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Knowledgebase: Data processing
What are the primary data products that the Spitzer Science Center generated? What is a BCD? What is a post-BCD product?
Posted by z-Schuyler Van Dyk on 02 December 2008 11:45 AM

In general, the eight Spitzer Science Center (SSC) data processing pipelines convert spacecraft engineering data into scientifically useful data. Raw data (engineering and science) were received at the ground tracking stations via telemetry and forwarded to the Spitzer Flight Operations Center at the Jet Propulsion Laboratory in Pasadena. The Flight Operations System at JPL received telemetry packets from the Spitzer spacecraft and repackaged them into FITS files containing sensor data, expressed in DN (data number) units. Instrument engineering and housekeeping data were also transferred to the SSC from the Flight Operations System. The archived raw data represent rationally organized, time-ordered data and include associated Observatory pointing data and calibration observations.

Basic Calibrated Data (BCD) are two-dimensional images in FITS format, and correspond to individual 'data collection events (DCEs)' within an observation. An image is flux and/or wavelength (if appropriate) calibrated, and surface brightness measurements are expressed in physical units. In addition, flat-fielding and cosmetic restoration (e.g., cosmic-ray removal) algorithms are applied to the BCD. Spatial 'world' coordinates are derived from Observatory pointing information only. The BCDs represent the most reliable product achievable through automated processing.

Extended pipeline products (also referred to as Post-BCD products, previously referred to as Browse Quality Data) are also available. Higher-level imaging products that include co-addition, mosaicing, and source extraction are available.

The description of SSC data products depends on the science instrument and observing mode. High-level descriptions of BCDs for each of the observing modes are available in the Spitzer Observer's Manual, and details appear in the corresponding Instrument Handbook (IRAC, IRS, MIPS).

The SSC provided routine calibrations for each of the observing modes. These data entered the Spitzer public archive immediately upon processing and verification (unless a proprietary observation embargoed the release of the data). The investigator was able to propose to undertake special calibrations. For Legacy Science projects, these special calibration data also entered the public archive immediately upon processing and verification.