The reflection of airborne UV laser pulses from the ocean

Abstract

It is experimentally shown here for the first time that the normalized laser backscatter cross‐section of the sea surface is a function of elevation or height position on the ocean wave. All data were taken off‐nadir, resulting in incidence angles of ∼6.5° measured relative to the normal to mean sea level (MSL). In the limited data sets analyzed to date, the normalized backscatter cross‐section was found to be higher in wave crest regions and lower in wave troughs for a swell‐dominated sea over which the wind speed was 5 m/s. The reverse was found to be the case for a sea that was driven by a 14 m/s wind. These isolated results show that the MSL, as measured by an off‐nadir and/or multibeam type satellite laser altimeter, will be found above, at, or below the true MSL, depending on the local sea conditions existing in the footprint of the altimeter. Airborne nadir‐pointed laser altimeter data for a wide variety of sea conditions are needed before a final determination can be made of the effect of sea state on the back‐