## 4 Results and Discussion
### Spatial Distribution  
Because the purpose of this study is to retrieve the spatial distribution of LST that can be used for monitoring regional surface heat fluxes, it is important to assess the spatial distribution of the retrieved LST from the HJ-1B data. Figure 6 shows examples of the spatial distribution of the HJ-1B/IRS and MODIS 1 km LST. Both satellite images were acquired on 22 August 2012, and the MODIS 1 km LST data were resampled to 300 m. The HJ-1B/IRS data were acquired at approximately 3:50 UTC, (11:50 Beijing Time) while the MODIS data were acquired at 3:30 UTC (11:30 Beijing Time). Figure 5: _In situ_ LST _vs._ satellite-retrieved LST for three different land cover types: (**a**) vegetable (1 site), (**b**) maize (14 sites), and (**c**) orchard (1 site) from mid-June to mid-September 2012. Figure 7 shows the input parameters for the HJ-1B/IRS LST retrieval. The TOA radiance is between 4 and 11 W\(\cdot\)m\({}^{-2}\cdot\)sr\({}^{-1}\cdot\)um\({}^{-1}\). In the solid square (the irrigated oasis), the TOA radiance is approximately 9 W\(\cdot\)m\({}^{-2}\cdot\)sr\({}^{-1}\cdot\)um\({}^{-1}\) when including the 16 AMS sites. The LSE is between 0.96 and 0.99, and the mean LSE is approximately 0.99. The WVC is approximately 1.5 cm. The WVC of the irrigated oasis is higher than that in the mountainous areas (the DEM shown in Figure 7d is higher than 4200 m) and desert (or sparsely vegetated in Figure 7e) because in the irrigated oasis, the irrigation provided more moisture. As mentioned (Figure 3b), when the WVC is approximately 1.5 cm, the WVC differences between the MOD05 product and the CE318 data are lower than 0.4 cm; thus, the LST differences between the MODIS and MODIS are larger than 0.4 cm. Figure 6: **(a)** The retrieved LST images with a 300 m resolution on 22 August 2012 (3:50 UTC, 11:50 Beijing Time); **(b)** the MODIS LST (3:30 UTC, 11:30 Beijing Time), where the white color is the MODIS cloud mask; **(c)** the density of the HJ-1B/IRS and MODIS derived LST for the 10000 pixels in the solid square; and **(d)** the difference between HJ-1B/IRS and MODIS derived LST. MOD05-based LST and CE318-based LST are less than 1 K. Figure 7d shows the Digital Elevation Data (DEM) obtained from the Shuttle Radar Topography Mission (SRTM) of the study area. The irrigated oasis is a nearly flat plain. Figure 7e shows the IGBP land cover type from MCD12Q1 product. These data are also the source data for LSE production. It should be mentioned that the spatial resolution of land cover data from MCD12Q1 is 500 m, which may have certain scaling effects on the LSE production that is used as a spatial resolution of 300 m in LST retrieval. The spatial patterns of the retrieved HJ-1B/IRS LST over part of the middle stream and upstream regions of the Heihe River Basin generally agree well with the MODIS 1 km LST product (Figure 6). Generally, the HJ-1B/IRS LST product (Figure 6a) provides a more detailed texture for the study area (and other complex landscapes) than the MODIS product (Figure 6b) because of the higher spatial resolution of the HJ-1B data. Although the cloud mask (pixels in white color) in the MODIS 1 km product is not used in the HJ-1B/IRS product, the actual low temperatures could be discriminated from the image, such as the dark blue color in the image of Figure 6a. In the solid square, the mean LST is approximately 300 K for both images. Figure 6c shows the density comparison between HJ-1B/IRS and MODIS derived LST for the 10,000 pixels in the solid square. In Figure 6c, the cloud mask data (80 pixels in the solid square) in MODIS are excluded. To analyze the difference between HJ-1B/IRS and MODIS derived LST, the difference image between them is also obtained in Figure 6d. In the solid square and other flat and homogeneous places (cropland and grassland in Figure 7e), the differences between the two sensors derived LST are clearly shown to be within 1 K. The large differences occur both in mountainous areas and desert in the southwest and north of the image, respectively.