In addition, a reference TerraSAR-X image of the un-flooded area
was acquired almost exactly one year after the flood to allow comparison
between flooded and un-flooded areas (Giustarini et al.,
2013). This was acquired from the same orbit and with the same
incidence angle, polarisation and resolution as the flood image. The
vegetation state should also be similar in both images, as they were
acquired at the same time of year. Normally, a pre-flood un-flooded
image would be used as a comparison, but as TerraSAR-X was still
in its commissioning phase in July 2007, a post-flood reference was
selected instead. The images were calibrated and geo-referenced,
and filtered with a 3
×
3-pixel Gamma-MAP filter to reduce speckle.
The processed flood and reference images are shown in Fig. 6.