TERCOM is an automated navigation system used by unmanned aerial vehicles, such as cruise missiles. It uses a predefined contour map of the flight path and a radar altimeter to make precise course corrections and avoid radar detection. The system is highly accurate and reliable, but lacks pre-launch flexibility.
TERCOM is an automated navigation system used primarily by an unmanned aerial vehicle, such as a long-range cruise missile. The system uses a predefined contour map of the flight path that acts as a master comparison image. The missile is equipped with a sophisticated radar altimeter that constantly reads the terrain it is crossing and compares the readings with the master image. When deviations are detected, the missile’s guidance system makes the necessary corrections to its flight path. This makes extremely precise navigation and collision avoidance possible, thus allowing the missile to fly closer to the ground and avoid radar detection.
Terrain Contour Mapping, or TERCOM as it is more commonly known, is one of the most accurate and reliable reference navigation systems for long-range UAVs such as cruise missiles. In the early stages of long-range missile development, various navigation methods were used, such as graphical comparison systems on early intercontinental ballistic missiles (ICBMs). These systems used surveillance photography as a master, while an onboard camera took a series of photos along the way for comparison material. The master and en-route photos were scanned by a computer for high-contrast similarities, and the missile navigated according to the results. This process was extremely slow and laborious and resulted in a navigation validation process based on very few waypoints.
The advent of reliable satellite mapping allowed system designers to incorporate highly accurate digital terrain maps as masters of comparison. Equally sophisticated radar altimeters on the missile supply accurate, real-time ground clearance readings that form a running terrain profile for comparison with the master file. This allows the missile’s guidance system to make instantaneous and precise course corrections to maintain the programmed trajectory throughout the flight without any of the “drifts” experienced with older inertial reference systems (INS). TERCOM master terrain maps consist of a strip of terrain detail representing the ideal course, as well as an additional area on each side of the center court. This allows diversions to be made without the missile “walking away” into uncharted territory.
The high degree of precision possible in terms of exact altitude over all terrain profiles allows TERCOM-equipped missiles to maintain low-altitude flight paths while avoiding obstacles. This ground-hugging ability confuses enemy ground radar systems, particularly during the final pre-impact phase of flight. The only real downside to TERCOM technology is the lack of pre-launch flexibility. The entire flight must be planned from a specific launch site, and any unexpected change in this constant can mean mission abort. In this regard, the latest global positioning satellite (GPS) systems are superior to terrain mapping technology by allowing a missile to be launched from any location.
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