Minimize Land Surface Temperature

Land Surface Temperature (LST) is the radiative skin temperature of the land derived from solar radiation. A simplified definition would be how hot the "surface" of the Earth would feel to the touch in a particular location. From a satellite's point of view, the "surface" is whatever it sees when it looks through the atmosphere to the ground. It could be snow and ice, the grass on a lawn, the roof of a building or the leaves in the canopy of a forest. Land surface temperature is not the same as the air temperature that is included in the daily weather report.

In the SLSTR project, "skin" temperature refers to the temperature of the top surface in bare soil conditions and to the effective emitting temperature of vegetation "canopies" as determined from a view of the top of a canopy.

LST is a basic determinant of the terrestrial thermal behaviour, as it controls the effective radiating temperature of the Earth's surface. However, because of the extreme heterogeneity of most natural land surface, this parameter is difficult to estimate and validate. Several factors can fundamentally influence the derivation of LST including:

  • temperature variations with angles
  • sub-pixel in-homogeneities in temperature and cover
  • surface spectral emissivity at the channel wavelengths
  • atmospheric temperature and humidity variations
  • clouds and large aerosol particles such as dust.

The SLSTR thermal bands used for SST retrieval (the three infra-red channels S7, S8 and S9 at 3.74, 10.85 and 12 µm) are also available over land and are used to retrieve LST in the SLSTR Level-2 products. Algorithms for deriving LST using split-window radiances are sufficiently advanced that accuracy of 1 K is possible (especially at night when differential surface heating is absent).

SLSTR also includes two low-gain, wide-dynamic range IR (fire and high temperature) channels (F1 and F2) designed to deliver the radiometric data necessary for the generation of quantitative active fire products. This prevents saturation of the thermal channels and applies to targets with an upper limit of 500°C.

Figure 1: Distribution of fire hotspots derived from the (A)ATSR instruments (ESA ATSR World Fire Atlas). SENTINEL-3 provides an enhanced fire-monitoring capability compared to AATSR. (Credit: ESA)

For further information about the principles of measurements of the SLSTR , see the Technical Guide SLSTR Instrument Description.