HR: 08:45h
AN: G51D-04    [Abstracts]
TI: A Comprehensive Evaluation of the Errors Inherent in the use of a 2-Dimensional Shell for Modeling the Ionosphere
AU: * Smith, D
EM: dru.smith@noaa.gov
AF: NOAA, National Geodetic Survey, 1315 East-West Highway SSMC3, N/NGS, Silver Spring, MD 20910, United States
AU: Araujo-Pradere, E
AF: NOAA, Space Environment Center, 325 Broadway W/NP9, Boulder, CO 80305, United States
AU: Minter, C
AF: NOAA, Space Environment Center, 325 Broadway W/NP9, Boulder, CO 80305, United States
AU: Fuller-Rowel, T
AF: NOAA, Space Environment Center, 325 Broadway W/NP9, Boulder, CO 80305, United States
AB: The ionosphere is a complex, dynamic part of the Earth's atmosphere and impacts many different frequencies of electromagnetic propagation passing through it, such as those of the Global Positioning System (GPS). For this reason, the ionosphere is frequently studied and modeled so as to remove these impacts. Unfortunately, because of the complexity of the ionosphere, such models frequently make use of a so-called "2 dimensional shell", for simplicity of both modeling and data distribution. In 2004, a joint study between NOAA's National Geodetic Survey (NGS) and Space Environment Center (SEC) led to the development of SEC's operational "USTEC" model– a truly four dimensional representation of the ionosphere over the conterminous United States produced in near-real time from GPS data collected at Continuously Operating Reference Stations (CORS). Because USTEC is spatially 3 dimensional, with values changing every 15 minutes (4-D), it allows for comprehensive examination of the complete distribution of electrons in the ionosphere over the U.S. Using USTEC, a study was performed to quantify the errors inherent in using a 2-D shell model, versus the more realistic 3-D model of the ionosphere. Errors of several percent were identified from purely geometrical sources related to the simplistic mapping function used in conjunction with 2-D shell models, but even larger errors were identified which were due to the inability of shell models to reflect even the most basic vertical mixing implicit in 3-D models. After quantifying all geometric errors associated with the well-known "cosine mapping function", an entirly new mapping function has been proposed to replace the cosine mapping function. This new function also relates the slant TEC to the vertical TEC within a shell model, just like the cosine mapping function, but removes as much as 50% of the errors inherent in the cosine mapping function. The final recommendation of this study is that users who require 1 TECU or better accuracy (approximately one L1 wavelength in GNSS positioning) should generally use a 3-D model of the ionosphere. Users who must rely on a 2-D model (for computational or bandwidth limits) should consider using the new mapping function in order to avoid large systematic errors associated with the long standing cosine mapping function.
DE: 1220 Atmosphere monitoring with geodetic techniques (6952)
DE: 2447 Modeling and forecasting
DE: 3252 Spatial analysis (0500)
SC: Geodesy [G]
MN: 2007 Fall Meeting