The Space Shuttle experiments used rather simple approaches of imaging based on the amplitude of a fixed-frequency return signal. Recently, a SIR-C experiment was also flown. The U.S. and Russian intelligence communities have flown SAR satellites to gain all-weather ship movement information. Multispectral SAR, using two or more frequencies simultaneously, can provide additional information about the size of ground materials and their dielectric constants. IR transitions into visible light at the red end, hence its name.
Most people think of infrared and thermal imaging as being synonymous.
A body at 20o Celsius emits most of its Figure 3. Lunar Lake Playa, Nevada. False-color composite of TIMS bands 5,3 and 1, respectively . The TM thermal band has much coarser spatial resolution than the other bands, however. Near-infrared radiation is only emitted in abundance by very hot bodies, such as our sun.