COSMIC掩星反演数据质量分析

Assessment of COSMIC Radio Occultation Retrieval Product

利用2007-2010年的中国探空资料评估GPS掩星探测系统COSMIC（constellation observing system for meteorology,ionosphere，and climate）反演产品，对比数据在空间上限定掩星事件发生地和探空站的水平距离在100km以内，在时间上相差不超过1小时，对比高度范围为925～10hPa。对比结果表明，COSMIC反演大气温度略低于探空仪测量值，平均绝对偏差为-0．08K，标准差为1．67K。两者水汽资料在200hPa以上高度有系统性偏差；在200hPa以下，比湿的平均偏差约为＋0．080g／kg，标准差为0．692g／kg，水汽压平均相对误差约为＋69．6％，标准差为160．O％，水汽压存在极端低值的异常情况。通过对全球不同区域6种探空仪的对比，COSMIC反演产品在700hPa以下高度显著受背景场影响，由于背景场误差随区域改变，因此，只有在精度要求不高的情况下，COSMIC反演产品才适合用于评估其他资料。

The retrieval product of COSMIC （constellation observing system for meteorology, ionosphere, and climate） radio occultation sounding system was verified using the Chinese radiosonde from 2007 to 2010. The horizontal distance between radiosonde station and the occultation event is within 100 km, and the time window is 1 hour. The comparison is performed from 925 hPa to 10 hPa. Result shows that the temperature of COSMIC agrees well with Chinese radiosonde. The mean temperature bias is -0.08 K, and the standard deviation is 1.67 K. The water vapor pressure of COSMIC has notable systematic bias from radiosonde on layers above 200 hPa. On layers below 200 hPa, the mean absolute deviation of specific humidity is about ＋0.080 g/kg, and the standard deviation is about 0.692 g/kg, the mean relative error of water vapor pressure is about ＋69.6%, and the standard deviation is about 160.0%. The COSMIC quality control process fails to detect some extremely small humidity data which causes large relative error. Here also provides a comparison of 6 radiosonde types with COSMIC product. As result is affected by the background bias from radiosonde which differs on different regions, the COSMIC retrieval product could be used as benchmark if precision requirement is not strictness.