3.6.FIELD METERS 
Field meters detect ore bodies or discontinuities in 
the subsurface structure by sensing the disruption of the 
natural pattern of terrestrial magnetism. Field meters 
are being used successfully aboard low-flying airplanes 
or afuot, but probably will not be practicable for mine- 
ral prospecting from satellites. 
It is necessary to point out that the design of remo- 
te sensing systems requires the employment of many engine- 
ering approximations, comprises, and judgments about when 
to approximate and how to compromise. Nevertheless, there 
is information in the corresponding literature, to deve- 
lop a sensor that has all the requirements for an optimal 
device in all parts of the electromagnetic spectrum, in 
the final analysis it seems remote sensing is accomplis- 
hed best by a system of devices, each contributing its 
special information for interpretation and analysis. 
From the cartopgraphic point of view, it is needed 
to point out the general problem of the remote sensing 
cystems, namely their various geometrical properties. Al- 
so, in this respect, intensive research is being conducted 
to fined the most appropriate parameters for system cor- 
rection and precision correction. 
TELEMETRY AND DATA REDUCTION 
Telemetry is the proces by which a measurement of a 
quantity is transferred to a remote location to be re- 
corded, to be displayed, or to actuate a process. Radio- 
frequency /rf/ telemetry utilizes & radiowave type of car- 
rier to transmit information from one location to another. 
Today, nearly every airoraft, satellite and other types 
of platform carry a form of rf telemetry. In the evalua- 
tion of the performance of & telemetrio system, the first 
step is the generation and reception of data. The second 
step is the extraction of useful information from recor- 
ded signals. Because of a large variety of telemetry sys- 
tems and types of data, large amount of recorded signals 
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