Rhine Flooding (ERS-1 SAR / LANDSAT TM data merge)

The reliable data source from the ERS-1 SAR can serve as up-to-date information in the absence of conventional optical satellite or other data. This is often the case in bad weather condition during catastrophic events such as floods.
A data merge of "historical" data from optical sensors (Landsat, Spot satellite) with latest SAR data acquisitions by a rather simple procedure can be produce. They form the basis for thematic maps of high actuality and of a quality equal or even enhanced with respect to the original optical data.
In our case a LANDSAT TM scene of 11 May 1993 (the only cloud-free scene in a convenient time period) was superimposed geometrically to a actual ERS-1 SAR scene acquired on 25/12/93 during the flood period. For the merge TM channels 4,5 and 3 (2 infrared 1 visible) were used and a conventional IHS (intensity/hue/saturation) colour transformation performed. Subsequently the intensity channel was replaced by the Lee-filtered SAR data and the reverse transformation was computed.
red: ERS-1 SAR as Intensity,
green: Landsat TM453 as hue,
blue: Landsat TM453 as saturation
In this way the SAR determine the intensity of the colours in the scene.
E.g. dark colours (but with the different objects still visible) are the flooded areas and the very bright spots are mainly industrial plants; while a granular light bluish tone would indicate residential areas. The light brown indicates woods.
Within the field pattern the surface of the flooded area can be measured (each image element or pixel represents 30m x 30m) separately, for the grassland and cereals (red) and of other crop (bluish).
This wealth of information may contribute to the management of catastrophic events and later for an independent assessment of the extension of the affected area.

(ERS Data Utilization Section ESA/ESRIN)

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