For long term use and ease of understanding, the Spitzer Heritage Archive adopted a different terminology for the various data products it delivers than what was used during the mission. Level 0 is raw data, Level 1 are the products delivered by the BCD pipeline, and Level 2 are the products produced by the post-BCD pipeline. Within this document we use both definitions.
5.1 Level 1: Basic Calibrated Data (BCD) Pipeline
This chapter, combined with the next one, covers how the data was processed at the SSC, or what was done to your data between when it left the spacecraft and when you get it. As of this writing, the Level 1 BCD products are for the most part what you should start with when working with MIPS data. The Level 2 post-BCD data products are a good way to get an overview of your data, but to do science (at least at 70 and 160 microns), you should revert to the BCDs.
As of this writing, the most comprehensive, best description of our BCD pipelines is in a Publications of the Astronomical Society of the Pacific (PASP) article by Karl Gordon et al. (2005, PASP, 117, 503). Although the Gordon et al. article specifically covers the Data Analysis Tool (DAT) developed by the MIPS instrument team for processing of its own data, the SSC worked very closely with the MIPS team and treated the DAT as a testbed for changes to the actual online SSC pipelines, as changes ccould be made to the DAT on a much more rapid timescale than to the SSC pipelines.
As of the Archive opening in May 2004, the DAT and the SSC pipeline produce essentially identical results at the BCD level. The post-BCD processing is so customized to the science and the observation (primarily for Ge data) that the automated pipeline does not reproduce the hand-processed DAT products; see discussions below.
5.1.1 Pipeline Updates
The overall data processing and calibration of the MIPS data by SSC was stable for quite some time early after launch. Yet, in an effort to take care of well known artifacts or features and to keep track of improvements in calibration, smaller modifications were introduced. A history of pipeline changes is available in Appendix B.