Single and two epoch analysis of ICESat full waveform data over forested areas

Abstract

Analysis of full‐waveform pulses from space‐based laser altimeter systems are expected to improve our ability of measuring forests globally. Moreover, with the increase in the number of waveform data sets, it is now possible to study temporal changes in waveform returns over the same spatial domain. ICESat full waveform data from two epochs, i.e. winter and summer (2003) along near‐coincident ground tracks, are studied. Data analysis methods are discussed, including normalization and matching of near‐coincident waveforms, Gaussian decomposition, and derivation of forest measurement and forest change parameters. We quantify differences between winter and summer waveforms, acquired over broad‐leaved, mixed‐wood, and needle‐leaved forests in Europe. The results indicate that, although maximum tree height barely changes over six months, i.e. <2.2% for all three cover types, the Height of Median Energy (HOME) changed most in broad‐leaved (a 148% change) and least for conifers (a 36% change, winter to summer). Ratios of ground energy to canopy energy of normalized waveforms also changed noticeably over time: 67% in broad‐leaved, 62% in mixed‐wood, and 47% in conifers. Attempts are made to differentiate and classify these three cover types on the basis of these and other canopy metrics. The initial results, with a coefficient κ of agreement between reference and classified data of 0.57, provide a baseline against which improvements in data and methodology can be gauged.

Acknowledgements

The authors would like to thank David Korn from the National Snow and Ice Data Center and Gerard Hazeu from Wageningen University for their guidelines and data distribution. We would like to thank our anonymous reviewers for their numerous comments, which considerably helped to increase the quality of this paper. We also would like to thank Merel Keijzer for her correction of the English. This project is funded by the Delft Research Centre Earth.