ERS-2/NSCAT co-located database

Abstract

Cersat is the French Processing and Archiving Facility for ERS-1 and ERS-2 satellites. During the last two years, CERSAT has processed five years of ERS1 data and distributed them on CDROM to more than 120 laboratories. In August 1996, ADEOS, a Japanese satellite, was successfully launched. A double swath scatterometer , NSCAT, was on board. In December 1996, we started the distribution on FTP of NSCAT data in Europe, in collaboration with JPL (Jet Propulsary Laboratory) in charge of NSCAT distribution, and ESA. We have decided to generate a database of collocated products, taking advantage of the ERS scatterometer database already available at CERSAT:

• ERS/Ami-Wind and NSCAT
• ERS/ Radar Altimeter and NSCAT
• as we archive the ECMWF wind fields we have also collocated these data with NSCAT

These products are very useful for calibrating and validating NSCAT products. Since December they have been distributed through FTP to the user community. A user-friendly WEB interface is now provided. It allows temporal and geographical extraction regarding the data available on FTP and also in our archive.Some preliminary results obtained using this database will also be presented

ERS-2 CO-LOCATED DATABASE

CERSAT is the French Processing and Archiving Facility for the ERS-1 and ERS-2 satellites. CERSAT is part of IFREMER, the French Institute of Research for the Sea, and is under contract with the European Space Agency. It processes off-line products for the ERS Radar Altimeter and Scatterometer sensors. These products are archived and then distributed on CDROM to the user community.

Two years ago, CERSAT started processing all ERS-1 Scatterometer data using a processing chain developed by Y. Quilfen and all. /IFREMER and a model developed by A. Bentamy and all. /IFREMER. During Summer 1996, all ERS-1 data were processed and distributed to users. The total dataset represents 75 CDROMs and has been distributed to more than 120 laboratories all over the world.

In August 1996, ADEOS, a Japanese satellite, was successfully launched. A double swath scatterometer called NSCAT was on board. This scatterometer, a Ku band radar, measures s 0 with a spatial resolution of 12.5 km. NSCAT data are first processed at NASDA/Japan and then processed and distributed by JPL (Jet Propulsion Laboratory/NASA). During the commissioning phase, NSCAT data (s 0 and wind vectors over oceans) are distributed on the network. Later, they will be distributed on CDROM.

IFREMER is a PI for NSCAT. Thus, the Department of Oceanography from Space needs NSCAT data. This department is composed of a scientific laboratory and of CERSAT. As regards this project, the schedule was very tight : the data were distributed to the NSCAT Team scientists mid-November and the first results were presented mid-January, less than two months after the distribution started.

In collaboration with JPL, we have decided to provide for the European Community, a NSCAT FTP server mirroring that of JPL's. Because network transfers are very slow between Europe and USA during working hours, it is essential to set up a FTP relay site. We decided to implement a NSCAT database, financed by ESA, at CERSAT. Using NSCAT and ERS databases, CERSAT is now able to provide co-located datasets between ERS Scatterometer and NSCAT, and between ERS Radar Altimeter and NSCAT. This data is distributed through the CERSAT FTP server.

For each NSCAT 50 x 50 km cell, co-located with an ERS measurement, these co-located products consist of :

• the NSCAT parameters
• ERS parameters for the nearest ERS cell
• statistics on the next closest cells

We say that NSCAT and ERS data are co-located when :

• Radar Altimeter :
  • temporal separation is less than 1 hour
  • geographical separation is less than 25 km
  • ERS data are valid

• Scatterometer :
  • temporal separation is less than 1 hour
  • geographical separation is less than 100 km

These data are distributed in HDF format used for NSCAT distribution by NASA. You can find more details on these products in the User Manual, available with the data on the IFREMER FTP site : ftp.ifremer.fr. The NSCAT Data are in the directory /ifremer/nscat/DIF. For further information, you can send an email to fpaf@ifremer.fr. These co-located products, very useful for NSCAT validation are now distributed through a user-friendly WEB interface visible on the FPAF demonstration area.

Once algorithms will be developed by the scientists of the Department of Oceanography from Space, we plan to generate mixed ERS/NSCAT products such as krigged wind fields and Sea Ice products. These types of products have already been processed for ERS by CERSAT and are distributed to users on CDROM.

NSCAT provides us with useful preparation as regards new scatterometers that will be launched in the future, and above all it is a good start for METOP which uses the same Ku band technology.

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