I have estimated land surface temperature (LST) to investigate the cooling effects of vegetation including tree cover over an area. However, I am wondering if what captures by LST only represents the LST above the tree crown or also an indication of its shading effect under the canopy. Does LST account for ground surface under canopy?
I do not think derivation of land surface temperature (lst) by itself accounts for the ground surface that falls under tree canopy's shade or shadows. Although the term 'land' surface temperature represents the surface temperature of the land, in the strictest sense, whatever is reflected off the top surface of a target on the ground is what is measured by the satellite sensor. This is especially true in case of satellite images of dense vegetation acquired by passive multi-spectral sensors such as OLI/TIRS on board Landsat 8. In any case, lst represents only a few micrometers of the land surface or whatever is encountered first. That is why it is also known as the radiative 'skin temperature' of the land surface. I generally use the 'Quality Assurance' (pixel_qa) band provided with landsat data while deriving LST for Landsat 8 scenes. This band helps in identifying and subsequently mask pixels affected by shadows and clouds, among others.
LST is a measure of the temperature of the surface viewed by a satellite. LST is not air temperature. So the LST of a forest is the temperature of the crown of the canopy, not ground surface, although it is possible that ground surface may indirectly influence canopy temperature :)
I do not think it will account for it. After computing the LST, you may a simple experiement by puting the cursor in a shaded area and copmare it with a near by area without shade. In particular, you can choose an area with a dense shade and compare it with a near by area without a shade.
The cool spots of vegetation on LST images correspond mainly with high water content of vegetation and its evapotranspiration. The effect ot shadows can be noticed only on very high resolution thermal images (ex. unmanned aerial thermography in urban regions).
Landsat spatial resolution is 100m and you can not see tree shadow on that resolution. I agree with Andrew Paul McKenzie Pegman.
BR
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