A new algorithm for retrieving GPS radio occultation total electron content

Abstract

A new algorithm for retrieving the relative ionospheric satellite‐to‐satellite total electron content during Global Positioning System (GPS) radio occultations is proposed. The algorithm consists of a linear combination of the L1 and L2 excess phase data using precise orbit information of the transmitter and receiver. The combination eliminates the effects of refractive bending and dispersion to first order. Simulations, representative of solar maximum conditions, show that using the “traditional” combination of the L1 and L2 phases, bending and dispersion may cause a systematic residual error of up to 20 TECU. Using only the L1 excess phase, the corresponding maximum residual error is about 7 TECU. The proposed combination results in a residual error due to bending and dispersion less than 0.1 TECU. Uncertainty in satellite orbit determination, as well as an unmodeled residual related to the geomagnetic field, result in a total systematic error of 1–2 TECU.

Estimating E region density profiles from radio occultation measurements assisted by IDA4D

“…The excess phase can be converted to radio occultation TEC (ROTEC) given the relationship between the integrated refractive index and the integrated electron density prescribed by the Appleton‐Hartree equation [e.g., Hajj et al , 2000]. The desired straight‐line TEC can be computed using a classical approach that involves differencing the excess phase measurements on L1 and L2, which has the benefit of removing errors associated with transmitter and receiver clock uncertainties and orbital information, at the expense of additional random noise [e.g., Schreiner et al , 1999; Hajj et al , 2000; Syndergaard , 2002]. Alternatively, using precise orbital information, ROTEC can be computed on a single frequency using a more accurate differencing technique that essentially eliminates errors associated with bending and dispersion [ Syndergaard , 2002].…”

“…The desired straight‐line TEC can be computed using a classical approach that involves differencing the excess phase measurements on L1 and L2, which has the benefit of removing errors associated with transmitter and receiver clock uncertainties and orbital information, at the expense of additional random noise [e.g., Schreiner et al , 1999; Hajj et al , 2000; Syndergaard , 2002]. Alternatively, using precise orbital information, ROTEC can be computed on a single frequency using a more accurate differencing technique that essentially eliminates errors associated with bending and dispersion [ Syndergaard , 2002]. This approach has the form where L 1 and L 2 (units of meters) are the excess phase measurements on f 1 and f 2 , respectively, and C = 40.3082 m 3 /s 2 .…”

“…This approach has the form where L 1 and L 2 (units of meters) are the excess phase measurements on f 1 and f 2 , respectively, and C = 40.3082 m 3 /s 2 . The resulting residuals are associated with a term due to the presence of the geomagnetic field in the Appleton‐Hartree equation, although errors associated with the LEO velocity are in general larger [ Syndergaard , 2002]. The total system error is then ∼1–2 TECU (1 TECU = 10 16 electrons/m 2 ) [ Syndergaard , 2002].…”

Midlatitude sporadic-E episodes viewed by L-band split-spectrum InSAR

“…In the literature regarding high-precision GNSS positioning, the secondorder geomagnetic and the third-order bending effects are estimated to be orders of magnitude smaller than the first-order TEC, whereas these higher-order terms are currently taken into account in the operational GNSS positioning (e.g., Syndergaard 2002;Kedar et al 2003). Dual frequency phase data for both GNSS and InSAR are used to simply solve for the first two terms of Eq.…”

Performance of the improved Abel transform to estimate electron density profiles from GPS occultation data

“…Hajj et al (2000) and Syndergaard (2002) recommend the use of TEC computed directly the L1 carrier phase observable (or a geometric combination of L1 and L2) corrected for nondispersive terms in order to diminish the bending effect (the departure of the ray from the straight line) that can reach up to 20 TECUs (in an occultation that has a maximum TEC value above 2000 TECUs). However, Schreiner et al (1998Schreiner et al ( , 1999, who applied the classical Abel inversion, did not find significant differences between the uses of such different TECs when they estimate the foF2.…”