Xuehu Zhang

Fully polarimetric bistatic radar scattering behavior of forested hills

The bistatic radar scattering measurements of forested hills were performed at grazing incidence and at azimuth scattering angles from 28/spl deg/ to 66/spl deg/ from the forward scatter plane. Using pulse-to-pulse switching between orthogonal transmitted polarizations, the radar simultaneously measures two orthogonally polarized components of the scattered wave to obtain full polarimetric information about the scattering process. These are the first fully polarimetric terrain clutter measurements to be conducted at large bistatic angles. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to examine the polarization sensitivity of the bistatic clutter. It is found that the polarization state of the EM wave scattered out of the plane of incidence strongly depends on the polarization orientation of the incident electric field. Unlike the monostatic case, these two incident wave polarization states are found to produce substantially different scattered wave behavior when trees are viewed at large bistatic angles. Scattered fields resulting from vertically oriented incident fields are found to be highly polarized and to produce bistatic clutter power levels that are strongly dependent on the polarization of the receiving antenna. In contrast, horizontally oriented incident fields are found to produce weakly polarized scattered waves with bistatic clutter power levels that are insensitive to the polarization of the receiving antenna.

The Imaging Wind and Rain Airborne Profiler - a dual frequency dual polarized conically scanning airborne profiling radar

The University of Massachusetts (UMass), with support from ONR, NOAA and NASA, has developed a novel radar system called the Imaging Wind and Rain Airborne Profiler (IWRAP). IWRAP is a dual frequency (C/Ku band) dual polarized airborne radar that profiles the volume and surface backscatter and Doppler simultaneously at 30, 35, 40 and 50 degrees incidence, while conically scanning at 30 to 90 rpm. Its range resolution can be set at 15, 30, 60 or 120 m. From these measurements the ocean surface wind field, 3-D boundary layer winds within rain bands can be mapped. IWRAP was flown during the 2002 NOAA/NESDIS/ORA Hurricane Ocean Winds Experiment, which was conducted in conjunction with the 2002 NOAA/AOML/HRD Hurricane Field Program. This paper presents the system design, radar processing algorithms and initial results from the 2002 hurricane flights.

Effect of precipitation on ocean wind scatterometry

This paper presents preliminary results of precipitation effect on microwave scatterometry wind estimates at C and Ku band. The results show that microwave scatterometer underestimates the wind speed by up to 10 m/s for rain rate condition of 15 mm/hr and wind speed condition of 25 to 30 m/s for both frequency bands

Hurricane wind and rain measurements using a dual polarized C/Ku-band airborne radar profiler

Airborne ocean backscatter dual polarization measurements at C and Ku-band obtained in high wind speed conditions (20 to 60 m/s) are presented. The VV and HH NRCS measurements are compared. The preliminary comparisons show that the HH NRCS measurements are slightly more sensitive to the surface wind speeds for high wind speed and precipitation conditions.

3-D hurricane boundary layer wind retrieval algorithm for airborne Doppler radar measurements

This paper presents a 3D boundary layer wind retrieval algorithm for airborne Doppler radar measurements of precipitation inside hurricanes. The data was collected, inside Hurricane Lili during NOAAs 2002 Atlantic Hurricane Ocean Winds Field Experiment with University of Massachusettss newly developed Imaging Wind and Rain Airborne Profiler. Two forms of Kalman filters for 3D wind retrieval are analyzed for accuracy using simulations. Preliminary results of the actual 3D wind estimates using the chosen algorithm were obtained and compared with simultaneous and independent wind vector measurements by GPS dropwindsondes, surface wind speed measurements by a microwave radiometer and flight level wind vector measurements

Polarization and look-direction dependencies observed in radar imagery of the Chesapeake Bay Outflow Plume front

In May 1997 and May 1999, the Remote Sensing Division of the Naval Research Laboratory conducted phases Two and Five of the Chesapeake Bay Outflow Plume Experiment (COPE2 and COPE5, respectively). In both experiments, an airborne, X-band, real-aperture radar was used to image the outflow plume front that forms in the mouth of the Chesapeake Bay. On an interleaved, pulse-to-pulse basis, both horizontally and vertically polarized imagery was collected. In COPE5, backscatter intensity were observed polarization when the look direction and grazing angle were varied, with the largest across-the-front backscatter contrast occurring at an 80 degree incidence angle when a landward look direction was used. The strongest backscatter was observed on the continental shelf side, regardless of look direction. In COPE2, large contrasts in backscatter intensity were also observed for horizontal polarization, but the look dependency was reversed: larger contrasts were observed when a seaward look direction was used, and the strongest backscatter was observed on the plume-side of the front. In this paper, these observations will be quantified, and an explanation for this interesting behavior will be given that involves the interaction of wind waves and opposing currents.

Effect of precipitation on Ku-band scatterometer ocean wind measurements

This paper presents preliminary results of the 3D-wind retrieval algorithm developed for the multi-look airborne Doppler radar measurements using various forms of Kalman filters. The data was collected inside Hurricane Lili during NOAAs 2002 Atlantic Hurricane Ocean Winds Field Experiment with University of Massachusettss newly developed Imaging Wind and Rain Airborne Profiler (IWRAP). Two forms of Adaptive Kalman filter are presented for 3-D wind retrieval. Simulations of different wind field and radar parameters are made to investigate the performance of the selected filter. Preliminary results of the actual 3-D wind estimates are then obtained and compared with simultaneous and independent wind vector measurements by GPS dropwindsondes, surface wind speed measurements by a microwave radiometer and flight level wind vector measurements.

Preliminary results of 3D hurricane boundary layer wind estimation with multilook Doppler radar measurements of the precipitation

This paper presents preliminary results of the 3D-wind retrieval algorithm developed for the multi-look airborne Doppler radar measurements using various forms of Kalman filters. The data was collected inside Hurricane Lili during NOAAs 2002 Atlantic Hurricane Ocean Winds Field Experiment with University of Massachusettss newly developed Imaging Wind and Rain Airborne Profiler (IWRAP). Two forms of Adaptive Kalman filter are presented for 3-D wind retrieval. Simulations of different wind field and radar parameters are made to investigate the performance of the selected filter. Preliminary results of the actual 3-D wind estimates are then obtained and compared with simultaneous and independent wind vector measurements by GPS dropwindsondes, surface wind speed measurements by a microwave radiometer and flight level wind vector measurements.