## 2 Methodology  
When the sky is clear and a local thermodynamic equilibrium exists in the troposphere, the LST can be calculated from the Top Of Atmosphere (TOA) Brightness Temperature (BT) observations on the basis of the radiative transfer theory as follows Equation (1) [1]:  
\[T_{s}=B_{i}^{-1}(\frac{B_{i}(T_{h})-L_{i}\uparrow-(1-\varepsilon_{i})L_{i} \downarrow\cdot\tau_{i}}{\varepsilon_{i}\cdot\tau_{i}}) \tag{1}\]  
where \(T_{s}\) is the LST (K), \(B_{i}\) is the Planck function (W\(\cdot\)m\({}^{-2}\cdot\)sr\({}^{-1}\cdot\)um\({}^{-1}\)), \(i\) is the channel of the sensor, \(L_{i}\uparrow\) is the upwelling atmospheric radiance (W\(\cdot\)m\({}^{-2}\cdot\)sr\({}^{-1}\cdot\)um\({}^{-1}\)), \(L_{i}\downarrow\) is the downwelling atmospheric irradiance divided by \(\pi\) (W\(\cdot\)m\({}^{-2}\cdot\)sr\({}^{-1}\cdot\)um\({}^{-1}\)), \(\varepsilon_{i}\) is the land surface emissivity, and \(\tau_{i}\) is the total atmospheric transmittance along the path between the land surface and the satellite sensor. The LSE can be estimated either based on the vegetation cover method [19], or on the classification-based method [15, 20, 21]. The effective emissivity of the land surface is calculated as follows Equation (2) [4]:  
\[\varepsilon=\varepsilon_{v}FVC+\varepsilon_{g}(1-FVC) \tag{2}\]  
where \(\varepsilon_{v}\) is the vegetation emissivity, \(\varepsilon_{g}\) is the bare soil emissivity, and \(FVC\) is the fractional vegetation cover of a pixel and is calculated from the MODIS Normalized Difference Vegetation Index (NDVI) product (MOD13Q1) as follows Equation (3) [4]:  
\[FVC=\left(\frac{NDVI-NDVI_{s}}{NDVI_{v}-NDVI_{s}}\right)^{2} \tag{3}\]  
where \(NDVI_{v}\) and \(NDVI_{s}\) are the \(NDVI\) values of fully covered vegetation and bare soil, respectively. In this paper, \(NDVI_{v}\) and \(NDVI_{s}\) are taken as the maximum and minimum values of the image, respectively. Directional hemispherical reflectance values for different land cover types are provided by the Johns Hopkins University (JHU) spectral library, Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) spectral library and MODIS spectral library (University of California, Santa Barbara (UCSB)) [22]. The channel land surface emissivities of HJ-1B/IRS are calculated by convolving the Spectral Response Function (SRF) with the spectral library emissivities as follows Equation (4) [15]:_Remote Sens._**2015**, \(7\)  
\[\varepsilon=\frac{\int_{\lambda_{i}}^{\lambda_{i}}f(\lambda)\varepsilon(\lambda)d \lambda}{\int_{\lambda_{i}}^{\lambda_{2}}f(\lambda)d\lambda} \tag{4}\]  
where _f(\(\lambda\))_ is the HJ-1B/IRS SRF (Figure 1), \(\lambda_{1}\) to \(\lambda_{2}\) is the wavenumber range in the SRF, and \(\lambda\) is the wavenumber. Another essential procedure in the LST retrieval is to obtain the atmospheric parameters (including the atmospheric transmittance, atmospheric upward radiation and atmospheric downward radiation) for atmospheric correction. In the simulation using atmospheric transfer model MODTRAN 4.0 to acquire these parameters, Cloudless Land Atmosphere Radiosounding (CLAR), including 382 equally distributed global atmospheric profiles, is used in the method proposed by [PERSON] [15]. The relationship between the simulated atmospheric parameters (transmittance \(\tau\), upwelling atmospheric radiance \(L\)!and downwelling atmospheric radiance \(L\)!) and water vapor content (\(w\)) are established by statistical regression from the simulation above. However, [PERSON] [15] notes that the quadratic relationship between atmospheric parameters and WVC proposed by [PERSON] and [PERSON] [13] could lead major errors when the WVC is lower than 0.5 cm. Therefore, these parameters are derived as the cubic function of the WVC in our study as shown in Equations (5) to (7) [15]. The regression correlation coefficient (R) for each equation is 0.995, 0.990 and 0.992, respectively. Consequently, the atmospheric parameters could also be obtained with WVC when detailed relatively high accuracy atmospheric profiles are not available.