Landsat DN Band Computations

You can do band computations for new grids, like band ratios and NDVI, using

• DN: this is an integer with the amount of energy detected by the satellite.  Unitl Landsat 8, these were typically 8 bit bytes which could store 256 values.  They are now most commonly a 16 bit unsigned integer, with the potential for 64K values.  Landsat 8 acutallly used 12 bits, and Landsat 9 uses 14 bits.  The metadata for the satellite scene contains constants to convert the DN to top of atmosphere spectral radiance or reflectance.  The transformation is linear, with a slope and intercept.  Each band will have different constants, and they could vary over time as the instrument ages.  By storing these as as integer, the storage is greatly reduced as a floating point value would require 4 bytes instead of 1 (older Landsats) or 2 (Landsat 8).
• TOA Radiance: the variable measured by the sensor, and is the amount of energy that reached the sensor.  It depends on the albedo of the surface material, and the angles between the sun, the ground, and the satellite.  It has units of  (Watts/( m2 * srad * ?m)).  A stereoradian is a 3D angular measurement.
• Reflectance for the bands with reflected solar radiation.  This should be in the range of 0-1; values greater than 1 can occur if cases such as around clouds.
• TOA Reflectance: the ratio of energy striking the target and being reflected, and is a property of the material and geometry.
• TOA Reflectance corrected for sun elevation (which accounts for differences with the time of year the imagery was acquired).
• For the bands with emitted terrestrial radiation
• TOA Brightness temperture (TB): the temperature that a black body emitting the same amount of radiation would have.  If the surface emissivity were one, this would be the surface temperature.  If you knew the surface emissivity, you could compute the surface temperature.

All of these will have correlation coefficents among themselves typically over 0.99.

These all use TOA (top of atmosphere values where the satellite orbits), since we do not currently use an atmospheric correction model.

Corrections use the constants in the metadata file for each scene (https://www.usgs.gov/land-resources/nli/landsat/using-usgs-landsat-level-1-data-product

These are currently not yet implemented for Sentinel-2, but its DN is really a reflectance

Select which you want on the Imagery tab of the options form,

You can create grids with each of the parameters.

Landsat Thermal computations.

Remote sensing right click on map, includes band values at point

Last revision 1/23/2022