Satellite stereoscopic pair images of very high resolution: a step forward for the development of landslide inventories

Development of landslide inventories based on remote sensing techniques has become one of the main tools in assessment of hazards and risk. Among those techniques, visual and automatic and semi-automatic analysis of high- and very high-resolution (VHR) satellite images, or a combination of these, has recently been considered as a promising way to identify and map landslides at local and regional scales. In this context, a landslide inventory for the municipality of Pahuatlán, Puebla, in central Mexico was prepared by combining three techniques: (1) visual analysis of stereoscopic pairs of VHR satellite images (GeoEye-1), (2) visual analysis of monoscopic VHR satellite images (SPOT 5 and Google Earth images), and (3) field surveying. In this paper, particular attention is given to landslide identification and mapping based on the GeoEye-1 stereo-pairs. Additionally, as a preliminary step in the use of VHR imagery, a general review is presented of the available VHR satellite images, software and hardware that can be useful for digital mapping of landslides. The landslide inventory included a total of 577 landslides, corresponding to an average density of 10.5 landslides per km2. Of these, 385 were classified as recent, 171 as old, and 21 as very old, regardless of state of activity. The total mapped area was 54.9 km2; 57.7 % of it had been affected by landsliding. The mean area occupied by recent landslides was of the order of 1,066 m2; for old landslides, it was 82,559 m2 and for very old landslides 1,173,952 m2. Debris flows were the most frequent type of movement (217), followed by 167 translational slides, 97 complex movements, 79 rotational slides, and 17 falls and topples. The cost–benefit relationships of a number of these techniques remain debatable because of the high cost of some of the VHR images and the related software and hardware. However, the appearance of new satellite sensors is likely to generate market competence, so this type of image will probably be available at a much lower cost in the near future. Additionally, it is important to consider that the use of several stereo-high-resolution images involves no cost, as downloading high-resolution images from Google Earth, using Google Earth Pro is currently available. The relative rapidity of these techniques can be highly valuable after a regional landslide disaster has occurred, since damage to roads and infrastructure usually prevents the rapid and accurate evaluation of the impact of landsliding. Most importantly, these techniques can be of great value for hazard evaluation of potentially unstable inhabited slopes.