Estimation of Land Surface Heat Fluxes Based on Landsat 7 ETM+ Data and Field Measurements over the Northern Tibetan Plateau

Nan Ge,Xian Wang,Ziyu Huang,Mijun Zou,Meilin Cheng,Yaoming Ma,Lei Zhong

doi:10.3390/rs11242899

Abstract

Land surface heat fluxes consist of the net radiation flux, soil heat flux, sensible heat flux, and latent heat flux. The estimation of these fluxes is essential to the study of energy transfer in land–atmosphere systems. In this paper, Landsat 7 ETM+ SLC-on data were applied to estimate the land surface heat fluxes on the northern Tibetan Plateau using the SEBS (surface energy balance system) model, in combination with the calculation of field measurements at CAMP/Tibet (Coordinated Enhanced Observing Period (CEOP) Asia–Australia Monsoon Project on the Tibetan Plateau) automatic weather stations based on the combinatory method (CM) for comparison. The root mean square errors between the satellite estimations and the CM calculations for the net radiation flux, soil heat flux, sensible heat flux, and latent heat flux were 49.2 W/m2, 46.3 W/m2, 68.2 W/m2, and 54.9 W/m2, respectively. The results reveal that land surface heat fluxes all present significant seasonal variability. Apart from the sensible heat flux, the satellite-estimated net radiation flux, soil heat flux, and latent heat flux exhibited a trend of summer > spring > autumn > winter. In summer, spring, autumn, and winter, respectively, the median values of the net radiation flux (631.8 W/m2, 583.0 W/m2, 404.4 W/m2, 314.3 W/m2), soil heat flux (40.9 W/m2, 37.9 W/m2, 26.1 W/m2, 20.5 W/m2), sensible heat flux (252.7 W/m2, 219.5 W/m2, 221.4 W/m2, 204.8 W/m2), and latent heat flux (320.1 W/m2, 298.3 W/m2, 142.3 W/m2, 75.5 W/m2) exhibited distinct seasonal diversity. From November to April, the in situ sensible heat flux is higher than the latent heat flux; the opposite is true between June and September, leaving May and October as transitional months. For water bodies, alpine meadows and other main underlying surface types, sensible and latent heat flux generally present contrasting and complementary spatial distributions. Due to the 15–60 m resolution of the Landsat 7 ETM+ data, the distribution of land surface heat fluxes can be used as an indicator of complex underlying surface types over the northern Tibetan Plateau.

Highlights

Land surface heat fluxes include net radiation flux, soil heat flux, sensible heat flux, and latent heat flux, which are components of land surface energy balance [1]
The variability of land surface heat fluxes may originate from land use land cover changes and natural variations, which could serve as an indicator of land cover change over both the artificial and natural underlying surface [2]
Two-dimensional coordinate of each CAMP/Tibet AWS would fall inside the area of four Landsat pixels that are the nearest

Summary

Introduction

Land surface heat fluxes include net radiation flux, soil heat flux, sensible heat flux, and latent heat flux, which are components of land surface energy balance [1]. Net radiation flux reflects the total energy budget over the land surface, and soil heat flux depicts the heat absorption beneath the ground. Sensible heat flux and latent heat flux represent the heat transfer between the land surface and the atmosphere due to temperature differences and water vapor phase transitions, respectively. Land surface heat fluxes are essential to land–atmosphere interactions in the atmospheric boundary layer. Variations in land surface heat fluxes will have an impact on the atmospheric circulation and climate change, which are of great significance to the study of energy exchange in land–atmosphere interactions [5,6,7,8,9]

Methods

Results

Discussion

Conclusion