The algorithm for processing specular echoes

Abileah R., Vignudelli S., Scozzari A.

radar altimetry  specular echoes 

The poster will be a companion to the Inland radar altimetry for intermediate scale water bodies paper to provide extra time and setting to explain the processing ('retracking') specular echoes. The processing flow will be described and illustrated step-by-step in the poster and with live in-the-cloud processing. [For live demo we'll need Wifi and a small stand for a laptop.] The processing is little changed since the 2017 paper. Steps in processing IEs into range measurements are (1A) a water map from EO images (such as Google Earth) , (1B) identify a string of consecutive echoes over water. (2) Verifying that there is actually water with Doppler (expected to be zero), echo power (exceeding a threshold), and coherence (~1). (3) Verifying surface roughness below threshold. (4) Coherently sum IEs into a waveform profile. (5) A parametric fit to two or three range gates to derive sub-gate range accuracy. For the intermediate water bodies (50-250 m) processing is based on one or two S3 bursts. There are special considerations for very narrow (<50 m), and wide (>250 m) rivers or lakes. For <50 there is a fair chance the water body will fall in the gaps between S3 bursts so there are no nadir water IEs. The algorithm can be nudged a bit to handle those cases. For >250 there will be several bursts to combine optimally and some probability that the water surface will have variable roughness scales.

Source: ESA Coastal Altimetry Workshop, pp. 26–26, ESA-ESRIN, Frascati, 4/2/2020-7/2/2020