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Sloan Digital Sky Survey Data Processing and Products

Introduction and Resources

The Early Data Release (EDR) paper is the fundamental resource for understanding the processing and data products from the SDSS, describing the pipelines and contents of generated data products. Successive data release papers: DR1, DR2, DR3, DR4, DR5, DR6 and DR7, describe changes between data releases. The technical summary provides more general information on the survey. The SDSS Project Book, written for a funding proposal early in the survey, is the most exhaustive description of the survey but was last updated in 1997. The SDSS publications web page includes a list of additional SDSS technical papers.

The algorithms page includes links to pages describing algorithms used by the data reduction pipelines, and the DAS quick reference page has a table of the most commonly useful files in the DAS.

The remainder of this page starts with a brief overview of data processing, followed by sections that describe the steps in data processing in detail. In addition to the more detailed description, each detail section privedes references to papers that give additional details, and a table of the files associated with that step of the pipeline that can be found in the DAS. These tables include links to descriptions of the formats of those files and templates that can be used to generate DAS URLs for those files. The templates are in "C printf" format, and can be used in C, bash, Python, and many other languages to automatically generate URLs.

Most of the catalog data (but not the images themselves) have been loaded into the Catalog Archive Server (CAS) database. Users are often better off obtaining SDSS data through a carefully constructed CAS query than they are downloading the data files from the DAS. Simple queries can be used to select just the objects and parameters of interest, while more complex queries can be used to do complex calculations on many objects, thereby avoiding the need to download the data on them at all.

Overview

SDSS Data Processing top level activity diagram
Imaging Observing
We used three instruments when collecting imaging data: the imaging camera mounted on the primary 2.5m SDSS telescope, which collected the imaging data themselves; the 0.5m photometric telescope, which collected images of photometric standard stars and reference fields; and a 10 micron all sky scanner (and later camera), used to detect clouds.
Imaging Data Reduction
The SDSS data processing factory used a collection of pipelines to process and calibrate the data from the imaging camera and the photometric telescope, ultimately producing a variety of data products including images with instrumental signatures removed, a photometric solution for the night, and a catalog of objects found in the data.
Resolution and Calibration of Object Catalogs
The resolve step declares one observation on an object the primary observation, and others secondary, thereby avoiding unintentional duplication of objects. This step ultimately produces an astrometrically and photometrically calibrated catalog of objects found in the data from the imaging camera.
Selection of Targets for Spectroscopy
The SDSS spectrographs collect spectra through a set of 640 fibers plugged into holes in aluminum plates. To prepare for spectroscopy, we used software to select a set of targets from catalogs (generated from the imaging data), design the plates, and drill holes in the aluminum plates.
Spectroscopic Observing
The spectrographs mounted on the primary 2.5m telescope collected spectra from each plate. There were two spectrographs, each of which collected data from 320 fibers. Each spectrograph had two CCDs, so the instrument produced a total of four images for each exposure.
Spectroscopic Data Reduction
The spectroscopic pipelines extracted one dimensional spectra from the raw exposures produced by the spectrographs, calibrated them in wavelength and flux, measured features in these spectra, measured redshifts from these features, and classified the objects as galaxies, stars, or quasars.
Recalibration
Improved astrometric and photometric calibrations became possible at the end of the survey; we re-ran the astrometric pipeline on all data using updated reference catalogs and improved centroiding, and used a separate pipeline to refine the photometric calibrations.

Data reduction could occur multiple times for both images and spectra. Each time we repeated a data reduction, we labeled the output from that reduction process with a distinct rerun number.

In the case of imaging rerun numbers, different decades in the rerun number designate significant differences in the data reduction software. For example, rerun 1 and rerun 2 of a given run would have been processed by identical (or at least very similar) versions of the data reduction software, while rerun 40 would have been reduced with a significantly different version of the pipeline.

Imaging Observing

Imager
The imager collected survey data from the imager in drift scan (also called TDI) mode. We use the term "run" to designate a single scan along a great circle. The data acquisition system system divided the data from each CCD into frames, stored as FITS files; the observatory sent data to be processed as a collection of FITS files, each corresponding to an arc along the great circle 1361 rows (539 arcseconds) long from a single CCD. In addition to the images themselves, the data acquisition system also generated a variety of metadata and other engineering files, which included pixel statistics and a catalog of bright stars for each field.
DAS files generated in imager data collection
File Type in/out Description DAS URL format format parameters
idReport out records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
idR out raw imaging frames in http://das.sdss.org/unprocessed/imaging/%d/idR-Run-%d-Fields-%04d-%04d.tar run, run, fieldfirst, fieldlast
idGang out assorted data gathered by the data acquisition system in http://das.sdss.org/unprocessed/imaging/%d/idGang-Run-%d-%s-%d-%d.tar run, run, (rows/cols), start, end
idFrameLog out camera position information for each frame http://das.sdss.org/nightly/%05d/idFrameLog-%06d-%d.par mjd, run, crate
opCamera out imaging camera geometry http://das.sdss.org/nightly/%05d/opCamera-%05d.par mjd, mjd (of generation)
opConfig out CCD readout configurations http://das.sdss.org/nightly/%05d/opConfig-%05d.par mjd, mjd
opECalib out CCD electronic calibrations http://das.sdss.org/nightly/%05d/opECalib-%05d.par mjd, mjd (of generation)
Photometric Telescope
The photometric telescope collected images of standard stars ("primary standards") at a variety of airmasses throughout the night to measure the photometric solution for the night, and images that sample the survey area for each imaging run ("secondary patches") that can be used to calibrate the runs from the imager using photometric solutions generated by the photometric telescope.
DAS files generated in photometric telescope data collection
File Type in/out Description DAS URL format format parameters
mdReport out records exposures collected on a night http://das.sdss.org/nightly/%05d/mdReport-%05d.par mjd, mjd
Infrared All-Sky Camera
Clouds can be clearly seen at night in a 10 micron all-sky camera. We used two such cameras at different times in the survey to monitor the sky for cloud (and therefore non-photometric conditions).
DAS files generated by the infrared all sky camera or scanner
File Type in/out Description DAS URL format format parameters
IRSC out A movie of the clouds for the night (original scanner) http://das.sdss.org/nightly/%05d/irsc-%05d.mpg mjd, mjd
IRCam movie out A movie of the clouds for the night (new camera) http://das.sdss.org/nightly/%05d/ircam-%05d.mpg mjd, mjd
IRCam plot out A plot of the sky sigma (useful for identifying clouds) with time http://das.sdss.org/nightly/%05d/ircam-%05dgraph.png mjd, mjd
IRCam data out A log of statistics on ircam frames http://das.sdss.org/nightly/%05d/ircam-%05d.log mjd, mjd
Other metadata
The observatory produces an assortment of engineering and other metadata.
Other DAS files generated in observing
File Type in/out Description DAS URL format format parameters
night log out A prose account of the night http://das.sdss.org/nightly/%05d/nightLog-%05d.txt mjd, mjd
idWeather out A log of weather data http://das.sdss.org/nightly/%05d/idWeather-%05d.par mjd, mjd

Imaging Data Reduction

Serial Stamp Collecting Pipeline (SSC)
The SSC repackages some of the data produced by the data acquisition system and produces postage stamps of bright reference stars.
DAS files read by the SSC pipeline
File Type in/out Description DAS URL format format parameters
scPlan in the SSC processing plan http://das.sdss.org/imaging/%d/%d/ssc/scPlan-%d.par run, rerun, camcol
idReport in records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
opCamera in imaging camera geometry http://das.sdss.org/nightly/%05d/opCamera-%05d.par mjd, mjd (of generation)
opConfig in CCD readout configurations http://das.sdss.org/nightly/%05d/opConfig-%05d.par mjd, mjd
opECalib in CCD electronic calibrations http://das.sdss.org/nightly/%05d/opECalib-%05d.par mjd, mjd (of generation)
opBC in CCD bad pixel file http://das.sdss.org/nightly/%d/opBC-%d.par mjd, mjdbp (see fpPlan)
idR in raw imaging frames in http://das.sdss.org/unprocessed/imaging/%d/idR-Run-%d-Fields-%04d-%04d.tar run, run, fieldfirst, fieldlast
idGang in assorted data gathered by the data acquisition system in http://das.sdss.org/unprocessed/imaging/%d/idGang-Run-%d-%s-%d-%d.tar run, run, (rows/cols), start, end
koCat in the catalog of known bright stars http://das.sdss.org/imaging/%d/%d/ssc/koCat-%06d.fit run, rerun, run
Postage Stamp Pipeline (PSP) [2002AJ....123..485S, section 4.3]
The PSP measures the bias and global sky level, and fits a model for the point spread function for each field.
DAS files used or generated by the PSP pipeline
File Type in/out Description DAS URL format format parameters
psParam in PSP tunable parameters http://das.sdss.org/imaging/%d/%d/photo/psParam.par run, rerun
psPlan in the PSP processing plan http://das.sdss.org/imaging/%d/%d/photo/psPlan-%d.par run, rerun, camcol
opCamera in imaging camera geometry http://das.sdss.org/nightly/%05d/opCamera-%05d.par mjd, mjd (of generation)
opConfig in CCD readout configurations http://das.sdss.org/nightly/%05d/opConfig-%05d.par mjd, mjd
opECalib in CCD electronic calibrations http://das.sdss.org/nightly/%05d/opECalib-%05d.par mjd, mjd (of generation)
opBC in CCD bad pixel file http://das.sdss.org/nightly/%d/opBC-%d.par mjd, mjdbp (see fpPlan)
idB in bias vector http://das.sdss.org/imaging/%d/%d/photo/calib/idB-%06d-%c%d.fit run, rerun, run, filter, camcol
exPhotom in photometric solutions http://das.sdss.org/pt/solutions/%s/exPhotom-%05d.par version, mjd
kaCalObj in calibrated objects http://das.sdss.org/pt/objects/%s/%d/kaCalObj-%08d.fit version, stripe, sequenceId
psField out the initial photometric calibration and point spread function fit by field (see the extracting PSF images page) http://das.sdss.org/imaging/%d/%d/objcs/%d/psField-%06d-%d-%04d.fit run, rerun, camcol, run, camcol, field
Astrometric Pipeline (astrom) [2003AJ....125.1559P]
The astrometric pipeline calculates the astrometric solution. The astrometry and astrometry QA web pages provide more information on the algorithms used and the proper interpretation of the output.
DAS files used or generated by the astrom pipeline
File Type in/out Description DAS URL format format parameters
asParam in astrom tunable parameters http://das.sdss.org/imaging/%d/%d/astrom/asParam.par run, rerun
asPlan in the astrom processing plan http://das.sdss.org/imaging/%d/%d/astrom/asPlan.par run, rerun
opConfig in CCD configuration, specifying the readout characteristics for each CCD http://das.sdss.org/nightly/%d/opConfig-%d.par mjd, mjd
opCamera in positions of the CCDs in the camera http://das.sdss.org/nightly/%d/opCamera-%d.par mjd, mjdcam
idReport in records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
idWeather in A log of weather data http://das.sdss.org/nightly/%05d/idWeather-%05d.par mjd, mjd
asTrans out tranformation coefficients from row, column to great circle coordinates http://das.sdss.org/imaging/%d/%d/astrom/asTrans-%06d.fit run, rerun, run
Frames Pipeline (frames) [2002AJ....123..485S, section 4.4]
The frames pipeline applies flat field and bias corrections to each frame, and interpolates values for pixels in bad columns and bleed trails and those corrupted by cosmic rays to produce a "corrected frame" (fpC file). It then detects bright objects and estimates the varying sky background, detects fainter objects, and measures a variety of properties for each object. Several algorithms pages describe details of the processing performed by frames.
DAS files used or generated by the frames pipeline
File Type in/out Description DAS URL format format parameters
fpParam in frames tunable parameters http://das.sdss.org/imaging/%d/%d/photo/fpParam.par run, rerun
fpPlan in frames precessing plan http://das.sdss.org/imaging/%d/%d/photo/fpPlan-%d.par run, rerun, camcol
idReport out records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
koCat in the catalog of known bright stars http://das.sdss.org/imaging/%d/%d/ssc/koCat-%06d.fit run, rerun, run
opConfig in CCD configuration, specifying the readout characteristics for each CCD http://das.sdss.org/nightly/%d/opConfig-%d.par mjd, mjd
opECalib in CCD calibration file, specifying the electronic characteristics (read noise, gain, full-well, bias level, and linearity corrections) for each CCD http://das.sdss.org/nightly/%d/opECalib-%d.par mjd, mjdcal (see fpPlan)
opBC in CCD bad pixel file http://das.sdss.org/nightly/%d/opBC-%d.par mjd, mjdbp (see fpPlan)
idB in bias vector http://das.sdss.org/imaging/%d/%d/photo/calib/idB-%06d-%c%d.fit run, rerun, run, filter, camcol
psField in the initial photometric calibration and point spread function fit by field http://das.sdss.org/imaging/%d/%d/objcs/%d/psPlan-%06d-%d-%04d.fit run, rerun, camcol, run, camcol, field
asTrans in tranformation coefficients from row, column to great circle coordinates http://das.sdss.org/imaging/%d/%d/astrom/asTrans-%06d.fit run, rerun, run
fpFieldStat out field statistics http://das.sdss.org/imaging/%d/%d/objcs/fpFieldStat-%06d-%d-%04d.fit run, rerun, run, camcol, field
fpObjc out the (uncalibrated) object catalog http://das.sdss.org/imaging/%d/%d/objcs/fpObjc-%06d-%d-%04d.fit run, rerun, run, camcol, field
fpC out the image itself, bias subtracted, flat fielded, and with bad pixels replaced by interpolated values (the "corrected frame") http://das.sdss.org/imaging/%d/%d/corr/fpC-%06d-%c%d-%04d.fit run, rerun, run, filter, camcol, field
fpBIN out a 4x4 binned version of the corrected image after masking of objects and subtraction of sky, an image of the estimate of the sky, an image of the uncertainty in the sky estimate, and a table of bright star wings http://das.sdss.org/imaging/%d/%d/objcs/fpBIN-%06d-%c%d-%04d.fit run, rerun, run, filter, camcol, field
fpM out the frame masks (read using readAtlasImages) http://das.sdss.org/imaging/%d/%d/objcs/fpM-%06d-%c%d-%04d.fit run, rerun, run, filter, camcol, field
fpAtlas out the atlas images for all objects detected (read using readAtlasImages) http://das.sdss.org/imaging/%d/%d/objcs/fpAtlas-%06d-%d-%04d.fit run, rerun, run, camcol, field
Monitor Telescope Pipeline (mtpipe) [2006AN....327..821T]
On nights the primary SDSS telescope collects imaging data, the photometric telescope (PT), a second telescope at the same site, collects images of two types of standard star fields: primary and secondary. The primary fields contain standard stars with well established magnitudes, and are used to determine a photometric solution for the night. Secondary fields contain stars that overlap imaging runs, and allow calibration of those runs. (The survey originally planned to use a 0.6m telescope, the Monitor Telescope (MT), for these observations. We replaced the MT with a 0.5m telescope before the start of data collection. We called this new telescope the photometric telescope (PT) to distinguish it from the original 0.6m MT, but most of the reduction software, file formats and file name standards remained the same, and retained their original names.)
DAS files used or generated by the mtpipe pipeline
File Type in/out Description DAS URL format format parameters
mdReport in records exposures collected on a night http://das.sdss.org/nightly/%05d/mdReport-%05d.par mjd, mjd
metaFC in table of reference standard stars http://das.sdss.org/pt/metaFC.fit (none)
exPhotom out photometric solutions http://das.sdss.org/pt/solutions/%s/exPhotom-%05d.par version, mjd
kaCalObj out calibrated objects in the PT images http://das.sdss.org/pt/objects/%s/%d/kaCalObj-%08d.fit version, stripe, sequenceId
"Final" Calibration Pipeline (nfcalib) [2002AJ....123..485S, section 4.5.3]
fcalib generates the photometric calibration for a run based on photometric telescope data (the output of the monitor telescope pipeline). This was originally considered the "final" calibration of a run, but now the "ubercal" calibrations supersede these "final" calibrations.

The photometric flux calibration algorithms page describes the calibration and use of calibrated quantities in more detail, and includes sections on assessment of photometric calibration, converting SDSS counts to SDSS (asinh) magnitudes (and vice versa), converting SDSS to AB magnitudes, and converting SDSS asinh magnitudes to fluxes. Another page describes conversion between SDSS magnitudes and UBVRcIc, and ugriz colors of Vega and the Sun.

You can determine which version of the mt calibrations (the "version" parameters in the formats in the table describing the monitor telescope pipeline outputs) by looking at the mtVerPhotom parameter of the fpPlan file, below.

DAS files used or generated by the nfcalib pipeline
File Type in/out Description DAS URL format format parameters
fpParam in fcalib tunable parameters http://das.sdss.org/imaging/%d/%d/nfcalib/fpParam.par run, rerun
fpPlan in fcalib processing plan http://das.sdss.org/imaging/%d/%d/nfcalib/fpPlan-%d.par run, rerun, camcol
idReport in records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
asTrans in tranformation coefficients from row, column to great circle coordinates http://das.sdss.org/imaging/%d/%d/astrom/asTrans-%06d.fit run, rerun, run
exPhotom in photometric solutions http://das.sdss.org/pt/solutions/%s/exPhotom-%05d.par version, mjd
kaCalObj in calibrated objects http://das.sdss.org/pt/objects/%s/%d/kaCalObj-%08d.fit version, stripe, sequenceId
fpObjc in the (uncalibrated) object catalog http://das.sdss.org/imaging/%d/%d/objcs/fpObjc-%06d-%d-%04d.fit run, rerun, run, camcol, field
fcPCalib out the photometric calibration of a run http://das.sdss.org/imaging/%d/%d/nfcalib/fcPCalib-%06d-%d.fit run, rerun, run, camcol
Imaging Quality Assurance
The imaging QA algorithms page describes imaging quality assurance performed on the outputs of the imaging pipeline.

Resolve Multiple Detections and Produce Calibrated Catalogs

A given area on the sky may be observed by multiple runs. The final calibrated catalogs contain a field declaring whether the the specific observation of the object is "primary," and the canonical measurement of the object, or "secondary," a duplicate. These catalogs are generated twice, once based on the single run in isolation by exportChunk, and again in the resolve step. The catalogs produced by exportChunk declare an object primary or secondary based on position alone, introducing the possibility of inconsistencies due to errors in position; it is possible, for example, that two separate observation of an object be declared primary if the position measured for the object is slightly different in each detection.

The catalog generated by the resolve step, on the other hand, uses an operational database to search for other detections, and guarantees that one and only one detection be declared primary.

The catalogs produced by exportChunk can be found in the run directory of each run:
DAS files used or generated by the exportChunk
File Type in/out Description DAS URL format format parameters
tsObj out the calibrated object catalogs http://das.sdss.org/imaging/%d/%d/calibChunks/%d/tsObj-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field
tsField out the calibrated field statistics http://das.sdss.org/imaging/%d/%d/calibChunks/%d/tsField-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field
The catalogs produced by the resolve step are completed during target selection, and the table in target selection section gives their location. Note that the catalogs produced by target selection includes fields that flag which objects were selected for spectroscopy and why, while those generated by exportChunk do not.

See the EDR paper, 2002AJ....123..485S, section 4.7 for details on how objects are resolved.

Selection of Targets for Spectroscopy and Tiling

The target selection algorithms page describes how the pipeline performs target selection, including selection of Main Galaxy Sample, Luminous Red Galaxies (LRG), Quasars, Stars, ROSAT All-Sky Survey sources, Serendipity, and SEGUE targets. The target selection pipeline extracts calibrated catalogs of objects and corresponding field by field statistics from the operations database (which is itself loaded with data from the imaging data reduction pipelines):

DAS files used or generated by the target selection pipeline
File Type in/out Description DAS URL format format parameters
tsObj out the calibrated object catalogs http://das.sdss.org/imaging/inchunk_%s/stripe%d_mu%d_%d/%d/tsObj-%06d-%d-%d-%04d.fit (target or best), stripe, start mu, rerun type, camcol, run, camcol, rerun, field
tsField out the calibrated field statistics http://das.sdss.org/imaging/inchunk_%s/stripe%d_mu%d_%d/%d/tsField-%06d-%d-%d-%04d.fit (target or best), stripe, start mu, rerun type, camcol, run, camcol, rerun, field

The "rerun type" is 1 for best, 0 for target.

The tiling algorithms page describes the process by which the spectroscopic plates are designed and placed relative to each other.

Spectroscopic Observing

Plate Plugging (plug)
When the observatory is ready to observe a plate, the observatory staff plugs optical fibers into the holes drilled into the plates, and maps which fiber correponds to which hole (and therefor which object) by shining light through each fiber.
DAS files generated in plate plugging
File Type in/out Description DAS URL format format parameters
plPlugMapM out records which fiber corresponds to which hole in a plate (and therefore objects, and what coordinates on the sky) http://das.sdss.org/spectro/1d_%d/%04d/1d/plPlugMapM-%04d-%d-%02d.par rerun, plate, plate, mjd, plugging index
Data Collection
Observers mount cartridges containing the drilled, plugged plates on the telescope, and collected exposures on each plate until it reached a threshold estimated signal to noise and at least three exposures had been collected.
DAS files generated in spectroscopic data collection
File Type in/out Description DAS URL format format parameters
sdReport out records exposures collected on a night http://das.sdss.org/nightly/%05d/sdReport-%05d.par mjd, mjd
sdR out raw spectroscopic data frames http://das.sdss.org/unprocessed/spectro/%d/sdR-%c%d-%08d.fit.gz mjd, CCD (r or b), camera, exposure id

Spectroscopic Data Reduction

Two-dimensional Pipeline (spectro2d, also called idlspec2d) [2002AJ....123..485S, section 4.10.1]
The spectro2d pipeline reads science and calibration exposures from the spectrographs, reduces and calibrates the science exposures, extracts the one dimensional spectra from the two dimensional exposures, stacks multiple exposures into combined spectra, and produces corresponding masks and noise estimates.
DAS files used or generated by the spectro2d pipeline
File Type in/out Description DAS URL format format parameters
spPlan in the spectro2d processing plan http://das.sdss.org/spectro/2d_%d/%04d/spPlan-%04d-%d.par rerun, plate, plate, mjd
spPlancomb in the processing plan for combining spectra http://das.sdss.org/spectro/2d_%d/%04d/spPlancomd-%04d-%d.par rerun, plate, plate, mjd
plPlugMapM in records which fiber corresponds to which hole in a plate (and therefore objects, and what coordinates on the sky) http://das.sdss.org/spectro/1d_%d/%04d/1d/plPlugMapM-%04d-%d-%02d.par rerun, plate, plate, mjd, plugging index
sdReport in records exposures collected on a night http://das.sdss.org/nightly/%05d/sdReport-%05d.par mjd, mjd
sdR in raw spectroscopic readouts in http://das.sdss.org/spectro/%d/spectroRaw.%d.tar mjd, mjd
spCFrame out calibrated spectra for a single CCD and exposure http://das.sdss.org/spectro/2d_%d/%04d/spCFrame-%c%d-%08d.par rerun, plate, CCD (r or b), camera, exposure id
spPlate out the 640 combined flux- and wavelength-calibrated spectra over all exposures (potentially spanning multiple nights) for a given mapped plate http://das.sdss.org/spectro/2d_%d/%04d/spPlate-%04d-%d.par rerun, plate, plate, mjd
The idlspec2d product incorporates specBS (also called the Princeton-1D pipeline), an alternative to the standard spectro1d pipeline. specBS produces the following files:
DAS files generated by the specBS
File Type in/out Description DAS URL format format parameters
spZline out emission line fits http://das.sdss.org/spectro/2d_%d/%04d/spZline-%04d-%d.par rerun, plate, plate, mjd
spZall out all spectroscopic classifications and redshifts http://das.sdss.org/spectro/2d_%d/%04d/spZall-%04d-%d.par rerun, plate, plate, mjd
spZbest out spectroscopic classifications and redshifts http://das.sdss.org/spectro/2d_%d/%04d/spZbest-%04d-%d.par rerun, plate, plate, mjd
One-dimensional Pipeline (spectro1d) [2002AJ....123..485S, section 4.10.2]
The spectro1d pipeline measures emission and absorption lines and classifies the objects based on the spectrum; algorithms web pages describe the emission and absorption line fitting and the spectral type and redshift measurement algorithms. The redshift templates page provides the template spectra used for redshift measurement.
DAS files used or generated by the spec1d pipeline
File Type in/out Description DAS URL format format parameters
spPlan1d in spectro1d processing plan http://das.sdss.org/spectro/1d_%d/%d/spPlan1d-%d-%04d.par rerun, plate, mjd, plate
spParam1d in tunable software parameters for the spectro1d pipeline http://das.sdss.org/spectro/1d_%d/%d/1d/spParam1d-%d-%04d.par rerun, plate, mjd, plate
spManLog in a record of which classifications were corrected by hand http://das.sdss.org/spectro/1d_%d/%d/1d/spManLog-%d-%04d.par rerun, plate, mjd, plate
spPlate in the 640 combined flux- and wavelength-calibrated spectra over all exposures (potentially spanning multiple nights) for a given mapped plate http://das.sdss.org/spectro/2d_%d/%04d/spPlate-%04d-%d.par rerun, plate, plate, mjd
plPlugMapM in records which fiber corresponds to which hole in a plate (and therefore objects, and what coordinates on the sky) http://das.sdss.org/spectro/1d_%d/%04d/1d/plPlugMapM-%04d-%d-%02d.par rerun, plate, plate, mjd, plugging index
spDiag in spectro1d diagnostics http://das.sdss.org/spectro/1d_%d/%d/1d/spDiag-%d-%04d.par rerun, plate, mjd, plate
spSpec out line measurements and redshift determinations, as well as the spectrum, for a single object, summing over all of its exposures through a given mapped plate http://das.sdss.org/spectro/1d_%d/%d/1d/spSpec-%d-%04d-%03d.par rerun, plate, mjd, plate, fiber
Stellar Parameters Pipeline (sspp) [2007arXiv0710.5645L 2007arXiv0710.5778L 2007arXiv0710.5780A]
The SEGUE stellar parameters pipeline produces a number of files, stored together:
DAS files used or generated by the SSPP pipeline
File Type in/out Description DAS URL format format parameters
sspp gzipped tar files out Output of the sspp pipeline http://das.sdss.org/spectro/sspp_%d/%04d-%05d.tgz rerun, plate, mjd

Recalibration

Astrometric Recalibration
We recalibrated the astrometry for the final data release, using updated reference catalogs and improved centroiding:
DAS files used or generated in astrometric recalibration
File Type in/out Description DAS URL format format parameters
asParam in astrom tunable parameters http://das.sdss.org/imaging/%d/%d/fastrom/asParam.par run, rerun
asPlan in the astrom processing plan http://das.sdss.org/imaging/%d/%d/fastrom/asPlan.par run, rerun
opConfig in CCD configuration, specifying the readout characteristics for each CCD http://das.sdss.org/nightly/%d/opConfig-%d.par mjd, mjd
opCamera in positions of the CCDs in the camera http://das.sdss.org/nightly/%d/opCamera-%d.par mjd, mjdcam
idReport in records runs collected on a night http://das.sdss.org/nightly/%05d/idReport-%05d.par mjd, mjd
idWeather in A log of weather data http://das.sdss.org/nightly/%05d/idWeather-%05d.par mjd, mjd
asTrans out tranformation coefficients from row, column to great circle coordinates http://das.sdss.org/imaging/%d/%d/fastrom/asTrans-%06d.fit run, rerun, run
Photometric Recalibration (Ubercal) [2008ApJ...674.1217P]
The "ubercal" recalibration recalibrates the survey by simultaneously solving for the calibration parameters and relative stellar fluxes using overlapping observations. The algorithm used decouples the problem of relative calibrations from that of absolute calibrations; the absolute calibration is reduced to determining a few numbers for the entire survey. See the ubercal section of the photometric calibration algorithms page.
DAS files generated in photometric recalibration
File Type in/out Description DAS URL format format parameters
drObj out the final "ubercal" and astrometrically recalibrated object catalogs http://das.sdss.org/imaging/%d/%d/dr/%d/drObj-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field
drField out the final "ubercal" field statistics http://das.sdss.org/imaging/%d/%d/dr/%d/drField-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field
SuperNova Photometric Calibration [follows method of 2008MNRAS.386..887B]
DAS files generated in photometric calibration of SuperNova data
File Type in/out Description DAS URL format format parameters
tsObj out the calibrated object catalogs http://das.sdss.org/imaging/%d/%d/calibChunks/%d/tsObj-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field
tsField out the calibrated field statistics http://das.sdss.org/imaging/%d/%d/calibChunks/%d/tsField-%06d-%d-%d-%04d.fit run, rerun, camcol, run, camcol, rerun, field