Digital Photogrammetry

One of the main activities NGU has carried out during the last decade is landslide mapping. A common first approach to identify, characterize and monitor several types of landslides is the use of remote sensing imagery.

Picture: Example of a 3D-model (terrainmodel) produced by using aerial photogrammetry. 

Several techniques exist that are widely accepted and performed for landslide analysis (e.g.: photogrammetry, laser scanning, radar interferommetry). NGU has extensively used remote sensing techniques for landslide investigations.

Photogrammetry is the geometrical reconstruction of an object in 3D from photographic images. A point on an object is reconstructed when the point is intersected from at least two directions (two photographs from two different positions). Photogrammetry is based on images from passive sensors; it means that the sensor (photo camera) only records reflections of a natural energy source (i.e.: sunlight). Active sensors (e.g.: laser scanners), produce their own energy source, which is recorded when is back scattered.

Aerial and terrestrial (close range) photogrammetry are the two main type of photogrammetric techniques applied to landslide investigations. Aerial digital photogrammetry traditionally works with airborne-based imagery (aerial photographs), but in recent years, due to large improvements in spatial resolution and stereo capabilities, satellite imagery is being used too.  Common applications of aerial digital photogrammetry on landslide analysis are identification of morphological features of slope deformation on large instabilities (e.g.: scarps, counter scarps, cracks), and monitoring (multi-temporal analysis). Close range photogrammetry is a popular tool for structural and rock mass characterization of unstable rock slopes.