Radar System Engineering

SEC. 3,12] SPECULAR AND DIFFUSE REFLECTIO,V 89
radar system that is used. The identification and correlation are
based upon intensity contrasts which fall into se~-eral categories, such
as the contrasts between land and water, between hill and valley, and
between built-up areas and open countryside. As each type of contrast
is discussed, it will be illustrated by radar scope photographs.
3.12. Specular and Diffuse Reflection.-0f the several ways in which
airborne radar gives its information, the most important is through the
contrast between rough and smooth surfaces. .i smooth surface on
the ground appears as a black area in the radar picture, while a rough
surface appears bright in contrast, In the case of the smooth surface,
the incident radiation is deflected away, as in Fig. 316. l~here the
ground is rough, the incident raciiation is scattered in all directions, as
(a)
in Fig. 3.16, a part of it returning to the recei~f’r to bc amplifiwl and
sboff-n on the r:idiir scope,
The signal strength from land areas is so mtIch greater than that
ret urned }JY lf-:~ter surfaces that t hc iut erpretation ot’ hind -\\”atcrbound-
:~rirs is the simplest of all rcrognition problrms. In a region of highly
indrntcd comtline the prrwntati[)n is so strikingly- simil:w to ordinary
maps tlmt navi~aticon lJYpilotagc can be performed e~”enb}- ill(’x~]t’ric’llceci
operators. Situatlfnw of thi~ tJ-p(> are illllstr:ltml in I;igs. .3 I7, 3.18,
319, and 320. in Fig. 317, for example, the positi(m of the aircraft
(given by the spot at the center of the pict~lre) c:tn immetii:~tely be
identifie(l I)y rcfrr(,nr(’ to the ( )akl:ln(l 1!att,rfrt)nt. ‘~rt,:l.lllc I.luIId, and
the lla~ Bridge. I;igllr{, 32’() illll.tr:ites t lle :ii(l in r(,to~nil ion ai’to]ded
))y a broad
ri]-c,r f-:llle~.
‘1’he finenes.~ of the (Irt:iil Tvhich can be ..ho\f-n depen(k (Jn the range
an(~ :tzirnlith resolution ()[ the radar ::~stcnl and on the >h:irpne~s Of