Hi all
I have some doubts about these tiles corresponding to the same area:
S2A_MSIL2A_20240103T160651_N0510_R097_T16PFS_20240103T212452.SAFE
S2A_MSIL2A_20240103T160651_N0510_R097_T16PFT_20240103T212452.SAFE
We have found that the digital level of a shared pixel of the common area in both images is different, and we don’t know the cause of it (angle of solar incidence, etc). I would be very grateful if you could tell us if some kind of radiometric (or other) normalization is necessary to mosaic both images.
Best regards and thanks in advance.
Rubén
Dear @eleeeel
Thank you for your message.
As mentioned by @Marco_EOM in his answer to your other message, the values in tiles overlap region can be different due to the applied Atmospheric Correction (AC) scheme, that is performed independently for each tile.
In your example 16PFT & 16PFS on 03/01/2024, the AC relies on the Dark Dense Vegetation (DDV) algorithm and because of the large amount of cloudy pixels in tile 16PFT, the DDV algorithm is close to the limit of its domain of validity that requires at least 2% of DDV pixels respect to the whole tile.
So in the end, what happens is that the nature of the DDV pixels in the adjacent tiles (16PFT & 16 PFS) is slightly different and lead to the retrieval of two different ranges of aerosol content (respectively 0.15 and 0.09) that in consequence leads to different surface reflectances across the overlapping area.
Cheers,
@Sen2cor_dev_team
2 Likes
Thank you very much for the help
It has been really enlightening for us. After some statistical tests we have concluded that, for phenological products of the Biophysical Processor (LAI, FAPAR, etc) you can mosaic the PFS and PFT tiles without compromising the results. The error or variability is around 1 or 2 % of the reflectance in dry tropical forests.
Thanks again!
| Band 4 |
Media |
Median |
StDeviat |
Varianz |
| Dry forest |
0,0009 |
0,001 |
0,0002 |
0,00000007 |
| Wet Forest |
0,0074 |
0,0068 |
0,0026 |
0,0000072 |
| Grasslands |
0,0001 |
0,00008 |
0,0001 |
0,000000012 |
| Medium |
0,001 |
0,00096 |
0,00139 |
0,0000019 |
| Band 8 |
Media |
Median |
StDeviat |
Varianz |
| Dry forest |
0,00085 |
0,0004 |
0,001 |
0,000001 |
| Wet Forest |
0,042 |
0,02 |
0,05 |
0,002 |
| Grasslands |
0,00088 |
0,0005 |
0,00084 |
0,0000007 |
| Medium |
0,0023 |
0,0005 |
0,0129 |
0,000168 |
Band 8 (left) and Band 4 (right)
