TY - JOUR
T1 - Mapping root-zone soil moisture using a temperature-vegetation triangle approach with an unmanned aerial system
T2 - Incorporating surface roughness from structure from motion
AU - Wang, Sheng
AU - Garcia, Monica
AU - Ibrom, Andreas
AU - Jakobsen, Jakob
AU - Köppl, Christian Josef
AU - Mallick, Kaniska
AU - Looms, Majken C.
AU - Bauer-Gottwein, Peter
N1 - Funding Information:
Funding: This research was funded by the EU and Innovation Fund Denmark (IFD), in the frame of the collaborative international consortium AgWIT financed under the ERA-NET Co-fund Water Works 2015 Call. This ERA-NET is an integral part of the 2016 Joint Activities developed by the Water Challenges for a Changing World Joint Programme Initiative (Water JPI). This study was also supported by the Smart UAV project from IFD [125-2013-5]. S.W. was financed from an internal PhD grant from the Department of Environmental Engineering at DTU and was financed a short term research stage by the COST action OPTIMISE. K.M. was funded by HiWET consortium jointly funded by the Belgian Science Policy (BELSPO)—Fonds National de la Recherche (FNR)-Luxembourg under the program STEREOIII (INTER/STEREOIII/13/03/HiWET; CONTRACT NR SR/00/301), and CAOS-2 project grant (INTER/DFG/14/02) funded by FNR-DFG.
Publisher Copyright:
© 2018 by the authors.
PY - 2018/12/1
Y1 - 2018/12/1
N2 - High resolution root-zone soil moisture (SM) maps are important for understanding the spatial variability of water availability in agriculture, ecosystems research and water resources management. Unmanned Aerial Systems (UAS) can flexibly monitor land surfaces with thermal and optical imagery at very high spatial resolution (meter level, VHR) for most weather conditions. We modified the temperature-vegetation triangle approach to transfer it from satellite to UAS remote sensing. To consider the effects of the limited coverage of UAS mapping, theoretical dry/wet edges were introduced. The new method was tested on a bioenergy willow short rotation coppice site during growing seasons of 2016 and 2017. We demonstrated that by incorporating surface roughness parameters from the structure-from-motion in the interpretation of the measured land surface-atmosphere temperature gradients, the estimates of SM significantly improved. The correlation coefficient between estimated and measured SM increased from not significant to 0.69 and the root mean square deviation decreased from 0.045 m 3 ·m -3 to 0.025 m 3 ·m -3 when considering temporal dynamics of surface roughness in the approach. The estimated SM correlated better with in-situ root-zone SM (15-30 cm) than with surface SM (0-5 cm) which is an important advantage over alternative remote sensing methods to estimate SM. The optimal spatial resolution of the triangle approach was found to be around 1.5 m, i.e. similar to the length scale of tree-crowns. This study highlights the importance of considering the 3-D fine scale canopy structure, when addressing the links between surface temperature and SM patterns via surface energy balances. Our methodology can be applied to operationally monitor VHR root-zone SM from UAS in agricultural and natural ecosystems.
AB - High resolution root-zone soil moisture (SM) maps are important for understanding the spatial variability of water availability in agriculture, ecosystems research and water resources management. Unmanned Aerial Systems (UAS) can flexibly monitor land surfaces with thermal and optical imagery at very high spatial resolution (meter level, VHR) for most weather conditions. We modified the temperature-vegetation triangle approach to transfer it from satellite to UAS remote sensing. To consider the effects of the limited coverage of UAS mapping, theoretical dry/wet edges were introduced. The new method was tested on a bioenergy willow short rotation coppice site during growing seasons of 2016 and 2017. We demonstrated that by incorporating surface roughness parameters from the structure-from-motion in the interpretation of the measured land surface-atmosphere temperature gradients, the estimates of SM significantly improved. The correlation coefficient between estimated and measured SM increased from not significant to 0.69 and the root mean square deviation decreased from 0.045 m 3 ·m -3 to 0.025 m 3 ·m -3 when considering temporal dynamics of surface roughness in the approach. The estimated SM correlated better with in-situ root-zone SM (15-30 cm) than with surface SM (0-5 cm) which is an important advantage over alternative remote sensing methods to estimate SM. The optimal spatial resolution of the triangle approach was found to be around 1.5 m, i.e. similar to the length scale of tree-crowns. This study highlights the importance of considering the 3-D fine scale canopy structure, when addressing the links between surface temperature and SM patterns via surface energy balances. Our methodology can be applied to operationally monitor VHR root-zone SM from UAS in agricultural and natural ecosystems.
KW - Surface energy balance
KW - Thermal and optical remote sensing
KW - Tree height
KW - Unmanned Arial Systems (UAS)
KW - Very high spatial resolution
UR - http://www.scopus.com/inward/record.url?scp=85058876226&partnerID=8YFLogxK
U2 - 10.3390/rs10121978
DO - 10.3390/rs10121978
M3 - Article
AN - SCOPUS:85058876226
SN - 2072-4292
VL - 10
JO - Remote Sensing
JF - Remote Sensing
IS - 12
M1 - 1978
ER -