COSMIC計畫GPS掩星技術反演大氣溫度與壓力之模擬誤差分析

A Simulated Error Analysis of Temperature and Pressure Retrieval Using the GPS Occultation Technique for the COSMIC Project

高士杰(Shih-Chieh Kao) ； 楊名(Ming Yang)

《航測及遙測學刊》 6卷4期 (2001/12) Pp. 55-74

https://doi.org/10.6574/JPRS.2001.6(4).3

摘要

本文提出利用GPS（Global Positioning System）掩星技術探測地球大氣溫度與壓力之模擬誤差分析。GPS掩星技術是利用低軌衛星觀測來自高軌GPS衛星的訊號，進一步反演地球大氣溫度與壓力垂直剖面，以提供氣象預報及全球變遷等研究之應用。本文首先回顧反演大氣溫度與壓力之演算法則，並探討積分截尾誤差、GPS衛星軌道誤差、COSMIC（Constellation Observing System for Meteorology Ionosphere and Climate）衛星軌道誤差、以及GPS相位觀測量隨機誤差對GPS掩星技術反演大氣溫度與壓力之影響。實驗顯示當使用COSMIC精密軌道時，上述各項誤差來源在對流層及平流層部分對反演壓力之影響均不顯著（小於0.2mb）；在溫度反演方面，不同來源之誤差在對流層部分之影響量較小（小於1K），而在較高的平流層部分之影響量則有明顯提升的趨勢，可達到約10K之量級。目前國際上GPS掩星觀測成果仍存有一個尚未確切理解的問題，即在地表45公里以上反演所得的溫度經常出現波狀的擺動；而根據實驗成果顯示，此類波狀的擺動亦可能由GPS觀測量之偶然誤差所造成，並不必然為真實大氣溫度之變化。

關鍵字

COSMIC衛星 ； GPS掩星技術 ； 誤差分析 ； 大氣溫度與壓力

並列摘要

This paper presents a simulated error analysis of the GPS (Global Positioning System) occultation technique, which is used by the joint Taiwan-U.S. COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) project to study the Earth's atmosphere and monitor temperature and pressure profiles. A qualitative description of the GPS occultation technique of atmosphere limb sounding is reviewed, and retrieval algorithms for temperature and pressure profiles determination in the absence of water vapor are summarized in this paper. A simulation study was conducted to investigate the impact of various error sources, including integral truncation error, GPS and COSMIC orbit errors, and measurement noises, on the retrieved temperature and pressure profiles. Simulation results show that the induced effects of the above error sources on atmospheric pressure retrieval were less than O.2mb when precise COSMIC orbit ephemeris was used. The corresponding impacts on the retrieved temperature profiles were small (less than 1K) in the troposphere; however, they were substantially greater in the stratosphere (～10K). To date, there still remains an outstanding problem in GPS occultation data analysis - the retrieved temperature often displays wave-like fluctuations in the upper atmosphere (＞ 45km). According to the simulation results contained in this paper, these wave-like motions do not necessarily represent the actual atmospheric temperature behavior; they could also reflect the induced error pattern of the GPS measurement noises.

並列關鍵字

COSMIC satellites ； GPS occultation technique ； error analysis ； atmospheric temperature and pressure