High resolution scatterometry in the perspective of the ASCAT instrument.

 

   Y. Quilfen, B. Chapron, T. Elfouhaily, K. Katsaros, J. Tournadre

Institut Francais de Recherche pour l'Exploitation de la Mer, BP 70, 29280 Plou-
zane, FRANCE



Abstract

Unprecedented views of surface wind field in storms are provided by the Europe-
an Remote Sensing Satellite (ERS) C-band scatterometer. Scatterometer mea-
surements at C-band are able to penetrate thick convective storms clouds, 
observing the wind fields with good accuracy. 

It appears that the coarse resolution of the measurements (50 km) limits the inter-
pretation of the scatterometer signals. Indeed strong gradients in the surface wind 
exist at scales of a few kilometers and they are smoothed dramatically in the scat-
terometer measurements features (intensity and location of the maxima, position 
of the storm centre). Beyond the ERS systems, the NSCAT and ASCAT scatter-
ometers respectively designed by the Jet Propulsion Laboratory and by the Euro-
pean Space Agency (ESA) will be able to produce measurements of the 
backscattering coefficient at 25 km resolution in addition to that of 50 km.

To prepare for the new scatterometer, a few sets of ERS-1 orbits sampling storm 
cases were produced with an experimental 25 km resolution. It is shown that en-
hancing the resolution by a factor of 2 allows a better location of the wind maxi-
ma and of the storm centre. In addition, it appears that this also reduces the 
geophysical noise (sea-surface roughness variability in the cell + atmospheric ef-
fects) that dominates the radiometric noise. Thus the highest resolution improves 
the definition of the backscattering measurements. 

A comprehensive analysis of the backscattering measurements in the case of high 
winds and high sea-states obtained in TC's is proposed in order to examine the 
interpretation of the wind vector derived from a backscattering model that is cali-
brated up to moderate winds (< 20m/s)  in neutral conditions.



Keywords: Scatterometer, high resolution, storms

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry