title: Towards an Improved LAI Collection Protocol via Simulated and Field-Based PAR Sensing.
abstract: In support of NASA's next-generation spectrometer-the Hyperspectral Infrared Imager (HyspIRI)-we are working towards assessing sub-pixel vegetation structure from imaging spectroscopy data. Of particular interest is Leaf Area Index (LAI), which is an informative, yet notoriously challenging parameter to efficiently measure in situ. While photosynthetically-active radiation (PAR) sensors have been validated for measuring crop LAI, there is limited literature on the efficacy of PAR-based LAI measurement in the forest environment. This study (i) validates PAR-based LAI measurement in forest environments, and (ii) proposes a suitable collection protocol, which balances efficiency with measurement variation, e.g., due to sun flecks and various-sized canopy gaps. A synthetic PAR sensor model was developed in the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model and used to validate LAI measurement based on first-principles and explicitly-known leaf geometry. Simulated collection parameters were adjusted to empirically identify optimal collection protocols. These collection protocols were then validated in the field by correlating PAR-based LAI measurement to the normalized difference vegetation index (NDVI) extracted from the "classic" Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) data ( R 2 was 0.61). The results indicate that our proposed collecting protocol is suitable for measuring the LAI of sparse forest (LAI < 3-5 ( m 2 / m 2 )).
authors.affiliation: Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. wxy3806@rit.edu.
authors.forename: Wei
authors.initials: W
authors.lastname: Yao
authors.affiliation: Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. dave.kelbe@gmail.com.
authors.forename: David
authors.initials: D
authors.lastname: Kelbe
authors.affiliation: Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. vanleeuwen.martin@gmail.com.|Department of Geography, University College London, Pearson Building, Gower Street, London WC1E 6BT, UK. vanleeuwen.martin@gmail.com.
authors.forename: Martin van
authors.initials: Mv
authors.lastname: Leeuwen
authors.affiliation: Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. pavdpr@gmail.com.
authors.forename: Paul
authors.initials: P
authors.lastname: Romanczyk
authors.affiliation: Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. vanaardt@cis.rit.edu.
authors.forename: Jan van
authors.initials: Jv
authors.lastname: Aardt
keywords: AVIRIS; DIRSIG; HyspIRI; leaf area index; photosynthetically active radiation