GNSS radio occultation profiles in the neutral atmosphere from inversion of excess phase data

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new-generation payloads onboard the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. The GNOS was designed for acquiring setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou System (BDS) and the US Global Positioning System (GPS). An ultra-stable oscillator with 1 s stability (Allan deviation) at the level of 10−12 was installed on the FY-3C GNOS, and thus both zero-difference and single-difference excess phase processing methods should be feasible for FY-3C GNOS observations. In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing, in order to investigate the zero-difference feasibility for this new instrument, which after its launch in September 2013 started to use BDS signals from five geostationary orbit (GEO) satellites, five inclined geosynchronous orbit (IGSO) satellites and four medium Earth orbit (MEO) satellites. We used a 3-month set of GNOS BDS RO data (October to December 2013) for the evaluation and compared atmospheric bending angle and refractivity profiles, derived from single- and zero-difference excess phase data, against co-located profiles from European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. We also compared against co-located refractivity profiles from radiosondes. The statistical evaluation against these reference data shows that the results from single- and zero-difference processing are reasonably consistent in both bias and standard deviation, clearly demonstrating the feasibility of zero differencing for GNOS BDS RO observations. The average bias (and standard deviation) of the bending angle and refractivity profiles were found to be about 0.05 to 0.2 % (and 0.7 to 1.6 %) over the upper troposphere and lower stratosphere. Zero differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. The validation results indicate that GNOS can provide, on top of GPS RO profiles, accurate and precise BDS RO profiles both from single- and zero-difference processing. The GNOS observations by the series of FY-3 satellites are thus expected to provide important contributions to numerical weather prediction and global climate change analysis.

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Evaluation of atmospheric profiles derived from single- and zero-difference excess phase processing of BeiDou System radio occultation data of the FY-3C GNOS mission

10.5194/amt-2017-177 ◽

2017 ◽

Cited By ~ 1

Author(s):

Weihua Bai ◽

Congliang Liu ◽

Xiangguang Meng ◽

Yueqiang Sun ◽

Gottfried Kirchengast ◽

...

Keyword(s):

Standard Deviation ◽

Radio Occultation ◽

Weather Prediction ◽

Neutral Atmosphere ◽

Change Analysis ◽

Bending Angle ◽

New Instrument ◽

Beidou System ◽

Single Difference ◽

Excess Phase

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new generation payloads onboard the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth’s neutral atmosphere and ionosphere. GNOS was designed for acquiring setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou System (BDS) and the U.S. Global Positioning System (GPS). An ultra-stable oscillator with 1-sec stability (Allan deviation) at the level of 10−12 was installed on FY-3C GNOS, thus both zero-difference and single-difference excess phase processing methods should be feasible for FY-3C GNOS observations. In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing, in order to investigate the zero-difference feasibility for this new instrument, which after its launch in September 2013 started to use BDS signals from 5 geostationary orbit (GEO) satellites, 5 inclined geosynchronous orbit (IGSO) satellites and 4 medium earth orbit (MEO) satellites. We used a 3-month set of GNOS BDS RO data (October to December 2013) for the evaluation and compared atmospheric bending angle and refractivity profiles, derived from single- and zero-difference excess phase data, against co-located profiles from ECMWF (European Centre for Medium-Range Weather Forecasts) analyses. We also compared against co-located refractivity profiles from radiosondes. The statistical evaluation against these reference data shows that the results from single- and zero-difference processing are consistent in both bias and standard deviation, clearly demonstrating the feasibility of zero-differencing for GNOS BDS RO observations. The average bias (and standard deviation) of the bending angle and refractivity profiles were found to be as small as about 0.05 %–0.2 % (and 0.7 %–1.6 %) over the upper troposphere and lower stratosphere, including for the GEO, IGSO, and MEO subsets. Zero-differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. The validation results establish that GNOS can provide, on top of GPS RO profiles, accurate and precise BDS RO profiles both from single- and zero-difference processing. The GNOS observations by the series of FY-3 satellites will thus provide important contributions to numerical weather prediction and global climate change analysis.

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Parallelization Strategies for the GPS Radio Occultation Data Assimilation with a Nonlocal Operator in the Weather Research and Forecasting Model

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00195.1 ◽

2014 ◽

Vol 31 (9) ◽

pp. 2008-2014 ◽

Cited By ~ 2

Author(s):

Xin Zhang ◽

Ying-Hwa Kuo ◽

Shu-Ya Chen ◽

Xiang-Yu Huang ◽

Ling-Feng Hsiao

Keyword(s):

Data Assimilation ◽

Radio Occultation ◽

Weather Prediction ◽

Weather Research And Forecasting ◽

Forecasting Model ◽

Observation Operator ◽

Gps Radio Occultation ◽

Phase Observation ◽

Excess Phase ◽

Weather Research

Abstract The nonlocal excess phase observation operator for assimilating the global positioning system (GPS) radio occultation (RO) sounding data has been proven by some research papers to produce significantly better analyses for numerical weather prediction (NWP) compared to the local refractivity observation operator. However, the high computational cost and the difficulties in parallelization associated with the nonlocal GPS RO operator deter its application in research and operational NWP practices. In this article, two strategies are designed and implemented in the data assimilation system for the Weather Research and Forecasting Model to demonstrate the capability of parallel assimilation of GPS RO profiles with the nonlocal excess phase observation operator. In particular, to solve the parallel load imbalance problem due to the uneven geographic distribution of the GPS RO observations, round-robin scheduling is adopted to distribute GPS RO observations among the processing cores to balance the workload. The wall clock time required to complete a five-iteration minimization on a demonstration Antarctic case with 106 GPS RO observations is reduced from more than 3.5 h with a single processing core to 2.5 min with 106 processing cores. These strategies present the possibility of application of the nonlocal GPS RO excess phase observation operator in operational data assimilation systems with a cutoff time limit.

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Radio Occultation Exploration of Mars

Symposium - International Astronomical Union ◽

10.1017/s0074180900025523 ◽

1974 ◽

Vol 65 ◽

pp. 295-316 ◽

Cited By ~ 2

Author(s):

A.J. Kliore

Keyword(s):

Carbon Dioxide ◽

Surface Pressure ◽

Atmospheric Pressure ◽

Radio Occultation ◽

Extreme Ultraviolet ◽

Temperature Gradients ◽

Temperature Structure ◽

Neutral Atmosphere ◽

Quality Of Data ◽

Radio System

The radio occultation technique, consisting of the observation of changes in the phase, frequency, and amplitude of a radio signal from a spacecraft as it passes through the atmosphere of a planet before and after occultation, was first applied to measure the atmosphere of Mars with the Mariner IV spacecraft in 1965. The interpretation of these changes in terms of refraction of the radio beam by the neutral atmosphere and ionosphere of the planet provided the first direct and quantitative measurement of its vertical structure and established the surface atmospheric pressure of Mars as lying between 5 and 9 mb. The presence of a daytime ionosphere with a peak electron density of about 105 el cm−3 was also measured. The Mariner VI and VII spacecraft flew by Mars in 1969 and provided an additional four measurements of the atmosphere and surface radius of the planet. They confirmed the surface pressure values measured by Mariner IV and provided data for a crude estimate of the shape of the planet.By far the greatest volume of radio occultation information on the atmosphere and surface of Mars was returned by the Mariner IX orbiter which was placed in orbit about Mars in November of 1971. During three occultation episodes in November-December 1971, May-June 1972, and September-October 1972, the Mariner IX mission provided 260 successful radio occultation measurements.The early measurements, made at the time of the Martian dust storm of 1971, showed greatly reduced temperature gradients in the daytime troposphere, indicating the heating effect of the dust. The temperature gradients that were measured later in the mission, when the atmosphere was apparently free of dust, were still much lower than expected under conditions of radiative-convective balance, indicating that dynamics may play a large part in determining the temperature structure of the Martian troposphere. Temperatures taken at night near the winter poles were consistent with the condensation of carbon dioxide.The surface atmospheric pressure was observed to vary widely with topography ranging from about 1 mb at the summit of the Middle Spot volcano (Pavonis Mons) to over 10 mb in the North circumpolar region. In the South equatorial region the highest surface pressure of about 9 mb was measured at the bottom of the Hellas basin.The radius of the planet was measured with accuracies ranging from about 0.25 to about 2.1 km over latitudes ranging from 86° to −80°. These measurements have shown that Mars has pronounced equatorial and north-south asymmetries, which make it difficult to represent its shape by a simple triaxial figure.The daytime ionosphere measurements indicated that the main ionization peak was similar in behavior to a terrestrial F1 layer and is probably produced by photoionization of carbon dioxide by solar extreme ultraviolet. Comparison of the heights of the maximum between the early data taken in November-December, 1971, and the Extended Mission of May-June 1972, showed that the lower atmospheric temperatures decreased by about 25%, which is consistent with clearing of the atmosphere.The experience gained from Mars radio occultation experiments suggests that the quality of data can be significantly improved by such features of the spacecraft radio system as a stable oscillator, dual frequency downlink capability, and a steerable high-gain antenna.

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Estimation and evaluation of COSMIC radio occultation excess phase using undifferenced measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-10-1813-2017 ◽

2017 ◽

Vol 10 (5) ◽

pp. 1813-1821

Author(s):

Pengfei Xia ◽

Shirong Ye ◽

Kecai Jiang ◽

Dezhong Chen

Keyword(s):

Radio Occultation ◽

Weather Prediction ◽

Lower Troposphere ◽

Double Difference ◽

Cosmic Radio ◽

Processing Strategy ◽

Single Difference ◽

Excess Phase ◽

Mean Square Errors ◽

Better Than

Abstract. In the GPS radio occultation technique, the atmospheric excess phase (AEP) can be used to derive the refractivity, which is an important quantity in numerical weather prediction. The AEP is conventionally estimated based on GPS double-difference or single-difference techniques. These two techniques, however, rely on the reference data in the data processing, increasing the complexity of computation. In this study, an undifferenced (ND) processing strategy is proposed to estimate the AEP. To begin with, we use PANDA (Positioning and Navigation Data Analyst) software to perform the precise orbit determination (POD) for the purpose of acquiring the position and velocity of the mass centre of the COSMIC (The Constellation Observing System for Meteorology, Ionosphere and Climate) satellites and the corresponding receiver clock offset. The bending angles, refractivity and dry temperature profiles are derived from the estimated AEP using Radio Occultation Processing Package (ROPP) software. The ND method is validated by the COSMIC products in typical rising and setting occultation events. Results indicate that rms (root mean square) errors of relative refractivity differences between undifferenced and atmospheric profiles (atmPrf) provided by UCAR/CDAAC (University Corporation for Atmospheric Research/COSMIC Data Analysis and Archive Centre) are better than 4 and 3 % in rising and setting occultation events respectively. In addition, we also compare the relative refractivity bias between ND-derived methods and atmPrf profiles of globally distributed 200 COSMIC occultation events on 12 December 2013. The statistical results indicate that the average rms relative refractivity deviation between ND-derived and COSMIC profiles is better than 2 % in the rising occultation event and better than 1.7 % in the setting occultation event. Moreover, the observed COSMIC refractivity profiles from ND processing strategy are further validated using European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data, and the results indicate that the undifferenced method reduces the noise level on the excess phase paths in the lower troposphere compared to the single-difference processing strategy.

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The FengYun-3C radio occultation sounder GNOS: a review of the mission and its early results and science applications

Atmospheric Measurement Techniques ◽

10.5194/amt-11-5797-2018 ◽

2018 ◽

Vol 11 (10) ◽

pp. 5797-5811 ◽

Cited By ~ 11

Author(s):

Yueqiang Sun ◽

Weihua Bai ◽

Congliang Liu ◽

Yan Liu ◽

Qifei Du ◽

...

Keyword(s):

Quality Evaluation ◽

Radio Occultation ◽

Global Climate ◽

Weather Prediction ◽

Satellite System ◽

Navigation Satellite ◽

Neutral Atmosphere ◽

Scientific Applications ◽

Early Results ◽

Global Navigation Satellite

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new-generation payloads on board the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. FY-3C GNOS, on board the FY-3 series C satellite launched in September 2013, was designed to acquire setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou Navigation Satellite System (BDS) and the US Global Positioning System (GPS). So far, the GNOS measurements and atmospheric and ionospheric data products have been validated and evaluated and then been used for atmosphere- and ionosphere-related scientific applications. This paper reviews the FY-3C GNOS instrument, RO data processing, data quality evaluation, and preliminary research applications according to the state-of-the-art status of the FY-3C GNOS mission and related publications. The reviewed data validation and application results demonstrate that the FY-3C GNOS mission can provide accurate and precise atmospheric and ionospheric GNSS (i.e., GPS and BDS) RO profiles for numerical weather prediction (NWP), global climate monitoring (GCM), and space weather research (SWR). The performance of the FY-3C GNOS product quality evaluation and scientific applications establishes confidence that the GNOS data from the series of FY-3 satellites will provide important contributions to NWP, GCM, and SWR scientific communities.

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The Neutral Atmosphere of Venus as Studied with the Mariner V Radio Occultation Experiments

The Astronomical Journal ◽

10.1086/111096 ◽

1971 ◽

Vol 76 ◽

pp. 123 ◽

Cited By ~ 367

Author(s):

Gunnar Fjeldbo ◽

Arvydas J. Kliore ◽

Von R. Eshleman

Keyword(s):

Radio Occultation ◽

Neutral Atmosphere ◽

Atmosphere Of Venus

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Aspects of design antennas for radio occultation method of ionosphere diagnostics

ITM Web of Conferences ◽

10.1051/itmconf/20193005012 ◽

2019 ◽

Vol 30 ◽

pp. 05012

Author(s):

Alexander Generalov ◽

Elchin Gadzhiev ◽

Pavel Shmachilin ◽

Yuri Polushkovskiy ◽

Vladimir Skripachev ◽

...

Keyword(s):

Solar Radiation ◽

Radio Occultation ◽

Practical Importance ◽

Atmospheric Electricity ◽

Upper Atmosphere ◽

Radio Propagation ◽

Neutral Atmosphere ◽

The Earth

The ionosphere is the ionized part of Earth's upper atmosphere, from about 60 km to 1,000 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. The region below the ionosphere is called neutral atmosphere, or neutrosphere. In this paper aspects of design antennas for radio occultation method of ionosphere diagnostics are presented.

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Evaluation of a Linear Phase Observation Operator with CHAMP Radio Occultation Data and High-Resolution Regional Analysis

Monthly Weather Review ◽

10.1175/mwr3006.1 ◽

2005 ◽

Vol 133 (10) ◽

pp. 3053-3059 ◽

Cited By ~ 19

Author(s):

S. Sokolovskiy ◽

Y-H. Kuo ◽

W. Wang

Keyword(s):

High Resolution ◽

Radio Occultation ◽

Regional Analysis ◽

Observation Error ◽

Computationally Efficient ◽

Observation Operator ◽

Simple Implementation ◽

Excess Phase ◽

Occultation Data ◽

Radio Occultation Data

Abstract In this study a nonlocal, linear observation operator for assimilating radio occultation data is evaluated. The operator consists of modeling the excess phase, that is, integrating the refractivity along straight lines tangent to rays, below a certain height. The corresponding observable is the excess phase integrated through the Abel-retrieved refractivity, along the same lines, below the same height. The operator allows very simple implementation (computationally efficient) while accurately accounting for the horizontal refractivity gradients. This is due to significant cancellation of the linearization and discretization errors when modeling the observable. Evaluation of the operator with Challenging Minisatellite Payload (CHAMP) radio occultation data and grid refractivity fields from high-resolution regional analysis over the continental United States showed reduction of the observation error in the troposphere (below 7 km) 1.5–2 times, compared to the error of local refractivity. The operator is useful for the assimilation of radio occultation data by high-resolution weather models in the troposphere.

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Wave-optics uncertainty propagation and regression-based bias model in GNSS radio occultation bending angle retrievals

10.5194/amt-2017-145 ◽

2017 ◽

Author(s):

Michael Gorbunov ◽

Gottfried Kirchengast

Keyword(s):

Regression Analysis ◽

Systematic Uncertainty ◽

Radio Occultation ◽

Uncertainty Propagation ◽

Lower Troposphere ◽

Wave Optics ◽

Bending Angle ◽

Excess Phase ◽

Excess Phases ◽

Random Uncertainties

Abstract. A new reference occultation processing system (rOPS) will include a Global Navigation Satellite System (GNSS) radio occultation (RO) retrieval chain with integrated uncertainty propagation. In this paper, we focus on wave-optics bending angle retrieval in the lower troposphere and introduce 1. an empirically estimated boundary layer bias (BLB) model then employed to reduce the systematic uncertainty of excess phases and bending angles in the lowest about two kilometers of the troposphere, and 2. the estimation of (residual) systematic uncertainties and their propagation together with random uncertainties from excess phase to bending angle profiles. Our BLB model describes the estimated bias of the excess phase transferred from the estimated bias of the bending angle, for which the model is built, informed by analyzing refractivity fluctuation statistics shown to induce such biases. The model is derived from regression analysis using a large ensemble of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO observations and concurrent European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields. It is formulated in terms predictors and adaptive functions (powers and cross-products of predictors), where we use six main predictors derived from observations: impact altitude, latitude, bending angle and its standard deviation, canonical transform amplitude and its fluctuation index. Based on an ensemble of test days, independent of the days of data used for the regression analysis to establish the BLB model, we find the model very effective for bias reduction, capable of reducing bending angle and corresponding refractivity biases by about a factor of five. The estimated residual systematic uncertainty, after the BLB profile subtraction, is lower-bounded by the uncertainty from (indirect) use of ECMWF analysis fields but is significantly lower than the systematic uncertainty without BLB correction. The systematic and random uncertainties are propagated from excess phase to bending angle profiles, using a perturbation approach and the wave-optical method recently introduced by Gorbunov and Kirchengast (2015), starting with estimated excess phase uncertainties. The results are encouraging that this uncertainty propagation approach combined with BLB correction enables a robust reduction and quantification of the uncertainties of excess phases and bending angles in the lower troposphere.

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