Estimating Canopy Gap Fraction Using ICESat GLAS within Australian Forest Ecosystems

Research output: Contribution to journalArticle

Abstract

Spaceborne laser altimetry waveform estimates of canopy Gap Fraction (GF) vary with respect to discrete return airborne equivalents due to their greater sensitivity to reflectance differences between canopy and ground surfaces resulting from differences in footprint size, energy thresholding, noise characteristics and sampling geometry. Applying scaling factors to either the ground or canopy portions of waveforms has successfully circumvented this issue, but not at large scales. This study develops a method to scale spaceborne altimeter waveforms by identifying which remotely-sensed vegetation, terrain and environmental attributes are best suited to predicting scaling factors based on an independent measure of importance. The most important attributes were identified as: soil phosphorus and nitrogen contents, vegetation height, MODIS vegetation continuous fields product and terrain slope. Unscaled and scaled estimates of GF are compared to corresponding ALS data for all available data and an optimized subset, where the latter produced most encouraging results (R2 = 0.89, RMSE = 0.10). This methodology shows potential for successfully refining estimates of GF at large scales and identifies the most suitable attributes for deriving appropriate scaling factors. Large-scale active sensor estimates of GF can establish a baseline from which future monitoring investigations can be initiated via upcoming Earth Observation missions.

Details

Authors
External organisations
  • CSIRO Oceans and Atmosphere, Victoria
  • Swansea University
  • University of Lethbridge
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Geophysics

Keywords

  • vegetation, remote sensing, forestry, LiDAR
Original languageEnglish
Article number59
JournalRemote Sensing
Volume9
Issue number1
Publication statusPublished - 2017 Jan 11
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes