TERPROM

TERPROM is a highly accurate, passive terrain-referenced navigation system used primarily in military aviation. Developed by BAE Systems, it enables aircraft to navigate with extreme precision at low altitudes by comparing a stored digital terrain elevation database with real-time measurements from a radar altimeter. The system is a critical component for terrain-following and terrain-avoidance in all-weather conditions, significantly enhancing the survivability and mission effectiveness of combat aircraft.

Overview

TERPROM functions by continuously comparing the aircraft's height above ground, measured by its radar altimeter, against a pre-loaded digital map of the earth's surface. Using sophisticated Kalman filter algorithms, the system corrects the aircraft's estimated position from its inertial navigation system, providing highly accurate navigation without emitting detectable signals like radar or GPS. This passive operation is vital for stealth missions, allowing aircraft like the Panavia Tornado and Lockheed Martin F-35 Lightning II to penetrate defended airspace. The system's core capability is enabling safe, high-speed flight at very low levels, which is essential for evading enemy surface-to-air missile systems and air defense networks.

Development and History

The development of TERPROM began in the late 1970s by British Aerospace (now BAE Systems) in response to a Royal Air Force requirement for a reliable, all-weather, low-level navigation aid. Initial flight trials were conducted on a Hawker Siddeley Buccaneer aircraft, proving the concept's viability. The system entered operational service in the 1980s, first deployed on the Panavia Tornado GR1 used by RAF Strike Command. Its success led to adoption by the United States Air Force, which integrated it into aircraft like the General Dynamics F-111 Aardvark and later the Boeing B-52 Stratofortress. Continuous development has been driven by advancements in computer processing power and digital mapping data from sources like the United States Geological Survey.

Technical Description

Technically, TERPROM consists of three primary subsystems: a high-performance computer processor, a digital terrain elevation database, and interface units for the aircraft's inertial navigation system and radar altimeter. The database contains precise elevation data for the entire planned mission route, stored in a grid format. The system's software employs advanced terrain contour matching algorithms and Bayesian estimation techniques to resolve position. It provides outputs for the aircraft's flight control system, enabling automatic terrain-following when coupled with the autopilot, and delivers critical cues to the pilot via the head-up display and multi-function display. Integrity monitoring is a key feature, ensuring the system can detect and discount spurious data.

Operational Use

Operationally, TERPROM is a force multiplier for low-level flight tactics. It has been used extensively in combat, including during the Gulf War by RAF Panavia Tornado squadrons and by USAF B-1 Lancer bombers during operations over Afghanistan. The system allows crews to concentrate on mission tasks rather than navigation, flying pre-planned routes at high speeds just a few hundred feet above varied terrain. This capability is fundamental for precision-guided munition delivery and suppression of enemy air defenses missions. Modern integrations, such as on the Lockheed Martin F-35 Lightning II, fuse TERPROM data with inputs from the Distributed Aperture System for enhanced situational awareness.

Variants and Upgrades

Several variants and upgrades have been developed since the original system. TERPROM II introduced improved processing and larger database capacity. The TERPROM 2000 series, used on the Eurofighter Typhoon and Lockheed Martin F-16 Fighting Falcon, added a GPS receiver for hybrid navigation, enhancing reliability over featureless terrain like deserts or oceans. The latest iterations, often referred to as Digital Terrain Systems, feature faster mission planning tools, worldwide coverage, and compatibility with Helmet-mounted display technology. These upgrades ensure compatibility with modern glass cockpit avionics suites and network-centric warfare architectures like the Joint Tactical Information Distribution System.

Related Systems

TERPROM belongs to a family of terrain-referenced navigation systems. Its direct contemporary and competitor is the U.S.-developed TERPROM-like system used on the Rockwell B-1 Lancer. Other related technologies include SITAN (Sandia Inertial Terrain-Aided Navigation) and more modern Terrain Referenced Navigation solutions being developed for unmanned combat aerial vehicles. The principles underpinning TERPROM also relate to terrain-following radar systems, like that used on the General Dynamics F-111, though TERPROM is passive. Its digital mapping technology shares commonalities with civilian Enhanced Ground Proximity Warning System and Synthetic vision system used in commercial aviation.