Sea Fog Characteristics Based on MODIS Data and Streamer Model

摘要

To achieve sea fog detection in the China Sea with EOS MODIS data, the reflectance between band 1 -7 of sea fog and other cloud regions is the pre-work. Based on satellite observations and sampling from known sea fog and cloud regions, the spectral characteristics of sea fog and other clouds are analyzed. It shows that the visible reflectance (band 1-4) is generally from 0.2 to 0.4 in sea fog, while the reflectance of cloud regions is higher than 0.4. The near-infrared reflectance over different fog/cloud regions expresses some especial characteristics. At band 7, the reflectance varies observably relative to bands 1-4 over sea fog/cloud regions and it is smallest. The reflectance of bands 5 and 6 may be higher than other bands in sea fog regions. Those results deduced from some instances with statistical method may be present individual property. Therefore, with the Streamer radiative transfer model, the reflectance at the satellite altitude of the sea fog, low-cloud, mid-cloud and high-cloud with different cloud microphysical and observational conditions is simulated and re-analyzed. The simulations also show those results are consistent with the satellite observations. It shows that the near-infrared wavelength band 6 is useful to detect sea fog by MODIS. The reflectance of sea fog satisfies band3>band6>band2 while the general cloud is band3>band2>band6. Those properties are also simply explained by Mie scattering theory. It is the different scattering efficiency of sea fog and clouds at different wavelengths that contribute to these results. Those properties at sea fog in seven bands that is different from other clouds is useful for fog autodetection by EOS MODIS.