- Integration of very high resolution satellite imagery within the cartographic channels of the Walloon Region: change detection on numeric orthophoto maps

Project outcome

Expected scientific results

The topics discussed in this paper show that in order to define a policy for the progressive renewal of the coverage of ortho-photomaps derived from aerial photography, a viable alternative is to proceed to a diachronic analysis for change detection between the actual cover and VHR satellite imagery. The resulting analysis provides an indication of where a coverage renewal would be appropriate and constitutes thus an aid to any decision process for this matter. It is of course now up to the DGPL administration to proceed to the diachronic analysis and to produce the concomitant change detection map for the whole region.



For now, part of the proposed methodology rests on a somewhat tedious manual screen digitising procedure. However, in a near future, with increasing quality of the acquired orho-photomap coverage, as also with a progressive improvement of the organization of - and the access to - the available ground occupation databases, this task of updating will certainly evolve towards more automation. A particular attention should be paid to the existing PICC database which unfortunately could not be incorporated in time into this case study.



The proposed methodology relies on sophisticated technologies involving digital image and GIS processing for which specific training is required. This expertise could be provided with the aid of appropriate consultancy such as can be offered by university departments involved in remote sensing and GIS related matters. A symbiosis with some research departments would be an efficient manner to assist the introduction of high technology into the administrations and to keep the necessary knowledge and skills up to date. It would result in improved product and service quality and also enable the administrations to become less dependent of some monopolistic private companies.



Another topic of vital interest in relation with our subject is the rapid evolution of spatial imagery products. Although currently available satellite images can serve many purposes, 1 m resolution panchromatic imagery still doesn’t compete favourably with the 40 cm resolution colour images stemming from aerial photography, and are therefore less suitable for many spatial planning surveys and management activities at large scale. But that was for yesterday. Today, new generation satellites are planned, some are already orbiting, and start producing higher resolution images - for now up to about 70 cm resolution - at a very competitive price of a few tens of dollars per km2, depending upon the quality of the ordered product. Such images would almost certainly provide a viable alternative for replacing aerial ortho-photos in areas of slow rate of change such as rural and forest land. Whatever, these facts clearly show the evolutionary trends: better image quality, product homogeneity, reduced costs, complete coverage acquired within reasonable delays, and rapid revisit times. What else could we ask for ? Within this scenario the answer for updating an image database is of course immediate. And how logical and cost-effective would it be to get all the administrations concerned to agree on a common acquisition of such an image cover, all of them are hungering to use for their own needs. It would benefit to all.