船载激光雷达测量水体光学参数的仿真模拟研究

Simulation of water optical property measurement with shipborne lidar

激光雷达能够高效获取海洋光学特性的垂直剖面信息,是海洋光学探测的重要手段之一。利用蒙特卡罗仿真方法,基于Gordon(1982)的机载激光雷达测量水体光学参数模型,研究了船载激光雷达在水中的传输过程和水中光场分布。特别研究考虑了接收视场角和望远镜半径等参数的影响,建立了适用于船载海洋激光雷达的模拟系统。在激光雷达的传输等效为太阳光传输后,该模拟系统与常用的HydroLight的模拟进行了比对印证并获得了一致的结果。在此基础上,通过模拟得到的激光雷达回波信号分析了不同激光雷达测量模式及典型水体条件下激光雷达消光系数α和海水光学参数之间的关系。船载激光雷达结果表明,在窄接收视场角情况下,激光雷达消光系数α趋向于水体光束衰减系数c;在宽接收视场角情况下,α趋近于水体的向下辐照度漫射衰减系数K_d。相比机载观测,船载观测的α趋近K_d的速度变缓。在垂直分层水体中,激光雷达在下层水体中测量的α值会向上层水体的α值偏移。该结果为研究海洋激光雷达测量参数与海洋光学参数之间的关系提供了进一步的认知。

As an important instrument for optical observation in the water, lidar is able to efficiently obtain vertical profiles of ocean optical properties. Based on the airborne lidar model of Gordon(1982)for measuring water optical property, the processes of shipborne lidar radiative transfer and distribution of underwater light field were investigated using Monte Carlo simulation. In particular, taking into consideration receiving FOV and telescope aperture, a shipborne oceanographic lidar simulator was developed. After lidar radiative transfer was equivalent to solar radiative transfer, the simulator was validated with commonly used HydroLight which showed good coincidence. On this basis, using simulated lidar return signal, the relationships between lidar extinction coefficient α and ocean optical properties were analyzed for different observation modes and typical water bodies. The results of shipborne lidar show that with narrow receiving field of view(FOV), lidar extinction coefficient α is close to beam attenuation coefficient c, and with large receiving FOV, lidar extinction coefficient α gradually approaches to diffuse attenuation coefficient of downwelling irradiance K_d. The extinction coefficient αmeasured with shipborne lidar approaches to Kdslower than the airborne situation. The results of stratified water show that the α values measured in lower layer water shift towards the α values in upper layer water. The results provide the further understanding for researching the relationship between parameters measured by oceanographic lidar and ocean optical properties.