Depending on their processing level, the Herschel observational data products are defined as follows:
Level 0 data product: Raw telemetry data as measured by the instrument, minimally manipulated and ingested as Data Frames into the Herschel Science Archive.
Level 0.5 data product: Raw data processed to an intermediate point which is adequate for inspection or to start interactive analysis at a more advanced stage than Level 0.
Level 1 data product: Detector readouts calibrated and converted to physical units, in principle instrument and observatory independent. It is expected that Level 1 data processing can be performed without human intervention.
Level 2 data product: Level 1 data further processed to such a level that scientific analysis can be performed. For optimal results many of the processing steps involved to generate Level 2 data may require human interaction, based both on instrument understanding as well as understanding of the scientific aims of the observation.
The Level 2.5 products are created from combination of single scan direction observations including the following types:
Pairs of scan maps taken in the nominal and orthogonal directions.
Sets of parallel groups of scans (2 or more) at various orientations.
Groups of Large Map mode observations made in overlapping single scan direction.
The Level 3 products are mosaics obtained by merging all or a subset of contiguous observations (tracked SSO observations or fixed maps that are known to contain SSOs are excluded). This leads, in some cases, to very large maps which are broken up into reasonable smaller groupings. For instance, the Galactic Plane is cut into chunks of about 15 degrees length with some adjustments around the Galactic Centre.
Level 2.5 photometric products are maps (SimpleImage) produced with JScanam, Unimap and the high-pass filter pipelines, combining the scan and cross-scan AORs.
Level 2.5 spectroscopic products combine two observations obtained on-target and on a reference off-position in unchopped range scan observing mode.
Level 3 photometric products are Level 2.5 JScanam and Unimap overlapping maps on a given field combined with the Mosaic task.
Level 3 spectroscopic products are provided only for pointed chopNod observations taken in SED mode and they are combined spectrum tables derived from Level 2 products corresponding to several observations of the same target.
Level 2.5 single-point data products are stitched (i.e. only one concatenates spectrometer sub-band) spectra for each of the polarisations and backends applicable to the observation.
Level 2.5 map data products are regridded cubes for each of the polarisations and backend sub-bands associated to a given observation. The cube dimension is derived from the geometry of the executed map. For moving targets, the maps are provided in the co-moving frame.
Level 2.5 spectral scan data products are deconvolved Level 2 spectra (from both WBS-H and WBS-V data) using default parameters.
Tables with the detailed description of these products are available in the following sections: