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

2019 ◽  
Vol 276-277 ◽  
pp. 107627 ◽  
Author(s):  
Ahmed Elsherif ◽  
Rachel Gaulton ◽  
Alexander Shenkin ◽  
Yadvinder Malhi ◽  
Jon Mills
Author(s):  
A. Elsherif ◽  
R. Gaulton ◽  
J. P. Mills

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.


2015 ◽  
Vol 5 (4) ◽  
pp. 114-122
Author(s):  
Стариков ◽  
Aleksandr Starikov ◽  
Батурин ◽  
Kirill Baturin

Now for the decision of tasks of monitoring and evaluation of forest plantations the use of methods and means of laser scanning is one of the most act-sexual and priorities. Laser scanning can be performed independently, or in combination with digital aerial and space photos and video, and can also be carried out ground research on the sample areas. A number of indicators laser scanning is superior to other, currently known, remote evaluation methods qualitative and quantitative characteristics of the forest Fund Laser scanning of forest cover based on the use of modern tech-nologies of digital photogrammetry and geoinformation systems, as well as methods of digital processing and multidimensional modeling of the reflected signals. The article provides analysis of modern methods and means of aerial and terrestrial laser scanning of forest stands. The use of air-borne laser scanning will allow achieving high precision in the determination of basic inventory pa-rameters that are comparable to land-based taxation. Main advantages of laser ranging to other me-thods of monitoring of forest plantations is that the laser beam is able to penetrate the forest canopy, thereby scanning all the tiers of the stand. High density scanning (5-10 points per 1 m2) allows ob-taining three-dimensional images of individual trees with high accuracy. The obtained three-dimensional model requires no processing, unlike aerospace methods of remote sensing that are as-sociated with long and arduous races-encryption of the images. Terrestrial laser scanning, in fact, similar to traditional photogrammetric methods, but it allows you to get the coordinates from one point of standing with the possibility of control measurements directly in the field, while providing higher measurement accuracy, compared with photogrammetric methods.


2021 ◽  
Vol 875 (1) ◽  
pp. 012083
Author(s):  
N Begliarov ◽  
E Mitrofanov ◽  
V Kiseleva

Abstract Modern geodetic technologies of gathering three-dimensional spatial data incorporate terrestrial laser scanning and aerial photo survey from unmanned aerial vehicles. The combination of these technologies and joint result of survey provide the data of 3D point model and accurate information on trunks and crowns of individual trees. The paper examines the experiment with the application of method of formation of 3D measuring scene in the form of dense cloud of points combining the results of terrestrial laser scanning and materials of photogrammetric processing of UAV-provided data. The method eliminates basic shortcomings of each technology, enhances their advantages, and opens the way to the compilation of more representative 3D measuring scenes. A specific advantage of the method is the outcropping of detailed information on the form, size and condition of individual tree crowns. This option finds a practical application in landscape evaluation and design, remote measuring of trunk parameters excluding the felling of model trees for the compilation of regional timber account tables. The closest perspectives of method development are related to increasing the accuracy of combined survey by specifying flight missions and working with the light regime under forest canopy.


Author(s):  
A. Elsherif ◽  
R. Gaulton ◽  
J. P. Mills

<p><strong>Abstract.</strong> Terrestrial laser scanning (TLS) instruments have been widely utilized in measuring vegetation canopy structural parameters, being capable of providing high density point clouds. However, less attention has been paid to using TLS intensity data in estimating vegetation biochemical attributes, and calculating water status metrics, that can help in early detection of vegetation stress and risk of wildfire. Water status metrics, such as the leaf Equivalent Water Thickness (EWT) and the Fuel Moisture Content (FMC), are being commonly estimated from optical remote sensing data. However, such estimates mainly reflect the water status of canopy top and ignore the vertical heterogeneity of water content distribution within the canopy. The estimates are also affected by canopy structure and understory reflectance. Such limitations can potentially be addressed using TLS intensity data, as observations are performed in three dimensions (3D). This study therefore investigated the potential of using dual-wavelength TLS intensity data to estimate FMC in 3D. The calculated Normalized Difference Index (NDI) of 808 nm near infrared and 1550 nm shortwave infrared wavelengths was found to be correlated to FMC at leaf level for four different tree species. The correlation was moderate, and the relationships were not consistent between species. NDI was subsequently used to estimate FMC at canopy level in seven trees in a small tree plot with an average error &amp;lt;&amp;thinsp;5&amp;thinsp;%. The 3D estimates of FMC revealed vertical heterogeneity in all trees measured, which varied between species and also between trees from the same species.</p>


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