Single frequency processing of Ørsted GPS radio occultation measurements
Single frequency processing of Ørsted GPS radio occultation measurements
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DOI：
10.1007/s10291-005-0142-x
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发表时间：
2005-05
期刊：
影响因子：
4.9
通讯作者：
G. B. Larsen;S. Syndergaard;P. Høeg;M. Sørensen
中科院分区：
文献类型：
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作者：
G. B. Larsen;S. Syndergaard;P. Høeg;M. Sørensen
全球定位系统(GPS)无线电掩星测量采用了单频法进行处理，该测量是使用丹麦伊尔斯特德卫星上的TurboRogue GPS接收器获得的。根据欧洲中期天气预报中心(ECMWF)的数值天气预报数据，得到了大气折射率和温度的廓线，并进行了验证。2000年2月的ärsted全球定位系统测量活动的结果表明，单频法可以提供与使用两个频率的精度相当的精度。将实测的干温度廓线与ECMWF分析场得到的相应的干温度廓线进行比较，发现500和30百帕高度之间的平均差异小于0.5K，标准差为2-4K。在30千帕以上，电离层的影响变得更加主要，使用单频法更难消除，结果表明，与以前使用双频法对其他飞行任务的掩星数据进行分析时，精度有所下降。在纬度低于40°(表示为低纬度)时，标准偏差通常小于高于40°(表示为高纬度)时的标准偏差。观测到一个小的温度偏差，中心位置低纬为200百帕，高纬度为300百帕。这表明ECMWF的分析没有充分解决对流层顶最低温度。在对流层的最低部分，观测到的暖偏差被认为是由于在大气多路径传播的情况下对GPS信号的错误跟踪造成的。
The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation.