TABLE OF CONTENTS This chapter gives a brief discussion of the trades involved in designing a synthetic aperture radiometer for Earth remote sensing and then illustrates the concepts with two synthetic aperture radiometers. The first is an existing aircraft sensor called, ESTAR. ESTAR played an important role in the development of this technology for remote sensing and provided data to demonstrate the potential for remote sensing of soil moisture from space. A brief overview is given of the hardware and the techniques employed for image reconstruction and calibration. An image is shown from the soil moisture experiment at the Walnut Gulch Watershed an experiment that was critical in demonstrating the viability of this technology. The second example is a sensor called HYDROSTAR. This is an instrument that was proposed for remote sensing from space. Although HYDROSTAR was never actually flown, it does illustrate the potential of aperture synthesis for remote sensing from space. Design parameters are given together with expected performance. This instrument is similar in principle to the aircraft instrument, ESTAR; however there are many ways in which aperture synthesis could be implimented in space. In fact, at the time of this writing, a mission called SMOS that uses synthesis with small antennas arranged in the form of a Y is being built by the European Space Agency (ESA) for remote sensing of soil moisture and ocean salinity from space.
The primary penalty paid for employing aperture synthesis is a decrease in signal to noise for...
