Probability distribution of surface wave slope derived from spaceborne remote sensing data

海面坡度的概率分布已估计使用来自地球静止气象卫星（GMS）上的可见光波长辐射计和表面矢量风观测的星载散射计的太阳闪烁图像。可见光图像的亮度被转换为在0.25° x 0.25°（纬度x经度）的网格中将太阳光反射到GMS的波面的概率。根据GMS观测的几何形状和太阳的位置，为每个网格计算太阳光线反射到GMS所需的坡度和方位角。GMS图像，然后搭配由三个散射仪观测到的地面风数据。利用1995 ~ 1999年4年间获得的约3000万个点的同位数据集，估计了地面坡度随风速和相对于风向的方位角变化的概率分布函数。并与考克斯和蒙克（1954）的结果作了比较。与考克斯和芒克的研究结果相比，本文方法得到的地面坡度分布较窄，且方向性较弱。预计他们的数据是在风浪不断增长的条件下获得的。一般来说，风浪并不总是发展的，坡度分布可能与考克斯和芒克的结果不同。我们的大部分数据是在晴朗的天空条件下在亚热带海洋中获得的。这种条件上的差异可能是造成坡度分布差异的原因。

The probability distribution of the sea surface slope has been estimated using sun glitter images derived from the visible wavelength radiometer on the Geostationary Meteorological Satellite (GMS) and surface vector winds observed by spaceborne scatterometers. The brightness of the visible images is converted to the probability of wave surfaces which reflect the sunlight toward GMS in grids of 0.25° x 0.25° (latitude x longitude). The slope and azimuth angle required for the reflection of the sun's rays toward GMS are calculated for each grid from the geometry of GMS observation and location of the sun. The GMS images are then collocated with surface wind data observed by three scatterometers. Using the collocated data set of about 30 million points obtained in a period of 4 years from 1995 to 1999, the probability distribution function of the surface slope is estimated as a function of wind speed and azimuth angle relative to the wind direction. The results are compared with those of Cox and Munk (1954). The surface slope estimated by the present method shows a narrower distribution and much less directivity relative to the wind direction than that reported by Cox and Munk. It is expected that their data were obtained under conditions of growing wind waves. In general, wind waves are not always developing, and the slope distribution might differ from the results of Cox and Munk. Most of our data are obtained in the subtropical seas under clear-sky conditions. This difference in the conditions may be the reason for the difference of slope distribution.