A few examples of interferometry applications in space-related active and passive remote sensing

The paper describes only a few examples of interferometry applications for space related active and passive remote sensing scenarios. Pulses with defined bandwidths as needed in a total system picture are applied (active remote sensing). Several accurate radar remote-sensing satellites have been produced under ESA's technical management. Work continues (www.esa.inQ) and new missions are developed. Also, such activities are ongoing at the level of National Space Agencies (Italy, Germany, etc.). Stability in instrumentation and related signal settings permits to make further advances and interferometry applications are advancing strongly. Some examples are shown, from which one observes, that accuracy is a very important factor. Ultra stabile reference clock signals are needed in interferometry applications with as an extreme example an experiment to perform Very Long Baseline Interferometry (VLBI) tracking of a weak transmission signal at Saturn's distance. Clock stability, using masers with 10"14 to 10"15 sec accuracy is needed here.