The spatial distribution of the thermodynamic temperature
of the underlying surface was estimated due to daily
data from radiometers MODIS/Terra (product MOD11A1) and
MODIS/Aqua (product MYD11A1) available in the database
LP DAAC (https://lpdaac.usgs.gov). These products contain
day and night land surface temperature with a resolution of
∼1 km, an accuracy of ±1 K, and observation date and time.
MODIS algorithms for temperature retrieval [15] are based on
the results of passive scanning of upwelling radiation with a
wavelength of 10–12 μm.
Based on the ground measurements, it was found that, during
the morning flight of SMOS over the site, the temperature
gradient in the 0–10-cm layer was less than 0.5 K/cm. For
wetland soils and open areas of water, the thickness of the skin
layer does not exceed a few centimeters. In these conditions,
the difference between the temperatures in the skin layer and
on the surface is not higher than 0.5 K, i.e., it is within the
measurement error.