Remote sensing-based evapotranspiration algorithm: a case study of all sky conditions on a regional scale

Abstract

Accurate estimation of the land surface evapotranspiration (ET) over a heterogeneous ecosystem is important to understand the interaction between the land surface and the atmosphere with practical applications in integrated water resources management. Although numerous studies have been carried out to develop remote sensing technologies which could achieve more accurate prediction of the regional ET distributions, degrees of uncertainty remain due to the high spatiotemporal variability of the hydrometeorological parameters. A revised remote sensing-based Penman-Monteith algorithm under all sky conditions (Revised RS-PM allsky ) is proposed in this study using the MODerate resolution Imaging Spectroradiometer (MODIS) (ET MODIS ), and the model's capability was assessed over the complex topography of the Korean peninsula. The ground measurements taken at two flux sites with different land cover types in 2012 were employed. The results of ET MODIS represented temporal compatibility yielding biases of −0.18 mm day −1 at Seolmacheon (SMC) site and −0.14 mm day −1 at Cheongmicheon Farmland (CFC) site and root mean square error (RMSE) values of 1.42 mm day −1 at SMC site and 1.26 mm day −1 at CFC site. Overall, ET MODIS was verified to have similar error ranges as those of the previous studies conducted over flat and heterogeneous regions. The results suggest that the revised RS-PM algorithms can be applied on a regional scale with heterogeneous topography over long-term periods if handling of the input data is carefully conducted.

Soil Moisture–Vegetation–Carbon Flux Relationship under Agricultural Drought Condition using Optical Multispectral Sensor

“…South Korea the study area of this research, is located at a latitude of 33-39 • N and a longitude of 124-131 • E (Figure 1). According to the International Geosphere-Biosphere Programme (IGBP) land cover classification, the landmass of South Korea consists of mixed forests (40%), croplands (30%), deciduous broadleaf forests (14%), woody savannas (6%), and urban and built-up areas (5%) [7,31]. Western South Korea is mostly composed of croplands, while the central and east parts are covered with mixed and deciduous broadleaf forests.…”

“…Both the CO 2 flux and SM data used in this study were extracted every 30 min, and data from 2014 and 2015 were used to analyze the relationship between the variables during a period of extreme drought status in Korea. land cover classification, the landmass of South Korea consists of mixed forests (40%), croplands (30%), deciduous broadleaf forests (14%), woody savannas (6%), and urban and built-up areas (5%) [7,31]. Western South Korea is mostly composed of croplands, while the central and east parts are covered with mixed and deciduous broadleaf forests.…”

“…SMC is in the mixed forest area of a mountainous region, where the land surface albedo value is heterogeneous. This heterogeneity leads to bias when measured by remote sensing [31].…”

“…Although the difference in LAI is somewhat large, CMC is less sensitive to drought status as it is located in the rice paddy terrain where the irrigation system is built [7]. These characteristics narrowed the difference between the results of the statistical analyses of SMC and CMC [31]. [39] and Kim et al [5] analyzed droughts in Korea from 2013 to 2015.…”