Measuring alpine snow depths by digital photogrammetry. Part 1. Conjugate point identification

In this study, we examine the use of softcopy (digital) photogrammetry as a method of measuring the spatial distribution of snow depths, with the assumption that snow depth contributes most of the spatial variance associated with snow water equivalence in alpine basins. The primary obstacle with which we were confronted was the ability to determine the parallax of conjugate points in an aerial stereopair using automated pattern matching techniques. Snow is often considered to be one of the most difficult surfaces for pattern matching algorithms. We have found, however, that sufficient snow surface texture exists in our alpine study area on Niwot ridge to enable successful automated pattern matching in many locations. This sets the stage for using softcopy photogrammetry to measure spatial distribution of snow depth in alpine basins, thus is an important step forward in our use of distributed-parameter hydrologic models in snowmelt-dominated alpine basins.