ERS1 and ERS2 winds sinergy study during tandem phase

by              J.Johannessen [1], jjohannes@jw.estec.esa.nl, +31 71 565 5959
                J.Figa [1], jfiga@estec.esa.nl, +31 71 565 5370
                E.Korsbakken [2], erik.korsbakken@nrsc.no, +47 55 29 7288
                E.Attema [1], eattema@estec.esa.nl, +31 71 565 4461
[1]:    Earth Sciences Division, ESTEC
                Postbus 299, 2200 AG Noordwijk, The Netherlands
                FAX: +31 71 565 5675
[2]:    Nansen Environmental and Remote Sensing Center
                Edvard Griegsvei 3a, N-5037 Solheimsvriken, Bergen, Norway
                FAX: +47 55 20 0050

The tandem mission orbit configuration of ERS1 and ERS2 (launched in
April, 1995) consists of both satellites in the same orbit, ERS2 flying
about 30 minutes after ERS1. At high latitudes, that situation allows
the overlapping of the swaths of different instruments on board. This
situation opens a wide range of opportunnities for validation and
comparison of the data acquired by both satellites, in particular
allowing comparison of the geophysical parameters derived from those
data.

A good example for that is the sea surface wind. This parameter can be
retrieved from the Wind Scatterometer (SCATT), the Radar Altimeter (RA)
and the Synthetic Aperture Radar (SAR). It is interesting to compare
those values from different satellites, assuming that the sea surface
wind conditions do not change significantly during half an hour.

SAR- and RA-derived winds from ERS2 have been compared with "near
simultaneous" SCATT measurements from ERS1 over the Greenland Sea during
September 11th., 1995. The SCATT data used is the ERS1 WSC 25x25 km
cells winds and the RA data is the ERS2 D-PAF Quick-Look OPR wind
product. The winds retrieved from ERS2 SAR images have been obtained
using both image statistics and image intensity characteristics.
Coincident meteorological data has also been collected for validation
purposes. Preliminary results show a very good agreement between the RA
and the SCATT winds, differences of less than 2 m/s are encountered.
That is also the case for the wind value comparison between the SCATT
and the SAR winds.

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