中国区域COSMIC数据掩星反射信号特征分析

Analysis of Reflected Signals During GPS Radio Occultation Observations of COSMIC Products in China

掩星信号在传播过程中能够在地球表面发生反射,其反射信号中的低层大气信息在改进天气预报精准度和气候监测等方面存在很大的应用价值。基于COSMIC(constellation observing system for meteorology,ionosphere and climate)掩星廓线资料,提取了2011-2015年中国区域的包含反射信号的掩星廓线,揭示了廓线分布具有内陆少、海洋多的规律,且具有夏季少、冬季多的季节性变化特征,内陆地区冰雪覆盖和海洋表面更有利于掩星信号反射。将中国近海海域按照5°×5°格网划分,进一步分析了格网内含反射信号的掩星廓线百分比时间序列与欧洲中期天气预报中心提供的再分析水汽和温度数据之间的相关性。结果表明,在10°N以北海域,掩星廓线反射信号百分比与再分析水汽数据和再分析温度数据均呈现负相关(相关系数约为-0.28~-0.58);而在10°N以南海域,受南海季风影响,掩星廓线反射信号百分比与再分析水汽数据有一定程度的正相关(相关系数约为0.32~0.34),与再分析温度数据没有显著相关性。

Objectives:The global navigation satellite system(GNSS)radio occultation(RO) signals can be reflected on the earth surface during the propagation process. It is of great value to explore atmospheric information contained in the reflected occultation signal for improving the accuracy of weather forecast and climate monitoring. Methods:Using the constellation observing system for meteorology, ionosphere and climate(COSMIC) occultation data collected from January 2011 to December 2015 in China, this paper extracted the occultation profile containing the reflected signals, which were strong at oceans and weak at inland and also showed seasonal changes. It was found that the inland snowy areas and the ocean surface were easier to reflect the occultation signals. Further, the offshore areas of China were set into 5°×5° grids and the correlation between the percentage of occultation reflected signals and the reanalysis data from European Centre for Medium-Range Weather Forecasts in each grid was analyzed. Results:Around the offshore areas to the north of 10°N, the water vapor and temperature are negatively correlated with the percentage of occultation profile reflected signal, with a correlation coefficient from -0.28 to-0.58. However, around the offshore areas to the south of 10°N, affected by the monsoon at the South China Sea, the percentage of occultation profile reflection signal is positively correlated with the reanalyzed water vapor data, with a correlation coefficient from 0.32 to 0.34, but not significantly correlated with the reanalyzed temperature data.Conclusions:The RO reflected signals associate with atmospheric conditions, and it can be applied to the direct signals as supplementary data.