DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

saturation
Satellite ephemeris, r
Altimetric satellite
h, Observed satellite altitude
h DSSH
h MSS
r el , Reference ellipsoid height
Earth’s center of mass
Fundamental measurements of satellite altimetry.
from the station, reflecting it from the prisms,
and receiving the reflected laser beam. Since
the location of the satellite can be determined
independently, geodetic location of the station
can be determined within an accuracy of several
centimeters if the two-point distances are measured
for at least three different locations of the
satellite. Such observations are currently carried
out at different stations in the world; one
application is to measure the relative motion of
tectonic plates. Satellite laser ranging is also
used to provide information on Earth rotation
and Earth orientation.
saturation See current saturation.
saturation adiabat A type of adiabatic process
in movement of saturation moist air. Under
the saturation adiabatic condition, when a saturated
air parcel ascends, part of the vapor will
condense to water or ice, and the air parcel will
be still saturated. The latent heat released partly
compensates the ascending adiabatic cooling,
and the condensed water or ice remains in the
saturated air parcel.
saturation adiabatic lapse rate The adiabatic
cooling rate of rising air parcel which is
saturated, and in which condensation is taking
place as it rises, so that the latent heat release
moderates the adiabatic cooling, and causes the
saturation adiabatic lapse rate to be less than
the dry adiabatic lapse rate. The saturation adiabatic
lapse rate is not a constant, and varies
inversely with the temperature and somewhat
with change of pressure. The difference between
the saturation adiabatic lapse rate and dry
adiabatic lapse rate is determined by the possibly
released latent heat. Since the temperature at
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higher level atmosphere is lower, the saturation
adiabatic lapse rate has a smaller value at low
level and larger value at high level which can
approach or equal the dry adiabatic lapse rate.
saturation vapor pressure The pressure exerted
by the water vapor which is equilibrium
with its condensed phase, which may be water
or ice, the moist surface (or ice surface) saturation
vapor pressure. In this state the same number
of water molecules leave the water (ice) into
the air as move from the air into the water (ice).
Saturation vapor pressure is only a function of
temperature. Its formula for water surface is
E = E0 10 7.45t/(t+235)
where E is saturation vapor pressure, E0 =
6.1078 hPa, is the saturation vapor pressure at
0 ◦ C, t is vapor temperature( ◦ C).
The ice surface saturation vapor pressure is
E = E0 10 9.5t/(t+265) .
Saturn The sixth planet from the sun. Named
after the Roman elder god of agriculture, Saturn
has a mass M = 5.6841 × 10 29 g, and an
equatorial radius of R = 60,330 km, giving it a
mean density of 0.71 g cm −3 and a surface gravity
of 1.08 that of Earth. Its rotational period is
10 h 14 min. The rotation axis has an obliquity
of 26.7 ◦ . The rapid rotation gives the planet an
oblateness of 0.09. Saturn’s orbit around the sun
is characterized by a mean distance of 9.54 AU,
an eccentricity of e = 0.056, and an orbital inclination
of i = 2.5 ◦ . Its sidereal period is 29.46
years and its synodic period is 378 days. Its average
albedo is 0.47 but its atmospheric temperature
is determined by an internal heat source.
At one bar the temperature is about 140 K and
increases inward. Saturn is a “gas giant” being
composed primarily of hydrogen and helium and
is the least dense, most oblate planet in the solar
system. Saturn has prominent rings composed
of large particles and numerous moons including
Pan, Atlas, Prometheus, Pandora, Epimetheus,
Janus, Mimas, Enceladus, Tethys, Telesto, Calypso,
Dione, Helene, Rhea, Titan, Hyperion,
Iapetus, and Phoebe.
scalar A function or physical property that
depends only on the position and time at which it