High-resolution Satellite Imaging in Remote Regions, a Case Study in Bhutan

In remote developing countries, such as Bhutan, it is common for existing maps to be either out-of-date or to not exist. Showcasing forest covered peaks and broad valleys with ground elevations from 2000 m and climbing as high as 4200 m, the Bhutanese setting provides a unique and challenging environment for the generation of image-based products. Although picturesque, the rugged mountainous and largely inaccessible landscape is not well suited to traditional topographic surveying and mapping. This paper shows that even with limited ground control, satellite imagery has the potential to rectify the situation and vastly enhance mapping prospects in such an environment. By compensating exterior orientation biases inherent in the recorded sensor orientation data, the attainment of 1:5000 mapping scale ground measurement positions is possible with lowest cost QuickBird imagery. Two image matching algorithms were applied to produce DSM data. Firstly, intensity based matching procedure embodied in Z/I Imaging’s ImageStation Photogrammetry Suite 4.3 Image Station Automatic Elevations (ISAE); and secondly a multi-photo, geometrically constrained (MPGC) image matching approach incorporating a hybrid matching algorithm. A third DSM generated by radar was also assessed for the Bhutan test field and compared to the optically derived surfaces. The most accurate DSM generated (MPGC) was used to remove relief displacement, so that planimetric coordinates can be obtained from a single orthoimage to an accuracy of better than a metre. The results show that there is potential for QuickBird 'Basic' to be an effective and economically viable method of extracting 3D information to be used for high accuracy ground feature determination. The implications of using this imagery for precision geopositioning in remote areas include the generation of more accurate digital terrain models and cartographic maps and location data for incorporation into a GIS, providing useful information for development agencies and the wider community.