SATLASFrom detector to catalogue
Every archive takes its data through the same four levels, and the data changes shape on the way: detector readout becomes images, time series or event lists, then light curves, spectra and tables. The names differ from archive to archive (Level 0–3 at Chandra and Euclid, Stages 0–3 at JWST, uncal, rate, cal and i2d in file names); the ladder below is common to all of them.
1Raw
Telemetry as recorded, in detector units (ADU, counts, rampsup-the-ramp samplingReading an infrared detector repeatedly during one exposure without resetting it, so charge accumulates as a ramp. Fitting the slope gives a count rate and rejects cosmic-ray hits. or raw channels), with instrument signatures intact. Rarely needed for science and often proprietary.
- Detector readout
- Visibilities
2Calibrated
Single exposures or data segments with instrument signatures removed (bias, dark, flat fieldcalibrationRemoving instrument signatures and putting data in physical units: subtracting bias and dark current, dividing by the flat field (pixel-to-pixel sensitivity), correcting non-linearity and fitting the astrometric solution. Reference files hold these calibrations and are updated as the instrument is understood., non-linearity, gain) and an astrometricastrometryMeasuring positions and their changes on the sky: parallax, proper motion and orbital motion. Gaia reaches tens of µas for bright stars. or timing solution attached, in physical units.
Return here when the standard extraction does not suit the science, such as crowded fields, non-standard apertures, faint or extended sources, or a custom treatment of systematics.
- Image
- Time series
- Cube
- Spectrum
- Event list
- Visibilities
3Measured
Usual starting point for analysis
Per-source or per-event quantities extracted from calibrated data: photometryphotometryMeasuring the flux of a source in a passband. Aperture photometry sums pixels inside a region; PSF photometry fits the point-spread function; forced photometry measures at a position fixed in advance, whether or not a source is detected there. and light curveslight curveFlux of one source as a function of time. The basic product of transit searches, variable-star work and transient follow-up., extracted spectra, screened event listsevent listThe basic X-ray and gamma-ray data product: a table with one row per detected photon (arrival time, detector position, sky position, energy and quality flags). Images, spectra and light curves are all binned from it., triggers.
- Spectrum
- Catalogue
- Time series
- Event list
- Sky map
- Cube
- Posterior samples
4Combined
Usual starting point for analysis
Multi-epoch or multi-field combinations (coaddscoaddMany exposures of the same field resampled onto a common grid and combined, reaching deeper than any single exposure and rejecting artefacts. A mosaic stitches adjacent fields., mosaics, cubesdata cubeA three-dimensional array with two sky axes and one spectral axis (wavelength, frequency or velocity), produced by integral field units and radio interferometers.) and catalogues, often with derived physical parameters such as distance, massarcsecond1/3600 of a degree (″). A milliarcsecond (mas) is 10⁻³″ and a microarcsecond (µas) 10⁻⁶″. Atmospheric seeing limits ground telescopes to about 0.5–1″ without adaptive optics. or redshiftredshiftz = λ_observed/λ_emitted − 1, the stretching of light by cosmic expansion (or by recession). For distant sources it stands in for distance and look-back time: z ≈ 1 is about 8 Gyr ago, z ≈ 10 about 13.3 Gyr..
- Catalogue
- Image
- Cube
- Sky map
AlertsSearch in real time, from calibrated data
Low-latency notices of new or variable sources, issued seconds to days after detection for follow-up, ahead of full processing.
Each mission's products, level by level
Grouped by the kind of data, because that decides what the levels hold. Under each term is where to get it; underlined terms open the product's entry on the mission page.
| Mission | 1Raw | 2Calibrated | 3Measured | 4Combined | Alerts |
|---|---|---|---|---|---|
| Pixel detectorsCCDs and infrared arrays. Calibrated exposures are images in physical units; photometry, light curves and spectra are extracted from them. | |||||
| TESSProduct map → | Not public | Full-frame images and target pixel files *-ffic.fits, *_tp.fits | No distinct product | ||
| Kepler / K2 | Raw cadence data | Kepler Objects of Interest (KOI) and DR25 catalogues | No distinct product | ||
| Hubble | Drizzled images; Hubble Source Catalog *_drz.fits, *_drc.fits | No distinct product | |||
| JWSTProduct map → | Stage 1–2 count-rate and calibrated exposures *_rate.fits, *_cal.fits | Stage 3 mosaics, IFU cubes and catalogues *_i2d.fits, *_s3d.fits | No distinct product | ||
| Euclid | Level 1 (LE1) raw frames | Level 2 calibrated frames | Level 2 spectra and per-tile catalogues | Level 2 mosaics (MER); Level 3 (LE3) cosmology products | No distinct product |
| Rubin | Raw exposures raw | Processed visit images visit_image | Detections, including on difference images source, dia_source | Coadds and the object catalogue, in annual data releases deep_coadd, object | Alert stream through community brokers, 60 s latency target |
| SPHEREx | Level 1 raw images | Level 2 spectral images (Quick Release) | No distinct product | Level 3–4 all-sky spectral maps and source catalogues | No distinct product |
| Catalogue and spectroscopic surveysNo images are released. The products are per-source tables and spectra, reprocessed in full for each data release. | |||||
| GaiaProduct map → | Not public | ||||
| DESI | Raw exposures | Extracted, sky-subtracted spectra per exposure | Coadded spectra and Redrock redshifts | Large-scale-structure catalogues and BAO measurements | No distinct product |
| Photon countingEach photon is recorded with its time, position and energy, so the core product is an event list; images, spectra and light curves are binned from it. | |||||
| Chandra | Level 0 telemetry | Chandra Source Catalog | No distinct product | ||
| Scanning sky mapsDetectors sweep the sky continuously. Time-ordered data are projected into frequency maps, then separated into astrophysical components. | |||||
| Planck | Time-ordered data | Calibrated timelines | Frequency maps, 30–857 GHz | Component-separated CMB and foreground maps; likelihoods and parameters | No distinct product |
| InterferometryThe primary data are visibilities, one per antenna pair; images and cubes come from Fourier inversion and deconvolution. | |||||
| ALMA | Visibilities (ASDM) | Calibrated measurement sets | Image cubes from the pipeline | Archive-wide products and science-ready cubes | No distinct product |
| Gravitational wavesEach detector produces one calibrated time series, the strain; there are no images. Events are found by matched filtering and characterised by Bayesian inference. | |||||
| LIGOProduct map → | |||||