Research project S0/10/035 (Research action S0)
Context and objectives
Forests play a major economic and ecologic role in many countries. The sustainable management of these forests relies on the availability of up to date databases, that is a proper stand delineation combined with qualitative (e.g. species) or quantitative (e.g. dominant height) parameters.
Very high spatial resolution satellite images provide an alternative to aerial photography for forest stand description. They are compatible with large scale topographic maps and previous studies were successful in the extraction of key stand parameters.
The aim of this project is to transfer operational methods of image processing to produce cartographic products for forest managers. I-Mage Consult and the department of environmental science therefore joined their skills to identify user needs and the most appropriate methods to fulfil these requirements.
Methodology
• Survey to identify forest managers needs
• Description of products and primary feasibility assessment
• Orthorectification tests including choices of mathematic model and digital elevation model.
• Review of existing atmospheric correction and pansharpening algorithms.
• Planimetric quality control of segmented very high resolution satellite images, including the development of an object-based methodology for this purpose.
• Comparison of the effect on edge delineation accuracy for existing and new generalisation algorithms.
• Object-based classification to generate forest maps validated with field survey.
• Forest parameters estimation using on texture based regression.
• Stand height measurements using automated extraction and visual digitizing from IKONOS stereo images.
• Continuous technological transfer leading to the production of forest maps in Morocco.
Results
The technological transfer was conducted in such a way that I-Mage consult is now able to respond to some main requirements of forest managers thanks to very high resolution satellite images. Two end user products, namely forest stand delineation and extraction of stand parameters from existing vector database, were achieved through operational methodologies.
Considering the required planimetric quality of the final products and the processing costs, Toutin’s orbital model and polynomial function with RPC file were the most appropriate for SPOT 5 and IKONOS respectively. In all cases, the use of SRTM digital elevation model was suitable.
The planimetric quality of automated forest stand delineation mostly depended on the geometry of acquisition and on the spatial resolution. Multispectral IKONOS images with zenith angles lower than 15 degree were most appropriate for 1:20000, while PAN + XS SPOT 5 images were a much cheaper alternative when smaller scales were tolerated. The new generalization algorithm helped improving precision and enhancing visualization while conserving topology.
Fuzzy rule decision tree gave more than 90 % overall accuracy with 5 forest classes. In terms of forest stands characteristics, texture parameters were only successful in coniferous stands and species recognition was hindered by high variance due to age and stand structure. The use of a stereo imagery was very efficient in visual interpretation but resulted in 10% of errors with the automated height extraction.
Products and services
Notes and slides were produced for technological transfer. These notes were compiled in a booklet.
