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Set up an emergency plan!

Fringe image

As mentioned earlier, the use of radar interferometric techniques can highlight damaged areas following an earthquake. Radar interferometry can be explained as a technique to infer the difference between two (microwave) data acquisitions (one before and one after the earthquake) over the same area and from a unique point in space.

The interference pattern resulting from such computation is a fringe image showing the phase changes. A phase change is explained by the relative movements of the ground between the two acquisitions. In the case of the ERS satellite, one fringe corresponds to 28 millimetres of movement. In practical terms, this means that measuring a certain distance in the image, counting the fringes and multiplying the number by 28 mm, gives an indication of the movement of the Earth's surface. Where fringes are dense, the Earth's surface has moved during an earthquake more consistently, whilst less consistent movement is revealed by larger fringes - hence the destructive force was greater in the former case.

To establish which area was most affected, take a fringe image computed from two data sets recorded before and after the earthquake, respectively. Superimpose it onto a map or onto an interpreted satellite image (satellite image map). The finished product can prove highly effective in organising disaster management personnel as they plan and prioritise rescue and reconstruction operations.

Let's now consider the practical case of the Turkey earthquake.

Have a look at the fringe image and try to locate the point where the earthquake was stronger. You will notice dense fringes in some points that cannot be resolved. It is obvious that the earthquake was stronger and highly destructive here. In other places, the fringes are missing. This is a limitation of the technique: it is not valid over forested areas.

Compare the fringe image with available maps and satellite images. Based on the density of settlements and the strength of surface movement (density of the fringe pattern), set up an emergency (top level) plan and list all the priorities (first, second, third, etc) for the actions to be taken by rescue teams.

Technical information about the satellite images

Satellite and sensor: Landsat 7 ETM (Enhanced Thematic Mapper)
Acquired on 10 August, 1999 at Neustrelitz Ground Station (Germany)
Track: 179 Row: 32

Satellite and sensor: Landsat 7 ETM (Enhanced Thematic Mapper)
Acquired on 17 August 1999
Track: 180 Row: 32
Acquired by: Neustrelitz (Italy)

Satellite and sensor: ERS-1 and 2
Acquired on 12 and 13 August 1999
Orbits: ERS-1: 42229 / ERS-2: 22556
Track: 157 Frame: 815
Acquired by: Fucino (Italy)

Disaster monitoring
Introduction
Earthquakes
Introduction
Izmit earthquake
Introduction
Exercises
Earthquake damage assessment simulation