issues: 2062132750

What is your issue?

Sentinel-3 OLCI files (e.g. taken from Copernicus Data Space Ecosystem) come with duplicate dimensions which causes xarray 2023.12.0 to raise after https://github.com/pydata/xarray/pull/8491. Specifically instrument_data.nc cannot be opened anymore: ```python import xarray as xr

dataset = xr.open_dataset("instrument_data.nc", decode_cf=True, mask_and_scale=True, chunks="auto") Results in the now expected ValueError: ValueError: This function cannot handle duplicate dimensions, but dimensions {'bands'} appear more than once on this object's dims: ('bands', 'bands') `ncdump -h` prints: netcdf instrument_data { dimensions: bands = 21 ; columns = 4865 ; detectors = 3700 ; rows = 1953 ; variables: float FWHM(bands, detectors) ; FWHM:_FillValue = -1.f ; FWHM:ancillary_variables = "detector_index lambda0" ; FWHM:long_name = "OLCI bandwidth (Full Widths at Half Maximum)" ; FWHM:units = "nm" ; FWHM:valid_max = 650.f ; FWHM:valid_min = 0.f ; short detector_index(rows, columns) ; detector_index:_FillValue = -1s ; detector_index:coordinates = "time_stamp altitude latitude longitude" ; detector_index:long_name = "Detector index" ; detector_index:valid_max = 3699s ; detector_index:valid_min = 0s ; byte frame_offset(rows, columns) ; frame_offset:_FillValue = -128b ; frame_offset:long_name = "Re-sampling along-track frame offset" ; frame_offset:valid_max = 15b ; frame_offset:valid_min = -15b ; float lambda0(bands, detectors) ; lambda0:_FillValue = -1.f ; lambda0:ancillary_variables = "detector_index FWHM" ; lambda0:long_name = "OLCI characterised central wavelength" ; lambda0:units = "nm" ; lambda0:valid_max = 1040.f ; lambda0:valid_min = 390.f ; float relative_spectral_covariance(bands, bands) ; relative_spectral_covariance:_FillValue = NaNf ; relative_spectral_covariance:ancillary_variables = "lambda0" ; relative_spectral_covariance:long_name = "Relative spectral covariance matrix" ; float solar_flux(bands, detectors) ; solar_flux:_FillValue = -1.f ; solar_flux:ancillary_variables = "detector_index lambda0" ; solar_flux:long_name = "In-band solar irradiance, seasonally corrected" ; solar_flux:units = "mW.m-2.nm-1" ; solar_flux:valid_max = 2500.f ; solar_flux:valid_min = 500.f ;

// global attributes: :absolute_orbit_number = 29437U ; :ac_subsampling_factor = 64US ; :al_subsampling_factor = 1US ; :comment = " " ; :contact = "eosupport@copernicus.esa.int" ; :creation_time = "2023-12-20T07:20:24Z" ; :history = " 2023-12-20T07:20:24Z: PUGCoreProcessor JobOrder.3302865.xml" ; :institution = "PS2" ; :netCDF_version = "4.2 of Jan 13 2023 10:05:23 $" ; :processing_baseline = "OL__L1_.003.03.01" ; :product_name = "S3B_OL_1_EFR____20231220T045944_20231220T050110_20231220T072024_0085_087_290_1980_PS2_O_NR_003.SEN3" ; :references = "S3IPF PDS 004.1 - i2r6 - Product Data Format Specification - OLCI Level 1, S3IPF PDS 002 - i1r8 - Product Data Format Specification - Product Structures, S3IPF DPM 002 - i2r9 - Detailed Processing Model - OLCI Level 1" ; :resolution = "[ 270 294 ]" ; :source = "IPF-OL-1-EO 06.17" ; :start_time = "2023-12-20T04:59:43.719978Z" ; :stop_time = "2023-12-20T05:01:09.611725Z" ; :title = "OLCI Level 1b Product, Instrument Data Set" ; } ```

The relative_spectral_covariance variable has duplicate dimensions. What do you suggest doing in such cases?

I guess this is related to https://github.com/pydata/xarray/issues/1378.