Remote sensing of hydrometeors by means of interfermotric radiometry: theory and experimental results

Spaceborne and ground-based radiometric measurements at microwave and millimeterwave frequencies have proved able to monitor hydrometeors, but at present the angular resolution of those systems is limited by the radiometer's antenna beam width. Efforts to improve the angular resolution of such systems by applying the interferometric techniques successfully used in radio astronomy [Thompson et al, 1986; Ruf et al., 1988] have encountered two main limitations. First, imaging interferometric radiometers are extremely complex, with a very large number of antennas and correlators. Second, because of the wide field of view, the array size is restricted by spatial decorrelation effects that cannot be simply compensated for by an adjustable delay, as in radio astronomy. Bandwidth segmentation overcomes this limitation at the expense of an even higher system's complexity. To overcome these limitations, this paper presents a technique that may achieve high angular resolution with a minimum number of antennas, taking advantage of the spatial filtering due to signal decorrelation. It describes both the basic theory behind this process and the experimental results at X band with a random static distribution of rubber bits and with simulated rain. The experimental results agree well with theoretical predictions and computer simulations, showing the inevitable trade-off between angular resolution and radiometric sensitivity.