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

Elsherif, Ahmed; Gaulton, Rachel; Mills, J. P.

doi:10.3390/rs11192311

Cited by 14 publications

(21 citation statements)

References 64 publications

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“…A clear linkage between leaf water content, measured as equivalent water thickness (EWT), and TLS intensity has been shown in several studies (Elsherif et al, 2019a;Gaulton et al, 2013;Junttila et al, 2018Junttila et al, , 2016. Reflectance at the 1550 nm wavelength, which is often utilized in TLS sensors, increases as the leaf water content decreases (Junttila et al, 2016;Rallo et al, 2014).…”

Section: Introductionmentioning

confidence: 98%

“…Field experiments with DW-TLS have shown promising results for estimating EWT in deciduous species, but a low prediction accuracy for coniferous species due to the complications arising from distance calibration issues explained above (Elsherif et al, 2019b;Junttila et al, 2019). Elsherif et al (2019a) investigated the detection of changes in EWT during and after an intense drought event using two observation points in time and DW-TLS data at 808 nm and 1550 nm wavelengths. However, there is still limited understanding on the capability of TLS intensity in characterizing short-term changs in leaf water content that are related to the diurnal cycle of ΨL.…”

Section: Introductionmentioning

confidence: 99%

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Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

Junttila¹,

Hölttä²,

Puttonen³

et al. 2020

Preprint

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Drought-induced plant mortality has increased globally during the last decades and is forecasted to influence global vegetation dynamics. Timely information on plant water dynamics is essential for understanding and anticipating drought-induced plant mortality. The most common metric that has been used for decades for measuring water stress is leaf water potential (ΨL), which is measured destructively. To obtain information on water dynamics from trees and forested landscapes, remote sensing methods have been developed. However, the spatial and temporal resolution of the existing methods have limited our understanding of water dynamics and diurnal variation of ΨL within single trees. Thus, we investigated the capability of terrestrial laser scanning (TLS) intensity in observing diurnal variation in ΨL during a 50 hour monitoring period and aimed to improve understanding on how large part of the diurnal variation in ΨL can be captured using intensity observations. We found that TLS intensity at 905 nm wavelength was able to explain 78% of the variation in ΨL for three trees of two tree species with a root-mean square error of 0.137 MPa. Based on our experiment with three trees, time-series of TLS intensity measurements can be used in detecting changes in ΨL, and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

Junttila¹,

Hölttä²,

Puttonen³

et al. 2020

Preprint

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“…Typically, leaf samples are needed to calibrate the EWT estimation model. However, the NDI used in this study has previously been reported to be species-independent to an extent, meaning that a general EWT estimation model can be transferred to different sites with no need for a recalibration (Elsherif et al, 2018;Elsherif et al, 2019a;Elsherif et al, 2019b). This was examined in this study by developing a general EWT model, using PROSPECT radiative transfer model simulations and the canopy NDI and EWT values reported in the aforementioned studies.…”

Section: Ewt Estimation Modelmentioning

confidence: 99%

Dual-Wavelength Terrestrial Laser Scanning as a Calibration Tool for Satellite Estimation of Forest Canopy Moisture Content

Elsherif

Gaulton

Mills

2020

ISPRS Ann. Photogramm. Remote Sens. Spatial Inf. Sci.

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Abstract. Satellites can estimate forest canopy moisture content at the landscape level, and thus have been widely utilized in forest health monitoring. However, the calibration and validation of the estimation models can be challenging. Collecting a sufficient number of leaf samples from the canopy top layers in sampling plots that match the pixel size of the sensor is needed, which is a cost, time and effort consuming process. Dual-wavelength Terrestrial Laser Scanning (TLS) has been successfully used in estimating canopy moisture content of individual trees in three dimensions (3D) in several recent studies. Such 3D estimates, if produced at the plot level, can be used in the calibration and validation of satellite forest canopy moisture content estimation models. In this study, forest canopy moisture content, quantified as the leaf Equivalent Water Thickness (EWT), was estimated in 3D at the plot level in a mixed-species deciduous broadleaf forest plot using dual-wavelength TLS intensity data (808 nm near infrared and 1550 nm shortwave infrared wavelengths). The relative error in the EWT estimation was 6%, and the EWT point cloud revealed vertical heterogeneity in the EWT distribution. EWT was 37% higher in the canopy top layers than in the canopy bottom layers. The results obtained in this study showed that dual-wavelength TLS has the potential to be used in operational landscape-scale EWT estimation, and can be a useful tool for the calibration and validation of satellite EWT estimation models.

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“…Various approaches and techniques have been used with different application perspectives and varying level of success, for estimating leaf water content with wide ranging spatial scales, including terrestrial lidar (Elsherif et al, 2019a;Junttila et al, 2019;Junttila et al, 2021), imaging spectroscopy (Kotz et al, 2004), terahertz radiation spectroscopy (Browne et al, 2020) and microwave remote sensing (Konings et al, 2019). However, considering leaf water content monitoring from single trees several times a day (which is required for monitoring diurnal differences in leaf water content) there are still many limiting factors with existing remote sensing methodologies.…”

Section: Introductionmentioning

confidence: 99%

Close-range Hyperspectral Spectroscopy Reveals Leaf Water Content Dynamics

Junttila¹,

Hölttä²,

Saarinen³

et al. 2021

Preprint

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Water plays a crucial role in maintaining plant functionality and drives many ecophysiological processes. The distribution of water resources is in a continuous change due to global warming affecting the productivity of ecosystems around the globe, but there is a lack of non-destructive methods capable of continuous monitoring of plant and leaf water content that would help us in understanding the consequences of the redistribution of water. We studied the utilization of novel small hyperspectral sensors in the 1350-2450 nm spectral range in non-destructive estimation of leaf water content in laboratory and field conditions. We found that the sensors captured up to 96% of the variation in equivalent water thickness (EWT, g/m2) and up to 90% of the variation in relative water content (RWC). These laboratory findings were supported by field measurements, where repeated leaf spectra measurements were in good agreement (R2=0.79) with a time-lagged change of tree xylem diameter. Further tests were done with an indoor plant (Dracaena marginate Lem.) by continuously measuring leaf spectra while drought conditions developed, which revealed detailed diurnal dynamics of leaf water content. We conclude that close-range hyperspectral spectroscopy can provide a novel tool for continuous measurement of leaf water content at the single leaf level and help us to better understand plant responses to varying environmental conditions.

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

Cited by 14 publications

References 64 publications

Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

Dual-Wavelength Terrestrial Laser Scanning as a Calibration Tool for Satellite Estimation of Forest Canopy Moisture Content

Close-range Hyperspectral Spectroscopy Reveals Leaf Water Content Dynamics

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