Swell presence imprints visible modulation patterns onto radar altimeter Fully-Focussed SAR (FF-SAR) radargrams. One of the SARWAVE objectives is to develop an algorithm capable of retrieving ocean swell spectrum characteristics by means of Altimetry FF-SAR radargram cross-spectra processing.

Altiparmaki et al. (2022) demonstrated the feasibility of generating FF-SAR spectra and associating it to buoy-measured spectra. Moreover, Kleinherenbrink et al. (2024) showed that by dividing the radar aperture into sublooks, it is possible to calculate FF-SAR cross-spectra, allowing for the accurate determination of swell parameters.

Image description: By applying a 2D Fast Fourier Transform (FFT) to the tail of the geoprojected radar waveforms, we then compute the cross-product between sublooks to obtain the cross-spectra. This methodology provides along-track and across-track swell measurements, as seen in this example, where the cross-spectra between changes depending on the period, intensity and direction of long waves.