Analysis and validation of GPS/MET data in the neutral atmosphere

Rocken, Christian; Anthes, R. A.; Exner, Michael; Hunt, Doug; Sokolovskiy, Sergey; Ware, Randolph; Горбунов, М. Е.; Schreiner, William S.; Feng, D.; Herman, Benjamin M.; Kuo, Ying‐Hwa; Zou, Xiaolei

doi:10.1029/97jd02400

Cited by 546 publications

(483 citation statements)

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“…The accuracy of atmospheric variables retrieved from GPS/MET observations was found to be 0.4 % in refractivity and 1 K in temperature, at 0.5-1 km vertical resolution in the UTLS (Kursinski et al, 1996;Rocken et al, 1997;Steiner et al, 1999). The climatological analyses of CHAMP data revealed an accuracy of 0.4 K in the global-mean temperature in the UTLS and a 1 K standard deviation at an altitude of 10 km that increased to 2 K at 30 km (Wickert et al, 2004).…”

Section: Introductionmentioning

confidence: 87%

“…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%

“…However, these studies also showed that the errors in the RO retrievals above about 35 km were significant (Rieder and Kirchengast, 2001;Gobiet et al, 2007;Scherllin-Pirscher et al, 2011b). This is because from the stratosphere to the mesosphere, ionospheric error influences become more and more dominant (e.g., Mannucci et al, 2011;Liu et al, 2013).…”

Section: Introductionmentioning

confidence: 97%

“…Global Navigation Satellite System (GNSS) radio occultation (RO) (Melbourne et al, 1994;Kursinski et al, 1997;Hajj et al, 2002) is a relatively new atmospheric remote sensing technique. It can deliver data traceable to the international standard of time (the SI second) and has the potential for monitoring decadal-scale climate change (Steiner et al, 2009;Scherllin-Pirscher et al, 2011b;Lackner et al, 2011) due to its unique characteristics such as high vertical resolution, high accuracy and long-term stability of its observations, as well as self-calibration capability and global coverage (Gobiet and Kirchengast, 2004;Steiner et al, 2011). Figure 1 illustrates the GPS-to-LEO occultation geometry.…”

Section: Introductionmentioning

confidence: 99%

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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: Introductionmentioning

confidence: 87%

Section: Ionospheric Correction and Bending Angle Riementioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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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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“…Para o caso dos valores do IWV a partir das observações GPS, além dos fatores responsáveis pela latência já mencionados, existe também o tempo de processamento dos dados para a estimativa de valores do ZTD (Zenithal Tropospheric DelayAtraso Zenital Troposférico) em tempo real (Rocken et al, 1997b), os quais são convertidos em valores do IWV (Bevis et al, 1992). Para que tais valores tenham a menor latênciaé necessário que o método de processamento seja otimizado, de forma que o melhor resultado seja obtido com o menor custo computacional.…”

Section: Introductionunclassified

Assimilação do IWV-GPS no Brasil: otimização das estimativas do atraso zenital troposférico em tempo real

Sapucci¹,

Machado²,

Herdies³

et al. 2007

Rev. Bras. Geof.

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ABSTRACT. IWV (Integrated Water Vapor) values from the Brazilian Network for Continuous Monitoring (RBMC) of GPS (Global Positioning System) signals are additional sources of humidity information available for being used in Numerical Weather Prediction (NWP) models operating in the Brazilian meteorological centers.In order to obtain IWV-GPS values in an efficient approach, an optimization of the GPS data processing for estimating the ZTD values (Zenithal Tropospheric Delay) is involved, which should search for the best result with lowest computational cost. In this optimization process it is necessary to determine the ideal size of the so called sliding-window data involved in the real time data processing, which must be the as small as possible but providing results with the required quality. In this paper is investigated the ideal size of such sliding-window. An experiment was carried out in which GPS sliding-windows of different sizes were evaluated using simulations of a real time data processing. Comparing the obtained results with those from post-processed GPS data, it is observed that a sliding-window containing 7 hours of GPS data generated the best results from the operational point of view (rms of 1.61 and 1.82 kg m −2 for latency of 60 and 120 minutes, respectively).Keywords: IWV-GPS, ZTD, NWP, data assimilation. RESUMO. Valores do IWV (Integrated Water Vapor -Vapor D'água Integrado na coluna atmosférica) provenientes da Rede Brasileira de Monitoramento Contínuo(RBMC) dos Satélites GPS (Global Positioning System -Sistema de Posicionamento Global) compõem uma fonte adicional de informações da umidade para a assimilação em modelos operacionais de Previsão Numérica de Tempo (PNT) existentes no Brasil. Para que os valores do IWV-GPS sejam obtidos com maior eficiênciá e necessário uma otimização do processamento de dados GPS para a estimativa do ZTD (Zenithal Tropospheric Delay -Atraso Zenital Troposférico), de forma que resultados com qualidade adequada possam ser obtidos com custo computacional baixo. Nessa otimização deve-se definir o tamanho ideal da chamada janela deslizante (sliding window ) de dados GPS envolvidos no processamento em tempo real, a qual deve ser a menor possível, mas fornecendo resultados satisfatórios. O objetivo desse trabalhoé investigar sobre o tamanho ideal dessa janela de dados. Um experimento foi realizado envolvendo janelas de dados GPS de diferentes tamanhos, as quais foram testadas através de simulações de processamento em tempo real. Comparando os resultados simulados com aqueles obtidos no modo pós-processado, observou-se que do ponto de vista operacional o emprego de uma janela com 7 horas de dados proporciona os melhores resultados (Erro médio Quadrático de 1,61 e 1,82 kg m −2 para 60 e 120 minutos de latência, respectivamente).

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A noise‐aware combination of dual‐frequency measurements from GPS radio occultation

Wee

Kuo

2013

JGR Atmospheres

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[1] One of the fundamental difficulties that arise when using GPS Radio Occultation (RO) data in exploiting the stratosphere is that the air becomes rarefied with increasing height and accentuates the ionospheric effect and noise contained in the measurement. Customarily, the conventional linear combination (CLC) is used to extract neutral atmospheric components from dual-frequency (L1 and L2) RO data. The CLC combines and magnifies measurement noises, and thus works well only for those measurements of low noise. Although the L1 data are of considerably higher quality than the L2 data, the CLC does not take this into account and treats both equally; this makes the CLC-produced data less attractive. The authors propose a new approach, named Noise-Aware Combination (NAC), which is a generalized combination that factors in the presence of measurement noise. In this NAC method, the L1 and L2 data are each regarded independently, with each contributing to the combination according to its dynamically assessed accuracy. The performance of both the CLC and NAC are tested with two sets of data: one of synthetic data and the other of real data. The tests confirm that the NAC yields significant error reductions when compared to the CLC. While the noise in the CLC-produced data stands out in high altitudes and compels the data to be blended with the a priori, the NAC relies far less on this blending. The clear advantage of the NAC over the CLC would greatly enhance the value of RO for climate research.Citation: Wee, T.-K., and Y.-H. Kuo (2013), A noise-aware combination of dual-frequency measurements from GPS radio occultation,

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Analysis and validation of GPS/MET data in the neutral atmosphere

Cited by 546 publications

References 28 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

Assimilação do IWV-GPS no Brasil: otimização das estimativas do atraso zenital troposférico em tempo real

A noise‐aware combination of dual‐frequency measurements from GPS radio occultation

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