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L.M. Mitnik and V.A. Dubina
crests exceeded 350 km. The leading soliton of the second packet intrudes the rear
of the first packet that does not allow estimating the number of waves in the wave
packet and its width. The wavelength of the solitons monotonically decreases from
about 15 km to about 2 km in the rear of packet. The SAR images suggest a tidal
generation mechanism. The tide at the sill region is predominantly semi-diurnal
and estimates of the waves’ phase speed can be derived by measuring the distance
between the first solitons in the successive packets. Detailed examination shows that
the phase velocity increases from 2.4–2.6 m/s (propagation direction WNW-NNW)
to 2.9–3.1 m/s (N-NNE) and then decreases to 2.7 m/s (NE). These variations can
be caused by the differences in water properties along propagation directions.
Similar results were obtained by the analysis of medium-resolution MERIS, and
MODIS data and high-resolution SPOT and Landsat data. Figure 7.12a shows IWs
in the Banda Sea as seen in a MODIS image acquired on 30 September 2009. The
same area was sensed by Landsat-7 ETM+ 25 min before MODIS. The velocity
of the IWs, estimated by an analysis of the co-located MODIS and ETM+ images,
was about 3–3.2 m/s for leading solitons in the packets. Very likely, the detailed
study of the brightness field spatial structure in panchromatic Landsat images
(resolution 15 m × 15 m) will provide information about both the slope distribution of the surface waves and intensity of wave breaking. In turn, data on wave
breaking and whitecap/foaming induced by wind action, variable currents and other
causes are required for advancing radar backscatter theory.
7.5 Conclusions
With the recent launch of the new generation SARs (ALOS PALSAR L-band,
TerraSAR-X, and COSMO-SkyMed X-band and RADARSAT-2 C-band) and the
availability of high- and low-resolution visible, IR and passive/active microwave
sensors (Landsat-ETM+, MODIS, MERIS, AMSR-E, QuikSCAT, etc.), multisensor technology has become a reality in a growing series of oceanic and
atmospheric applications. SAR data in synergy with optical, IR and microwave
data can provide a better insight into oceanic and atmospheric processes at different scales with improved temporal resolution. Optical data are relatively easily
available, the measured parameters are more familiar and an extensive established
knowledge base for processing exists. Spaceborne SAR provides finely detailed
imagery of the ocean’s surface, which is the most complex and least understood
data provided by remote sensors. The sea surface can contain the signatures of surface currents, eddies, sea ice, IWs, examples of which were considered in the paper,
as well as such diverse phenomena as upwelling, shallow water bathymetry, wind,
mesoscale convective rolls and cells, atmospheric gravity waves, rains, storms, etc.
Variations of radar contrasts and superposition of signatures of various nature,
depending on several environmental factors, hinder their interpretation.
The fusion of multi-sensor and multi-resolution satellite imagery has become
an effective mean of exploiting the complementary nature of various images types,
improving our understanding of the geophysical content of SAR images and the
L.M. Mitnik and V.A. Dubina
crests exceeded 350 km. The leading soliton of the second packet intrudes the rear
of the first packet that does not allow estimating the number of waves in the wave
packet and its width. The wavelength of the solitons monotonically decreases from
about 15 km to about 2 km in the rear of packet. The SAR images suggest a tidal
generation mechanism. The tide at the sill region is predominantly semi-diurnal
and estimates of the waves’ phase speed can be derived by measuring the distance
between the first solitons in the successive packets. Detailed examination shows that
the phase velocity increases from 2.4–2.6 m/s (propagation direction WNW-NNW)
to 2.9–3.1 m/s (N-NNE) and then decreases to 2.7 m/s (NE). These variations can
be caused by the differences in water properties along propagation directions.
Similar results were obtained by the analysis of medium-resolution MERIS, and
MODIS data and high-resolution SPOT and Landsat data. Figure 7.12a shows IWs
in the Banda Sea as seen in a MODIS image acquired on 30 September 2009. The
same area was sensed by Landsat-7 ETM+ 25 min before MODIS. The velocity
of the IWs, estimated by an analysis of the co-located MODIS and ETM+ images,
was about 3–3.2 m/s for leading solitons in the packets. Very likely, the detailed
study of the brightness field spatial structure in panchromatic Landsat images
(resolution 15 m × 15 m) will provide information about both the slope distribution of the surface waves and intensity of wave breaking. In turn, data on wave
breaking and whitecap/foaming induced by wind action, variable currents and other
causes are required for advancing radar backscatter theory.
7.5 Conclusions
With the recent launch of the new generation SARs (ALOS PALSAR L-band,
TerraSAR-X, and COSMO-SkyMed X-band and RADARSAT-2 C-band) and the
availability of high- and low-resolution visible, IR and passive/active microwave
sensors (Landsat-ETM+, MODIS, MERIS, AMSR-E, QuikSCAT, etc.), multisensor technology has become a reality in a growing series of oceanic and
atmospheric applications. SAR data in synergy with optical, IR and microwave
data can provide a better insight into oceanic and atmospheric processes at different scales with improved temporal resolution. Optical data are relatively easily
available, the measured parameters are more familiar and an extensive established
knowledge base for processing exists. Spaceborne SAR provides finely detailed
imagery of the ocean’s surface, which is the most complex and least understood
data provided by remote sensors. The sea surface can contain the signatures of surface currents, eddies, sea ice, IWs, examples of which were considered in the paper,
as well as such diverse phenomena as upwelling, shallow water bathymetry, wind,
mesoscale convective rolls and cells, atmospheric gravity waves, rains, storms, etc.
Variations of radar contrasts and superposition of signatures of various nature,
depending on several environmental factors, hinder their interpretation.
The fusion of multi-sensor and multi-resolution satellite imagery has become
an effective mean of exploiting the complementary nature of various images types,
improving our understanding of the geophysical content of SAR images and the