Grids and land mask

Regridding ancillary fields onto the satellite grid.

Grid helpers: regrid lat/lon ancillary fields to the satellite grid, land mask.

MERRA-2 skin temperature (0.5 x 0.625 deg) and the CAMEL emissivity climatology (0.05 deg) live on regular lat/lon grids; every DEBRA computation happens on the sensor’s 2-km fixed grid, so ancillary data is interpolated onto the scene’s pyresample area (never the reverse). The land mask feeds DT3’s land/ocean surface shift (Eq. 15).

shachen.geo.regrid_latlon(source: DataArray | Dataset, area: AreaDefinition) → DataArray | Dataset

Bilinearly interpolate a regular lat/lon-gridded field onto area.

source must be dimensioned (lat, lon) or (latitude, longitude) with 1-D coordinate arrays (MERRA-2 and CAMEL conventions, respectively). Returns the field on dims (y, x) matching the area’s shape; target pixels outside the source extent or off the Earth disk become NaN.

shachen.geo.land_mask(area: AreaDefinition) → DataArray

Boolean land mask (True = land) on area’s grid, dims (y, x).

Backed by the global_land_mask lookup table. Off-disk pixels are False; their value never matters because every BT there is NaN and the confidence factor propagates NaN.