On-The-Fly Calibration

Last updated April 29, 2019

In observational astronomy an On-The-Fly Calibration (OTFC) system calibrates data when a user's request for the data is processed so that users can obtain data that are calibrated with up-to-date calibration files, parameters, and software.

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

History of OTFC

The OTFC processing system was developed at the Canadian Astronomy Data Centre (CADC) and the Space Telescope European Coordinating Facility (ST-ECF) and is implemented at both sites and at Space Telescope Science Institute (STScI). The OTFC system currently provides data calibration for the Wide Field and Planetary Camera 2 (WFPC2) and Space Telescope Imaging Spectrograph (STIS). In the future, the Advanced Camera for Surveys (ACS) and possibly the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) will be supported.

The Space Telescope – European Coordinating Facility (ST-ECF) was an institution which provided a number of support and service functions primarily for European observers of the NASA/ESA Hubble Space Telescope (HST). It was established in 1984 by the European Space Agency (ESA) and the European Southern Observatory (ESO), and was located at the ESO headquarters in Garching bei München, Germany. The ST-ECF ceased operations on 31 December 2010.

The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST) and for the James Webb Space Telescope (JWST). STScI is located on the Johns Hopkins University Homewood Campus in Baltimore, Maryland and was established in 1981 as a community-based science center that is operated for NASA by the Association of Universities for Research in Astronomy (AURA). In addition to performing continuing science operations of HST and preparing for scientific exploration with JWST, STScI manages and operates the Mikulski Archive for Space Telescopes (MAST), the Data Management Center for the Kepler mission and a number of other activities benefiting from its expertise in and infrastructure for supporting the operations of space-based astronomical observatories. Most of the funding for STScI activities comes from contracts with NASA's Goddard Space Flight Center but there are smaller activities funded by NASA's Ames Research Center, NASA's Jet Propulsion Laboratory, and the European Space Agency (ESA). The staff at STScI consists of scientists, software engineers, data management and telescope operations personnel, education and public outreach experts, and administrative and business support personnel. There are approximately 100 Ph.D. scientists working at STScI, 15 of which are ESA staff who are on assignment to the HST project. The total STScI staff consists of about 450 people.

Wide Field and Planetary Camera 2 Hubble telescope camera

The Wide Field and Planetary Camera 2 (WFPC2) is a camera formerly installed on the Hubble Space Telescope. The camera was built by the Jet Propulsion Laboratory and is roughly the size of a baby grand piano. It was installed by servicing mission 1 (STS-61) in 1993, replacing the telescope's original Wide Field and Planetary Camera (WF/PC). WFPC2 was used to image the Hubble Deep Field in 1995, the Hourglass Nebula and Egg Nebula in 1996, and the Hubble Deep Field South in 1998. During STS-125, WFPC2 was removed and replaced with the Wide Field Camera 3 as part of the mission's first spacewalk on May 14, 2009. After returning to Earth, the camera was displayed briefly at the National Air and Space Museum and the Jet Propulsion Laboratory before returning to its final home at the Smithsonian's National Air and Space Museum.

Goals of the system

The main goals behind the implementation of the OTFC system are to take advantage of better calibration files and the much smaller storage area required if only raw files are kept in the archives. The system can also offer more calibration steps than were available when the data was first released and can implement improved pipeline software.

Currently, for example, HST data are calibrated as they are received at the STScI. Raw and calibrated data are stored in the HST archive (DADS). Frequently, users must recalibrate the data at their home sites to take advantage of better calibration files or software. A large fraction (over 90%) of the calibrated data in the HST archive could be improved by recalibration, although the improvements are not always significant. In the past, instruments that undergo evolution of calibration files or calibration software often required users to carry out their own recalibrations at their home sites. With OTFC, the HST data archives carry out the recalibration.

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