Error Characteristics of GPS Retrieved Refractivity Using a Simulation Study

Chen, Shu Hua; Vandenberghe, François; Huang, Ching Yuang

doi:10.2151/jmsj.84.477

Cited by 5 publications

(6 citation statements)

References 31 publications

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“…1b), ex cept be low 6 km where a larger dif fer ence arises pos si bly due to the data scar city for CHAMP at lower al ti tudes. The ob serva tion er ror pro duced by lo cal op er a tor shows an ap prox imately ex po nen tial de cay with a max i mum in the low est level of about 3%, which is con sis tent with the es ti mate of Chen et al (2006) us ing a 50-km res o lu tion. The nonlocal op er a tor pro duces smaller er rors even at the low est height, and the er rors are gen er ally less than 1% at all the lev els and 0.5% above 6 km.…”

Section: Ob Ser Va Tion Er Rorsmentioning

confidence: 55%

“…Af ter ap ply ing the Abel inversion for bend ing an gles, GPS RO refractivity pro files can be ob tained at an occultation point as an in ter me di ate prod uct with pre sumed lo cal spher i cal sym me try. There are sev eral im pact stud ies us ing GPS RO refractivity soundings (Kuo et al 2004Huang et al 2005;Chen et al 2006;Cucurull et al 2006). For ex am ple, Huang et al (2005) assim i lated sev eral GPS RO refractivity soundings into the fifth-gen er a tion Penn syl va nia State Uni ver sity Na tional Cen ter for At mo spheric Re search Mesoscale Model (MM5) with a three-di men sional variational data as sim i la tion system (3DVAR) and showed that both track ing and ac cu mulated rain fall pre dic tions were im proved in sim u lat ing two ty phoons which struck Tai wan, Nari (2001) and Nakri (2002).…”

Section: Introductionmentioning

confidence: 99%

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Assimilation of GPS Refractivity from FORMOSAT-3/COSMIC Using a Nonlocal Operator with WRF 3DVAR and Its Impact on the Prediction of a Typhoon Event

Chen¹,

Huang²,

Kuo³

et al. 2009

Terr. Atmos. Ocean. Sci.

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A nonlocal ob ser va tion op er a tor has been de vel oped to as sim i late GPS ra dio occultation (RO) refractivity with WRF 3DVAR. For sim plic ity, in the past GPS RO refractivity was of ten as sim i lated us ing a lo cal ob ser va tion op er a tor with the as sump tion that the GPS RO ob ser va tion was rep re sen ta tive of a model lo cal point. Such an op er a tor did not take into ac count the ef fects of hor i zon tal inhomogeneity on the de rived GPS RO refractivity. In or der to more ac cu rately model the observables, Sokolovskiy et al. (2005a) de vel oped a nonlocal ob ser va tion op er a tor, which would take into ac count the ef fects of hor i zon tal inhomogeneity on GPS RO mea sure ments. This nonlocal ob ser va tion op er a tor cal cu lates the in te grated amount of the model refractivity along the ray paths cen tered at the peri gee points. For com par a tive pur poses, the nonlocal ob ser va tion op er a tor can be sim pli fied by lim it ing the length of in te gra tion near the RO point. This is called the "lo cal op er a tor vari ant", which is equiv a lent to the orig i nal lo cal op er a tor ex cept that the orig i nal one is per formed with fixed tan gent points at ob ser va tion lev els. For com pu ta tional ef fi ciency, as sim i la tion us ing both the nonlocal op er a tor and lo cal op er a tor vari ant now is per formed with smear tan gent points at the mean height of each model ver ti cal level. In this study, the sta tis tics of ob ser va tion er rors us ing both lo cal and nonlocal op er a tors were es ti mated based on WRF sim u la tions. The ob ser va tion er rors produced by the nonlocal operator are about two times smaller than those generated by the local operator and in agreement with Sokolovskiy et al. (2005b).Each of the three op er a tors is used to as sim i late GPS RO refractivity soundings from the FORMOSAT-3/COS MIC mis sion us ing the WRF 3DVAR sys tem. The WRF model then is ap plied to sim u late Ty phoons Kaemi (July 2006) which struck Tai wan with sig nif i cant tor ren tial rain fall. The anal y sis in cre ments pro duced by the nonlocal op er a tor and lo cal op er a tor vari ant are quite sim i lar in hor i zon tal and ver ti cal dis tri bu tions; whereas, the for mer is slightly stretched along the ray's di rec tion, as a re sult of the lon ger in te gra tion length. The sim u lated ty phoon tracks prior to land fall are quite sim i lar for the three op er a tors. Both the nonlocal op er a tor and lo cal op er a tor vari ant im prove the de toured track af ter land fall as pre dicted by the lo cal op er a tor. The nonlocal op er a tor out per forms the two lo cal op er a tors in rain fall pre dic tion at later times. The per for mances of the nonlocal op er a tor in gen eral are promising and can replace the local operator at no marked cost of computational efficiency.Key words: FORMOSAT-3/COS MIC, Data as sim i la tion, Typhoon Ci ta tion: Chen, S. Y., C. Y. Huang, Y. H. Kuo, Y. R. Guo, and S. Sokolovskiy, 2009: As sim i la tion of GPS refractivity from FORM...

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Section: Ob Ser Va Tion Er Rorsmentioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Assimilation of GPS Refractivity from FORMOSAT-3/COSMIC Using a Nonlocal Operator with WRF 3DVAR and Its Impact on the Prediction of a Typhoon Event

Chen¹,

Huang²,

Kuo³

et al. 2009

Terr. Atmos. Ocean. Sci.

Self Cite

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“…1, covering latitudes from about 108S to 508N and longitudes from 808 to 1608E, with a model top of 50 hPa (31 model vertical levels) with varied vertical resolution. The horizontal resolution of 45 km in this study should be appropriate for the error estimation according to Chen et al (2006). They computed the innovation using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) with different horizontal resolutions and found that the representativeness error from 30-km resolution is compatible with that of 10-km resolution.…”

Section: E Model Settings and Calculation Stepsmentioning

confidence: 94%

Observational Error Estimation of FORMOSAT-3/COSMIC GPS Radio Occultation Data

Chen

Huang

Kuo

et al. 2011

Monthly Weather Review

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The Global Positioning System (GPS) radio occultation (RO) technique is becoming a robust global observing system. GPS RO refractivity is typically modeled at the ray perigee point by a ''local refractivity operator'' in a data assimilation system. Such modeling does not take into account the horizontal gradients that affect the GPS RO refractivity. A new observable (linear excess phase), defined as an integral of the refractivity along some fixed ray path within the model domain, has been developed in earlier studies to account for the effect of horizontal gradients.In this study, the error statistics of both observables (refractivity and linear excess phase) are estimated using the GPS RO data from the Formosa Satellite 3-Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) mission. The National Meteorological Center (NMC) method, which is based on lagged forecast differences, is applied for evaluation of the model forecast errors that are used for estimation of the GPS RO observational errors. Also used are Weather Research and Forecasting (WRF) model forecasts in the East Asia region at 45-km resolution for one winter month (midJanuary to mid-February) and one summer month (mid-August to mid-September) in 2007.Fractional standard deviations of the observational errors of refractivity and linear excess phase both show an approximately linear decrease with height in the troposphere and a slight increase above the tropopause; their maximum magnitude is about 2.2% (2.5%) for refractivity and 1.1% (1.3%) for linear excess phase in the lowest 2 km for the winter (summer) month. An increase of both fractional observational errors near the surface in the summer month is attributed mainly to a larger amount of water vapor. The results indicate that the fractional observational error of refractivity is about twice as large as that of linear excess phase, regardless of season. The observational errors of both linear excess phase and refractivity are much less latitude dependent for summer than for winter. This difference is attributed to larger latitudinal variations of the specific humidity in winter.

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“…The ray tracing technique has been applied to assess the impact of data assimilation (Zou et al 1999;Liu and Zou 2003;Zhang et al 2004) and support the RO observation (Lusignan et al 1969;Beyerle and Hocke 2001;Yeh et al 2012). It also has been applied to develop retrieval methods or estimate retrieval errors (Zou et al 2002;Jensen et al 2003;Chen et al 2006;Li and Kiang 2011;Mannucci et al 2011).…”

Section: Introductionmentioning

confidence: 99%

“…For this purpose the earth's atmosphere is assumed to be nonspherically symmetric. The analytic atmosphere models, such as the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF), are used in the ray tracing operator (Zou et al 1999(Zou et al , 2002Liu and Zou 2003;von Engeln et al 2003;Zhang et al 2004;Chen et al 2006) with the elliptical earth. Nevertheless, the initial and end points of the signal in the former ray tracing operators are not considered to correspond to the position of the GPS and LEO satellites.…”

Section: Introductionmentioning

confidence: 99%

Ray Tracing Simulation in Nonspherically Symmetric Atmosphere for GPS Radio Occultation

Yeh¹,

Huang²,

Chiu³

et al. 2014

Terr. Atmos. Ocean. Sci.

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A three-dimensional ray tracing model with aiming algorithms for global positioning system (GPS) signal is proposed to make simulations conform to the realistic radio occultation (RO) signal propagation. The two aiming algorithms used in this study ensure the initial and end point ray trajectories are located in the prescribed region. In past studies, the ray tracing techniques applied to the RO signal simulation usually assumed a spherically symmetrical atmosphere for simplicity. The exact GPS and low earth orbit (LEO) satellite locations are not considered in the simulation. These two assumptions make the simulation unrealistic for GPS signal propagation in the RO technique. In the proposed model, the shape of the earth is assumed as an ellipse. The information from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is used to setup the atmosphere in the simulation. Two aiming algorithms are developed to determine the initial signal propagating direction to make the simulated signal start from the prescribed GPS satellite position and end in the close vicinity of the LEO satellite position. An ideal spherical symmetric atmospheric structure is used to verify the ray tracing model. The fractional difference between real and simulated refractivity results is less than 0.1%. Otherwise, the GPS and LEO satellite position in the Formosat-3/COSMIC observation and the ECMWF analysis, considering the earth's flattening, is also used to verify the aiming algorithms. All of the simulated signals end in close vicinity to the LEO satellite position in the simulation results.

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Error Characteristics of GPS Retrieved Refractivity Using a Simulation Study

Cited by 5 publications

References 31 publications

Assimilation of GPS Refractivity from FORMOSAT-3/COSMIC Using a Nonlocal Operator with WRF 3DVAR and Its Impact on the Prediction of a Typhoon Event

Assimilation of GPS Refractivity from FORMOSAT-3/COSMIC Using a Nonlocal Operator with WRF 3DVAR and Its Impact on the Prediction of a Typhoon Event

Observational Error Estimation of FORMOSAT-3/COSMIC GPS Radio Occultation Data

Ray Tracing Simulation in Nonspherically Symmetric Atmosphere for GPS Radio Occultation

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