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Figure 1 Click on image for higher resolution | Figure 2 Click on image for higher resolution |
The top image (figure 1) is the first global wet path delay map created
with data from the Advanced Microwave Radiometer (AMR) onboard the Ocean
Surface Topography Mission/Jason-2 satellite. The spacecraft, launched on
June 20, 2008, uses a radar altimeter to measure ocean height. The science
instruments on the spacecraft were turned on for the first time after
launch on June 22 and began returning data almost immediately. This map
shows the amount of water vapor in the atmosphere beneath the satellite
during the period June 22, 2008, to June 29, 2008.
Water vapor will delay the time it takes for the radar pulse from the
spacecraft's altimeter to travel to the ocean surface and back. By knowing
exactly how much water vapor is in the signal's path together with the time it
takes for the signal to bounce back, mission scientists can calculate the
exact distance between the satellite and the ocean surface. This
information along with the precise location of the spacecraft allows them
to determine the height of the sea surface to just a few centimeters from
measurements made 800 miles above Earth.
Like the altimeter, the radiometer looks straight down at the ocean
surface. It senses three microwave wavelengths: the signature thermal
signals emitted by water vapor, clouds and the ocean surface roughed up by
wind. The measurements at the three wavelengths are used together to
derive the total amount of water vapor present in the atmosphere in the
altimeter's path. In this image, blues represent dry areas where there is
little water to delay the radar signal and reds represent moist regions
where the signal will be slowed. The color index at the bottom shows the
path delay value in the map in units of centimeters.
The lower image (figure 2) is a wet path delay map created with data from
the Jason Microwave Radiometer (JMR) on the Jason-1 satellite collected
during the same time period. Jason-1 has been using an altimeter to
measure the height of the ocean since 2001. OSTM/Jason-2 and Jason-1 are
now flying in the same orbit, only 55 seconds apart, while mission
personnel ensure that the new satellite is working well and that its
measurements are accurate. The similarity between the two path delay maps
shows that the two radiometers are in close agreement.
When its calibration and validation period is complete, OSTM/Jason-2 will
remain in the orbit now occupied by Jason-1 and will continue the
long-term record of ocean surface topography begun by Topex/Poseidon in
1992 and carried on by Jason-1. Jason-1 will be moved to a new orbit
beside OSTM/Jason-2 to provide additional measurements of ocean surface
topography for as long as the older spacecraft remains healthy.
Both the radiometers onboard OSTM/Jason-2 and Jason-1 were built at NASA's
Jet Propulsion Laboratory, Pasadena, Calif.
OSTM/Jason-2 is a collaboration between NASA; the National Oceanic and
Atmospheric Administration (NOAA); CNES; and the European Organisation for
the Exploitation of Meteorological Satellites (EUMETSAT). After completing
the on-orbit commissioning of the spacecraft, CNES will hand over its
operation and control to NOAA. NOAA and EUMETSAT will generate the
near-real-time products and distribute them to users. JPL manages the
mission for NASA's Science Mission Directorate in Washington.
More information about the mission is available at http://sealevel.jpl.nasa.gov/.