is a HF radar called AIS-INGV; Advanced Ionospheric Sounder designed both for the purpose of research and for routine service of the HF radio wave propagation forecast. The second is a VHF radar called GLACIORADAR, which will be substituting the high power envelope radar used by the Italian Glaciological group. This will be employed in studying the sub glacial structures of Antarctica, giving information about layering, the bed rock and sub glacial lakes if present. These are low power radars, which heavily rely on advanced hardware and powerful real time signal processing. Additional information is included in the original extended abstract.

Arokiasamy, B. J.; Bianchi, C.; Sciacca, U.; Tutone, G.; Zirizzotti, A.; Zuccheretti, E.

2005-01-01

161

Digital Beamforming Synthetic Aperture Radar (DBSAR): Performance Analysis During the Eco-3D 2011 and Summer 2012 Flight Campaigns  

NASA Technical Reports Server (NTRS)

The Digital Beamforming Synthetic Aperture radar (DBSAR) is a state-of-the-art airborne radar developed at NASA/Goddard for the implementation, and testing of digital beamforming techniques applicable to Earth and planetary sciences. The DBSAR measurements have been employed to study: The estimation of vegetation biomass and structure - critical parameters in the study of the carbon cycle; The measurement of geological features - to explore its applicability to planetary science by measuring planetary analogue targets. The instrument flew two test campaigns over the East coast of the United States in 2011, and 2012. During the campaigns the instrument operated in full polarimetric mode collecting data from vegetation and topography features.

Rincon, Rafael F.; Fatoyinbo, Temilola; Carter, Lynn; Ranson, K. Jon; Vega, Manuel; Osmanoglu, Batuhan; Lee, SeungKuk; Sun, Guoqing

2014-01-01

162

Digital Terrestrial Video Broadcast Interference Suppression in Forward-Looking Ground Penetrating Radar Systems  

NASA Astrophysics Data System (ADS)

In this paper we show how radio frequency interference (RFI) generated by digital video broadcasting terrestrial and digital audio broadcasting transmitters can be an important noise source for forward-looking ground penetrating radar (FLGPR) systems. Even in remote locations the average interference power sometimes exceeds ultra-wideband signals by many dB, becoming the limiting factor in the system sensitivity. The overall problem of RFI and its impact in GPR systems is briefly described and several signal processing approaches to removal of RFI are discussed. These include spectral estimation and coherent subtraction algorithms and various filter approaches which have been developed and applied by the research community in similar contexts. We evaluate the performance of these methods by simulating two different scenarios submitted to real RFI acquired with a FLGPR system developed at the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR), (GER). The effectiveness of these algorithms in removing RFI is presented using some performance indices after suppression.

Rial, F. I.; Mendez-Rial, Roi; Lawadka, Lukasz; Gonzalez-Huici, Maria A.

2014-11-01

163

Modelling of the electromagnetic scattering by sea surfaces at grazing incidence. Application to HF surface wave radars  

Microsoft Academic Search

The object of the study is to model the electromagnetic scattering by time-evolving sea surfaces illuminated by high frequency surface wave radars. A common way to simulate this case is to consider the scattering at grazing incidence. Recent studies have focused on so-called exact methods. As such methods are very time and memory consuming, it becomes important to implement techniques

Yaël Demarty; Laetitia Thirion-Lefevre; Vincent Gobin

2010-01-01

164

HF Radar Sounding of TIDs with the Use of the DPS System and Signals from Broadcasting Stations  

Microsoft Academic Search

Atmospheric gravity waves (AGW) propagating in the ionosphere produce quasiperiodic varia- tions of the ionospheric electron density, known as traveling ionospheric disturbances (TID). In its turn, these wavelike processes modulate parameters of the radio signals in the medium; this effect is widely used for the remote sensing of TIDs. For example, paper (1) presents a bistatic radar technique for recovering

V. S. Beley; V. G. Galushko; D. Paznukhov; B. W. Reinisch; Y. M. Yampolski

165

A simple method for optimizing radar absorbent material coatings on HF rope antennas for the increased attenuation of unwanted reflections  

Microsoft Academic Search

The research presented here examines the maximum attenuation available from concentric layers of radar absorbing materials (RAM) surrounding an infinitely long perfect electrically conducting circular cylinder. The electrical phenomenology of normally incident transverse magnetic (TM) and transverse electrical (TE) waves associated with backscattered and bistatic behavior is investigated for a frequency range up to 25 GHz. Some of the more

George W. Jarriel; Lloyd S. Riggs; Michael E. Baginski

1997-01-01

166

HF radar polar patch and its relation with the cusp during BY-dominated IMF: Simultaneous observations at two altitudes  

NASA Astrophysics Data System (ADS)

Recent studies have shown that the motion of the cusp can be deduced from the energetic neutral atom signals detected in the magnetosphere by the Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft. We use this approach to understand the characteristics of the formation of a polar patch seen in the dayside ionosphere. During a period of the 28 March 2001 LENA cusp signal event, the SuperDARN radars at Syowa East, Syowa South, and Kerguelen Island identified large-scale features of a polar patch. A region of high backscatter power observed by the radars separates into two parts around 77°, and its high-latitude part moves in the poleward and duskward direction. The separation latitude is about 5° higher than the equatorward boundary of the cusp, which is deduced from the LENA cusp signal. We interpret these observations, including features obtained with other SuperDARN radars in the northern hemisphere, as being due to the IMF B Y -controlled zonal jet flow that occurred during a period of increase in |B Y /B Z |, without requiring the change in B Y polarity that has been often invoked in previous studies. The sharp equatorward boundary of the radar signatures of the polar patch would be an interface between the preexisting flow generally in the antisunward direction and the enhanced zonal flow. The flow enhancement appears to be a fundamental process that forms the large-scale polar patch at latitudes several degrees higher than the cusp.

Taguchi, S.; Hosokawa, K.; Nakao, A.; Collier, M. R.; Moore, T. E.; Sato, N.; Yukimatu, A. S.

2009-02-01

167

A Model for Radar Images and Its Application to Adaptive Digital Filtering of Multiplicative Noise  

Microsoft Academic Search

Standard image processing techniques which are used to enhance noncoherent optically produced images are not applicable to radar images due to the coherent nature of the radar imaging process. A model for the radar imaging process is derived in this paper and a method for smoothing noisy radar images is also presented. The imaging model shows that the radar image

Victor S. Frost; Josephine Abbott Stiles; K. S. Shanmugan; Julian C. Holtzman

1982-01-01

168

A review of propagation and scattering factors in remote-sensing and ship-tracking by HF radar  

NASA Astrophysics Data System (ADS)

The propagation-loss, noise and scattering mechanisms involved in ground-wave radar for sea state sensing and ship-tracking are first reviewed, taking as an example a coastal installation in the U.K. Techniques for extracting surface-current, surface-wind and directional sea-wave spectrum from first and second-order sea-echo are described, with reference to the influence of the antenna directivity and propagation factors. The special factors affecting ship-tracking in range, azimuth and Doppler are illustrated. The use of sky-wave radar for sea-state sensing and for assessing the ionospheric layer configuration and propagation mode patterns is discussed. Sea-state sensing is shown to require real-time propagation assessment for effective frequency-management. Rapid sweep frequency, sweep-azimuth and Doppler analysis are shown to be desirable.

Shearman, E. D. R.

1983-08-01

169

A 3D Optimal Interpolation Assimilation Scheme of HF Radar Current Data into a Numerical Ocean Model  

NASA Astrophysics Data System (ADS)

In this work a technique for the 3D assimilation of ocean surface current measurements into a numerical ocean model based on data from High Frequency Radar (HFR) systems is presented. The technique is the combination of supplementary forcing on the surface and of and Ekman layer projection of the correction in the depth. Optimal interpolation through BLUE (Best Linear Unbiased Estimator) of the model predicted velocity and HFR observations is computed in order to derive a supplementary forcing applied at the surface boundary. In the depth the assimilation is propagated using an additional Ekman pumping (vertical velocity) based on the correction achieved by BLUE. In this work a HFR data assimilation system for hydrodynamic modelling of Galway Bay in Ireland is developed; it demonstrates the viability of adopting data assimilation techniques to improve the performance of numerical models in regions characterized by significant wind-driven flows. A network of CODAR Seasonde high frequency radars (HFR) deployed within Galway Bay, on the West Coast of Ireland, provides flow measurements adopted for this study. This system provides real-time synoptic measurements of both ocean surface currents and ocean surface waves in regions of the bay where radials from two or more radars intersect. Radar systems have a number of unique advantages in ocean modelling data assimilation schemes, namely, the ability to provide two-dimensional mapping of surface currents at resolutions that capture the complex structure related to coastal topography and the intrinsic instability scales of coastal circulation at a relatively low-cost. The radar system used in this study operates at a frequency of 25MHz which provides a sampling range of 25km at a spatial resolution of 300m.A detailed dataset of HFR observed velocities is collected at 60 minute intervals for a period chosen for comparison due to frequent occurrences of highly-energetic, storm-force events. In conjunction with this, a comprehensive weather station, tide gauge and river monitoring program is conducted. The data are then used to maintain density fields within the model and to force the wind direction and magnitude on flows. The Data Assimilation scheme is then assessed and validated via HFR surface flow measurements.

Ragnoli, Emanuele; Zhuk, Sergiy; Donncha, Fearghal O.; Suits, Frank; Hartnett, Michael

2013-04-01

170

The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images  

NASA Astrophysics Data System (ADS)

Comparison of the Lunar Radar Sounder (LRS) data to the Multiband Imager (MI) data is performed to identify the subsurface reflectors in Mare Serenitatis. The LRS is FM-CW radar (4-6 MHz) and the 2 MHz bandwidth leads to the range resolution of 75 m in a vacuum, whereas the sampling interval in the flight direction is about 75 m when an altitude of the spacecraft with polar orbit is nominal (100 km). Horizontally continuous reflectors were clearly detected by LRS in limited areas that consist of about 9% of the whole maria. The typical depth of the reflectors is estimated to be a few hundred meters. Layered structures of mare basalts are also discernible on some crater walls in the MI data of the visible bands (VIS). The VIS range has nine wavelengths of 415, 750, 900, 950, and 1000 nm, and their spatial resolution is 20 m/pixel at a nominal altitude. The stratigraphies around Bessel and Bessel-H craters in Mare Serenitatis are examined in this paper. It was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions. In addition, model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high-porosity contrast. These results suggest that the detected reflectors in Mare Serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change, not instantaneously. Therefore combination of the LRS and MI data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in Mare Serenitatis and other maria.

Oshigami, Shoko; Okuno, Shinya; Yamaguchi, Yasushi; Ohtake, Makiko; Haruyama, Junichi; Kobayashi, Takao; Kumamoto, Atsushi; Ono, Takayuki

2012-03-01

171

Integration of radar altimeter, precision navigation, and digital terrain data for low-altitude flight  

NASA Technical Reports Server (NTRS)

Avionic systems that depend on digitized terrain elevation data for guidance generation or navigational reference require accurate absolute and relative distance measurements to the terrain, especially as they approach lower altitudes. This is particularly exacting in low-altitude helicopter missions, where aggressive terrain hugging maneuvers create minimal horizontal and vertical clearances and demand precise terrain positioning. Sole reliance on airborne precision navigation and stored terrain elevation data for above-ground-level (AGL) positioning severely limits the operational altitude of such systems. A Kalman filter is presented which blends radar altimeter returns, precision navigation, and stored terrain elevation data for AGL positioning. The filter is evaluated using low-altitude helicopter flight test data acquired over moderately rugged terrain. The proposed Kalman filter is found to remove large disparities in predicted AGL altitude (i.e., from airborne navigation and terrain elevation data) in the presence of measurement anomalies and dropouts. Previous work suggested a minimum clearance altitude of 220 ft AGL for a near-terrain guidance system; integration of a radar altimeter allows for operation of that system below 50 ft, subject to obstacle-avoidance limitations.

Zelenka, Richard E.

1992-01-01

172

Digital tapped delay lines for HWIL testing of matched filter radar receivers  

Microsoft Academic Search

Matched filter processing for pulse compression of phase coded waveforms is a classic method for increasing radar range measurement resolution. A generic approach for simulating high resolution range extended radar scenes in a Hardware in the Loop (HWIL) test environment is to pass the phase coded radar transmit pulse through an RF tapped delay line comprised of individually amplitude- and

Richard F. Olson; William J. Braselton; Richard D. Mohlere

2009-01-01

173

An analysis of the data collection modes of a digital weather radar system with respect to significant severe weather features  

E-print Network

, ubstituting Eq (6) into Eq (5) we get log Z = 2 log r + log P + 9. 0 e3 r log Z = 2 log r + log P + 10. 1 e10 r (7 a) (7b) The digital value of P is converted to its dBm equivalent (always r negative) through the use of calibration data for each... shades of grey is called video contouring. These threshold levels can be set digitally in 0. 5 dB steps. A radar return that falls within level 1 is displayed as grey (half bright- ness), level 2 is displayed as white (full brightne s), and level 3 i...

Neyland, Michael Arthur

2012-06-07

174

Surveillance Technology Study and Analysis. Volume IV. Considerations in the Analysis and Performance of Radar Systems.  

National Technical Information Service (NTIS)

This report presents results of studies, investigations, and technique developments which will be useful in future HF long range radar applications. This report is intended to aid the radar engineer in design and evaluation of HF radar systems. Major emph...

R. M. Davis, L. C. Widmann

1967-01-01

175

Integration of radar altimeter, precision navigation, and digital terrain data for low-altitude flight  

NASA Technical Reports Server (NTRS)

A Kalman filter for the integration of a radar altimeter into a terrain database-dependent guidance system was developed. Results obtained from a low-altitude helicopter flight test data acquired over moderately rugged terrain showed that the proposed Kalman filter removes large disparities in predicted above-ground-level (AGL) altitude in the presence of measurement anomalies and dropouts. Integration of a radar altimeter makes it possible to operate a near-terrain guidance system at or below 50 ft (subject to obstacle-avoidance limitations), whereas without radar altimeter integration, a minimum clearance altitude of 220 AGL is needed, as is suggested by previous work.

Zelenka, Richard E.

1992-01-01

176

In-flight detection of errors for enhanced aircraft flight safety and vertical accuracy improvement using digital terrain elevation data with an inertial navigation system, global positioning system and radar altimeter  

Microsoft Academic Search

This dissertation discusses integration architectures using digital terrain elevation data (DTED) with an inertial navigation system (INS), a global positioning system (GPS) and a radar altimeter. Two integration architectures are considered: DTED with INS, GPS and radar altimeter for aircraft vertical accuracy improvement during the final approach; and DTED with kinematic GPS (KGPS) and a radar altimeter for enhanced aircraft

Robert Anthony Gray

1999-01-01

177

A digital elevation model of the Greenland Ice Sheet derived from combined laser and radar altimetry data  

NASA Astrophysics Data System (ADS)

When estimating elevation changes of ice-covered surfaces from radar altimetry, it is important to correct for slope-induced errors. They cause the reflecting point of the pulse to move up-slope and thus return estimates in the wrong coordinates. Slope-induced errors can be corrected for by introducing a Digital Elevation Model (DEM). In this work, such a DEM is developed for the Greenland Ice Sheet using a combination of Envisat radar and ICESat laser altimetry. If time permits, CryoSat radar altimetry will be included as well. The reference year is 2010 and the spatial resolution 2.5 x 2.5 km. This is in accordance with the results obtained in the ESA Ice Sheets CCI project showing that a 5 x 5 km grid spacing is reasonable for ice sheet-wide change detection (Levinsen et al., 2013). Separate DEMs will be created for the given data sets, and the geostatistical spatial interpolation method collocation will be used to merge them, thus adjusting for potential inter-satellite biases. The final DEM is validated with temporally and spatially agreeing airborne lidar data acquired in the NASA IceBridge and ESA CryoVex campaigns. The motivation for developing a new DEM is based on 1) large surface changes presently being observed, and mainly in margin regions, hence necessitating updated topography maps for accurately deriving and correcting surface elevation changes, and 2) although radar altimetry is subject to surface penetration of the signal into the snowpack, data is acquired continuously in time. This is not the case with e.g. ICESat, where laser altimetry data were obtained in periods of active lasers, i.e. three times a year with a 35-day repeat track. Previous DEMs e.g. have 2007 as the nominal reference year, or they are built merely from ICESat data. These have elevation errors as small as 10 cm, which is lower than for Envisat and CryoSat. The advantage of an updated DEM consisting of combined radar and laser altimetry therefore is the possibility of achieving a high spatial and temporal coverage, as well as the opportunity to continuously map surface changes relative to an updated topography and slopes. References: Levinsen, J. F., Khvorostovsky, K., Ticconi, F., Shepherd, A., Forsberg, R., Sørensen, L. S., Muir, A., Pie, N., Felikson, D., Flament, T., Hurkmans, R., Moholdt, G., Gunter, B., Lindenbergh, R. C., and Kleinherenbrink, M.: ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland - Round Robin results, The Cryosphere Discuss., 7, 5433-5460, 2013.

Fredenslund Levinsen, Joanna; Smith, Ben; Sørensen, Louise S.; Forsberg, René

2014-05-01

178

Low resolution radar digital interface. [with data recorder for precipitation measurements  

NASA Technical Reports Server (NTRS)

This document describes the design and operation of a low resolution radar data recording system for precipitation measurements. This system records a full azimuth scan on seven track magnetic tapes every five minutes. It is designed to operate on a continuous basis with operator intervention required only for changing tape reels and calibration.

1973-01-01

179

Monte-Carlo Analysis of a Radar-Fuze Digital Integrator.  

National Technical Information Service (NTIS)

The memory time of an RC integrator (i.e., a single-pole, low-pass filter) is proportional to the product of the resistance R and the capacitance C. Thus, the memory time will tend to vary with environment and from unit to unit in production. In a radar f...

C. S. Williams, L. T. James

1975-01-01

180

The family of atomic functions and digital signal processing in synthetic aperture radar  

Microsoft Academic Search

The report consists of two parts. In the first part, the sampling analysis of weight windows is conducted on the basis of atomic functions (AF) and their application in problems of the classical method of synthetic aperture radar (SAR) is considered. The second part contains fundamentals of a modified method of synthetizing the aperture. The modified ambiguity function for different

V. F. Kravchenko; V. K. Volosyuk; V. V. Pavlikov

2007-01-01

181

High resolution vertical profiles of wind, temperature and humidity obtained by computer processing and digital filtering of radiosonde and radar tracking data from the ITCZ experiment of 1977  

NASA Technical Reports Server (NTRS)

Results are presented from computer processing and digital filtering of radiosonde and radar tracking data obtained during the ITCZ experiment when coordinated measurements were taken daily over a 16 day period across the Panama Canal Zone. The temperature relative humidity and wind velocity profiles are discussed.

Danielson, E. F.; Hipskind, R. S.; Gaines, S. E.

1980-01-01

182

Using X-band Weather Radar Measurements to Monitor the Integrity of Digital Elevation Models for Synthetic Vision Systems  

NASA Technical Reports Server (NTRS)

Synthetic Vision Systems (SVS) provide pilots with displays of stored geo-spatial data representing terrain, obstacles, and cultural features. As comprehensive validation is impractical, these databases typically have no quantifiable level of integrity. Further, updates to the databases may not be provided as changes occur. These issues limit the certification level and constrain the operational context of SVS for civil aviation. Previous work demonstrated the feasibility of using a realtime monitor to bound the integrity of Digital Elevation Models (DEMs) by using radar altimeter measurements during flight. This paper describes an extension of this concept to include X-band Weather Radar (WxR) measurements. This enables the monitor to detect additional classes of DEM errors and to reduce the exposure time associated with integrity threats. Feature extraction techniques are used along with a statistical assessment of similarity measures between the sensed and stored features that are detected. Recent flight-testing in the area around the Juneau, Alaska Airport (JNU) has resulted in a comprehensive set of sensor data that is being used to assess the feasibility of the proposed monitor technology. Initial results of this assessment are presented.

Young, Steve; UijtdeHaag, Maarten; Sayre, Jonathon

2003-01-01

183

Practical problems with covariance matrix estimation for adaptive MTI and space-time adaptive processing for target detection in HF surface wave radars  

Microsoft Academic Search

Surface wave over the horizon radar systems have a potential to detect targets, that are hidden under optical horizon. This possibility is, however, difficult to implement as a result of first and second order clutter scattered from the ocean surface in combination with interferences. In this paper we compare adaptive MTI and space-time adaptive processing algorithms applied to the surface

T. Gorski; Giuseppe Fabrizio; J.-M. Le Caillec; A. Kawalec; N. Thomas

2008-01-01

184

An analysis of HF radar measured surface currents to determine tidal, wind-forced, and seasonal circulation in the Gulf of the Farallones, California, United States  

Microsoft Academic Search

A complete year of hourly 3 km resolution high-frequency radar measured surface currents covering the Gulf of the Farallones were analyzed with the following three primary objectives: (1) describe the seasonal surface circulation, (2) identify tidal currents, and (3) determine the influence of wind forcing. Three predominant seasonal circulation regimes were identified: relaxation, storm, and upwelling. The relaxation period exhibited

Matt K. Gough; Newell Garfield; Erika McPhee-Shaw

2010-01-01

185

RF interference suppression for bistatic HF surface wave SIAR  

Microsoft Academic Search

Intense RF (radio frequency) interference is the one of the impediments in target detection for high frequency surface wave radar (HFSWR). A novel type of HFSWR, bistatic HF surface wave SIAR (synthesis impulse and aperture radar), has been presented recently. In this paper, the RF interference of this radar is analyzed. Combining with the theoretical analyses and experimental samples, the

Liu Chunbo; Chen Baixiao; Zhang Shouhong

2008-01-01

186

Atmospheric gravity waves/traveling ionospheric disturbances study with digital ionosondes and incoherent scatter radar  

NASA Astrophysics Data System (ADS)

The problem of radiowave propagation in the ionosphere in the presence of a wavelike disturbance has been solved in a generalized formulation using the model of a perfectly reflecting surface. The solution obtained has made it possible to develop a remote sensing technique for studying the ionosphere irregular wavelike phenomena, namely, traveling ionospheric disturbances, which are a manifestation of neutral atmosphere phenomena, atmospheric gravity waves. Implementation of this technique in the Digisonde Portable Sounder of the University of Massachusetts Lowell, Center for Atmospheric Research allowed development of a dedicated data acquisition system for ionospheric disturbance diagnostics. The experimental validation of the developed method has been obtained by comparison of the results of simultaneous disturbance diagnostics made with the Digisonde Portable Sounder and the Millstone Hill Incoherent Scatter Radar. Differences in disturbance parameters measured by the two techniques was no greater than 15%. The link between the atmospheric gravity waves and the moving solar terminator has been experimentally investigated using the Digisonde Portable Sounder and Millstone Hill Incoherent Scatter Radar and evidence of solar terminator generated disturbances has been demonstrated.

Paznukhov, Vadym Volodymyrovych

187

A mathematical modeling and FPGA-based digital receiver in a continuous wave Doppler radar  

Microsoft Academic Search

This paper deals with synthesizing in FPGA a digital correlator for signal processing in a Doppler radiolocation station (RLS) with continuous wave and pulse compression. A MATLAB-based mathematical model of a correlator has been developed and investigated. Part of the data, received as a result of these investigations, has been used for the simulation of the circuit, synthesized in FPGA.

D. M. Kovachev; N. G. Georgieva

2004-01-01

188

High-Resolution Digital Mapping of Soil Surface Water Content at the Field Scale Using Ground Penetrating Radar  

NASA Astrophysics Data System (ADS)

Measuring soil surface water content spatial variability is essential for many environmental and agricultural researches and engineering applications, as this variable controls important key processes of the hydrological cycle such as infiltration, runoff, evaporation, and energy exchanges between the earth and the atmosphere. In particular, the characterization of spatial patterns and heterogeneities over a continuous range of scales is presently subject to intensive research for developing, calibrating and testing distributed hydrological models, with, e.g., the installation of field- to watershed-scale observatories. In that respect, ground penetrating radar (GPR) appears to be a promising tool for real-time, high resolution digital soil mapping at the field scale. Yet existing GPR techniques for quantitative soil characterization still suffer from a series of limitations, mainly arising from the strong simplifying assumptions that are commonly made with respect to electromagnetic wave propagation phenomena. We have developed a new GPR methodology based on full-waveform forward and inverse modelling, that inherently maximizes radar information retrieval capabilities thanks to an accurate electromagnetic model and system calibration procedure. The radar system consists of a vector network analyzer combined with an off- ground, zero-offset, ultra-wideband horn antenna, thereby setting up a stepped-frequency continuous-wave (SFCW) GPR. A full-waveform model describes accurately the radar signal by accounting for (1) all antenna effects and antenna-soil interactions through a linear system of frequency dependent, complex transfer functions, and (2) wave propagation in three-dimensional multilayered media through a Green's function as exact solution of Maxwell's equations. A fast procedure was developed to evaluate the involved spatial Green's function from its spectral counterpart, whose integral is singular. The soil electromagnetic properties and their vertical distribution are estimated by inverse modeling using various iterative optimization strategies, depending on the model complexity. The method presents especially considerable advantages compared to the current surface characterization techniques using GPR, namely, the ground wave and common reflection methods. The proposed methodology was successfully validated for a series of model configurations of increasing complexity. For the particular case of soil surface water content retrieval, we especially addressed the impact of shallow soil layering on the inverse estimates in case it is or not accounted for in the inverse model configuration. The results show that thin layers should not be neglected, especially when high contrasts between soil layers are encountered. The method is now routinely used for real-time, automated mapping of soil surface water content in the field. GPR-derived maps are compared to ground-truth measurements and satellite radar data products. Stochastic approaches are used for assessing the uncertainty on the inverse estimates. The proposed method constitutes in particular a robust alternative to other GPR approaches for shallow soil characterization.

Minet, J.; Lambot, S.; Slob, E.; Vereecken, H.; Vanclooster, M.

2009-05-01

189

Comparison of digital elevation models over Australia and external validation using ERS?1 satellite radar altimetry  

Microsoft Academic Search

Digital elevation models (DEMs) are widely relied upon as representations of the Earth's topographic morphology. The most widely used global DEMs available are ETOPO5, TerrainBase and JGP95E at a 5?arc?minute spatial resolution, and the GTOPO30 and GLOBE (version 1) global DEMs at a 30?arc?second spatial resolution. This paper presents the results of intercomparisons of these global DEMs over Australia, and

R. D. Hilton; W. E. Featherstone; P. A. M. Berry; C. P. D. Johnson; J. F. Kirby

2003-01-01

190

Radar applications  

NASA Astrophysics Data System (ADS)

Papers are presented on air-traffic control radar, surveillance radar, missile guidance radar, and high-performance tactical three-dimensional radar. Also considered are the airborne early warning radar, the Foxhunter airborne intercept radar, and environmental remote sensing. Other topics include spaceborne SARs, the Pioneer Orbiter radar, and a bistatic pulse-Doppler intruder-detection radar.

Skolnik, Merrill I.

191

Radar applications  

Microsoft Academic Search

Papers are presented on air-traffic control radar, surveillance radar, missile guidance radar, and high-performance tactical three-dimensional radar. Also considered are the airborne early warning radar, the Foxhunter airborne intercept radar, and environmental remote sensing. Other topics include spaceborne SARs, the Pioneer Orbiter radar, and a bistatic pulse-Doppler intruder-detection radar.

Merrill I. Skolnik

1988-01-01

192

Radar data processing and analysis  

NASA Technical Reports Server (NTRS)

Digitized four-channel radar images corresponding to particular areas from the Phoenix and Huntington test sites were generated in conjunction with prior experiments performed to collect X- and L-band synthetic aperture radar imagery of these two areas. The methods for generating this imagery are documented. A secondary objective was the investigation of digital processing techniques for extraction of information from the multiband radar image data. Following the digitization, the remaining resources permitted a preliminary machine analysis to be performed on portions of the radar image data. The results, although necessarily limited, are reported.

Ausherman, D.; Larson, R.; Liskow, C.

1976-01-01

193

Remote sensing of sea state by radar  

Microsoft Academic Search

In recent years several radar techniques have evolved which allow the remote measurement of certain parameters important in the description of sea state. At MF and HF, monostatic and bistatic configurations employing satellites, ships, islands, and\\/or land based stations can measure the ocean waveheight spectrum with several frequencies via first-order Bragg scatter. At high HF and VHF, the ocean waveheight

D. Barrick

1972-01-01

194

Detecting and quantifying mountain permafrost creep from in situ inventory, space-borne radar interferometry and airborne digital  

E-print Network

Detecting and quantifying mountain permafrost creep from in situ inventory, space-borne radar permafrost creep are compared: (1) rock glacier inventory and characterization from in situ indicators, (2 detailed in situ investigations. 1. Introduction Permafrost, i.e. underground with temperatures below 0C

Kääb, Andreas

195

Water slope and discharge in the Amazon River estimated using the shuttle radar topography mission digital elevation model  

Microsoft Academic Search

We find that the standard deviation, hence error, of the water surface elevation data from the Shuttle Radar Topography Mission (SRTM) is 5.51 m for basin-wide, regional and local Amazon mainstem reaches. This error implies a minimum reach length of 733km in order to calculate a reliable water-surface slope. Resulting slopes are 1.92 +\\/- 0.19 cm\\/km for Manacapuru, 2.86 +\\/-

Gina LeFavour; Doug Alsdorf

2005-01-01

196

Meteor observations with the European incoherent scatter UHF radar  

Microsoft Academic Search

The European Incoherent Scatter (EISCAT) UHF radar, which operates at a nominal frequency of 930 MHz, is introduced as a powerful meteor radar. Its high sensitivity is utilized to detect transient enhanced ionization trails caused by meteors of all orientations, in contrast to conventional HF and VHF backscatter radars, which observe only the meteor trails oriented approximately normal to the

Asta Pellinen-Wannberg; Gudmund Wannberg

1994-01-01

197

Lunar Radar Cross Section at Low Frequency  

NASA Technical Reports Server (NTRS)

Recent bistatic measurements of the lunar radar cross-section have extended the spectrum to long radio wavelength. We have utilized the HF Active Auroral Research Program (HAARP) radar facility near Gakona, Alaska to transmit high power pulses at 8.075 MHz to the Moon; the echo pulses were received onboard the NASA/WIND spacecraft by the WAVES HF receiver. This lunar radar experiment follows our previous use of earth-based HF radar with satellites to conduct space experiments. The spacecraft was approaching the Moon for a scheduled orbit perturbation when our experiment of 13 September 2001 was conducted. During the two-hour experiment, the radial distance of the satellite from the Moon varied from 28 to 24 Rm, where Rm is in lunar radii.

Rodriguez, P.; Kennedy, E. J.; Kossey, P.; McCarrick, M.; Kaiser, M. L.; Bougeret, J.-L.; Tokarev, Y. V.

2002-01-01

198

Two-dimensional adaptive processing for ionospheric clutter mitigation in High Frequency Surface Wave Radar  

Microsoft Academic Search

High Frequency Surface Wave Radar (HFSWR) is a technology used for over-the-horizon detection of ocean vessels. This radar exploits the diffraction of electromagnetic waves around the curved surface of the Earth. To minimize the attenuation of the diffracted waves, the radar must operate at frequencies in the lower part of the high frequency (HF) band. However, radar signals at these

Ryan J. Riddolls; Raviraj S. Adve

2009-01-01

199

Investigation and Development of Data-Driven D-Region Model for HF Systems Impacts  

NASA Technical Reports Server (NTRS)

Space Environment Corporation (SEC) and RP Consultants (RPC) are to develop and validate a weather-capable D region model for making High Frequency (HF) absorption predictions in support of the HF communications and radar communities. The weather-capable model will assimilate solar and earth space observations from NASA satellites. The model will account for solar-induced impacts on HF absorption, including X-rays, Solar Proton Events (SPE's), and auroral precipitation. The work plan includes: I . Optimize D-region model to quickly obtain ion and electron densities for proper HF absorption calculations. 2. Develop indices-driven modules for D-region ionization sources for low, mid, & high latitudes including X-rays, cosmic rays, auroral precipitation, & solar protons. (Note: solar spectrum & auroral modules already exist). 3. Setup low-cost monitors of existing HF beacons and add one single-frequency beacon. 4. Use PENEX HF-link database with HF monitor data to validate D-region/HF absorption model using climatological ionization drivers. 5. Develop algorithms to assimilate NASA satellite data of solar, interplanetary, and auroral observations into ionization source modules. 6. Use PENEX HF-link & HF-beacon data for skill score comparison of assimilation versus climatological D-region/HF absorption model. Only some satellites are available for the PENEX time period, thus, HF-beacon data is necessary. 7. Use HF beacon monitors to develop HF-link data assimilation algorithms for regional improvement to the D-region/HF absorption model.

Eccles, J. V.; Rice, D.; Sojka, J. J.; Hunsucker, R. D.

2002-01-01

200

Micropower impulse radar  

SciTech Connect

Invented and developed at Lawrence Livermore National Laboratory is an inexpensive and highly sensitive, low-power radar system that produces and samples extremely short pulses of energy at the rate of 2 million per second. Called micropower impulse radar (MIR), it can detect objects at a greater variety of distances with greater sensitivity than conventional radar. Its origins in the Laboratory`s Laser Directorate stem from Nova`s transient digitizer. The MIR`s extraordinary range of applications include security, search and rescue, life support, nondestructive evaluation, and transportation.

Azevedo, S.; McEwan, T.E.

1996-01-01

201

Satellite Remote Sensing of Landscape Freeze/Thaw State Dynamics for Complex Topography and Fire Disturbance Areas Using Multi-Sensor Radar and SRTM Digital Elevation Models  

NASA Astrophysics Data System (ADS)

The annual freeze/thaw cycle drives the length of the growing season in the boreal forest, and is a major factor determining annual productivity and associated exchange of CO2 with the atmosphere. Variations in freeze/thaw processes are spatially and temporally complex in boreal environments, particularly in areas of complex topography and in fire disturbance regimes. We investigate the spatial and temporal characteristics of seasonal freeze/thaw dynamics in complex boreal landscapes, as derived from radar backscatter measured with ERS (C-band, VV polarization, 200m resolution) and JERS-1 (L-band, HH polarization, 100m resolution) Synthetic Aperture Radars (SARs), and with the SeaWinds scatterometer (Ku-band, 25km resolution). C- and L-band backscatter are applied to characterize freeze/thaw transitions for a chronosequence of recovering burn sites near Delta Junction, Alaska, and for a region of complex topography on the Kenai Peninsula, Alaska. We characterize differences in radar-derived freeze/thaw state, examining transitions over complex terrain and landscape disturbance regimes. In areas of complex terrain, we explore freeze/thaw dynamics related to elevation, slope aspect and varying landcover. In the burned regions, we explore the timing of seasonal freeze/thaw transition as related to the recovering landscape, relative to that of a nearby control site. We apply in situ biophysical measurements, including flux tower measurements to validate and interpret the remotely sensed parameters. A multi-scale analysis is performed relating high-resolution SAR backscatter and moderate resolution scatterometer measurements to assess trade-offs in spatial and temporal resolution in the remotely sensed fields. A temporal change discriminator is applied to classify time series radar imagery to classify the landscape freeze-thaw state. We apply a 30m-resolution digital elevation model (DEM) derived from Shuttle Radar Topography Mission (SRTM) data to orthorectify the time series SAR imagery over the complex terrain site. This DEM was integrated with the SAR imagery to examine elevation and slope aspect effects on freeze/thaw transitions. Scaling assessments of the relationship between SAR and SeaWinds backscatter provide a means for determining sub-grid spatial variability in land cover, terrain and freeze/thaw processes, based on semi-variogram analyses. Results show that the high-resolution SARs may be applied to map freeze/thaw transitions in complex landscapes. In regions of complex terrain, dynamics related to elevation and slope aspect are delineated. Fusion with accurate DEM information as provided by SRTM facilitates orthorectification and analysis of terrain effects. The SARs also observe distinguishable differences in backscatter amplitude response and in the timing of freeze/thaw transitions associated with varying disturbance regimes driven by forest fire. These findings demonstrate the importance of considering landscape heterogeneity for development of remote sensing techniques for monitoring phenological processes across complex, heterogeneous landscapes in boreal ecosystems. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, and the University of Montana under contract with the National Aeronautics and Space Administration.

Podest, E.; McDonald, K.; Kimball, J.; Randerson, J. T.

2003-12-01

202

Study of Two ANN Digital Implementations of a Radar Detector Candidate to an On-Board Satellite Experiment  

Microsoft Academic Search

The Microelectronics and Photonics Testbed (MPTB) is a scientific satellite carrying twenty-four experiments on-board in a\\u000a high radiation orbit since November 1997. The first objective of this paper is to summarize one year flight results, telemetred\\u000a from one of its experiments, a digital “neural board” programmed to perform texture analysis by means of an Artificial Neural\\u000a Network (ANN). One of

Raoul Velazco; Ch. Godin; Ph. Cheynet; Santiago Torres-alegre; Diego Andina; M. B. Gordon

1999-01-01

203

Digital Base Band Converter As Radar Vlbi Backend / Dbbc K? Ciparošanas Sist?ma Radara Vlbi Nov?rojumiem  

NASA Astrophysics Data System (ADS)

A digital base band converter (DBBC) system has been developed by the Istituto di Radioastronomia (Noto, Italy) for increasing the sensitivity of European VLBI Network (EVN) by expanding the full observed bandwidth using numerical methods. The output data rate of this VLBI-backend is raised from 1 to 4 Gbps for each radiotelescope. All operations related to the signal processing (frequency translation, amplification, frequency generation with local oscillators, etc.) are transferred to the digital domain, which allows - in addition to well-known advantages coming from digital technologies - achieving better repeatability, precision, simplicity, etc. The maximum input band of DBBC system is 3.5 GHz, and the instantaneous bandwidth is up to 1 GHz for each radio frequency/intermediate frequency (RF/IF) out of the eight possible. This backend is a highly powerful platform for other radioastronomy applications, and a number of additional so-called personalities have been developed and used. This includes PFB (polyphase filter bank) receivers and Spectra for high resolution spectroscopy. An additional new development with the same aim - to use the DBBC system as a multi-purpose backend - is related to the bi-static radar observations including Radar VLBI. In such observations it is possible to study the population of space debris, with detection of even centimetre class fragments. A powerful transmitter is used to illuminate the sky region to be analyzed, and the echoes coming from known or unknown objects are reflected to one or more groundbased telescopes thus producing a single-dish or interferometric detection. The DBBC Radar VLBI personality is able to realize a high-resolution spectrum analysis, maintaining in the central area the echo signal at the expected frequency including the Doppler shift of frequency. For extremely weak signals a very large integration time is needed, so for this personality different input parameters are provided. The realtime information can then allow exploring easily the desired range of search for unknown or not fully determined orbit objects. These features make Radar VLBI personality most useful in the space debris measurements. DBBC sist?ma izstr?d?ta Noto Radioastronomijas instit?t?. Sist?mas galvenaisuzdevums - palielin?t visa Eiropas VLBI t?kla jut?bu - realiz?ts, palielinotvisas nov?rojam?s joslas platumu un pielietojot ciparu sign?lu apstr?des metodes.Izejas datu pl?sma palielin?ta no 1 l?dz 4 Gbps katram radioteleskopam un visasoper?cijas, kas saist?tas ar sign?lu apstr?di (frekvences p?rveidošana, pastiprin?jums,iekš?jie ?eneratori, utt.), realiz?tas digit?l? form?, kas ?auj ieg?t noz?m?gusuzlabojumus atk?rtojam?b?, precizit?t?, vienk?rš?b?, nemaz neminot visp?rzin?m?spriekšroc?bas, ko nodrošina digit?lo tehnolo?iju izmantošana. Maksim?l? ieejassign?la frekven?u josla ir 3.5 GHz, un moment?nais joslas platums ir l?dz 1 GHz uzkatru no asto?iem iesp?jamajiem RF/IF kan?liem. Š? datu re?istr?cijas sist?ma ir?oti veiktsp?j?ga platforma ne tikai EVN, bet ar? citiem radioastronomijas pielietojumiem,un papildus tiek izstr?d?ta vesela virkne programmat?ras pakot?u, kasv?l vair?k paplašina sist?mas funkcionalit?ti. Tas ietver PFB (Polif?zes FiltruBanka) uztv?r?jus "Spectra”, kas piem?roti augstas izš?irtsp?jas spektroskopijasvajadz?b?m. Papildus realiz?ts jaunas programmat?ras risin?jums, ar m?r?iizmantot DBBC sist?mu k? daudzfunkcion?lu datu ciparošanas iek?rtu, kasizmantojama bistatiskiem radara nov?rojumiem, tai skait? ar? rad

Tuccari, G.; Bezrukovs, Vl.; Nechaeva, M.

2012-12-01

204

Bistatic radar sea state monitoring  

NASA Technical Reports Server (NTRS)

Bistatic radar techniques were examined for remote measurement of the two-dimensional surface wave height spectrum of the ocean. One technique operates at high frequencies (HF), 3-30 MHz, and the other at ultrahigh frequencies (UHF), approximately 1 GHz. Only a preliminary theoretical examination of the UHF technique was performed; however the principle underlying the HF technique was demonstrated experimentally with results indicating that an HF bistatic system using a surface transmitter and an orbital receiver would be capable of measuring the two-dimensional wave height spectrum in the vicinity of the transmitter. An HF bistatic system could also be used with an airborne receiver for ground truth ocean wave spectrum measurements. Preliminary system requirements and hardware configurations are discussed for both an orbital system and an aircraft verification experiment.

Ruck, G. T.; Barrick, D. E.; Kaliszewski, T.

1972-01-01

205

Alpine snow distribution from-ground based radar measurements compared with a high resolution digital elevation model from ground-based LiDAR observations  

NASA Astrophysics Data System (ADS)

Collection of snow depth and precipitation measurements is exceedingly difficult above treeline in exposed areas of alpine terrain. Variability in surface topography combined with wind can cause large variations in snow depth and snow water equivalent over tens of meters, and precipitation measurements are often unreliable where wind speeds are high. Total snow depth and water equivalent measurements are often not representative in these highly variable snowpacks, while alpine locations often contain a large percentage of the water stored as snow in many watersheds. We use two different ground-based radar systems to measure snow distribution near an alpine weather station at 3719 m (12,200 ft) in SW Colorado at the Center for Snow and Avalanche Studies' Senator Beck Basin Study Area. The spatial distribution of snow is compared with a high resolution digital elevation model derived from ground-based LiDAR observations in snow-free conditions. The length scales of variation in both subsurface topography and snow depth are investigated in the region surrounding the weather station to help place the continuous snow depth observations at the weather station in the context of the snow distribution at the slope scale across this low angle site.

Marshall, H.; Deeb, E. J.; Gleason, A.; Heilig, A.; Finnegan, D. C.; Deems, J. S.; Havens, S.; Kormos, P. R.; Landry, C.; McCreight, J. L.

2011-12-01

206

Periodic structures to efficiently launch HF surface waves  

Microsoft Academic Search

To enhance the performances of HF Surface Wave Radar, two periodic structures able to sustain a sole surface wave are proposed in this communication. Starting from the identification of a proper value of electric permittivity that permits surface wave's propagation, we study a \\

Luca Petrillo; Florent Jangal; Muriel Darces; Jean-Louis Montmagnon; Marc Helier

2011-01-01

207

Automated registration of synthetic aperture radar imagery to LIDAR  

Microsoft Academic Search

The registration of synthetic aperture radar imagery to other images is difficult, especially in mountainous terrain. We introduce a new approach to this problem that registers radar images to digital elevation models derived from LIDAR. The algorithm generates a predicted image from the elevation model using the radar geometry and then registers the predicted image to the radar image with

Mark D. Pritt; Kevin J. LaTourette

2011-01-01

208

Radar sector blanker  

NASA Astrophysics Data System (ADS)

A radar sector blanker comprises in analog-to-digital converter and a sector controller unit. The analog-to-digital converter receives the analog synchro voltages describing the positioning of a radar antenna and changes these voltages into binary-coded decimal (BCD) information. The sector controller unit comprises a portable housing, a controller system, and a power supply. The controller system includes an OFF comparator circuit, an ON comparator circuit, an S-R latch, and a solid-state switch. Each comparator circuit comprises three cascaded transistor-transistor logic (TTL) integrated chips. The power supply gives a direct-current voltage to the solid-state switch and the TTL chips. The sector blanker blocks transmission for a predetermined rotational region or sector of a radar system.

Hall, Roger B.

1994-03-01

209

Application of ground-penetrating radar, digital optical borehole images, and cores for characterization of porosity hydraulic conductivity and paleokarst in the Biscayne aquifer, southeastern Florida, USA  

USGS Publications Warehouse

This paper presents examples of ground-penetrating radar (GPR) data from two study sites in southeastern Florida where karstic Pleistocene platform carbonates that comprise the unconfined Biscayne aquifer were imaged. Important features shown on resultant GPR profiles include: (1) upward and lateral qualitative interpretative distribution of porosity and hydraulic conductivity; (2) paleotopographic relief on karstic subaerial exposure surfaces; and (3) vertical stacking of chronostratigraphic high-frequency cycles (HFCs). These characteristics were verified by comparison to rock properties observed and measured in core samples, and identified in digital optical borehole images. Results demonstrate that an empirical relation exists between measured whole-core porosity and hydraulic conductivity, observed porosity on digital optical borehole images, formation conductivity, and GPR reflection amplitudes-as porosity and hydraulic conductivity determined from core and borehole images increases, formation conductivity increases, and GPR reflection amplitude decreases. This relation allows for qualitative interpretation of the vertical and lateral distribution of porosity and hydraulic conductivity within HFCs. Two subtidal HFCs in the uppermost Biscayne aquifer have significantly unique populations of whole-core porosity values and vertical hydraulic conductivity values. Porosity measurements from one cycle has a median value about two to three times greater than the values from the other HFC, and median values of vertical hydraulic-conductivity about three orders of magnitude higher than the other HFC. The HFC with the higher porosity and hydraulic conductivity values is shown as a discrete package of relatively low-amplitude reflections, whereas the HFC characterized by lower porosity and hydraulic-conductivity measurements is expressed by higher amplitude reflections. Porosity and hydraulic-conductivity values measured from whole-core samples, and vuggy porosity identified on digital borehole images from shallowing-upward, peritidal HFCs show that the highest porosity occurs at the base of the cycles, moderate porosity at the middle of the cycles, and lowest porosity occurs at the top of cycles. Hydraulic conductivity is also highest at the base of the peritidal cycles and lowest in the middle to upper parts of cycles. This change in porosity and hydraulic conductivity from bottom to top is visible as an upward variation in reflection amplitude on GPR profiles-lowest amplitudes at the base and highest at the cycle tops. This study demonstrates that GPR can be used to show the qualitative distribution of porosity and hydraulic conductivity within a cycle-stratigraphic framework composed of carbonate HFCs. The distribution of porosity and hydraulic conductivity within HFCs is related to depositional textures. The upward and lateral patterns of the rock facies within the HFCs can be translated to geophysical-log properties and radar facies configurations that could aid in interpretation and prediction of ground-water flow through a carbonate aquifer. ?? 2003 Elsevier B.V. All rights reserved.

Cunningham, K. J.

2004-01-01

210

The Newcastle meteor radar  

NASA Technical Reports Server (NTRS)

A brief history and development of the Newcastle Meteor Radar system is given. Also described are its geographical coordinates and its method of operation. The initial objective when the project was commenced was to develop an entirely digital analyzer capable of recognizing meteor echo signals and recording as many of their parameters as possible. This objective was achieved.

Keay, Colin

1987-01-01

211

HiCIRF: A high-fidelity HF channel simulation  

NASA Astrophysics Data System (ADS)

A high-fidelity HF channel simulation has been developed that is suitable for Over-the-Horizon Radar (OTHR) and HF communication system design studies and test planning. The simulation capability is called HiCIRF, for High-frequency Channel Impulse Response Function. HiCIRF provides simulated HF signals corresponding to transmissions from individual transmitter array elements to individual receiver array elements for propagation through the naturally disturbed or undisturbed ionospheric channel. Both one-way link geometries and two-way radar geometries can be simulated. HiCIRF incorporates numerical ray tracing and stochastic signal structure computations to realistically simulate signal scatter by small-scale ionization structure. Stochastic signal generation is employed to generate signal realizations that can be used for OTHR array design and advanced signal processing studies.

Nickisch, L. J.; St. John, Gavin; Fridman, Sergey V.; Hausman, Mark A.; Coleman, C. J.

2012-04-01

212

Multichannel Receiver Design, Instrumentation, and First Results at the National Weather Radar Testbed  

Microsoft Academic Search

When the National Weather Radar Testbed (NWRT) was installed in 2004, a single-channel digital receiver was implemented so that the radar could mimic typical Weather Surveillance Radar (WSR) version 1988 Doppler (WSR-88D) capability. This, however, left unused eight other channels, built into the antenna. This paper describes the hardware instrumentation of a recently completed project that digitizes the radar signals

Mark Yeary; Gerald Crain; Allen Zahrai; Christopher D. Curtis; John Meier; Redmond Kelley; Igor R. Ivic; Robert D. Palmer; Richard J. Doviak; G. Zhang; Tian-You Yu

2012-01-01

213

A theoretical model for the temporal evolution of HF-enhanced plasma lines  

NASA Technical Reports Server (NTRS)

The HF-enhanced plasma lines (HFPLs) observed in the Arecibo heating experiments refer to the radar returns at frequencies near the sum and difference of the radar frequency and the HF-heatear frequency. Those enhanced spectral lines are caused by backscatter of radar signals from parametrically excited plasma waves having a wavenumber of 18 n. A nonlinear theory was developed to describe the temporal evolution of those specified plasma waves and their originating altitude interval of HFPLs observed at Arecibo, Puerto Rico are explained. The theoretical resultsagree well with the observation (Djuth and Sulzer, 1989).

Kuo, S. P.; Ho, A. Y.; Lee, M. C.; Djuth, F. T.

1990-01-01

214

Radar applications overview  

NASA Astrophysics Data System (ADS)

During the fifty years since its initial development as a means of providing early warning of airborne attacks against allied countries during World War II, radar systems have developed to the point of being highly mobile and versatile systems capable of supporting a wide variety of remote sensing applications. Instead of being tied to stationary land-based sites, radar systems have found their way into highly mobile land vehicles as well as into aircraft, missiles, and ships of all sizes. Of all these applications, however, the most exciting revolution has occurred in the airborne platform arena where advanced technology radars can be found in all shapes and sizes...ranging from the large AWACS and Joint STARS long range surveillance and targeting systems to small millimeter wave multi-spectral sensors on smart weapons that can detect and identify their targets through the use of highly sophisticated digital signal processing hardware and software. This paper presents an overview of these radar applications with the emphasis on modern airborne sensors that span the RF spectrum. It will identify and describe the factors that influence the parameters of low frequency and ultra wide band radars designed to penetrate ground and dense foliage environments and locate within them buried mines, enemy armor, and other concealed or camouflaged weapons of war. It will similarly examine the factors that lead to the development of airborne radar systems that support long range extended endurance airborne surveillance platforms designed to detect and precision-located both small high speed airborne threats as well as highly mobile time critical moving and stationary surface vehicles. The mission needs and associated radar design impacts will be contrasted with those of radar systems designed for high maneuverability rapid acquisition tactical strike warfare platforms, and shorter range cued air-to-surface weapons with integral smart radar sensors.

Greenspan, Marshall

1996-06-01

215

Portable temperate ice depth sounder radar (TIDSoR)  

Microsoft Academic Search

Glaciers in several parts of the world are reported to be retreating and thinning rapidly over the last decade. Radar instruments can be used to provide information on the internal and basal conditions of large and small ice masses. Radars operating in the lower part of the HF spectrum are required for sounding temperate glaciers. Also, low-frequency sounders are useful

Victor A. Jara; Kevin M. Player; Deebu Abi; Fernando Rodriguez-Morales; Sivaprasad Gogineni; Ayyangar R. Harish; Carl Leuschen

2008-01-01

216

Tsunami signature in the ionosphere: A simulation of OTH radar observations  

E-print Network

monitoring. OTH radars operate in High Frequency (HF) band and sounding the bottomside ionosphere they couldTsunami signature in the ionosphere: A simulation of OTH radar observations Pierdavide Coïsson,1 technique, nominally the use of overthehorizon (OTH) radars, for tsunami detection through ionospheric

Occhipinti, Giovanni "Ninto"

217

Radar principles  

NASA Technical Reports Server (NTRS)

Discussed here is a kind of radar called atmospheric radar, which has as its target clear air echoes from the earth's atmosphere produced by fluctuations of the atmospheric index of refraction. Topics reviewed include the vertical structure of the atmosphere, the radio refractive index and its fluctuations, the radar equation (a relation between transmitted and received power), radar equations for distributed targets and spectral echoes, near field correction, pulsed waveforms, the Doppler principle, and velocity field measurements.

Sato, Toru

1989-01-01

218

Synthetic aperture radar interferometry of Okmok volcano, Alaska: Radar observations  

Microsoft Academic Search

ERS-1\\/ERS-2 synthetic aperture radar interferometry was used to study the 1997 eruption of Okmok volcano in Alaska. First, we derived an accurate digital elevation model (DEM) using a tandem ERS-1\\/ERS-2 image pair and the preexisting DEM. Second, by studying changes in interferometric coherence we found that the newly erupted lava lost radar coherence for 5-17 months after the eruption. This

Zhong Lu; Dörte Mann; Jeffrey T. Freymueller; David J. Meyer

2000-01-01

219

Digital monopulse  

NASA Astrophysics Data System (ADS)

A digitally formed monopulse radar employing dynamic real-time calibration during operation is described. The invention has a transmitter section, timing circuit, RF section, IF section, in-phase and quadrature section and a digital signal processor. A portion of the transmit signal is diverted from the transmitter section for preparation of calibration factors during the calibration period between receive signals. The calibration factors prepared by the digital signal processor are applied by the processor to antenna received signals during the receive mode and to produce the corrected sum and delta pitch, and delta yaw signals and the tracking errors Ey.

Ghaleb, Sam; Stokes, Michael

1994-05-01

220

Radar image registration and rectification  

NASA Technical Reports Server (NTRS)

Two techniques for radar image registration and rectification are presented. In the registration method, a general 2-D polynomial transform is defined to accomplish the geometric mapping from one image into the other. The degree and coefficients of the polynomial are obtained using an a priori found tiepoint data set. In the second part of the paper, a rectification procedure is developed that models the distortion present in the radar image in terms of the radar sensor's platform parameters and the topographic variations of the imaged scene. This model, the ephemeris data and the digital topographic data are then used in rectifying the radar image. The two techniques are then used in registering and rectifying two examples of radar imagery. Each method is discussed as to its benefits, shortcomings and registration accuracy.

Naraghi, M.; Stromberg, W. D.

1983-01-01

221

A radar image time series  

NASA Technical Reports Server (NTRS)

A set of ten side-looking radar images of a mining area in Arizona that were aquired over a period of 14 yr are studied to demonstrate the photogrammetric differential-rectification technique applied to radar images and to examine changes that occurred in the area over time. Five of the images are rectified by using ground control points and a digital height model taken from a map. Residual coordinate errors in ground control are reduced from several hundred meters in all cases to + or - 19 to 70 m. The contents of the radar images are compared with a Landsat image and with aerial photographs. Effects of radar system parameters on radar images are briefly reviewed.

Leberl, F.; Fuchs, H.; Ford, J. P.

1981-01-01

222

Data volume reduction for imaging radar polarimetry  

NASA Technical Reports Server (NTRS)

Two alternative methods are disclosed for digital reduction of synthetic aperture multipolarized radar data using scattering matrices, or using Stokes matrices, of four consecutive along-track pixels to produce averaged data for generating a synthetic polarization image.

Zebker, Howard A. (Inventor); Held, Daniel N. (Inventor); van Zul, Jakob J. (Inventor); Dubois, Pascale C. (Inventor); Norikane, Lynne (Inventor)

1989-01-01

223

Measured ionospheric Doppler spreading of HF ground backscatter  

NASA Astrophysics Data System (ADS)

Doppler spectra from ionospherically propagated ground backscatter are presented. These spectra show how the ionosphere distorts HF backscatter radio waves by frequency speading. The ground backscatter spectra presented here show that ionospheric Dopper spreading is so ubiquitous that its effect should never be disregarded, even when a narrow azimuth beam radar such as ours is used. Nevertheless, Doppler spreading varies so quickly that it usually pays to wait for it to diminish.

Jones, R. M.; Riley, J. P.; Georges, T. M.

1983-03-01

224

HF Antenna Optimization Study.  

National Technical Information Service (NTIS)

The report presents a summation of a study to determine the optimum log periodic dipole array design for a high gain, low coverage HF antenna over real and/or ground screen covered earth. The major problem encountered is one of determining antenna electri...

C. T. Elfving, D. L. Johnstone, U. R. Embry, V. R. Arens

1969-01-01

225

Electro optical radar transmission chain modeling and simulation  

Microsoft Academic Search

In traditional radar systems, the use of electronic analog devices, such as mixers and oscillators, introduces some noise sources which complicate the realization of a completely digital radar systems. In fact, non linear behaviors of such systems as well as low Spurious Free Dynamic Range (SFDR) and low phase coherence, compromise radar performance in terms of detection and coherent signal

Francesco Laghezza; Amerigo Capria; Andrea Cacciamano; Fabrizio Berizzi; Paolo Ghelfi; Antonella Bogoni

2011-01-01

226

Limits on the detection of low-Doppler targets by a High Frequency hybrid sky-surface wave radar system  

Microsoft Academic Search

A high frequency (HF) radar system comprising a skywave transmit channel and surface wave receive channel is studied. Simple analytic expressions for the resolution of this radar system are determined by considering the spreading of radar signals in Doppler and angle during the ionospheric propagation. The detection of ocean surface targets within the patch of ocean surface illuminated by the

Ryan J. Riddolls

2008-01-01

227

Longitudinal and seasonal variations in the occurrence of sunrise undulation at the dip equator: A study using Trivandrum and Jicamarca Digital Ionosonde and Jicamarca Incoherent Scatter radar measurements  

NASA Astrophysics Data System (ADS)

At night, the absence of photo ionization in combination with sustained downward plasma motion means that the F region can be severely depleted at the magnetic equator at the end of the night. As a result, there can be, at sunrise, a sudden upward jump in altitude of the F region peak which is then followed by a quick descent in association with the downward motion of the photo ionization production peak. This constitutes what has been described as the equatorial sunrise undulation. Its anecdotal existence has been reported over Jicamarca (120 S, 76.90 W, 1.70 S dip-latitude) while it has been seen repeatedly over Trivandrum (8.470 N, 76.920 E, 0.170 S dip latitude), India, particularly during equinox conditions. Seasonal variations in the occurrence of sunrise undulation in the F-region peak height (hmF2) at two longitudinally separated geomagnetic equatorial stations, namely Jicamarca and Trivandrum are being presented. Measurements from Digital ionosondes, located at these two stations, have been used in this study. A fast descends in hmF2 after the local F region sunrise was quite visible at both the stations. The frequency of occurrence of sunrise undulation at Trivandrum, however, was high compared to the same at Jicamarca. There were noticeable differences in the seasonal occurrence of sunrise undulation at the two places. While it was observed throughout the year at Trivandrum, there was a distinct seasonal preference of occurrence at Jicamarca, at least in the year 2010, a low solar active period. Its frequency of occurrence at Jicamarca was high during winter (June) solstice, low during equinox (March) and had almost negligible occurrence during summer solstice (December). We show that (1) plasma density during sunrise at Jicamarca on average was twice as much as at Trivandrum, and (2) average height of hmF2 during night at Jicamarca was higher (~100km ) during equinox and solstice months compared to the same at Trivandrum. Our results suggest that the background density plays an important role in the observation of a sunrise undulation in the F region peak which itself is quite sensitive to the electric field seen by the plasma between sunset and sunrise. Using incoherent backscatter radar data from Jicamarca we show that the sunrise undulation can be masked when remnant plasma from the previous night does not come down to low enough altitude. We argue that this is the reason behind the lack of sunrise undulations in December at Jicamarca, given the fact that there is often very strong plasma uplift in the evening at that time of year. Thus the seasonal and longitudinal variation of sunrise ionosphere is a proxy to understand the electro-dynamical features of the night before.

Ambili, K. M.; St-Maurice, Jean-Pierre; Choudhary, Raj Kumar

228

Estimation algorithm of Doppler shift and time delay in HF channel sounding  

Microsoft Academic Search

Doppler shift and propagation time delay are important parameters that require measuring in HF channel sounding. For the purpose of exact measurement of Doppler shift and time delay of HF channel, a parameter estimation algorithm is proposed on the basis of digital pulse compression technique, which achieves precise estimation of Doppler shift and channel time delay by means of performing

Liu Yueliang; Jiang Yuzhong; Jiang Wei; Feng Yanqing

2011-01-01

229

Laser radar  

Microsoft Academic Search

The general theory of laser tracking and ranging and the principles governing the design of laser radar systems are examined. Major problems related to optimum reception of laser radar signals and parameter measurement are analyzed from the standpoint of the theory of statistical solutions. Attention is given to methods for processing trajectory measurements and various methods for obtaining noncoordinate information,

I. N. Matveev; V. V. Protopopov; I. N. Troitskii; N. D. Ustinov

1984-01-01

230

Joint utilization of incoherently and coherently integrated radar signal in helicopter categorization  

Microsoft Academic Search

Radar signal based helicopter categorization is a challenging task for all types of radars. Airborne pulse Doppler radar with an appropriate digital signal processing unit has a good potential to perform categorization or even classification, providing that radar parameters are carefully selected. This paper presents a helicopter categorization method, which is based on estimation of the main rotor blade tip

Jani M. Tikkinen; Elina E. Helander; A. Visa

2005-01-01

231

The Patriot radar in tactical air defense  

NASA Astrophysics Data System (ADS)

The Patriot radar is a C-band, phased-array, multifunction radar that, under the control of the weapon control computer in the engagement control station, performs target search and track; missile search, track, and communications during midcourse guidance; and target-via-missile terminal guidance. This paper describes the functions the radar performs and provides descriptions of the subsystems. The use of a multichannel, multifunction receiver and digital signal processor is emphasized to demonstrate the control and processing for multiple radar actions required to support the tactical air defense mission. A summary of results of an extensive test program at the White Sands Missile Range is presented.

Carey, David R.; Evans, William

1988-05-01

232

Digital communications study  

NASA Technical Reports Server (NTRS)

Research is reported dealing with problems of digital data transmission and computer communications networks. The results of four individual studies are presented which include: (1) signal processing with finite state machines, (2) signal parameter estimation from discrete-time observations, (3) digital filtering for radar signal processing applications, and (4) multiple server queues where all servers are not identical.

Boorstyn, R. R.

1973-01-01

233

Use of the Hualien, Taiwan, dynasonde for surveillance of HF environmental radio and positioning of transmitting stations  

NASA Astrophysics Data System (ADS)

Since 2010, a 2nd generation NOAA HF radars, also referred as dynasonde, has been built at Hualien (23.89 N, 121.55 E), Taiwan. The Hualien dynasonde has a new design of ionospheric radar of fully digitizing the complex signal records and using multiple parallel receiver channels for simultaneous measurements of signals from multiple spaced receiving antennas. The Hualien dynasonde utilizes interferometric sounding pulse patterns and a receiving antenna array (including eight receivers connected to different spaced dipole antennas) to receive not only ionospherical echoes but also environmental radio signals. We have applied the Hermite normal form method to solve the phase-measurement aliasing and least squares problem and improve measurements of radio angles of arrival (AOA). The further ray-tracing experiments can be used for the study of radio wave propagation in the ionosphere. In this study we present a numerical and step by step ray-tracing method on a phenomenological ionospheric electron density model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3 / Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data and global ionosonde foF2 data. The three-dimensional TWIM consists of vertically-fitted ?-Chapman-type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. The methodology is successfully applied to a practical HF transmitter for oblique incidence ray tracing. Then, the AOA data will be used for backward ray tracing in the TWIM model and be used to determine ground-based transmitting station position.

Tsai, L.-C.; Chen, G. H.; Tian, M. H.; Zhang, Y.

2012-04-01

234

Integrated photonic analog-to-digital converters  

E-print Network

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical ...

Khilo, Anatol (Anatol M.)

2011-01-01

235

Measurement of ocean wave spectra using narrow-beam HE radar  

Microsoft Academic Search

A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix

Randy Howell; John Walsh

1993-01-01

236

Optimal Pollution Mitigation in Monterey Bay Based on Coastal Radar Data and Nonlinear  

E-print Network

Optimal Pollution Mitigation in Monterey Bay Based on Coastal Radar Data and Nonlinear Dynamics run-off which is a typical source of pollution in the bay. We show that a HF radar-based pollution release scheme using this flow structure reduces the impact of pollution on the coastal envi- ronment

Marsden, Jerrold

237

HAL-3 radar test set  

NASA Astrophysics Data System (ADS)

This paper presents the HAL-3 radar test set (called the set in the following) used to measure the technical specifications of the HAL-3 airborne radar and to maintain it based on tested results. Some new techniques are employed in the set, including sinusoidal pulsewidth modulation (SPWM) in the power supply, digital gyro simulator and automatic test module (ATM) with STD industrial control microprocessor series. The specially designed software implements man-machine interaction with menu in Chinese, selects parameters and operation mode, and controls testing procedures. These techniques may be extensively applied to other automatic test instruments.

Fang, Zhenhe; Zhang, Ming-Xing; Shen, Chang-Hong; Wang, Yi

1994-07-01

238

Requirements for space shuttle scatter radar experiments  

NASA Technical Reports Server (NTRS)

The feasibility of carrying out scatter radar experiments on the space shuttle was analyzed. Design criteria considered were the required average transmitter power, frequency resolution, spatial resolution, and statistical accuracy. Experiments analyzed were measurement of the naturally enhanced plasma line and the ion component of the incoherent scatter spectrum, and the plasma line artificially enhanced by an intense HF radio wave. The ion component measurement does not appear feasible, while the other two appear reasonable for short ranges only.

Harker, K. J.

1975-01-01

239

Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory  

NASA Astrophysics Data System (ADS)

High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

Sheerin, J. P.; Adham, N.; Roe, R. G. E.; Keith, M. R.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.; Selcher, C. A.

2010-11-01

240

Low power High Frequency Surface Wave Radar application for ship detection and tracking  

Microsoft Academic Search

High-frequency (HF) radars are operated in the 3-30 MHz frequency band and are known to cover ranges up to some thousand kilometers. Sky wave over-the-horizon radars (OTHR) utilize reflection by the ionosphere, but they require a transmit power up to 100 kilowatts. Especially for oceanographic applications, low power high frequency surface wave radar (HFSWR) systems have been developed, which use

Anna Dzvonkovskaya; Klaus-Werner Gurgel; Hermann Rohling; Thomas Schlick

2008-01-01

241

PACE and EISCAT radar observations of short-lived flow bursts on the nightside  

NASA Technical Reports Server (NTRS)

Concurrent observations from two widely spaced radar experiments of quasi periodic flow bursts in the nightside are presented. The flow bursts closely resemble single radar observations reported by Williams et al. By using the Polar Anglo-American Conjugate Experiment (PACE) HF radar array at Halley Bay in conjunction with the EISCAT Common Program (CP) 2-D experiment, the flow bursts are shown to be a global phenomenon and important information as to their development and propagation can be determined.

Freeman, M. P.; Morelli, J. P.; Cowley, S. W. H.; Pinnock, M.; Williams, P. J. S.; Farrugia, C. J.

1991-01-01

242

Plasma structure within poleward-moving cusp/cleft auroral transients: EISCAT Svalbard radar observations and an explanation  

E-print Network

, Longyearbyen, Norway 5 CETP, 4, avenue Neptune, F-94107 Saint-Maur, CEDEX France 6 Science Institute, Dunhaga 3 system) HF radars. An overview of the large-scale auroral and convection morphology seen on this day has

Paris-Sud XI, Université de

243

Improved range resolution for FMCW HF surface wave radar  

Microsoft Academic Search

A modified signal processing for FMCW waveform has been proposed that yields an improved range resolution without increasing the transmitted signal bandwidth. The chirp duration is reduced by an appropriate factor while the interval of the beat signal sequence considered for the range transform is kept constant. This modification implies a range transform over several chirp sweeps and an interleaving

T. Fickenscher; R. Herschel; M. Holters; A. Gupta; J. Hinz

2010-01-01

244

Doppler characteristics of HF backscatter - The Jindalee 'mini-radar'  

NASA Astrophysics Data System (ADS)

The use of the Jindalee miniradar, incorporated in the frequency management system, to deduce sea-state parameters, is reported. Estimation of the dominant wave direction, and hence surface wind direction, can be achieved by measuring the relative intensities of the two Bragg lines. The fundamental problem is to ascertain for which Doppler spectra the second-order spectrum represents a clean spectrum free from ionospheric contamination.

Ward, B. D.

245

Satellite remote sensing of landscape freeze/thaw state dynamics for complex Topography and Fire Disturbance Areas Using multi-sensor radar and SRTM digital elevation models  

NASA Technical Reports Server (NTRS)

We characterize differences in radar-derived freeze/thaw state, examining transitions over complex terrain and landscape disturbance regimes. In areas of complex terrain, we explore freezekhaw dynamics related to elevation, slope aspect and varying landcover. In the burned regions, we explore the timing of seasonal freeze/thaw transition as related to the recovering landscape, relative to that of a nearby control site. We apply in situ biophysical measurements, including flux tower measurements to validate and interpret the remotely sensed parameters. A multi-scale analysis is performed relating high-resolution SAR backscatter and moderate resolution scatterometer measurements to assess trade-offs in spatial and temporal resolution in the remotely sensed fields.

Podest, Erika; McDonald, Kyle; Kimball, John; Randerson, James

2003-01-01

246

Analysis of synthetic aperture radar imagery  

NASA Technical Reports Server (NTRS)

Some problems faced in applications of radar measurements in hydrology are: (1) adequate calibration of the radar systems and direct digital data will be required in order that repeatable data can be acquired for hydrologic applications; (2) quantitative hydrologic research on a large scale will be prohibitive with aircraft mounted synthetic aperture radar systems due to the system geometry; (3) spacecraft platforms appear to be the best platforms for radar systems when conducting research over watersheds larger than a few square kilometers; (4) experimental radar systems should be designed to avoid use of radomes; and (5) cross polarized X and L band data seem to discriminate between good and poor hydrologic cover better than like polarized data.

Blanchard, B. J.

1977-01-01

247

Highly Integrated Radar Sensor-on-Chip  

NASA Astrophysics Data System (ADS)

A highly integrated 24 GHz radar sensor is presented, based on a Radio Frequency Integrated Circuit (RFIC) which was specifically developed for a Frequency Modulated Shift Keying (FMSK) based Radar system design. Antenna, waveform, the Radio Frequency (RF) and Digital Signal Processor (DSP) module, the software design, cost and performance aspects will be described. The significant technical and economical advantages of the implemented Silicon-Germanium (SiGe) Bipolar CMOS (BiCMOS) transceiver are demonstrated. Some automotive and other applications based on this technology and new radar system design will be explained.

Mende, Ralph

2012-05-01

248

Recognition of the major scattering sources on complex targets based on the high frequency radar cross section integrated calculation technique  

Microsoft Academic Search

Based on the high frequency (HF) integrated radar cross section (RCS) calculation approach, a technique of detecting major\\u000a scattering source is developed by using an appropriate arithmetic for scattering distribution and scattering source detection.\\u000a For the perfect adaptability to targets and the HF of the HF integrated RCS calculation platform, this technique is suitable\\u000a to solve large complex targets and

Min-jie Huang; Ming-yun Lü; Jun Huang; Zhe Wu

2009-01-01

249

Modulation recognition for HF signals  

NASA Astrophysics Data System (ADS)

High-frequency (HF) communications is undergoing resurgence despite advances in long-range satellite communication systems. Defense agencies are using the HF spectrum for backup communications as well as for spectrum surveillance applications. Spectrum management organizations are monitoring the HF spectrum to control and enforce licensing. These activities usually require systems capable of determining the location of a source of transmissions, separating valid signals from interference and noise, and recognizing signal modulation. Our ultimate aim is to develop robust modulation recognition algorithms for real HF signals, that is, signals propagating by multiple ionospheric modes. One aspect of modulation recognition is the extraction of signal identifying features. The most common features for modulation recognition are instantaneous phase, amplitude, and frequency. However, this paper focuses on two feature parameters: coherence and entropy. Signal entropy and the coherence function show potential for robust recognition of HF modulation types in the presence of HF noise and multi-path. Specifically, it is shown that the methods of calculation of coherence and entropy are important and that appropriate calculations ensure stability in the parameters. For the first time a new metric, called Coherence-Median Difference (CMD), is introduced that provides a measure of the dominance of coherence at specific frequencies to coherence at all other frequencies in a particular bandwidth.

Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

2005-02-01

250

Design and implementation of a smart radar absorber  

Microsoft Academic Search

In this paper we have introduced a new topology for a digitally-controlled smart radar absorbing structure based on the phase-switched screen and presented initial experimental data which support the theoretical concept.

B. Chambers; A. Tennant

2003-01-01

251

Adap'itve Antenna Architectures For AEW Radar  

Microsoft Academic Search

Recent technology improvements have made it feasible to consider digital spaceltime adaptive antenna beamforming, with associated sophisticated adaptive weight generation algorithms, for Airborne Early Warning (AEW) radar and other applications. These technologies are of particullar interest with AEW radar because of its potential vulnerability to large ground clutter returns combined with casual and intentional interference (i.e., electromagnetic interference (EMI), jamming).

James K. Day

1992-01-01

252

A Monostatic Ocean Scattering Cross Section for the Case of Surface Wave Radar Operating from a Floating Barge  

Microsoft Academic Search

An understanding of the parameters affecting the high frequency surface wave radar (HFSWR) cross sections of the ocean surface is essential to employing such formulations in remote sensing models. Available techniques to date have not explicitly included the effect of antenna motion on the ocean clutter spectra derived from HF Doppler radar data. Here, a model, which assumes the incident

John Walsh; Eric Gill; Weimin Huang

2008-01-01

253

Weather Radar Fundamentals  

NSDL National Science Digital Library

This 2-hour module presents the fundamental principles of Doppler weather radar operation and how to interpret common weather phenomena using radar imagery. This is accomplished via conceptual animations and many interactive radar examples in which the user can practice interpreting both radar reflectivity and radar velocity imagery. Although intended as an accelerated introduction to understanding and using basic Doppler weather radar products, the module can also serve as an excellent refresher for more experienced users.

Comet

2012-03-21

254

Interim report of the Lunar Radar Sounder on-board SELENE spacecraft  

NASA Astrophysics Data System (ADS)

The Lunar Radar Sounder (LRS) on-board the SELENE will provide subsurface stratification and tectonic features in the shallow part (several km depth) of the lunar crust, by using an FM/CW radar technique in HF (˜ 5MHz) frequency range. Knowledge of the subsurface structure is crucial to better understanding not only of the geologic history of the moon, but also of the regional and global thermal history of the Moon, and also of the origin of the Earth-Moon system. In addition to the subsurface radar experiment, LRS will provide the spectrum of plasma waves, and solar and planetary radio waves in wide frequency range covering from 10 Hz to 30 MHz. The SELENE spacecraft will be launched in 2006. The fundamental technique of the instrumentation of LRS is based on the plasma waves and sounder experiments which have been established through the observations of the earth's magnetosphere, plasmasphere and ionosphere on-board EXOS-B (Jikiken), EXOS-C (Ohzora) and EXOS-D (Akebono) satellites, and it has been extended to observations of the Martian ionosphere as well as surface land shape on-board the Planet-B (Nozomi) spacecraft. By using digital signal processing techniques for the generation of the sounder RF waveform and on-board data analyses, it becomes possible to improve the S/N ratio and resolution for the subsurface sounding of the Moon. The instrumental and theoretical studies for developing the LRS system for subsurface sounding of the Moon showed that the observations on-board the SELENE spacecraft will provide detailed information about the subsurface structures within a depth of 5 km from the lunar surface, with a range resolution of less than 75 m for a region with a horizontal scale of several tens of km. The present state of the SELENE project is under the 1st stage of the system integration test of the spacecraft. This paper provides results from theoretical approach and an intermittent report of development of the LRS system on-board the SELENE spacecraft. References T. Ono and H. Oya, Lunar Radar Sounder (LRS) experiment on-board the SELENE spacecraft, Earth Planets Space, 52, 629-637, 2000. T. Kobayashi, H. Oya, and T. Ono, A-scope analysis of subsurface radar sounding of lunar mare region, Earth Planets Space, 54, 973-982, 2002. T. Kobayashi1, H. Oya, and T. Ono, B-scan analysis of subsurface radar sounding of lunar highland region, Earth Planets Space, 54, 983-991, 2002.

Ono, T.; Kobayashi, T.; Oya, H.

255

Metrology, attitude, and orbit determination for spaceborne interferometric synthetic aperture radar  

Microsoft Academic Search

The Shuttle Radar Topography Mission (SRTM), scheduled for an 11 day Space Shuttle flight in 1999, will use an Interferometric Synthetic Aperture Radar instrument to produce a near-global digital elevation map of the earth's land surface with 16 m absolute vertical height accuracy at 30 meter postings. SRTM will achieve the required interferometric baseline by extending a receive-only radar antenna

Riley M. Duren; Ed Wong; Bill Breckenridge; Scott Shaffer; Courtney Duncan; Eldred F. Tubbs; Phil M. Salomon

1998-01-01

256

ISRO's programmable digital waveform generator  

Microsoft Academic Search

One of the major and common requirements for all active microware sensors is generation of the transmit modulation signal-like chirp\\/LFM signal, MSK, etc., which can be generated by analog or digital means. With the increasing demands of side bandwidth, longer duration chirp signals in radar systems, digital signal generation, and processing has emerged as a preferred alternative. Design and development

S. Gangele; N. M. Desai; R. Senthil Kumar; J. G. Vachhani; V. R. Gujraty

2008-01-01

257

An N-Bit Digitally Variable Ultra Wideband Pulse Generator for GPR and UWB Applications  

E-print Network

has found military applications such as ground penetrating radar (GPR), wall penetrating radar, secure. Particularly, in UWB ground penetrating radar, a digitally tunable pulse generator allows the pulse width on the resolution of the radar. If the impulse radio is used as GPR to provide high penetration depth, higher pulse

Yanikoglu, Berrin

258

Spectral characteristics of High Frequency (HF) backscatter for high latitude ionospheric irregularities: Preliminary analysis of statistical properties  

Microsoft Academic Search

OTH-B radar signals backscattered from ionospheric irregularities can be very intense, and any effort to mitigate against their influence requires knowledge of at least the Doppler shift and spread that they introduce in the backscattered signals. This report presents the Doppler spectral characteristics of HF signals backscattered from F-region ionospheric irregularities at high latitudes. The report will show that the

K. B. Baker; R. A. Greenwald; J. P. Villian; S. Wing

1988-01-01

259

HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects  

NASA Astrophysics Data System (ADS)

In addition to being scattered by the ionospheric field-aligned irregularities, HF radar signals can be reflected by the ionosphere toward the Earth and then scattered back to the radar by the rugged ground surface. These ground scatter (GS) echoes are responsible for a substantial part of the returns observed by HF radars making up the Super Dual Auroral Radar Network (SuperDARN). While a GS component is conventionally used in studying ionosphere dynamics (e.g., traveling ionospheric disturbances, ULF waves), its potential in monitoring the state of the scattering surface remains largely unexploited. To fill this gap, we investigated diurnal and seasonal variation of the ground echo occurrence and location from a poleward-looking SuperDARN radar at Rankin Inlet, Canada. Using colocated ionosonde information, we have shown that seasonal and diurnal changes in the high-latitude ionosphere periodically modulate the overall echo occurrence rate and spatial coverage. In addition, characteristics of GS from a particular geographic location are strongly affected by the state of the underlying ground surface. We have shown that (1) ice sheets rarely produce detectable backscatter, (2) mountain ranges are the major source of GS as they can produce echoes at all seasons of the year, and (3) sea surface becomes a significant source of GS once the Arctic sea ice has melted away. Finally, we discuss how the obtained results can expand SuperDARN abilities in monitoring both the ionosphere and ground surface.

Ponomarenko, P. V.; St. Maurice, J.-P.; Hussey, G. C.; Koustov, A. V.

2010-10-01

260

Estimation of planetary surface roughness by HF sounder observation  

NASA Astrophysics Data System (ADS)

Japanese Martian exploration project "Nozomi" was to carry out several science missions. Plasma Wave Sounder, one of those onboard missions, was an HF sounder to study Martian plasma environment, and Martian surface with the altimetry mode (Oya and Ono, 1998) as well. The altimetry mode observation was studied by means of computer simulations utilizing the KiSS code which had been originally designed to simulate the SELENE Lunar Radar Sounder, a spaceborne HF GPR, based on Kirchhoff approximation theory (Kobayashi, Oya and Ono, 2002). We found an empirical power law for the standard deviation of observed altitudes over Gaussian random rough surfaces: it varies in proportion to the square of the RMS gradient of the surface ?{2} hRMS{?_0, where hRMS and ?_0 are the RMS height of the surface and the correlation distance of the surface, respectively. We applied Geometrical optics to understand this empirical power law, and derived a square power law for the standard deviation of the observed altitude. Our Geometrical optics model assumed the followings: 1) the observed surface is a Gaussian random rough surface, 2) the mean surface is a flat horizontal plane, 3) the observed surface echo is the back scattering echoes, 4) the observed altitude is the mean value of the apparent range of those back scattering echoes. These results imply that HF sounder may be utilized to measure the surface roughness of planetary bodies in terms of the RMS gradient of the surface. Refrence: H. Oya and T. Ono, A new altimeter for Mars land shape observations utilizing the ionospheric sounder system onboard the Planet-B spacecraft, Earth Planets Space, Vol. 50, pp.229-234, 1998 T. Kobayashi, H. Oya, and T. Ono, A-scope analysis of subsurface radar sounding of lunar mare region, Earth Planets Space, Vol. 54, pp.973-982, 2002

Kobayashi, T.; Ono, T.

261

Soviet oceanographic synthetic aperture radar (SAR) research  

SciTech Connect

Radar non-acoustic anti-submarine warfare (NAASW) became the subject of considerable scientific investigation and controversy in the West subsequent to the discovery by the Seasat satellite in 1978 that manifestations of underwater topography, thought to be hidden from the radar, were visible in synthetic aperture radar (SAR) images of the ocean. In addition, the Seasat radar produced images of ship wakes where the observed angle between the wake arms was much smaller than expected from classical Kelvin wake theory. These observations cast doubt on the radar oceanography community's ability to adequately explain these phenomena, and by extension on the ability of existing hydrodynamic and radar scattering models to accurately predict the observability of submarine-induced signatures. If one is of the opinion that radar NAASW is indeed a potentially significant tool in detecting submerged operational submarines, then the Soviet capability, as evidenced throughout this report, will be somewhat daunting. It will be shown that the Soviets have extremely fine capabilities in both theoretical and experimental hydrodynamics, that Soviet researchers have been conducting at-sea radar remote sensing experiments on a scale comparable to those of the United States for several years longer than we have, and that they have both an airborne and spaceborne SAR capability. The only discipline that the Soviet Union appears to be lacking is in the area of digital radar signal processing. If one is of the opinion that radar NAASW can have at most a minimal impact on the detection of submerged submarines, then the Soviet effort is of little consequence and poses not threat. 280 refs., 31 figs., 12 tabs.

Held, D.N.; Gasparovic, R.F.; Mansfield, A.W.; Melville, W.K.; Mollo-Christensen, E.L.; Zebker, H.A.

1991-01-01

262

Role of oxygen vacancies in HfO2-based gate stack breakdown  

NASA Astrophysics Data System (ADS)

We study the influence of multiple oxygen vacancy traps in the percolated dielectric on the postbreakdown random telegraph noise (RTN) digital fluctuations in HfO2-based metal-oxide-semiconductor transistors. Our electrical characterization results indicate that these digital fluctuations are triggered only beyond a certain gate stress voltage. First-principles calculations suggest the oxygen vacancies to be responsible for the formation of a subband in the forbidden band gap region, which affects the triggering voltage (VTRIG) for the RTN fluctuations and leads to a shrinkage of the HfO2 band gap.

Wu, X.; Migas, D. B.; Li, X.; Bosman, M.; Raghavan, N.; Borisenko, V. E.; Pey, K. L.

2010-04-01

263

Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana  

NASA Astrophysics Data System (ADS)

Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high-resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango Rift Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben. Faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the rift exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault systems through a process of "fault piracy" have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along-axis linkage of segments), the rift is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). Finally, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3-D view of the faults and fault systems, providing new insight into fault growth and propagation during the nascent stages of continental rifting.

Kinabo, B. D.; Hogan, J. P.; Atekwana, E. A.; Abdelsalam, M. G.; Modisi, M. P.

2008-06-01

264

The SIR-C/X-SAR synthetic aperture radar system  

NASA Technical Reports Server (NTRS)

SIR-C/X-SAR, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-SAR system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry; and testing.

Jordan, Rolando L.; Huneycutt, Bryan L.; Werner, Marian

1991-01-01

265

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN)  

NASA Astrophysics Data System (ADS)

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN) S. Sathishkumar1, R. Dhanya1, K. Emperumal1, D. Tiwari2, S. Gurubaran1 and A. Bhattacharyya2 1. Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India 2. Indian Institute of Geomagnetism, Navi Mumbai, India Email: sathishmaths@gmail.com Abstract The equatorial atmosphere-ionosphere system has been studied theoretically and observationally in the past. In the equatorial atmosphere, oscillations with periods of 3-4 days are often observed in the medium frequency (MF) radar over Tirunelveli (8.7oN, 77.8oE, 1.34oN geomag. lat.). Earlier observations show the clear evidence that these waves can propagate from the stratosphere to ionosphere. A digital ionosonde has been providing useful information on several ionospheric parameters from the same site. Simultaneous observations of mesospheric winds using medium frequency radar and F-layer height (h'F) from ionosonde reveal that the 3-4 day wave was evident in both the component during the 01 June 2007 and 31 July 2007. The 3-4 day wave could have an important role in the day to day variability of the equatorial ionosphere evening uplift. Results from an extensive analysis that is being carried out in the direction of 3-4 day wave present in the ionosphere will be presented.

Sundararaman, Sathishkumar

266

Radar electronic warfare  

Microsoft Academic Search

An overview of radar and electronic warfare is given. Definitions, common terms, and principles of radar and electronic warfare, and simple analyses of interactions between radar systems and electronic countermeasures (ECM) are presented. Electronic counter-countermeasure and electronic support measures are discussed. Background material in mathematics, electromagnetics, and probability necessary for an understanding of radar and electronic warfare is given and

August Golden Jr.

1987-01-01

267

Radar cross section  

Microsoft Academic Search

The technological evolution in signal processing that has been made in last decades led to improvements in radar performances. Increasing the radar range by improving its sensitivity has been made by the designers of aircraft and other military systems to try to decrease the radar cross section of these types of equipment. The radar cross section is a matter of

L. Nicolaescu; Teofil Oroian

2001-01-01

268

Wind shear radar simulation  

NASA Technical Reports Server (NTRS)

Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.

Britt, Charles L.

1988-01-01

269

Shuttle imaging radar-C science plan  

NASA Technical Reports Server (NTRS)

The Shuttle Imaging Radar-C (SIR-C) mission will yield new and advanced scientific studies of the Earth. SIR-C will be the first instrument to simultaneously acquire images at L-band and C-band with HH, VV, HV, or VH polarizations, as well as images of the phase difference between HH and VV polarizations. These data will be digitally encoded and recorded using onboard high-density digital tape recorders and will later be digitally processed into images using the JPL Advanced Digital SAR Processor. SIR-C geologic studies include cold-region geomorphology, fluvial geomorphology, rock weathering and erosional processes, tectonics and geologic boundaries, geobotany, and radar stereogrammetry. Hydrology investigations cover arid, humid, wetland, snow-covered, and high-latitude regions. Additionally, SIR-C will provide the data to identify and map vegetation types, interpret landscape patterns and processes, assess the biophysical properties of plant canopies, and determine the degree of radar penetration of plant canopies. In oceanography, SIR-C will provide the information necessary to: forecast ocean directional wave spectra; better understand internal wave-current interactions; study the relationship of ocean-bottom features to surface expressions and the correlation of wind signatures to radar backscatter; and detect current-system boundaries, oceanic fronts, and mesoscale eddies. And, as the first spaceborne SAR with multi-frequency, multipolarization imaging capabilities, whole new areas of glaciology will be opened for study when SIR-C is flown in a polar orbit.

1986-01-01

270

Method for orthorectification of terrestrial radar maps  

NASA Astrophysics Data System (ADS)

The vehicle-based PELICAN radar system is used in the context of mobile mapping. The R-SLAM algorithm allows simultaneous retrieval of the vehicle trajectory and of the map of the environment. As the purpose of PELICAN is to provide a means for gathering spatial information, the impact of distortion caused by the topography is not negligible. This article proposes an orthorectification process to correct panoramic radar images and the consequent R-SLAM trajectory and radar map. The a priori knowledge of the area topography is provided by a digital elevation model. By applying the method to the data obtained from a path with large variations in altitude it is shown that the corrected panoramic radar images are contracted by the orthorectification process. The efficiency of the orthorectification process is assessed firstly by comparing R-SLAM trajectories to a GPS trajectory and secondly by comparing the position of Ground Control Points on the radar map with their GPS position. The RMS positioning error moves from 5.56 m for the raw radar map to 0.75 m for the orthorectified radar map.

Jaud, Marion; Rouveure, Raphaël; Faure, Patrice; Moiroux-Arvis, Laure; Monod, Marie-Odile

2014-11-01

271

Range rate–Doppler correlation for HF propagation in traveling ionospheric disturbance environments  

Microsoft Academic Search

Using ionospheric sounding together with fast computational inverse processing, it is now possible to obtain good real-time ionospheric models for use in geolocation for over-the-horizon (OTH) radar. However, deflection of HF propagation paths by traveling ionospheric disturbances (TIDs) remains a troubling cause of coordinate registration errors. Bandwidth and coverage limitations in ionospheric soundings preclude the ability to model TID structure

L. J. Nickisch; Mark A. Hausman; Sergey V. Fridman

2006-01-01

272

Range rate-Doppler correlation for HF propagation in traveling ionospheric disturbance environments  

Microsoft Academic Search

Using ionospheric sounding together with fast computational inverse processing, it is now possible to obtain good real-time ionospheric models for use in geolocation for over-the-horizon (OTH) radar. However, deflection of HF propagation paths by traveling ionospheric disturbances (TIDs) remains a troubling cause of coordinate registration errors. Bandwidth and coverage limitations in ionospheric soundings preclude the ability to model TID structure

L. J. Nickisch; Mark A. Hausman; Sergey V. Fridman

2006-01-01

273

Predictions of HF system performance for propagation through disturbed ionospheres measured using low-Earth-orbit satellite radio beacon tomography  

NASA Astrophysics Data System (ADS)

CERTO radio beacon on the C/NOFS satellite sends VHF/UHF radio signals at 150 and 400 MHz to provide measurements of integrated electron density or Total Electron Content (TEC) by an east-west chain of ground receivers in Peru. Computerized Ionospheric Tomography (CIT) is used to convert the TEC data into two-dimensional images of electron densities with maximum 5 × 5 km resolution in Longitude-Altitude space. These images are updated every 95 min as the C/NOFS satellite passes over the receiver network in its low-latitude orbit with an inclination of 12°. The 2-D, high-resolution images of the ionosphere are used to predict the impact of equatorial plasma structures on HF propagation of radar and radio signals. Electron density measurements from the NRL radio tomography chain across Peru are used for simulations of the performance by HF one-way links. HF rays from transmitter to receiver are traced through the electron density images produced by radio beacon tomography. Eight separate paths are found between a transmitter and ground receiver separated by 2000 km. A total of 36 backscatter echoes are found with unique group delay, Doppler frequency shift, phase delay, and echo amplitude. This multipath effect explains the range and Doppler spreading of observations for HF monostatic radar propagation through F layer irregularities. This type of analysis is useful for prediction and interpretation of range and Doppler observations from HF systems including over-the-horizon and SuperDARN radars, HF Geolocation Arrays, and HF communications networks.

Bernhardt, Paul A.; Hei, Matthew A.; Siefring, Carl L.; Wilkens, Matthew R.

2014-07-01

274

Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves  

NASA Technical Reports Server (NTRS)

The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high-resolution space and time variation of the electron temperature as a high-power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time-dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations.

Mantas, G. P.; Lahoz, C. H.; Carlson, H. C., Jr.

1981-01-01

275

Space shuttle synthetic aperture radar. [using real time  

NASA Technical Reports Server (NTRS)

Results of a feasibility study to investigate a digital signal processor for real-time operation with a synthetic aperture radar system aboard the space shuttle are presented. Pertinent digital processing theory, a description of the proposed system, and size, weight, power, scheduling, and development estimates are included.

1975-01-01

276

Radar precipitation echo patterns associated with midwestern severe storms  

E-print Network

sequnmes. 'The radar echo vsrhe widely fxum sttatiform type (light, fussy eche with ill- defbied edges) to caevecttve type. Generally, the prectp5atkou is of Ught-co-moderate intensity, but lightuhg is often xeporced by surface stations and ls sometimes... ?oak cold front lytnN on a Ni SW lhN just to ON TIorONlest of DOU84 ~ Tones, 'fhs norIhwoet edge of the echooo observed at DuncauvQIO, Tease, wite defbNd hf this cohl front. ~ oortNdcos or funnel clouds were reported wtodn tense of the radar site oc...

Inman, Rex Lee

2012-06-07

277

Radar observations of wave transformations in the vicinity of islands  

NASA Technical Reports Server (NTRS)

Remote sensing by ground-based HF radar and airborne synthetic aperture radar and in situ wave measurements performed on March 25, 1977 during the West Coast Experiment have made it possible to form an overall picture of the 7-sec-period wave climate over a 35,000 sq km region off the southern California coast. The picture which emerges from these measurements shows a broad deep-ocean directional distribution arriving from the west and being significantly modified as it travels coastward passing San Clemente and Santa Catalina islands.

Vesecky, J. F.; Teague, C. C.; Hsiao, S. V.; Shemdin, O. H.; Pawka, S. S.

1980-01-01

278

HF Channel Availability under Ionospheric Disturbances: Model, Method and Measurements as Contributions  

NASA Astrophysics Data System (ADS)

A small group at METU has been developing data driven models in order to forecast some critical parameters, which affect the communication and navigation systems, since 1990. The background on the subjects supports new achievements in terms of theoretical and experimental basis contributing the COST 296 WG2 activities. This work mentions the representative contributions. (i) A method has been proposed for the assessment of HF Channel Availability under ionospheric disturbances. Signal to Noise Ratio (SNR), Doppler Spread and Modified Power Delay Spread were considered. The study relates the modem performance to ionospheric disturbances. Ionospheric disturbance was characterised by Disturbance Storm Type (DST) index. Radar data including Effective Multipath Spread, Composite Doppler Spread and SNR values were obtained from the experiment conducted between Leicester UK (52.63° N; 1.08° W) and Uppsala, Sweden (59.92° N; 17.63° E) in the year 2001. First, joint probability density function (PDF) of SNR, Doppler Spread, and Effective Multipath Spread versus DST were considered. It was demonstrated by determining the conditional PDFs, and by using Bayes' Theorem, that there were dependencies between DST and the above mentioned parameters [Sari, 2006]. Thus, it is concluded that the availability of the HF channel is a function of DST. As examples of modem characterizations, Military Standards were considered. Given a magnetic condition, the modem availability was calculated. The model developed represents the ionospheric HF channel, and it is based on a stochastic approach. Depending on the new experimental data, the conditional PDFs could be updated continuously. The HF channel availability under various ionospheric Space Weather (SW) conditions can be determined using the model. The proposed method is general and can include other indices as well. The method can also be applied to a variety of other processes. (ii) The effects of space weather conditions on the variation of group range and line-of-sight Doppler velocity of the HF Radar echo signal were investigated. HF radar system under ionospheric disturbances has been identified globally and some operational suggestions have been presented. It is possible for the HF radar operator to estimate the possible skip distance and possible single hop group ranges for the given frequencies of 11 MHz and 14 MHz [Buyukpabuscu, 2007]. (iii) The measurements over the HF band during the 29 March 2006 total solar eclipse in Antalya (36° N; 30° E) Turkey was conducted from the channel occupancy and atmospheric noise points of view. The whole HF band ranging from 1 to 30 MHz has been swept using 10 kHz peak and 200 Hz average detectors of a certified EMI receiver equipped with a calibrated active monopole antenna. The changes in the atmospheric noise during the eclipse were reported [Tulunay, 2006]. The model based, theoretical and experimental works mentioned are promising and have potential for future research and developments. References Buyukpabuscu S.O. (2007), System Identification with Particular Interest On The High Frequency Radar Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, February 2007. Sari M.O. (2006), A New Approach For The Assessment Of Hf Channel Availability Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, September 2006. Tulunay E., E. M. Warrington, Y. Tulunay, Y. Bahad?rlar, A.S. Türk, R. Çaputçu, T. Yap?c? , E.T. ?enalp (2006), Propagation Related Measurements during Three Solar Eclipses in Turkey, IET 10th International Conference on Ionospheric Radio Systems & Techniques, IRST 2006, 18-21 July 2006, London, UK.

Tulunay, E.; Senalp, E. T.; Tulunay, Y.; Warrington, E. M.; Sari, M. O.

2009-04-01

279

Modification of the high latitude F region of the ionosphere by X-mode powerful HF radio waves: Experimental results from multi-instrument diagnostics  

NASA Astrophysics Data System (ADS)

We present the experimental results for strong plasma modifications induced by the X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. A large number of experiments in the course of Russian EISCAT heating campaigns were conducted in 2009 - 2013 under different background conditions in a wide heater frequency range from 4 to 8 MHz. The EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar in Finland, SEE receiver at Tromsø, the HF Doppler equipment near St. Petersburg, and the EISCAT ionosonde (dynasonde) were used as diagnostic instruments. The results show that the X-mode HF pump wave can generate: (1) strong small-scale artificial field aligned irregularities (AFAIs); (2) HF-induced plasma and HF-enhanced ion lines (HFPLs and HFILs) from UHF radar spectra; (3) strong electron density enhancements along magnetic field line in a wide altitude range; (4) spectral components (few tens of Hz) in the Doppler spectra of the heater signal measured at a distance of 1200 km from the Tromsø HF heating facility. The experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization. For heater frequencies in the range of about 4 - 6 MHz the mentioned above phenomena are generated when the heater frequency is equal or above the ordinary-mode critical frequency (foF2). Under high background electron density and the heater frequencies used of 6.5 - 8.0 MHz, the strong X-mode HF-induced phenomena were observed both when the heater frequency is equal or above the foF2 and the heater frequency is below the foF2.

Blagoveshchenskaya, Nataly; Rietveld, Michael; Haggstrom, Ingemar; Borisova, Tatiana; Yeoman, Tim

280

Radar electronic warfare  

NASA Astrophysics Data System (ADS)

An overview of radar and electronic warfare is given. Definitions, common terms, and principles of radar and electronic warfare, and simple analyses of interactions between radar systems and electronic countermeasures (ECM) are presented. Electronic counter-countermeasure and electronic support measures are discussed. Background material in mathematics, electromagnetics, and probability necessary for an understanding of radar and electronic warfare is given and radar tracking models are examined. The effects of various ECM emissions on radar systems are analyzed, including discussion of active ECM and angle scanning systems, angle measurement in monopulse, and automatic gain control.

Golden, August, Jr.

281

Analysis of parameters for a space-based debris-tracking radar  

E-print Network

ANALYSIS OF PARAMETERS FOR A SPACE-BASED DEBRIS-TRACKING RADAR A Thesis hflCHAEL ALAN POLLOCK Submitted to the Graduate College of Texas Aft hf Hniversity in partial fulfillment of the requirement for the degree of MASTEII OF SCIENCE... Pollock, B. S. , Texas ARM University Chairmen of Advisory Committee: Dr. Richard W. Newton Dr. Richard E. Thomas The purpose of the following report is to present an evaluation of system requirements for a millimeter wave, phased array tracking radar...

Pollock, Michael A

2012-06-07

282

Radar investigation of barium releases over Arecibo Observatory, Puerto Rico  

NASA Technical Reports Server (NTRS)

The NASA Combined Release and Radiation Effects Satellite (CRRES) El Coqui rocket campaign was successfully carried out in Puerto Rico during the period 18 May through 12 July 1992. This report describes five chemical release experiments in the upper ionosphere supported by Geospace Research, Inc. during the El Coqui campaign. Additional spin-off science is also discussed. The El Coqui releases are designated AA-1 (rocket 36-082), AA-2 (rocket 36-081), AA-3b (rocket 36-064), AA-4 (rocket 36-065), and AA-7 (rocket 36-083). Particular attention is paid to releases AA-2 and AA-4. These two experiments involved the illumination of ionospheric release regions with powerful high-frequency (HF) radio waves transmitted from the Arecibo HF facility. In the AA-2 experiment, microinstabilities excited by the HF wave in a Ba(+) plasma were examined. This release yielded a smooth plasma cloud that helped clarify several fundamental issues regarding the physics of wave plasma instabilities. During AA-2 extremely strong HF-induced Langmuir turbulence was detected with the Arecibo 430 MHz radar. CF3Br was released in the AA-4 study to create an ionospheric hole that focused the HF beam. This experiment successfully explored wave-plasma coupling in an O(+) ionosphere under conditions of very high HF electric field strengths.

Djuth, Frank T.

1995-01-01

283

Monitoring tsunami propagation using OTH radar  

NASA Astrophysics Data System (ADS)

Ionospheric anomalies following tsunamis are now observable after major events as Total Electron Content (TEC) fluctuations. GPS and altimeters are important tools for this purpose, but the detection depends on satellites-receivers geometry, when the line of sight crosses the moving perturbation parallel to the wave fronts. All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. Most of these ionospheric anomalies are deterministic and reproducible by numerical modeling via the coupling mechanism between ocean, neutral atmosphere and ionosphere. This numerical modeling supplies useful information for the estimation of expected anomalies and to explore and identify new techniques to detect the ionospheric tsunami signature. [|#18#|][|#5#|][|#23#|]The Over-The-Horizon (OTH) radars recently proved to be able to measure seismic Rayleigh wave in the ionosphere, consequently we explore here numerically the possibility to detect the ionospheric signature of tsunamis. OTH operate in High Frequency (HF) band and can be used to monitor the bottomside ionosphere over large regions. Those regions can be strongly perturbed by tsunami generated IGW. We reproduce numerically those atmospheric/ionospheric waves as well as the effect that they produce on synthetic radar measurements. The effects of the tsunami directionality are analyzed underlining the radar capabilities to follow the ionospheric perturbations. The large coverage of OTH radar and its sensitivity to plasma anomalies open new perspectives in the future oceanic monitoring and tsunami warning systems.

Coisson, P.; Occhipinti, G.; Lognonne, P.; Rolland, L. M.

2010-12-01

284

Beijing MST radar: Overview and preliminary results  

NASA Astrophysics Data System (ADS)

As one of the main facilities of so-called China Meridian Project which is focusing on the monitoring solar-terrestrial link and space weather, as well as sun-earth climate connection study, Beijing MST radar has been completed in the middle of 2011 and started its quasi-continuous operational observation since the end of 2011. Beijing MST radar is located in IAP's field observatory (39.4 N,117.0 E) which is a large scale full coherent VHF Doppler radar, with antenna area 9,110 m^2, power-aperture product 3.1×108 W.m^2. It's antenna array is consisted of 24×24 three element YAGI antenna with square digital active phased array, with beam width equal to or less than 4.5 degree and active five antenna beam azimuth directions and zenith angle ranging from zenith to 20 degree with 1 degree steps. Also the radar uses direct digital receivers and high speed signal processing system. The expected observation altitude is 3-25 km and 60-90 km, for which low, middle and high observation modes can be selected with different vertical resolutions. Same as other MST radars worldwide, Beijing MST radar may observe the 3D wind, backscattering power, and signal noise ratio, for different altitude ranges. Based on preliminary observation in certain time periods, results have been shown that both wind profiling from 3-25 km and 60-90 km are observed. Preliminary results show that the present radar can observe the altitude of lower thermosphere, at least in 90-100 km, even to 110 km. Further results will be given.

Lu, Daren; Chen, Zeyu; Wang, Yong; Zhang, Wenxing; Duan, Shu

2012-07-01

285

The Atmospheric Radiation Measurement Program Cloud Profiling Radars: Second-Generation Sampling Strategies, Processing, and Cloud Data Products  

Microsoft Academic Search

The United States Department of Energy Atmospheric Radiation Measurement program operates millimeter-wavelength cloud radars in several climatologically distinct regions. The digital signal processors for these radars were recently upgraded and allow for enhancements in the operational parameters running on them. Recent evaluations of millimeter-wavelength cloud radar signal processing performance relative to the range of cloud dynamical and microphysical conditions encountered

Pavlos Kollias; Eugene E. Clothiaux; Mark A. Miller; Edward P. Luke; Karen L. Johnson; Kenneth P. Moran; Kevin B. Widener; Bruce A. Albrecht

2007-01-01

286

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 44, NO. 9, SEPTEMBER 2006 2393 Landmines Ground-Penetrating Radar Signal  

E-print Network

Ground-Penetrating Radar Signal Enhancement by Digital Filtering Delphine Potin, Emmanuel Duflos, Member problems have been raised by these sensors. Ground-penetrating radars (GPRs) are key sensors for landmine. Thanks to the sensors, the technology is available. The ground-penetrating radar (GPR) has an im- portant

Paris-Sud XI, Université de

287

Radar/radiometer facilities for precipitation measurements  

NASA Technical Reports Server (NTRS)

The OSU ElectroScience Laboratory Radar/Radiometer Facilities are described. This instrumentation includes a high-resolution radar/radiometer system, a fully automated low-resolution radar system, and a small surveillance radar system. The high-resolution radar/radiometer system operates at 3, 9, and 15 GHz using two 9.1 m and one 4.6 m parabolic antennas, respectively. The low-resolution and surveillance radars operate at 9 and 15 GHz, respectively. Both the high- and low-resolution systems are interfaced to real-time digital processing and recording systems. This capability was developed for the measurement of the temporal and spatial characteristics of precipitation in conjunction with millimeter wavelength propagation studies utilizing the Advanced Technology Satellites. Precipitation characteristics derived from these measurements could also be of direct benefit in such diverse areas as: the atmospheric sciences, meteorology, water resources, flood control and warning, severe storm warning, agricultural crop studies, and urban and regional planning.

Hodge, D. B.; Taylor, R. C.

1973-01-01

288

Low level range coverage performance prediction for VHF radar  

NASA Astrophysics Data System (ADS)

A VHF radar frequencies the range coverage is not strictly limited by the quasi-optical horizon like at microwave radar frequencies but is extended due to diffraction propagation. This effect, here called beyond-the-horizon (BTH) detection capability is strongly dependent on the propagation path and thus on the terrain structure. The availability of digital terrain maps gives way to the use of computerized methods for the prediction of radar range coverage in real environment. In combination with wave propagation models suitable for diffraction at terrain structures, digital terrain data can even be used for the prediction of BTH target detectability at VHF radar. Here the digital landmass system (DLSS) terrain database was used in combination with a multiple-knife-edge diffraction model to predict the diffraction attenuation between the radar and the potential target positions, especially beyond the optical horizon. The propagation paths extracted from the database are modeled as a sequence of diffraction screens suited for the application of a Fresnel-Kirchhoff algorithm yielding the knife-edge-diffraction attenuation. This terrain related propagation model was verified by a large number of measurements at different frequencies. Implemented in a fast computer system, this prediction model can be used for mission planning of air operations. Considering hostile VHF radar coverage and terrain condition for flight path optimization or, on the other hand it can assist in siting mobile radars for gap filling according to the actual threat situation. Calculations of the diffraction propagation using the prediction model, yield range coverage patterns in real terrain situations, allowing to quantify the BTH detection advantage of VHF radar compared to microwave radar. An experimental large wavelength radar LARA (VHF) built flying targets beyond the close horizon. Here, especially the detection of hiding helicopters by exploiting diffractive wave propagation was examined. Measurements at different VHF frequencies were carried out, to validate the results obtained by simulation.

Kuschel, H.

1989-09-01

289

Imaging Radar Applications in the Death Valley Region  

NASA Technical Reports Server (NTRS)

Death Valley has had a long history as a testbed for remote sensing techniques (Gillespie, this conference). Along with visible-near infrared and thermal IR sensors, imaging radars have flown and orbited over the valley since the 1970's, yielding new insights into the geologic applications of that technology. More recently, radar interferometry has been used to derive digital topographic maps of the area, supplementing the USGS 7.5' digital quadrangles currently available for nearly the entire area. As for their shorter-wavelength brethren, imaging radars were tested early in their civilian history in Death Valley because it has a variety of surface types in a small area without the confounding effects of vegetation. In one of the classic references of these early radar studies, in a semi-quantitative way the response of an imaging radar to surface roughness near the radar wavelength, which typically ranges from about 1 cm to 1 m was explained. This laid the groundwork for applications of airborne and spaceborne radars to geologic problems in and regions. Radar's main advantages over other sensors stems from its active nature- supplying its own illumination makes it independent of solar illumination and it can also control the imaging geometry more accurately. Finally, its long wavelength allows it to peer through clouds, eliminating some of the problems of optical sensors, especially in perennially cloudy and polar areas.

Farr, Tom G.

1996-01-01

290

Rain-Mapping Radar  

NASA Technical Reports Server (NTRS)

Orbiting radar system measures rates of rainfall from 0.5 to 60 mm/h. Radar waves scattered and absorbed by rainfall to extents depending on wavelength, polarization, rate of rainfall, and distribution of sizes and shapes of raindrops. Backscattered radar signal as function of length of path through rain used to infer detailed information about rain. Accumulated radar return signals processed into global maps of monthly average rainfall for use in climatological studies.

Im, K. E.; Li, F. K.; Wilson, W. J.; Rosing, D.

1988-01-01

291

Nostradamus: The radar that wanted to be a seismometer  

NASA Astrophysics Data System (ADS)

Surface waves emitted after large earthquakes are known to induce, by dynamic coupling, atmospheric infrasonic waves propagating upward through the neutral and ionized atmosphere. Those waves have been detected in the past at ionospheric heights using a variety of techniques, such as HF Doppler sounding or GPS receivers. The HF Doppler technique, particularly sensitive to the ionospheric signature of Rayleigh waves is used here to show ionospheric perturbations consistent with the propagation of Rayleigh wave phases R1 and R2 following the Sumatra earthquake on the 28 March 2005 (M = 8.6). This is in our knowledge the first time that the phase R2 is detected by ionospheric sounding. In addition, we prove here that the ionospheric signature of R2 is also observed by over-the-horizon (OTH) Radar. The latter was never used before to detect seismic signature in the ionosphere. Adding the OTH Radar to the list of the “ionospheric seismometers” we discuss and compare the performances of the three different instruments mentioned above, namely HF Doppler sounding, GPS receivers and OTH radar.

Occhipinti, Giovanni; Dorey, Philippe; Farges, Thomas; Lognonné, Philippe

2010-09-01

292

Radar augmentation device  

NASA Technical Reports Server (NTRS)

The radar augmentation device (RAD) serves to increase the radar response of a target body and thus expedite radar acquisition. The design and development of the RAD are discussed with particular emphasis on technical problems that were encountered and solved. Discussions of the mode of operation of the RAD and the ground test history are also included.

Riedel, J. K.

1972-01-01

293

Micropower impulse radar  

Microsoft Academic Search

Invented and developed at Lawrence Livermore National Laboratory is an inexpensive and highly sensitive, low-power radar system that produces and samples extremely short pulses of energy at the rate of 2 million per second. Called micropower impulse radar (MIR), it can detect objects at a greater variety of distances with greater sensitivity than conventional radar. Its origins in the Laboratory`s

S. Azevedo; T. E. McEwan

1996-01-01

294

Lunar radar backscatter studies  

NASA Technical Reports Server (NTRS)

The lunar surface material in the Plato area is characterized using Earth based visual, infrared, and radar signatures. Radar scattering in the lunar regolith with an existing optical scattering computer program is modeled. Mapping with 1 to 2 km resolution of the Moon using a 70 cm Arecibo radar is presented.

Thompson, T. W.

1979-01-01

295

Controlling radar signature  

SciTech Connect

Low observable technologies for military and tactical aircraft are reviewed including signature-reduction techniques and signal detection/jamming. Among the applications considered are low-signature sensors and the reduction of radar cross section in conjunction with radar-absorbing structures and materials. Technologies for reducing radar cross section are shown to present significant technological challenges, although they afford enhanced aircraft survivability.

Foulke, K.W. (U.S. Navy, Naval Air Warfare Center, China Lake, CA (United States))

1992-08-01

296

Controlling radar signature  

Microsoft Academic Search

Low observable technologies for military and tactical aircraft are reviewed including signature-reduction techniques and signal detection\\/jamming. Among the applications considered are low-signature sensors and the reduction of radar cross section in conjunction with radar-absorbing structures and materials. Technologies for reducing radar cross section are shown to present significant technological challenges, although they afford enhanced aircraft survivability.

Foulke

1992-01-01

297

Radar hydrology: rainfall estimation  

Microsoft Academic Search

Radar observations of rainfall and their use in hydrologic research provide the focus for the paper. Radar-rainfall products are crucial for input to runoff and flood prediction models, validation of satellite remote sensing algorithms, and for statistical characterization of extreme rainfall frequency. In this context we discuss the issues of radar-rainfall product development, and the theoretical and practical requirements of

W. F. Krajewski; J. A. Smith

2002-01-01

298

Radar Location Equipment Development Program: Phase I  

SciTech Connect

The work described in this report represents the first phase of a planned three-phase project designed to develop a radar system for monitoring waste canisters stored in a thick layer of bedded salt at the Waste Isolation Pilot Plant near Carlsbad, New Mexico. The canisters will be contained in holes drilled into the floor of the underground waste storage facility. It is hoped that these measurements can be made to accuracies of +-5 cm and +-2/sup 0/, respectively. The initial phase of this project was primarily a feasibility study. Its principal objective was to evaluate the potential effectiveness of the radar method in the planned canister monitoring application. Its scope included an investigation of the characteristics of radar signals backscattered from waste canisters, a test of preliminary data analysis methods, an assessment of the effects of salt and bentonite (a proposed backfill material) on the propagation of the radar signals, and a review of current ground-penetrating radar technology. A laboratory experiment was performed in which radar signals were backscattered from simulated waste canisters. The radar data were recorded by a digital data acquisition system and were subsequently analyzed by three different computer-based methods to extract estimates of canister location and tilt. Each of these methods yielded results that were accurate within a few centimeters in canister location and within 1/sup 0/ in canister tilt. Measurements were also made to determine the signal propagation velocities in salt and bentonite (actually a bentonite/sand mixture) and to estimate the signal attenuation rate in the bentonite. Finally, a product survey and a literature search were made to identify available ground-penetrating radar systems and alternative antenna designs that may be particularly suitable for this unique application. 10 refs., 21 figs., 4 tabs.

Sandness, G.A.; Davis, K.C.

1985-06-01

299

Cloud and Precipitation Radar  

NASA Astrophysics Data System (ADS)

Precipitation or weather radar is an essential tool for research, diagnosis, and nowcasting of precipitation events like fronts or thunderstorms. Only with weather radar is it possible to gain insights into the three-dimensional structure of thunderstorms and to investigate processes like hail formation or tornado genesis. A number of different radar products are available to analyze the structure, dynamics and microphysics of precipitation systems. Cloud radars use short wavelengths to enable detection of small ice particles or cloud droplets. Their applications differ from weather radar as they are mostly orientated vertically, where different retrieval techniques can be applied.

Hagen, Martin; Höller, Hartmut; Schmidt, Kersten

300

Single- and dual-wavelength radar determination of liquid-water content in a Texas thunderstorm  

E-print Network

, proposed by Ulbrich and Atlas (1975), also requires dual-wave- length radars and is based, for the most part, upon a theoretically derived relationship between the liquid-water content and combined measurements of the radar-reflectivity factor... is necessary to process and analyze radar data The citations on the following pages follow the style of the 1 F G~hf 1 R *h. in a manner which is consistent with the latest techniques available for that purpose. Furthermore, this unfortunate situation...

Linn, Charles Theodore

2012-06-07

301

Magellan: Radar performance and data products  

USGS Publications Warehouse

The Magellan Venus orbiter carries only one scientific instrument: a 12.6-centimeter-wavelength radar system shared among three data-taking modes. The syntheticaperture mode images radar echoes from the Venus surface at a resolution of between 120 and 300 meters, depending on spacecraft altitude. In the altimetric mode, relative height measurement accuracies may approach 5 meters, depending on the terrain's roughness, although orbital uncertainties place a floor of about 50 meters on the absolute uncertainty. In areas of extremely rough topography, accuracy is limited by the inherent line-of-sight radar resolution of about 88 meters. The maximum elevation observed to date, corresponding to a planetary radius of 6062 kilometers, lies within Maxwell Mons. When used as a thermal emission radiometer, the system can determine surface emissivities to an absolute accuracy of about 0.02. Mosaicked and archival digital data products will be released in compact disk (CDROM) format.

Pettengill, G.H.; Ford, P.G.; Johnson, W.T.K.; Raney, R.K.; Soderblom, L.A.

1991-01-01

302

The Apollo Lunar Sounder radar system  

NASA Technical Reports Server (NTRS)

The objectives of the Apollo 17 Lunar Sounder Experiment (ALSE) were to detect subsurface geologic structures, to generate a continuous lunar profile, and to image the moon at radar wavelengths. A three-wavelength synthetic-aperture radar (SAR) operating at 60, 20, and 2 m wavelengths was designed to attain these objectives. The design choices reflected a balance of scientific requirements versus Apollo mission and hardware constraints. The radar data from the lunar mission were recorded on photographic film in a conventional SAR format, and were returned to earth for processing. A combination of optical and digital processing and exploitation techniques was applied to the scientific interpretation of the data. Some preliminary results from the lunar mission have been obtained.

Porcello, L. J.; Zelenka, J. S.; Adams, G. F.; Jackson, P. L.; Jordan, R. L.; Phillips, R. J.; Brown, W. E., Jr.; Ward, S. H.

1974-01-01

303

Advanced Radar Research Center The University of Oklahoma seeks an exceptional, dynamic leader to serve as Director of its Advanced Radar Research Center  

E-print Network

in surface, airborne and space-based defense, security and intelligence. Principal capabilities of the ARRC has expanded capabilities in radar and other electromagnetic technologies, with applications technology; digital signal/array processing; automated algorithms; decision support tools; data assimilation

Oklahoma, University of

304

Hf diversity in S-type granites  

NASA Astrophysics Data System (ADS)

The 176Hf/177Hf composition of inherited and magmatic zircon in the 538 Ma S-type Peninsula pluton (South Africa) has been determined at different scales. In the smallest rock samples investigated (<0.5 dm3), as well as within individual thin sections, magmatic zircon crystals exhibit the same wide range in ?Hf(538) as the pluton (8? units). In addition, across a significant range of bulk-rock compositions, both the range and average of the magmatic zircon Hf isotopic composition do not vary significantly with compositional parameters that are expected to scale with the proportion of mantle-derived magma addition (e.g., Mg# and Ca). At all scales, the ?Hf variability in the magmatic zircon fraction matches well with that portrayed by the time-evolved inherited zircon population [i.e., with the ?Hf(538) range of the inherited zircon cores]. This evidence suggests that the ?Hf heterogeneity of magmatic zircon is directly inherited from the source. However, the analysis of zircon core-rim pairs reveals that the 176Hf/177Hf composition of the inherited crystals does not directly transfer to their magmatic overgrowths. Small-scale modeling of zircon dissolution and re-precipitation in a static magma generates sub-mm melt domains having variable Zr content and Hf isotope composition. The composition of these domains is controlled by the size and isotope composition of the nearest dissolving zircon crystals and the cooling rate of the magma. These results suggest that in magma systems with a substantial inherited zircon load, zircon crystals within the same rock should record variable 176Hf/177Hf in the magmatic zircon fraction.

Farina, F.; Stevens, G.; Gerdes, A.; Frei, D.

2014-10-01

305

Simultaneous Multi-angle Radar Observations of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP  

NASA Astrophysics Data System (ADS)

The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

Sheerin, J. P.; Watanabe, N.; Rayyan, N.; Spry, D.; Adham, N.; Watkins, B. J.; Bristow, W. A.; Spaleta, J.; Bernhardt, P. A.

2012-12-01

306

Wavelets: a Versatile Tool for the High Frequency Surface Wave Radar  

Microsoft Academic Search

Widely used in image processing, wavelets seem to be a promising versatile tool for the high frequency surface wave radar (HFSWR). HFSWR is based on the ability of HF waves (3 MHz to 30 MHz) to propagate along the earth curvature. HFSWR can detect targets up to few hundred kilometers beyond the horizon. The two main applications of the HFSWR

Florent Jangal; S. Saillant; M. Helier

2007-01-01

307

Detection and tracking of go-fast boats using high-frequency surface wave radar  

Microsoft Academic Search

This paper summarises the results of a 6 month deployment of a HF Surface Wave Radar (HFSWR) to demonstrate the detection and tracking of Go-Fast Boats (GFBs). Measured Doppler and Track data is compared to theoretical predictions. It is shown that HFSWR is a viable sensor for tracking GFBs in a target rich environment. Data is presented that demonstrates that

Anthony M. Ponsford

2004-01-01

308

A method to estimate subspace via Doppler for ocean clutter suppression in skywave radars  

Microsoft Academic Search

To detect ship targets within short coherent integration time (CIT), the ocean clutter suppressing technique has been used in high frequency (HF) skywave over-the-horizon-radar (OTHR). The clutter cancellation methods in time field are affected by estimate precision of frequency, amplitude and phase. The methods based on subspace are limited by the difficulty in determining the order of clutter subspace, and

Zhao Zhiguo; Jianwen Chen; Bao Zheng

2011-01-01

309

High frequency radar and its application to fresh water Lorelle A. Meadows a,  

E-print Network

High frequency radar and its application to fresh water Lorelle A. Meadows a, , Chad Whelan b,1. Because HF radiation is known to propagate less efficiently over fresh water than seawater, it has been., Ann Arbor, MI 48109-2143, USA a b s t r a c ta r t i c l e i n f o Article history: Received 28

Ruf, Christopher

310

Performance Evaluation of SeaSonde High-Frequency Radar for Vessel Detection  

E-print Network

P A P E R Performance Evaluation of SeaSonde High-Frequency Radar for Vessel Detection A U T H O R collaborated on the development of vessel detection and tracking capabilities from compact HF ra- dars., 2010a). Technology demonstrations determined (a) that vessels could be detected, (b) that multilook

311

Accuracy of topographic maps derived from ERS-1 interferometric radar  

Microsoft Academic Search

An interferometric radar technique for topographic mapping of surfaces promises a high-resolution approach to the generation of digital elevation models. The authors present analyses of data collected by the synthetic aperture radar instrument on-board the ERS-1 satellite on successive orbits. Use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity; also

Howard A. Zebker; Charles L. Werner; Paul A. Rosen; Scott Hensley

1994-01-01

312

Coherent radar measurement of ocean currents from geostationary orbit  

NASA Technical Reports Server (NTRS)

A coherent HF radar system developed by Barrick has successfully measured ocean surface currents near shore. This innovative system, called CODAR, can map the current vector for coastal areas as large as 10,000 sq km. CODAR's range is limited owing to the strong attenuation suffered by HF ground waves. An alternate technique was proposed by Schuler, in which the cross-product power spectrum of two (different frequency) microwave signals is processed. The frequency of the resonant peak corresponds close by to the Doppler shift of an ocean gravity wave traveling toward the radar at the phase velocity, v(sub p). The slight difference between the frequency of the measured resonant delta K peak and the Doppler frequency shift caused by the motion of the gravity wave is attributed to be the current velocity in the pointing direction of the radar. The Microwave Remote Sensing Laboratory (MIRSL) has considered the feasibility of using this technique to measure ocean surface currents from geostationary satellite platforms. Problems are discussed that must be overcome if a satellite current measurement system is to be realized. MIRSL research activities that address some of these problem areas are discussed. Current measurements are presented that were made using a specially-designed C-Band, step-frequency delta K radar. These measurements suggest that progress is being achieved in detecting ocean surface current motion for a wide variety of ocean surface conditions.

Mcintosh, R. E.

1989-01-01

313

Ground-penetrating radar simulation in engineering and archaeology  

SciTech Connect

Forward modeling of ground penetration radar is developed using exact ray-tracing techniques. Structural boundaries for a ground model are incorporated via a discrete grid with interfaces described by splines, polynomials, and in the case of special structures such as circular objects, the boundaries are given in terms of their functional formula. In the synthetic radar gram method, the waveform contributions of many different wave types are computed. Using a finely digitized antenna directional response function, the radar cross-section of buried targets and the effective area of the receiving antenna can be statistically modeled. Attenuation along the raypaths is also monitored. The forward models are used: (1) as a learning tool to avoid pitfalls in radar gram interpretation, (2) to understand radar signatures measured across various engineering structures, and (3) to predict the response of cultural structures buried beneath important archaeological sites in Japan.

Goodman, D. (Univ. of Miami Japan Div., Ishikawa (Japan). Geophysical Archaeometry Lab.)

1994-02-01

314

ECE 468 Digital Signal Processing 1. History  

E-print Network

ECE 468 Digital Signal Processing 1. History: · Digital signal processing has its roots in 17th on a computer before implementing it in analog hardware. 1 #12;Broadcasting: television and radio programs the depth. On the other hand, radars make use of radio waves in order to communicate the locations

Chen, Ying "Ada"

315

2. VIEW SOUTHWEST, prime search radar tower, height finder radar ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

2. VIEW SOUTHWEST, prime search radar tower, height finder radar towards, height finder radar towers, and radar tower (unknown function) - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

316

Progress toward a practical skywave sea-state radar  

NASA Astrophysics Data System (ADS)

Recent advances in propagation modeling, ionospheric diagnostics, and signal processing have helped overcome the limitations the ionosphere imposes in sea-state measurements with HF skywave radar. Wind-direction fields in tropical storms can be routinely mapped under most ionospheric conditions, but waveheight and wave-spectrum extraction is more sensitive to ionospheric distortions and requires care in signal processing and in selecting an ionospheric path. Spot measurements with a high-resolution radar have verified its ability to measure (in order of increasing difficulty) wind-direction fields, rms waveheight, and the scalar ocean-wave spectrum at ranges up to 300 km using one ionospheric hop. Although such a radar can in principle map these quantities over millions of square kilometers of an ocean area, the time required to do so under various ionospheric conditions remains to be determined. A minimum objective of one map of rms waveheight per day seems attainable.

Georges, T. M.

1980-11-01

317

Lunar Radar Sounder (LRS) experiment on-board the SELENE spacecraft  

NASA Astrophysics Data System (ADS)

The Lunar Radar Sounder (LRS) experiment on-board the SELENE (SELenological and ENngineering Explorer) spacecraft has been planned for observation of the subsurface structure of the Moon, using HF radar operating in the frequency range around 5 MHz. The fundamental technique of the instrumentation of LRS is based on the plasma waves and sounder experiments which have been established through the observations of the earth's magnetosphere, plasmasphere and ionosphere by using EXOS-B (Jikiken), EXOS-C (Ohzora) and EXOS-D (Akebono) satellites; and the plasma sounder for observations of the Martian ionosphere as well as surface land shape are installed on the Planet-B (Nozomi) spacecraft which will arrive at Mars in 2003. For the exploration of lunar subsurface structures applying the developed sounder technique, discrimination of weak subsurface echo signals from intense surface echoes is important; to solve this problem, a frequency modulation technique applied to the sounder RF pulse has been introduced to improve the resolution of range measurements. By using digital signal processing techniques for the generation of the sounder RF waveform and on-board data analyses, it becomes possible to improve the S/N ratio and resolution for the subsurface sounding of the Moon. The instrumental and theoretical studies for developing the LRS system for subsurface sounding of the Moon have shown that the LRS observations on-board the SELENE spacecraft will give detailed information about the subsurface structures within a depth of 5 km from the lunar surface, with a range resolution of less than 75 m for a region with a horizontal scale of several tens of km. This capability is evaluated to be sufficient for study of the thermal history of the lunar surface region relating to a time scale of several tens of millions of years.

Ono, T.; Oya, H.

2000-09-01

318

Rendezvous radar for the orbital maneuvering vehicle  

NASA Technical Reports Server (NTRS)

This paper describes the development of the Rendezvous Radar Set (RRS) for the Orbital Maneuvering Vehicle (OMV) for the National Aeronautics and Space Administration (NASA). The RRS was to be used to locate, and then provide vectoring information to, target satellites (or Shuttle or Space Station) to aid the OMV in making a minimum-fuel-consumption approach and rendezvous. The RRS design is that of an X-Band, all solid-state, monopulse tracking, frequency hopping, pulse-Doppler radar system. The development of the radar was terminated when the OMV prime contract to TRW was terminated by NASA. At the time of the termination, the development was in the circuit design stage. The system design was virtually completed, the PDR had been held. The RRS design was based on Motorola's experiences, both in the design and production of radar systems for the US Army and in the design and production of hi-rel communications systems for NASA space programs. Experience in these fields was combined with the latest digital signal processor and micro-processor technology to design a light-weight, low-power, spaceborne radar. The antenna and antenna positioner (gimbals) technology developed for the RRS is now being used in the satellite-to-satellite communication link design for Motorola's Iridium telecommunications system.

Locke, John W.; Olds, Keith; Parks, Howard

1991-01-01

319

A fully photonics-based coherent radar system  

NASA Astrophysics Data System (ADS)

The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

Ghelfi, Paolo; Laghezza, Francesco; Scotti, Filippo; Serafino, Giovanni; Capria, Amerigo; Pinna, Sergio; Onori, Daniel; Porzi, Claudio; Scaffardi, Mirco; Malacarne, Antonio; Vercesi, Valeria; Lazzeri, Emma; Berizzi, Fabrizio; Bogoni, Antonella

2014-03-01

320

3. VIEW NORTHWEST, height finder radar towers, and radar tower ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

3. VIEW NORTHWEST, height finder radar towers, and radar tower (unknown function) - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

321

A HWIL test facility of infrared imaging laser radar using direct signal injection  

Microsoft Academic Search

Laser radar has been widely used these years and the hardware-in-the-loop (HWIL) testing of laser radar become important because of its low cost and high fidelity compare with On-the-Fly testing and whole digital simulation separately. Scene generation and projection two key technologies of hardware-in-the-loop testing of laser radar and is a complicated problem because the 3D images result from time

Qian Wang; Wei Lu; Chunhui Wang; Qi Wang

2005-01-01

322

Modulation recognition for real HF signals  

NASA Astrophysics Data System (ADS)

High-frequency (HF) communications is undergoing resurgence despite advances in long-range satellite communication systems. Defense agencies are using the HF spectrum for backup communications, as well as for spectrum surveillance applications. Spectrum management organizations are monitoring the HF spectrum to control and enforce licensing. These activities usually require systems capable of determining the location of a source of transmissions, separating valid signals from interference and noise, and recognizing signal modulation. Our ultimate aim is to develop robust modulation recognition algorithms for real HF signals, that is, signals propagating by multiple ionospheric modes with cochannel signals and non-Gaussian noise. One aspect of modulation recognition is the extraction of signal identifying features. This paper continues our work of applying various feature parameters to real HF signals and gives guidance on which features show potential for use in robust recognition of HF modulation types in the presence of HF noise and multi-path. It also defines a measure of mean separation distance between modulation types based on an entropy parameter, and discusses the probability density function of HF noise.

Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

2005-12-01

323

Range rate-Doppler correlation for HF propagation in traveling ionospheric disturbance environments  

NASA Astrophysics Data System (ADS)

Using ionospheric sounding together with fast computational inverse processing, it is now possible to obtain good real-time ionospheric models for use in geolocation for over-the-horizon (OTH) radar. However, deflection of HF propagation paths by traveling ionospheric disturbances (TIDs) remains a troubling cause of coordinate registration errors. Bandwidth and coverage limitations in ionospheric soundings preclude the ability to model TID structure in real time in most cases. It would be useful if TID-induced path deflections could be related to radar-measurable quantities like Doppler shift. As a first step in studying this possibility, we have considered the relationship between Doppler shift and group range rate for point-to-point HF propagation paths in TID environments. The nature of group range rate-Doppler correlation is exposed in three ways: (1) simple theoretical modeling, (2) ray tracing in simulated TID environments, and (3) analysis of OTH radar measurements of a fixed beacon. It is shown that group range rate and Doppler shift for fixed-point propagation paths are usually proportional with a ratio that depends on whether ionospheric motion or density changes predominate in the TID environment.

Nickisch, L. J.; Hausman, Mark A.; Fridman, Sergey V.

2006-10-01

324

Measurements of spatial and frequency coherence of an equatorial hf path during spread-F  

NASA Astrophysics Data System (ADS)

In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four CW tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the CW broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the 'damage' is done by the bottomside spread F.

Fitzgerald, T. J.; Argo, P. E.; Carlos, R. C.

325

Measurements of spatial and frequency coherence of an equatorial hf path during spread-F  

SciTech Connect

In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four cw tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the cw broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the {open_quotes}damage{close_quotes} is done by the bottomside spread F.

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

1993-07-01

326

Measurements of spatial and frequency coherence of an equatorial hf path during spread-F  

SciTech Connect

In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four cw tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the cw broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the [open quotes]damage[close quotes] is done by the bottomside spread F.

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

1993-01-01

327

Planetary radar studies  

NASA Technical Reports Server (NTRS)

A catalog of lunar and radar anomalies was generated to provide a base for comparison with Venusian radar signatures. The relationships between lunar radar anomalies and regolith processes were investigated, and a consortium was formed to compare lunar and Venusian radar images of craters. Time was scheduled at the Arecibo Observatory to use the 430 MHz radar to obtain high resolution radar maps of six areas of the lunar suface. Data from 1978 observations of Mare Serenitas and Plato are being analyzed on a PDP 11/70 computer to construct the computer program library necessary for the eventual reduction of the May 1981 and subsequent data acquisitions. Papers accepted for publication are presented.

Thompson, T. W.; Cutts, J. A.

1981-01-01

328

Laser radar in robotics  

SciTech Connect

In this paper the authors describe the basic operating principles of laser radar sensors and the typical algorithms used to process laser radar imagery for robotic applications. The authors review 12 laser radar sensors to illustrate the variety of systems that have been applied to robotic applications wherein information extracted from the laser radar data is used to automatically control a mechanism or process. Next, they describe selected robotic applications in seven areas: autonomous vehicle navigation, walking machine foot placement, automated service vehicles, manufacturing and inspection, automotive, military, and agriculture. They conclude with a discussion of the status of laser radar technology and suggest trends seen in the application of laser radar sensors to robotics. Many new applications are expected as the maturity level progresses and system costs are reduced.

Carmer, D.C.; Peterson, L.M. [Environmental Research Inst. of Michigan, Ann Arbor, MI (United States)

1996-02-01

329

Integrating a Microwave Radiometer into Radar Hardware for Simultaneous Data Collection Between the Instruments  

NASA Technical Reports Server (NTRS)

The conventional method for integrating a radiometer into radar hardware is to share the RF front end between the instruments, and to have separate IF receivers that take data at separate times. Alternatively, the radar and radiometer could share the antenna through the use of a diplexer, but have completely independent receivers. This novel method shares the radar's RF electronics and digital receiver with the radiometer, while allowing for simultaneous operation of the radar and radiometer. Radars and radiometers, while often having near-identical RF receivers, generally have substantially different IF and baseband receivers. Operation of the two instruments simultaneously is difficult, since airborne radars will pulse at a rate of hundreds of microseconds. Radiometer integration time is typically 10s or 100s of milliseconds. The bandwidth of radar may be 1 to 25 MHz, while a radiometer will have an RF bandwidth of up to a GHz. As such, the conventional method of integrating radar and radiometer hardware is to share the highfrequency RF receiver, but to have separate IF subsystems and digitizers. To avoid corruption of the radiometer data, the radar is turned off during the radiometer dwell time. This method utilizes a modern radar digital receiver to allow simultaneous operation of a radiometer and radar with a shared RF front end and digital receiver. The radiometer signal is coupled out after the first down-conversion stage. From there, the radar transmit frequencies are heavily filtered, and the bands outside the transmit filter are amplified and passed to a detector diode. This diode produces a DC output proportional to the input power. For a conventional radiometer, this level would be digitized. By taking this DC output and mixing it with a system oscillator at 10 MHz, the signal can instead be digitized by a second channel on the radar digital receiver (which typically do not accept DC inputs), and can be down-converted to a DC level again digitally. This unintuitive step allows the digital receiver to sample both the radiometer and radar data at a rapid, synchronized data rate (greater than 1 MHz bandwidth). Once both signals are sampled by the same digital receiver, high-speed quality control can be performed on the radiometer data to allow it to take data simultaneously with the radar. The radiometer data can be blanked during radar transmit, or when the radar return is of a power level high enough to corrupt the radiometer data. Additionally, the receiver protection switches in the RF front end can double as radiometer calibration sources, the short (four-microsecond level) switching periods integrated over many seconds to estimate the radiometer offset. The major benefit of this innovation is that there is minimal impact on the radar performance due to the integration of the radiometer, and the radiometer performance is similarly minimally affected by the radar. As the radar and radiometer are able to operate simultaneously, there is no extended period of integration time loss for the radiometer (maximizing sensitivity), and the radar is able to maintain its full number of pulses (increasing sensitivity and decreasing measurement uncertainty).

McLinden, Matthew; Piepmeier, Jeffrey

2013-01-01

330

Caribbean Radar Cases  

NSDL National Science Digital Library

This module presents radar case studies taken from events in the Caribbean that highlight radar signatures of severe weather. These cases include examples of deep convection, squall lines, bow echoes, tornadoes, and heavy rain resulting in flooding. Each case study includes a discussion of the conceptual models of each type of event as a review before showing the radar signatures and allowing the learner to analyze each one.

Comet

2013-12-31

331

Three-Dimensional Views of Titan's Diverse Surface Features from Cassini RADAR Stereogrammetry  

Microsoft Academic Search

Cassini RADAR has returned high resolution stereo images of dozens of areas on Titan. Digital topography extracted from the images provides new insight into lakes, dunes, mountains, flows, and other features including the enigmatic Ganesa Macula.

R. L. Kirk; E. Howington-Kraus; B. L. Redding; T. L. Becker; E. M. Lee; B. W. Stiles; S. Hensley; A. G. Hayes; R. M. C. Lopes; R. D. Lorenz; K. L. Mitchell; J. Radebaugh; F. Paganelli; L. A. Soderblom; E. R. Stofan; C. A. Wood; S. D. Wall

2009-01-01

332

Basic characteristics of FM-CW radar systems  

NASA Astrophysics Data System (ADS)

Due to rapid technological progress in real-time signal processing, FM-CW radar systems are expected to become a more serious competitor to pulse radar systems. This paper deals with basic radar principles such as modulating waveforms and ambiguity functions characteristics. Advantages and disadvantages of FM-CW radar systems are compared to pulse radar systems. The inherent signal processing used in FM-CW radar systems allows a flexible choice of system parameters. In this context aspects like sensitivity, range and velocity resolution are discussed. It is elucidated that the use of digital processors for signal processing (frequency determination, filtering, etc.) offers the possibility to exchange dedicated hardware solutions with software implementations. Attention is paid to equipment like the antennas, diplexer, transmitter and receiver, and to isolation problems between transmitter and receiver. Results of an experimental FM-CW research radar are shown. In addition, the future prospects of FM-CW radar, with the aerial and solid-state R.F. head-end integrated, are indicated.

Ligthart, L. P.; Nieuwkerk, L. R.; Vansinttruyen, J. S.

1986-07-01

333

The quadriphase code - A radar pulse compression signal with unique characteristics  

NASA Astrophysics Data System (ADS)

A unique class of radar signals (the quadriphase codes) which may be of use in pulse compression applications is described. The codes investigated are particularly attractive for radars using digital processing for Doppler filtering, pulse compression, and CFAR operation. The quadriphase code employs subpulses of half-cosine shape, resulting in a spectrum fall-off of 12 dB/octave.

Taylor, J. W., Jr.; Blinchikoff, H. J.

334

Comparação entre modelos digitais de elevação gerados por sensores ópticos e por radar  

Microsoft Academic Search

The aim of this paper is to compare the quality and accuracy of Digital Elevation Models (DEM) generated from different sources. Three different DEMs, covering the same geographic area (region of Uberaba, MG), are tentatively evaluated in this work. The first is a DEM derived from radar interferometry, through the Shuttle Radar Topographic Mission (SRTM). The other two are DEMs

Lucas de Melo Melgaço; Roberto de Souza; Michael Steinmayer; Caixa Postal; R. Felipe Neri

2005-01-01

335

A New Implementation of the Mellin Transform and its Application to Radar Classification of Ships  

Microsoft Academic Search

A modified Mellin transform for digital implementation is developed and applied to range radar profiles of naval vessels. The scale invariance property of the Mellin transform provides a means for extracting features from the profiles which are insensitive to the aspect angle of the radar. Past implementations of the Mellin transform based on the FFT have required exponential sampling, interpolation,

Philip E. Zwicke; Imre Kiss

1983-01-01

336

The Invisible Radar Triangle  

NSDL National Science Digital Library

Students learn about radar imaging and its various military and civilian applications that include recognition and detection of human-made targets, and the monitoring of space, deforestation and oil spills. They learn how the concepts of similarity and scaling are used in radar imaging to create three-dimensional models of various targets. Students apply the critical attributes of similar figures to create scale models of a radar imaging scenario using infrared range sensors (to emulate radar functions) and toy airplanes (to emulate targets). They use technology tools to measure angles and distances, and relate the concept of similar figures to real-world applications.

RET-ENET Program, Electrical Engineering Department,

337

Description and availability of airborne Doppler radar data  

NASA Technical Reports Server (NTRS)

An airborne, forward-looking, pulse, Doppler radar has been developed in conjunction with the joint FAA/NASA Wind Shear Program. This radar represents a first in an emerging technology. The radar was developed to assess the applicability of an airborne radar to detect low altitude hazardous wind shears for civil aviation applications. Such a radar must be capable of looking down into the ground clutter environment and extracting wind estimates from relatively low reflectivity weather targets. These weather targets often have reflectivities several orders of magnitude lower than the surrounding ground clutter. The NASA radar design incorporates numerous technological and engineering achievements in order to accomplish this task. The basic R/T unit evolved from a standard Collins 708 weather radar, which supports specific pulse widths of 1-7 microns and Pulse Repetition Frequencies (PRF) of less than 1-10 kHz. It was modified to allow for the output of the first IF signal, which fed a NASA developed receiver/detector subsystem. The NASA receiver incorporated a distributed, high-speed digital attenuator, producing a range bin to range bin automatic gain control system with 65 dB of dynamic range. Using group speed information supplied by the aircraft's navigation system, the radar signal is frequency demodulated back to base band (zero Doppler relative to stationary ground). The In-phase & Quadrature-phase (I/Q) components of the measured voltage signal are then digitized by a 12-bit A-D converter (producing an additional 36 dB of dynamic range). The raw I/Q signal for each range bin is then recorded (along with the current radar & aircraft state parameters) by a high-speed Kodak tape recorder.

Harrah, S. D.; Bracalente, E. M.; Schaffner, P. R.; Baxa, E. G.

1993-01-01

338

Improved HF183 Quantitative Real-Time PCR Assay for Characterization of Human Fecal Pollution in Ambient Surface Water Samples  

PubMed Central

Quantitative real-time PCR (qPCR) assays that target the human-associated HF183 bacterial cluster within members of the genus Bacteroides are among the most widely used methods for the characterization of human fecal pollution in ambient surface waters. In this study, we show that a current TaqMan HF183 qPCR assay (HF183/BFDrev) routinely forms nonspecific amplification products and introduce a modified TaqMan assay (HF183/BacR287) that alleviates this problem. The performance of each qPCR assay was compared in head-to-head experiments investigating limits of detection, analytical precision, predicted hybridization to 16S rRNA gene sequences from a reference database, and relative marker concentrations in fecal and sewage samples. The performance of the modified HF183/BacR287 assay is equal to or improves upon that of the original HF183/BFDrev assay. In addition, a qPCR chemistry designed to combat amplification inhibition and a multiplexed internal amplification control are included. In light of the expanding use of PCR-based methods that rely on the detection of extremely low concentrations of DNA template, such as qPCR and digital PCR, the new TaqMan HF183/BacR287 assay should provide more accurate estimations of human-derived fecal contaminants in ambient surface waters. PMID:24610857

Green, Hyatt C.; Haugland, Richard A.; Varma, Manju; Millen, Hana T.; Borchardt, Mark A.; Field, Katharine G.; Walters, William A.; Knight, R.; Sivaganesan, Mano; Kelty, Catherine A.

2014-01-01

339

Digital Libraries  

NSDL National Science Digital Library

This projects introduces digital libraries, digital initiatives, search techniques, and the Instructional Architect Review Rubric. Digital Library Information : The Scope of the Digital Library D-Lib Journal article, 1998 2008 Joint Conference on Digital Libraries (JCDL) Annual meeting devoted to Digital Libraries Initiatives : Digital Libraries Initiative The Initiative's focus is to dramatically advance the means to collect, store, and organize information in digital forms, and make it available for searching, retrieval, and processing via communication networks -- all in ...

Heather

2008-09-29

340

Noncooperative rendezvous radar system  

NASA Technical Reports Server (NTRS)

A fire control radar system was developed, assembled, and modified. The baseline system and modified angle tracking system are described along with the performance characteristics of the baseline and modified systems. Proposed changes to provide additional techniques for radar evaluation are presented along with flight test data.

1974-01-01

341

Micropower impulse radar  

Microsoft Academic Search

Invented and developed at LLNL (Lawrence Livermore National Laboratory), this inexpensive and highly sensitive radar system produces and samples extremely short pulses of energy. This novel technology is finding dozens of new uses in Laboratory programs and in sensor devices for homes, automobiles, factories, and hospitals. We have invented and patented a fundamentally different type of compact, low-power radar system

S. Azevedo; T. E. McEwan

1997-01-01

342

Radar illusion via metamaterials  

NASA Astrophysics Data System (ADS)

An optical illusion is an image of a real target perceived by the eye that is deceptive or misleading due to a physiological illusion or a specific visual trick. The recently developed metamaterials provide efficient approaches to generate a perfect optical illusion. However, all existing research on metamaterial illusions has been limited to theory and numerical simulations. Here, we propose the concept of a radar illusion, which can make the electromagnetic (EM) image of a target gathered by radar look like a different target, and we realize a radar illusion device experimentally to change the radar image of a metallic target into a dielectric target with predesigned size and material parameters. It is well known that the radar signatures of metallic and dielectric objects are significantly different. However, when a metallic target is enclosed by the proposed illusion device, its EM scattering characteristics will be identical to that of a predesigned dielectric object under the illumination of radar waves. Such an illusion device will confuse the radar, and hence the real EM properties of the metallic target cannot be perceived. We designed and fabricated the radar illusion device using artificial metamaterials in the microwave frequency, and good illusion performances are observed in the experimental results.

Jiang, Wei Xiang; Cui, Tie Jun

2011-02-01

343

Java Radar Analysis Tool  

NASA Technical Reports Server (NTRS)

Java Radar Analysis Tool (JRAT) is a computer program for analyzing two-dimensional (2D) scatter plots derived from radar returns showing pieces of the disintegrating Space Shuttle Columbia. JRAT can also be applied to similar plots representing radar returns showing aviation accidents, and to scatter plots in general. The 2D scatter plots include overhead map views and side altitude views. The superposition of points in these views makes searching difficult. JRAT enables three-dimensional (3D) viewing: by use of a mouse and keyboard, the user can rotate to any desired viewing angle. The 3D view can include overlaid trajectories and search footprints to enhance situational awareness in searching for pieces. JRAT also enables playback: time-tagged radar-return data can be displayed in time order and an animated 3D model can be moved through the scene to show the locations of the Columbia (or other vehicle) at the times of the corresponding radar events. The combination of overlays and playback enables the user to correlate a radar return with a position of the vehicle to determine whether the return is valid. JRAT can optionally filter single radar returns, enabling the user to selectively hide or highlight a desired radar return.

Zaczek, Mariusz P.

2005-01-01

344

Computing Ocean Surface Currents from Satellite Synthetic Aperture Radar Imagery  

NASA Astrophysics Data System (ADS)

Ocean surface currents play an important role in ocean-atmosphere interactions and global ocean circulation, and are also significant for fishing, ocean navigation, and search & rescue. Existing in-situ and remote sensing techniques for measuring ocean surface currents are limited by spatial and temporal data coverage, and thermal IR feature tracking methods are limited by clouds and weak thermal gradients. High-resolution spaceborne Synthetic Aperture Radar (SAR) offers repeatable cloud-penetrating measurements of the ocean surface. This research explores methods for ocean surface current measurement through satellite-based SAR. The major part of this research is concerned with the development and application of a semi-automated algorithm to generate ocean surface currents at ˜1.9 km resolution from sequential spaceborne C-band SAR intensity images using the Maximum Cross-Correlation(MCC) method. The primary geographical area of study is the coastal California Current System (CCS), and nearly two years (2008-2009) of 30-min lag data from the Envisat ASAR and ERS-2 AMI SAR sensors is analyzed. The velocity wavenumber spectrum of the derived MCC SAR currents agrees with the k-2 power law as predicted by submesoscale resolution models, and also shows seasonal mesoscale variability. The derived MCC SAR currents are validated against High frequency (HF) radar currents, and the two show some agreement in vector direction, with MCC SAR vectors oriented slightly anti-clockwise relative to HF radar vectors. The unimodal mean-symmetric residual histograms indicate that errors between the two datasets are random, except for a mean positive bias of ? 11 cm/s in MCC SAR currents relative to HF radar currents. This magnitude difference occurs primarily in the along-shore component ( ? 6 cm/s) and is negligible in the cross-shore component. Doppler Centroid Cross-Track (XT) radial currents from Envisat Wide Swath Mode (WSM) scenes are compared with HF radar radial currents, and are seen to have much larger extreme values, which is attributed to the Doppler wind correction process. Ignoring the extreme values, errors between the two datasets appear to be random, with a near-zero mean bias, and are also linked with the Doppler radial estimation errors attributed to model wind corrections. Comparison of Doppler radials with MCC SAR radials for two ? 12-hour lag cases also shows promising results. Finally, experiments conducted with TerraSAR-X experimental Dual Receive Aperture (DRA) mode Along-Track Interferometry (ATI) datasets suggest possible solutions for the absolute phase calibration problem using interferometric phase over ocean only.

Qazi, Waqas A.

345

HF sideband generation in the ionosphere  

SciTech Connect

The temporal development of sidebands excited near sunrise by two strong HF waves separated by a few hertz is presented. Sidebands are not observed before sunrise when the ionospheric critical frequency is less than the heater frequency. As the ionospheric density increases following sunrise and overdense conditions are established, strong sidebands emerge. Even though these results favor a mechanism which phase modulates the reflected HF wave over one which first downconverts the HF power to ULF before exciting sidebands, it is possible that either mechanism could at times contribute to sideband production. 8 refs.

Noble, S.T.; Gordon, W.E.; Duncan, L.M.; Mccoy, J.E. (Rice Univ., Houston, TX (USA); Los Alamos National Lab., NM (USA); NASA, Johnson Space Center, Houston, TX (USA))

1989-06-01

346

Equatorial MU Radar project  

NASA Astrophysics Data System (ADS)

Research Institute for Sustainable Humanosphere, Kyoto University (RISH) has been studying the atmosphere by using radars. The first big facility was the MU (Middle and Upper atmosphere) radar installed in Shiga, Japan in 1984. This is one of the most powerful and multi-functional radar, and is successful of revealing importance of atmospheric waves for the dynamical vertical coupling processes. The next big radar was the Equatorial Atmosphere Radar (EAR) installed at Kototabang, West Sumatra, Indonesia in 2001. The EAR was operated under close collaboration with LAPAN (Indonesia National Institute for Aeronautics and Space), and conducted the long-term continuous observations of the equatorial atmosphere/ionosphere for more than 10 years. The MU radar and the EAR are both utilized for inter-university and international collaborative research program for long time. National Institute for Polar Research (NIPR) joined EISCAT Scientific Association together with Nagoya University, and developed the PANSY radar at Syowa base in Antarctica as a joint project with University of Tokyo. These are the efforts of radar study of the atmosphere/ionosphere in the polar region. Now we can find that Japan holds a global network of big atmospheric/ionospheric radars. The EAR has the limitation of lower sensitivity compared with the other big radars shown above. RISH now proposes a plan of Equatorial MU Radar (EMU) that is to establish the MU-radar class radar next to the EAR. The EMU will have an active phased array antenna with the 163m diameter and 1055 cross-element Yagis. Total output power of the EMU will be more than 500kW. The EMU can detect turbulent echoes from the mesosphere (60-80km). In the ionosphere incoherent-scatter observations of plasma density, drift, and temperature would be possible. Multi-channel receivers will realize radar-imaging observations. The EMU is one of the key facilities in the project "Study of coupling processes in the solar-terrestrial system" for Master Plan 2014 of the Science Council of Japan (SCJ). We show the EMU project and its science in the presentation.

Yamamoto, Mamoru; Hashiguchi, H.; Tsuda, Toshitaka; Yamamoto, Masayuki

347

Digital Range Unit Theory of Operation and Circuit Description.  

National Technical Information Service (NTIS)

The report describes the experimental digital range unit used with the M-33D radar. The unit, designed and built for use with both the M-33D and Nike-Ajax radar sets, is part of the testing facility constructed at NOTS for the Surface Launched Weapon Cont...

K. O. Bryant, S. G. Valdivia

1965-01-01

348

Spaceborne weather radar  

NASA Technical Reports Server (NTRS)

The present work on the development status of spaceborne weather radar systems and services discusses radar instrument complementarities, the current forms of equations for the characterization of such aspects of weather radar performance as surface and mirror-image returns, polarimetry, and Doppler considerations, and such essential factors in spaceborne weather radar design as frequency selection, scanning modes, and the application of SAR to rain detection. Attention is then given to radar signal absorption by the various atmospheric gases, rain drop size distribution and wind velocity determinations, and the characteristics of clouds, as well as the range of available estimation methods for backscattering, single- and dual-wavelength attenuation, and polarimetric and climatological characteristics.

Meneghini, Robert; Kozu, Toshiaki

1990-01-01

349

Micropower impulse radar imaging  

SciTech Connect

From designs developed at the Lawrence Livermore National Laboratory (LLNL) in radar and imaging technologies, there exists the potential for a variety of applications in both public and private sectors. Presently tests are being conducted for the detection of buried mines and the analysis of civil structures. These new systems use a patented ultra-wide band (impulse) radar technology known as Micropower Impulse Radar (GPR) imaging systems. LLNL has also developed signal processing software capable of producing 2-D and 3-D images of objects embedded in materials such as soil, wood and concrete. My assignment while at LLNL has focused on the testing of different radar configurations and applications, as well as assisting in the creation of computer algorithms which enable the radar to scan target areas of different geometeries.

Hall, M.S.

1995-11-01

350

Laser radar improvements  

NASA Astrophysics Data System (ADS)

A short history of the uses of various laser radars is presented, and appropriate applications of laser and microwave radars are discussed. CO2 laser radar, operating at 10.6 microns, is considered for use in aircraft navigation systems, fire-control systems for armored vehicle and aircraft, missile guidance, severe storm research, line-of-sight command of missiles, wind turbine site surveys, clear-air turbulence monitors for aircraft, and satellite tracking. Microwave radar is all-weather, but is subject to multipath inaccuracies, countermeasures, and angular resolution limitations, so hybrid laser microwave systems look promising for microwave target acquisition and laser tracking. Advantages and disadvantages of the use of ruby, YAG, and CO2 lasers in varying atmospheric conditions are discussed. Development of a laser radar pod for obstacle detection, Doppler navigation, automatic terrain following, hover control, weapon delivery, and precision searching is noted.

Jelalian, A. V.

1981-11-01

351

The RITMARE coastal radar network and applications to monitor marine transport infrastructures  

NASA Astrophysics Data System (ADS)

Coastal radars provide information on the environmental state of oceans, namely maps of surface currents at time intervals of the order of one hour with spatial coverage of the order of several km, depending on the transmission frequency. The observations are of crucial importance for monitoring ports and ship tracks close to the coast, providing support for safe navigation in densely operated areas and fast response in case of accidents at sea, such as oil spill or search and rescue. Besides these applications, coastal radar observations provide fundamental support in MPAs surveillance, connectivity and marine population circulation. In the framework of the Italian RITMARE flagship project coordinated by CNR (Consiglio Nazionale delle Ricerche), a coastal radar network has been designed and implemented with a number of innovative characteristics. The network includes both HF and X-band radars, allowing coverage of wide areas with different spatial and temporal resolutions. HF radars cover up to 80 km with a spatial resolution ranging between 1 and 5 km, while X-band radars provide 5 km coverage with a spatial resolution of 10 m. Joining these two capabilities, the RITMARE coastal radar network enables both a highly effective coverage of wide coastal areas and integrated monitoring of different phenomena, thus allowing the collection of current and wave parameters and detection of bathymetries of both open sea and coastal areas. A dedicated action to foster interoperability among data providers has been undertaken within RITMARE; an IT framework is under development to provide software tools for data collection and data sharing. It suggests standard, data format definitions, Quality Control strategies, data management and dissemination policies. In particular, the implementation of tools exploits both standards of OGC (Open Geospatial Consortium) and web services offered to manage, access and deliver geospatial data. Radar data produced in RITMARE by the coastal radar network represent a challenge to the nowadays definition of OGC web services: the network will suggest and test solutions.

Carrara, Paola; Corgnati, Lorenzo; Cosoli, Simone; Griffa, Annalisa; Kalampokis, Alkiviadis; Mantovani, Carlo; Oggioni, Alessandro; Pepe, Monica; Raffa, Francesco; Serafino, Francesco; Uttieri, Marco; Zambianchi, Enrico

2014-05-01

352

4. VIEW NORTHEAST, radar tower (unknown function), prime search radar ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

4. VIEW NORTHEAST, radar tower (unknown function), prime search radar tower, emergency power building, and height finder radar tower - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

353

5. VIEW EAST, height finder radar towers, radar tower (unknown ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. VIEW EAST, height finder radar towers, radar tower (unknown function), prime search radar tower, operations building, and central heating plant - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

354

Spectral characteristics of High Frequency (HF) backscatter for high latitude ionospheric irregularities: Preliminary analysis of statistical properties  

NASA Astrophysics Data System (ADS)

OTH-B radar signals backscattered from ionospheric irregularities can be very intense, and any effort to mitigate against their influence requires knowledge of at least the Doppler shift and spread that they introduce in the backscattered signals. This report presents the Doppler spectral characteristics of HF signals backscattered from F-region ionospheric irregularities at high latitudes. The report will show that the variability in spread of the Doppler returns make it difficult to discriminate against ionospheric clutter by Doppler techniques alone. The data presented have been obtained with the Johns Hopkins University/Applied Physics Laboratory (APL) HF radar located at Goose Bay, Labrador. This is an auroral site and signals from the radar are subjected to ionospheric clutter from magnetic-field-aligned irregularities at high latitudes. The report discusses the various procedures that may be used for spectral and/or autocorrelation analysis of backscattered radar signals, the method by which these autocorrelation functions are obtained to remove contributions from ground backscatter and unwanted signal sources. The autocorrelation functions are analyzed to determine their decorrelation time and finally, the parameters are converted to Doppler velocity width and shift.

Baker, K. B.; Greenwald, R. A.; Villian, J. P.; Wing, S.

1988-07-01

355

Statistical gamma transitions in {sup 174}Hf  

SciTech Connect

Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S. [Rutgers--the State Univ., New Brunswick, NJ (United States); Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T. [Argonne National Lab., IL (United States); Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U. [Notre Dame Univ., IN (United States); Kaplan, M.S.; Saladin, J.X.; Winchell, D. [Pittsburgh Univ., PA (United States)

1992-08-01

356

Statistical gamma transitions in sup 174 Hf  

SciTech Connect

Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S. (Rutgers--the State Univ., New Brunswick, NJ (United States)); Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T. (Argonne National Lab., IL (United States)); Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U. (Notre Dame Univ., IN (United States)); Kaplan, M.S.; Saladin, J.X.; Winchell, D. (Pittsburgh Univ., PA (Un

1992-01-01

357

A model for simulation and processing of radar images  

NASA Technical Reports Server (NTRS)

A model for recording, processing, presentation, and analysis of radar images in digital form is presented. The observed image is represented as having two random components, one which models the variation due to the coherent addition of electromagnetic energy scattered from different objects in the illuminated areas. This component is referred to as fading. The other component is a representation of the terrain variation which can be described as the actual signal which the radar is attempting to measure. The combination of these two components provides a description of radar images as being the output of a linear space-variant filter operating on the product of the fading and terrain random processes. In addition, the model is applied to a digital image processing problem using the design and implementation of enhancement scene. Finally, parallel approaches are being employed as possible means of solving other processing problems such as SAR image map-matching, data compression, and pattern recognition.

Stiles, J. A.; Frost, V. S.; Shanmugam, K. S.; Holtzman, J. C.

1981-01-01

358

High performance ground penetrating radar survey of TA-49/Area 2. Final report  

SciTech Connect

The results of high performance ground penetrating radar study of Area 2 at Technical Area 49 are presented. The survey was commissioned as part of Los Alamos Laboratory`s continuing Environmental Remediation program and was completed and analyzed before borehole studies in Area 2 were started. Based upon the ground penetrating radar results, the location of one of the planned boreholes was moved to assure the drilling area was as safe as possible. While earlier attempts to use commercial radar devices at this facility had not been successful, the radar and digital processing system developed at Los Alamos were able to significantly improve the buried physical detail of the site.

Hoeberling, R.F. [Los Alamos National Lab., NM (United States); Rangel, M.J. III [Analysis Programming Processing Instrumentation, Santa Barbara, CA (United States)

1994-09-01

359

Radar image enhancement and simulation as an aid to interpretation and training  

NASA Technical Reports Server (NTRS)

Greatly increased activity in the field of radar image applications in the coming years demands that techniques of radar image analysis, enhancement, and simulation be developed now. Since the statistical nature of radar imagery differs from that of photographic imagery, one finds that the required digital image processing algorithms (e.g., for improved viewing and feature extraction) differ from those currently existing. This paper addresses these problems and discusses work at the Remote Sensing Laboratory in image simulation and processing, especially for systems comparable to the formerly operational SEASAT synthetic aperture radar.

Frost, V. S.; Stiles, J. A.; Holtzman, J. C.; Dellwig, L. F.; Held, D. N.

1980-01-01

360

Model for optimal parallax in stereo radar imagery  

NASA Technical Reports Server (NTRS)

Simulated stereo radar imagery is used to investigate parameters for a spaceborne imaging radar. Incidence angles ranging from small to intermediate to large are used with three digital terrain model areas which are representative of relatively flat, moderately rough, and mountaneous terrain. The simulated radar imagery was evaluated by interpreters for ease of stereo perception and information content, and rank ordered within each class of terrain. The interpreter's results are analyzed for trends between the height of a feature and either parallax or vertical exaggeration for a stereo pair. A model is developed which predicts the amount of parallax (or vertical exaggeration) an interpreter would desire for best stereo perception of a feature of a specific height. Results indicate the selection of angle of incidence and stereo intersection angle depend upon the relief of the terrain. Examples of the simulated stereo imagery are presented for a candidate spaceborne imaging radar having four selectable angles of incidence.

Pisaruck, M. A.; Kaupp, V. H.; Macdonald, H. C.; Waite, W. P.

1984-01-01

361

The evolution of the SEASAT imaging radar  

NASA Technical Reports Server (NTRS)

The paper describes the design parameters and development of a synthetic aperture radar for use on the SEASAT spacecraft. This imaging radar is designed to operate at altitudes of 800 km with an orbital inclination of 108 deg, a nominal resolution of 25 m, and a swath width of 100 km. The design evolved from planetary imaging radar studies conducted over many years where an L-band imaging radar was developed and tested on aircraft flights as a prototype system to map the surface of Venus. A solid-state transmitter is used where the pulse repetition frequency is a function of altitude and will be about 2kHz for a 12-m long antenna. The receiver consists of the receiver protector, input filters, the gain control, and the RF amplifier. The ground station uses the standard NASA receiver with a 10-m antenna. The correlator, either optical or digital, must be able to compensate for the pitch and yaw variations of the spacecraft as well as the inherent effective yaw caused by the rotation of the earth, and extract the range curvature and range walk effects.

Brown, W. E., Jr.

1975-01-01

362

Band-partitioned sidelobe canceller for a wideband radar  

Microsoft Academic Search

A generic electronic counter-counter measure (ECCM) system consisting of band-partitioned (BP) sidelobe canceller (SLC) is investigated for wideband radar. This paper describes trade-off studies performed on the BP digital SLC and identifies techniques and parameters that are capable of providing improved cancellation performance.

Feng-ling C. Lin; Karl Gerlach; Michael L. Picciolo

2003-01-01

363

Acceleration and deformation measurements using coherent laser radar  

Microsoft Academic Search

A solid state coherent laser radar system was employed to measure accelerations and\\/or deformations of metal foils. The foils were ablatively accelerated by a short laser pulse to velocities of approximately 1 km\\/s. Velocity profiles were determined by digitizing the chirped waveform produced by the target as its velocity changes. This waveform was analyzed to determine the Doppler shift as

M. G. Roe; A. L. Huston; B. L. Justus

1990-01-01

364

Design and calibration of a CW coherent laser radar  

Microsoft Academic Search

The design, calibration and performance of a CW coherent laser radar testbed system is described. Detector responsiveness and detector noise in a heterodyne system is considered. A detailed evaluation of beam propagation and phase front matching is given. The final system is supplemented with a digital image memory, a galvanometer scanner and a boresighted TV camera. Analysis of images obtained

T. Claesson; K. Gullberg; D. Letalick; I. Renhorn; O. Steinvall; A. Widen

1984-01-01

365

Discrimination of geophysical phenomena in satellite radar interferograms  

Microsoft Academic Search

Various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar (SAR) images. The fringes generated by the topographic relief can be removed using a digital elevation model (DEM). The remaining fringes map the change in satellite-to-ground range which occurred between the acquisition times of the two images. By comparing different pairs of images spanning

Didier Massonnet; Kurt L. Feigl

1995-01-01

366

Improving the detection limit for 182Hf  

Microsoft Academic Search

A nearby supernova would deposit radionuclides on earth. The long-lived radionuclide 182Hf (t1\\/2=8.9Ma) is one of a number of candidates for an isotopic signature of such an event. Together with 60Fe, observation of 182Hf would be direct evidence for a supernova site of the r-process. The most suitable site for searching for such a signature would be a deep-sea sediment

S. Winkler; L. K. Fifield; S. G. Tims; C. R. Morton

2007-01-01

367

Improving the detection limit for 182Hf  

Microsoft Academic Search

A nearby supernova would deposit radionuclides on earth. The long-lived radionuclide 182Hf (t1\\/2 = 8.9 Ma) is one of a number of candidates for an isotopic signature of such an event. Together with 60Fe, observation of 182Hf would be direct evidence for a supernova site of the r-process. The most suitable site for searching for such a signature would be

S. Winkler; L. K. Fifield; S. G. Tims; C. R. Morton

2007-01-01

368

HF (High Frequency) absolute time of arrival sensing  

NASA Astrophysics Data System (ADS)

In late 1980 questions arose concerning whether the ionosphere was sufficiently stable to allow precisely measured time of arrival of skywave signals to be used for geolocation in the high frequency (HF) band between 2 and 32 MHz. The chief limitation in the accuracy of this type of system is the amount of uncertainty in the ionospheric height estimation and its temporal stability. Traditional ionospheric research resources did not address the issue in sufficient detail and time resolution to be of any assistance. In order to understand the exact nature of the ionospheric uncertainties and to quantify their extent, experimentation was proposed to sense the variation in the refraction height of the ionosphere as it relates to the time of arrival of the HF signal. The objective of this work was to determine the range of environmentally induced errors in a skywave Time Difference of Arrival (TDOA) measurement, thereby bounding the ultimate geolocation accuracy one could expect from this technique. The first experimental measurement system started operation in early 1981. This effort involved establishing a continuous absolute Time of Arrival (TOA) experiment over the one-hop midlatitude path between San Diego, California and Fort Collins, Colorado. The system is fully digital and stabilized with a cesium beam standard. This work was supplemented with vertical incidence sounder data at both ends of the path, a collateral Doppler sensing system, and coincident satellite solar data.

Rose, R. B.

1986-02-01

369

Spaceborne meteorological radar studies  

NASA Technical Reports Server (NTRS)

Various radar designs and methods are studied for the estimation of rainfall parameters from space. An immediate goal is to support the development of the spaceborne radar that has been proposed for the Tropical Rain Measuring Mission (TRMM). The effort is divided into two activities: a cooperative airborne rain measuring experiment with the Radio Research Laboratory of Japan (RRL), and the modelling of spaceborne weather radars. An airborne rain measuring experiment was conducted at Wallops Flight Facility in 1985 to 1986 using the dual-wavelength radar/radiometer developed by RRL. The data are presently being used to test a number of methods that are relevant to spaceborne weather radars. An example is shown of path-averaged rain rates as estimated from three methods: the standard reflectivity rain rate method (Z-R), a dual-wavelength method, and a surface reference method. The results from the experiment shows for the first time the feasibility of using attenuation methods from space. The purposes of the modelling are twofold: to understand in a quantitative manner the relationships between a particular radar design and its capability for estimating precipitation parameters and to help devise and test new methods. The models are being used to study the impact of various TRMM radar designs on the accuracy of rain rate estimation as well as to test the performance of range-profiling algorithms, the mirror-image method, and some recently devised graphical methods for the estimation of the drop size distribution.

Meneghini, R.

1988-01-01

370

Planetary Radar Astronomy  

NASA Technical Reports Server (NTRS)

Radar is a powerful technique that has furnished otherwise unavailable information about solar system bodies for three decades. The advantages of radar in planetary astronomy result from: (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice. Planetary radar astronomy has primarily involved observations with Earth-based radar telescopes, but also includes some experiments with a spaceborne transmitter or receiver. In addition to providing a wealth of information about the geological and dynamical properties of asteroids, comets, the inner planets, and natural satellites, radar experiments have established the scale of the solar system, have contributed significantly to the accuracy of planetary ephemerides, and have helped to constrain theories of gravitation. This review outlines radar astronomical techniques and describes principal observational results.

Ostro, Steven J.

1993-01-01

371

Space object observation with radar  

NASA Astrophysics Data System (ADS)

FGAN developed a High Power Radar System, able to track and image low Earth orbiting objects, for experimental radar research. The system is unique in Germany; it consists of a narrow band tracking radar and a high resolution imaging radar. The radars are supported from one 34-m parabolic dish antenna. They operate simultaneously on the object of interest. All information which a radar can gain about physical characteristics of targets have to be extracted from the backscattered electromagnetic field of transmitted pulses. L-band tracking data provide information on range, range rate, angular direction, and radar cross-section. From high resolution polarimetric Ku-band radar data projections of the 1- and 2-dimensional scatter centre distributions are computed. This paper gives a brief description of the FGAN radar and summarizes some radar based methods for orbit analysis, orbital lifetime prediction, reconstruction of object images, assessment of object dimensions, shape, attitude, and mass.

Mehrholz, D.

1993-08-01

372

Holographic surveillance radar  

NASA Astrophysics Data System (ADS)

Since the 1940s, radar development has focused on narrow-beam, scanning sensors. A wide field of view has advantages in terms of extended acquisition time for any target, and when combined with a high Doppler sampling frequency can yield high-resolution Doppler spectra. Unambiguous range and Doppler can be achieved under certain circumstances, resulting in enhanced ability to evaluate the characteristics of targets and clutter. Holographic radar has a range of applications in which the ability to discriminate targets among clutter is key. An example of such an application is in mitigation of wind farm interference with Air Traffic Control radar.

Oswald, Gordon K. A.

2009-05-01

373

Space Radar Image of Rocky Mountains, Montana  

NASA Technical Reports Server (NTRS)

This is a three-dimensional perspective of the eastern front range of the Rocky Mountains, about 120 kilometers (75 miles) west of Great Falls, Montana. The image was created by combining two spaceborne radar images using a technique known as interferometry. Visualizations like this are useful to scientists because they show the shapes of the topographic features such as mountains and valleys. This technique helps to clarify the relationships of the different types of materials on the surface detected by the radar. The view is looking south-southeast. Along the right edge of the image is the valley of the north fork of the Sun River. The western edge of the Great Plains appears on the left side. The valleys in the lower center, running off into the plains on the left, are branches of the Teton River. The highest mountains are at elevations of 2,860 meters (9,390 feet), and the plains are about 1,400 meters (4,500 feet) above sea level. The dark brown areas are grasslands, bright green areas are farms, light brown, orange and purple areas are scrub and forest, and bright white and blue areas are steep rocky slopes. The two radar images were taken on successive days by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on board the space shuttle Endeavour in October 1994. The digital elevation map was produced using radar interferometry, a process in which radar data are acquired on different passes of the space shuttle. The two data passes are compared to obtain elevation information. Radar image data are draped over the topography to provide the color with the following assignments: red is L-band vertically transmitted, vertically received; green is C-band vertically transmitted, vertically received; and blue are the differences seen in the L-band data between the two days. This image is centered near 47.7 degrees north latitude and 112.7 degrees west longitude. No vertical exaggeration factor has been applied to the data. SIR-C/X-SAR, a joint mission of the German, Italian and United States space agencies, is part of NASA's program entitled Mission to Planet Earth.

1994-01-01

374

Earth resources shuttle imaging radar. [systems analysis and design analysis of pulse radar for earth resources information system  

NASA Technical Reports Server (NTRS)

A report is presented on a preliminary design of a Synthetic Array Radar (SAR) intended for experimental use with the space shuttle program. The radar is called Earth Resources Shuttle Imaging Radar (ERSIR). Its primary purpose is to determine the usefulness of SAR in monitoring and managing earth resources. The design of the ERSIR, along with tradeoffs made during its evolution is discussed. The ERSIR consists of a flight sensor for collecting the raw radar data and a ground sensor used both for reducing these radar data to images and for extracting earth resources information from the data. The flight sensor consists of two high powered coherent, pulse radars, one that operates at L and the other at X-band. Radar data, recorded on tape can be either transmitted via a digital data link to a ground terminal or the tape can be delivered to the ground station after the shuttle lands. A description of data processing equipment and display devices is given.

1975-01-01

375

The 94 GHz MMW imaging radar system  

NASA Technical Reports Server (NTRS)

The 94 GHz MMW airborne radar system that provides a runway image in adverse weather conditions is now undergoing tests at Wright-Patterson Air Force Base (WPAFB). This system, which consists of a solid state FMCW transceiver, antenna, and digital signal processor, has an update rate of 10 times per second, 0.35x azimuth resolution and up to 3.5 meter range resolution. The radar B scope (range versus azimuth) image, once converted to C scope (elevation versus azimuth), is compatible with the standard TV presentation and can be displayed on the Head Up Display (HUD) or Head Down Display (HDD) to aid the pilot during landing and takeoff in limited visibility conditions.

Alon, Yair; Ulmer, Lon

1993-01-01

376

Caribbean Radar Products  

NSDL National Science Digital Library

This module provides examples of radar imagery from various locations in the Caribbean to demonstrate the different types of images available. Also, examples of different meteorological and non meteorological features are presented to show features seen in island locations.

Comet

2013-12-31

377

Radar Calibration Test Satellite  

Microsoft Academic Search

A satellite has been designed for application to radar calibration. Electromagnetic and mechanical characteristics of the satellite and their influence on the selection of shape and other parameters are discussed. Theoretical and experimental scattering data are included.

L. J. Kaplan; J. F. A. Ormsby; EVERT N. FOWLE; KENT R. JOHNSON; Richard T. Bates; S. H. Bickel

1969-01-01

378

A smart radar absorber  

Microsoft Academic Search

This paper proposes a configuration for a smart radar absorber which is capable of both self-tuning and absorb while scan operation. The discussion is complemented by modelled and measured performance data.

Barry Chambers

1999-01-01

379

Laser Radar Animation  

NASA Video Gallery

Laser and radar instruments aboard NASA aircraft provide measurements of the snow and ice surface and down to the bedrock under the ice. Lasers, with a shorter wavelength, measure the surface eleva...

380

Investigation of the differences in stability of the OCxxxHF and COxxxHF complexes  

SciTech Connect

The structure and energetics of the isomeric H-bonded complexes OCxxxHF and COxxxHF have been investigated by ab initio molecular orbital theory and by natural bond orbital analysis. Only with the inclusion of electron correlation is a significant preference for the experimentally observed OCxxxHF isomer found. The large effect of correlation upon the relative stability of the two isomers is apparently entirely an electrostatic effect caused by the correlation-induced sign reversal of the dipole moment of CO. Nevertheless, a molecular multipole expansion is found inadequate to account for the principal features of these H-bonded complexes and their relative stability. Contrary to a recent study, we find that ''charge transfer'' effects are highly significant contributions to the binding in these complexes. The differences in stability of OCxxxHF and COxxxHF are attributed primarily to differences in the interaction of carbon and oxygen lone pairs of CO donating into the unfilled antibond on HF, i.e., to differences in n/sub C/..-->..sigma/sub HF/( and n/sub O/..-->..sigma/sub HF/( matrix elements.

Curtiss, L.A.; Pochatko, D.J.; Reed, A.E.; Weinhold, F.

1985-03-15

381

Soil moisture detection from radar imagery of the Phoenix, Arizona test site  

NASA Technical Reports Server (NTRS)

The Environmental Research Institute of Michigan (ERIM) dual-polarization X and L band radar was flown to acquire radar imagery over the Phoenix (Arizona) test site. The site was covered by a north-south pass and an east-west pass. Radar response to soil moisture was investigated. Since the ERIM radar does not have accurately measured antenna patterns, analysis of the L band data was performed separately for each of several strips along the flight line, each corresponding to a narrow angle of incidence. For the NS pass, good correlation between the radar return and mositure content was observed for each of the two nearest (to nadir) angular ranges. At higher angular ranges, no correlation was observed. The above procedure was not applied to the EW pass due to flight path misalignments. The results obtained stress the importance of radar calibration, the digitization process, and the angle of incidence.

Cihlar, J.; Ulaby, F. T.; Mueller, R.

1975-01-01

382

Phased-array radars  

NASA Astrophysics Data System (ADS)

The operating principles, technology, and applications of phased-array radars are reviewed and illustrated with diagrams and photographs. Consideration is given to the antenna elements, circuitry for time delays, phase shifters, pulse coding and compression, and hybrid radars combining phased arrays with lenses to alter the beam characteristics. The capabilities and typical hardware of phased arrays are shown using the US military systems COBRA DANE and PAVE PAWS as examples.

Brookner, E.

1985-02-01

383

Downhole pulse radar  

DOEpatents

A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole. 7 figs.

Chang, Hsi-Tien

1987-09-28

384

Downhole pulse radar  

DOEpatents

A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole.

Chang, Hsi-Tien (Albuquerque, NM)

1989-01-01

385

An experimental adaptive radar MTI filter  

NASA Astrophysics Data System (ADS)

The theoretical and practical features of a self-adaptive filter designed to remove clutter noise from a radar signal are described. The hardware employs an 8-bit microprocessor/fast hardware multiplier combination along with analog-digital and digital-analog interfaces. The software here is implemented in assembler language. It is assumed that there is little overlap between the signal and the noise spectra and that the noise power is much greater than that of the signal. It is noted that one of the most important factors to be considered when designing digital filters is the quantization noise. This works to degrade the steady state performance from that of the ideal (infinite word length) filter. The principal limitation of the filter described here is its low sampling rate (1.72 kHz), due mainly to the time spent on the multiplication routines. The methods discussed here, however, are general and can be applied to both traditional and more complex radar MTI systems, provided that the filter sampling frequency is increased. Dedicated VLSI signal processors are seen as holding considerable promise.

Gong, Y. H.; Cooling, J. E.

386

On wave radar measurement  

NASA Astrophysics Data System (ADS)

The SAAB REX WaveRadar sensor is widely used for platform-based wave measurement systems by the offshore oil and gas industry. It offers in situ surface elevation wave measurements at relatively low operational costs. Furthermore, there is adequate flexibility in sampling rates, allowing in principle sampling frequencies from 1 to 10 Hz, but with an angular microwave beam width of 10° and an implied ocean surface footprint in the order of metres, significant limitations on the spatial and temporal resolution might be expected. Indeed there are reports that the accuracy of the measurements from wave radars may not be as good as expected. We review the functionality of a WaveRadar using numerical simulations to better understand how WaveRadar estimates compare with known surface elevations. In addition, we review recent field measurements made with a WaveRadar set at the maximum sampling frequency, in the light of the expected functionality and the numerical simulations, and we include inter-comparisons between SAAB radars and buoy measurements for locations in the North Sea.

Ewans, Kevin; Feld, Graham; Jonathan, Philip

2014-09-01

387

Sporadic E ionization layers observed with radar imaging and ionospheric modification  

NASA Astrophysics Data System (ADS)

Sporadic E ionization layers have been observed in the daytime subauroral ionospheric E layer by a 30 MHz radar in Alaska. The radar detects coherent backscatter from meter-scale field-aligned plasma density irregularities. The irregularities were generated by ionospheric modification—by the emission of strong HF electromagnetic waves directly beneath the layers—making the layers visible to the radar. Aperture-synthesis methods are used to generate imagery of the layers from the radar data. The layers are patchy, with patches organized along fronts spaced by tens of kilometers and propagating slowly toward the southwest. Similar, naturally occurring layers are commonly observed at middle latitudes at night in the absence of ionospheric modification. That the patchy layers can be found at high magnetic latitudes during the day argues that they are most likely produced through the interaction of the ionospheric layer with neutral atmospheric waves and instabilities. Attenuation of the radar echoes when the HF emission frequency exceeded the third harmonic of the electron gyrofrequency was observed and is discussed.

Hysell, D. L.; Munk, J.; McCarrick, M.

2014-10-01

388

Target identification by means of impulse radar  

NASA Astrophysics Data System (ADS)

The scattering interaction of short electromagnetic pulses with a spherical target is studied. The target is assumed penetrable and is modeled as an air-filled dielectric shell. The radar cross-section (RCS) of such a target is obtained and its resonance features are analyzed. A dielectric composition makes the resonance features become very prominent compared with the case of an ideally conducting sphere. When the interrogating waveform is a pulse of short duration, the resonance features of the backscattering cross-section can be extracted within the frequency band of the incident pulse. To verify theoretical predictions, spherical targets were illuminated with short broad-band pulses using an impulse radar system. The actual shape of the pulse that is incident on the target is theoretically modeled using a digital filter design techniques, and the predicted backscattered returns of spherical targets are compared with selected echoes of the pulses transmitted by the impulse radar. The authors verify that the shape of the predicted backscattered pulse that results from the design method agrees well with the experimental findings using metal spheres of three different sizes. By means of an incident pulse of designed shape, the form-function in the backscattering radar cross-section of a dielectric target is predicted using a discrete Fourier transform (DFT) technique. It is shown that many of the resonance features of a dielectric spherical shell can be extracted from the frequency band of the incident pulse employing this method. The methodology that is developed can handle broadband pulses of any sufficiently smooth spectrum, interacting with (lossy or lossless) dielectric scatterers, and can extract the resonance features within the frequency band of the transmitted pulse. Accordingly, this methodology could also be used for assessing the performance of high-power impulse radar systems.

Abrahamson, Steffan; Brusmark, B.; Gaunaurd, Guillermo C.; Strifors, Hans C.

1991-08-01

389

SEMICONDUCTOR PHYSICS: Effect of annealing on characteristics of a HfOxNy-HfO2-HfOxNy sandwich stack compared with HfO2 film  

NASA Astrophysics Data System (ADS)

HfOxNy-HfO2-HfOxNy sandwich-stack (SS) film was investigated in comparison with HfO2 film of the same thickness. Higher thermal stability and better surface morphology can be observed for the SS film. This structure also shows stronger immunity to interfacial oxidation compared with HfO2 film. Meanwhile, unlike the HfOxNy dielectric, the capacitance performance of SS film was not worse (but was even better) than a pure HfO2 film of the same thickness. The SS structure appears to be a promising high-k gate dielectric compared with both pure HfOxNy and HfO2 dielectrics for future ULSI devices. Additionally, PDA treatment plays an important role in improving the characteristics of SS film, which is confirmed by effective channel electron mobility and stress induced leakage current (SILC) investigations.

Yan, Zhang; Ran, Jiang

2009-08-01

390

Digital materials for digital fabrication  

E-print Network

This thesis introduces digital materials by analogy with digital computation and digital communications. Traditional fabrication techniques include pick-and-place, roll-to-roll, molding, patterning and more. Current research ...

Popescu, George A

2007-01-01

391

A statistical approach for determining radiometric precisions and accuracies in the calibration of synthetic aperture radar imagery  

Microsoft Academic Search

A model that estimates a relative error bound for the radiometric calibration of synthetic aperture radar (SAR) imagery is presented. This model is based on a statistical `Coefficient of Variation of Error Model', which produces a relative error bound by propagating the measured or estimated uncertainties in the radar system parameters utilized to correct digitally processed SAR image intensity values.

E. S. Kasischke; G. W. Fowler

1989-01-01

392

Common volume coherent and incoherent scatter radar observations of sporadic E layers  

NASA Astrophysics Data System (ADS)

Nearly all the available observations of quasi-periodic (QP) echoes associated with sporadic E layers have used coherent scatter radars operating in the HF or VHF range. Such radar observations have provided extensive measurements of the range rates, Doppler shifts, and apparent altitudes of the echoing regions, but the interpretation of the measurements is not always clear. During June and July 2003, a 30-MHz coherent scatter radar was operated on St. Croix in the Virgin Islands so that it had a common observing volume with the Arecibo Observatory 430-MHz incoherent scatter radar at E-region altitudes above Puerto Rico. The Arecibo radar provided high-resolution altitude profiles of the electron density structure within the regions where the coherent scatter radar detected QP echoes. Furthermore, the Arecibo radar was scanned in azimuth during some of the observation periods to map out the horizontal structure within the scattering layers. The relationship between the two sets of measurements will be discussed and data from several sample nights will be presented.

Larsen, M.; Hysell, D.; Zhou, Q.

2003-04-01

393

Removal of uranium from aqueous HF solutions  

DOEpatents

This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separting the solution from the settled particulates. The CaF.sub.2 is selected to have a nitrogen surface area in a selected range and is employed in an amount providing a calcium fluoride/uranium weight ratio in a selected range. As applied to dilute HF solutions containing 120 ppm uranium, the method removes at least 92% of the uranium, without introducing contaminants to the product solution.

Pulley, Howard (West Paducah, KY); Seltzer, Steven F. (Paducah, KY)

1980-01-01

394

Imaging Radar in the Mojave Desert-Death Valley Region  

NASA Technical Reports Server (NTRS)

The Mojave Desert-Death Valley region has had a long history as a test bed for remote sensing techniques. Along with visible-near infrared and thermal IR sensors, imaging radars have flown and orbited over the area since the 1970's, yielding new insights into the geologic applications of these technologies. More recently, radar interferometry has been used to derive digital topographic maps of the area, supplementing the USGS 7.5' digital quadrangles currently available for nearly the entire area. As for their shorter-wavelength brethren, imaging radars were tested early in their civilian history in the Mojave Desert-Death Valley region because it contains a variety of surface types in a small area without the confounding effects of vegetation. The earliest imaging radars to be flown over the region included military tests of short-wavelength (3 cm) X-band sensors. Later, the Jet Propulsion Laboratory began its development of imaging radars with an airborne sensor, followed by the Seasat orbital radar in 1978. These systems were L-band (25 cm). Following Seasat, JPL embarked upon a series of Space Shuttle Imaging Radars: SIRA (1981), SIR-B (1984), and SIR-C (1994). The most recent in the series was the most capable radar sensor flown in space and acquired large numbers of data swaths in a variety of test areas around the world. The Mojave Desert-Death Valley region was one of those test areas, and was covered very well with 3 wavelengths, multiple polarizations, and at multiple angles. At the same time, the JPL aircraft radar program continued improving and collecting data over the Mojave Desert Death Valley region. Now called AIRSAR, the system includes 3 bands (P-band, 67 cm; L-band, 25 cm; C-band, 5 cm). Each band can collect all possible polarizations in a mode called polarimetry. In addition, AIRSAR can be operated in the TOPSAR mode wherein 2 antennas collect data interferometrically, yielding a digital elevation model (DEM). Both L-band and C-band can be operated in this way, with horizontal resolution of about 5 m and vertical errors less than 2 m. The findings and developments of these earlier investigations are discussed.

Farr, Tom G.

2001-01-01

395

Precision aided inertial navigation using SAR and digital map data  

Microsoft Academic Search

The authors describe a novel scheme for obtaining position update information for an inertial navigation system through the use of imagery from a synthetic aperture radar (SAR) sensor and an onboard digital map database. Updated information is obtained through comparison of the locations of terrain features extracted from the SAR imagery with locations predicted using the digital map and current

J. E. Bevington; C. A. Marttila

1990-01-01

396

Digital Preservation.  

ERIC Educational Resources Information Center

Reviews research on digital preservation issues, including born-digital and digitally recreated documents. Discusses electronic records research; metadata and other standards; electronic mail; Web-based documents; moving images media; selection of materials for digitization, including primary sources; administrative issues; media stability…

Yakel, Elizabeth

2001-01-01

397

Digital printing  

Microsoft Academic Search

Digital printing is described as a tool to replace conventional printing machines completely. Still this goal was not reached until now with any of the digital printing technologies to be described in the paper. Productivity and costs are still the main parameters and are not really solved until now. Quality in digital printing is no problem anymore. Definition of digital

Werner K. Sobotka

1997-01-01

398

Microwave emissions from police radar  

E-print Network

The purpose of this study was to evaluate police officers exposures to microwaves emitted by traffic radar units at the ocular and testicular level. Additionally, comparisons were made of the radar manufacturers published maximum power density...

Fink, John Michael

2012-06-07

399

Venus wind-altitude radar  

NASA Technical Reports Server (NTRS)

A design study on adding a radar altimeter to the Pioneer Venus small probe is review. Block and timing diagrams are provided. The inherent and interface ambiguities, resolution, and data handling logic for radar altimeters are described.

Levanon, N.

1974-01-01

400

Phase modulating the Urbana radar  

NASA Technical Reports Server (NTRS)

The design and operation of a switched phase modulation system for the Urbana Radar System are discussed. The system is implemented and demonstrated using a simple procedure. The radar system and circuits are described and analyzed.

Herrington, L. J., Jr.; Bowhill, S. A.

1983-01-01

401

Special applications of radar systems  

Microsoft Academic Search

Developments at Dornier in radar equipment are discussed. Characteristics of the Tasyll-1 scoring system for air target simulation are examined with emphasis on the Doppler radar principle for missile location. The RADOBS-R (Radar-object shield panorama sensor) system creates a ring-shaped alarm zone around an object for protection and has an operating frequency around 14 GHz. A Synthetic Aperture Radar and

U. Knepper; R. Kremer; H. Lamprecht; R. Schotter

1980-01-01

402

Radar data smoothing filter study  

NASA Technical Reports Server (NTRS)

The accuracy of the current Wallops Flight Facility (WFF) data smoothing techniques for a variety of radars and payloads is examined. Alternative data reduction techniques are given and recommendations are made for improving radar data processing at WFF. A data adaptive algorithm, based on Kalman filtering and smoothing techniques, is also developed for estimating payload trajectories above the atmosphere from noisy time varying radar data. This algorithm is tested and verified using radar tracking data from WFF.

White, J. V.

1984-01-01

403

Characteristics of Sunset radar  

NASA Technical Reports Server (NTRS)

Located in a narrow canyon 15 km west of Boulder, Colorado, the Sunset pulsed Doppler radar was the first radar designed and constructed specifically as a VHF ST radar. The antenna system is a phased array of coaxial-colinear dopoles with computer-controlled phase shifters for each line of dipoles. It operates at a frequency of 40.475 MHz and a wavelength of 7.41M. Peak transmitter power is 100 kW. Aperture efficiency is 0.58 and resistive loss is 0.30 for its 3600 sq m area. The practical steering rate is 1 record/minute/position to any arbitrary antenna beam position. The first clear-air turbulence echoes and wind velocity measurements were obtained in 1974. Significant accomplishments are listed.

Green, J. L.

1983-01-01

404

Acidizing of Sandstone Reservoirs Using HF and Organic Acids  

E-print Network

Mud acid, which is composed of HCl and HF, is commonly used to remove the formation damage in sandstone reservoirs. However, many problems are associated with HCl, especially at high temperatures. Formic-HF acids have served as an alternative...

Yang, Fei

2012-10-19

405

Side looking radar calibration study  

NASA Technical Reports Server (NTRS)

Calibration of an airborne sidelooking radar is accomplished by the use of a model that relates the radar parameters to the physical mapping situation. Topics discussed include: characteristics of the transmitters; the antennas; target absorption and reradiation; the receiver and map making or radar data processing; and the calibration process.

Edwards, W. D.

1975-01-01

406

Augmented reality using ultra-wideband radar imagery  

NASA Astrophysics Data System (ADS)

The U.S. Army Research Laboratory (ARL) has been investigating the utility of ultra-wideband (UWB) synthetic aperture radar (SAR) technology for detecting concealed targets in various applications. We have designed and built a vehicle-based, low-frequency UWB SAR radar for proof-of-concept demonstration in detecting obstacles for autonomous navigation, detecting concealed targets (mines, etc.), and mapping internal building structures to locate enemy activity. Although the low-frequency UWB radar technology offers valuable information to complement other technologies due to its penetration capability, it is very difficult to comprehend the radar imagery and correlate the detection list from the radar with the objects in the real world. Using augmented reality (AR) technology, we can superimpose the information from the radar onto the video image of the real world in real-time. Using this, Soldiers would view the environment and the superimposed graphics (SAR imagery, detection locations, digital map, etc.) via a standard display or a head-mounted display. The superimposed information would be constantly changed and adjusted for every perspective and movement of the user. ARL has been collaborating with ITT Industries to implement an AR system that integrates the video data captured from the real world and the information from the UWB radar. ARL conducted an experiment and demonstrated the real-time geo-registration of the two independent data streams. The integration of the AR sub-system into the radar system is underway. This paper presents the integration of the AR and SAR systems. It shows results that include the real-time embedding of the SAR imagery and other information into the video data stream.

Nguyen, Lam; Koenig, Francois; Sherbondy, Kelly

2011-06-01

407

Polarization diversity in radars  

NASA Astrophysics Data System (ADS)

Many polarization techniques, which have been proposed and analyzed to enhance radar performance, are reviewed in this paper in order to assess the possible improvement they can provide in the signal-to-disturbance ratio, target detectability, target discrimination and resolution, and target classification and identification. Some recent experimentally-based results relating to these applications are also presented. Those techniques are emphasized for which polarization-based capabilities appear sufficiently assessed, such as adaptive polarization cancellation of clutter, chaff, and jamming. Polarization Doppler processing of dual-polarization radar signals, meteorologic applications, and polarization adaptation for target detection in the clear (in free space) are also examined.

Giuli, D.

1986-02-01

408

Spaceborne Imaging Radar Symposium  

NASA Technical Reports Server (NTRS)

An overview of the present state of the art in the different scientific and technological fields related to spaceborne imaging radars was presented. The data acquired with the SEASAT SAR (1978) and Shuttle Imaging Radar, SIR-A (1981) clearly demonstrated the important emphasis in the 80's is going to be on in-depth research investigations conducted with the more flexible and sophisticated SIR series instruments and on long term monitoring of geophysical phenomena conducted from free-flying platforms such as ERS-1 and RADARSAT.

Elachi, C.

1983-01-01

409

Nostradamus: the Radar that wonted be a Seismometer  

NASA Astrophysics Data System (ADS)

Surface waves emitted after large earthquakes are known to induce, by dynamic coupling, atmospheric infrasonic waves propagating upward through the neutral and ionized atmosphere. Those waves have been detected in the past at ionospheric heights using a variety of techniques, such as HF Doppler sounding or GPS receivers. The HF Doppler technique, particularly sensitive to the ionospheric signature of Rayleigh waves is used here to show ionospheric perturbations consistent with the propagation of Rayleigh wave phases R1 and R2 following the Sumatra Earthquakes on the 28 March 2005. This is in our knowledge the first time the the phase R2 is detected by ionospheric sounding. In addition, we prove here that the ionospheric signature of R2 is also observed by over-the-horizon (OTH) Radar. This latter was never used before to detect seismic signature in the ionosphere. Adding the OTH Radar to the list of the "ionospheric seismometers" we discuss and compare the performances of the different instruments mentioned above.

Giovanni, O.; Farge, T.; Dorey, P.; Lognonné, P.

2008-12-01

410

Tunable, Solid State Laser for HF Mirror Metrology.  

National Technical Information Service (NTIS)

HF mirror metrology is currently costly and time consuming, requiring laser component delivery to an HF laser site, and operation of another HF laser to reach relevant wavelengths. Coherent Technologies, Inc (CTI) has developed a solid state Cr:ZnSe laser...

A. L. Oien, C. J. Urbina, G. J. Wagner, J. W. Arenberg, T. J. Carrig

2002-01-01

411

Clutter processing of SEEK IGLOO: A modern long range 3-D radar  

NASA Astrophysics Data System (ADS)

The radar is being developed to replace the outmoded and expensive to maintain AN/FPS-93 and AN/FPS-90 radars now used in Alaska. The AN/FPS-93 is a two-dimensional surveillance radar and the AN/FPS-90 is a two-dimensional height finder radar; both of these older radars have been in operation since the early 1950's. The specification requirements for SEEK IGL00 were set by a combination of the following: (1) performance characteristics of the AN/FPS-90 and AN/FPS-93 radars; (2) performance characteristics of the Semi-Automatic Ground Environment (SAGE) System and the Joint Surveillance System (JSS); (3) sensor requirements using the new generation fighter aircraft; and (4) stringent reliability, maintainability and availability requirements to reduce on-site maintenance and operations personnel. The SEEK IGLOO radar will provide digital output messages (as opposed to the conventional "blip' signals used with many radar displays) containing range, azimuth and height information for radar and beacon targets.

Smith, R. C.

1983-04-01

412

Assessment of forest cover changes using multidate spaceborne imaging radar  

NASA Technical Reports Server (NTRS)

Data obtained in 1978 by Seasat and in 1984 by SIR-B over a forested area in northern Florida are analyzed. The objective of the study was to determine the potential for detecting major changes in forest cover utilizing synthetic aperture radar obtained from satellite altitudes, and to define an effective methodology for processing and analyzing digital synthetic aperture radar data obtained on two different dates. It is found that multitemporal synthetic aperture radar data obtained from satellite altitudes can be used to detect major changes in forest cover conditions such as deforestation and reforestation. A suprisingly good level of detectivity was obtained for identifying areas of regrowth after they had been clearcut and replanted.

Lee, Kyu-Sung; Hoffer, Roger M.

1988-01-01

413

Description, characteristics and testing of the NASA airborne radar  

NASA Technical Reports Server (NTRS)

Presented here is a description of a coherent radar scattermeter and its associated signal processing hardware, which have been specifically designed to detect microbursts and record their radar characteristics. Radar parameters, signal processing techniques and detection algorithms, all under computer control, combine to sense and process reflectivity, clutter, and microburst data. Also presented is the system's high density, high data rate recording system. This digital system is capable of recording many minutes of the in-phase and quadrature components and corresponding receiver gains of the scattered returns for selected spatial regions, as well as other aircraft and hardware related parameters of interest for post-flight analysis. Information is given in viewgraph form.

Jones, W. R.; Altiz, O.; Schaffner, P.; Schrader, J. H.; Blume, H. J. C.

1991-01-01

414

Doppler radar echoes of lightning and precipitation at vertical incidence  

NASA Technical Reports Server (NTRS)

Digital time series data at 16 heights within two storms were collected at vertical incidence with a 10-cm Doppler radar. On several occasions during data collection, lightning echoes were observed as increased reflectivity on an oscilloscope display. Simultaneously, lightning signals from nearby electric field change antennas were recorded on an analog recorder together with the radar echoes. Reflectivity, mean velocity, and Doppler spectra were examined by means of time series analysis for times during and after lightning discharges. Spectra from locations where lightning occurred show peaks, due to the motion of the lightning channel at the air speed. These peaks are considerably narrower than the ones due to precipitation. Besides indicating the vertical air velocity that can then be used to estimate hydrometeor-size distribution, the lightning spectra provide a convenient means to estimate the radar cross section of the channel. Subsequent to one discharge, we deduce that a rapid change in the orientation of hydrometeors occurred within the resolution volume.

Zrnic, D. S.; Rust, W. D.; Taylor, W. L.

1982-01-01

415

Development of land based radar polarimeter processor system  

NASA Astrophysics Data System (ADS)

The processing subsystem of a land based radar polarimeter was designed and constructed. This subsystem is labeled the remote data acquisition and distribution system (RDADS). The radar polarimeter, an experimental remote sensor, incorporates the RDADS to control all operations of the sensor. The RDADS uses industrial standard components including an 8-bit microprocessor based single board computer, analog input/output boards, a dynamic random access memory board, and power supplis. A high-speed digital electronics board was specially designed and constructed to control range-gating for the radar. A complete system of software programs was developed to operate the RDADS. The software uses a powerful real time, multi-tasking, executive package as an operating system. The hardware and software used in the RDADS are detailed. Future system improvements are recommended.

Kronke, C. W.; Blanchard, A. J.

1983-09-01

416

The Shuttle Imaging Radar B (SIR-B) experiment report  

NASA Technical Reports Server (NTRS)

The primary objective of the SIR-B experiment was to acquire multiple-incidence-angle radar imagery of a variety of Earth's surfaces to better understand the effects of imaging geometry on radar backscatter. A complementary objective was to map extensive regions of particular interest. Under these broad objectives, many specific scientific experiments were defined by the 43 SIR-B Science Team members, including studies in the area of geology, vegetation, radar penetration, oceanography, image analysis, and calibration technique development. Approximately 20 percent of the planned digital data were collected, meeting 40 percent of the scientific objectives. This report is an overview of the SIR-B experiment and includes the science investigations, hardware design, mission scenario, mission operations, events of the actual missions, astronaut participation, data products (including auxiliary data), calibrations, and a summary of the actual coverage. Also included are several image samples.

Cimino, Jo Bea; Holt, Benjamin; Richardson, Annie

1988-01-01

417

Spaceborne precipitation radar  

NASA Technical Reports Server (NTRS)

The performances and characteristics of a satelliteborne radar operating in the millimeter wavelength region of the spectrum with emphasis placed on the 35 and 94 GH3 frequency bands are discussed. It is concluded that millimetric wavelengths provide an acceptable solution for the design of satelliteborne active microwave equipment.

Eckerman, J.; Meneghini, R.

1981-01-01

418

RADAR “SAIL” satellite concept  

Microsoft Academic Search

The Radar SAIL concept is based on the use of a rectangular antenna lying in the dawn-dusk orbital plane with the length (along speed vector) smaller than the height. Such geometry makes it possible to place the solar cells on the back of the antenna, to use gravity gradient stabilisation, and to implement multipath-free GPS interferometric measurement of the antenna

Jean Paul Aguttes; Jacques Sombrin; Eric Conde

1996-01-01

419

Thin Wideband Radar Absorbers  

Microsoft Academic Search

A procedure for the optimal design of thin wideband radar absorbers is presented. The resulting absorbers are implemented by printing a frequency selective surface on a lossy perforated substrate. A binary hill climbing optimization scheme with random restart is used to find optimal solutions. The method of moments in conjunction with the transmission line method is used to calculate the

Arya Fallahi; Alireza Yahaghi; Hans-Rudolf Benedickter; Habibollah Abiri; Mahmoud Shahabadi; Christian Hafner

2010-01-01

420

25. Perimeter acquisition radar building room #2M4, (mezzanine), power supply ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

25. Perimeter acquisition radar building room #2M4, (mezzanine), power supply room; computer power supply on left and water flow on right. This room is directly below data processing area (room #318). Sign on right reads: High purity water digital rack - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

421

Nimbus-7 SMMR precipitation observations calibrated against surface radar during TAMEX  

NASA Technical Reports Server (NTRS)

This paper represents a continuation of work begun by Petty and Katsaros (1990) on refining an attenuation-based technique for estimating rainfall parameters from polarized 37-GHz brightness temperatures. In the present work, Nimbus-7 SMMR normalized 37-GHz polarization differences P are compared with surface digital radar observations of oceanic precipitation, made during the Taiwan Area Mesoscale Experiment (TAMEX) for cases when the SMMR and the radar coverages of significant precipitation features were nearly simultaneous. After the radar data were corrected for range-dependent errors, relationships were determined between the 37-GHz P and the radar reflectivity factor Z. The relationship was used to generate a large set of simulated SMMR observations from all available TAMEX radar scans, to produce histograms and mean values of pixel-averaged rain rate as a function of P.

Petty, Grant W.; Katsaros, Kristina B.

1992-01-01

422

Space Radar Image of Long Valley, California - 3D view  

NASA Technical Reports Server (NTRS)

This is a three-dimensional perspective view of Long Valley, California by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar on board the space shuttle Endeavour. This view was constructed by overlaying a color composite SIR-C image on a digital elevation map. The digital elevation map was produced using radar interferometry, a process by which radar data are acquired on different passes of the space shuttle and, which then, are compared to obtain elevation information. The data were acquired on April 13, 1994 and on October 3, 1994, during the first and second flights of the SIR-C/X-SAR radar instrument. The color composite radar image was produced by assigning red to the C-band (horizontally transmitted and vertically received) polarization; green to the C-band (vertically transmitted and received) polarization; and blue to the ratio of the two data sets. Blue areas in the image are smooth and yellow areas are rock outcrops with varying amounts of snow and vegetation. The view is looking north along the northeastern edge of the Long Valley caldera, a volcanic collapse feature created 750,000 years ago and the site of continued subsurface activity. Crowley Lake is off the image to the left. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laboratory. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR), the major partner in science, operations and data processing of X-SAR.

1994-01-01

423

Space Radar Image of Long Valley, California in 3-D  

NASA Technical Reports Server (NTRS)

This three-dimensional perspective view of Long Valley, California was created from data taken by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar on board the space shuttle Endeavour. This image was constructed by overlaying a color composite SIR-C radar image on a digital elevation map. The digital elevation map was produced using radar interferometry, a process by which radar data are acquired on different passes of the space shuttle. The two data passes are compared to obtain elevation information. The interferometry data were acquired on April 13,1994 and on October 3, 1994, during the first and second flights of the SIR-C/X-SAR instrument. The color composite radar image was taken in October and was produced by assigning red to the C-band (horizontally transmitted and vertically received) polarization; green to the C-band (vertically transmitted and received) polarization; and blue to the ratio of the two data sets. Blue areas in the image are smooth and yellow areas are rock outcrops with varying amounts of snow and vegetation. The view is looking north along the northeastern edge of the Long Valley caldera, a volcanic collapse feature created 750,000 years ago and the site of continued subsurface activity. Crowley Lake is the large dark feature in the foreground. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laboratory. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.v. (DLR), the major partner in science, operations and data processing of X-SAR.

1994-01-01

424

Digital orthophotos  

USGS Publications Warehouse

A digital orthophoto is a digital image of an aerial photograph with displacements caused by the camera angle and the terrain removed. It, thus, combines the image characteristics of a photograph with the geometric qualities of a map.

1993-01-01

425

Measurement of the condition of the sea by ionospheric backscatter radar  

NASA Astrophysics Data System (ADS)

The principles of meteo-oceanic parameter measurements are introduced, and the HF sky-wave radar equipment at Valensole is described. The maximum range of the radar, which depends on the reflector-layer altitude and on the frequency used, varies between 2500 and 4000 km. Consideration is given to the question of how to recognize the noise signal that is received and how to extract from it the information concerning the sea surface. The solution involves not only the detection of the echo amplitude but also a comparison of the phase of the received signal with that of the emitted signal. Results are presented which show that wind-directions measured by the radar are in good agreement with meteorological maps.

Parent Du Chatelet, J.

1985-04-01

426

Clutter cancellation techniques for use in a space-based radar system  

NASA Astrophysics Data System (ADS)

The ability of a space-based radar surveillance system to obtain target information from a clutter corrupted radar echo signal is dependent on the clutter cancellation technique employed. To thoroughly understand the nature of clutter so as to efficiently and effectively design and develop clutter cancellation techniques, fundamental mathematical relationships dealing with radar signal representation, probability theory, detection and estimation theory and signal comparison techniques were established and defined. Since the implementation of the mathematical expressions which describe clutter and clutter cancellation techniques are accomplished digitally, digital signal representation and digital filter characterization via FFt's were also established and defined. Drawing upon the established mathematical principles, as well as temporal probability models, spectral models and average backscatter coefficient models, clutter was described. Capitalizing on the different spectral characteristics between clutter and targets, three representative Doppler cancellation schemes were developed. The three schemes were delay line cancelers, Doppler filter banks and multiple look systems.

Devenuto, J.

1983-12-01

427

Alterations of Visual Reaction Time and Short Term Memory in Military Radar Personnel  

PubMed Central

Background Radar transmitters emit high-power radiofrequency radiation by creation of a high-voltage and high-frequency alternating electrical current. Methods: Health effects of occupational exposure to military radar were investigated. Visual reaction time was recorded with a simple blind computer-assisted-visual reaction time test. To assess the short-term memory, modified Wechsler Memory Scale test was performed. Results: The mean +/- SD reaction time in radar works (N=100) and the control group (N=57) were 238.58 +/? 23.47 milliseconds and 291.86 +/? 28.26 milliseconds (P<0.0001), respectively. The scores of forward digit span in radar works and the control group were 3.56 +/? 0.77 and 4.29 +/? 1.06 (P<0.0001), while the scores of backward digit span in radar works and the control group were 2.70 +/? 0.69 and 3.62 +/? 0.95 (P<0.0001). The scores of word recognition in radar works and the control group were 3.37 +/? 1.13 and 5.86 +/? 1.11 (P<0.0001). Finally, the scores of paired words in radar works and the control group were 13.56 +/? 1.78 and 15.21 +/? 2.20 (P<0.0001). It can be concluded that occupational exposures to radar radiations decreases reaction time, which may lead to a better response to different hazards. Conclusion: To the best of our knowledge, this is the first study to show that occupational exposure to radar microwave radiation leads to decreased reaction time and the lower performance of short-term memory. Altogether, these results indicate that occupational exposure to radar microwave radiations may be linked to some non-detrimental and detrimental health effects. PMID:23785684

MORTAZAVI, Seyed Mohammad Javad; TAEB, Shahram; DEHGHAN, Naser

2013-01-01

428

Materials performance in HF-alkylation units  

SciTech Connect

Materials selection in HF-alkylation units is mostly based on long time experience. The most widely used material in the Station units is standard carbon steel, because it is capable to form a thick protective FeF{sub 2} layer in concentrated or anhydrous hydrofluoric acid. The corrosion resistance decreases, when the acid is dilute (less than 64% HF) or the temperature is above 160F (70 C). The composition and metallurgical state are also suspected to affect the corrosion resistance of carbon steel. The effect of composition appears more complicated than believed, especially the A-106 specification on the total amount of Cr+Ni+Cu+Mo+V < 1% should be studied more closely from the corrosion point of view. Laboratory tests showed that the uniform corrosion rate may be 100 times higher in galvanic contact of two dissimilar steels. The effect of galvanic contacts can neither be excluded in the process equipment corrosion cases.

Forsen, O.; Aromaa, J.; Somervuori, M. [Helsinki Univ. of Technology, Espoo (Finland). Lab. of Corrosion and Material Chemistry; Tavi, M. [BAC Engineering Oy, Espoo (Finland)

1995-11-01

429

Miniature L-Band Radar Transceiver  

NASA Technical Reports Server (NTRS)

A miniature L-band transceiver that operates at a carrier frequency of 1.25 GHz has been developed as part of a generic radar electronics module (REM) that would constitute one unit in an array of many identical units in a very-large-aperture phased-array antenna. NASA and the Department of Defense are considering the deployment of such antennas in outer space; the underlying principles of operation, and some of those of design, also are applicable on Earth. The large dimensions of the antennas make it advantageous to distribute radio-frequency electronic circuitry into elements of the arrays. The design of the REM is intended to implement the distribution. The design also reflects a requirement to minimize the size and weight of the circuitry in order to minimize the weight of any such antenna. Other requirements include making the transceiver robust and radiation-hard and minimizing power demand. Figure 1 depicts the functional blocks of the REM, including the L-band transceiver. The key functions of the REM include signal generation, frequency translation, amplification, detection, handling of data, and radar control and timing. An arbitrary-waveform generator that includes logic circuitry and a digital-to-analog converter (DAC) generates a linear-frequency-modulation chirp waveform. A frequency synthesizer produces local-oscillator signals used for frequency conversion and clock signals for the arbitrary-waveform generator, for a digitizer [that is, an analog-to-digital converter (ADC)], and for a control and timing unit. Digital functions include command, timing, telemetry, filtering, and high-rate framing and serialization of data for a high-speed scientific-data interface. The aforementioned digital implementation of filtering is a key feature of the REM architecture. Digital filters, in contradistinction to analog ones, provide consistent and temperature-independent performance, which is particularly important when REMs are distributed throughout a large array. Digital filtering also enables selection among multiple filter parameters as required for different radar operating modes. After digital filtering, data are decimated appropriately in order to minimize the data rate out of an antenna panel. The L-band transceiver (see Figure 2) includes a radio-frequency (RF)-to-baseband down-converter chain and an intermediate- frequency (IF)-to-RF up-converter chain. Transmit/receive (T/R) switches enable the use of a single feed to the antenna for both transmission and reception. The T/R switches also afford a built-in test capability by enabling injection of a calibration signal into the receiver chain. In order of decreasing priority, components of the transceiver were selected according to requirements of radiation hardness, then compactness, then low power. All of the RF components are radiation-hard. The noise figure (NF) was optimized to the extent that (1) a low-noise amplifier (LNA) (characterized by NF < 2 dB) was selected but (2) the receiver front-end T/R switches were selected for a high degree of isolation and acceptably low loss, regardless of the requirement to minimize noise.

McWatters, Dalia; Price, Douglas; Edelstein, Wendy

2007-01-01

430

3-D laser radar simulation for autonomous spacecraft landing  

NASA Astrophysics Data System (ADS)

A sophisticated 3D laser radar sensor simulation, developed and applied to the task of autonomous hazard detection and avoidance, is presented. This simulation includes a backward ray trace to sensor subpixels, incoherent subpixel integration, range dependent noise, sensor point spread function effects, digitization noise, and AM-CW modulation. Specific sensor parameters, spacecraft lander trajectory, and terrain type have been selected to generate simulated sensor data.

Reiley, Michael F.; Carmer, Dwayne C.; Pont, W. F.

1991-08-01

431

The Apollo 17 Lunar Sounder. [lunar orbit coherent radar experiment  

NASA Technical Reports Server (NTRS)

The Apollo Lunar Sounder Experiment, a coherent radar operated from lunar orbit during the Apollo 17 mission, has scientific objectives of mapping lunar subsurface structure, surface profiling, surface imaging, and galactic noise measurement. Representative results from each of the four disciplines are presented. Subsurface reflections have been interpreted in both optically and digitally processed data. Images and profiles yield detailed selenomorphological information. The preliminary galactic noise results are consistent with earlier measurements by other workers.

Phillips, R. J.; Brown, W. E., Jr.; Jordan, R.; Adams, G. F.; Jackson, P.; Peeples, W. J.; Porcello, L. J.; Ryu, J.; Eggleton, R. E.; Schaber, G.

1973-01-01

432

HF excited instabilities in space plasmas  

Microsoft Academic Search

Radio waves delivering sufficiently strong electric field strengths to a plasma can excite parametric instabilities in the plasma for properly matched conditions. Technology had advanced by 1970 to the stage where this could be effected in the ionospheric plasma by ground-based installations. High-power HF transmitters, in the nominal 3-12 MHz range, deposited substantial energy in the ionospheric plasma, raising thermal

H. C. Carlson; L. M. Duncan

1977-01-01

433

Adaptive Equalization Techniques for HF Channels  

Microsoft Academic Search

Data transmission at rates of 1.2 kbits\\/s or higher through voiceband ionospheric channels is subject to impairment from severe linear distortion, fast channel time variations, and severe fading. In this paper, we have focused on the performance of DFE (decision feedback equalization) receivers for communication over 3 kHz bandwidth HF channels. We describe the results of simulations for a wide

EVANGELOS ELEFTHERIOU; DAVID D. FALCONER

1987-01-01

434

41. Perimeter acquisition radar building radar element and coaxial display, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

41. Perimeter acquisition radar building radar element and coaxial display, with drawing of typical antenna section. Drawing, from left to right, shows element, aluminum ground plane, cable connectors and hardware, cable, and back-up ring. Grey area is the concrete wall - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

435

Shuttle radar topography mapper (SRTM)  

NASA Astrophysics Data System (ADS)

The use of interferometric SAR (IFSAR) to measure elevation is one of the most powerful and promising capabilities of radar. A properly equipped spaceborne IFSAR system can produce a highly accurate global digital elevation map, including cloud-covered areas, in significantly less time and at significantly lower cost than with other systems. For accurate topography, the interferometric measurements must be performed simultaneously in physically sperate receive system, since measurements made at different times with the same system suffer significant decorrelation. The US/German/Italian spaceborne imaging radar C/X-band SAR (SIR-C/X-SAR), successfully flown twice in 1994 aboard the Space Shuttle Endeavor, offers a unique opportunity for global multifrequency elevation mapping by the year 2000. With appropriate augmentation, SIR-C/X-SAR is capable of producing an accurate elevation map covering 80 percent of the Earth's land surface in a single 10-day Shuttle flight. The existing US SIR-C SCANSAR mode provides a 225-km swath at C-band, which makes this coverage possible. Addition of a C-band receive antenna, extended from the Shuttle bay on a mast and operating in concert with the existing SIR-C antenna, produces an interferometric pair. Accuracy is enhanced by utilizing the SIR-C dual polarizations simultaneously to form separate SCANSAR beams. Due to the practical limitation of approximately 60 meters for the mast length, the longer SIR-C L-band wavelength does not produce useful elevation measurement accuracy. IFSAR measurements can also be obtained by the German/Italian X-SAR, simultaneously with SIR-C, by utilizing an added outboard antenna at X-band to produce a swath coverage of about 50 km. Accuracy can be enhanced at both frequencies by processing both ascending and descending data takes. It is estimated that the 90 percent linear absolute elevation error achievable is less that 16 meters for elevation postings of 30 meters. This will be the first use of spaceborne IFSAR to acquire accurate topographic data on a global scale.

Jordan, Rolando L.; Caro, Edward R.; Kim, Yunjin; Kobrick, Michael; Shen, Yuhsyen; Stuhr, Frederick V.; Werner, Marian U.

1996-12-01

436

Electron-ion temperature ratio estimations in the summer polar mesosphere when subject to HF radio wave heating  

NASA Astrophysics Data System (ADS)

We have inferred the electron temperature enhancements above mesospheric altitudes under Polar Mesospheric Summer Echoes (PMSE) conditions when the ionosphere is exposed to artificial HF radio wave heating. The proposed method uses the dependence of the radar cross section on the electron-to-ion temperature ratio to infer the heating factor from incoherent scatter radar (ISR) power measurements above 90 km. Model heating temperatures match our ISR estimations between 90 and 130 km with 0.94 Pearson correlation index. The PMSE strength measured by the MORRO MST radar is about 50% weaker during the heater-on period when the modeled electron-to-ion mesospheric temperature is approximately 10 times greater than the unperturbed value. No PMSE weakening is found when the mesospheric temperature enhancement is by a factor of three or less. The PMSE weakening and its absence are consistent with the modeled mesospheric electron temperatures. This consistency supports to the proposed method for estimating mesospheric electron temperatures achieved by independent MST and ISR radar measurements.

Pinedo, H.; La Hoz, C.; Havnes, O.; Rietveld, M.

2014-10-01

437

Real-time determination of meteor-related parameters utilizing modern digital technology  

Microsoft Academic Search

Modern fast digitization techniques and computer methods have been combined with both new and old theoretical approaches to permit construction of a new class of meteor radar. This radar can simultaneously stream data into memory, detect occurrences of meteors, and determine the location of meteor trails (range and angle), as well as find their radial drift speeds and decay times.

W. K. Hocking; B. Fuller; B. Vandepeer

2001-01-01

438

RADAR Reveals Titan Topography  

NASA Technical Reports Server (NTRS)

The Cassini Titan RADAR Mapper is a K(sub u)-band (13.78 GHz, lambda = 2.17 cm) linear polarized RADAR instrument capable of operating in synthetic aperture (SAR), scatterometer, altimeter and radiometer modes. During the first targeted flyby of Titan on 26 October, 2004 (referred to as Ta) observations were made in all modes. Evidence for topographic relief based on the Ta altimetry and SAR data are presented here. Additional SAR and altimetry observations are planned for the T3 encounter on 15 February, 2005, but have not been carried out at this writing. Results from the T3 encounter relevant to topography will be included in our presentation. Data obtained in the Ta encounter include a SAR image swath

Kirk, R. L.; Callahan, P.; Seu, R.; Lorenz, R. D.; Paganelli, F.; Lopes, R.; Elachi, C.

2005-01-01

439

Floor-plan radar  

NASA Astrophysics Data System (ADS)

Urban-warfare specialists, law-enforcement officers, counter-drug agents, and counter-terrorism experts encounter operational situations where they must assault a target building and capture or rescue its occupants. To minimize potential casualties, the assault team needs a picture of the building's interior and a copy of its floor plan. With this need in mind, we constructed a scale model of a single- story house and imaged its interior using synthetic-aperture techniques. The interior and exterior walls nearest the radar set were imaged with good fidelity, but the distal ones appear poorly defined and surrounded by ghosts and artifacts. The latter defects are traceable to beam attenuation, wavefront distortion, multiple scattering, traveling waves, resonance phenomena, and other effects not accounted for in the traditional (noninteracting, isotropic point scatterer) model for radar imaging.

Falconer, David G.; Ueberschaer, Ronald M.

2000-07-01

440

Advanced ground penetrating radar  

SciTech Connect

An advanced Ground Penetrating Radar (GPR) system has the potential for efficiently and reliably providing high resolution images for inspecting concrete civil structures for defects and damage assessment. To achieve the required performance, improvements in radar hardware, and development and adaptation of advanced 2- and 3-dimensional synthetic aperture imaging techniques are needed. Recent and continuing advancement in computer and computer-related technology areas have made it possible to consider more complex and capable systems for a variety of imaging applications not previously conceived. The authors developed conceptual designs, analyzed system requirements, and performed experiments, modeling, and image reconstructions to study the feasibility of improving GPR technology for non-destructive evaluation of bridge decks and other high-value concrete structures. An overview and summary of practical system concepts and requirements, are presented.

Warhus, J.P.; Mast, J.E.; Johansson, E.M.; Nelson, S.D. [Lawrence Livermore National Lab., CA (United States). Electronics Engineering Dept.

1994-07-26

441

New weather radar coming  

NASA Astrophysics Data System (ADS)

What would you call the next generation of radar for severe weather prediction? NEXRAD, of course. A prototype for the new system was recently completed in Norman, Okla., and by the early 1990s up to 195 stations around the United States will be tracking dangerous weather and sending faster, more accurate, and more detailed warnings to the public.NEXRAD is being built for the Departments of Commerce, Transportation, and Defense by the Unisys Corporation under a $450 million contract signed in December 1987. Th e system will be used by the National Weather Service, the Federal Aviation Administration (FAA), and the U.S. Air Force and Navy. The NEXRAD radar tower in Norman is expected to be operational in October.

Maggs, William Ward

442

Radar signal processing  

NASA Astrophysics Data System (ADS)

The role of clutter in radar signal processing is considered with particular reference to an air-traffic environment. The characteristics of clutter are described, and the use of conventional moving-target indication filters to reduce the effects of clutter is considered. Adaptive clutter suppression schemes are addressed, and the adaptive detection of a moving target in the presence of clutter of unknown statistics is discussed. The use of a parametric spectrum estimation procedure as the basis of clutter classification is described.

Haykin, S.

1985-04-01

443

Airborne bistatic radar applications  

Microsoft Academic Search

Applications of bistatic radar when one or both of the units are airborne are discussed. Scenarios that merit deeper consideration are covert strike and head-on SAR using a stand-off illuminator, either airborne or space-based; area air defense with passive ground-based receivers and stand-off illuminators; an airborne picket line to detect stealth aircraft and missiles; AWACS aircraft providing mutual support in

James A. Foster

1987-01-01

444

Imaging synthetic aperture radar  

DOEpatents

A linear-FM SAR imaging radar method and apparatus to produce a real-time image by first arranging the returned signals into a plurality of subaperture arrays, the columns of each subaperture array having samples of dechirped baseband pulses, and further including a processing of each subaperture array to obtain coarse-resolution in azimuth, then fine-resolution in range, and lastly, to combine the processed subapertures to obtain the final fine-resolution in azimuth. Greater efficiency is achieved because both the transmitted signal and a local oscillator signal mixed with the returned signal can be varied on a pulse-to-pulse basis as a function of radar motion. Moreover, a novel circuit can adjust the sampling location and the A/D sample rate of the combined dechirped baseband signal which greatly reduces processing time and hardware. The processing steps include implementing a window function, stabilizing either a central reference point and/or all other points of a subaperture with respect to doppler frequency and/or range as a function of radar motion, sorting and compressing the signals using a standard fourier transforms. The stabilization of each processing part is accomplished with vector multiplication using waveforms generated as a function of radar motion wherein these waveforms may be synthesized in integrated circuits. Stabilization of range migration as a function of doppler frequency by simple vector multiplication is a particularly useful feature of the invention; as is stabilization of azimuth migration by correcting for spatially varying phase errors prior to the application of an autofocus process.

Burns, Bryan L. (Tijeras, NM); Cordaro, J. Thomas (Albuquerque, NM)

1997-01-01

445

Radar response to vegetation  

Microsoft Academic Search

Active microwave measurements of vegetation backscatter were conducted to determine the utility of radar in 1) mapping soil moisture through vegetation and 2) mapping crop types. Using a truck-mounted boom, spectral response data were obtained for four crop types (corn, milo, soybeans, and alfalfa) over the 4-8 GHz frequency band, at incidence angles of0deg-70degin10degsteps, and for all four linear polarization

F. Ulaby

1975-01-01

446

A review of array radars  

NASA Astrophysics Data System (ADS)

Achievements in the area of array radars are illustrated by such activities as the operational deployment of the large high-power, high-range-resolution Cobra Dane; the operational deployment of two all-solid-state high-power, large UHF Pave Paws radars; and the development of the SAM multifunction Patriot radar. This paper reviews the following topics: array radars steered in azimuth and elevation by phase shifting (phase-phase steered arrays); arrays steered + or - 60 deg, limited scan arrays, hemispherical coverage, and omnidirectional coverage arrays; array radars steering electronically in only one dimension, either by frequency or by phase steering; and array radar antennas which use no electronic scanning but instead use array antennas for achieving low antenna sidelobes.

Brookner, E.

1981-10-01

447

Cognitive processing for nonlinear radar  

NASA Astrophysics Data System (ADS)

An increasingly cluttered electromagnetic environment (EME) is a growing problem for radar systems. This problem is becoming critical as the available frequency spectrum shrinks due to growing wireless communication device usage and changing regulations. A possible solution to these problems is cognitive radar, where the cognitive radar learns from the environment and intelligently modifies the transmit waveform. In this paper, a cognitive nonlinear radar processing framework is introduced where the main components of this framework consist of spectrum sensing processing, target detection and classification, and decision making. The emphasis of this paper is to introduce a spectrum sensing processing technique that identifies a transmit-receive frequency pair for nonlinear radar. It will be shown that the proposed technique successfully identifies a transmit-receive frequency pair for nonlinear radar from data collected from the EME.

Martone, Anthony; Ranney, Kenneth; Hedden, Abigail; Mazzaro, Gregory; McNamara, David

2013-05-01

448

An ionization duct explanation of some plasma line observations with a 46.8-MHz radar and with a 430-MHz radar  

NASA Astrophysics Data System (ADS)

Recently published HF-enhanced plasma line observations using a 46.8-MHz radar show that the upshifted decay line is absent. The upshifted spectrum considered of a single 'growing line' within a few hertz of 51.9 MHz (46.8 MHz plus the heating wave frequency of 5.1 MHz). The downshifted line was obscured by interference. The authors explain their observations by considering Langmuir wave propagation in the electron density depression generated by the ponderomotive force of the heating wave near reflection. Another approach, considered here, is to consider Langmuir wave propagation in magnetic field-aligned ionization ducts which are generated by the HF heating wave. This latter approach appears to yield a more satisfactory explanation of the observations. Using the duct model, it is predicted that for a radar frequency near 50 MHz the downshifted decay line will have a higher intensity and occur at a lower altitude than the upshifed decay line. Some published observations showing an 'early rise' time for the plasma line using a 430-MHz radar can also be explained using the duct model.

Muldrew, D. B.

1985-07-01

449

Radar gun hazards  

SciTech Connect

Radar guns - hand-held units used by the law to nail speeders - have been in use since the early '60s. Now they've been accused of causing cancer. Police officers in several states have so far filed eight suits against the manufacturer, claiming that they have contracted rare forms of cancer, such as of the eyelid and the testicle, from frequent proximity to the devices. Spurred by concerns expressed by police groups, researchers at the Rochester Institute of Technology are conducting what they believe to be the first research of its kind in the nation. Last month psychologist John Violanti, an expert in policy psychology and health, sent out a one-page survey to 6,000 active and retired police officers in New York State, asking them about their health and their use of radar guns. Violanti says melanoma, leukemia, and lymph node cancer may be linked to these as well as other electromagnetic devices. The Food and Drug Administration earlier this year issued a warning about radar guns, telling users not to operate them closer than 6 inches from the body. But this may not be a sufficient safeguard since the instruments can give off crisscrossing wave emissions within a police vehicle. The survey will be used to help determine if it would be safer to mount the guns, which are currently either hand-held or mounted on dashboards, outside troopers' cars.

Not Available

1991-12-20

450

Spaceborne Imaging Radar Project  

NASA Technical Reports Server (NTRS)

In June of 1985 the Project Initiation Agreement was signed by the Jet Propulsion Laboratory and the NASA Office of Space Science and Applications for the Spaceborne Imaging Radar Project (SIR). The thrust of the Spaceborne Imaging Radar Project is to continue the evolution of synthetic aperture radar (SAR) science and technology developed during SEASAT, SIR-A and SIR-B missions to meet the needs of the Earth Observing System (EOS) in the mid 1990's. As originally formulated, the Project plans were for a reflight of the SIR-B in 1987, the development of a new SAR, SIR-C, for missions in mid 1989 and early 1990, and the upgr