libera_utils.footprint_matching.readers.cldpix#

CERES CLDPIX imager-pixel cloud reader plugin.

Data source: CERES Cloud Pixel (CLDPIX) imager-resolution cloud retrievals

  • Example product: CER_CLDPIX_NOAA20-VIIRS

  • Format: NetCDF4 with flat (root-level) variables on a 2-D imager swath (Scanlines, Pixels) grid (e.g. 16120 × 400).

  • Geolocation: per-pixel 2-D Latitude / Longitude arrays. Despite its name, Latitude holds colatitude (see below), converted here to latitude; longitude is stored 0..360 and normalized here to -180..180.

  • Native scale: ~1 km (VIIRS imager pixel).

Geolocation conventions: colatitude and 0..360 longitude#

CERES products store geolocation in the colatitude convention inherited from the CERES processing system: the root-level variable named Latitude carries colatitude in degrees, 0° at the North Pole increasing to 180° at the South Pole, i.e. latitude = 90 − colatitude. The file itself advertises this via the variable’s valid_range attribute of [0, 180] (a true latitude would be [-90, 90]), and it is confirmed physically: binning the granule’s 10.8 µm brightness temperature (BTemp1080) by the raw value peaks near 90 (the equator, ~285 K) and is coldest near 0 and 180 (the poles, ~245 K).

Reading the raw values as latitudes would place every pixel at the wrong latitude and discard the entire southern hemisphere (colatitude > 90 falls outside a −90..90 valid-range filter), so the conversion below is mandatory. Longitude uses the CERES 0..360 degrees-east convention and is wrapped to −180..180 by normalize_longitude.

Native pixels, matched by time#

CLDPIX is a swath (the 2-D (Scanlines, Pixels) arrays are not a regular lat/lon grid – each pixel carries its own geolocation). Every pixel is served at its own position, with its own observation time, as a PointSamples point, so the Libera PSF weigher is the first place a value is weighted. The reader base class sorts the points into 1 degree bins once, at load, and answers each footprint’s box query from that index.

Variable set#

The CLDPIX cloud properties: seven continuous cloud properties (optical depth, water path, effective temperature, height and pressure, top height and particle radius) and two mode-aggregated categories (particle phase and cloud mask). All are carried by FMATCH-IMAGER and FMATCH-IMAGER-CAMTIME, the products CLDPIX feeds.

Surface-type variables (IGBP_Ecosystem, Snow_Map_Value, Ice_Map_Value) are intentionally NOT extracted here. The pipeline uses the dedicated IGBPReader and NISEReader as the authoritative sources for land-cover and ice/snow classification, avoiding duplication and ensuring consistency across all operational modes.

References

CERES cloud products: https://ceres.larc.nasa.gov/data/ File naming: CER_CLDPIX_{platform}-{imager}_{config}_{prod}.{YYYYMMDDHH}.nc

Classes

CLDPIXReader(file_paths)

Read CERES CLDPIX imager-pixel cloud data as time-stamped native points.