issues: 146975644

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
146975644 MDU6SXNzdWUxNDY5NzU2NDQ= 822 value scaling wrong in special cases 206773 closed 0     13 2016-04-08T16:29:33Z 2019-02-19T02:11:31Z 2019-02-19T02:11:31Z NONE      

For the same netCDF file used in #821, the value scaling seems to be wrongly applied to compute float64 surface temperature values from a (signed) short variable analysed_sst:

short analysed_sst(time=1, lat=3600, lon=7200); :_FillValue = -32768S; // short :units = "kelvin"; :scale_factor = 0.01f; // float :add_offset = 273.15f; // float :long_name = "analysed sea surface temperature"; :valid_min = -300S; // short :valid_max = 4500S; // short :standard_name = "sea_water_temperature"; :depth = "20 cm"; :source = "ATSR<1,2>-ESACCI-L3U-v1.0, AATSR-ESACCI-L3U-v1.0, AVHRR<12,14,15,16,17,18>_G-ESACCI-L2P-v1.0, AVHRRMTA-ESACCI-L2P-v1.0"; :comment = "SST analysis produced for ESA SST CCI project using the OSTIA system in reanalysis mode."; :_ChunkSizes = 1, 1196, 2393; // int

Values are roughly -50 to 600 Kelvin instead of 270 to 310 Kelvin. It seems like the problem arises from misinterpreting the signed short raw values in the netCDF file.

Here is a notebook that better explains the issue: https://github.com/CCI-Tools/sandbox/blob/4c7a98a4efd1ba55152d2799b499cb27027c2b45/notebooks/norman/xarray-sst-issues.ipynb

 
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