Regularized estimation of vertical total electron content from GPS data for a desired time period

Abstract

[1] 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.

Probability density function estimation for characterizing hourly variability of ionospheric total electron content

“…The raw data for the GPS stations are obtained from the Web site of ftp://cddisa.gsfc.nasa.gov/gps/products/ionex/. The geographic and geomagnetic coordinates and station ID's of the selected 18 GPS stations are provided in Table 1 [13] The raw GPS data recordings for each station is processed with Reg-Est method and TEC estimates are obtained using www.ionolab.org as IONOLAB-TEC [Arikan et al, 2003;Arikan et al, 2004;Arikan et al, 2007;Nayir et al, 2007]. For each GPS station in Table 1, and lama, both midlatitude stations, are presented, respectively.…”

Scale factor mitigating non-compliance of double-frequency altimeter measurements of the ionospheric electron content over the oceans with GPS-TEC maps

“…The most common sources of error for GPS TEC estimates are (1) the pseudorange estimate model that includes frequency-dependent satellite and receiver clock biases; (2) an assumption of azimuthal homogeneity of the ionosphere; (3) an assumption of inherent temporal stability of the ionosphere for 15 min to 2 h; (4) conversion from slant TEC to vertical TEC (mapping function); (5) determination of thin shell height corresponding to the maximum ionization height of the ionosphere; detection of cycle slips and resolving integer phase ambiguity; (6) scaling the absolute TEC to the relative TEC in order to estimate low noise TEC estimates for each satellite in view; (7) combination of TEC estimates from different satellites in view to obtain one value of vertical TEC for a given instant for any location; (8) estimation of satellite and receiver DCBs (Arikan et al, 2003(Arikan et al, , 2004(Arikan et al, , 2008Nayir et al, 2007). Global or regional mapping or interpolating TEC from sparse samples is another issue that needs to be handled very carefully.…”

“…In GPS TEC computations, the TEC on the slant ray path from the satellite to the receiver is called the slant TEC (STEC). When the STEC values are projected to the local zenith at the ionospheric pierce point, accepting the assumption of the thin shell model of the ionosphere with a mapping function, the computed TEC value is called the vertical TEC (VTEC) (Arikan et al, 2003(Arikan et al, , 2004Nayir et al, 2007). A more sophisticated 3-D model of the ionosphere would improve the accuracy of the conversion of the slant TEC to the vertical TEC (Smith et al, 2008).…”

Tomographic reconstruction of the ionospheric electron density as a function of space and time

“…The TEC computation methods and their advantages and disadvantages are widely discussed in the literature (Jakowski et al, 1996;Liao, 2000;Arikan et al, 2003). Regularized Estimation of TEC (Reg-Est) is a technique for estimation of high resolution, reliable and robust TEC estimation as discussed in detail by Arikan et al (2003Arikan et al ( , 2004Arikan et al ( , 2007. In a study conducted by Arikan et al (2003), regularized estimation of vertical total electron content from Global Positioning System data is researched and a new method is proposed.…”