wiki:glossary
Last modified 7 years ago Last modified on 09/07/2010 02:10:03 PM

Glossary and Acronyms

from: LSST Table of Contents.

Glossary

Also see the EA Model Glossary for additional definitions used within the EA Model.

Alert A signal (e.g. XML-formatted RSS feed) to the astronomical research community that something has changed at a given location on the sky: either the brightness or position of an object, or the serendipitous appearance of some totally new object.
Alert Production Formerly known as 'Nightly Processing' or 'Nightly Alert Processing'. The processing that occurs at the Base Camp in near-realtime. Produces and analyzes difference images in order to generate Alerts.
algorithm a class that implements some method of processing.
Association Pipeline An application that matches detected Sources or DIASources or generated Objects to an existing catalog of Objects, producing a (possibly many-to-many) set of associations and a list of unassociated inputs. Association Pipelines are used in the Nightly Alert processing after DIASource generation and in the final stages of Data Release processing to ensure continuity of Object identifiers.
(Astronomical) Object A star, galaxy, asteroid, or other physical object of astronomical interest. Beware: in non-LSST usage, these are often known as sources.
Base Camp ...
butler A middleware component that retrieves datasets (raw or processed) based on a dataset type and a set of key/value pairs. Typically, the butler will also use a "root" path in the filesystem to locate datasets stored in files. The key/value pairs might specify the particular visit, snap, raft, sensor, and channel desired, for example.
cadence The sequence of pointings and 30-second-equivalent visit exposures performed by LSST over the duration of the survey.
Calibrated Science Image A raw image that has been processed through the ISR Pipeline and has had its background and PSFs estimated.
Calibration Image Any of a set of images used in the ISR Pipeline to remove distortions caused by the telescope, detector, or other sources. Includes darks, flats, tunable-laser dome flats, etc.
Camera Crosstalk-Corrected (C3) Image An image from the Camera system that has had crosstalk removed but has not been processed by the ISR Pipeline. Beware: this is not the same as a raw image (which has not had crosstalk removed).
channel An amplifier on an LSST camera CCD (see sensor). The 16 channels comprising a sensor are numbered from "0,0" through "1,7".
Data Release processing Now known as 'Data Release Production'.
Data Release Production Formerly known as 'Data Release processing'.The processing that occurs periodically at the Archive Center to generate a Data Release, including Instrument Signature Removal, Deep Detection, Multifit Source Measurement, Photometric Calibration, Astrometric Calibration, Difference Template Generation, Co-Add Generation, Difference Image Analysis, and at least one version of Association. This is distinct from the Nightly Archive processing that also occurs at the Archive Center that includes some of the same steps.
difference image ...
difference image source ...
ephemeris An ephemeris (plural: ephemerides) - in MOPS, it refers to a predicted position (RA/Dec/time/etc) of a MovingObject
footprint A set of pixels that are determined to be part of a Source (or DIASource). It is implemented as a list of spans. A span contains coordinates of a stripe of pixels: row (y) given span belongs to, and a section of a column (xStart, xEnd).
Image Processing Pipeline ...
Instrument Signature Removal (ISR) Pipeline An application that removes telescope, detector, and other distortions from a raw image.
metadata attributes of astronomical objects (e.g. images, sources, astroObjects, etc.) that are characteristics of the objects themselves. Refer to and contrast with provenance.
Moving object ...
Nightly Alert processing Now known as 'Alert Production'. The processing that occurs at the Base Camp in near-realtime. Produces and analyzes difference images in order to generate Alerts.
Nightly Archive processing The processing that occurs at the Archive Center on a daily basis. This includes a duplicate of the Nightly Alert processing, but it may also include additional processing to update the Unreleased Catalog and the image caches.
Object See Astronomical Object. Beware: in computing, "object" refers to an instance of a class (a data structure with methods) that may represent anything, including an Object, a Source, or an Exposure.
pipeline a configured sequence of Stages. Example: Association Pipeline. See also semantic description of pipeline within the LSST Project.
policy ...
Point Spread Function (PSF) The function that maps a photon-emitting point in space to its resulting image as seen by the detector.
production overarching set of coordinated Pipelines and Sub-Productions. Example: Data Release Production.
provenance information about how astronomical objects (e.g. images, sources, astroObjects, etc.) were created and how to recreate them. Refer to and contrast with metadata. There is no such thing as "pipeline metadata". Rather there is image, source, and object provenance, and that provenance includes information about what pipelines, stages, policies etc. were used to process them.
raft A replaceable unit in the LSST camera. Each raft is made up of 9 butted sensors or CCDs. There are 21 science rafts in the camera plus 4 additional corner rafts with specialized, non-science sensors. Each science raft has 9 sensors or CCDs, making for a total of 189 CCDs per focal plane image. The 21 science rafts are numbered from "0,1" through "0,3", "1,0" through "3,4", and "4,1" through "4,3". (In other words, the 25 combinations from "0,0" through "4,4" minus the four corners which are non-science.)
Raw Image The image of the sky as received from the detector, with crosstalk present.
sensor An LSST camera CCD. Each sensor is divided into 16 channels or amplifiers. The 9 sensors that make up a raft are numbered from "0,0" through "2,2".
slice ...
snap One 15-second exposure within a visit in the LSST cadence. Each visit contains two back-to-back snaps. The two snap images are combined to form a 30-second-deep image; the combining algorithm uses the differences between the images to improve cosmic ray rejection.
Source A detection of an Object in a particular Exposure. Beware: in non-LSST usage, these are often known as detections, while "source" is used for what LSST calls an Object.
SDQA Metric The name of a quantity that is calculated for image data by SDQA-related pipeline processes (e.g., mean, standard deviation, number of saturated pixels, mean PSF width, etc.). Associated with the metric name are the physical units of the calculated quantity and whether the quantity's data type is integer or floating-point.
SDQA Rating The value and error associated with an SDQA metric. An image can have a set of different SDQA ratings.
SDQA Status The status assigned to an image by the SDQA subsystem (e.g., pass, fail, unknown, etc.). Database tables that store image metadata will include a field containing an ID number that corresponds to an SDQA status.
SDQA Threshold The set of lower and upper thresholds associated with an SDQA Metric. Some metrics have only either a lower or upper threshold. In general, the thresholds depend on observing conditions (e.g., atmospheric seeing, filter, etc.).
sky tile A region of the sky used for processing in a spatially-localized manner. Sky tiles are typically a tessellation of the sphere, although they may overlap to some extent. Sky tiles may vary in size and shape depending on the needs of the processing being performed. Typical sky tile geometries are based on HEALPix or quadsphere tessellations; rectangular tangent-plane projections may also be used.
source classification ..
stage wraps an algorithm into an API which is pluggable into a pipeline which may support serial and/or parallel processing.
sub-production set of coordinated pipelines i.e. larger than a single pipeline. Example: Astrometry Sub-Production
subsystem a defined combination of hardware, a software stack, a set of running processes, and the people who manage them. It refers to a major component of the DM System operations, i.e. "Archive Operations Subsystem", "Data Processing Subsystem".
template table A database table that contains no data, and is used to create short-lived tables using syntax "CREATE TABLE x LIKE y"
visit A 30-second-equivalent exposure within the LSST cadence. Each visit is composed of two snaps. Consecutive visits may be at the same pointing (perhaps for deep drilling fields) but will typically be at different pointings on the sky.
xrootd Server for low latency high bandwidth data access, see xrootd for more details.

Acronyms

ADQL Astronomical Data Query Language
AP Association Pipeline
AOS Archive Operations System
CM Configuration Management
CSS Community Service System
CTIO Cerro Tololo Inter-American Observatory
DAF Data Access Framework
DBMS Database Management System
DES Dark Energy Survey
DFS Distributed File System
DIASource Difference Image Source
DLS Deep Lens Survey
DP Detection Pipeline
DPS Distributed Processing Services
DR Data Release
DWDM Dense Wavelength Division Multiplexing
GFS Google File System
IPAC Infrared Processing and Analysis Center
JHU Johns Hopkins University
MOPS Moving Object Processing System
NCSA National Center for Supercomputing Applications
NOAO National Optical Astronomy Observatory
OCS Online Control System
PanSTARRS Panoramic Survey Telescope & Rapid Response System
REN Research and Educational Networking
SQA Software Quality Assurance
SDP Software Development Process
SDQA Science Data Quality Analysis
SDSS Sloan Digital Sky Server
SLAC SLAC National Accelerator Laboratory, formerly known as Stanford Linear Accelerator Center
V&V Verification and Validation
VO Virtual Observatory

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