ESTAR - A SYNTHETIC-APERTURE MICROWAVE RADIOMETER FOR REMOTE-SENSING APPLICATIONS

ESTAR represents a new technology being developed for passive microwave I-emote sensing of the environment from space. The instrument employs an interferometric ic technique called aperture synthesis in which the coherent product from pails of antennas is measured as a function of pair spacing. Substantial reductions in the antenna aperture needed for a given spatial resolution can be achieved with this technique. As a result, aperture synthesis could lead to practical passive microwave remote sensing instruments in space to measure parameters such as soil moisture and ocean salinity which require observations at long wavelengths and, therefore, large antennas. ESTAR is an L-band, aircraft prototype built as part of research to develop this technique. ESTAR is a hybrid real-and-synthetic aperture radiometer which employs stick antennas to achieve resolution along track and uses aperture synthesis to achieve resolution across track. Experiments to validate the instrument's ability to measure soil moisture have recently been conducted at the USDA watersheds at Walnut Gulch in Arizona and the Little Washita River in Oklahoma. The results of both experiments indicate that a valid image reconstruction and calibration have been obtained for this remote sensing technique.