199 1 In the Gulf War that broke out at the beginning of the year, the sky over the battlefield was often overcast and sometimes rainy, which brought difficulties to aerial reconnaissance. However, there is a radar reconnaissance satellite named "hockey stick" in the United States, but it can see objects on the ground 1 cubic meter day and night through clouds. It drew thousands of radar images over the bay. The hockey stick satellite cooperated with other reconnaissance satellites, and also found and tracked the night shift of the Iraqi Scud missile launcher, and even could see through the disguised false targets.

The "eye" of radar satellite is synthetic aperture radar. Like a telescope, the larger the diameter of the radar antenna, the clearer the target can be seen. However, the satellite can't be equipped with a large antenna, so scientists let the spaceborne radar send and receive pulse waves accurately and repeatedly, so that the small antenna seems to become a large-diameter antenna while traveling, and the resolution is obviously improved.

Radar satellites can also be used for peaceful purposes, such as exploration and disaster reduction. Marine satellites equipped with radar can remotely detect clear waveforms and moving directions, monitor sea ice drift, and provide disaster warning for ships and ports. During the flood, radar satellites can "see" the river banks and waters through the clouds, and timely forecast the flood peak movement and water level changes. Radar wave has certain penetrability to vegetation and soil, and can measure soil moisture and forecast drought.

Now, spaceborne synthetic aperture radar (SAR) has played a great role outside the earth. Venus is shrouded in dense clouds all the year round. A spacecraft carrying radar can lift its veil and draw a very accurate topographic map of Venus.