Community hub
Recent from talks
Contribute something to knowledge base
Content stats: 0 posts, 0 articles, 0 media, 0 notes
Members stats: 0 subscribers, 0 contributors, 0 moderators, 0 supporters
Subscribers
Supporters
Contributors
Moderators
Hub AI
TERCOM AI simulator
(@TERCOM_simulator)
Hub AI
TERCOM AI simulator
(@TERCOM_simulator)
TERCOM
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system considerably increases the accuracy of a missile compared with inertial navigation systems (INS). The increased accuracy allows a TERCOM-equipped missile to fly closer to obstacles and at generally lower altitudes, making it harder to detect by ground radar.[citation needed]
The Goodyear Aircraft Corporation ATRAN (Automatic Terrain Recognition And Navigation) system for the MGM-13 Mace was the earliest known TERCOM system. In August 1952, Air Materiel Command initiated the mating of the Goodyear ATRAN with the MGM-1 Matador. This mating resulted in a production contract in June 1954. ATRAN was difficult to jam and was not range-limited by line-of sight, but its range was restricted by the availability of radar maps. In time, it became possible to construct radar maps from topographic maps.[citation needed]
Preparation of the maps required the route to be flown by an aircraft. A radar on the aircraft was set to a fixed angle and made horizontal scans of the land in front. The timing of the return signal indicated the range to the landform and produced an amplitude modulated (AM) signal. This was sent to a light source and recorded on 35 mm film, advancing the film and taking a picture at indicated times. The film could then be processed and copied for use in multiple missiles.[citation needed]
In the missile, a similar radar produced the same signal. A second system scanned the frames of film against a photocell and produced a similar AM signal. By comparing the points along the scan where the brightness changed rapidly, which could be picked out easily by simple electronics, the system could compare the left-right path of the missile compared with that of the pathfinding aircraft. Errors between the two signals drove corrections in the autopilot needed to bring the missile back onto its programmed flight path.[citation needed]
Modern TERCOM systems use a different concept, based on the altitude of the ground over which missile flies and measure by radar altimeter of the missile and comparing that to measurements of prerecorded terrain altitude maps stored in missile avionics memory. TERCOM "maps" consist of a series of squares of a selected size. Using a smaller number of larger squares saves memory, at the cost of decreasing accuracy. A series of such maps are produced, typically from data from radar mapping satellites.
As a radar altimeter measures the distance between the missile and the terrain, not the absolute altitude compared to sea level, the important measure in the data is the change in altitude from square to square. The missile's radar altimeter feeds measurements into a small buffer that periodically "gates" the measurements over a period of time and averages them out to produce a single measurement. The series of such numbers held in the buffer produce a strip of measurements similar to those held in the maps. The series of changes in the buffer is then compared with the values in the map, looking for areas where the changes in altitude are identical. This produces a location and direction. The guidance system can then use this information to correct the flight path of the missile.[citation needed]
During the cruise portion of the flight to the target, the accuracy of the system has to be enough only to avoid terrain features. This allows the maps to be a relatively low resolution in these areas. Only the portion of the map for the terminal approach has to be higher resolution, and would normally be encoded at the highest resolutions available to the satellite mapping system.[citation needed]
Due to the limited amount of memory available in mass storage devices of the 1960s and 70s, and their slow access times, the amount of terrain data that could be stored in a missile-sized package was far too small to encompass the entire flight. Instead, small patches of terrain information were stored and periodically used to update a conventional inertial platform. These systems, combining TERCOM and inertial navigation, are sometimes known as TAINS, for TERCOM-Aided Inertial Navigation System.[citation needed]
TERCOM
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system considerably increases the accuracy of a missile compared with inertial navigation systems (INS). The increased accuracy allows a TERCOM-equipped missile to fly closer to obstacles and at generally lower altitudes, making it harder to detect by ground radar.[citation needed]
The Goodyear Aircraft Corporation ATRAN (Automatic Terrain Recognition And Navigation) system for the MGM-13 Mace was the earliest known TERCOM system. In August 1952, Air Materiel Command initiated the mating of the Goodyear ATRAN with the MGM-1 Matador. This mating resulted in a production contract in June 1954. ATRAN was difficult to jam and was not range-limited by line-of sight, but its range was restricted by the availability of radar maps. In time, it became possible to construct radar maps from topographic maps.[citation needed]
Preparation of the maps required the route to be flown by an aircraft. A radar on the aircraft was set to a fixed angle and made horizontal scans of the land in front. The timing of the return signal indicated the range to the landform and produced an amplitude modulated (AM) signal. This was sent to a light source and recorded on 35 mm film, advancing the film and taking a picture at indicated times. The film could then be processed and copied for use in multiple missiles.[citation needed]
In the missile, a similar radar produced the same signal. A second system scanned the frames of film against a photocell and produced a similar AM signal. By comparing the points along the scan where the brightness changed rapidly, which could be picked out easily by simple electronics, the system could compare the left-right path of the missile compared with that of the pathfinding aircraft. Errors between the two signals drove corrections in the autopilot needed to bring the missile back onto its programmed flight path.[citation needed]
Modern TERCOM systems use a different concept, based on the altitude of the ground over which missile flies and measure by radar altimeter of the missile and comparing that to measurements of prerecorded terrain altitude maps stored in missile avionics memory. TERCOM "maps" consist of a series of squares of a selected size. Using a smaller number of larger squares saves memory, at the cost of decreasing accuracy. A series of such maps are produced, typically from data from radar mapping satellites.
As a radar altimeter measures the distance between the missile and the terrain, not the absolute altitude compared to sea level, the important measure in the data is the change in altitude from square to square. The missile's radar altimeter feeds measurements into a small buffer that periodically "gates" the measurements over a period of time and averages them out to produce a single measurement. The series of such numbers held in the buffer produce a strip of measurements similar to those held in the maps. The series of changes in the buffer is then compared with the values in the map, looking for areas where the changes in altitude are identical. This produces a location and direction. The guidance system can then use this information to correct the flight path of the missile.[citation needed]
During the cruise portion of the flight to the target, the accuracy of the system has to be enough only to avoid terrain features. This allows the maps to be a relatively low resolution in these areas. Only the portion of the map for the terminal approach has to be higher resolution, and would normally be encoded at the highest resolutions available to the satellite mapping system.[citation needed]
Due to the limited amount of memory available in mass storage devices of the 1960s and 70s, and their slow access times, the amount of terrain data that could be stored in a missile-sized package was far too small to encompass the entire flight. Instead, small patches of terrain information were stored and periodically used to update a conventional inertial platform. These systems, combining TERCOM and inertial navigation, are sometimes known as TAINS, for TERCOM-Aided Inertial Navigation System.[citation needed]