Comparison of stereo-optical and dual-band InSAR DEMs in Papua New Guinea

Abstract

This paper describes comparison of digital elevation data derived from synthetic aperture radar (SAR) and stereo optical imagery used to understand temporal changes of tropical forest and to estimate tree height in tropical regions. Tree height information is important for forest management and global carbon cycle studies. An intereferometric SAR (InSAR) potentially unhampered by tropical cloud cover. InSAR heights depend on the microwave frequency: low frequency P-band penetrates to the forest floor and ground-volume scattering yields a height close to terrain height, high frequency X-band displays only shallow canopy penetration, and may yield heights several metres below the canopy surface. The exact behaviours depend on the nature of both terrain and forest. A stereo-optical sensor may be used to derive digital elevation data using photogrammetry. Several recent satellite-based stereo-optical instruments operate with fine spatial resolution however optical imagery is affected by clouds. The forest height derived from optical images is essentially the top of the canopy. This research investigates whether it is possible to understand forest changes in tropical regions by comparing digital elevations from dual-frequency, single-pass airborne InSAR with satellite-based stereo-optical data in Papua New Guinea. The results indicate the possibility of forest change and tree height estimation using this combination of data.