High Rate Waveforms Analysis: 10 years of geophysical applications
Jean Tournadre(1) , Bertrand Chapron(1) , and Douglass Vandemark(2)
(2) NASA, Goddard Space Flight Center,, Wallops Island, Virginia, United States
High rate altimeter waveforms (10 Hz for Topex, 20 Hz for Jason and Envisat) contains a
wealth of information on the variation of the Normalized Radar Cross section (NRCS) at
scales smaller than the altimeter footprint. However, the complexity of their analysis and the
quantity of data to be processed have limited their use and very few studies involving their
analysis for geophysical studies (other than tracking) have been published. Over the past 10
years, the Laboratoire d'Océanographie Spatiale of IFREMER has developed several
applications based on the analysis of the high rate waveforms, i.e. the determination of rain
cells characteristics, the detection of surface slicks (associated with sigma0 bloom) and the
detection of ships, small islands.
The presence of small scale phenomena within the altimeter footprint, such as rain cells which
attenuate the signal, surface slicks that enhance it, or above sea level objects (light house,
ships, etc..) leads to characteristic V-shaped patterns in the waveforms fields. They result
from the relative movement of the satellite above the surface phenomena. Specifics models of
waveforms based on the Brown model and on the modulation of the surface NRCS within the
altimeter footprint have been developed to explain and characterise the signatures of these
different processes. The models and methods have been validated by data/model comparison.
In this paper, we describe these three main applications of high rate waveforms analyses and
present what operational use could be foreseen as the computing capabilities improved.