Estimation of surface heat fluxes using multi-angular observations of radiative surface temperature

Authors: SONG, L. - Southwest University; BIAN, Z. - Chinese Academy Of Sciences; Kustas, William - Bill; LIU, S. - Beijing Normal University; XIAO, Q - Chinese Academy Of Sciences; NIETO, H. - University Of Alcala; XU, Z. - Beijing Normal University; YANG, Y. - US Department Of Agriculture (USDA); XU, T. - Beijing Normal University

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2020
Publication Date: 1/28/2020
Citation: Song, L., Bian, Z., Kustas, W.P., Liu, S., Xiao, Q., Nieto, H., Xu, Z., Yang, Y., Xu, T. 2020. Estimation of surface heat fluxes using multi-angular observations of radiative surface temperature. Remote Sensing of Environment. 239:111674. https://doi.org/10.1016/j.rse.2020.111674.
DOI: https://doi.org/10.1016/j.rse.2020.111674

Interpretive Summary: Remotely sensed land surface temperature from satellites has been shown to be a key boundary condition in energy balance modeling used to estimate spatially distributed crop water use or evapotranspiration (ET). However, determining crop water use and stress requires reliable estimation of plant canopy temperatures, which is challenging using coarse resolution satellite data since it is a mixture of soil and vegetation temperatures. This study utilized multi-angular land surface temperature observations from an aircraft in an energy balance model to more reliably estimate soil and crop canopy temperatures. The results indicated that with multiple view angles of land surface temperature, not only were soil and plant temperatures more reliably estimated, but ET was in better agreement with measurements. This study suggests that satellite-based sensors that include multi-angular land surface temperature observations will likely provide more reliable crop temperatures leading to improved crop water use and stress monitoring.

Technical Abstract: The retrieval of canopy and soil component temperatures for estimating evapotranspiration in the two source energy balance (TSEB) model depends on a relatively accurate partitioning of soil/substrate evaporation and canopy transpiration when using a single observation of directional radiometric land surface temperature. The canopy transpiration algorithm typically used is the Priestley-Taylor formulation which is sensitive to the Priestley-Taylor coefficient, PT and the green vegetation fraction. To avoid the need for a transpiration formulation, this study applies the TSEB model using radiometric land surface temperature observations at different view angles in order to estimate soil and canopy temperatures directly. The TSEB model uses airborne multiangle thermal infrared at six different angular observations (TSEB-6AG) for computing canopy and soil sensible heat fluxes and determining soil and canopy latent heat fluxes. This purely component temperature based TSEB formulation improved the agreement between observed and modeled surface heat fluxes, reducing mean absolute percentage error (MAPE) in latent heat fluxes (LE) from about 17% using the original Priestley-Taylor based TSEB model (TSEB-PT) to 15% using TSEB with thermal infrared observations from two substatially different view angles (TSEB-2AG). The use of all 6 view angles (TSEB-6AG) reduces the MAPE to less than 7% and can produce reasonable spatially-distributed LE under a range of vegetation cover and environmental conditions. This increased accuracy of soil and vegetation component temperature separation using multinagle radiometric temperatura observations is useful for evaluating the utility of single thermal radiometer measurtements in the TSEB model.