OCS Field Descriptions
- Start Time
- The Earth Receive Time at which
the first radio occultation data sample was acquired.
- Stop Time
- The Earth Receive Time at which
the last radio occultation data sample was acquired.
- Occultation Time
- The time at Mars when the
geometrical ray path grazed the limb. This is computed
by subtracting the limb-to-Earth light time from the
appropriate Earth Receive Time.
- Orbit Number
- Orbit number from which the data
were acquired; set to zero if not known.
- DSN Antenna Number
- Number of the DSN antenna used
to collect the data (e.g., 14, 43, 65, ...).
- Ray Path Direction
- The angle between local north
and the tangent to the ray path at the occultation point,
measured positive from local north toward local east. The
tangent to the ray path indicates the direction of signal
propagation. A signal traveling from west toward east as
it grazed the surface would have a ray-path-direction of
90 degrees.
- Angle From Diametric
- Angle at which the spacecraft
rises or sets behind the planet limb, measured clockwise from
the planet radial direction as viewed from Earth. An
angle-from-diametric equal to zero indicates a diametric occultation
with motion of the ray away from the surface (e.g., occultation
egress). A value near 180 degrees is a nearly diametric ingress
occultation.
- Latitude at Surface
- Areocentric (north) latitude of
the occultation point.
- Sigma Latitude
- One standard deviation uncertainty
in LATITUDE AT SURFACE. Set to -9.999 if not known.
- Longitude at Surface
- Areocentric east longitude of the
occultation point in body fixed coordinates.
- Sigma Longitude
- One standard deviation uncertainty
in LONGITUDE AT SURFACE. Set to -9.999 if not known.
- Sub-Solar Latitude
- Areocentric (north) latitude of
the sun at OCCULTATION TIME.
- Sub-Solar Longitude
- Areocentric east longitude of the
sun in body fixed coordinates at OCCULTATION TIME.
- Solar Longitude
- Value of the angle between the
Mars-Sun line at the time of geometric occultation and the
Mars-Sun line at the Mars vernal equinox. Measured positive
with increasing time following the vernal equinox. Sometimes
denoted L-sub-s.
- Radius at Surface
- Radius of Mars at the occultation
point.
- Sigma Radius
- One standard deviation uncertainty
in RADIUS AT SURFACE. Set to -9999. if not known.
- Surface Pressure
- Atmospheric pressure at the
occultation point -- i.e., at the point defined by RADIUS AT
SURFACE, LATITUDE AT SURFACE, and LONGITUDE AT SURFACE.
Obtained by extrapolating from the lowest sample in the retrieved
atmospheric profile to the estimated RADIUS AT SURFACE.
- Sigma Surface Pressure
- One standard deviation uncertainty
in SURFACE PRESSURE. Set to -9.99 if not known.
- Temperature Near Surface
- Atmospheric temperature at lowest
sample in temperature-pressure profile. Note that the height
of this sample above the surface varies among profiles. No
attempt has been made to extrapolate to surface because thermal
structure of boundary layer varies strongly with local time.
- Sigma Temperature Near Surface
- One standard deviation uncertainty
in TEMPERATURE NEAR SURFACE.
- Spacecraft to Limb Distance
- Distance from spacecraft to
occultation point at time when ray path grazed planetary
surface.
- Spacecraft to DSN Distance
- Distance from spacecraft to DSN
receiving antenna at time when ray path grazed planetary
surface.
- Local True Solar Time of Occultation
- Local true solar time (LTST) at the
time and location of the occultation measurement. LTST at the
sub-solar longitude is defined as 12 solar hours. LTST on other
meridians changes by one solar hour for each 15 degree increment
in longitude. Thus, LTST for the occultation measurement is
given by 12 + (LONGITUDE_AT_SURFACE - SUB-SOLAR_LONGITUDE)/15.
- Solar Zenith Angle
- Angle between the direction to Sun
and local vertical direction on Mars at time and location of the
occultation measurement.
- Sun-Earth-Spacecraft Angle
- Approximate angle between Sun and
spacecraft as viewed from Earth during experiment.
- DSN Elevation Angle
- Approximate angle between
direction to spacecraft and local horizon at DSN receiving
antenna during experiment.
- Gravity Field Model
- File name of gravity field spherical
harmonic model used in profile retrieval and calculation of
geopotential.
- Geopotential Reference
- Reference value for geopotential.
Reference geoid has mean equatorial radius of 3396 kilometers.
- PCK File Name
- File name of the NAIF Planetary
Constants File used in this retrieval and calculation (name
of the PCK file as stored in the MGS RST data system).
- Trajectory File Name
- File name of the spacecraft and
planetary ephemeris file used in this retrieval and calculation
(name of the file as stored in the MGS RST data system).
- Spacecraft Attitude File Name
- File name of the spacecraft
attitude file used in this retrieval and calculation (name
of the file as stored in the MGS RST data system). Left
blank if not known or no attitude file was used.
- TPS File Name
- File name of complete temperature-pressure
profile from which these parameters derive.
Last updated: November 04, 1998
Joe Twicken