Canopy Reflectance Model Inversion in Multiple Forward Mode

Abstract

Remote estimation of canopy structure is important in forestry and a variety of environmental applications. Multiple Forward Mode (MFM) look-up table (LUT) inversion of canopy reflectance models is one approach for obtaining forest canopy biophysical-structural information (BSI). MFM provides inversion results from models that are not invertible directly, and has advantages in terms of software requirements, model complexity, computational demands, and provision of physically-based BSI output. Proper handling of MFM-LUT parameterization and inherent uncertainty in the inversion procedure at the critical final BSI retrieval stage is essential, and is the theme of this paper. Three approaches are presented for deriving BSI from MFMLUT multiple solution sets: reflectance equality (REQ), nearest spectral distance (NSD), and spectral range domain (SRD). These approaches were validated at a Rocky Mountain test site, for which SRD corresponded best with field data, with RMSE 0.4 m and 0.8 m obtained for horizontal and vertical crown radius, respectively. Recommendations for selecting MFM inversion approaches are provided for future applications.