I would like to find the snow cover area and snow grain size hence using S3 OLCI product. I am new to the use of S3 and its related plugins on SNAP.
I have a few queries:
What bands are necessary for snow properties and snow cover retrieval from the 21 spectral bands apart from band 1, 6, 10, 11, 17, 21 if any. In case, you have any good literature/manual on snow properties retrieval for better understanding, I would appreciate it.
I have used OLCI EFR product>>>applied IdePix masking plugin and rayleigh correction on the EFR product. When I apply OLCI SICE snow property plugin, it shows the following error:
Kindly help me figure out the error in this process. I am using the radiance product (IdePix). Am I supposed to use the raw file and rayleigh product instead?
If so, is there any use of the IdePix product as input for snow properties retrieval?
Only the bands 1, 6, 10, 11, 17, 21 are ultimately needed for the snow retrievals. - As a starting point for publications and documentation related to the OLCI SICE Snow properties processor, we recommend http://snow.geus.dk/index.php/publications-and-presentations/
From your screenshot it seems that you specified your input products incorrectly:
OLCI L1b radiance product: should be the product [1] in your Product Explorer
OLCI Rayleigh corrected product: the product [4] (or [5]?) in your Product Explorer
Cloud mask product (optional): This can be your IdePix product [3]. It is optional, but we recommend to use it. In this case, cloudy pixels which would likely lead to wrong snow retrievals are excluded.
Thankyou!!! It worked!!
I just had one more query:
There are two plugins in S3 Snow Properties Processor:
(A) OLCI SICE snow properties (B) OLCI snow properties.
[5]th product (in my attached image in an earlier post) is a result of the OLCI snow properties plugin.
As far as I understand now from the help guides in SNAP, the SICE plugin(a) is an improvement after OLCI snow properties(b). Hence it’s better to use only the SICE snow properties plugin instead.
Is that correct?
PS: Thankyou for the cloud mask IdePix recommendation
The use of raw S3 OLCI EFR product with its rayleigh product and its idepix product for cloud mask is working without error.
But in the result, by visual interpretation, I reckon the snow cover area depicted by NDSI is not correct as shown below:
I hoped that the ndsi can be the output for the snow cover area. It clearly is wrong. I didn’t change any default values during processing. Please help me out!
For a discussion of the scientific results of the processor you may better contact Dr. Alex Kokhanovsky who developed the algorithm. I was responsible for the technical implementation. In any case, it is a bit hard to judge this NDSI result without a colour bar indicating the numbers.
I had another look at your image, and it seems that the dark-grey areas in the NDSI just represent invalid (i.e. cloudy) pixels, as it looks like exactly “the same grey”. You may double-check this by clicking the symbol “Show/hide no-data overlay for the selected image” in the SNAP toolbar.
Apart from this, we are also checking if there might be an issue in the way how the NDSI is computed. We will keep you informed.
I used the no-data overlay and it shows that by using the SICE plugin the snow-covered area is falling into no data range. The image is not cloudy in the red box i.e., my AOI.
The initially developed Snow Properties plugin is giving me at least some values in the NDSI band on computation while SICE plugin is giving no data. Here is an image with the color bar for the SICE output for your reference. (The only positive value of NDSI is where there is no snow, as per my inference)
Dear Swapnil,
in the meantime we checked the computation of NDSI in the SICE plugin,and indeed we found a problem. Deviating from the documentation, NDSI was computed from TOA reflectances rather than from BRR, which at least for your example leads to unrealistic values. Obviously, this was a remainder from an experimental setup. As your previous image already indicated, the implementation in the ‘old’ Snow processor was correct, using BRR. - See attached the NDSI result after having this fixed in the SICE plugin. Only NDSI > 0.03, used as default threshold for snow, is shown.
Please download the new SICE plugin s3tbx-snow-3.1.nbm from the ftp, and install in SNAP 8.
Sorry for the inconvenience and thanks a lot for spotting this issue and your careful analysis. We highly appreciate this kind of user feedback!
Thank you for your time, attention and efforts @dolaf ! This acknowledgment made my day!
I would download the new plugin for further processing.
Thanks again!
: Sometimes it can take a few days.
