NCEP has been receiving the real-time "fast delivery" scatterometer wind
data from the European Space Agency (ESA)  for operational use since 1992.  
There are two primary requirements for the use of these data; subjectively, 
by operational marine meteorologists to improve ocean surface weather analyses, 
and objectively by the global data assimilation system to improve initial 
conditions for numerical weather prediction models.   In order to use these 
data in real-time, attention was directed toward three major areas: 1) development of quality control
procedures, 2) evaluation of transfer functions and 3) experiments in the global data assimilation
system.  When the ERS-1 data first arrived at NCEP, it was determined that there were  problems
with the wind vector retrievals, primarily poor wind direction selections.  A  system was
developed to process the radar backscatter values, combining quality control and data
management procedures designed at NCEP, along with a minimization using the CMOD4 transfer
function to go from radar backscatter to wind. Multiple solutions for wind directions  exist,
therefore  the ambiguity removal and directional selection scheme,  adapted from the United
Kingdom Meteorological Office, is then applied. 
        
Evaluations of the ERS-1 (and ERS-2) wind data against collocated NOAA and TOGA fixed
buoy data  show that the NCEP processing system improves the wind direction selection
substantially. The reprocessing of the ERS1 data was implemented  in the NCEP operational
network during September, 1994 . 
 
Data assimilation experiments have been carried out to determine impact on global analyses and
forecasts.  Because of the relatively narrow coverage of the ERS1 swath,  these experiments show
that the data have only a small but positive impact in the Northern Hemisphere. The impact is
larger in the Southern Hemisphere, but there is not much "ground truth" data for evaluation. 
Operational assimilation of these data in the global Aviation model became   effective during
November  1995.  But, the special investigation of specific cases shows that the scatterometer
wind data does  contribute in a significant way to resolve wind patterns within individual synoptic
systems.     

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