Spacecraft Z spatial coordinate, relative to the geocentric terrestrial reference frame, in meters, at the mid-point of the exposure, using the J2000 (ECI) coordinate system. 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_Z 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_Z 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_Z 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_Z geocentric value is used. In the unlikely case that neither ephemeris type has bracketing data, the JWST_Z 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 | meters |
| example | |
| default value | |
| special processing | VALUE_REQUIRED |
| source | Science Data Processing (SDP) |
| software source | |
| calculation | The JWST_Z geocentric value obtained from the observatory ephemeris data is converted from km to m and assigned to OBSGEO-Z. |
| DB destination | ['ScienceCommonExt.obsgeo_z', 'GuideStarExt.obsgeo_z'] |
| data type in DB | float |
| instrument | ALL |
| mode | All |
| product level | 1b |
| FITS hdu | SCI |
| FITS header section | Ephemeris |