In semi-arid regions, the surface water can be discriminated with standard Spot/VGT S10 data because of the contrast between water and dry soil [Gond et al, 2004]. The waterbodies detection products generated by VITO in the framework of Geosuccess from a methodology developed at JRC (Gond & al 2004), indicate free water, humid area and mix of free water and humid area.
Although Spot/VGT provides images with a 1-km resolution, it was demonstrated that it is sufficient to accurately map and monitor the presence of water in ponds and swamps of about 1 km² in size. The accuracy obtained is in the order of 90%, i.e. 90% of the water bodies detected with the method over an area of 1 million km² were found to be correct.
From these data sets, two main products are developed at JRC within GEOLAND OLF: to provide
- the date for start of replenishment
- the end of draining/evaporation
A validation mask is also delivered to the user. It helps the user to discard the remaining noise in the water bodies detection. This mask is built on GLWD (Global Lakes and Wetlands database) and the analysis of historical occurence of detection in the VGT images. Because this validation mask is manually checked, it is proposed on a restricted area in a first step, and will be updated to a larger extent in next steps.
| Spatial resolution | 1/112 degree |
|---|---|
| Geolocation accuracy | 300m |
| Projection | Geographic WGS84 |
| Product accuracy | better than 90% |
| Frequency delivery | 10 days |
| Ancillary data | GLWD, SRTM |
| Archive available | An archive from mid 1999 onwards |
| Size of Africa | Approx. 50 MB |
| Coding | 16bits for dates products, 8bits for waterbodies products |
More information can be found on: http://www.geosuccess.net
Historical Small Water Bodies can be downloaded after login on the images tab.
More technical information can be found in the Waterbodies Product sheet .
Information on Global Lakes and Wetlands Database GLWD can be found on: http://www.wwfus.org/science/data.cfm
Information on Drainage from DCW or equivalent can be found on: http://www.maproom.psu.edu/dcw/dcw_about.shtml
References :
[Gond 2004] Gond V., Bartholomé E., Ouattara F., Nonguierma A. and Bado I, 2004, « Surveillance et cartographie des plans d’eau et des zones humides et inondables en régions arides avec l’instrument VEGETATION embarque sur Spot 4 », international Journal of Remote Sensing, 25,5,987-1004
Lehner B. and Doll P., 2004,« Development and validation of a global database of lakes, reservoirs and wetlands”, Journal of hydrology, 296, 1-22
More information can be found on:
http://www.spot-vegetation.com
http://www.vgt.vito.be