A study was carried out to determine the feasibility of a man-portable receiver system for land survey, which would be capable of detecting the optical scatter due to molecular and aerosol constituents of the atmosphere from a vertical laser beam. Tests were run with a beacon and receiver separated by approximately one mile. The system was consistently able to detect the laser signal regardless of background conditions

Caudill, L. O.

English

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196 GODDARD SPACE FLIGHT CENTER
LONG RANGE LASER TRAVERSING SYSTEM
Louis O. Caudill
In December 1968, the U.S. Forest Service approached Goddard Space
Flight Center to see if NASA-developed laser technology could be applied to
the problems involved in surveying land in areas where the direct line of
sight between property corners located on one mile centers is obscured by
various types of obstacles, such as terrain or vegetation. As an indication of
the magnitude of this requirement, the U.S. Forest Service controls 270,000
miles of property lines consisting of more than 1,000,000 property corners,
the majority of which are located on one mile centers. Maintaining these
property lines requires a never-ending program of land survey. The Forest
Service estimates that an instrument with a range capability of one mile and
an azimuth accuracy of +1 minute of arc will support 95 percent of their
surveying requirements at a savings in excess of $100.00 per mile in cost.
In support of the U.S. Forest Service request, a study was carried out to
determine if the concept of detecting optical scatter from a vertically
oriented laser beam with a portable receiver system located up to a mile
away was theoretically feasible, and if feasible, could a laser transmitter and
receiver be built that would be man-portable and meet our theoretical
requirements such as power output and receiver detectability. The results of
the study verified the feasibility of a system which would be both
man-portable and capable of detecting the optical scatter due to molecular
and aerosol constituents of the atmosphere from a vertical laser beana.
Figure 1 shows the basic concept of the system. The laser transmitter,
located up to one mile from the receiver, is aligned to the local gravity
vertical by the use of precision bubble levels attached to the unit. The
receiver is set up on a reference corner, leveled, and pointed in the direction
of the laser beacon specified by compass data. The receiver is elevated to
clear terrain obstacles and the transmitter is commanded to fire either upon
command of the receiver operator via a radio link or in a continuous 1/5-s
mode. The receiver then begins an azimuth search until the beacon is
https://ntrs.nasa.gov/search.jsp?R=19720018152 2020-03-17T03:55:18+00:00Z
TECHNOLOGYACCOMPLISHMENTS,1970 197
detected. The receiver is then aligned to the laser beacon using the azimuth
sensing capability built into the receiver system.
Figure 2 shows the laser transmitter and receiver units of our prototype
surveying system. The laser vertical beacon consists of a ruby laser system
with an energy output in excess of 150 mJ and an angular divergence of less
than one mrad. The narrowness of the laser beam is basic to our azimuth
accuracy. This laser divergence represents a beam width of 30.5 cm at an
altitude of 457.5 m. The unit is powered by a 28-V battery pack at a
maximum rate of one pulse every five seconds.
The receiver system is a modified DKM-3A astronomical theodolite
with a basic instrumental accuracy of less than 0.5 arc seconds. The unit has
a 2.83 arc-second optical aperture and a 50.8-cm focal length. The unit
shown has an acquisition field of +20 arc minutes and an azimuth sensing
accuracy of -+0.5 arc minutes at a range of one mile and a receiving elevation
angle of 45 deg.
The system shown in Figure 2 has been operated in the field under a
variety of daylight conditions. The tests were run with the beacon and
receiver separated by approximately one mile. The system was consistently
able to detect the laser signal regardless of background conditions.
_p__MOL£CU LAR AND
TIE I AEaOSOL SCATTERING
Figure 1-Laser traversing system.
L__
198 GODDARD SPACE FLIGHT CENTER 
LASER TRANSMITTER 
POWER OUTPUT 
OPTICAL WAVELENGTH 
PULSE LENGTH 
PULSE RATE 
DIVERGENCE 
POWER INPUT 
WE IGHT-LASE R 
BATTE R l  ES 
TRIPOD 
TOTAL 
RECEIVER 
OBJECTIVE APERTURE 
FOCAL LENGTH 
ACQUISITION FOV 
OPTICAL BW 
SENSITIVITY OF LEVELS 
INSTRUMENT ACCURACY 
WEIGHT-RECEIVER 
E LECTRON I CS 
BATTE RlES 
TRIPOD 
TOTAL 
0.15J 
6943A 
<20 rns 
12/min MAX 
0.75 X rad 
28 V dc 
10.80 kg 
6.75 kg 
10.35 kg 
27.90 kg 
2.83” 
50.8 crn 
40’ 
1 0 ” h m  
11.25 kg 
4.50 kg 
6.75 kg 
9.00 kg 
31.50 kg 
8 A  
0.5’ 
Figure 2-Prototype surveying system. 


Long range laser traversing system

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