Title: Digital Beamforming Synthetic Aperture Radar (DBSAR) Polametric Upgrade
Author: Rafael Rincon
Organization: NASA Goddard Space Flight Center

For several years NASA/GSFC has been investing through internal research and development (IRAD) in the development of a new generation airborne L-Band radar system known as the Digital Beamforming Synthetic Aperture Radar (DBSAR). DBSAR combines advanced radar technologies, real-time on-board processing, and innovative signal processing techniques in order to enable multi-mode radar techniques in a single radar architecture. Although DBSAR's original configuration had a dual-polarization antenna, the rest of the system had been designed for single polarization operation. Nevertheless, polarimetric measurements provide more accurate estimates of important scientific parameters and are critical in supporting future airborne and spaceborne applications.

DBSAR's upgrade to polarimetric operation was accomplished through an ESTO awarded project aimed at enhancing DBSARís capability as a science instrument. Two polarimetric designs were chosen after considering several design options. The first approach modified the existing radar architecture to enable interleaved polarimetric operation (e.g., sequentially transmit and receive horizontal and vertical polarizations). Although this option did not provide the full polarimetric capability, it was less risky, made use of a proven architecture, and provided all radar polarizations in a sequential manner. The second approach developed new polarimetric L-band transceivers that can enable a full polarimetric operation (e.g., simultaneously transmit and receive orthogonal polarizations). The new transceivers were to be designed on printed circuit boards and made use of surface mount miniature components, reducing the size by a factor 4 while exhibiting an RF performance similar to the exiting transceivers.

Both approaches were successfully carried out and will be demonstrated in 2011/2012 campaigns as the DBSAR system is flown on board of the NASA P3 aircraft over forest on the US East Coast to characterize biomass and ecosystem structure, as well as planetary analog terrains.