The traditional methods to detect underwater objects are based on the acoustic detecting techniques. However, since the
transmutation of the sound wave in ocean is often influenced by the oceanic boundary conditions and ambient factors
such as salinity, temperature and pressure of the sea water, acoustic detecting techniques will cause large error in
orientation and direction, which makes it difficult to capture and discriminate small objects. Instead, the photoelectric
detection technology for underwater objects has the advantages of precise direction and orientation due to the high
propagation velocity of light in water, consequently, the influence of ambient factors can be negligible. In this paper, we
described the theory of underwater photoelectric detection and the system structure. Two kinds of experimental system
are set up. One is imaging photoelectric detecting system; the other is non-imaging photoelectric detecting system. The
underwater photoelectric detecting systems are made up of a short pulsed laser, a received optical system, narrowband
optical filters, high-speed photoelectric detectors, a high-speed data acquisition and processing system etc. Both of the
imaging and non-imaging photoelectric systems are employed to detect the reflection of target plane and simulated ship
wakes. The key factors that affect the detection performance are analyzed in the paper. The experimental results show
that for the imaging system, utilizing range-gated techniques can decrease the interference from background optical
noise, while for the non-imaging system, using combining filters can suppress the backscattered optical noise from water.
The conclusion is that both imaging and non-imaging photoelectric detection system are suitable for detecting
underwater objects or their wakes.