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CHAPTER 5

HASTY SURVEY TECHNIQUES



Section I

SURVEY CONTROL


5-1. REQUIREMENTS

a. Common survey reduces the amount of survey error between fire units. Although the survey may contain errors, survey related error is considered to be constant. Common survey is required to accurately mass fires. Normally, accurate survey data are provided as time and the tactical situation permit. However, sometimes accurate survey data are not available. Errors in firing, due to a lack of survey control, can be eliminated by registration. However, registrations may not be possible or practical due to security and ammunition considerations. Consequently, battery supervisors must be proficient in the use of the hasty survey techniques described in this chapter. Thus, they can provide their own survey control, effectively mass fires, and deliver effective unobserved fires.

b. If accurate survey data are not available, the procedures described in this chapter will enable firing units to establish acceptable survey control.

5-2. ELEMENTS OF SURVEY CONTROL

a. The three elements of survey control are direction, location, and altitude.

(1) Direction. This is the most important element of common survey. The inherent error is directly related to the range to each target. The mil relation formula states that 1 mil of error in direction at 1,000 meters will result in a lateral deviation from the target of 1 meter.

EXAMPLES

A 1 mil error at 10,000 meters will result in a deviation from the target of 10 meters.

A 10 mil error at 10,000 meters will result in deviation from the target of 100 meters.

An error such as the one in the last example will cause the rounds to have little, if any effect on the target. (See paragraph D-9.)

(2) Location. Accurate location of the firing unit is second in order of importance. When higher order survey techniques are used to establish the tiring unit location, a high degree of accuracy is assured. An alternative is to estimate, by map spot, the location of the firing unit. If the unit's position is map-spotted, for example, 200 meters too far to the east, the initial rounds will impact 200 meters to the east of the actual location of the target.

(3) Altitude. Altitude is the last of the three elements of survey control. If not established by formal survey procedures, it must be obtained through the use of contour lines on the map sheet covering the area of operations. Generally, a map spotted altitude introduces only a minor error into the computation of site.

b. The hasty survey techniques discussed in this chapter fall into two categories-directional control and determining location.


Section II

DIRECTION


5-3. SIMULTANEOUS OBSERVATION

a. Simultaneous observation (SIMO) of a celestial body is a fast and easy method of transferring directional control. It is ideally suited for field artillery units, because many units can be placed on common directional control in minutes. The principle of simultaneous observation is that any celestial body is so far away that, for practical purposes, the lines of sight to it from two or more points on the surface of the earth are parallel (Figure 5-1).

Note: For units equipped with BUCS revision 1 ROMs, a similar technique know as a hasty astro will provide accurate directional control. A hasty astro has the advantage of not requiring a master station or radio communications as the simo does. Step by step procedures for conducting the hasty astro technique are listed in FM 6-2 and in the BUCS revision 1 job aids (ST 6-40-31).

b. During daylight, the sun is used for observation. At night, any predetermined celestial object may be tracked. Simultaneous observation requires the following:

  • Clear weather that permits observation of a celestial object.
  • Communications between the master and the flank stations.
  • Known directional control (a grid azimuth to known point).
  • Distance between the master and flank stations cannot exceed 26 km (distances greater than 26 km may result in exceeding hasty survey direction tolerances of 2 mils).

c. Procedures for the conduct of a SIMO are:

(1) The point having known directional control (a grid azimuth to a known point) becomes the master station. It can be occupied by survey personnel or personnel from the firing unit. All positions requiring the establishment of directional control become flank stations.

CAUTION

Place the sun filter over the aiming circle eyepiece before tracking the sun.

(2) The M2A2 aiming circle at the flank station is set up to observe the prearranged celestial object. It becomes the orienting station for the tiring unit. If the SIMO is prearranged, the flank station can maintain radio silence during the procedure.

(3) The specific steps for the master station and the flank station(s) and sample radio communications for SIMO are shown in Table 5-1.

5-4. POLARIS-KOCHAB METHOD

a. Observation of Polaris is another technique for establishing directional control to within 2 mils. It is simple, fast and has the distinct advantage of requiring no radio or wire communications. The instrument operator must be trained in finding the stars Polaris and Kochab, which are in the constellation known as Ursa Minor (Little Dipper).

(1) Polaris. Polaris is one of the two brightest stars in the constellation Ursa Minor. Because it appears to move in a small elliptical orbit about the North Pole, it is commonly referred to as the North Star. Polaris is the last star in the handle of the Little Dipper as shown in Figure 5-2. Two stars in the bowl of the Big Dipper actually point toward Polaris and are called the Pointers. Polaris is approximately five times the distance between the Pointers along an imaginary line from the Big Dipper. On the side opposite the Little Dipper is the constellation Cassiopeia, which looks like a lazy W.

(2) Kochab. The second star needed to perform the observation is Kochab, which is the other bright star (as bright as Polaris) in the Little Dipper. It is the front star of the bowl and is the only bright star between Polaris and the Big Dipper. Of the two front stars in the bowl of the Little Dipper, Kochab is the brighter and the closer to Polaris.

b. For rough orientation of the aiming circle, the operator first sets the declination constant on the upper motion and centers the magnetic needle with the lower motion. Next, he determines his latitude, to the nearest degree, from a map and converts it to mils by multiplying by 18. He then sets this value on the elevation scale of the aiming circle. This should place his line of sight very close to Polaris. As instrument operators become more proficient at identifying Polaris through an aiming circle, they can eliminate this orientation procedure.

c. To establish the orienting line, the horizontal clockwise angle from Kochab to Polaris is measured. Then the true azimuth is extracted from the appropriate table and the true azimuth is converted to a grid azimuth. The steps for establishing direction by observing Polaris are as follows:

(1) Measure the angle.

(a) Set up and level the aiming circle over the selected point.

(b) Using the upper motion, set 0.0 mils on the azimuth scale.

(c) Place the vertical cross hair of the instrument on Kochab using the lower motion and the elevation micrometer knob.

(d) Turn the azimuth micrometer knob (upper motion) clockwise until the vertical cross hair is centered on Polaris. (The telescope may have to be elevated or depressed.)

(e) Read the value on the azimuth scale to the nearest mil. (This is the entry value used to enter Tables 5-2 through 5-5)

(f) Depress the telescope to ground level. Emplace an aiming post, at least 30 meters, along the line of sight of the vertical cross hair line. This will serve as the EOL, and the aiming circle becomes the OS.

(2) Extract the true azimuth to Polaris.

(a) Select Table 5-2, 5-3, 5-4, or 5-5, whichever pertains to the latitude closest to that of the instrument operator. If the instrument operator's location is exactly half-way between the latitudes listed on any two tables, either table may be used.

(b) Enter the appropriate table on the left side with the value from the upper motion of the aiming circle. Visually interpolate, if necessary, by using the value from (1)(e) above.

(c) Determine whether to intersect with Graph 1 (Kochab is below Polaris) or Graph 2 (Kochab is above Polaris). If in doubt, compare the vertical angle of the two stars.

(d) From the intersection of the measured angle from Kochab to Polaris on the appropriate graph, read the true azimuth to Polaris from the bottom of the table. Interpolate for odd-numbered values.

(3) Convert true azimuth to grid azimuth.

(a) Determine the grid convergence (the angle between true north and grid north) in mils, from the map sheet for the area of operations; or obtain it from the survey section.

(b) Convert the true azimuth to grid azimuth as shown in Figure 5-3.

(c) This computation results in the determination of the grid azimuth from the OS to the EOL.

5-5. POLARIS 2 METHOD

Polaris 2 is a hasty survey technique used to establish accurate direction. It is simple, fast and has the distinct advantage of requiring no radio or wire communications. The instrument operator, however, must be in the Northern hemisphere and must be able to locate the stars 43H Cephei, Polaris, and Delta Ursae Minoris (Figure 5-2).

Note: The Polaris II reticle will exceed its original service life in January 1996. In January 1996, the accuracy is 2.5 mils. The reticle can still be used, but the accuracy is degraded 0.1 mils each year after January 1996.

The procedures for establishing direction by the Polaris 2 method are as follows:

a. Locate the stars.

(1) Locate Polaris by using the procedures in paragraphs 5-4a(1) or 5-4b.

(2) To locate Delta Ursa Minoris and 43H Cephei, the instrument operator may have to reduce the light intensity in the telescope. The three brightest stars appearing in his field of view will be Polaris, 43H Cephei, and Delta Ursa Minoris. When Polaris is used as the vertex, the angle formed by Delta Ursa Minoris and 43H Cephei is about 1,800 mils (Figure 5-4). This relationship remains the same and rotates counterclockwise at about 15° each hour.

b. Establish direction.

(1) Determine the grid convergence (the angle between true north and grid north) in mils, from the map sheet for the area of operation or from a survey section (Figure 5-5). Record this information.

(2) Set up and level the aiming circle over the selected point.

(3) Using the azimuth micrometer knob (upper motion), set the grid convergence on the azimuth scale (Figure 5-5).

(4) Using the elevation micrometer knob, set the predetermined elevation to Polaris (paragraph 5-4b) on the elevation scale.

(5) Using the orienting knob (lower motion), sight on Polaris. Ensure that the grid convergence remains correctly set on the azimuth scales.

(6) When Polaris is in the field of view, use the elevation knob and lower motion to place the stars on their respective circles as shown in Figure 5-4. There is no specific point on the circle on which the stars must be positioned. (The actual location of the stars on the circle depends on the time of year and the time of observation.)

(7) Emplace an aiming post, at least 30 meters from the aiming circle, at the desired location of the EOL.

(8) Using the elevation knob, lower the telescope. Use the upper motion to rotate the instrument clockwise until the vertical hairline is centered and at the lowest visible point on the aiming post.

(9) Read the azimuth to the nearest 0.5 mil directly from the azimuth scales.

(10) Using the procedures in paragraphs (3) through (9) above, determine a second azimuth to the EOL.

(11) The two azimuths determined to the EOL must agree within 2 mils. If the two azimuths agree within these limits, determine the mean grid azimuth. This is the grid azimuth to the EOL.

5-6. DIRECTIONAL TRAVERSE

a. Directional traverse is another means of transferring azimuth from one point to another. It gives more accurate results than scaling an azimuth from a map or floating the needle of an aiming circle. However, it should be used only when conditions prohibit the use of the simultaneous observation, Polaris-Kochab, or the Polaris two-reticle method. The only fieldwork required is to measure horizontal clockwise angles at each of the traverse stations (Figure 5-6). At the occupied station (Point A), these angles are always measured from the rear station clockwise to the forward station (Point B). At Point A, the azimuth to an azimuth mark (EOL) is known. The azimuth from A to B can be found by measuring the angle at A and adding that angle to the known azimuth from A to the azimuth mark.

b. The number of stations in a directional traverse should be kept to a minimum to minimize the loss of accuracy. The only limiting factor on the length of a traverse leg is line of sight. The directional traverse should be planned so that the final forward station is the orienting station for the battery or platoon. The orienting line then becomes the back-azimuth of the last leg.

c. At battery or platoon level, angles are measured with the M2A2 aiming circle to the nearest 0.5 mil. Each angle that is measured degrades the accuracy of the initial azimuth by 0.5 mil. For example, a directional traverse requiring four angles to establish the azimuth to the EOL would have an accuracy of 2 mils. The steps for conducting a directional traverse are as follows:

(1) Set up and level the aiming circle over the occupied station.

(2) With the upper motion, set 0.0 mils on the aiming circle.

(3) With the lower motion, sight on the known reference point (rear station).

(4) With the upper motion, measure the angle to the unknown point (forward station). Read this first reading to the nearest 0.5 mil, and record it.

(5) With this reading still on the scales, sight again, using the lower motion, on the known reference point (rear station).

(6) With the upper motion, again measure the angle to the forward station. Read this second reading to the nearest 0.5 mil, and record it.

(7) Divide the second reading by 2 to determine the mean angle. If the second reading is smaller than the first reading, 6400 mils must be added to the second reading before dividing by two. Express the quotient to the nearest 0.1 mil. The mean angle must agree with the first reading within 0.5 mil. If it does not, the angle must be remeasured. The mean angle is the angle used in the computation of the directional traverse and is referred to as the station angle.

EXAMPLE 1

1st reading = 1036.0
2d reading = 2072.5
2072.5/2 = 1036.2
The mean angle is valid because it agrees with the 1st reading within 0.5 mil.

EXAMPLE 2

1st reading = 3966.0
2d reading = 1533.5
1533.5 + 6400 = 7933.5
7933.5 12 = 3966.8
The mean angle is not valid because it does not agree with the first reading
within 0.5 mil. The angle must be remeasured.

d. A directional traverse is shown in Figure 5-7, and the following example.

EXAMPLE

The known data are as follows:

Azimuth from A to the azimuth mark = 0805.0. The mean station angles measured were as follows:

Station A                                                      4997.5

TS-1                                                            2248.2

TS-2                                                            5168.8

The method of determining the azimuth from B to TS-2 is as follows:

Known azimuth A to azimuth mark is:            0805.0

Plus station angle at A:                               + 4997.5

AZ station A to TS-1:                                   5802.5

(To determine back azimuth, the next step is always required.)

+3,200 mils                                                - 3200.0

AZ TS-1 to station A                                    2602.5

Plus station angle at TS                              + 2248.2

AZ TS-1 to TS-2                                         4850.7

3,200 mils                                                  - 3200.0

AZ TS-2 to TS-1                                         1650.7

Plus station angle at TS-2                          + 5168.8

(If sum of an azimuth 6819.5 and a station angle exceeds 6,400 mils, then 6,400 mils must be subtracted).                                               - 6400.0

AZ TS-2 to station B                                   0419.5

3,200 mils                                                + 3200.0

AZ B to TS-2                                             3619.5

AZ from OS A to EOL                               3619.5


Section III

LOCATION


5-7. METHODS OF LOCATION

Whenever the tactical situation permits, the firing units position should be surveyed before the unit arrives. Information provided by the survey section will include coordinates and height of the orienting station, and the grid azimuth from the orienting station to the EOL. When survey control is not available, the desired location may be determined through the use of graphic resection or graphic traverse.

Note: If automated fire direction capability is not available, battery center, in addition to the orienting station, should be surveyed.

5-8. GRAPHIC RESECTION

a. Graphic resection is a quick method of determining a position based on the known locations of certain visible points. The equipment needed to perform a graphic resection includes an aiming circle, map sheet, grid sheet, overlay paper and standard FDC plotting equipment. Graphic resection may be done in one of two ways, both of which are discussed below.

(1) No azimuth control available.

(a) Select a location from which three distant points, which appear on a map, are visible. These points should be well defined vertical features, such as towers, trig markers or church steeples.

(b) With the aiming circle, measure the three clockwise angles between these points. For each angle, use the standard measuring procedure outlined in paragraph 5-6c. (See Figure 5-8.)

(c) Check that the sum of the three angles equals 6400 mils, 1.5 mils. This verifies that each angle is accurate to 0.5 mil and that the three angles together encompass the entire horizon.

(d) Scale the coordinates of the three known points off a map (to eight digits), and transfer the plots onto a grid sheet (standard 1:25,000 firing chart). A trig list of known points may also be used.

(e) Place a pin at a random point near the center of the overlay (tracing) paper. Using target grid a mil graduated protractor, or a range-deflection protractor (RDP), draw a line from the pinhole to any comer of the paper and label it as the ray to the first of the three points. With the target grid, protractor, or RDP, measure clockwise the number of mils corresponding to the angle between the first and second known points. Draw and label the secondray to represent the second known point. Measure clockwise the number of mils corresponding to the angle between the second and third known points. Draw and label a third ray representing the third known point. You will note that the third angle (between the third and first known point) is now already constructed on the overlay paper. It should be measured to ensure that plotting errors have not occurred. (See Figure 5-9.)

(f) Place the overlay paper on the grid sheet and position it so that the three rays pass directly through their respective points. The position of the pin now represents the location of the aiming circle on the grid sheet. (See Figure 5-10.)

(2) Azimuth control available. In some cases, the aiming circle is positioned over the orienting station with a known orienting line established. If only two known points are visible, the resection may also be performed, by a somewhat different procedure.

(a) Measure the clockwise angles to each of the two known points from the EOL.

(b) Determine the azimuth to each known point by adding the azimuth of the orienting line to the appropriate angle measured in (a) above.

(c) Convert each of these azimuths to back-azimuths by applying 3,200 mils.

(d) Transfer the coordinates of the known points from the map to the grid sheet.

(e) Using the RDP, plot the back azimuths from the two known points on the grid sheet. The point of intersection of the two rays is the position of the aiming circle.

b. Regardless of which method of graphic resection is used, the end result is always the location of the aiming circle. If the resection was not performed from the orienting station, the coordinates may be determined by graphic traverse, hasty traverse, or estimation based on the results of the resection. The resection should be checked against the map to preclude a gross error.

5-9. GRAPHIC TRAVERSE

Graphic traverse is a means of transferring direction and location control from one point to another by uses of angle and distance measurements. It may be used to provide direction and coordinates to a battery position. It is also ideal for transferring survey control to an offset registration position or to a roving gun from a surveyed battery or platoon position. The technique is similar to that used in directional traverse. However, the personnel performing the traverse must measure not only the horizontal angle at each occupied station but also the distance to each forward station. The data needed to begin a graphic traverse include the coordinates of a known point and the direction to an azimuth mark. The only equipment required is an aiming circle, aiming posts (for the marking of stations), and FDC equipment. The procedures for conducting a graphic traverse are as follows:

a. Begin the traverse at the known survey control point (SCP). Follow the procedures for directional traverse to measure the station angle from the azimuth mark (rear station) to the first forward station. Compute the azimuth of the first leg of the traverse.

b. Measure the distance from the occupied station to the forward station. The procedures for making this measurement are discussed in paragraph 5-10.

c. Plot the coordinates of the SCP (starting point) on the FDC grid sheet. Using a target grid, a protractor, or an RDP, establish an azimuth index that corresponds to the computed azimuth from the starting point to the forward point; and draw a line representing the azimuth of the first traverse leg. Scale this azimuth line as close as possible. With the plotting (boxwood) scale, measure the distance of the traverse leg; and mark the forward station with a plotting pin.

d. Continue the fieldwork for the traverse as described above. Forward stations are successively established as needed, station angles are measured accordingly, and the azimuth of each leg computed as in directional traverse. The distance of each leg is plotted in the same manner as above. The traverse will appear on the grid sheet as a series of successive polar plots.

e. The traverse is planned so that the final forward station is the orienting station or other needed position. The EOL is the final occupied station in the traverse. The orienting line is the back-azimuth of the last traverse leg.

5-10. DISTANCE MEASURING

When graphic traverse is used to transfer survey control, the distance of each traverse leg must be measured. Since this distance is plotted on a grid sheet, it must be the horizontal distance along the traverse leg, not the slope distance obtained by measuring along the contour of the earth. In simplified survey operations, this horizontal distance can be easily measured in one of three ways (subtense, pacing, and using premeasured communications wire).

a. Subtense. The subtense method is the fastest of three distance-measuring procedures. It yields accuracy equivalent to that obtained with a premeasured piece of wire. An advantage is that a horizontal distance is obtained indirectly; that is, the distance is computed, rather than measured. This allows subtense to be used over terrain where obstacles, such as streams, ravines, or steep slopes may prohibit pacing or the use of wire.

(1) The subtense method uses precise values with a trigonometric solution (listed in tables 5-6 through 5-8). Subtense is based on a principle of visual perspective--the farther away an object is the smaller it appears.

(2) There are two procedures involved in subtense measurement:

  • Establishing a base of known length.
  • Measuring the angle of that base with the use of the aiming circle.

(3) The subtense base may be any desired length. However, if a 60 meter base, a 2 meter bar, or the length of an M16A1 or M16A2 rifle is used, precomputed subtense tables are available. The M16 or 2 meter bar must be held perpendicular to the line of sight by a soldier facing the aiming circle. The instrument operator sights on one end of the M16 or 2 meter bar and measures the horizontal clockwise angle to the other end of the rifle or bar. He does this twice and means the angles. He then enters the appropriate subtense table with the mean angle and extracts the distance. Accurate distances can be obtained with the M16 out to approximately 150 meters, with the 2 meter bar out to 250 meters, and with the 60 meter base out to 1,000 meters. If a base of another length is desired, a distance can be computed by using the following formula:

Note: During advance party operations at night, subtense may be obtained by attaching two lights on the pantel marker. The lights are separated by the length of an M16 rifle. The aiming circle operator measures the vertical distance from one light to the other using the elevation micrometer knob. He performs this twice and determines the mean angle.

b. Pacing. A soldier who has measured his pace should be able to pace 100 meters to an accuracy of 1 meter over level ground. However, the paced distance follows the contour of the earth. Therefore, in sloping or rough terrain, the determination of a horizontal distance becomes more difficult. A soldier can try to adjust his pace length to the degree of slope he is pacing, but his accuracy is decreased. Pacing should be used only over relatively flat terrain or when no other method is available.

c. Use of Premeasured Length of Communications Wire. A premeasured length of communications wire (WD-1) also may be used as a means of distance measurement. This method is substantially more accurate than pacing, but requires two soldiers to hold the ends of the wire. The wire may be of any length, although it is recommended that a length of 60 meters be used. The wire should be marked with tape at every meter increment and with color-coded tape at every 10-meter increment.

(1) The two soldiers holding the wire begin at the occupied-station and measure in a straight line to the forward station. As the soldiers move along the traverse leg, they should count the number of whole wire lengths measured. By use of the meter increments marked on the wire, they measure the last partial length of wire. The distance of the leg can be determined by multiplying the number of whole wire lengths by 60 (the length of the wire) and adding the partial length.

(2) The premeasured wire method is fast and meets accuracy requirements for hasty survey techniques. However, the wire must be held horizontally to obtain a horizontal distance. That means that in rough terrain, when one end of the wire is much higher or lower than the other, it will be extremely difficult to measure long horizontal distances. In such cases, a portion of the 60-meter wire can be held horizontally and the entire distance measured using these shorter lengths.

EXAMPLE

You are using a 2-meter (m) subtense bar and measure an angle of 10.5 mils (). You determine the horizontal distance by use of the formula:

Distance =     1/2 base     =         1         =        1        =   194 meters
                 tan 1/2(angle)      tan(5.25)        0.005154

Note: You must convert mils to degrees by dividing 17.778 into the angle determined. To determine the tangent (tan) of an angle, you will need a calculator or TM 6-230.

5-11. AUTOMATED COMPUTATIONS

a. The BCS and LCU allow battery commanders to disperse their howitzers over larger position areas than ever before. BCS and BUCS have weapon location routines that allow us to determine the grid location and altitude of each howitzer by simply entering the azimuth, distance, and vertical angle to the howitzer from the orienting station (mnemonic ORSTA). Thus, we can use this application to help us determine grid locations and altitudes to traverse stations while performing a graphic traverse.

b. Location and altitude at each of the traverse stations are determined by entering a number of successive polar coordinates (direction, distance, and vertical angle) in the weapon location file.

5-12. AFU INPUT FOR GRAPHIC TRAVERSE USING BUCS, REV 1

Note: ST 6-40-31 is the user's manual for BUCS Rev 1. Any Rev 1 read only memory (ROM) can be used for this procedure. The caliber of weapon system does not matter. The only information required in the database to begin this procedure is the map modification (MAPMOD).

Follow the steps and information in Table 5-9 to determine location and altitude with BUCS.

5-13. ALTITUDE DETERMINATION

In the absence of altitude data provided by battalion surveyors, altitude is obtained directly from the map. Once the coordinates of the desired point have been determined by the precision lightweight GPS receiver, graphic resection or graphic traverse, the altitude of this point is taken from the map sheet. Normally, altitude can be considered to be accurate to half the contour interval.




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