This provides the basis for the measurement of wind speed. The twin mirrors are mounted at the end of a short boom. The white object is a calibration heat source. Click on image for the whole picture. The idea is simple.
Foam tends to collect on the lee side of waves.
Looking at the same piece of ocean from different angles, and comparing the two signals, should tell which direction the wind is blowing from. The radiometers were put on a turntable that spins once every 10 seconds to look ahead and then behind of the ER-2 aircraft. The aft-looking scan covers ocean seen 4 minutes earlier by a forward scan. Data from the flights were converted into images in which one can see images of Catalina and other islands, and wind shadows on the lee sides of the islands. When the color of the images is enhanced, Hood said, differences appear that should yield wind direction information.