Three dimensional mapping of forest canopy equivalent water thickness using dual-wavelength terrestrial laser scanning

Four Dimensional Mapping of Vegetation Moisture Content Using Dual-Wavelength Terrestrial Laser Scanning

“…The aim here was not to derive species-specific models but to build a pooled EWT estimation model on each date. The NDI-EWT relationship was previously reported to be species-independent to an extent [38,46], and the leaf sampling aimed at further investigating this observation. On the other hand, leaf samples for validation were collected from a small volume, approximately 0.5 × 0.5 × 0.5 m, with a known crown location in a specific tree from each species.…”

“…The trees were successfully classified into three classes (no, low, and moderate infestation levels) with an overall accuracy of 66%. Elsherif, et al [46] used an NDI of 808 and 1550 nm wavelengths with the Leica P20 and Leica P40 TLS instruments, respectively, to generate 3D EWT estimates at the canopy level in a mixed-species broadleaf forest plot; they reported EWT vertical heterogeneity in all sampled 13 trees. To our knowledge, no other studies have successfully estimated EWT at the canopy level in field campaigns using TLS, and no previous studies have used TLS to monitor changes in EWT.…”

“…This study used the same scanning methodology described by Elsherif, et al [46] to investigate the potential of using dual-wavelength TLS to monitor temporal changes in EWT at the canopy level in 3D. A mixed-species tree plot was scanned twice, during and after the 2018 European heatwave.…”

“…The Leica P20 utilizes the 808 nm near infrared wavelength, while the Leica P50 operates at the 1550 nm shortwave infrared wavelength. The NDI of the two wavelengths can minimize incidence angle effects [38] and leaf internal structure effects [46] with no need for additional radiometric corrections. Furthermore, point-clouds from the two instruments can be aligned with a high accuracy, allowing for the calculation of the NDI on a point-by-point basis as a result of the similarities between the instruments' laser beam exit locations, chassis, and scanning mechanisms [47].…”

“…Furthermore, point-clouds from the two instruments can be aligned with a high accuracy, allowing for the calculation of the NDI on a point-by-point basis as a result of the similarities between the instruments' laser beam exit locations, chassis, and scanning mechanisms [47]. Methods to calibrate the intensity data to apparent reflectance using external reference targets with a known reflectance have been successfully developed for the Leica P20 [38,46] and the Leica P50 [47]. The intensity correction models described in the aforementioned studies were used to calibrate the intensity to apparent reflectance in all experiments described in this study.…”