PIC netCDF files - scale and offset values for pic variable
Posted: Thu May 18, 2023 6:16 am America/New_York
Hello,
I have extracted daily PIC data for a couple of areas in the South Pacific through the Ocean Colour website. According to the variable attributes, the PIC scale_factor is 2.0e-6f and the add_offset 0.065f (I am uploading a screenshot from Panoply that shows the variable attributes). I have extracted the PIC values at specific locations using netCDF4 python library and they seem to have the scale_factor already applied (because of the magnitude of the values I am getting) but only the scale_factor, no the add_offset, even though I have not scripted that.
I have a couple of questions related to this:
1- Why am I extracting PIC values of the same order of magnitude as the scale_factor even though I have not apply this in my script? My understanding is that python netCDF4 library extracts the values as they are stored in the file without applying scale and offset unless scripted.
2 - From the variable attributes on the downloaded netCDF files, it seems that the add_offset value is several order of magnitude larger than the scale_factor and so, if applied, all PIC values are going to be equal to the add_offset value.
I would be very grateful if someone can help me understand these two issues I have described. I am happy to provide further information if my description is not clear.
Thank you very much.
I have extracted daily PIC data for a couple of areas in the South Pacific through the Ocean Colour website. According to the variable attributes, the PIC scale_factor is 2.0e-6f and the add_offset 0.065f (I am uploading a screenshot from Panoply that shows the variable attributes). I have extracted the PIC values at specific locations using netCDF4 python library and they seem to have the scale_factor already applied (because of the magnitude of the values I am getting) but only the scale_factor, no the add_offset, even though I have not scripted that.
I have a couple of questions related to this:
1- Why am I extracting PIC values of the same order of magnitude as the scale_factor even though I have not apply this in my script? My understanding is that python netCDF4 library extracts the values as they are stored in the file without applying scale and offset unless scripted.
2 - From the variable attributes on the downloaded netCDF files, it seems that the add_offset value is several order of magnitude larger than the scale_factor and so, if applied, all PIC values are going to be equal to the add_offset value.
I would be very grateful if someone can help me understand these two issues I have described. I am happy to provide further information if my description is not clear.
Thank you very much.