@article{fdi:010070842,
  title = {{M}apping plant area index of tropical evergreen forest by airborne laser scanning. {A} cross-validation study using {LAI}2200 optical sensor},
  author = {{V}incent, {G}r{\'e}goire and {A}ntin, {C}. and {L}aurans, {M}. and {H}eurtebize, {J}. and {D}urrieu, {S}. and {L}avalley, {C}. and {D}auzat, {J}.},
  editor = {},
  language = {{ENG}},
  abstract = {{L}eaf area index estimates in dense evergreen tropical moist forest almost exclusively rest on indirect methods most of which being of limited accuracy or spatial resolution. {I}n this study we examine the potential of full waveform {A}erial {L}aser {S}canning ({ALS}) to derive accurate spatially explicit estimates of {P}lant {A}rea {I}ndex ({PAI}). {A} discrete representation of the forest canopy is introduced in the form of a 3{D} voxelized space. {F}or each voxel (elementary volume, typically one cubic m) a first estimate of local transmittance of vegetation is computed as the ratio of the sum of energy exiting a voxel to the sum of energy entering the same voxel. {A} spatially hierarchical model is subsequently applied to refine estimates of individual voxel transmittance. {P}lant area density ({PAD}) profiles are then computed from the local transmittance values by applying {B}eer {L}ambert's turbid medium approximation. {PAI} values are obtained from vertical integration of {PAD} profiles. {T}he model is shown to be robust to low sampling intensity and high occlusion rates. {W}e further compared simulated values of gap fraction obtained by ray tracing for 5 angular sectors with in situ {LAI}2200 measurements taken at 135 positions in a 05 ha forest plot located in the center of the scene. {T}he overall patterns of simulated and measured values (average value per inclination and pattern of variation along a 70 m transect line) were highly consistent. {A} slight but systematic discrepancy was observed along the inclination gradient, gap fractions derived from ray tracing in the voxelized scene being slightly lower than the measured values. {T}his difference might be the consequence of multiple reflections which have been found to bias gap fractions estimates produced by {LAI}2200. {PAI} estimates derived from {LAI}2200 measurements (either simulated 6.8 or observed 5.9) are much lower than the {PAI} derived from vertical integration of local {PAD} (13.6). {T}his large difference reflects the fact that distribution of foliage is strongly spatially structured and that this structural information is not properly accounted for in {PAI} estimates derived from mean gap fraction per elevation angle. {A}fter adjusting local transmittance to match mean {LAI} 2200 profiles the {PAI} at plot level was found to be 13.2 m(2).m(-2). {W}e conclude that {A}erial {L}aser {S}canning can produce accurate maps of {P}lant {A}rea {I}ndex over large areas with unmatched efficacy, accuracy and ease. {T}his should be of major relevance for many forest ecological studies.},
  keywords = {{AIS} ; {L}eaf area index ; {R}ay tracing ; {V}oxel space ; {G}ap fraction ; {GUYANE} {FRANCAISE}},
  booktitle = {},
  journal = {{R}emote {S}ensing of {E}nvironment},
  volume = {198},
  numero = {},
  pages = {254--266},
  ISSN = {0034-4257},
  year = {2017},
  DOI = {10.1016/j.rse.2017.05.034},
  URL = {https://www.documentation.ird.fr/hor/fdi:010070842},
}