Envisat ASAR images are used to observe atmospheric gravity waves over the East China Sea. Several case studies are
presented in detail. It is shown that the atmospheric gravity waves are well organized in the form of wave packets. The
wavelengths are ranging from 0.5 to 10 km. The atmospheric gravity waves locate near the stationary meteorological
fronts. The generation mechanism is discussed.
It is well known that synthetic aperture radars (SARs) can image oceanic internal waves (OIWs). The signatures of
OIWs on SAR images result from the modulation of wind-generated surface waves by the surface currents associated
with the OIWs. The role of surface winds in SAR signatures of OIWs in the northern South China Sea is examined using
SAR images and BlendQscat wind data. A radar imaging model for simulating SAR signatures of OIWs is also used to
estimate the dependence of the radar signatures associated with OIWs on wind conditions. The results show that the
signatures of OIWs on SAR images in the northern South China Sea are highly dependent on the wind speed. The
temporal variations of the OIWs observed by SAR are closely related with the temporal variations of the wind speed in
the study area.
A new method for mapping shallow water topography surface currents from SAR image is introduced based on the
shallow water topography SAR imaging mechanism. M4S (presented by Romeiser R.) was used to forward simulate
radar signatures of the oceanic features over the ocean surface. The first guessed surface currents can be estimated from
the normalized radar cross section (NRCS) of the shallow water topography profile in the SAR image according to the
Apers-Hennings linear theory, the NRCS induced by the varying shallow water topography surface currents could be
simulated by the forward simulating model. The wind speed and shallow water topography surface currents gradients are
modified using the iterative method until the simulated radar signals close to the NRCS calculated from SAR image. By
this method, the wind speed and the surface currents can be retrieved finally. This method is tested on an ERS-2 SAR
image in the Taiwan Shoal. Results show that the simulated shallow water topography radar signal is consistent with the
NRCS extracted from SAR image, and their correlation coefficient is up to 90%, which means that this method is
convergent and applicable.
A new method for retrieving shallow water topography surface currents from SAR image is introduced based on the
shallow water topography SAR imaging mechanism. M4S was applied to forward simulate radar signatures of the
oceanic features over the ocean surface. The first guessed surface currents can be estimated from the normalized radar
cross section (NRCS) of the shallow water topography profile in the SAR image according to the AH linear theory, the
NRCS induced by the varying shallow water topography surface currents could be simulated by the forward simulating
model. The wind speed and shallow water topography surface currents gradients are modified using the iterative method
for the simulated radar signals close to the NRCS calculated from SAR image. Finally, the wind speed and the surface
currents can be retrieved. This method is tested on an ERS-2 SAR image in the Taiwan Shoal. The result shows that the
simulated shallow water topography radar signal is consistent with the NRCS measured from SAR image, and their
correlation coefficient is up to 90%, which means that this method is convergent and applicable.
This paper discusses the relationship between the observations of submarine sand wave SAR images in Taiwan shoal and
sea surface wind. A total of 43 SAR images over 11 years are collected and 496 profiles of sand wave SAR images are
used, the wind are estimated from blended wind data and current direction is from mode. Results show submarine sand
waves are observed by SAR under wind speed of 10 m/s, only littlie are imaged above 10 m/s. The number of observed
sand waves reaches its maximum under the adverse wind direction, while the crosswind has its minimum. These support
that low and middle wind speed and adverse wind direction are favorable for SAR imaging submarine sand waves, high
wind speed and crosswind are unfavorable. The comparison between monthly mean wind speed and sand waves
observed by SAR also shows a strong correlation between both, which is lower wind speeds, the higher probability of
sand waves observed by SAR. This may indicate that the higher observation of the sand waves by SAR is partly due to
wind speed.
Based on the Kelvin ship wake mode, the ocean wave mode and the two-scale mode for electromagnetic scattering from
rough surfaces, we propose a new method of simulation for Kelvin ship wake imaging by multi-look direction SAR. We
have simulated the VV normalized radar backscattering cross-section (NRCS) of the ship wakes from different look
directions in 2-D space firstly. The results show that the transverse waves can be viewed clearly when the radar look
direction is parallel to the ship's track direction, while the divergent waves can be viewed clearly when the radar look
direction is perpendicular to the ship's track direction. When the radar look direction is neither perpendicular nor parallel
to the ship's track direction, Kelvin arms are imaged as a bright line and a dark line according to the relationship between
spread direction of crest waves and ship's track direction. The waves whose track direction is more parallel to the ship's
track direction can be imaged as a brighter line. Moreover, the simulation results also draw this conclusion another, when
radar look direction is more near perpendicular to the ship's track direction, the angle between two Kelvin arms is
smaller as a result of these circumstances gunpoint at the stern wave scattering cross-section is as large as bow wave. It's
show that the simulated results agree quite well with the ERS-1/2 images.
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