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CHAPTER 3

TECHNICAL ASPECTS OF
TARGET ACQUISITION EMPLOYMENT

Figure 3-1.



To effectively use the full capabilities of FA target acquisition assets, we
must first consider the technical characteristics of the radars themselves
and of their employment. The radar operators provide the technical
expertise to complement the tactical employment planning done by the
FA headquarters controlling the radars. Radar operators must be able to
explain technical requirements of the radar to planners during the planning
process. Once the plan for use of radars in support of the operation is
finalized, radar operators must exploit the technical aspects of the radars
not only to maximize their effectiveness but also to enhance their own
survivability.

Section I. RADAR SYSTEM CHARACTERISTICS

WEAPONS-LOCATING RADARS

Missions

The primary mission of Q-36 and Q-37 weapons-locating radars is to detect and locate enemy mortars, artillery, and rockets quickly and accurately enough to permit immediate engagement. Their secondary mission is to observe registrations and help the FDC adjust fire for friendly artillery units. The secondary mission should be performed only when absolutely necessary. Radiation should be reserved for the primary mission.

The AN/TPQ-36 Radar

The AN/TPQ-36 is optimized to locate short-range high-angle weapons such as mortars. However, it can also locate artillery and rockets. For planning purposes, the AN/TPQ-36 has a minimum system range of 750 meters and a maximum range of 12,000 meters for artillery and mortars and 24,000 meters for rockets. The antenna electronically scans a horizontal sector from 230 mils minimum to 1,600 mils maximum width. Minimum and maximum detection ranges can be established; however, at least 900 meters difference in maximum and minimum ranges is required. The AN/TPQ-36 can search up to 6,400 mils by using the extended azimuth search function. With extended azimuth search, the computer automatically moves the antenna up to four positions and performs its target location functions.

The highly mobile AN/TPQ-36 is normally located 3 to 6 kilometers (km) behind the forward line of own troops (FLOT). The AN/TPQ-36 can be emplaced and ready for operation within 20 minutes. It can be march-ordered within 10 minutes. (These emplacement and march-order times do not include the time needed to set up or take down camouflage nets.) For tactical employment considerations, see Chapter 4. For further characteristics of the radars, see the target acquisition radar planning table. For technical operating characteristics and operational limitations during adverse conditions, such as extremely hot or cold weather, see TM 11-5840-354-10-1.

AN/TPQ-37 Radar

The AN/TPQ-37 radar is optimized to locate long-range low-angle weapons. For planning purposes, it has a minimum system range of 3 kilometers and a maximum range of 30 kilometers for artillery (50 kilometers for rockets). Minimum and maximum detection ranges can be established for the AN/TPQ-37, but like those for the AN/TPQ-36, at least 900 meters difference in maximum and minimum ranges is required. The AN/TPQ-37 will also locate short-range high-angle weapons, complementing the AN/TPQ-36.

The AN/TPQ-37 sector of search is from 300 mils minimum to 1,600 mils maximum. Although the AN/TPQ-37 is not equipped with the extended azimuth search function as is the AN/TPQ-36, the antenna can traverse a full circle. The AN/TPQ-37 is normally deployed 8 to 12 kilometers behind the FLOT. The AN/TPQ-37 can be emplaced and ready for operation within 30 minutes. It can be march-ordered within 15 minutes. (These emplacement and march-order times do not include the time needed to set up or take down camouflage nets.) For tactical employment considerations, see Chapter 4. For further characteristics of the radar, see the target acquisition radar planning table. For technical operating characteristics and operational limitations during adverse conditions, such as extremely hot or cold weather, see TM 11-5840-355-10-1.

Figure 3-2. AN/TPQ-36 Weapons-Locating Radar

Figure 3-3. AN/TPQ-37 Weapons-Locating Radar

MOVING-TARGET-LOCATING
RADARS

Mission

The field artillery has two MTLR systems--the AN/TPS-25A and the AN/TPS-58B radars. The mission of the AN/TPS-25A and AN/TPS-58B radars is to detect, identify, locate, and track moving ground targets. Through proper positioning and use, the MTLRs give the field artillery the ability to acquire moving targets in enemy territory. MTLRs can also enhance the counterreconnaissance mission by detecting enemy reconnaissance elements. There is one AN/TPS-25A or AN/TPS-58B radar section in each target acquisition battery and corps target acquisition detachment. Both of these radars are Doppler systems. They locate and track targets by changes in the frequency of the return signal produced by movement of the targets. The specific audio return of a target enables the operator to identify it as personnel, a light or heavy wheeled vehicle, or a tracked vehicle. Both MTLRs can be used to vector friendly forces.

The AN/TPS-25A Radar

The AN/TPS-25A is a transportable, battlefield surveillance, noncoherent Doppler radar. To detect a moving target, a noncoherent Doppler radar requires a return signal from a stationary object. The AN/TPS-25A requires electronic line of sight (ELOS) to the moving target. It has a selectable beam width of either 36 mils for tracking or 180 mils for surveillance. It also has a search area of 360 or 540 mils. The AN/TPS-25A can locate moving personnel at ranges between 450 and 12,000 meters and vehicles between 450 and 18,280 meters to an accuracy of 100 meters. (The stated accuracy is the maximum system capability and assumes exact survey positioning.) For employment considerations, see Chapter 4. For characteristics of radar, see the radar planning table.

The antenna can be emplaced on the receiver-transmitter or raised on its mast section up to 7.6 meters. The operations shelter can be remoted up to 68 meters from the antenna site. A well-trained crew can emplace the radar on its three mast sections and be ready to operate within 40 minutes. It can be march-ordered within 25 minutes (exclusive of camouflage emplacement time).

Figure 3-4. AN/TPS-35A Moving-Target-Locating Radar

The AN/TPS-58B
Radar

The AN/TPS-58B is a lightweight, mobile, coherent Doppler radar. A coherent Doppler radar generates its own reference signal to detect moving targets. The AN/TPS-58B requires electronic line of sight to the moving target. It can locate moving personnel at ranges between 300 and 10,000 meters and vehicles between 300 and 20,000 meters to an accuracy of 50 meters. (The stated accuracy is the maximum system capability and assumes exact survey positioning.) It has a beam width of 75 mils and a variable sector scan of 500 to 2,500 mils. The AN/TPS-58B can automatically track moving targets and predict their future location. A well-trained crew can emplace or march-order the AN/TPS-58B within 15 minutes. The operations shelter can be remoted up to 48 meters from the antenna site. For employment considerations see Chapter 4. For characteristics of the radar, see the radar planning table.

Figure 3-5. AN/TPS-58B Radar

Section II. TECHNICAL ASPECTS OF SITE SELECTION
AND POSITIONING

POSITION SELECTION
CONSIDERATIONS

This section discusses position selection criteria for the radar section chief. In addition to the technical and tactical factors of the radar, the overriding considerations in selecting a radar site are the factors of mission, enemy, terrain, troops, and time available (METT-T).

The controlling headquarters S2 designates the general position area. The area should be large enough to permit the selection of primary and alternate sites on the basis of technical and tactical considerations. (See Chapter 4 for specific details on the selection of general position areas.)

RECONNAISSANCE

After receiving the general position area, the radar technician conducts reconnaissance before selecting the actual position. If time permits, the technician should make both a map reconnaissance and a ground reconnaissance.

NOTE: Frequently, the MTLR will be emplaced
during darkness or periods of poor visibility.
Tactical considerations will require a great deal
of planning and preparation. As visibility improves,
camouflage and concealment will become an
important consideration. Cover from enemy fire
will be virtually nonexistent for the antenna because
of line-of-sight (LOS) requirements.

Map Reconnaissance

The map reconnaissance is made to determine, at least, the following:

  • Routes into and out of the area.

  • Identifying landmarks that will aid in hasty survey and land navigation to the position.

  • Adjacent units that may help establish a defensive perimeter.

  • Possible radar sites for ground reconnaissance. These can be determined by constructing and evaluating a hasty visibility diagram for the MTLR. (See Appendix D.)

Ground Reconnaissance

A ground reconnaissance should follow the map reconnaissance to ensure rapid occupation of the selected position. The ground reconnaissance is based on the METT-T factors and the tactical and technical considerations that influence radar operations. During the ground reconnaissance, the radar technician or section chief should--

  • Search and mark the area for mines.

  • Determine routes of entrance to and exit from the area.

  • Determine exact locations for emplacing the radar antenna and shelter.

  • Measure and evaluate the screening crest.

  • Determine a location for the generator to minimize its effects on operations.

  • Determine vehicle locations that will aid in movement into and out of the position.

  • Obtain survey control or perform hasty survey.

  • Provide for local security (to include camouflage and defense against air and ground attack).

  • Select alternate positions.

TACTICAL AND TECHNICAL
CONSIDERATIONS

During the actual site selection process, the radar technician or chief of section will analyze the factors of METT-T and consider the following points.

Accessibility

The radar site must be accessible by road, air, or both, depending on mission requirements.

Communications

The communications requirements depend on the mission and therefore will vary. The site must permit establishment of the required communications. The normal means of communications for the radar section is wire and/or radio. Appendix E covers communications for radar sections.

Concealment

Maximum use of natural concealment, such as trees and shrubs, should be considered in selecting a site for the radar. (Concealment must not interfere with the radar beam.)

Cover

When possible, the radar should be emplaced in defilade. This affords protection from hostile fire. The exception to this is the MTLR antenna, which must have line of sight to the target area.

Routes of Approach

The site selected should have more than one covered route of approach. These routes will allow occupation that is unobserved by the enemy. One must consider road conditions, overhead clearances, bridges, and stream fords. See the radar planning table for weights and dimensions.

Security

The radar technician should try to locate the radar site within the perimeter of defense of an adjacent unit. This will improve his local security. If feasible, the radar section could be augmented with personnel from the supported unit.

Survey

To provide accurate target locations, the FA radars must be sited accurately. Making survey control available near the radar site helps in determining site data.

The primary means of obtaining survey control for radars is the position and azimuth determining system. PADS survey can be supplemented with conventional survey teams. When PADS survey is not available before the radar section occupies the radar site, survey will be provided by a conventional survey team. If common control is not available, the radar section will conduct a hasty survey. The hasty survey will provide the data needed to initialize the radar. If the PADS or conventional survey team arrives after the hasty survey has been done, the data delivered by PADS or conventional survey will be entered into the radar computer. Survey requirements for FA radars are as shown in the table below.

The site altitude accuracy required by Firefinder radars is 10 meters probable error (PE) for AN/TPQ-36 and 3 meters PE for the AN/TPQ-37. The azimuth accuracy provided by hasty survey is +/-2.0 mils for Polaris 2, Polaris-Kochab, or simultaneous observation. This accuracy is good only for temporary use by the radar section. The location accuracy provided by hasty survey is considered to be approximately 50 meters circular error probable (CEP). Data provided by the PADS or conventional survey will always take precedence over data obtained from a hasty survey.

Slope

The slope of the ground is important for proper drainage and for quick leveling of the antenna.

Area in Front of the Antenna

The area in front of the antenna for the radars should be clear of objects and heavy foliage that extends above the bottom of the antenna. This clear area minimizes the attenuation of the radar beam. The clear area should be 200 meters for the AN/TPQ-36 and 300 meters for the AN/TPQ-37. The ideal site will have a clear area in front of the antenna that slopes downward from the antenna for about 200 (or 300)meters and then gradually rises up to the screening crest. This reduces multipath errors. Multipath errors are errors in target location created when the transmit or return signals travel by more than one path.

Electronic Line of Sight

The overriding consideration in the selection of a radar site for moving target detection is electronic line of sight. Line of sight to the target area for the MTLR and to the projectile on the ascending leg of its trajectory for the WLR is required for antenna location. The radar technician should construct a hasty visibility profile before occupying a site. This can save valuable time by exposing a useless position before it is occupied. After occupation, the section must develop a more detailed visibility profile and construct a visibility diagram. A visibility diagram will show the areas that are masked or hidden from the radar. This diagram is then forwarded to the div arty S2 for use in constructing a consolidated visibility diagram of all radars within the division sector. (See Appendix D for details on constructing visibility profiles and visibility diagrams.)

SURVEY REQUIREMENTS
MAXIMUM ALLOWABLE ERROR MTLR AN/TPQ-36 AN/TPQ-37
horizontal CEP (meters) 10.0 10.0 10.0
vertical PE (meters) 10.0 10.0 3.0
direction PE (mlls) 0.4 0.4 0.4

Screening Crest

A screening crest is not a technical requirement for the weapons-locating radar. However, it reduces the radar's susceptibility to detection and jamming from ground-based electronic intelligence (ELINT) systems. Ideally, the screening crest should be in friendly territory and approximately 1,000 meters from the radar. The screening crest should be between 15 and 30 mils in elevation for the AN/TPQ-36 and between 5 and 15 mils for the AN/TPQ-37. Also, the difference between the highest and lowest points on the screening crest should not exceed 30 mils. A difference of more than 30 mils will reduce the ability of the radar to provide sufficient vertical track (track volume) in order to make a location.

Aspect Angle

Aspect angle is the angle between the radar antenna and the target path. Since the MTLR is a Doppler radar, a target moving directly toward or away from the radar causes the greatest change in frequency and thus provides a more accurate target location.

Track Volume

Both WLRs must have optimum vertical coverage. Both systems should have approximately 50 mils of elevation track volume to optimize vertical coverage. To ensure the proper track volume, the high or low mask angle difference should not exceed 30 mils. For further information on Firefinder mask considerations, see Appendix F.

Cable Lengths

Once technical aspects of choosing a radar site have been addressed, the lengths of the system cables must be considered. These cables attach the shelter and the generator to the radar. The cable lengths are limiting factors in the actual layout of the radar position area. System cable lengths are shown in the table below.

SURVIVABILITY

Reduce Radiating Time

The shorter time the radar transmits, the less likely it is to be acquired. Maximum continuous transmission time for FA radars should never exceed 2 minutes when an EW threat exists. Transmission time should be kept to the absolute minimum when feasible. The Firefinder survivability flowchart should be used in conjunction with the EW threat associated with the IPB as determined at the S2 or G2 level. The flowchart can help to determine a practical way of employing Firefinder according to the tactical situation. The chart allows flexibility in determining how long to radiate (cumulatively) from any position. It can also be used to determine how long a particular position can be occupied on the basis of the tactical situation and mission.

Figure 3-7. Cable Lengths

Using the Firefinder Survivability
Flowchart

The Firefinder survivability flowchart provides the TA radar technician (MOS 131A) and concerned commanders and staff with survivability guidance for radar operations once the ground-based threat against Firefinder has been determined. Use of the chart is to be based on the EW threat associated with the IPB and a commonsense approach to employing Firefinder. It will also be based on the tactical situation and the factors of METT-T. The flowchart is a realistic tool that can be used during the decision process for Firefinder employment. When used properly, the flowchart enables TA personnel to realistically support the maneuver commander by keeping the Firefinder radar in position long enough to maximize its effectiveness. To use the chart, simply begin at the START point, and answer each question posed. Then move through the chart according to your answer.

Ground-Based EW Threat. If you determine that no ground-based EW threat against Firefinder exists, there is no EW limit on radiation time. However, the radar still should radiate only as the mission requires. You should always monitor and update the EW situation.

Optimum Radar Site. If you determine that you have an optimum radar site, the radar can radiate 15 minutes or more. (See cautions on the chart.) Remember that the radiate time should depend on the situation. You must also continue to monitor and update the EW situation.

Optimum Screening Crest Only. If you determine that you have an optimum screening crest only, the radar can radiate for 8 minutes or more. (See cautions on the chart.) Remember, the radiate time should depend on the situation. You must also continue to monitor and update the EW situation.

No Optimum Screening Crest. If you determine that an optimum screening crest does not exist, the radar can radiate for 8 minutes minus the march-order time or 2 minutes, whichever is greater. For survivability, move at least 500 meters and observe your previous position. Once the survivability move has been made, determine if the new site is optimum. If it is not, do you have an optimum screening crest and was your previous position attacked within a specified number of minutes?

No Optimum Site. If the new site is not optimum, if you do not have an optimum screening crest, and if the previous position was not attacked within a specified number of minutes, you can increase the radar radiate time by 2 minutes. Then make another survivability move, observe your previous position, and so forth. Be cautious. Always monitor and update the EW situation. Always use common sense and consider the factors of METT-T, especially when an optimum radar site and/or an optimum screening crest is not available.

NOTES:
1. The length of cumulative radiation time exceeding
2 minutes in any one position depends in part
on the training level of the radar section. For
example, the Army training and evaluation program
(ARTEP) standard for a Q-36 section to march-order
is 10 minutes. A well-trained section can cut that
time considerably and be allowed more time for
the radar to radiate.

2. See Chapter 4 for general tactical survivability
considerations. The Firefinder survivability matrix
(In Chapter 4) is based on the survivability flowchart.
It is designed as a quick reference for operations
personnel.

Figure 3-8. Firefinder Survivability Flowchart

Figure 3-9a. Target Acquisition Radar Planning Table

Figure 3-9b. Target Acquisition Radar Planning Table (Continued)





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