Radar System Engineering

SEC!. 3.12] SPECULAR A.IJLJ DIF’FC’SE ILYII’LECTIO.Y 91
airport runways stand out clearly against the grass-covered ground
between the runways. At the wavelength of 1.25 cm the grass isthoroughlyrough
and the runways quite smooth, resulting in strong contrast.
The contrast is reduced at much shorter wavelengths (ordinary light),
for which the runways as well as the grass appears rough. At much
N
FIG. 31S.-Coastal areasof Kyushuand Shikokuin the vicinityof Uwajima,Japan.
Wavelength= 3.2 cm, 3° beam, altitude 10,000 ft, radius 24 nautical mi. 33”03’N.
132”20’E.
longer wavelengths both the grass and the runways appear smooth in
comparison with wooded areas around the airport. There isstill a small
signal from the grass and a smaller signal from the pa~-ed runway,
(because any irregularity scatters a certain amount of power), but on
the radar picture a surface that is flat in comparison with the wavelength
appears dark in comparison with a rough surface, except when the
flat surface is viewed at normal incidence.