Active Systems

As we have noted elsewhere, 1 mW in a 1 MHz bandwidth corresponds to a brightness temperature of 10¹⁴ K, vastly higher than ambient temperatures. Even with broader bandwidth detectors, the illumination temperatures are still high, especially for rapidly scanning systems [1]. While active imaging is attractive from a S/N point of view, it introduces two new challenges: coherent speckle and the need to strategically orient what are ordinarily uncooperative targets.