PODPS; sometimes called OPUS, and usually just called the "pipeline"), photometric calibration derived from standard star observations and the measured filter profiles, and derived determinations of the plate scale, distortion, and so on. The first set of these calibrations was provided to the STScI by the WFPC2 IDT from the Servicing Mission Observatory Verification (SMOV) and System Level Thermal Vacuum (SLTV) testing periods, and has been maintained and updated thereafter by the STScI with assistance from the IDT as part of the long term calibration program. For measurements requiring more precise calibrations, special calibration observations may need to be obtained as part of the observing proposal. Please consult the STScI WFPC2 Instrument Scientists for guidance if the routine calibration appears unlikely to support the requirements of a proposed observation. Individual GO programs requiring special calibrations must directly request these observations as part of their Phase I proposal.
A database of laboratory characterizations of optical components, CCD sensors, filters, and the flat field channel has been collected to support the instrument calibration. On-orbit pointed calibrations require large HST resources, taking time that could otherwise be used for direct scientific observations. They can also be unsatisfactory due to the limitations of the available astronomical reference sources. For WFPC2, the inherent stability and uniformity of the CCD sensors, the well calibrated filters, the internal flat field calibration system, and an archive populated with flat field images obtained in SLTV prior to launch improve the scientific data analysis and productivity. Hence the need for on-orbit calibrations has been minimized.