Atmospheric Toolbox

Issues with CH4 between January 11 and January 18

#1

Hi Sander,
I’m making my methane map for January 2020 and using this code to create the daily files:

product = harp.import_product(r"/Users/varsharao/Downloads/JAN 11 CH4/*.nc", operations=‘CH4_column_volume_mixing_ratio_dry_air_validity>50;keep(latitude_bounds,longitude_bounds,CH4_column_volume_mixing_ratio_dry_air);bin_spatial(1801,-90,0.1,3601,-180,0.1)’, post_operations=“bin();squash(time, (latitude_bounds,longitude_bounds));derive(latitude {latitude});derive(longitude {longitude});exclude(latitude_bounds,longitude_bounds,latitude_bounds_weight,longitude_bounds_weight,count,weight)”)

While for days before January 11 or after January 18th, this works fine, when I run this code for days between January 11 and January 18 this is what happens:
product = harp.import_product(r"/Users/varsharao/Downloads/JAN 17 CH4/*.nc", operations=‘CH4_column_volume_mixing_ratio_dry_air_validity>50;keep(latitude_bounds,longitude_bounds,CH4_column_volume_mixing_ratio_dry_air);bin_spatial(1801,-90,0.1,3601,-180,0.1)’, post_operations=“bin();squash(time, (latitude_bounds,longitude_bounds));derive(latitude {latitude});derive(longitude {longitude});exclude(latitude_bounds,longitude_bounds,latitude_bounds_weight,longitude_bounds_weight,count,weight)”)
Traceback (most recent call last):
File “”, line 1, in
File “/opt/anaconda3/envs/visan/VISAN.app/Contents/lib/python3.7/site-packages/harp/_harppy.py”, line 1103, in import_product
raise NoDataError()
harp._harppy.NoDataError: product contains no variables, or variables without data

#2

Hi James,

I haven’t looked at the data, but what this probably means is that there were no measurements for which the validity threshold was reached.
You might want to check the files using a e.g. harpdump -d -a 'keep(CH4_column_volume_mixing_ratio_dry_air_validity)' S5P_....nc to look at the QA values.
These are likely all <=50.

#3

So could I just change CH4_column_volume_mixing_ratio_dry_air_validity>50 to CH4_column_volume_mixing_ratio_dry_air_validity>0.
I did this and got values/a normal map. In fact, this map had more data on it then usual because normally methane values over central Africa aren’t displayed. Is it ok to use values with no quality filter like this?

#4

ESA currently recommends to use that filter. See also the PRF-CH4 document on the S5P documentation website.
If you want more information on this, I would recommend that you contact ESA directly.

My recommendation would be to treat that week of data as a week with no sensible CH4 results.