VESAS: a novel concept for fully-electronic passive MW imaging

Abstract

These days passive microwave (MW) remote sensing has found many applications. For example, in Earth observation missions, it is possible to estimate the salinity of oceans, the soil moisture of landscapes, or to extract atmospheric parameters like the liquid water content of clouds [1, 2, 3]. Due to the penetration capabilities of microwaves through many dielectric materials, and the purely passive character of this kind of remote sensing, this technique nowadays is considered as well in many security and reconnaissance applications (e.g. observation of sensitive areas, detection of concealed objects, trough-wall imaging, etc.). Presently different imaging principles for MW radiometry are possible. Most of them still are based on pure mechanical scanning or they combine this with electronic scanning by using parts of a focal plane array [4]. Due to many advantages, the technological trend is going towards fully-electronic beam steering or two-dimensional focal plane arrays. These systems are able to achieve high frame rates, but they are still very expensive because of a significantly higher number of receiver modules, compared to a mechanical scanning system. In our approach a novel concept for a Ka band fully-electronic wide swath MW imaging radiometer system is introduced [5]. It is based on a combination of beam steering by frequency shift for one scanning direction using a slotted-waveguide antenna, and the application of aperture synthesis in the other. In the following a proof of concept is outlined using a two-element interferometer system called VESAS ( V oll e lektronischer S canner mit A pertursynthese) demonstrator. The advantage of using the aperture synthesis technique is the possibility to implement minimal redundant sparse arrays without a degradation of the antenna pattern. In combination with the beam steering by frequency shift, one requires a one dimensional receiver/antenna array for a two dimensional imaging, hence a low-cost, fully-electronic wide swath microwave radiometer system with high frame rates is feasible. In the following a proof of concept is outlined by presenting different MW imaging measurement results, using this kind of imaging principle.