ARMY TM 5-6675-308-12
MARINE CORPS TM 08837A-12/1A
b. Mean Horizontal Angle Measurement. See figure
3-6, view B.
ments may be performed any time throughout the survey
mission, but must always be performed when the update point
Autoreflect on porro prism.
(1)
is inaccessible to the PADS vehicle, when a position to be
Measure direct angle (in mils) from porro prism
(2)
established is inaccessible to the PADS vehicle, or when an
clockwise to azimuth target.
azimuth line of less than 100 meters is required.
Plunge theodolite telescope and measure reverse
(3)
NOTE
angle (in mils) from azimuth target to porro prism
(autoreflect).
To increase visibility, color the theodolite
(4)
sight white. At night, illuminate the sight
If the difference between direct and reverse
with the theodolite handlamp.
pointings is greater than 0.2 mil, repeat the
measurements.
Autoreflection. Prior to making any optical mea-
a.
Determine the mean of the direct and reverse point-
(5)
surements, the PADS operator must achieve autore-
ings to obtain the mean horizontal angle.
flection. To achieve autoreflection, perform the
following:
c.
Offset Distance Measurement.
NOTE
Stop vehicle close to SCP, GPS update point or
(1)
point to be established, exit vehicle, and perform a
At night, illuminate porro prism scale with
zero-velocity correction by pressing CDU STOP.
PADS mounted flashlight. Porro prism has
(2)
Set up theodolite over SCP, GPS update point or
two scales for inverting and noninverting
point to be established. If an azimuth is required,
instruments.
set up a range pole over azimuth marker.
(1) If distance between porro prism scale and theodo-
lite is less than 8 meters, locate left vertical stadia
Uncover and roughly level the porro prism.
(3)
line on porro prism scale zero mark. Read the scale
The vehicle operator makes certain that the CDU
(4)
where the right stadia line intersects the scale.
has a flashing "GO" light and maneuvers the
Example, figure 3-6, view C: stadia lines on 0 and
vehicle so that the porro prism is visible from the
3.8 on scale. Offset distance is 3.8 meters.
theodolite and is within 16 meters. The PADS oper-
(2) If offset distance is between 8 and 16 meters, locate
ator, standing behind the theodolite, instructs the
left stadia line on zero mark and read the distance to
vehicle operator to slowly maneuver the vehicle
the center vertical crosshair where it intersects the
until the theodolite is reflected in the porro prism
scale; then, multiply it by two. Example, figure
and autoreflection is obtained. An alternate proce-
dure, especially useful for helicopter operations, is
crosshair is on 4.8 of scale, offset distance equals
to keep the vehicle stationary and move the theodo-
4.8 x 2 or 9.6 meters.
lite until autoreflection is achieved.
Vehicle operator exits the vehicle, presses the
(5)
Using Theodolite.
STOP key, and fine-levels the porro prism.
NOTE
The PADS operator then checks to see if autore-
(6)
flection can still be achieved. If not, repeat steps(1)
At the completion of an update, PADS will
through (5) as necessary.
not adjust the azimuth obtained in a posi-
tion, azimuth and elevation mark using a
Focus the theodolite so the reflected image of the
(7)
theodolite.
theodolite front sight is centered on the vertical
a. Stop vehicle close to SCP, GPS update point or point
crosshair (see figure 3-6, view A). The theodolite
line-of-sight is now perpendicular to the porro
to be established. Exit vehicle and perform a zero-
velocity correction by pressing STOP key on CDU.
prism.
3-36.17
Change 3
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