Inversion and error estimation of GPS radio occultation data
Inversion and error estimation of GPS radio occultation data
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DOI：
10.2151/jmsj.2004.507
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发表时间：
2004-03-01
影响因子：
3.1
通讯作者：
Anthes, RA
中科院分区：
文献类型：
--
作者：
Kuo, YH;Wee, TK;Anthes, RA
本文介绍了美国大学大气研究公司（UCAR） COSMIC（星座气象、电离层和气候观测系统）数据分析与档案中心（CDAAC）目前使用的GPS射电掩星（RO）反演过程。然后，我们利用主要来自2001年12月的数据，评估了CDAAC软件处理的CHAMP （challenge mini - Satellite Payload）和SAC-C （Satellite de应用科学卫星- c）任务的RO折射率探测精度。结果表明，RO测深在5 ~ 25 km范围内精度最高。在大气的这个区域，观测误差（包括测量误差和代表性误差）一般在折射率的0.3%至0.5%的范围内。热带对流层低层的观测误差向地表方向增大，在大气底部几公里处接近3%。RO观测误差在25公里以上也增加，特别是在冬季半球的高纬度地区。一般来说，这些误差估计比以前的理论预测要大。热带对流层低层观测误差较大，主要是由于湿度结构复杂、超折射和接收机跟踪误差所致。25 km以上的较大误差与观测噪声（主要是未校准的电离层效应）和通过优化程序使用辅助数据进行降噪有关。我们证明，只选择低噪声掩星可以大大减少25公里以上的RO误差。我们的结果表明，与分析和短期预报相比，即使在热带对流层下层，RO探测的折射率观测误差也比无线电探空小。这种差异很可能与提供现场（点）测量的无线电探空仪相关的较大代表性误差有关。除了3公里以下的热带对流层下层外，RO观测误差与NCEP（国家环境预测中心）航空（AVN）模式的12小时预报误差相当或小于。这表明RO观测将改善全球天气分析和预报。预计在今后的任务中，如COSMIC，使用先进的信号跟踪技术（开环跟踪），可以进一步提高反卫星探测的精度。
In this paper, we describe the GPS radio occultation (RO) inversion process currently used at the University Corporation for Atmospheric Research (UCAR) COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) Data Analysis and Archive Center (CDAAC). We then evaluate the accuracy of RO refractivity soundings of the CHAMP (CHAllenging Minisatellite Payload) and SAC-C (Satellite de Aplicaciones Cientificas-C) missions processed by CDAAC software, using data primarily from the month of December 2001. Our results show that RO soundings have the highest accuracy from about 5 km to 25 km. In this region of the atmosphere, the observational errors (which include both measurement and representativeness errors) are generally in the range of 0.3% to 0.5% in refractivity. The observational errors in the tropical lower troposphere increase toward the surface, and reach similar to3% in the bottom few kilometers of the atmosphere. The RO observational errors also increase above 25 km, particularly over the higher latitudes of the winter hemisphere. These error estimates are, in general, larger than earlier theoretical predictions. The larger observational errors in the lower tropical troposphere are attributed to the complicated structure of humidity, superrefraction and receiver tracking errors. The larger errors above 25 km are related to observational noise (mainly, uncalibrated ionospheric effects) and the use of ancillary data for noise reduction through an optimization procedure. We demonstrate that RO errors above 25 km can be substantially reduced by selecting only low-noise occultations.Our results show that RO soundings have smaller observational errors of refractivity than radiosondes when compared to analyses and short-term forecasts, even in the tropical lower troposphere. This difference is most likely related to the larger representativeness errors associated with the radiosonde, which provides in situ (point) measurements. The RO observational errors are found to be comparable with or smaller than 12-hour forecast errors of the NCEP (National Centers for Environmental Prediction) Aviation (AVN) model, except in the tropical lower troposphere below 3 km. This suggests that RO observations will improve global weather analysis and prediction. It is anticipated that with the use of an advanced signal tracking technique (open-loop tracking) in future missions, such as COSMIC, the accuracy of RO soundings can be further improved.