What format of Primary RADAR is used for RADALT?

The correct answer is Continuous Wave (CW). Primary RADAR that is used for radar altimetry (RADALT) operates on a continuous wave basis, allowing for precise measurement of altitude by transmitting a continuous signal. This signal reflects off the surface below, and the time it takes for the echo to return is measured to determine altitude.

In the context of radar systems, Continuous Wave radar is beneficial for tracking and measuring altitude as it provides high-resolution data. The system continuously emits electromagnetic waves, which results in a more stable and consistent reflection from the ground or other surfaces, improving the accuracy of altitude readings.

The other formats, such as Pulse Width Modulation, Frequency Modulation, and Square Wave, are not typically associated with primary RADAR systems used in radar altimetry. Pulse Width Modulation and Frequency Modulation are used in different contexts, often related to communication systems or other forms of modulation in radar technology, while Square Wave is a form of waveform that does not effectively measure altitude in radar applications.