Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners

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http://hdl.handle.net/10138/174745

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Junttila , S , Vastaranta , M , Liang , X , Kaartinen , H , Kukko , A , Kaasalainen , S , Holopainen , M , Hyyppä , H & Hyyppä , J 2017 , ' Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners ' , Remote Sensing , vol. 9 , no. 1 , 8 . https://doi.org/10.3390/rs9010008

Title: Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners
Author: Junttila, Samuli; Vastaranta, Mikko; Liang, Xinlian; Kaartinen, Harri; Kukko, Antero; Kaasalainen, Sanna; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha
Contributor: University of Helsinki, Department of Forest Sciences
University of Helsinki, Department of Forest Sciences
University of Helsinki, Department of Forest Sciences
Date: 2017
Language: eng
Number of pages: 20
Belongs to series: Remote Sensing
ISSN: 2072-4292
URI: http://hdl.handle.net/10138/174745
Abstract: Decreased leaf moisture content, typically measured as equivalent water thickness (EWT), is an early signal of tree stress caused by drought, disease, or pest insects. We investigated the use of two terrestrial laser scanners (TLSs) employing different wavelengths for improving the understanding how EWT can be retrieved in a laboratory setting. Two wavelengths were examined for normalizing the effects of varying leaf structure and geometry on the measured intensity. The relationship between laser intensity features, using red (690 nm) and shortwave infrared (1550 nm) wavelengths, and the EWT of individual leaves or groups of needles were determined with and without intensity corrections. To account for wrinkles and curvatures of the leaves and needles, a model describing the relationship between incidence angle and backscattered intensity was applied. Additionally, a reflectance model describing both diffuse and specular reflectance was employed to remove the fraction of specular reflectance from backscattered intensity. A strong correlation (R-2 = 0.93, RMSE = 0.004 g/cm(2)) was found between a normalized ratio of the two wavelengths and the measured EWT of samples. The applied intensity correction methods did not significantly improve the results of the study. The backscattered intensity responded to changes in EWT but more investigations are needed to test the suitability of TLSs to retrieve EWT in a forest environment.
Subject: 4112 Forestry
kaukokartoitus
laserkeilaus
remote sensing
laser scanning
forest health
water content
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