FM-3-09 Fire Support and Field Artillery Operations Download
Page 198 of 256
Appendix C C-6 FM 3-09 30 April 2020 remarks, when necessary, to clarify the notes. The best survey fieldwork is of no value to the using unit if the notes are not accurate, legible, and complete in every detail. HASTY SURVEY C-27. Determining location when survey or GPS equipment are not available, the desired location may be determined through a graphic resection or graphic traverse. For more information on procedures for determining location, see ATP 3-09.50. DIRECTION C-28. Direction is the most important element of survey control. The mil relation formula states that one mil of error in direction at 1,000 meters will result in a one meter lateral deviation from the target. As the range increases, so does the deviation. C-29. FA personnel will use the M2A2 aiming circle to perform directional control in a GPS degraded, disrupted, or denied environment. Soldiers can perform directional observations using the sun and stars. Soldiers can also provide directional control using a declinated lensatic or M2 compass. Note. Units equipped with the gun laying and positioning system have an organic capability to establish an orienting station and end of the orienting line for the unit. ARTILLERY ASTRONOMIC OBSERVATION USING THE SUN C-30. Using the aiming circle in the artillery astronomic method of determining azimuth; two sides of the Pole-Zenith Star triangle, the polar distance and colatitude, and one angle are used to solve for the azimuth angle. This computation is based on the time of the observation. The problem of determining azimuth consists of taking a horizontal reading at the observer's station between the mark and sun, the azimuth of which can be computed. The simple operation of subtracting this horizontal angle from the computed azimuth of the sun gives the desired azimuth to the mark. For more information on this procedure see ATP 3-09.02. CAUTION The sun must never be viewed through the telescope without a sun filter. The filter should be inspected before use to ensure that the coated surface is free from scratches or other defects. Serious eye damage will result if proper precautions are not taken. If the sun filter has been damaged or lost, a solar observation may be completed by use of the card method. The image of the sun is projected onto a card held 3 to 6 inches behind the eyepiece and the telescope is focused so that the cross hairs are clearly defined. ARTILLERY ASTRONOMIC OBSERVATION USING A STAR C-31. The artillery astronomic method can be used with observations on Polaris or on east-west stars. Used with Polaris, this method yields the most accurate azimuths. When the artillery astronomic method is used with east-west stars, the requirement for accurate time is a disadvantage, but the method can be used when no stars meet the position requirements for the altitude method. Computation of artillery astronomic star is the same as the computations for artillery astronomic sun. For more information on this procedure see ATP 3-09.02.