Z component of the JWST velocity vector, relative to the geocentric terrestrial reference frame, in meters/second, at the mid-point of the exposure in the J2000 (ECI) coordinate system, which is an Earth-centered inertial frame defined by the Earth's mean equator and equinox on 2000-Jan-01. Science Data Processing code (SDP) obtains this from the observatory ephemeris data according to the following precedence: When the definitive ephemeris contains data bracketing and within 60 seconds of the exposure's MJD-AVG time, the JWST_DZ geocentric value is linearly interpolated from that data. If there is only definitive ephemeris data prior to but still within 60 seconds of the exposure's MJD-AVG time, that JWST_DZ geocentric value is used. Otherwise, if the predicted ephemeris contains data bracketing and within 60 seconds of the exposure's MJD-AVG time, the JWST_DZ geocentric value is linearly interpolated from that data. If there is only predicted ephemeris data prior to but still within 60 seconds of the exposure's MJD-AVG time, that JWST_DZ geocentric value is used. In the unlikely case that neither ephemeris type has bracketing data, the JWST_DZ geocentric value used is the definitive or predicted (in that order of precedence) ephemeris value at the latest ephem_time that is prior to the exposure's MJD-AVG time.
| Attribute | Value |
|---|---|
| data type | float |
| enumerated Values | not defined |
| units | m/sec |
| example | |
| default value | |
| special processing | VALUE_REQUIRED |
| source | Science Data Processing (SDP) |
| software source | |
| calculation | The JWST_DZ geocentric value obtained from the observatory ephemeris data is converted from km/s to m/s and assigned to OBSGEODZ. |
| DB destination | ['ScienceCommonExt.obsgeodz', 'GuideStarExt.obsgeodz'] |
| data type in DB | float |
| instrument | ALL |
| mode | All |
| product level | 1b |
| FITS hdu | SCI |
| FITS header section | Ephemeris |