Hello everybody.
I have an important issue about TOA reflectances calculation on EO Browser that I am trying to solve.
I work with TOA reflectances from Level 1C for Sentinel-2 and L1 for Landsat-8 and -9.
Most importantly, I work with Landsat 8 and 9 datasets downloaded from reprocessing level Collection 2.
This means that for the calculation of TOA reflectances from DNs in L8 and L9, I do not have to apply the classical equations passing by radiances and then by Earth-Sun distance and ESUNλ parameters (like here explained How to convert Landsat DNs to Top of Atmosphere (ToA) Reflectance | Center for Earth Observation), but instead converting directly the DNs to Top of Atmosphere reflectance or radiance using the radiometric scaling factors provided in each scene metadata file (Using the USGS Landsat Level-1 Data Product | U.S. Geological Survey).
Now, here is the issue. When I calculate TOA Reflectances from Level-1 Landsat 8 and 9 OLI images I have completely different values from those calculated and shown in EO Browser for the same level and same Landsat 8 and 9 images.
Do you know why?
Does somebody know the toa reflectances script for Eo Browser?
When dealing with the data, it’s important to understand the native SampleType of your data source so that you can output the data to the correct/expected values. My colleague wrote a post about this recently.
If you are still struggling, perhaps you can share the script that you are using.
Yes, I checked the example you posted.
The problem is that my values do not fit just with Landsat 8 and Landsat 9.
My question is: which is the algorithm that EO Browser uses to calculate reflectance values from DN for Landsat 8 and Landsat 9 Collection 2 Level 1?
Mine is very simple, the one indicated by USGS:
ρλ′=MρQcal+Aρ
where:
ρλ’ = TOA planetary reflectance, without correction for solar angle. Note that ρλ’ does not contain a correction for the sun angle. Mρ=Band-specific multiplicative rescaling factor from the metadata (REFLECTANCE_MULT_BAND_x, where x is the band number) Aρ =Band-specific additive rescaling factor from the metadata (REFLECTANCE_ADD_BAND_x, where x is the band number) Qcal = Quantized and calibrated standard product pixel values (DN)
TOA reflectance with a correction for the sun angle is then:
ρλ=ρλ′cos(θSZ)=ρλ′sin(θSE)
where:
ρλ= TOA planetary reflectance θSE = Local sun elevation angle. The scene center sun elevation angle in degrees is provided in the metadata (SUN_ELEVATION). θSZ =Local solar zenith angle; θSZ = 90° - θSE
I use raw data Landsat 8 and 9 Collection 2 Tier 1 Level 1
These values are not the same on Eo Browser, even if I apply the correction from UINT16 explained in the post of your colleague.
And I really don’t get how is it possible, actually.
Thanks!
Please can you share the exact steps you are using to download Landsat Level-1 data from EO Browser. I can then use that to replicate your steps and help solve the issue for you.