Passive microwave remote sensing - a tool for maritime surveillance?

Abstract

Microwave radiometry deals with the measurement of the natural thermally caused electromagnetic radiation of matter at a physical temperature above 0K. In the case of Earth observation significant contrasts can be observed between reflective and absorbing materials due to the impact of reflected sky radiation of cosmic origin. The main MMW windows for sufficient atmospheric penetration and low sky brightness temperatures are at frequencies around 35, 94, 140 and 220GHz. For Earth observation, an approximate brightness temperature range from 3K to more than 300K can be observed. In the microwave region the spatial two-dimensional brightness temperature distribution can be used as a daytime and almost weather independent indicator for many different physical phenomena. Hence, interesting application areas incorporate geo science, climatology, agriculture, pollution and disaster control, detection, reconnaissance, surveillance, and status registration in general. Since a few years security applications like personnel screening and the monitoring of critical infrastructures are also of major interest. Many of those applications require high spatial and radiometric resolution, high precision, large fields of view, and high frame rates. The paper gives a brief introduction to the physical background of microwave radiometry and illustrates the three mostly considered imaging principles, the linescanner approach, the innovative aperture synthesis and the focal plane array technique. Typical examples from current practice of security related imaging and basic experimental measurements for future applications and of maritime scenarios are shown.