SITING AND COVERAGE OF GROUND RADARS 73 
terrain at the terminals of the propagation path. 
Siting refers to the general problem of selecting and 
utilizing available locations for the best operation 
of the equipment involved. With some types of 
equipment the effects of local conditions are minor, 
and with other types the requirements are most 
exacting. In many cases practical and tactical con- 
siderations will compel the use of unfavorable loca- 
tions. Performance may then be considerably below 
that obtained in the laboratory or under ideal condi- 
tions, and familiar characteristics may be drastically 
modified. 
Field personnel are frequently called upon to 
predict or explain abnormal operation, to devise 
methods of improving poor performance, and to 
make modifications to fit local requirements. This 
discussion will be limited to general principles, and 
reference is made to the instructions furnished with 
the individual equipment for specific details. 
Elements of a communication or radar network 
should ordinarily be viewed as parts of a system and 
not as isolated, self-sufficient units. From this point 
of view a site that gives outstanding results would 
not be satisfactory if it did not help achieve the 
mission of the system. This interrelation between 
‘various parts of a system, which may extend over 
hundreds of miles, raises numerous problems of 
orientation, visibility, and coverage. 
Maps and Surveys 
Where available, topographic maps of a scale on 
1 or 2 miles to the inch and contour intervals of not 
more than 100 ft, preferably 20 ft, should be secured. 
Hydrographic charts are valuable in coastal areas. 
If there are no reliable maps, aerial photographs 
may be used to a limited extent. 
Due consideration should be given to the suit- 
ability of the map projection for the purposes for 
which it is to be used. The grid system used for 
reporting should be based on the Lambert polyconic 
projection, and not on the Mercator projection. 
Otherwise important errors in azimuth may occur. 
This is especially true at high latitudes. If in coordi- 
nating with other services, such as the Navy, it is 
required to use the Mercator projection, the transfer 
‘from the Lambert projection may be made with a. 
transparent overlay of one grid system on the other. 
A transit and a stadia rod are most useful for 
orientation, surveys, profiles, ete. Compasses, clinom- 
eters, and other surveying instruments should be 
provided. In the absence of some of this equipment 
much may be done with improvised devices made 
with plumb bobs and protractors. Rough surveys 
may be made with only a sketching board and by 
pacing off distances. Navigation instruments may be 
used for approximate determination of position. 
Engineer and artillery publications describe orien-’ 
tation methods in detail. Close attention should be 
given to the grid system used for reporting nets so 
that all stations are accurately located. Grid errors 
may be minimized by making all charts from a 
master copy. 
Profiles 
The height of the center of the antenna should be 
determined to within a few per cent. The reference 
level is the main refleeting surface, which is normally 
the sea. Heights given on maps should be checked 
against available bench marks and the terrain. 
Barometers or airplane altimeters are useful for 
height determinations, but their readings should be 
corrected for temperature. 
Where the reflection surface is part or all land, a 
profile is usually necessary for estimation of the 
effective antenna height and the reflection charac- 
teristics of the terrain. Profiles should be prepared 
of several representative azimuths in the operating 
sector. The accuracy required decreases with the 
distance from the transmitter. In most cases suffi- 
cient detail is not available on maps so that a 
personal inspection of the terrain should be made 
to become familiar with the nature of the soil and 
the degree of roughness. Special attention should be 
given to ridges, flat areas, bodies of water, distance 
to the shore, hills to the rear, obstacles in the operat- 
ing area and at the boundaries. A knowledge of the 
antenna pattern in both the vertical and horizontal 
planes is necessary for judging what parts of the 
terrain should be more closely examined. 
Orientation 
Where long distances and directive beams are 
involved fairly accurate orientation is required. This 
is especially true of the narrow beam, precision type 
radars. Of the many ways of determining the direc- 
tion of north, one of the most convenient is observa- 
tion of the azimuth of the sun. Care must be taken 
when using compasses because of local attractions 
or inadequate information of the declinations. Star 
observations are capable of good accuracy, but where 
Polaris is not visible they require thesame procedure 
as solar shots. Caution must be used m aligning on 
permanent echoes because nonstandard refraction 
may bring in confusing distant echoes, or side lobes 
may give false echoes. In general several methods 
should be used in order to obtain independent checks. 
When an accurate orientation has been obtained 
reference marks should be provided so that the 
azimuth may be readily checked. 
Solar azimuths, correct to the nearest quarter of 
a degree, may be determined from the date, time 
to the nearest minute, and the latitude and longitude 
to the nearest degree. Two methods will be given 
for obtaining the azimuth of the sun: (1) by calcu- 
lation, (2) from tables. A third method gives true 
