The scattering properties of bubble

The scattering properties of bubble clouds in water is usually regarded as inevitable noise, which distorts lidar returns or underwater images of those objects we are interested. However, bubble clouds can also be a valuable target in various remote sensing applications. In situ long range sensing of bubble clouds can be achieved based on their optical property. In this paper we describe the fabrication and results obtained from an underwater lidar system for micro-bubble clouds detection. A peak of the backscatter lidar signal corresponds to backscatter of the bubble cloud is detected and its characteristic is in good agreement with previous Monte Carlo simulationIn addition, we tested the performance of this lidar system by detecting bubbles in the size range of several millimeters as well as tens of micrometers. Results show that backscatter of the bubble cloud that consists of bubbles that are millimeter in diameter has similar characteristic of reflection from other solid objects, but backscatter from micro-bubbles that are micrometers in diameter is relatively small. This does not only mean that the backscatter intensity is influenced by the size distribution of bubbles, but also that detection ability of a lidar system will be challenged when bubble size gets smaller. In order to get improved detection capability, some particular technology should be deployed in the lidar system design.Through our experimental results, it is concluded that the location of a bubble cloud can be inferred from the location of a corresponding backscatter peak, which can then be used as a criterion for location of a bubble cloud. Other information about the bubble cloud is explored by processing experiment results. Some property of a bubble cloud such as location, concentration, size distribution and thickness influences amplitude and width of this peak. For bubbles of constant size distribution, the backscatter peak increase linearly with respect to the increasing of concentration of bubbles, and exponential decay with distance between the bubble cloud and lidar system under the assumption that thickness of bubble cloud stays the same. An increase in the thickness of the bubble cloud does not only cause an increase in amplitude of backscatter peak, but also widens the pulse-width exponentially. Those methods can be used to characterize bubble clouds in the future and has potential applications in remote sensing.Although the results were constrained by the operational limitations on range and bubble concentration posed by the experimental setup, this lidar configuration could be developed for at-sea deployment. In this paper, some common characteristics of bubble clouds that influence backscatter signal were considered, however, more factors that influences the performance of the lidar, such as water quality, have not been discussed. These factors would be more meaningful if applied in the context of field experiments in natural waters.