Two-dimensional Doppler-radiometers for Earth observation

Compared to synthetic aperture radars the angular resolution of microwave radiometers is quite poor. Traditionally it has been limited by the physical size of the antenna. However, the angular resolution can be improved by means of aperture synthesis interferometric techniques. Aperture synthesis techniques synthesize a narrow beam during the image formation processing of the cross-correlations measured at zero-lag between pairs of signals collected by an array of antennas. The angular resolution is then determined by the maximum antenna spacing normalized to the wavelength (baseline). The next step in improving the angular resolution is the Doppler-radiometer concept, which is related to the super-synthesis radiometers and the radiometer-SAR. This paper presents the concept of a three-antenna Doppler-radiometer for 2D-imaging. The performance of such a concept-instrument is evaluated in terms of spatial resolution and radiometric sensitivity, and an L-band illustrative example is presented