Context and objectives
The Green areas department of the IBGE-BIM (the user organisation) has
build a geographical database in order to manage and plan the development
of green and blue open spaces. This database was achieved through the use
of aerial photography, topographic database and ground survey. To remain
useful this database has to be updated and completed, which cannot be
achieved by aerial photography (costs), nor by an exhaustive ground survey.
Therefore, this feasibility study aims to establish needs, technical and
economical feasibility of high and very high resolution satellite data for
the monitoring of vegetation and water areas in urban zone.
More precisely, the objectives are :
- Update the mapping of vegetation types at 1 : 10 000 of some green open
- Monitor the annual evolution of some green open spaces in rapid mutation
(such as fallows, railways banks, ...)
- Follow the vegetation state over a season for some green open spaces
submitted to a hydric stress, a pest, or a particular anthropic pressure
- Follow the state of some ponds and green open spaces
- Assess areas of principal types of vegetation and of land cover of
internal part of build blocks
Expected scientific results
- The orthorectification of the IKONOS images reduces the horizontal geometric accuracy from 50 m to 5 m.
- The comparison of vegetation index at several times is useful to detect greenness changes in the city. This vegetation index can updated the greenness index of each block as well as the green open area. It is more recent and reliable than the index that are currently included in the database.
- Both classification methods give similar accuracies (kappas of 0.83 and 0.84). The method based on the segmentation has a generalisation level which is more relevant that the maximum likelihood applied on filtered images. This classification result allows to update and refine the vegetation zones included in the objects of the database.
- A economical analysis showed that the annual update of these results could be obtained and extended to the whole region of Brussels at a minimal cost of 900 000 FB. Nevertheless, the price of very high resolution is in constant evolution; the launch of new civilian satellites should lead to decreased acquisition costs.