Abstract
Spaceborne thermal sensors provide important physical parameters for urban studies. However, due to technical constraints, spaceborne thermal sensors yield a trade-off between their spatial and temporal resolution. The aims of this study are (1) to downscale the three originally low spatial resolution (960 m) Moderate Resolution Imaging Spectroradiometer (MODIS/Terra) land surface temperature image products (MOD11_L2, MOD11A1 and MOD11A2) to resolutions of 60, 90, 120, 240 and 480 m; and (2) to propose an improved version of the DisTrad method for downscaling the MODIS/Terra land surface temperature products over urban areas. The proposed improved DisTrad is based on a better parameterization of the original DisTrad residuals in urban areas. The improved resampling technique is based on a regression relationship between the residuals of the temperature estimation and the impervious percentage index. Validation of the improved DisTrad, the original DisTrad, and the uniformly disaggregated MODIS land surface temperature images (UniTrad) are performed by comparative analysis with a time-coincident Landsat 7 ETM+ thermal image. Statistical results indicate that the improved DisTrad method shows a higher correlation (R2 = 0.48) with the observed temperatures than the original DisTrad (R2 = 0.43) and a lower mean absolute error (MAE = 1.88 °C) than the original DisTrad (MAE = 2.07 °C). It is concluded that the improved DisTrad method has a stronger capability to downscale land surface temperatures in urban areas than the original DisTrad.
Highlights
Land surface temperature (LST) is a key parameter in numerous scientific studies [1]
The wide range of impervious percentage and surface temperatures in Dublin city makes the area an adequate case to evaluate an improved Disaggregation of radiometric surface temperature (DisTrad) methodology for land surface temperature downscaling over urban areas
Comparing the six observed Moderate-Resolution Imaging Spectrometer (MODIS)/Terra land surface temperature products to the Landsat 7 ETM+ land surface temperature in the urban mask (Table 2), we notice that the MODIS/Terra mean land surface temperatures are considerably lower than the Landsat 7 ETM+ mean land surface temperature
Summary
Land surface temperature (LST) is a key parameter in numerous scientific studies [1] It is used as an input parameter in surface energy balance algorithms to make estimates of net radiation, sensible and latent heat flux, thermal inertia, precipitation, evapotranspiration, and urban-induced surface runoff [2]. Construction materials typically used in urban areas, such as concrete, roofing, asphalt, etc., are characterized by a high heat capacity, high heat conductivity, low albedo, low emissivity and low permeability [2]. These specific physical thermal characteristics of the urban zone yields considerable temperature differences in contrast with the generally cooler rural periphery, a phenomenon that is defined as urban heat island (UHI)
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