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R.K. Raney
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ABSTRACT: A synthetic aperture radar (SAR) often is constrained to transmit only one polarization. Within this constraint, two aggressive measurement objectives are 1) full characterization and exploitation of the backscattered field, and 2) invariance to geometrical orientations of features in the scene. Full characterization implies coherent dual-polarization to support the four Stokes parameters. These are rotationally invariant with respect backscatterer orientation if and only if the transmission is circularly polarized. Given that the data products are the Stokes parameters, the receivers can use any orthogonal polarization basis. A SAR in hybrid-polarity architecture (CL-pol) transmits circular polarization and receives two orthogonal mutually coherent linear polarizations, which is one manifestation of compact polarimetry. The resulting radar is relatively simple to implement, and has unique self-calibration features and low susceptibility to noise and cross-channel errors. It is the architecture of choice for two lunar radars scheduled for launch in 2008. Data from a CL-pol SAR yield to decomposition strategies such as the m -delta method introduced in this paper.
IEEE Transactions on Geoscience and Remote Sensing 12/2007; · 2.89 Impact Factor
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R.K. Raney
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ABSTRACT: For a given transmission polarization, the four-element Stokes vector captures all of the information inherent to the dual-polarized backscattered signals. Stokes parameters are linear combinations of the like-polarized power, the cross-polarized power, and the cross product between the complex image amplitudes in the two receive channels. Most so-called dual-polarized synthetic aperture radar (SAR) systems provide only the like- and cross-product images, ignoring the cross product. In so doing, potentially valuable information is thrown away. For most dual-polarized SARs, data sufficient to generate the Stokes parameters can be generated with small marginal cost. A practical and sufficient output data format would be a mapping of the (complex) cross product between the two channels, as well as their respective images
IEEE Geoscience and Remote Sensing Letters 08/2006; · 1.56 Impact Factor
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ABSTRACT: Bathymetric survey lines cover the remote ocean basins about as sparsely as the Interstate Highway System covers the United States. Therefore the most complete global bathymetric models employ reconnaissance deep sea bottom topography ("bathymetry from space") combining conventional acoustic soundings with detailed marine gravity field information derived from densely spaced satellite altimeter profiles of sea surface slope. Gravity and bathymetry may be correlated over spatial scales (half-wavelengths) of roughly 5 to 80 km. The vertical precision and horizontal resolution of derived bathymetry depends on the signal-to-noise characteristics of the satellite altimetry over the correlated band. Comparison between gravity anomalies derived from existing satellite altimeter data and gravity anomalies measured with shipboard gravimeters shows root-mean-square differences around 5 milliGals (mGal) and spectral coherency (signal exceeding noise) for half-wavelengths longer than about 13 km. Reconnaissance bathymetry estimates derived from these data have a similar scale of resolution (roughly 15 km half wavelength) and vertical errors of approximately 125 to 250 meters, depending on conditions such as regional water depth and the spectrum of the local topographic signal. The most challenging error situation is predicting the summit depth of a narrow and steep seamount rising from deep water. In the area of the USS San Francisco collision, for example, the altimetric bathymetry map shows a ridge with a local summit at 278 meters depth near the crash site, rising from a regional background depth of more than 3000 m of water. Landsat imagery near the crash site suggests that the seamount the San Francisco hit is probably shallower than 40 m at its summit. State-of-the-art shipboard gravimetry has an error level around 1 mGal, and cross-spectral comparisons of shipboard measurements of gravity and bathymetry show coherency down to half wavelengths as short as 5 km. Thus if a new mission could reduce the error in gravity maps derived from satellite altimetry by as much as a factor of five, one could expect significant improvements in the horizontal resolution and vertical error of estimated reconnaissance bathymetry. While the error propagation from gravity to estimated-
bathymetry depends on the local conditions as above, we can expect a five-fold reduction in the bathymetry error from a five-fold reduction in gravity error. Recent advances in altimetry - the delay-Doppler technology - make this five-fold gain readily achievable with a low-cost mission. The limiting error in altimetry of sea surface slopes is random noise in the altimeter's range measurement, and the delay-Doppler altimeter is superior to conventional altimeters in this respect by a factor of at least two. The mission should have an orbit with a ground track pattern that does not repeat for at least 1.2 to 1.5 years or so, in order to obtain dense spatial sampling to support short-wavelength horizontal resolution. Thus a 5 to 6 year mission would yield four-fold data redundancy, reducing the error another factor of two. An additional noise reduction factor of roughly 1-1/4 or so can be gained by choosing an optimal orbital inclination.
OCEANS, 2005. Proceedings of MTS/IEEE; 02/2005
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ABSTRACT: Elevation data derived from space-based altimeter measurements over landand sea-ice are key to understanding the Earth's ice mass balance. This importance is recognized by both NASA, as expressed in the laser altimeter GLAS on ICESat, and ESA, as expressed in the radar altimeter SIRAL on CryoSat. The JHU/APL Delay-Doppler Phase-monopulse (D2P) radar altimeter has shown its value as a scientific/calibration/validation instrument, and has participated in two airborne field campaigns sponsored by NASA and ESA to collect simultaneous radar and laser altimeter measurements over land and sea ice. These measurements are unique; they provide colocated, cross-calibrated, and high-precision altimetry data over a variety of geophysical ice conditions in two very different frequency regimes. In this paper, we give an overview of the CryoVEx field campaign in 2003 including basic system parameters, flight tracks, and sample waveforms from the airborne experiment.
Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International; 10/2004
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ABSTRACT: A constellation of (nominally) three DDA satellites can all be placed in the same orbit plane by a single launch vehicle. Earth rotation spreads their respective nadir tracks by a spacing that is proportional to their along-orbit separation. This constellation which we have called WITTEX (Water Inclination Topography and Technology Experiment) is a candidate approach that would meet nearly all of the requirements identified by the user community for oceanographic altimetry. The WITTEX constellation can be tuned to favor dense spatial coverage, relatively tight temporal coverage, or other priorities. In addition the constellation can be used in a dual-use mode as was Geosat, in that geoid observations over a dense ground track can be made, after which the constellation can be maneuvered into an oceanographic exact repeat mission.
OCEANS 2003. Proceedings; 10/2003
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ABSTRACT: A delay-Doppler radar altimeter exploits coherent signal processing in addition to incoherent waveform averaging to achieve significantly better measurement precision and instrument efficiency than are possible from a conventional incoherent instrument such as TOPEX or Jason-1. The required processing can be built into the on-board system, whose output waveforms yield geophysical parameters with the analysis algorithms already developed for conventional altimetric data. The approach enables new architectures, ranging from a single-frequency geodetic instrument (Abyss-Lite), to a three-satellite constellation of TOPEX-class altimeters (WITTEX) small enough to fit into one launch vehicle.
OCEANS 2003. Proceedings; 10/2003
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ABSTRACT: We describe the rationale, scientific basis, and implementation of a mission to map the ocean's bottom topography with a spatial resolution of 6 km based on a high-precision radar altimeter on a dedicated free-flying spacecraft.
Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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ABSTRACT: The primary objectives of LaRA-2002 were to assemble measurements of land and sea ice with simultaneous observations from a low-altitude aircraft by laser and radar altimeters. Data from the mission was expected to illustrate similarities and differences between these two very different means of measuring surface height. These objectives were met. This paper provides an overview of the project, and includes highlights of the results.
Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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ABSTRACT: Describes a bistatic extension to the original WITTEX approach to oceanographic radar altimetry from space. An error analysis of the bistatic link shows that the system timing and height measurement strategy can be designed to retain accuracy comparable to that of nadir-sensing instruments. In a WITTEX constellation, two or more radar altimeter satellites are inserted from one launch vehicle into the same orbit plane. Earth rotation separates their respective surface tracks by distances that are proportional to the along-orbit spacing between the satellites. Monostatic altimeters on n spacecraft together with bistatic altimetric links between adjacent spacecraft generate (2n-1) surface tracks of accurate height data in a bistatic WITTEX constellation.
Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 07/2002
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ABSTRACT: Through airborne flight tests over the ocean and the ice of southern Greenland, we have successfully demonstrated the technical viability and waveform characteristics of an innovative radar altimeter concept (D2P), the first of its kind. The D2P takes advantage of range-curvature-corrected, multi-look Doppler processing along-track, and interferometric angle measurement across-track. The radar's performance met or exceeded expectations. The D2P radar serves as an airborne prototype of CryoSat.
Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 07/2002
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ABSTRACT: The Water Inclination Topography and Technology Experiment
(WITTEX) consists of three TOPEX-class radar altimeters on individual
satellites in the same orbit plane. If built with delay-Doppler radar
altimeter technology, the WITTEX satellites will be sufficiently small
that all three can be launched simultaneously by one vehicle. Even
though the WITTEX satellites will be in a common inertial orbit plane,
Earth rotation separates their tracks at nadir. Cross-track separation
will be proportional to intersatellite spacing. WITTEX will provide
near-simultaneous and accurate measurement of sea surface heights along
three parallel tracks, providing oceanographic data not previously
available, including the two-dimensional (2-D) surface gradient. WITTEX
offers a variety of beneficial solutions to the classic time/space
sampling tradeoff that confronts oceanic radar altimetry
IEEE Transactions on Geoscience and Remote Sensing 12/2001; · 2.89 Impact Factor
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ABSTRACT: Over the past few years, the interest in exploring Mars has grown, with several missions in the planning stages for the next decade. One motivating theme is the potential of discovering substantial sub-surface aqueous reservoirs. This paper outlines the simulation and development of a lightweight, low-power, ground-penetrating radar system intended for the subsurface exploration of Mars. I.
08/2001;
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ABSTRACT: Over the past few years, the interest in exploring Mars has grown,
with several missions in the planning stages for the next decade. One
motivating theme is the potential of discovering substantial subsurface
aqueous reservoirs. This paper outlines the simulation and development
of a lightweight, low-power, ground-penetrating radar system intended
for the subsurface exploration of Mars
Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International; 02/2001
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ABSTRACT: New concepts, which improve the design and performance of spaceborne
radar altimeters for remote sensing of the Earth, can be applied to the
mapping of extraterrestrial bodies. An inherent advantage of a radar
altimeter is that it is capable of application where the atmosphere of
the body being observed is opaque to micron-scale wavelengths.
Furthermore, radar altimeters are typically pulse-limited, so the
measurement area is determined by the intersection of the transmitted
pulse with the surface. This limits the sensitivity of the altitude
measurement to the spacecraft attitude knowledge. The recently developed
and demonstrated delay/Doppler concept combines these advantages with a
reduction in the size of the altimeter through more efficient use of the
backscattered power and improvement in the along-track spatial
resolution. The delay/Doppler altimeter was originally proposed because
of its many advantages in Earth altimetry (open water, sea ice,
continental ice sheets, etc.), but the basic concept has wide
application, including subsurface sounding as well as altimetry. This
sounding application is being considered for the search for subsurface
water on Mars and Europa. Altimetry is also a primary data set for
geophysical studies (e.g., measurements of planetary tides, rotation
state/libration) which provide fundamental constraints on origins and
evolution, as well as geological processes (e.g., volcanic, tectonic)
that affect topography. This instrument orbiting Europa or Triton can
provide key measurements for the understanding of crustal tidal effects,
which have implications for geologic processes that may contribute to
resurfacing. A delay/Doppler altimeter can distinguish between diffuses
and specular reflecting surfaces and therefore between solid and liquid
surfaces which can be useful in determining the presence of methane
ponds on Titan. Additional information is contained in the original
extended abstract.
12/2000; -1:44.
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ABSTRACT: The delay/Doppler radar altimetry algorithm is extended to the
radar ice sounding application. Improved performance is demonstrated,
both in theory and through analysis of ice sounding data from Greenland
Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International; 02/1999
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R.K. Raney
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ABSTRACT: The key innovation in the delay/Doppler radar altimeter is delay
compensation, analogous to range curvature correction in a burst-mode
synthetic aperture radar (SAR). Following delay compensation, height
estimates are sorted by Doppler frequency, and integrated in parallel.
More equivalent looks are accumulated than in a conventional altimeter.
The relatively small along-track footprint size is a constant of the
system, typically on the order of 250 m for a Ku-band altimeter. The
flat-surface response is an impulse rather than the more familiar step
function produced by conventional satellite radar altimeters. The radar
equation for the delay/Doppler radar altimeter has an
h<sup>-5/2</sup>(CT)<sup>1/2</sup> dependence on height h and compressed
pulse length τ, which is more efficient than the corresponding
h<sup>3</sup>CT factor for a pulse-limited altimeter. The radiometric
response obtained by the new approach would be 10 dB stronger than that
of the TOPEX/Poseidon altimeter, for example, if the same hardware were
used in the delay/Doppler altimeter mode. This new technique leads to a
smaller instrument that requires less power, yet performs better than a
conventional radar altimeter. The concept represents a new generation of
altimeter for Earth observation, with particular suitability for coastal
ocean regions and polar ice sheets as well as open oceans
IEEE Transactions on Geoscience and Remote Sensing 10/1998; · 2.89 Impact Factor
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ABSTRACT: A delay/Doppler radar altimeter (DDA) has many advantages over a
conventional spaceborne radar altimeter. This paper presents new results
that quantify the measurement precision improvements of a DDA when
observing the ocean surface. The improvement is established through
simulation, and is explained in terms of the increased amount of
incoherent averaging available to the DDA
Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International; 08/1998
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R.K. Raney
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ABSTRACT: Electronic publication, as an alternative to more traditional
media, will be adopted by the scientific and engineering community when
it meets the needs of that community, when it overcomes the principal
problems with conventional publication, and when the electronic option
offers more useful capabilities. Certain electronic techniques satisfy
the latter criterion. Electronic means provide desirable adjuncts to,
but not displacement alternatives for, conventional journal publications
Socioeconomic Dimensions of Electronic Publishing Workshop, 1998. Proceedings; 05/1998
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ABSTRACT: Satellite radar altimeters have proven to be a reliable source of
data on sea surface elevation to the precision of several centimeters.
Conventional instruments are limited to open ocean applications. This
paper describes a new approach to radar altimetry that circumvents most
of those limitations. The concept exploits unfocused SAR processing in
the along-track direction, and monopulse techniques in the cross-track
direction. The result is an instrument that is insensitive (to first
order) to small angles of surface slope, is not confused by hill tops or
other prominent terrain features, and has a sharper flat surface impulse
response than conventional radar altimeters. Full Doppler integration
and range curvature correction allow more independent looks than TOPEX,
for example, while achieving a resolved footprint of about 250 meters,
and requiring less radiated power. An instrument including real-rate
on-board processing is described, suitable for a small satellite
Geoscience and Remote Sensing Symposium, 1996. IGARSS '96. 'Remote Sensing for a Sustainable Future.', International; 06/1996
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R.K. Raney
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ABSTRACT: The new radar altimeter concept described exploits both Doppler
beam sharpening and range curvature delay compensation to eliminate most
of the disadvantages that plague satellite pulse-limited ocean sensing
altimeters when observing polar ice sheets
Geoscience and Remote Sensing Symposium, 1995. IGARSS '95. 'Quantitative Remote Sensing for Science and Applications', International; 08/1995
