ACOLITE forum

Hello,

I run ACOLITE for a scene of Landsat 8 and Sentinel 2 for seagrass mapping in the lagoon. For this purpose, I just need the Rrs of water pixel. Could you please to clarify some issues for me as follows:

1. How can we check the retrieval of ancillary data? From the log file?

2. The using of default values of uoz, uow, pressure... still keep a good correction and produce goog Rrs for a specific site?

3. If the retrieval of ancillary data is fail, may I use the values from this database:
https://oceandata.sci.gsfc.nasa.gov/Anc ... /2017/176/ - an example for my Landsat 8 scene on 25/6/2017.

or will be sufficient to use the default values in the setting file?

My study site is a lagoon in New Zealand will small area https://www.google.com/maps/@-37.564198 ... a=!3m1!1e3

The retrieval of ancillary data should be mentioned in the log file, but currently only by transfer times. The NetCDF global attributes will also mention if ancillary data were used (several attributes starting with anc_).

You can also check the data/MET directory for the files. If for some reason the automated download fails, you can manually download and put the files in data/MET/YYYY/DOY/ folders. You will need the files for the day itself (00, 06, 12, 18) and the first from the day after (00).

Overall, the use of ancillary data is not essential, as the differences with the default uwv and uoz are generally rather small. The pressure may be the most important parameter.

Hope this helps!

Hi,

As I understood, downloading ancillary data has been disabled in the ACOLITE GUI due to some bug. However, as you mentioned, if we can place the required ancillary data in data/MET/yyyy/DOY the software must fetch the data from the folder.

But I see when I can keep ancillary data=True, it is saying the above message and replacing with "False". I really don't know whether the software is utilizing the ancillary data kept under the MET folder. Can you please guide me, what is to be done in the settings file especially when we are working offline. I have placed the ancillary data in the MET folder.


regards
Arun

Hi Arun

I would recommend using the CLI to resolve this. Otherwise you could manually enter the proper values (e.g. from the ancillary data) in your settings file. Note that for the regions I tested the use of ancillary data did not make a large difference. I submitted a paper about this in May which will hopefully be available at some point!

Quinten