HMI/AIA Observable Processing
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Data Definitions
Most spacecraft mission data is typically divided into "levels" of processing and refinement. We do the same.
- "Raw" data is the basic telemetry transferred from the spacecraft to the ground station, packaged as a file, with only basic r/f integrity checks run, and no processing done to it. This data is only useful as input to the "level-0" extraction programs.
- Level Zero refers to the lowest level of accessible data for a given instrument or spacecraft. Telemetry Checking, APID (Application ID) Lookup, Housekeeping telemetry processing and Image Reconstruction are performed at this level. The only processing done is typically the removal of duplicate data points (due to multiple file sends or a solid state recorder overlap), the removal or minimal repair of bad r/f data, the sorting of the different APIDs, and the matching of the end of one packet to the beginning of the next. The images taken by an instrument are left "as is" - not manipulated, not flat-fielded nor otherwise calibrated. All of the Level Zero data is recorded in the JSOC DRMS (database). In principle the level-0 data could be converted back to telemetry formatted data and is thus redundant with it but is in a more easily usable form using standard data storage protocols. JSOC image data is stored in compressed FITS files. JSOC metadata is stored in DRMS records but may be exported in several standard protocols (e.g. as part of exported FITS format images or tab delimited text tables).
- Level One data is calibrated Level Zero data. JSOC supports several steps of "level-1" processing. Level-1.0 data has where images converted from on-board form to regular array formats, bad pixels removed, and gains calibrated (i.e. flat-fielded). It is data in the cleanest state possible while remaining "pure" (no significant, irreversible data alteration). This data is time-sequenced, and quality-filtered. Level-1.5 data (for HMI) has been converted to physical observables such as Dopplergrams and Magnetograms which are constructed from many individual Filtergrams. AIA Level-1 data will be scaled and flat fielded with MTF corrections for vignetting and other such "always needed" processing applied.
- Level Two data has been irrevocably filtered, time-sequence-merged, Fourier-transformed or otherwise changed from Level 0ne in a way that is irreversible. Level Two data can be re-created from Level One data, but one cannot create Level One data from Level Two data. Level-2 data is often used as intermediate products for later production of mission Science Data Products such as Helioseismic inferrences of solar subsurface flows.