Remotely Sensing the Earth’s Atmosphere Using the Global Positioning System (GPS)—The GPS/MET Data Analysis

Feng, D.; Herman, Benjamin M.

doi:10.1175/1520-0426(1999)016<0989:rstesa>2.0.co;2

Cited by 53 publications

(39 citation statements)

References 34 publications

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“…The combination of two bending angles is more effective than the phase combination expressed by Eq. (2) in the RO context (Hocke, 1997;Kursinski et al, 1997;Rocken et al, 1997;Gorbunov and Gurvich, 1998;Feng and Herman, 1999;Steiner et al, 1999), since it not only accounts for the separation of the dual-frequency carriers but also considers the fact that most of the total bending angle is accumulated near the ray perigee (Vorob'ev and Krasil'nikova, 1994;Ladreiter and Kirchengast, 1996). Due to its smaller ionospheric residual, the bending angle correction has become the most popular ionospheric correction approach nowadays in GPS RO data processing.…”

Section: Ionospheric Correction and Bending Angle Riementioning

confidence: 99%

Quantifying residual ionospheric errors in GNSS radio occultation bending angles based on ensembles of profiles from end-to-end simulations

et al. 2015

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Abstract. The radio occultation (RO) technique using signals from the Global Navigation Satellite System (GNSS), in particular from the Global Positioning System (GPS) so far, is currently widely used to observe the atmosphere for applications such as numerical weather prediction and global climate monitoring. The ionosphere is a major error source in RO measurements at stratospheric altitudes, and a linear ionospheric correction of dual-frequency RO bending angles is commonly used to remove the first-order ionospheric effect. However, the residual ionospheric error (RIE) can still be significant so that it needs to be further mitigated for high-accuracy applications, especially above about 30 km altitude where the RIE is most relevant compared to the magnitude of the neutral atmospheric bending angle. Quantification and careful analyses for better understanding of the RIE is therefore important for enabling benchmark-quality stratospheric RO retrievals. Here we present such an analysis of bending angle RIEs covering the stratosphere and mesosphere, using quasi-realistic end-to-end simulations for a full-day ensemble of RO events. Based on the ensemble simulations we assessed the variation of bending angle RIEs, both biases and standard deviations, with solar activity, latitudinal region and with or without the assumption of ionospheric spherical symmetry and co-existing observing system errors. We find that the bending angle RIE biases in the upper stratosphere and mesosphere, and in all latitudinal zones from low to high latitudes, have a clear negative tendency and a magnitude increasing with solar activity, which is in line with recent empirical studies based on real RO data although we find smaller bias magnitudes, deserving further study in the future. The maximum RIE biases are found at low latitudes during daytime, where they amount to within −0.03 to −0.05 µrad, the smallest at high latitudes (0 to −0.01 µrad; quiet space weather and winter conditions). Ionospheric spherical symmetry or asymmetries about the RO event location have only a minor influence on RIE biases. The RIE standard deviations are markedly increased both by ionospheric asymmetries and increasing solar activity and amount to about 0.3 to 0.7 µrad in the upper stratosphere and mesosphere. Taking also into account the realistic observation errors of a modern RO receiving system, amounting globally to about 0.4 µrad (unbiased; standard deviation), shows that the random RIEs are typically comparable to the total observing system error. The results help to inform future RIE mitigation schemes that will improve upon the use of the linear ionospheric correction of bending angles and also provide explicit uncertainty estimates.

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Section: Ionospheric Correction and Bending Angle Riementioning

confidence: 99%

Quantifying residual ionospheric errors in GNSS radio occultation bending angles based on ensembles of profiles from end-to-end simulations

et al. 2015

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“…The high accuracy of the radio occultation sounding was demonstrated using the Global Positioning System (GPS) at wavelengths 19 and 24 cm (Melbourne et al, 1994;Ware et al, 1996;Kursinski et al, 1996Kursinski et al, , 1997Rocken et al, 1997;Feng and Herman, 1999;Schreiner et al, 1999). First experiments in another frequency bands have been provided in 1989-1998 years at wavelengths 2 and 32 cm as described by Yakovlev et al (1995) and Yakovlev (1998).…”

Section: Introductionmentioning

confidence: 99%

Radio holographic principle for observing natural processes in the atmosphere and retrieving meteorological parameters from radio occultation data

et al. 2014

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The radio holographic principle is briefly described and tested by using radio occultation data of the GPS/MET and MIR/GEO experiments. Sub-Fresnel spatial resolution ∼12 m/pixel was achieved using focused synthetic aperture radio holographic approach, and direct evidence of multibeam propagation effects in the atmosphere was obtained. The achieved instrumental accuracy in angular distance measurements was near 0.004 milliradian/pixel, and observed angular distance between different rays was equal to 0.3 milliradians. The angular resolution of the radio holographic method depends on the wavelength as λ 1 compared to λ 1/2 in conventional methods. In general case the principal limit of the vertical resolution may be determined using focused synthetic aperture antenna theory and may achieve a value ∼20-40 m under assumptions of spherical symmetry and quiet atmospheric conditions. Wave structures were discovered in the altitude distribution of the gradient electron density at a height interval of 60-95 km with spatial period 1-2 km and vertical resolution 300-500 m. Good correspondence was found between the temperature profiles revealed by radio holographic analysis and those obtained by traditional retrieval using UCAR GPS/MET data.

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“…However, RO data possess retrieval errors (occurring in the course of imperfect atmospheric data processing) as well as measurement errors (those in the primary observable). A number of studies analyzed the error sources and propagation of the errors through the retrieval process (e.g., Kursinski et al, 1997;Feng and Herman, 1999;Syndergaard, 1999;Rieder and Kirchengast, 2001;Hajj et al, 2002;Kuo et al, 2004;. Some of the error sources are particularly hard to tackle including ionospheric residuals (e.g, Syndergaard, 2000), the influence of a priori error on the statistical optimization of bending angle (e.g., Wee and Kuo, 2014), horizontal inhomogeneity in the atmosphere (e.g., Poli and Joiner, 2004), abnormal propagations of radio waves (e.g., Sokolovskiy, 2003), strong multipath effects in the lower troposphere (e.g., Gorbunov et al, 2006), and the ambiguity in separating moisture and dry air density from the bending angle or the refractivity (e.g., Kursinski et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

A perspective on the fundamental quality of GPS radio occultation data

Wee

Kuo

2015

Atmos. Meas. Tech.

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Abstract. Radio occultation (RO) is a promising source of observation for weather and climate applications. However, the uncertainties arising from imperfect retrieval algorithms may weaken the overall confidence in the data and discourage their use. As an alternative approach of assessing the quality of RO data while avoiding the nuisance of retrieval errors, this study proposes to use minimally processed data (measurement) instead of derived RO data. This study compares measured phase paths with their model counterparts, simulated with an effective ray tracer for which the refractive indices along the complete ray path linking the transmitter and the receiver are realistically specified. The comparison of phase measurements with the European Centre for Medium-Range Weather Forecasts (ECMWF) data made in the observation space shows that the RO measurements are of sufficient accuracy to uncover regional-scale systematic errors in ECMWF's operational analysis and the 45-year reanalysis (ERA40), and to clearly depict the error growth of short-term ERA40 forecasts. In the southern hemispheric stratosphere, in particular, the RO measurements served as a robust reference against which both of the two analyses were significantly biased in opposite directions even though they were produced by the same center using virtually the same set of data. The measurement and ECMWF analyses showed a close agreement in the standard deviation except for the regions and heights that the quality of the ECMWF data is controversial. This confirms the high precision of RO measurements and also indicates that the main problem of the ECMWF analyses lies in their systematic error.

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Remotely Sensing the Earth’s Atmosphere Using the Global Positioning System (GPS)—The GPS/MET Data Analysis

Cited by 53 publications

References 34 publications

Quantifying residual ionospheric errors in GNSS radio occultation bending angles based on ensembles of profiles from end-to-end simulations

Quantifying residual ionospheric errors in GNSS radio occultation bending angles based on ensembles of profiles from end-to-end simulations

Radio holographic principle for observing natural processes in the atmosphere and retrieving meteorological parameters from radio occultation data

A perspective on the fundamental quality of GPS radio occultation data

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