Two-dimensional Kaiser apodization function for interferometric radiometry from space

Abstract

In radiometric interferometry from space [e.g., European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) interferometer], apodization or tapering functions can be used to ensure that ground resolution elements (synthetic antenna footprints) have equal area and shape. If resolution can be made uniform, subsequent processing—which relies on multiangular processing of the information from the same point of the Earth but seen from different directions, from snapshot to snapshot—is less prone to errors. This is called strip adaptive processing. We describe how to use two-dimensional (2D) Kaiser apodization functions to achieve the strip adaptive process and describe its relation to conventional Blackman nonadaptive apodization. In particular, we show how to compute the Kaiser parameters from sampling specifications within the complete field of view (FOV) of the instrument. This is achieved by setting up suitable regressions between a Kaiser parameters–dependent function, the array function half width at half maximum (HWHM), and the nominal elliptical footprints' area and eccentricity. The performance of the suggested methodology is compared to the baseline, based on nonadaptive Blackman apodization.