Im trying to see what lies beneath a forest canopy (e.g. water content in the soil).
With which spectral band in Landsat would show the most 'interference' caused by water in a forest canopy?
The absorption of electromagnetic radiation by water is at its lowest on the UV range and increases exponentially with the increase in wavelength [0]. Therefore, the Landsat 5 sensor most susceptible to absorption by water is that operating on the Thermal range (Band 6). However, this band also corresponds to the thermal signal of living things, flora in particular, therefore its usage in calculating vegetation indexes.
The sensor in this satellite that operated in closer wavelengths was the Mid-Infrared (2.08 - 2.35 µm), known as Band 7 [1]. That is the band with which I would start.
[0] http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html
[1] https://landsat.usgs.gov/about_landsat5.php
follow this article :
https://www.researchgate.net/publication/285574324_Assessing_spatio-temporal_health_of_forest_cover_using_forest_canopy_density_model_and_forest_fragmentation_approach_in_Sundarban_reserve_forest_India
Article Assessing spatio-temporal health of forest cover using fores...
Perhaps I've is misunderstood your question, my apologies if so. From your subject line, it appears you are attempting to see features below the canopy and not the canopy itself. If that is the case, depending on the density of canopy cover,I'm not sure how Landsat imagery will help you as it is a passive sensor and only detects what is reflected by thermal or solar radiation. If the canopy cover is dense, the reflected radiation will only be of the canopy and very little or no radiation will be from the 'soil.'
It seems Landsat may not be the preferred sensor for this. Although if you need Landsat 5 data you are probably looking for historic data so Landsat may be your only choice. I hope this helps.
Thanks Dorn.
Indeed im interested in features below the canopy with Landsat imagery.
We can tell more or less which features are represented in each pixel (soil/vegetation/water,etc.) using sub pixel information (reflectance). We also know that the leaf structure allows certain amount of radiation pass through and hit features underneath.
My question relates to which band(s) will 'show' the most difference when there is water in the background compared to when there is no water.
Nicholas: I agree with Dorn regarding Landsat. A radar sensor that allows you to detect features beneath the canopies is the SAR P-Band (there are airborne systems). But it is more useful for mapping man-made structures beneath the canopies than for soil moisture measurements. There are several research worldwide on the use L-Band SAR for soil moisture measurements, but L-Band has no the same penetration beneath the canopies than the P-Band (that is close to 80 cm wavelength).
Regards
Gabriel
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