Interpolating onto a regular UTM grid resulting in "speckles"

[obentley02]

Hi,
I've been using xesmf inorder to regrid xarray data from one coordinate system to a regular grid in a UTM zone. Looking at the original data there is no "speckling" and if using xarray.Dataset.interp to interpolate onto the points of the regular UTM grid transformed back into the native coordinate system there is also no "speckling". I was wondering if you might know what causes this and if there is a workaround?

    # Create the 2D meshgrid
    xx, yy = np.meshgrid(x_values, y_values)

    # Create a transformer to perform the coordinate transformation
    transformer = Transformer.from_crs(epsg, 4326, always_xy=True)

    # Perform the coordinate transformation
    new_xx, new_yy = transformer.transform(xx, yy)
    ds = ds.rename({'XLAT': 'lat', 'XLON': 'lon'})

    # Step 1: Create the regridder from the source grid (latitude-longitude) to the target grid (UTM)
    regridder = xe.Regridder(ds, xr.Dataset(data_vars={},
                                            coords={'lon': (['y', 'x'], new_xx),
                                            'lat': (['y', 'x'], new_yy)}),
                            'bilinear', periodic=True)

[aulemahal]

Interesting issue! Do you think, it would be possible to provide a complete working example ? What are x_values, y_values and Transformer ? I am asking because it might be an issue with the data, or at least that there's something with the data that xESMF doesn't like.