An automotive electronics and software concept defining networked computation, sensing, and control used to operate vehicle functions and driver-assistance features. It governs in-vehicle communication, software deployment, diagnostics, and perception and decision pipelines where applicable. It does not ensure safe behavior without rigorous validation, fault handling, and security controls for critical functions. It materially affects feature capability, reliability, and maintainability by shaping architectures, interfaces, and update processes. The concept is generally stable, though architectures and toolchains evolve rapidly over time.

Principle

Determine altitude above ground by measuring the time delay (or phase difference) of reflected radar pulses and converting that delay into a height using the speed of radio propagation and signal processing corrections.

Demonstration

During final approach, the radar altimeter provides precise height-above-terrain to automatic landing systems, autothrottle logic and terrain-warning functions below system-specified altitudes.

Misapplication

Using radar altimeter readings over very rough sea states, sloping terrain, or highly reflective obstacles without recognizing clutter, multipath, or false returns that bias the reported height.

Consequence

When accurate, radar altitude enables flare guidance, terrain alerts and low-altitude automation; its failure or misinterpretation can compromise automatic landing and warning effectiveness.

Reversal

A barometric altimeter which reports altitude relative to a pressure datum (mean sea level) and does not provide direct measurement of height above the immediate terrain.

Boundary

Operates only within its specified altitude envelope above ground (typically limited to a few thousand feet AGL); does not replace barometric altitude for en-route flight level references nor measure absolute MSL altitude.

Semantic Tension

Contrasted with barometric and GNSS altitude: radar altimeter gives precise AGL height but is sensitive to reflectivity and clutter, whereas barometric altitude is stable for en-route reference and GNSS gives geometric altitude.

Synthesis

A radar altimeter is the aircraft's downward-looking radio sensor that directly measures height above terrain, providing precise low-altitude information for guidance and safety systems.