No abstract

No abstract

No abstract

An overview of the commonly applied evapotranspiration (ET) models using remotely sensed data is given to provide insight into the estimation of ET on a regional scale from satellite data. Generally, these models vary greatly in inputs, main assumptions and accuracy of results, etc. Besides the generally used remotely sensed multi-spectral data from visible to thermal infrared bands, most remotely sensed ET models, from simplified equations models to the more complex physically based two-source energy balance models, must rely to a certain degree on ground-based auxiliary measurements in order to derive the turbulent heat fluxes on a regional scale. We discuss the main inputs, assumptions, theories, advantages and drawbacks of each model. Moreover, approaches to the extrapolation of instantaneous ET to the daily values are also briefly presented. In the final part, both associated problems and future trends regarding these remotely sensed ET models were analyzed to objectively show the limitations and promising aspects of the estimation of regional ET based on remotely sensed data and ground-based measurements.

No abstract

As an intrinsic property of natural materials, land surface emissivity (LSE) is an important surface parameter and can be derived from the emitted radiance measured from space. Besides radiometric calibration and cloud detection, two main problems need to be resolved to obtain LSE values from space measurements. These problems are often referred to as land surface temperature (LST) and emissivity separation from radiance at ground level and as atmospheric corrections in the literature. To date, many LSE retrieval methods have been proposed with the same goal but different application conditions, advantages, and limitations. The aim of this article is to review these LSE retrieval methods and to provide technical assistance for estimating LSE from space. This article first gives a description of the theoretical basis of LSE measurements and then reviews the published methods. For clarity, we categorize these methods into (1) (semi-)empirical or theoretical methods, (2) multi-channel temperature emissivity separation (TES) methods, and (3) physically based methods (PBMs). This article also discusses the validation methods, which are of importance in verifying the uncertainty and accuracy of retrieved emissivity. Finally, the prospects for further developments are given.

： Land surface temperature (LST) is an important parameter at the 23 land-atmosphere interface. The Collection 6 (C6) MODIS LST products are publicly 24 available. Three refinements were performed over bare soil surfaces in the C6 MODIS 25 LST products when compared with the Collection 5 (C5) MODIS LST products. To 26 facilitate the use of the LST products in a wide range of applications, it is necessary to 27 comprehensively evaluate the accuracies of the C6 MODIS LST products. In this 28 study, we validated the C6 MODIS LST products using the temperature-based method 29 2 over various land cover types, including grassland, cropland, cropland/natural 30 vegetation mosaic, Gobi, sandy dune, and desert steppe. In situ measurements were 31 collected from sites under different atmospheric and surface conditions, including six 32 SURFRAD sites in the United States, two KIT sites in Portugal and Namibia, and four 33 HiWATER sites in China. In general, the accuracies of the C6 MODIS LST products 34 at night are better than those during daytime. The daytime RMSE varies from 35 approximately 1.5 K to 5.6 K, whereas the night-time RMSE is less than 2 K at all 36 sites except for the HiWATER SSW site. Furthermore, the accuracies of the C6 37 MODIS LST products were compared with those of the C5 MODIS LST products 38 over bare soil surfaces. The C6 MODIS LST products are in excellent agreement with 39 the in situ LST measurements at the KIT Gobabeb site, with biases of 0.36 K during 40 the day and 0.24 K at night, and RMSEs of 1.5 K during daytime and 0.74 K during 41 night-time. However, there are no improvements in the accuracies of the C6 MODIS 42 LST products when compared with the C5 MODIS LST products due to further 43 overestimation of emissivities at the four HiWATER sites. 44 45 Key words: Land surface temperature, MODIS, temperature-based validation method, 46 split-window algorithm, in situ measurements. 47 48 1. Introduction 49 Land surface temperature (LST) is an important climate variable, which is related 50 to surface energy and water balance. It is also a key parameter for various studies 51 including hydrology, climatology, environment, and ecology (Anderson et al., 2008; 52

No abstract