will fly in tandem with ADEOS-2 in a complementary orbit to optimize the coverage by the two
scatterometers, if QuikSCAT has a long life. The
two SeaWinds instruments are expected to demonstrate the importance of high-wavenumber and
high-frequency forcing of the ocean. The European
Space Agency will fly a series of dual-swathe
C-band operational scatterometers, called ASCAT,
on the Meteorology Operational Platform
(METOP) beginning in 2003. NASA is planning to
supply an improved scatterometer to the Global
Change Observation Mission (GCOM), paving the
way for an operational scatterometer system. If
this project is approved, global ocean winds will
be monitored by at least two wide-swathe scatterometers at the same time, starting in 2001. The
goal is to have decadal time series of wind stress at
a resolution sufficient to resolve the inertial frequency in the mid-latitude ocean (Large and
Crawford, 1995) and diurnal variation in the tropical ocean (Large and Gent, 1999).
CERES, the Multiangle Imaging Spectroradiometer (MISR), and the Moderate-Resolution
Imaging Spectroradiometer (MODIS) on NASA’s
Terra mission, launched in December 1999, will
provide estimates of the radiative forcing. Similarly, two instruments (the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Global
Earth Radiation Budget (GERB) sensor) will be
available on the Meteosat Second Generation, the
next European geostationary satellite. There are a
number of improved atmospheric temperature and
humidity sounders such as AIRS and the Advanced
Microwave Sounding Units (AMSU) that have
improved spectral and vertical resolutions, scheduled to be launched early in the twenty-first
century. They may advance the estimation of
evaporation and the sensible and long-wave net
heat fluxes.
Following TMI, surface hydrologic forcing
(both evaporation and precipitation) can be estimated from the Advanced Microwave Scanning
Radiometer (AMSR); it is similar to TMI but has
more channels. One will be launched on the NASA
Mission Aqua and the other on ADEOS-2, scheduled for 2000 and 2001, respectively. A single
polar orbiter may not be able to provide sufficient
sampling for precipitation, but two AMSR instruments in complementary polar orbits should
improve the monitoring of the hydrologic forcing.
NASA is also planning a global precipitation
mission, with international partners, which would
expand the tropical rain-measuring capability of
TRMM to high latitudes.
Even from the vantage point of space, no single
polar-orbiting instrument can monitor air–sea
exchanges with sufficiently high resolution, extensive coverage, and frequent sampling, nor can any
single instrument be expected to operate for the
long period needed to acquire climate-relevant
time series. International and interagency cooperation and coordination is required for keeping an
optimal suite of sensors operational for a long
period of time.
Present general circulation models are structured
to be initialized by and to assimilate traditional
ground-based measurements. Space-borne sensors
do not measure the same parameters. For example,
space-based sensors measure radiance and
backscatter averaged over an area, while groundbased instruments measure wind and temperature
at a single location. Space-based data are forced to
imitate and are compared against ground-based
standards because of historical bondage. Innovative
and revolutionary approaches will be needed for
optimal utilization of space-based measurements.
Developments in four-dimensional assimilation of
the plethora of measurements coming on line will
eventually allow atmospheric models to be sufficiently constrained to provide the correct surface
fluxes. An important aspect for development is
that NASA has made the data freely available to
scientists; the European and Japanese space agencies are following suit, with their data freely available to a large research community. Linkage to
websites with data access and information can be
found at http://airsea-www.jpl.nasa.gov/seaflux.
Acknowledgements
The research was performed at the Jet Propulsion
Laboratory, California Institute of Technology,
under contract with NASA, and at the NOAA
Atlantic Oceanographic and Meteorological Laboratory. It was jointly supported by the Physical
Oceanography Program, the Earth Observing
System Interdisciplinary Science Program, the
QuikSCAT Project, and the TRMM Project of
NASA. Assistance by Ms Gail Derr with production of the manuscript is gratefully acknowledged.
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
180
scatterometers, if QuikSCAT has a long life. The
two SeaWinds instruments are expected to demonstrate the importance of high-wavenumber and
high-frequency forcing of the ocean. The European
Space Agency will fly a series of dual-swathe
C-band operational scatterometers, called ASCAT,
on the Meteorology Operational Platform
(METOP) beginning in 2003. NASA is planning to
supply an improved scatterometer to the Global
Change Observation Mission (GCOM), paving the
way for an operational scatterometer system. If
this project is approved, global ocean winds will
be monitored by at least two wide-swathe scatterometers at the same time, starting in 2001. The
goal is to have decadal time series of wind stress at
a resolution sufficient to resolve the inertial frequency in the mid-latitude ocean (Large and
Crawford, 1995) and diurnal variation in the tropical ocean (Large and Gent, 1999).
CERES, the Multiangle Imaging Spectroradiometer (MISR), and the Moderate-Resolution
Imaging Spectroradiometer (MODIS) on NASA’s
Terra mission, launched in December 1999, will
provide estimates of the radiative forcing. Similarly, two instruments (the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Global
Earth Radiation Budget (GERB) sensor) will be
available on the Meteosat Second Generation, the
next European geostationary satellite. There are a
number of improved atmospheric temperature and
humidity sounders such as AIRS and the Advanced
Microwave Sounding Units (AMSU) that have
improved spectral and vertical resolutions, scheduled to be launched early in the twenty-first
century. They may advance the estimation of
evaporation and the sensible and long-wave net
heat fluxes.
Following TMI, surface hydrologic forcing
(both evaporation and precipitation) can be estimated from the Advanced Microwave Scanning
Radiometer (AMSR); it is similar to TMI but has
more channels. One will be launched on the NASA
Mission Aqua and the other on ADEOS-2, scheduled for 2000 and 2001, respectively. A single
polar orbiter may not be able to provide sufficient
sampling for precipitation, but two AMSR instruments in complementary polar orbits should
improve the monitoring of the hydrologic forcing.
NASA is also planning a global precipitation
mission, with international partners, which would
expand the tropical rain-measuring capability of
TRMM to high latitudes.
Even from the vantage point of space, no single
polar-orbiting instrument can monitor air–sea
exchanges with sufficiently high resolution, extensive coverage, and frequent sampling, nor can any
single instrument be expected to operate for the
long period needed to acquire climate-relevant
time series. International and interagency cooperation and coordination is required for keeping an
optimal suite of sensors operational for a long
period of time.
Present general circulation models are structured
to be initialized by and to assimilate traditional
ground-based measurements. Space-borne sensors
do not measure the same parameters. For example,
space-based sensors measure radiance and
backscatter averaged over an area, while groundbased instruments measure wind and temperature
at a single location. Space-based data are forced to
imitate and are compared against ground-based
standards because of historical bondage. Innovative
and revolutionary approaches will be needed for
optimal utilization of space-based measurements.
Developments in four-dimensional assimilation of
the plethora of measurements coming on line will
eventually allow atmospheric models to be sufficiently constrained to provide the correct surface
fluxes. An important aspect for development is
that NASA has made the data freely available to
scientists; the European and Japanese space agencies are following suit, with their data freely available to a large research community. Linkage to
websites with data access and information can be
found at http://airsea-www.jpl.nasa.gov/seaflux.
Acknowledgements
The research was performed at the Jet Propulsion
Laboratory, California Institute of Technology,
under contract with NASA, and at the NOAA
Atlantic Oceanographic and Meteorological Laboratory. It was jointly supported by the Physical
Oceanography Program, the Earth Observing
System Interdisciplinary Science Program, the
QuikSCAT Project, and the TRMM Project of
NASA. Assistance by Ms Gail Derr with production of the manuscript is gratefully acknowledged.
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
180