On the use of sentinel-3A SRAL altimeter waveforms at the finest posting rate (80 Hz) for the detection of ships

The detection of non-ocean scatterers over the sea surface by using pulse-limited satellite altimeters involves a series of challenging targets, such as icebergs, lighthouses and ships, which have been investigated in the literature. In particular, past works focused on the hyperbolic features observed in the thermal noise area of the received waveforms, in order to detect the presence of such non-ocean targets. Following previous analysis made with CryoSat-2 data, in this work we exploit the capabilities of Sentinel-3A SRAL delay- Doppler instrument for the detection and characterisation of ships. In particular, we analyse the shape of the waveforms at two along-track sampling rates: 20 Hz - 80 Hz, in order to investigate the effect of the two resolutions in the discrimination of ships. This analysis might help to investigate the possibility to estimate some geometric features of the detected vessels from the echoes returned by the altimeter. The presented approach offers the opportunity to: i) study the compatibility between the detected target(s) and the known ship traffic, by using the Automatic Identification System (AIS) data; ii) resolve ambiguities among multiple targets, by using two different alongtrack spatial resolutions, due to the different sampling rates. Ship traffic statistics, as introduced by the literature, may take benefit from the method described in this work, providing a contribution to improve the overall precision of such statistics. The Sentinel-3 mission used in this work will provide a constellation with global SAR coverage (S3A and the new S3B) and free accessibility to the data, with a potential enhancement to the estimation of the number and characteristics of the ships with respect to past literature approaches.