Images associated with underwater imaging systems are normally degraded by the intervening water medium. The
imaging instrument records not only the signal of interest, i.e., the radiance diffusely reflected from underwater target,
but also the radiance scattered into the field of view by water molecule and particulates. In order to improve the system
performance, range gated underwater imaging system is used to enhance image quality and visibility in turbid conditions.
Range gated imaging utilizes time discrimination to improve signal-to-backscattering noise ratio by rejecting
backscattered light from the medium. The range gated underwater imaging system basically consists of a pulsed laser
system, a control and synchronous logics and a high-speed gated camera. Because a laser is a highly coherent light
source, speckle noise results from the randomly constructive or destructive interference of the scattered light rays will
appear in the images obtained from the range gated underwater imaging system. The random granular speckle noise
brings great difficulty for the image processing. So the formation causes of speckle noise are discussed and several
different material objects under standard light source and laser are chosen to carry out speckle noise comparative
analysis. And a multidirectional morphological filtering algorithm for reducing speckle noise is proposed by using the
characteristics of morphology's multi-resolution analysis and fast-computing. In order to evaluate the method
objectively, equivalent number and speckle index are introduced. The experimental results demonstrate that the approach
that is adopted not only can reduce the speckle noise of the image effectively but also can preserve the feature detail
Range-gated underwater laser imaging technique can eliminate most of the backscattering and absorption noise
effectively. It has a range of from 4 to 6 times that of a conventional camera with floodlights in the strongly scattering
waters, which becomes a useful technique in oceanic research, deep-sea exploration, underwater remote control and
robotic works. While because of the laser pulse stretching, the image obtained through range gated underwater imaging
system has obvious nonuniformly illuminated character, such as brighter center and darker edge. Low contrast and
grayish white of the image also bring great difficulty for processing. In order to adjust the lightness of the nonuniformly
illuminated image of range-gated underwater imaging system, the water degradation is assumed as illumination variation
and retinal-cortex theory based on color constancy is introduced. Frame integral algorithm has to be applied first to
eliminate system noise for the reason that we adopt the system based on intensified gate imaging technology. And gray
stretch ensures that we can attain appropriate output. In retinal-cortex models, McCann model and McCann-Frankle
model have obvious effect. So we choose the two models for comparison and improve the second one considering the
exponential characteristics of eyes for illumination. In order to evaluate the methods objectively, strength uniformity of
signals is applied. The experimental results demonstrate that the approaches we adopted are all effective and can enhance
the image contrast. And the improved McCann-Frankle model gets more satisfying visual effect.
In ocean inspection, laser system has the advantages of high precision, high efficiency and being enacted on the
temperature or salinity of seawater. It has been developed greatly in recent years. But it is not yet a mature inspection
technique because of the complicacy of oceanic channel and water-scattering. There are many problems to be resolved.
In this paper, the work principle and of general developing situation of ocean lidar techniques are introduced first.
The author points out that the intense scattering and absorbing acting on light by water is the bottleneck to limit the
development of ocean lidar. The Monet Carlo method is adopted finally to be a basal way of study in this paper after
discussing several method of studying the light transmitting in seawater.
Based on the theory of photon transmitted in the seawater and the particularity of underwater target detecting, we
have studied the characters of laser scattering on underwater target surface and spatial and temporal characters of
forward scattering. Starting from the particularity of underwater target detecting, a new model to describe the characters
of laser scattering is presented. Based on this model, we developed the fast arithmetic, which enhanced the computation
speed greatly and the precision was also assured. It made detecting real-time realizable. Basing on the Monte Carlo
simulation and starting from the theory of photon transmitted in the seawater, we studied how the parameters of water
quality and other systemic parameters affect the light forward scattering through seawater at spatial and temporal region
and provided the theoretical sustentation of enhancing the SNR and operational distance.
A real-time 16-bit digital video grabber based on USB 2.0 protocol, thermal temperature measurement and dynamic analysis software are presented. One kind of 35 μm square pixel pitch's uncooled focal plane array thermal imaging module with 16-bit digital video output was selected. As long as being equipped with suitable camera lens, power supply and monitor, the module can be integrated as a thermal imaging system for observation, recognition, tracking and thermal images detection. Cypress Corp. CY7C68013 USB protocol chip is utilized. Main developments of video grabber are stressed on data transfer and logic control between imaging module and CY7C68013 with CPLD devices, and programming windows drivers based on Windriver. The measurement and dynamic analysis software involves not only traditional false color coding, point/line/area temperature analysis, but also several new functions: 1. Automatically mark and monitor the area when its temperature is higher than a setting threshold, and plot the curve of temperature histogram against time. 2. Monitor and plot the temperature movement versus time in manually setting points or area. 3. Database based on local area network convenient for sharing and managing data. Statistics form, curve plot, single-frame and sequence images can enter into database by manual operation or in term of some conditions set previously, such as files saving interval. Moreover, different functions are designed according to the authority of accessing local area network.