Radar System Engineering

112 PROPERTIES OF RADAR TARGETS [SEC. 317
miles on large targets are observed with 3-cm systems such as the AA”/-
APQ-13 and AN/APS-15, while with 1.25-cm systems like the AX/APS-
22 the ranges available at present are about 15 miles on ground return
and 30 miles on large targets, for average atmospheric conditions in the
Eastern United States. Under conditions of high atmospheric humidity,
N
FIG. 3.37.—Detroit, Mich. The Ford Rouge River plant showsas a bright patrh 7 mi
southeastof the amcraft. Wavelength = 1.25cm, 0,8° beam, altltude 4000ft. radius 10
IMUtiCalmi. 42°21’N, 83001‘TV,
the absorption of energy by water vapor becomes an important factor
limiting the maximum range of a radar set at 1.25 cm (see Sec. 2. 15).
Even strong signals from large cities are attenuated below noise level
if the cities are much beyond the maximum range for ground return.
Figure 3.39, which illustrates this uniform range cutoff, ~yas obtained
with a 1.25 cm system at an altitude of 20,000 ft near the Pacific entrance
of the Panama Canal, with an average water-vapor concentration of