Determining surface kinematics of glaciers, permafrost and slope movements using digital high-precision aerophotogrammetry

Contents of this page

• Introduction
  
• Digital photogrammetric methods
  
• Results

Introduction

Geometrical changes of glaciers, creeping mountain permafrost and slope movements are caused by a sum of complex 3-dimensional processes. Monitoring surface kinematics helps understanding the dynamics of glacial and periglacial processes and investigating the reaction of glaciers and mountain permafrost to climatic forcing.

Digital photogrammetric methods

From overlapping digital images DTMs are automatically derived using the commercial photogrammetric software SOCET SET (LH Systems, San Diego, California, USA). As a special measure to improve the relative accuracy between repeated image sets and their derived products, both image sets are oriented and adjusted as one image segment. For this purpose, only stable terrain points (i.e. outside the rock glacier) are used for ground control points and inter-annual image tie-points. The methodology of subsequent automatic DTM extraction and orthophoto generation from digital stereo imagery is well established and described. The measurement of individual terrain heights is based on automatic assigning of corresponding terrain features in two (or more) overlapping images. Elevation changes are derived as differences of repeated DTMs.

Horizontal surface displacements are derived from repeated orthophotos of two (or more) times of photography. Special photogrammetric software derives displacements of individual terrain features from multi-temporal digital orthophotos ('CIAS' Correlation Image Analysis). Measuring an individual horizontal displacement vector basically follows two steps (Figure): (1) In the orthophoto of time 1 an image section (so-called 'reference-block') with sufficient optical contrast is chosen. The ground co-ordinates of its central pixel are known from the orthophoto geo-reference. (2) The corresponding image section (so-called 'test-block') is searched for in a sub-area (so-called 'test-area') of the orthophoto of time 2. If successfully found, the differences in central pixel co-ordinates directly give the horizontal displacement between time 1 and 2. For identifying corresponding image blocks in both (or more) images double cross-correlation function based on gray values of the images is used.

Results

	2.5m-resolution changes in elevation between 1981 and 1994 on a section of Muragl rock glacier, Swiss Alps. Rectangles 1-4 mark boreholes.
	3m-resolution horizontal surface displacements between 1981 and 1994 on a section of Muragl rock glacier, Swiss Alps. Rectangles 1-4 mark boreholes.