CHAPTER 12
ELECTRONIC SURVEYING EQUIPMENT
Chapter 12 of the EA3 TRAMAN introduced you
to electronic surveying equipment, specifically
electronic distance-measuring equipment. This chapter
is intended to supplement what you learned in the EA3
TRAMAN discussion, and, in addition, introduces you
to the basic principles and uses of other types of
electronic surveying equipment.
As a rule, the EA seldom has the need or opportunity
to use any of the equipment discussed in this chapter;
however, when the need and occasion arise, the EA
should have at least a basic familiarity with the different
electronic equipment used in surveying. This chapter
provides that familiarization.
ELECTRONIC
DISTANCE-MEASURING (EDM)
EQUIPMENT
When electronically determining the straight-line
distance (horizontal or slope) between two points or
stations, you use equipment that (1) sends an electronic
impulse of known velocity or rate of speed and (2)
measures the time it takes for the impulse to travel the
length of the interval between the points. Then, by using
the well-known equation of distance = rate x time, the
length of the interval is determined.
Two types of electronic distance meters (simply
referred to as EDMs) are commonly used. They are the
electromagnetic (microwave) instruments and the
electro-optical (light wave) instruments. In this section,
we will briefly discuss both types of instruments;
however, since there are many different makes and
models of EDMs on the market and since you should
always study the manufacturer’s operating instructions
before you try to use the equipment, only the basic
principles of the operation and use of EDM equipment
is covered. For in-depth discussions of EDM principles,
you should read publications, such as Surveying Theory
and Practice, by Davis, Foote, Anderson, and Mikhail.
ELECTROMAGNETIC (MICROWAVE)
EDM INSTRUMENTS
Electromagnetic EDMs, first
1950s, use high-frequency radio
developed in the
waves. The first
generation of this equipment was very precise for
measuring long distances; however, it was too bulky and
heavy for the practicing surveyor’s needs. Over the
years, the equipment has undergone rapid improvement
to the extent that modern electromagnetic EDMs are
smaller, more portable, and are being equipped with
direct readout capability.
When used, two identical and interchangeable
instruments, such as shown in figure 12-1, are setup at
both ends of the line that you are measuring. This line
must be unobstructed, but intervisibility is not required;
so, you can make observations in fog or during other
unfavorable weather conditions. As illustrated in figure
12-2, the sending (master) instrument transmits a series
of modulated radio waves to the receiving (remote)
instrument. The remote instrument interprets these
signals and sends them back to the master unit that
measures the time required for the radio waves to make
the round trip. The distance is computed based on the
velocity of the radio waves. Because this velocity is
affected by atmospheric conditions, corrections for
temperature and barometric pressure are applied
according to the operating instructions provided with
the equipment.
ELECTRO-OPTICAL (LIGHT WAVE)
EDM INSTRUMENTS
Electro-optical EDMs use the velocity of light
waves to determine the distance between two points.
The earliest of these instruments, typified by the
Geodimeter, was developed during the same decade as
the electromagnetic EDMs. Figure 12-3 shows an
example of a Geodimeter. Like the electromagnetic
instruments, the first generation of electro-optical
instruments were heavy, bulky, and not well suited to the
needs of the practicing surveyor; however, through later
development, modern electro-optical EDMs are
smaller, lighter, easier to use, and require less power.
Modern short-range instruments have ranges from 0.3
miles to 3 miles. Longer range instruments, using
coherent laser light, have ranges from 50 feet to 36
miles.
To use an electro-optical EDM, you set up the
instrument at one end of the line being measured and a
12-1
