GPS/TEC Estimation with IONOLAB Method
ABSTRACT Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and disturbances. The Global Positioning System (GPS) can be used for TEC estimation making use of the recorded signals at the GPS receiver. Reg-Est method that is developed by F. Ankan, C.B. Erol and O. Arikan can be used to estimate high resolution, robust TEC values combining GPS measurements of 30 s resolution obtained from the satellites which are above the 10deg elevation limit. Using this method, it is possible to estimate TEC values for a whole day or a desired time period both for quiet and disturbed days of the ionosphere. Reg-Est provides robust TEC estimates for high-latitude, mid-latitude and equatorial stations. In this study, some important parameters of Reg-Est such as ionospheric thin shell height, weighting function and receiver-satellite biases are investigated. By incorporating the results of the investigation, Reg-Est algorithm is developed into IONOLAB method. Thin shell model height is an important parameter for Single Layer Ionosphere Model (SLIM). In this study, it is shown that IONOLAB provides reliable and robust TEC estimates independent of the choice of the maximum ionization height. Signals from the low elevation satellites are prone to multipath effects. In order to reduce the distortion due to multipath signals, the optimum weighting function is implemented in IONOLAB, minimizing the non-ionospheric noise effects. GPS receivers record both pseudorange and phase data of signals. IONOLAB can input absolute TEC computed from the pseudorange measurements or phase-corrected low-noise TEC. The TEC estimates for both of these inputs are in good accordance with each other. Thus, taking either pseoudorange or phase-corrected measurement data as input, high resolution, robust TEC estimates can be obtained from IONOLAB. Another important parameter for TEC estimation is satellite-receiver instrumental biases. The biases are the frequency dependent delays due- to satellite and receiver hardware. In order to compute TEC, satellite and receiver biases should be removed from GPS measurements correctly. However, the proper procedure of how to include them in the TEC computation is generally vaguely defined. IONOLAB suggests a technique for inclusion of the hardware biases obtained from the web for TEC estimates that are consistent with the results from the IGS analysis centers.
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ABSTRACT: 1] A novel regularization technique which can combine signals from all Global Positioning System (GPS) satellites for a given instant and a given receiver is developed to estimate the vertical total electron content (VTEC) values for the 24-hour period without missing any important features in the temporal domain. The algorithm is based on the minimization of a cost function which also includes a high pass penalty filter. Optional weighting function and sliding window median filter are added to enrich the processing and smoothing of the data. The developed regularized estimation algorithm is applied to GPS data for various locations for the solar maximum week of 23–28 April 2001. The parameter set that is required by the estimation algorithm is chosen optimally using appropriate error functions. This robust and optimum parameter set can be used for all latitudes and for both quiet and disturbed days. It is observed that the estimated TEC values are in general accordance with the TEC estimates from other global ionospheric maps, especially for quiet days and midlatitudes. Owing to its 30 s time resolution, the regularized VTEC estimates from the developed algorithm are very successful in representation and tracking of sudden temporal variations of the ionosphere, especially for high latitudes and during ionospheric disturbances.Journal of Geophysical Research 01/1469; 108. · 3.17 Impact Factor
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ABSTRACT: Total ionospheric electron contents (TEC) were measured by global positioning system (GPS) dual-frequency receivers developed by the Jet Propulsion Laboratory. The measurements included P-code (precise ranging code) and carrier phase data for six GPS satellites during multiple five-hour observing sessions. A set of these GPS TEC measurements were mapped from the GPS lines of sight to the line of sight of a Faraday beacon satellite by statistically fitting the TEC data to a simple model of the ionosphere. The mapped GPS TEC values were compared with the Faraday rotation measurements. Because GPS transmitter offsets are different for each satellite and because some GPS receiver offsets were uncalibrated, the sums of the satellite and receiver offsets were estimated simultaneously with the TEC in a least squares procedure. The accuracy of this estimation procedure is evaluated indicating that the error of the GPS-determined line of sight TEC can be at or below 1 x 10 to the 16th el/sq cm. Consequently, the current level of accuracy is comparable to the Faraday rotation technique; however, GPS provides superior sky coverage.09/1988;
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ABSTRACT: In this paper a new algorithm for short-term regularized estimation of vertical total electron content (VTEC) from Global Positioning System (GPS) data is developed. The regularization technique can combine signals, from all GPS satellites for a given instant and a given receiver, for a desired time duration within the 24 hour period without missing any important features in the temporal domain. The algorithm is based on the minimization of a cost function which includes a high pass penalty filter and detrend processing. With an optional weighting function the multipath effects are reduced. A final sliding window median filter is added to enrich the processing and smoothing of the data. The developed regularized estimation algorithm is applied to GPS data for various locations for the solar maximum week of 23-28 April 2001. The parameter set that is required by the estimation algorithm is chosen optimally using appropriate error functions. For this data set the chosen robust and optimum parameters can be used for all latitudes and for both quiet and disturbed days for a minimum of one hour time period. It is observed that the estimated TEC values are in very accordance with the TEC estimates for the 24 hour period. Owing to its 30 s time resolution, the regularized VTEC estimates from the developed algorithm are very successful in representation and tracking of sudden temporal variations of the ionosphere, especially for high latitudes and during ionospheric disturbances.Radio Science 12/2004; 39(6):6012-. · 1.00 Impact Factor