Methods

The main focus of the Case Study St. Anna is the investigation of the optimum time frame for ALS data acquisition in areas covered by deciduous trees and the advanced DTM generation for archaeological interpretation.

In order to enhance the quality of the DTMs and to allow for a reliable interpretation of the acquired data, an in-depth understanding of the interaction of the emitted laser beam with the sensed surface is essential. This additionally gained knowledge will help to develop advanced methods for DTM generation based on FWF-information.

As ALS constantly finds new fields of application, special demands are increasingly made on the results. Archaeology for example needs a high quality separation of terrain and off-terrain points to derive detailed DTMs displaying micro-topographic variation even under forest canopies. Biology and forestry are interested to extract individual trees from the point-clouds. During the last years, full-waveform ALS (FWF-ALS) turned out to have a high potential to meet many of these requirements. However, an in-depth understanding of the FWF-information is essential to enhance the quality of the DTM and to allow a reliable automated interpretation of the acquired data.

In St. Anna, this complex interaction of the laser beam with different types of vegetation cover was investigated by simultaneously scanning part of the forest by airborne and terrestrial laser scanning (Riegl LMS-Q680 and Riegl VZ-400). The combined data acquisition took place simultaneously on a calm day. Using tachymetry, the data sets were geo-referenced and the differences between the ALS and TLS data sets were minimized by an adjustment using planar control and tie patches.

The investigation of each individual FWF echo together with the derived FWF parameters and the digitised waveform could be done within the context of the object that is provided from the TLS data. In that way, we could gain interesting results especially from densely vegetated areas, which will help to improve algorithms for the advanced usage of FWF information