OBSGEO-Z

[m] geocentric JWST Z coordinate at MJD-AVG

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