R.K. Raney

Hybrid-Polarity SAR Architecture

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.

A delay/Doppler radar altimeter for ice sheet monitoring

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.

Improved Range Ambiguity Performance in Quad-Pol SAR

Conventional quadrature-polarimetric (quad-pol) synthetic aperture radar (SAR) systems operating from space are severely constrained by their limited range of useful incident angles and their reduced swath widths particularly at larger incidence. These limitations are due primarily to relatively severe range ambiguities in the cross-polarized measurement channels. The conventional approach for quad-pol SAR systems uses linear polarizations on both transmit and receive. Range ambiguities can be markedly reduced by adopting hybrid-polarimetric architecture. In this approach, the radar transmits circularly polarized waves but receives on orthogonal linear polarizations. The sense of the circular polarization-left or right-is reversed on alternate transmissions. Hybrid-polarimetric quad-pol architecture leads to hardware that is more readily calibrated because neither receive channel is cross polarized with respect to the transmitted polarization; hence, their mean signal levels are the same. The data provided by a hybrid-polarimetric quad-pol SAR may be transformed into the conventional linearly polarized scattering matrix, thus preserving compatibility with the rich heritage of analysis tools developed for such radars.

Hybrid-Quad-Pol SAR

Data products from a quadrature-polarized synthetic aperture radar (SAR) are fully characterized by Stokes parameters. It follows that choice of the polarization basis of either the transmitted or the received EM fields has no impact on the measurement potential of the system. Hence the polarization plan for a quad-pol SAR can be selected to optimize the radars engineering performance. The logical conclusion is that an optimal quad-pol radar should transmit circular polarization, and receive orthogonal linear polarizations. This paper shows that there is no loss in SNR on any polarization combination in the quad-pol data products as a result of this architecture, which is a more robust result than is true for a hybrid-dual-pol radar, in which SNR preservation is true if and only if the output polarization basis is chosen to match the input (circular) basis.

Simulation and design of ground-penetrating radar for Mars exploration

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.

Multi-mission radar altimeter: concept and performance

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.

Comments on hybrid-polarity SAR architecture

Recent work on compact polarimetry is reviewed in the context of the fifty-year history of polarimetric diversity. One promising form of this genre is hybrid-polarity (CL-pol), in which a synthetic aperture radar (SAR) transmits circular polarization and receives on two orthogonal mutually-coherent linear polarizations. The CL-pol technique is compared and contrasted to alternative compact polarimetric schemes. Useful characteristics that are unique to the hybrid-polarity architecture are described, especially rotational invariance and polarimetric calibration.

Optimal processing of radar ice sounding data

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.

Pathfinder Advanced Radar Ice Sounder: PARIS

The objective of the PARIS NASA Instrument Incubator Project was to demonstrate successful ice thickness sounding from a high-altitude airborne radar. This paper describes key features of the system, including the radar and the processing algorithm. Test flights over the ice sheets of Greenland produced good results.

Simultaneous laser and radar altimeter measurements over land and sea ice

Elevation data derived from space-based altimeter measurements over landand sea-ice are key to understanding the Earths 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.