ARMY TM 5-6675-308-12
MARINE CORPS TM 08837A-12/1A
Assuming the surveyor decides to use GPS data, he
c.
indicator lights. Troubleshoot in accordance with
should generate a mark with the GPS receiver, noting
the FOM. It is recommended that a FOM of less than
by the operator.
25 meters (PADS entry of 1) always be used and
3-22.13. Updating.
50 meters (PADS entry of 2) only in emergency situa-
tions. Greater than 50 meters should never be used
NOTE
due to the inaccuracy associated with the data.
An update may be cancelled any time
d. E will enable the software to accept GPS related data.
before completion by pressing UPDT a
The next cue will be for the differential mode. The
second time. A completed update cannot be
very first update will ignore the differential mode
eliminated.
whether or not it is entered because it is meaningless
at that time. The surveyor should observe and main-
Position and elevation updates may be per-
tain correct system inputs. The operator should clear
formed independently.
the differential input request. The next cue should be
PADS must be updated after initialization before it
for FOM. 1 through 9 is flashed, but the system will
a.
accept 1 or 2, rejecting 3 and up (refer to paragraph
can supply survey data. The accuracy of the survey
data is dependent upon the accuracy of the update
entry, the cueing will restart with GPS C-E.
data. This is required, assuming the mission will be
assessing local map coordinate data. Control data can
After the correct FOM has been entered, the system
e.
be obtained by astronomic, conventional survey,
will cue for antenna on vehicle (AOV C-E). C means
local map, etc. with generally a bench mark
the antenna is remote to the vehicle, or the GPS data
embedded in concrete defining the point. A relatively
may have been placed previously, with a marker
new method of determining position, as indicated in
locating the point. The system will revert to the
vehicle's standard lever arms for the plumb bob or the
cies, with the best figure of merit (FOM) and low
porro prism.
(four or better) geometric dilution of precision
(GDOP), is 25 meters spherically. Typically, how-
f.
An E means the GPS receiver antenna is hard
ever, they are generally much better. For increased
mounted to the vehicle, the lever arms of the antenna
GPS accuracy, another method utilizing two receiv-
to the IMU are in place, and current GPS data is
ers has been devised. One receiver travels with the
planned on being entered into PADS. The cue will be
surveying group and a second receiver remains at a
for casting data. The operator surveyor must be sure
stationary base. The two receivers are initially
the GPS receiver datum and associated reference
compared at the first station with receiver differences
ellipsoid (spheroid) agrees with the spheroid (ellip-
recorded. When the survey team desires a secondary
soid) that had been entered into PADS during initial-
update, radio communication with the base station is
ization. If there is any question as to the PADS entered
made and any changes from the station position as
spheroid, the operator must press SPH to identify the
determined by the stationary receiver is given to the
spheroid PADS is operating within. Refer to table
mobile receiver for adjustment of the mobile receiver
data. This is commonly known as differential GPS
are utilizing the same reference ellipsoid (spheroid).
operation. PADS update inputs includes survey con-
If a change is required, the GPS receiver may be
trol, differential GPS, and GPS in the descending
changed without reinitializing. To change the PADS
order of accuracy.
spheroid, a shutdown and reinitialization is required.
b. After an update is requested, the PADS will cue for
g. Horizontal position updates are completed separately
from elevation, therefore making it possible to mix
the following: GPS C-E, where C means known sur-
vey control data will be entered. The data entered will
updates if necessary, i.e., a known horizontal control
may be available with no, or questionable, vertical
be referenced to the plumb bob suspension point and
the expected data will be trig list data obtained from
control. The operator should proceed with updating
known control.
the horizontal position with the known control by
3-36.12
Change 3
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