中文摘要：

掩星观测资料的误差特性是GPS气象学研究的热点之一，COSMIC（the Constellation Observing System for Meteorology，Ionosphere and Climate）计划在技术上做了很多改进，包括采用“开环”跟踪技术，以改进对低对流层掩星信号的跟踪能力，从而减小掩星数据的反演误差。本文采用2006年7月29日至12月31号的COSMIC掩星数据与全球探空资料进行对比，统计了掩星数据在不同地区、不同高度层的分布以及其折射率的误差特性，结果表明：（1）与探空资料匹配后的掩星事件主要集中在中纬度地区陆地上；在垂直方向5km以上，掩星探测趋于稳定。（2）“开环”技术的应用修正了以前掩星计划中出现在低对流层的折射率负偏差，但是却引进了折射率正偏差。在低纬地区，这种正偏差最大，在地表到1km范围内达到0．6％；随着纬度增加，正偏差减小，在中纬度地区10km以下最大值为0．3％；到高纬度地区，正偏差减小到0．2％以内。

英文摘要：

The error analysis of GPS RO data has became one of the focuses in the field of GPS meteorology investigation. To reduce the errors of the radio occultation data, some new techniques has been implemented by COSMIC（ the Constellation Observing System for Meteorology, Ionosphere and Climate） mission including ＂open loop＂ tracking to solve the tracking errors of RO signals and muhipath propagation problem in the low troposphere. In this paper, a comparison of COSMIC RO soundings with the radiosonde data for one month of July 29 to twelve 31 2006 indicated： （ 1 ） The GPS occultation event that matched with the radiosonde stations in this paper occurred in the middle latitude is distinct more than tropics and polar regions ; In the vertical direction, the RO sounding tends to be steady over 5 km. （2） While the negative refractivity bias appeared in the low troposphere in the former occultation mission （GPS/MET, CHAMP etc） has been revised by using the ＂open loop＂ tracking technique, a plus refractivity bias has been found in the whole altitude from 1 to 25 km and is most distinct with the mean refractivity errors as large as 0. 6% below 1 km in the tropics. With the increased latitudes , the plus refractivity bias is reduced with values dropping to less than 0. 2% in the polar regions.