Problem with scale_factor and off_set with opening netCDF file

I downloaded netcdf data and opened it in matlab, when I have done this in previous times the scale_factor =1 and add_offset=0 and the data is int32

In this new file I downloaded I get the following (the code is exactly the same):

scale_factor = 1.298e-05

add_offset = 0.50271

The values should be between 0 and 1 and instead I get really high and low numbers

I am not really sure what to do in order to get the scale factor and offset to the right values again, also the data is int16

Answer 1

[Shushant]

Hi @Michelle Bachrach,

My understanding of your problem is that when you previously read a netcdf data file you got the “scale_factor” as 1 and “add_offset” as 0 and datatype was int32. But when you downloaded a new file having datatype as int16 and ran the same code again you got a different value for “scale_factor” and “add_offset”. And that you are getting a really high and low numbers which I assume is the value of your data inside the netcdf file and not the “scale_factor/add_offset” as they are already in the range of 0 and 1. The main aim of your problem is getting correct values of “scale_factor” and “add_offset” again.

When reading NetCDF data in MATLAB using the “ncread” the MATLAB automatically finds the best match for the data file and applies both the “scale_factor” and “add_offset”. So, the change in the datatype of the file is reflected on the values of “scale_factor” and “add_offset”. This is the reason you might be getting different values as the file format is different (int32 and int16). Check out this documentation (vardata – variable and More About section).

You can always normalize the data after reading it from the file by scaling and setting offset based on your requirements.

[Michelle Bachrach]

Thank you very much :) I was able to figure out that indeed my problem was that I didn’t adjust the data with the given scale factor and offset