基于MTSAT卫星的海上沙尘自动监测

Dust Automatic Detection over Ocean Using MTSAT Data

为实现海上沙尘的全天时自动监测,分析了大量MTSAT卫星观测数据,表明海上沙尘样本区在11μm和12μm的热红外亮温差为负,可见光反射率一般高于晴空海面而低于云区,11μm通道的亮温高于云区而低于晴空海区;同时运用Libradtran辐射传输程序包模拟不同水汽含量和不同下垫面温度时沙尘区热红外通道亮温差,表明在水汽含量相对较高的海面,沙尘区热红外通道亮温差仍为负值,这一特性可作为海上沙尘识别的重要指标。在沙尘辐射特性分析和模拟的基础上,通过红外亮温差判断,在白天结合可见光通道的反射率与3pixel×3pixel标准偏差;在夜间利用上一时相的沙尘区设定亮温阈值,提出一种简单有效的海上沙尘全天时自动监测算法。以2008年3月1～2日、2010年3月19～21日两次沙尘过程的MTSAT卫星数据为例进行我国海上沙尘的监测试验,结果表明,利用该算法能够有效提取出海上沙尘区的分布范围,客观反映沙尘的运移过程,监测结果利于反演沙尘气溶胶光学厚度、估算海上沙尘沉降通量等问题。

For the purpose of automatic detection of dust over ocean from satellites, reflection and emission characteristic of water surface, cloud and dust regions are analyzed based on lots of MTSAT satellite data, which show that the brightness temperature at thermal infrared channel 1 BT11 is less than the brightness temperature at thermal infrared channel 2 BT12 in dust sample regions. The visible reflectance of dust sample is generally greater than water surface but less than clouds, while it is opposite at BT11, which confirms that even the atmospheric water vapor content over ocean is relatively high; BT11 is less than BT12 in dust regions by using Libradtran radiative transfer model package. This can be used as an important feature of dust detection over ocean. So an easy dust automatic detection algorithm over ocean by remote sensing using MTSAT satellite data is developed. The thresholds of this algorithm are derived from reflectance, 3 pixel×3 pixel standard deviation of visible channel, BT11 and difference between BT11 and BT12. Then progress of dust storms over the Bohai Sea and the Yellow Sea from March 1st to 2nd, 2008 and from March 19th to 21st, 2010 was monitored both the daytime and nighttime. Result indicates that the method can extract distribution area of dust over ocean and shows transportation process of dust storms objectively. This is in favor of aerosol optical thickness retrieval to estimate the flux of dust sedimentation over ocean.