John Sahr | University of Washington (original) (raw)
Papers by John Sahr
Along Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique inte... more Along Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique intended for measuring surface currents. As presented in [1] and [2] the current vector measurements are biased by the presence of surface winds and waves. It was shown in [3] that these biases are due to the contribution of the orbital velocity of the gravity waves (V o ) to the measured Doppler velocity by the ATI-SAR.
Annales Geophysicae, 1995
AGU Fall Meeting Abstracts, Dec 18, 2015
A comprehensive system error source analysis and calibration of an airborne along-track interfero... more A comprehensive system error source analysis and calibration of an airborne along-track interferometric FMCW SAR for ocean surface currents velocity retrieval is presented. Starting with the observed phase errors from a stationary test site, three major error sources are analyzed and possible calibration approaches are derived. The range-dependent phase offsets are demonstrated to be introduced by the phase imbalance between receive channels and receive antennas of the transceiver. The phase undulations in the along-track direction are likely due to the uncompensated motion errors caused by inaccurate aircraft attitude and velocity measurements. After calibration, most of the system phase errors are removed which greatly improves the accuracy for surface velocity retrieval by ATI-SAR.
Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique for ... more Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique for measuring surface currents. The current vector measurements are biased by the presence of surface winds and waves, so their effect must be accommodated in order to yield accurate currents estimates using ATI-SAR
Radar-sounding of ice sheets on Earth yields crucial information on ice history and dynamics, inc... more Radar-sounding of ice sheets on Earth yields crucial information on ice history and dynamics, including discoveries of subglacial lakes beneath 3-4 km of ice [1]. Mars Express and the Mars Reconnaissance Orbiter (MRO) have now demonstrated the corresponding power of orbital radar sounding for planetary exploration, in particular by imaging structures within and beneath kilometers of Martian water ice [2-4]. Based on this experience, a sophisticated orbital radar sounder is planned for a flagship mission to Europa, with the aim of imaging stratigraphy, faults, diapirs and other geological structure in the upper few kilometers of the water-ice mantle there, and possibly even detecting the upper surface of the (likely) underlying ocean [5]. Recent modeling of the formation and evolution of volatilerich bodies suggests that oceans or lakes of liquid water occur beneath water-ice mantles in a surprising variety of places, including Ceres in the outer asteroid belt [6], 3 of the 4 Galilea...
Ratio
Page 1. A NUMERICAL STUDY OF POLARIZATION SENSITIVITY FOR VHF RADAR OBSERVATION OF METER-SCALE EL... more Page 1. A NUMERICAL STUDY OF POLARIZATION SENSITIVITY FOR VHF RADAR OBSERVATION OF METER-SCALE ELECTROJET IRREGULARITIES Dawn M. Gidner ¢¡¤£ , Chucai Zhou ¥¦£ , Melissa G. Meyer §¦£ , John D. Sahr ¨©£ ...
IEE proceedings, 2005
Passive radars provide excellent Doppler spectral estimates for deep, fluctuating targets. Becaus... more Passive radars provide excellent Doppler spectral estimates for deep, fluctuating targets. Because the radar illumination is unpredictable, a full lag-profile or cross-ambiguity analysis must be performed to extract the scatterer power spectrum as a function of range. Two techniques (coherent integration and channelisation) that may be used to achieve significant speed improvements are demonstrated. Coherent integration reduces the data bandwidth. While this step reduces the computational burden to an effort readily achievable by modern desktop computers for observing FM broadcasts from a single receiver, the load increases from observing more transmitters, using more antennas in interferometric analysis, and using a larger bandwidth source such as DTV. A further improvement, which works by 'channelising' the illuminating and scattered signals, splitting the spectral bandwidth by an integer factor, resulting in a computational reduction is developed. The initial coherent integration method is presented, then a variety of implementations of the channelised improvements are shown. Properly implemented, these methods produce significant speed increases on ordinary desktop workstations. Channelised methods work nicely with transmitters whose spectral content is not white, permitting the elimination of noise power which lies outside the transmitter bandwidth, as well as beyond the decimation filter bandwidth of digital receivers.
Atmospheric scientists need to observe fluctuations in the ionosphere, both to probe the underlyi... more Atmospheric scientists need to observe fluctuations in the ionosphere, both to probe the underlying atmospheric physics, and to remove the effects of these fluctuations from other measurements. We have built an FPGA-based, pipelined array processor that allows us to make these observations in real-time, using passive radar techniques. Our array processor time-multiplexes 16 multiply--accumulators across 1536 radar ranges, performing a pipelined correlation and integration of the radar signal for each range. A DSP-based postprocessor generates realtime range-Doppler profiles of the ionospheric targets.
Chapter 1. Fundamentals Of Bistatic Synthetic Aperture Radar. 1.1 Introduction. 1.2 BSAR Basic Ge... more Chapter 1. Fundamentals Of Bistatic Synthetic Aperture Radar. 1.1 Introduction. 1.2 BSAR Basic Geometry and Resolutions. 1.3 Scientific Applications of BSAR . 1.3.1 Position and Velocity Measurements. 1.3.2 Bistatic Stereo-Radargrammetry . 1.4 Summary. 1.5 Abbreviations. 1.6 Variables. 1.7 References. Chapter 2. Spaceborne Bistatic Synthetic Aperture Radar. 2.1 Introduction. 2.2 Key Design Issues in Spaceborne BSAR. 2.2.1 Basic Trade-Offs in Spaceborne Bsar Configurations. 2.2.2 Impact of Bistatic Observation on Mission and System Design. 2.2.3 Payload-Bus Performance Trade-Off. 2.2.4 BSAR Missions Functional/Technological Key Issues. 2.3 Mission Analysis of Spaceborne BSAR. 2.3.1 BSAR Orbit Design. 2.3.2 BSAR Attitude and Antenna Pointing Design. 2.4 Summary. 2.5 Abbreviations. 2.6 Variables. 2.7 References. Chapter 3. Bistatic SAR for Earth Observation. 3.1 Introduction. 3.2 BISSAT Scientific Rationale and Technical Approach. 3.3 Bistatic Payload Main Characteristics and Architect...
The proposed Low Frequency Array will be a powerful new radio telescope operating in the 15 to 24... more The proposed Low Frequency Array will be a powerful new radio telescope operating in the 15 to 240 MHz range. LOFAR will be a fully digital instrument with tens of thousands of antennas and receivers. In the currently proposed configuration LOFAR will also be capable of operating as a high performance passive radar system using FM radio stations as signals of opportunity. In this mode of operation LOFAR will observe geophysical targets such as ionospheric irregularities and meteor trails with high resolution in range, velocity, azimuth, and elevation. These phenomenon may be important to the operation of LOFAR as a radio telescope because of their potential to interfere with astronomical observations.
Communications …, 2008
A new Ricean parameter estimator is considered in the context of wireless communications. In comp... more A new Ricean parameter estimator is considered in the context of wireless communications. In comparison to existing methods, the proposed estimator is especially useful in low signal-to-noise environments. It is less reliant on knowledge of the ...
Radio Sci, 2004
In this work, we describe a new method for remote sensing of ionospheric plasma turbulence: an ex... more In this work, we describe a new method for remote sensing of ionospheric plasma turbulence: an extension of the passive radar technique to include interferometry. We discuss the implementation of a passive radar interferometer, and show many observations of varied targets, including ground clutter, aircraft, and meteor trails, as well as plasma density irregularities in the E-region ionosphere. Because of the very fine resolution of our instrument (as fine as 0.06 • in azimuth, or 1.5 km 2 at a distance of 1000 km), we can form two dimensional images of these targets, and we are able to show that many E-region irregularities exist in compact scattering volumes (as narrow as 30 km in the transverse dimension), and that significant structure exists on very fine scales. We also describe in detail the passive radar interferometer cross-correlation estimator and its statistical properties, and perform an analysis of the resolution capability of the instrument. Finally, we demonstrate how the interferometer can be used to measure geophysical information, such as electric fields and velocity shears across scattering volumes in the ionosphere.
Abstract We will discuss the application of coherent software radio technology to remote sensing ... more Abstract We will discuss the application of coherent software radio technology to remote sensing of the ionosphere. Using networks of advanced software radio systems it is possible to make observations of the ionosphere with both wide spatial coverage and simultaneous ...
Recent technological advances enable a new class of passive radar instruments. These radars have ... more Recent technological advances enable a new class of passive radar instruments. These radars have no dedicated transmitter, observing serendipitous scatter of existing sources. Such radars may have very high performance and cost far less than conventional radars. The resulting equipment is essentially reduced to simple antennas, desktop computers, and Global Positioning System equipment. The safety hazards, interference problems, licensing issues, and ÿnancial costs associated with high-power transmitters are conspicuously absent. We will o er general design considerations and describe our own instrument, which observes the scatter of commercial FM broadcasts. Our system provides far better range and Doppler resolution than any conventional radar used in ionospheric coherent scatter studies, and is completely free of any range or Doppler aliasing problems. There are two principal drawbacks to passive radars: the "front end" signal processing cost is very large, and there is a signiÿcant data transport problem. However, spectacular advances in low-cost computing and internet bandwidth have rendered these problems quite easy to solve.
Commercial FM broadcasts near 100 MHz illuminate the natural environment with continuous, high po... more Commercial FM broadcasts near 100 MHz illuminate the natural environment with continuous, high power illumination. By fortunate coincidence these broadcasts are superb for radar applications. With proper signal processing and a bistatic, synchronous receiver ...
2016 IEEE Radar Conference (RadarConf), 2016
Image Processing Ieee Transactions on, Feb 1, 1997
We present a systematic design method for quadratic filters, and show an example for an edge dete... more We present a systematic design method for quadratic filters, and show an example for an edge detector. Our design maximizes the output signal-to-noise ratio (SNR) constrained to detect desired signals while ignoring specified error signals such as shot noise. This filter compares favorably with Sobel and morphological detectors of similar complexity.
Along Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique inte... more Along Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique intended for measuring surface currents. As presented in [1] and [2] the current vector measurements are biased by the presence of surface winds and waves. It was shown in [3] that these biases are due to the contribution of the orbital velocity of the gravity waves (V o ) to the measured Doppler velocity by the ATI-SAR.
Annales Geophysicae, 1995
AGU Fall Meeting Abstracts, Dec 18, 2015
A comprehensive system error source analysis and calibration of an airborne along-track interfero... more A comprehensive system error source analysis and calibration of an airborne along-track interferometric FMCW SAR for ocean surface currents velocity retrieval is presented. Starting with the observed phase errors from a stationary test site, three major error sources are analyzed and possible calibration approaches are derived. The range-dependent phase offsets are demonstrated to be introduced by the phase imbalance between receive channels and receive antennas of the transceiver. The phase undulations in the along-track direction are likely due to the uncompensated motion errors caused by inaccurate aircraft attitude and velocity measurements. After calibration, most of the system phase errors are removed which greatly improves the accuracy for surface velocity retrieval by ATI-SAR.
Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique for ... more Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) is a remote sensing technique for measuring surface currents. The current vector measurements are biased by the presence of surface winds and waves, so their effect must be accommodated in order to yield accurate currents estimates using ATI-SAR
Radar-sounding of ice sheets on Earth yields crucial information on ice history and dynamics, inc... more Radar-sounding of ice sheets on Earth yields crucial information on ice history and dynamics, including discoveries of subglacial lakes beneath 3-4 km of ice [1]. Mars Express and the Mars Reconnaissance Orbiter (MRO) have now demonstrated the corresponding power of orbital radar sounding for planetary exploration, in particular by imaging structures within and beneath kilometers of Martian water ice [2-4]. Based on this experience, a sophisticated orbital radar sounder is planned for a flagship mission to Europa, with the aim of imaging stratigraphy, faults, diapirs and other geological structure in the upper few kilometers of the water-ice mantle there, and possibly even detecting the upper surface of the (likely) underlying ocean [5]. Recent modeling of the formation and evolution of volatilerich bodies suggests that oceans or lakes of liquid water occur beneath water-ice mantles in a surprising variety of places, including Ceres in the outer asteroid belt [6], 3 of the 4 Galilea...
Ratio
Page 1. A NUMERICAL STUDY OF POLARIZATION SENSITIVITY FOR VHF RADAR OBSERVATION OF METER-SCALE EL... more Page 1. A NUMERICAL STUDY OF POLARIZATION SENSITIVITY FOR VHF RADAR OBSERVATION OF METER-SCALE ELECTROJET IRREGULARITIES Dawn M. Gidner ¢¡¤£ , Chucai Zhou ¥¦£ , Melissa G. Meyer §¦£ , John D. Sahr ¨©£ ...
IEE proceedings, 2005
Passive radars provide excellent Doppler spectral estimates for deep, fluctuating targets. Becaus... more Passive radars provide excellent Doppler spectral estimates for deep, fluctuating targets. Because the radar illumination is unpredictable, a full lag-profile or cross-ambiguity analysis must be performed to extract the scatterer power spectrum as a function of range. Two techniques (coherent integration and channelisation) that may be used to achieve significant speed improvements are demonstrated. Coherent integration reduces the data bandwidth. While this step reduces the computational burden to an effort readily achievable by modern desktop computers for observing FM broadcasts from a single receiver, the load increases from observing more transmitters, using more antennas in interferometric analysis, and using a larger bandwidth source such as DTV. A further improvement, which works by 'channelising' the illuminating and scattered signals, splitting the spectral bandwidth by an integer factor, resulting in a computational reduction is developed. The initial coherent integration method is presented, then a variety of implementations of the channelised improvements are shown. Properly implemented, these methods produce significant speed increases on ordinary desktop workstations. Channelised methods work nicely with transmitters whose spectral content is not white, permitting the elimination of noise power which lies outside the transmitter bandwidth, as well as beyond the decimation filter bandwidth of digital receivers.
Atmospheric scientists need to observe fluctuations in the ionosphere, both to probe the underlyi... more Atmospheric scientists need to observe fluctuations in the ionosphere, both to probe the underlying atmospheric physics, and to remove the effects of these fluctuations from other measurements. We have built an FPGA-based, pipelined array processor that allows us to make these observations in real-time, using passive radar techniques. Our array processor time-multiplexes 16 multiply--accumulators across 1536 radar ranges, performing a pipelined correlation and integration of the radar signal for each range. A DSP-based postprocessor generates realtime range-Doppler profiles of the ionospheric targets.
Chapter 1. Fundamentals Of Bistatic Synthetic Aperture Radar. 1.1 Introduction. 1.2 BSAR Basic Ge... more Chapter 1. Fundamentals Of Bistatic Synthetic Aperture Radar. 1.1 Introduction. 1.2 BSAR Basic Geometry and Resolutions. 1.3 Scientific Applications of BSAR . 1.3.1 Position and Velocity Measurements. 1.3.2 Bistatic Stereo-Radargrammetry . 1.4 Summary. 1.5 Abbreviations. 1.6 Variables. 1.7 References. Chapter 2. Spaceborne Bistatic Synthetic Aperture Radar. 2.1 Introduction. 2.2 Key Design Issues in Spaceborne BSAR. 2.2.1 Basic Trade-Offs in Spaceborne Bsar Configurations. 2.2.2 Impact of Bistatic Observation on Mission and System Design. 2.2.3 Payload-Bus Performance Trade-Off. 2.2.4 BSAR Missions Functional/Technological Key Issues. 2.3 Mission Analysis of Spaceborne BSAR. 2.3.1 BSAR Orbit Design. 2.3.2 BSAR Attitude and Antenna Pointing Design. 2.4 Summary. 2.5 Abbreviations. 2.6 Variables. 2.7 References. Chapter 3. Bistatic SAR for Earth Observation. 3.1 Introduction. 3.2 BISSAT Scientific Rationale and Technical Approach. 3.3 Bistatic Payload Main Characteristics and Architect...
The proposed Low Frequency Array will be a powerful new radio telescope operating in the 15 to 24... more The proposed Low Frequency Array will be a powerful new radio telescope operating in the 15 to 240 MHz range. LOFAR will be a fully digital instrument with tens of thousands of antennas and receivers. In the currently proposed configuration LOFAR will also be capable of operating as a high performance passive radar system using FM radio stations as signals of opportunity. In this mode of operation LOFAR will observe geophysical targets such as ionospheric irregularities and meteor trails with high resolution in range, velocity, azimuth, and elevation. These phenomenon may be important to the operation of LOFAR as a radio telescope because of their potential to interfere with astronomical observations.
Communications …, 2008
A new Ricean parameter estimator is considered in the context of wireless communications. In comp... more A new Ricean parameter estimator is considered in the context of wireless communications. In comparison to existing methods, the proposed estimator is especially useful in low signal-to-noise environments. It is less reliant on knowledge of the ...
Radio Sci, 2004
In this work, we describe a new method for remote sensing of ionospheric plasma turbulence: an ex... more In this work, we describe a new method for remote sensing of ionospheric plasma turbulence: an extension of the passive radar technique to include interferometry. We discuss the implementation of a passive radar interferometer, and show many observations of varied targets, including ground clutter, aircraft, and meteor trails, as well as plasma density irregularities in the E-region ionosphere. Because of the very fine resolution of our instrument (as fine as 0.06 • in azimuth, or 1.5 km 2 at a distance of 1000 km), we can form two dimensional images of these targets, and we are able to show that many E-region irregularities exist in compact scattering volumes (as narrow as 30 km in the transverse dimension), and that significant structure exists on very fine scales. We also describe in detail the passive radar interferometer cross-correlation estimator and its statistical properties, and perform an analysis of the resolution capability of the instrument. Finally, we demonstrate how the interferometer can be used to measure geophysical information, such as electric fields and velocity shears across scattering volumes in the ionosphere.
Abstract We will discuss the application of coherent software radio technology to remote sensing ... more Abstract We will discuss the application of coherent software radio technology to remote sensing of the ionosphere. Using networks of advanced software radio systems it is possible to make observations of the ionosphere with both wide spatial coverage and simultaneous ...
Recent technological advances enable a new class of passive radar instruments. These radars have ... more Recent technological advances enable a new class of passive radar instruments. These radars have no dedicated transmitter, observing serendipitous scatter of existing sources. Such radars may have very high performance and cost far less than conventional radars. The resulting equipment is essentially reduced to simple antennas, desktop computers, and Global Positioning System equipment. The safety hazards, interference problems, licensing issues, and ÿnancial costs associated with high-power transmitters are conspicuously absent. We will o er general design considerations and describe our own instrument, which observes the scatter of commercial FM broadcasts. Our system provides far better range and Doppler resolution than any conventional radar used in ionospheric coherent scatter studies, and is completely free of any range or Doppler aliasing problems. There are two principal drawbacks to passive radars: the "front end" signal processing cost is very large, and there is a signiÿcant data transport problem. However, spectacular advances in low-cost computing and internet bandwidth have rendered these problems quite easy to solve.
Commercial FM broadcasts near 100 MHz illuminate the natural environment with continuous, high po... more Commercial FM broadcasts near 100 MHz illuminate the natural environment with continuous, high power illumination. By fortunate coincidence these broadcasts are superb for radar applications. With proper signal processing and a bistatic, synchronous receiver ...
2016 IEEE Radar Conference (RadarConf), 2016
Image Processing Ieee Transactions on, Feb 1, 1997
We present a systematic design method for quadratic filters, and show an example for an edge dete... more We present a systematic design method for quadratic filters, and show an example for an edge detector. Our design maximizes the output signal-to-noise ratio (SNR) constrained to detect desired signals while ignoring specified error signals such as shot noise. This filter compares favorably with Sobel and morphological detectors of similar complexity.