Simulating the Influence of Horizontal Gradients on Retrieved Profiles from ATOMS Occultation Measurements — a Promising Approach for Data Assimilation

Syndergaard, Stig; Flittner, D. E.; Kursinski, E. R.; Feng, D.; Herman, Benjamin M.; Ward, D.

doi:10.1007/978-3-662-09041-1_20

Cited by 13 publications

(12 citation statements)

References 14 publications

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“…1: Syndergaard et al (2003) suggested to invert S mod (r tp ) on the assumption of spherical symmetry of refractivity, thus modeling the AR refractivity N ar (r) more accurately than it can be modeled by local refractivity. In our approach we do not invert the phase, S mod (r tp ), instead, we calculate its observation counterpart S obs (r tp ) by integrating the AR refractivity along the same straight lines below H top :…”

Section: The Excess Phase Linear Observation Operatormentioning

confidence: 99%

“…Accurate modeling of RO observables by ray tracing is computationally expensive (Liu and Zou 2003;Gorbunov and Kornblueh 2003;Poli and Joiner 2004). Alternative approaches consist of using simplified nonlocal observation operators that provide sufficient accuracy and are computationally efficient (Poli 2004;Sokolovskiy et al 2005;Syndergaard et al 2003Syndergaard et al , 2005.…”

Section: Introductionmentioning

confidence: 99%

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

Sokolovskiy

Kuo

Wang

2005

Monthly Weather Review

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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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Section: The Excess Phase Linear Observation Operatormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Sokolovskiy

Kuo

Wang

2005

Monthly Weather Review

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“…We restricted the simulations to GPS radio occultation measurements, that is, only considering the measurements and mapping of the real part of the refractivity for a frequency of about 1.5 GHz. Other simulation experiments using the mapping operator, including the simulation of absorption measurements, have been reported elsewhere (Syndergaard et al , 2004Herman et al 2003). Also, Sokolovskiy et al (2005) presents simulation results using the refractivity mapping principle as well as a very similar approach.…”

Section: Numerical Verificationmentioning

confidence: 98%

“…The details and different aspects of the processing and inversion of GPS occultation signals have been described by a number of authors (e.g., Melbourne et al 1994;Kursinski et al 1997;Rocken et al 1997;Syndergaard 1998;Gorbunov and Gurvich 1998;Schreiner et al 1998;Steiner et al 1999;Feng and Herman 1999;Healy and Eyre 2000;Healy 2001b;Hajj et al 2002;Gorbunov 2002;Kuo et al 2004). Briefly, the GPS signals, which are observed by a receiver in LEO, are converted into profiles of ray path bending angle, ␣, versus impact parameter, a (the perpendicular distance between either of the derived ray asymptotes and the local center of curvature of the earth), using as a constraint an assumption of local spherical symmetry of the refractive index field.…”

Section: Introductionmentioning

confidence: 99%

A Refractive Index Mapping Operator for Assimilation of Occultation Data

Syndergaard

Kursinski

Herman

et al. 2005

Monthly Weather Review

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This paper describes the details of a fast, linear, forward-inverse refractive index mapping operator that can be used for assimilation of occultation data of various kinds into NWP models. Basically, the mapping consists of the integration of the refractive index along finite straight lines, mimicking the observational geometry as well as the subsequent retrieval of a refractive index profile, assuming spherical symmetry. Line integrals are discretized such that the refractivity is evaluated along the horizontal at fixed levels that can be chosen to coincide with the pressure levels of an NWP model. Integration of the hydrostatic equation at a large number of locations is thereby avoided. The mapping operator is tested using an idealized model of a weather front with large horizontal gradients. Mapped refractivity profiles are compared with retrieved refractivity profiles obtained via accurate 3D ray tracing simulations of GPS radio occultation events with ray path tangent points near the weather front. The simulations indicate that the mapping is a good representation of occultation measurements, including the influence large horizontal gradients have on retrieved refractivity profiles. To further the results, a simple ad hoc modification is introduced to approximately account for the ray path bending near the tangent points. The forward-inverse mapping allows for the near cancellation of otherwise crude approximations-for example, straight-line propagation-and the general concept could perhaps be adapted for the development of fast and accurate observation operators for the assimilation of other types of remote sensing data.

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“…A non-local refractivity or excess phase delay scheme is a compromise of the simulation accuracy and computational efficiency [23][24][25][26]. In such a scheme, the simulated GPS refractivity is expressed as a weighted sum of the atmospheric refractivity along the ray path, accounting for the along-track gradient of the refractivity.…”

Section: Introductionmentioning

confidence: 99%

Test of a non-local excess phase delay operator for GPS radio occultation data assimilation

Shao

Zou

Hajj

2009

J. Appl. Remote Sens

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A physically-sound, non-local excess phase delay observation operator is developed for simulating excess phase delay measurements from GPS radio occultation (RO) missions. By approximating an observed ray by a straight line, the refractivity gradient information along an observed ray path is included in the simulated excess phase delay. This observation operator is used to simulate observations from the German CHAllenging Minisatellite Payload (CHAMP) RO mission based on large-scale analysis. The need to use such an observation operator for GPS RO data assimilation in spherically asymmetric regions is shown by results from a set of forward simulation and data assimilation experiments. A modification that renders the non-local excess phase delay observation operator more suitable for parallel implementation of GPS RO data assimilation is proposed.

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Simulating the Influence of Horizontal Gradients on Retrieved Profiles from ATOMS Occultation Measurements — a Promising Approach for Data Assimilation

Cited by 13 publications

References 14 publications

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

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

A Refractive Index Mapping Operator for Assimilation of Occultation Data

Test of a non-local excess phase delay operator for GPS radio occultation data assimilation

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