THE NEAR-SURFACE LAYER OF THE OCEAN
ocean surface (for instant with SSM/I) is not affected by clouds, but its
accuracy is far below that of infrared sensors. Also, rains affect the
microwave measurement by modification of the sea surface reflectance.
The fundamental approach to address the problem of cloud interference
of SST measurements is to enhance the remote sensing techniques with
mixed-layer modeling capable of reproducing diurnal warming and
precipitation effects (as well as the cool skin) and being forced with
remotely sensed heat and momentum fluxes (Soloviev and
,
2001). This approach, however, requires assimilation of multi-satellite and
multi-sensor data. Several issues have yet to be resolved for this approach.
Substantial progress has been made in the development of remote sensing
techniques for latent and sensible heat fluxes with accuracies of satellite
products approaching the accuracy of buoy and shipboard bulk-flux
measurements (Benthamy et al., 2003; Jo et al., 2004).
7.1.3 Sea surface salinity
The measurement of the sea surface salinity from space can significantly
improve understanding of ocean circulation, air–sea interaction, and the
global climate as a result (Lagerloef et al., 1995; Topliss et al., 2002). The
water emissivity in the microwave range depends on salinity. In the long
wavelength end of the microwave spectrum (L or C band), the response due
to changes in salinity is sufficiently strong to distinguish from the
temperature dependence though it is still a second order effect. In order to
obtain adequate resolution at the surface for longer wavelengths, large
antennas must be placed in space.
The measurement of salinity from space becomes more practical with
the emergence of aperture synthesis, the new microwave radiometer
technology that does not require such large antennas. Le Vine et al. (1998)
have shown the theoretical possibility of measuring sea surface salinity with
airborne synthetic aperture radar. Figure 7-3 compares remote (airborne) and
shipboard measurements of sea surface salinity made by these authors in the
vicinity of the Delaware coastal current. The remote sensing measurements
were made from an aircraft with the Electronically Scanned Thinned Array
Radiometer (ESTAR), which is an L-band synthetic aperture microwave
radiometer. Both thermosalinograph- and microwave radiometer–derived
salinity maps clearly show the freshwater signature of a coastal current and
generally are in agreement to within about 1 psu
The sensors working in the L (O = 24 cm) and C (O = 6 cm) bands
receive signals from approximately the upper 12 cm and 3 cm of the ocean
respectively. Increasing the accuracy of salinity remote sensing will require
incorporation of detailed knowledge of near-surface salinity structure into
444
Schl ssel
ü
ocean surface (for instant with SSM/I) is not affected by clouds, but its
accuracy is far below that of infrared sensors. Also, rains affect the
microwave measurement by modification of the sea surface reflectance.
The fundamental approach to address the problem of cloud interference
of SST measurements is to enhance the remote sensing techniques with
mixed-layer modeling capable of reproducing diurnal warming and
precipitation effects (as well as the cool skin) and being forced with
remotely sensed heat and momentum fluxes (Soloviev and
,
2001). This approach, however, requires assimilation of multi-satellite and
multi-sensor data. Several issues have yet to be resolved for this approach.
Substantial progress has been made in the development of remote sensing
techniques for latent and sensible heat fluxes with accuracies of satellite
products approaching the accuracy of buoy and shipboard bulk-flux
measurements (Benthamy et al., 2003; Jo et al., 2004).
7.1.3 Sea surface salinity
The measurement of the sea surface salinity from space can significantly
improve understanding of ocean circulation, air–sea interaction, and the
global climate as a result (Lagerloef et al., 1995; Topliss et al., 2002). The
water emissivity in the microwave range depends on salinity. In the long
wavelength end of the microwave spectrum (L or C band), the response due
to changes in salinity is sufficiently strong to distinguish from the
temperature dependence though it is still a second order effect. In order to
obtain adequate resolution at the surface for longer wavelengths, large
antennas must be placed in space.
The measurement of salinity from space becomes more practical with
the emergence of aperture synthesis, the new microwave radiometer
technology that does not require such large antennas. Le Vine et al. (1998)
have shown the theoretical possibility of measuring sea surface salinity with
airborne synthetic aperture radar. Figure 7-3 compares remote (airborne) and
shipboard measurements of sea surface salinity made by these authors in the
vicinity of the Delaware coastal current. The remote sensing measurements
were made from an aircraft with the Electronically Scanned Thinned Array
Radiometer (ESTAR), which is an L-band synthetic aperture microwave
radiometer. Both thermosalinograph- and microwave radiometer–derived
salinity maps clearly show the freshwater signature of a coastal current and
generally are in agreement to within about 1 psu
The sensors working in the L (O = 24 cm) and C (O = 6 cm) bands
receive signals from approximately the upper 12 cm and 3 cm of the ocean
respectively. Increasing the accuracy of salinity remote sensing will require
incorporation of detailed knowledge of near-surface salinity structure into
444
Schl ssel
ü