A Trihedral Corner Reflector for Radar Altimeter Calibration

A trihedral corner reflector has been used to evaluate the capability of passive reflectors to calibrate radar altimeters, such as the Poseidon-4 altimeter on board Sentinel- 6A. The reflector location, placed on the top of a mountain ridge and about 4-km off-nadir of the Sentinel- 6A subsatellite track, allows capturing echoed signals with a signal-to-clutter ratio (SCR) around 40 dB when processing the received data with a fully-focused synthetic aperture radar (FF-SAR) algorithm. Results obtained show a range bias of 33.9 with 8.5 mm of standard deviation and datation bias of
$- 2.3\,\,\mu \text{s}$
with a standard deviation of
$1.8~\mu \text{s}$
for the measurement campaign between September 2021 and April 2022. Such values are comparable to what is currently achieved by means of active transponders, and therefore, it is demonstrated that passive reflectors may be of interest to support radar altimeter regular calibration.