Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
A range-gated underwater laser imaging system is designed and implemented in this article, which is made up of laser illumination subsystem, photoelectric imaging subsystem and control subsystem. The experiment of underwater target drone detection has been done, the target of distance 40m far from the range-gated underwater laser imaging system can be imaged in the pool which water attenuation coefficient is 0.159m<sup>-1</sup>. Experimental results show that the range-gated underwater laser imaging system can detect underwater objects effectively.
Range-gated underwater laser imaging system is a kind of underwater photoelectric imaging system which is based on the principle of time label for target. Through controlling the imaging time of photoelectric equipment precisely, it can effectively restrain the backscatter of water, having longer detective distance than generic ones. A range-gated underwater laser imaging system consists of pulse laser illumination system, photoelectric imaging system (ICCD) and control system commonly. When the moment and the time of ICCD opening gate are given, the lights that could be received by ICCD include the backscatter of water, the direct component and forward scatter of reflected light of the target in the imaging processing of range-gated underwater laser imaging system. Computing model of light energy received by ICCD was built in this paper. The direct component and forward scatter of reflected light energy were analyzed and the calculation methods based on PSF theory were studied. The backscatter light energy of water was calculated through water layering. The signal to noise ratio of range-gated underwater laser imaging system was defined. The impact of target range, target reflection ratio, ICCD gating width and water attenuation coefficient on the signal to noise ratio were analyzed and simulation results were given.
There is currently considerable in developing underwater target detection, the underwater imaging
system can be divided into active imaging system and passive system. The main feature of the active
imaging system is that they use light sources to illuminate the targets and collect the reflection from
targets. The advantages of active imaging system over passive imaging systems are high contrast and
without the affection of environment sources. In this article, a range-gated underwater laser imaging
system is built, which consists of laser illumination system, photoelectric imaging system and control
system. The laser illumination system includes a light-pumped solid state doubled ND-YAG
laser(532nm) which laser power and frequency can be adjusted and an optics expanding system of
variable ratio. The photoelectric imaging system includes a gated Intensified CCD(ICCD) cameras
which ICCD scheduling, gate width, delay time and gain can be adjusted and a optics received system
of variable ratio. In order to acquire effectual target image using range-gated underwater laser imaging
system, appropriate control parameters that include laser power and frequency, ICCD scheduling, gate
width, delay time and gain, optics expanding system ratio and optics received system ratio must be given accurately. A control system which used C8051F320 and C8051F040 (MCU) as the core is designed, the control system can effectively control seven parameters that given above. The construction of software and hardware of the control system is introduced. And target image of underwater distance 25 m and 40m is given, Experimental results showed that the control system has high control precision, safe and stable operation and good speed adjusting performance can be achieved. It can be satisfied to apply to underwater target detection.
A new kind of underwater imaging system is introduced, called double-channel
imaging system, to both improve the detection distance and solve the problem of inherent delay. A
image processing subsystem built on TMS320DM642 DSP is in charge of the two channel videos.
And software algorithm is used to degrade the noise and improve the contrast of the videos before
they are displayed on the monitor. The trails show that images can be acquired at long distance
and very close distance. The quality of the images are greatly improved through the image