Surface temperature. The surface temperature is currently derived from the thermal bands from Landsat 8 (day time) and from ASTER (night time). The Landsat 8 scenes used for the surface temperature calculation are the same as those for the reflectance calculation. The available ASTER scenes are recorded in 2015 on August 17 and 25 (Basel), July 19, August 2 and 18 (Heraklion) and August 6 (London) in the evening. To achieve the high temporal resolution of 4 images per day, data from MODIS are considered as well.
Surface temperature. Also for the calculation of surface temperature ATCOR can be used (Xxxxxxx and Xxxxxxxxx 2015). ATCOR allows the use of variable emissivity based on land cover. This option, available for single band or multispectral thermal sensors, assumes various fixed emissivity values to solve the temperature-emissivity separation. This is the preferred approach when analyzing urban areas, because the emissivity of urban materials (asphalt, brick, metals) covers a larger range of values than the emissivity of natural materials (vegetation, water, soil). However, when using Landsat 8 data, ATCOR has to make use of a split window approach on band 10 and 11. For the calculation, an overall emissivity of 0.98 is assumed. A variable emissivity depending on land cover is not available within ATCOR for Landsat 8. However, an offset can be applied, e.g. to adjust the surface temperature to measured temperatures. The resulting images show the surface temperature in Celsius with a spatial resolution of 30 m. Additionally, a surface temperature map resampled to the 100 m grid is provided. The accuracy of the surface temperature depends on the selected surface emissivity. If the selected emissivity deviates less than 2% from the real emissivity, the accuracy of the surface temperature can reach 1-2 K [15]. Each error of 1% emissivity will result in an additional error of 0.5-0.8 K surface temperature (Xxxxxxx und Xxxxxxxxx 2015). In addition to the uncertainty induced by the temperature retrieval method, the TIRS data of Landsat 8 is currently suffering calibration issues (xxxx://xxxxxxx.xxxx.xxx/calibration_notices.php and xxxxx://xxxxxxx.xxxx.xxx/l8handbook_appendixa.php). These calibration issues can result in an overestimation of the surface temperature by 2 K or more. An approach to downscale low spatial resolution thermal measurements (i.e. MODIS or Sentinel-3) to local scale (hundreds of meters) will be applied within URBANFLUXES (Mitraka et al., 2015). The methodology to be used is a multi-step procedure for enhancing the spatial resolution of satellite thermal observations and estimating high-resolution emissivity, with an ultimate goal of deriving LST in high spatial and temporal resolution. The surface cover information is derived from high spatial resolution VNIR observations (tens of meters), and it is then used to improve the low spatial resolution of thermal measurements (hundreds of meters). Emissivity is estimated using the high spatial resolution VNIR data and i...
Surface temperature. To make the rectifier assembly safe for handling in- operation, accessible surfaces should not exceed a temperature of 70°C.
