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27. Naples (Italy)

Naples The image on the left side is an intensity image acquired over the Naples area (I) by ERS-1 in August 1991. The image has been "stretched" in the horizontal direction in order to show a better perspective view.
In the center of this image one can clearly distinguish the volcano Vesuvius. Below Vesuvius is the bay of Naples, and below Naples are the Caldera features of the Phlagrean Fields stretching to the coast. In the image, the white areas correspond to urban centres, and dark lines to motorways.
The figure on the right side shows an interferogramme of the same location.
The height contours of the Vesuvius are particularly striking. Note that no phase differences are given over the sea as the phase between passes is totally decorrelated due to the motion of the sea surface.

(Rocca, POLIMI, Milano)

28. Coherence image of Bonn area (Germany)

Bonn A series of ERS-1 SAR (Slant Range Complex) data sets of an area near Bonn, acquired during early spring 1994 has been analysed using interferometric methods. As the images were sampled at 3 days intervals, good phase-coherence between image-pairs could be expected. Images between 1st and 28th March were considered and totally 9 coherence images from different image-pairs have been generated.
Agricultural fields appear in general quite bright in the coherence images, however some appear dark, indicating low coherence. In this cases, one can expect that coherence was lost due to farmer activities during the time between the two data acquisitions.

In order to verify this all coherence-images were provided to agricultural experts of the Bonn-University. They inquire about the farmers activities during March 1994, especially with respect to the dark-appearing fields in the coherence images. With respect to the relevant dates all fields were listed for type of crop and farmers activities.
In all cases a reason for the loss of coherence could be identified.

To demonstrate the farmers activities over a longer period a multitemporal colour image was produced (see figure) choosing 3 of the 9 coherence images, namely.
-07/03/1994-10/03/1994 shown in red image channel.
-10/03/1994-13/03/1994 shown in green image channel.
-13/03/1994-16/03/1994 shown in blue image channel.
All fields with equal grey-values in all three channels, i. e. with no change in coherence over the whole period from 07/03/1994 to 16/03/1993 appear not coloured, in black and white. The coloured fields result from different grey values in at least one of the three image planes (red or green or blue). The red fields have low coherence in the green and blue image plane, and hence no contribution from those to the colour-combination.
In fact the farmer ploughed the field twice, once between 13/03/1993 and 16/03/1993 and a second time between 16/03/1993 and 19/03/1993.
In yellow appear the fields with no coherence in the blue image plane, i. e. farming activities in this case must have taken place after the 13/03/1994.
In fact the field verification proved that farmer activities on these field were carried out between the 13th and the 16th of March. In the same manner all other colours could be explained.

Not only farmers activities, but also meteorological effects (rain, wind-fall), irrigation and of course all changes linked to vegetation growth can be reasons for de-correlation.
In our case, a loss of coherence especially related with growth can be neglected as vegetation canopy in March, if available at all is still very low and further, only a rather short time interval between two ERS-1 acquisition was considered.

(Wegmüller, Werner, Nuesch, RSL, Univ. Zurich)

29. Interferogram and DEM of Gennargentu (Italy)

The figure shows an example of a DEM computed from ERS-1 SAR data gathered over the Gennargentu area (I) using the INSAR technique. The DEM has been derived from the interferogram of the same zone. The area consists of vegetated peaks rising rapidly from the coastline to a height of about 1200 m.

(Rocca, POLIMI, Milano)