ATSIS
for measuring 3D breaking waves (Wanek and Wu,
2006)
TSV
software (Bechle and Wu, 2007)
A novel Automated Trinocular Stereo Imaging System (ATSIS) is
developed
for non-intrusively measuring temporal evolution of
three-dimensional
wave
characteristics. The system consists of three progressive digital
cameras
to provide three independent stereo-pairs, i.e., left-right,
left-center,
and center-right, for accurately estimating depth of a scene. A
third
camera
assists to resolve correspondence problems due to specular
reflection
on
the water surface and provides additional constraints on image
matching,
dramatically reducing the chance of a mismatch. An oblique
configuration
for the trinocular system effectively increases spatial coverage,
allowing
observations of wave phenomena over a broad range of spatial scales.
A
new exterior calibration procedure is also developed to determine
the
orientation
of cameras in the field. The height resolution is increased with the
optical
axes of the cameras pointed at an oblique angle with respect to
vertical
surface wave displacements. Results
for a 3D breaking wave evolution can be seen here. A software
package, Trinocular Stereo Vision
(TSV), has been developed to faciliate the tedious/challenging tasks
of
camera calibration
and steroe matching on moving surfaces. The combination of
ATSIS
and TSV assists us to realize four dimensional surface wave or solid body motion measurements.
In recent years, a virtual wave gauge (VWG) technique based on
stereo
imaging is developed to remotely measure water wave height, period,
and
direction. VWG minimizes computational costs by directly tracking
the
elevation of the water surface at selected points of interest using
an
Eulerian based dynamic searching algorithm. Results show that the
VWG
technique developed in this paper dramatically improves efficiency
by
two orders of magnitude compared to the traditional
Lagrangian-Eulerian
based point cloud method of stereo image processing. VWG is tested
against traditional wave wire gauges to within 98% accuracy for
significant wave height. Furthermore, the flexibility of the VWG is
demonstrated in several field applications. For example in an
offshore
breaking wave case, an array of VWGs is used to efficiently measure
wave directionality. Furthermore to investigate the reflection
coefficient of a rock-mounted structure interacting with nearshore
waves, linear and spatial VWG arrays are designed and implemented
based
on a priori information of the wave field from a preliminary VWG
measurement. Overall, we demonstrate that the VWG technique has the
flexibility and computational efficiency to potentially make
real-time
remote stereo imaging wave measurements a reality.
References:
Bechle, A.J. and Wu, C.H., Virtual wave gauges based upon
stereo
imaging for measuring surface wave characteristics, Coastal
Engineering, Coastal Engineering, 58(4), 305-316, 2011.
Wanek, J.M. and Wu, C.H., Automated trinocular stereo imaging
system
for three-dimensional surface wave measurements, Ocean
Engineering,
33(5-6)
723-747, 2006.
