Modeling the radiometric signatures of the Earth from space: a tool to study the performance of new radiometers

Abstract

In the last years two new kinds of microwave radiometers are being studied for Earth observation: aperture synthesis interferometric radiometers and polarimetric radiometers. The first ones are formed by an array of small antennas whose outputs are cross-correlated and then, properly processed to obtain a map of the apparent brightness temperature of the whole scene being imaged. One- and two-dimensional systems have been studied by some space agencies, e.g. ESTAR by NASA, and MIRAS by ESA, as a solution that avoids the implementation of large steerable antennas at low frequencies (L-band), while reaching a relatively high spatial resolution: about 20 - 30 Km. More recently preliminary studies of mm-wave systems have also been studied to improve the spatial resolution achieved by today's radiometers. On the other hand, polarimetric radiometers are formed by a dual-polarization antenna. The real and the imaginary parts of the complex cross-correlation computed from the H/V outputs leads to the third and fourth Stokes parameters of the incoming thermal radiation, which are basically related to roughness state of the surface being imaged. At present, a number of studies are being conducted to establish the relationship with the wind direction over the sea surface. The performance analysis of those systems requires the modeling of the apparent brightness temperature map of the Earth and/or sea surface that would be imaged at the microwave and the mm-wave frequencies, which is the object of this paper.