Biologists study on the biological behavior of various marine creatures in situ using underwater observation systems. The darkness in an underwater environment is always one of the most difficult problems to overcome in order to clearly monitor the life cycle of underwater creatures. This illumination would be solved employing the Master-Slave (camera-light platform) coordination tracking structure. The control of underwater platform is a challenging issue due to the complex external forces in the underwater environment. Comparing of tracking control between linear proportional-derivative (PD) and nonlinear PD for the Pan/Tilt camera platform were conducted. The variable structure control (VSC), i.e., sliding mode control (SMC), was employed to the tracking control of the underwater Pan/Tilt camera platform. The disadvantage of SMC is that the discontinuous control signal would excite the high frequency unmodeled dynamic which produces the chattering. One of the methods which eliminate the chattering is to use the boundary layer (BL). However, the width of BL can introduce a trade off between the tracking performance and chattering elimination. Large width of BL can much more eliminate the chattering, but lead to less accurate control results versa. A simple, easily implemented method to vary the width of BL according to the value of tracking error is illustrated and verified in this paper.

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