Sunlight glitter on a wind-ruffled sea: further studies.
Time-averaged intensities are computed for the glitter pattern of sunlight on a wind-ruffled sea. In the present work the azimuthally asymmetric form of the wave-slope distribution measured by Cox and Munk is used, so that the glitter pattern depends on the wind direction as well as magnitude. Results are calculated for both a clean ocean surface and one covered with an oil film. The glitter pattern is quite different with the oil film due to the quieting action of the oil on the waves, the greater reflectivity of the surface when oil is on the surface, and the larger values of polarization for the reflected light at most typical angles in the glitter pattern. These effects are illustrated and discussed as possible methods for the detection of oil slicks. The glitter pattern observed at satellite altitudes is also calculated.
Airborne measurements of laser backscatter from the ocean surface.
Laser backscatter data for the ocean surface near nadir have been acquired from an airborne lidar platform. The unique capability of this lidar instrument to scan both transmitted laser beam and receiver field of view up to 15° off nadir have made these data sets possible. Backscatter data were collected on eight separate missions using laser wavelengths at 337 and 532 nm and 9.5 μm. Statistics of the mean, standard deviation, and probability density function of backscatter were computed and analyzed in terms of prior analytical work that relates backscatter to wind speed and mean-square wave-slope statistics. We found the full width at half-maximum of the Gaussian-shaped mean backscatter pattern to range from 11 to 24° and the normalized standard deviation at a nadir-viewing angle to range from 0.1 to 0.6. We calibrated mean backscatter at nadir for the ocean surface in terms of an effective Lambertian reflectance by comparison of beach sand and ocean backscatter. Results were 16 and 24% reflectance on two missions where calibration was possible. Our data are compared with prior laser backscatter measurements and the general literature on optical scattering from the ocean surface.
Atmospheric drag effects on the KOMPSAT-1 satellite during geomagnetic superstorms
We examine the atmospheric drag on the low earth-orbiting satellite, KOMPSAT-1 in a sun-synchronous orbit at ~685-km altitude starting in 1999, during a 3-month (October-December) period in 2003. This 3-month interval includes the October 29-30 and November 20 magnetic superstorms and weak to moderate storms. We observed that the daily KOMPSAT-1 drag acceleration transiently responses to transient storm-time disturbances. That is, there is an one-to-one correspondence between the KOMPSAT-1 drag accelerations and the storm events. We find that the drag acceleration correlates strongly with the level of geomagnetic disturbance. This indicates that the trajectory of KOMPSAT-1 is significantly perturbed during extremely disturbed intervals because of atmospheric density increase. The main contributor to the density increase is Joule heating associated with the geomagnetic activity rather than the solar EUV radiation, as reported by previous studies. We suggest that understanding how the upper atmosphere responses to the geomagnetic-associated heating is important to predict space weather impacts on low earth-orbiting satellites.