Ground Surveillance Radar (GSR)

The AN/PPS-4 and AN/PPS-5 radar sets were short range ground surveillance radars that made use of the doppler effect to detect a target. The sets detected the difference in frequency between the echoes reflected from stationary objects and the echoes reflected from moving objects, and presented this information as a target indication to the radar operator. To detect a moving target the radar set needed to receive echoes from a fixed object together with the echo from a moving target.

The echoes from fixed objects were called ground clutter. The radar sets presented audio indications of targets from only a relatively small segment of the radar beam at any given time. This segment of range is called a range gate. Target echoes were constantly being received by the radar receiver throughout the length of the beam however, only target echoes from the range gate segment of the radar beam were indicated audibly to an operator.

Range gates could be positioned either manually or automatically. Positioning them manually was the method generally used when tracking a target. Automatic positioning of the range gate is called strobing and was used by a radar operator to search large segments of the range.

Ground surveillance radars where frequently used in NDP's, Laagers and Fire Support Bases. In these positions they were employed to cover the most likely avenues of approach and could thus give the Commanding Officer some forewarning of an impending attack.

Ground Surveillance Radar Applications

GSR systems can be used in a variety of tactical battlefield applications. A battlefield commander requires much intelligence to command and control his assets proficiently. For ground combat situations, information that is useful includes:

• Enemy Troop and Vehicle Concentrations
• Enemy Vehicle Classification
• Enemy Personnel & Vehicle Movement
• Movement of a Possible Counterattack Force Conducting a Flanking Attack
• Information about Avenues of Approach and Infiltration Routes used by Enemy

This information can be used as targeting data to support effective attacks, as early warning for force protection, or simply as surveillance to find the enemy. In general, GSRs provide timely surveillance and tactical near-real time data and are very versatile.

GSRs are used to search for enemy activity on critical chokepoints, mobility corridors, and likely infiltration routes. They are used to observe point targets such as bridges, road junctions, or narrow passages to detect movements. GSR systems can extend the surveillance capability of patrols by surveying surrounding areas for enemy movement, and survey target areas immediately after an attack to detect enemy activity and determine the effectiveness of the attack. Radars can assist in visual observation of targets partially hidden by haze, smoke, fog, or bright sunlight, and can confirm targets sensed by other types of sensors.

GSR systems have a few weaknesses that must be overcome by using other types of sensors in conjunction with the radar. Radars require line-of-site to the target area, and their performance is degraded by heavy rain, snow, dense foliage, and high winds. Also, they are active emitters, and are subject to enemy detection and electronic countermeasures (ECM). Finally, radars are unable to distinguish between friend and foe, only able to detect and classify moving targets by type.

Using the AN/PPS-4 and AN/PPS-5

The following was emailed to me by Doug Huffman, a Veteran of 1st Battalion (Mechanised), 5th Infantry who, after serving with a Mortar Platoon, later went on to serve as a radar operator;

The PPS-4 was a small self contained unit. It sits on a tripod, in total about four feet high, and could be carried by a single person. The dish and controls were all part of a single unit which we would set up on its tripod right on the ground. We plugged the earphone into it and panned the unit back and forth manually. Output was through the earphones and dials on the unit showing distance to the target.

The other type of radar operated by our radar section was one PPS-5. This was a larger unit. A typical installation was to set up the dish on top of a tower at a fire support base. Cables ran down to a bunker on the ground where the control unit was located. This unit had a square screen similar to the round radar screens you've seen with blips and so forth. A line representing the radar beam would move across the screen from side to side. The dish was motorized. The PPS-5 was much less portable though at times we did take it into the field. It was run off a generator whereas the PPS-4 used batteries.

Our targets typically were within one to five hundred meters (I'm referring to the PPS-4 which I operated most of the time) and usually seemed to be squad size groups. I only know of one confirmed target destroyed. Most of the time I think that if the target was real we accomplished our mission when the resultant fire scared the enemy away or interrupted their operations. We usually responded to targets with Bravo Company's 81mm mortars or small arms.

The confirmed target I mention was farther away than what I believed to be the realistic maximum range for the PPS-4. This was at about 1000 meters and I identified it as an ox cart. I directed artillery fire using the radar set. I could hear the sound of the rounds splashing. By Pointing the radar a little each way I could tell the difference in azimuth between the target and the artillery rounds. My mortar training and experience came in handy here as I was able to estimate the adjustments in meters by knowing the distance to the target and the angle between. After about three salvos the target was quiet. A sweep through the area at a later date discovered a three wheeled Lambretta destroyed along with it's cargo of AK-47 rifles.