The ground survey work consisted of locating the retroreflector sites,
which were generally at township or section corners, measuring the posi-
tion by distance and direction observations from an established National
Geodetic Survey (NGS) station on a nearby peak, marking the point with a
cloth panel to assist spotting from the air during future visits, and
driving a 5/8" steel rod into the ground to support the retroreflectors.
Several problems were encountered that made this phase of work take much
longer than expected:
9 A 4" x 4" post rising only 1 foot above the ground is very
difficult to locate from a helicopter in the near featureless
salt and mud flats (see fig. 6). In some instances, the township
lines are weakly marked by motor vehicle tracks, which could be
followed using the helicopter. When this technique proved
unsuccessful, the party occupying the NGS station would aim a
theodolite toward the USGS map position and bring the helicoptor
party on line by radio communication.
e Most of the project area was in restricted airspace where prior
approval for physical entry had to be arranged with Hill Air
Force Base Bombing Range schedulers. This was the busiest time
of the year for the Range, and unlimited access could generally
be obtained only on Saturday afternoons and all day Sunday.
Occasionally a few hours were obtained at other times. Once in
the air, radio contact was maintained with the Range Control
Center, which monitored the Range by radar and radio.
e Any ground activity within the Bombing Range had to be preceded
by an inspection performed by an Air Force demolition expert.
This meant that an Air Force representative accompanied all
helicopter flights where landings in the Bombing Range were
expected.
This phase of work was completed in mid-June with positions established at
all of the 55 retroreflector sites. Elevations were established at 12
points by vertical angle traverses using a total station instrument. Pre-
cise gravity measurements were made at all 55 retroreflector sites with a
LaCoste and Romberg gravimeter.
APTS PROFILE SURVEY FLIGHTS
The APTS Twin-Otter aircraft arrived at the Salt Lake International Airport
on June 17th. A power hookup in the hangar was available for the necessary
continuous operation of the APTS instruments, and an air-conditioning unit
was furnished to maintain a cabin temperature of about 75? F. While the
plane was flying, the power was supplied by an auxiliary power unit (APU)
and the cabin temperature was controlled by air cycle machines.
Plans called for daily missions to proceed as follows:
9 Perform an overnight calibration and alignment on the ground.
e Fly to the Wendover Airport and park over a survey mark for a
short calibration and alignment procedure and refueling.
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