Potential applications

Mapping storm damage

The storms that left a trail of destruction through France in December 1999 took a devastating human and economic toll. Following initial emergency response, maps and statistical data had to be produced rapidly to assess the extent of the damage. To this end, large volumes of Earth observation data including SPOT imagery and aerial photographs were combined with field surveys. Simulated SPOT 5 imagery was also analysed to gauge its ability to aid damage mapping.



Local-scale damage mapping of small parcels of forest currently relies on analysis of aerial photographs at 1:30 000 and on field surveys by ONF, the French national forestry service, or by private contractors. Remote sensing data speeds up assessment, which can be very time-consuming where storm damage is spread over a vast area. SPOT 5's capacity to acquire timely, accurate and reliable geographic information covering large tracts of forest is therefore a precious aid.

 

Haguenau forest (Alsace, north-east France)
Haguenau forest is France's second largest plain forest, covering 13,472 hectares. It is some 30 kilometres north of Strasbourg, stretching 30 kilometres east to west across the Alsace plain and 10 kilometres north to south.

 

 


The advantages of SPOT 5 XS imagery Vegetation index variations were calculated from two simulated SPOT 5 colour images with 10-metre resolution, the first acquired before the storms (in July 1998) and the second after the storms (in June 2000).
These variations highlighted:

 

Results with SPOT 4 and SPOT 5 images closely match those obtained by ONF (to within around two per cent). The best damage assessments are obtained with SPOT 5 10-metre colour and 2.5-m black-and-white imagery.

 

 

 
Results obtained with SPOT 4
Results obtained with SPOT 5 -
10-m colour
Results obtained with SPOT 5 -
2.5-m black and white
ONF reference data
Damage class
Parcel
area
%
Number
of
parcels
%
Parcel
area
%
Number
of
parcels
%
Parcel
area
%
Number
of
parcels
%
Parcel
area
%
Number
of
parcels
%
Less than 10%
33
37
31
34
27
31
26
33
10 to 40%
21
21
19
21
26
25
25
26
40 to 80%
22
21
28
26
30
29
31
25
More than 80%
24
21
22
19
17
15
18
16

For 578 forest parcels, results obtained with SPOT 5 compare very well with parcel damage maps produced by ONF.

 

Damage zones can be mapped accurately by comparing 10-metre colour images acquired by SPOT 5 before and after a storm. Results for forest parcels are very close to those obtained by ONF, working at a scale of about 1:10 000. In comparison with a similar data set acquired by SPOT 4, detection errors using SPOT 5 data are reduced by half.
With SPOT 5 2.5-metre black-and-white data, damage can be mapped at a scale of around 1:3 000. Results show that increased resolution enables much more accurate damage mapping, with variations of just one per cent with respect to ONF data.


SPOT 5 - A clearer view of forests

HRG instrument (High Resolution Geometric) Multi-resolution, wide-swath imaging.

A new range of spatial resolutions for forest management :

- Finer ground resolution in black-and-white mode: 2.5 metres and 5 metres (instead of 10 metres).
- Finer resolution in colour mode: 10 metres (instead of 20 metres) in the three visible and near-infrared spectral bands. The 20-metre short-wave infrared (SWIR) band is essential for studying forests.

Wide-area imaging:

- Like all their predecessors, each SPOT 5 instrument covers a 60-kilometre swath.
- Oblique viewing makes it possible to revisit areas of interest frequently.

 

References: