  The scattering of light observed through the turbid underwater channel is
often regarded as the leading challenge when designing underwater
electro-optical imaging systems. There have been many approaches to address the
effects of scattering such as using pulsed laser sources to reject scattered
light temporally, or using intensity modulated waveforms and matched filters to
remove the scattered light spectrally. In this paper, a new method is proposed
which primarily uses the backscattering asymmetry property for object detection
and geometric profiling. In our approach, two parallel and identical continuous
wave (CW) laser beams with narrow beam widths (~2mm) are used as active
illumination sources. The two beams also have controllable spacing and aiming
angle, as well as initial phase difference for convenience of scanning and
profiling a target. Through theory and experimental results, it will be shown
that when an object leans or tilts towards one of the beam's central
trajectory, the asymmetry in the backscattered signals can be used to indicate
the location or slope of the target's surface, respectively. By varying the
spacing or aiming angle of the two beams, a number of surface samples can be
collected to reconstruct the object's shape geometrically. The resolution and
range limit of our approach are also measured and reported in this work. In
application, our proposed method provides an economic solution to perform
imaging through turbid underwater environments. Additionally, the idea can be
combined with the pulsed or modulated laser signals for enhanced imaging
results.
