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Remote Sens. 2018, 10(3), 423; https://doi.org/10.3390/rs10030423

UAV Capability to Detect and Interpret Solar Radiation as a Potential Replacement Method to Hemispherical Photography

1
Department of Forest management, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences (CULS), Kamýcká 129, Prague 165 21, Czech Republic
2
Department of Silviculture, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences (CULS), Kamýcká 129, Prague 165 21, Czech Republic
*
Author to whom correspondence should be addressed.
Received: 30 January 2018 / Revised: 28 February 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract

Solar radiation is one of the most significant environmental factors that regulates the rate of photosynthesis, and consequently, growth. Light intensity in the forest can vary both spatially and temporally, so precise assessment of canopy and potential solar radiation can significantly influence the success of forest management actions, for example, the establishment of natural regeneration. In this case study, we investigated the possibilities and perspectives of close-range photogrammetric approaches for modeling the amount of potential direct and diffuse solar radiation during the growing seasons (spring–summer), by comparing the performance of low-cost Unmanned Aerial Vehicle (UAV) RGB imagery vs. Hemispherical Photography (HP). Characterization of the solar environment based on hemispherical photography has already been widely used in botany and ecology for a few decades, while the UAV method is relatively new. Also, we compared the importance of several components of potential solar irradiation and their impact on the regeneration of Pinus sylvestris L. For this purpose, a circular fisheye objective was used to obtain hemispherical images to assess sky openness and direct/diffuse photosynthetically active flux density under canopy average for the growing season. Concerning the UAV, a Canopy Height Model (CHM) was constructed based on Structure from Motion (SfM) algorithms using Photoscan professional. Different layers such as potential direct and diffuse radiation, direct duration, etc., were extracted from CHM using ArcGIS 10.3.1 (Esri: California, CA, USA). A zonal statistics tool was used in order to extract the digital data in tree positions and, subsequently, the correlation between potential solar radiation layers and the number of seedlings was evaluated. The results of this study showed that there is a high relation between the two used approaches (HP and UAV) with R2 = 0.74. Finally, potential diffuse solar radiation derived from both methods had the highest significant relation (−8.06% bias) and highest impact in the modeling of pine regeneration. View Full-Text
Keywords: fisheye camera; unmanned aerial vehicle; canopy height model; solar radiation; crown openness fisheye camera; unmanned aerial vehicle; canopy height model; solar radiation; crown openness
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Abdollahnejad, A.; Panagiotidis, D.; Surový, P.; Ulbrichová, I. UAV Capability to Detect and Interpret Solar Radiation as a Potential Replacement Method to Hemispherical Photography. Remote Sens. 2018, 10, 423.

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