Comparison of Ray-Tracing Packages for Troposphere Delays

Nafisi, Vahab; Urquhart, Landon; Santos, Marcelo C.; Geremia‐Nievinski, Felipe; Böhm, Johannes; Wijaya, Dudy D.; Schuh, Harald; Ardalan, Alireza A.; Hobiger, Thomas; Ichikawa, Ryuichi; Zus, Florian; Wickert, Jens; Gégout, P.

doi:10.1109/tgrs.2011.2160952

Cited by 66 publications

(59 citation statements)

References 26 publications

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“…Such inaccuracies could be avoided by using a ray-tracing algorithm. For a comprehensive overview on ray-tracing algorithms and comparisons the reader is referred to Nafisi et al (2012).…”

Section: Assessment Of the Hydrostatic Wet And Hydrometeor Contributmentioning

confidence: 99%

Inter-technique validation of tropospheric slant total delays

et al. 2017

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Abstract. An extensive validation of line-of-sight tropospheric slant total delays (STD) from Global Navigation Satellite Systems (GNSS), ray tracing in numerical weather prediction model (NWM) fields and microwave water vapour radiometer (WVR) is presented. Ten GNSS reference stations, including collocated sites, and almost 2 months of data from 2013, including severe weather events were used for comparison. Seven institutions delivered their STDs based on GNSS observations processed using 5 software programs and 11 strategies enabling to compare rather different solutions and to assess the impact of several aspects of the processing strategy. STDs from NWM ray tracing came from three institutions using three different NWMs and ray-tracing software. Inter-techniques evaluations demonstrated a good mutual agreement of various GNSS STD solutions compared to NWM and WVR STDs. The mean bias among GNSS solutions not considering post-fit residuals in STDs was −0.6 mm for STDs scaled in the zenith direction and the mean standard deviation was 3.7 mm. Standard deviations of comparisons between GNSS and NWM ray-tracing solutions were typically 10 mm ± 2 mm (scaled in the zenith direction), depending on the NWM model and the GNSS station. Comparing GNSS versus WVR STDs reached standard deviations of 12 mm ± 2 mm also scaled in the zenith direction. Impacts of raw GNSS post-fit residuals and cleaned residuals on optimal reconstructing of GNSS STDs were evaluated at intertechnique comparison and for GNSS at collocated sites. The use of raw post-fit residuals is not generally recommended as they might contain strong systematic effects, as demonstrated in the case of station LDB0. Simplified STDs reconstructed only from estimated GNSS tropospheric parameters, i.e. without applying post-fit residuals, performed the best in all the comparisons; however, it obviously missed part of tropospheric signals due to non-linear temporal and spatial variations in the troposphere. Although the post-fit residuals cleaned of visible systematic errors generally showed a slightly worse performance, they contained significant tropospheric signal on top of the simplified model. They are thus recommended for the reconstruction of STDs, particularly during high variability in the troposphere. Cleaned residuals also showed a stable performance during ordinary days while containing promising information about the troposphere at low-elevation angles.

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“…Such inaccuracies could be avoided by using a ray-tracing algorithm. For a comprehensive overview on ray-tracing algorithms and comparisons the reader is referred to Nafisi et al (2012).…”

Section: Assessment Of the Hydrostatic Wet And Hydrometeor Contributmentioning

confidence: 99%

Inter-technique validation of tropospheric slant total delays

et al. 2017

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“…The difference between these two excess phase-paths is about 5 m at all elevation angles. Other parameters like slant delays and slant factors involved in a typical ray-tracing method were discussed in [27]. However, the minimum altitude required to acquire accurate phase-paths was not conclusive for ground-based RO techniques, and 40 km was frequently adopted as the upper bound of integration for computing phase-paths [18].…”

Section: Effect Of Upper Bound On Excess Phase-pathmentioning

confidence: 99%

Retrieval of Refractivity Profile With Ground-Based Radio Occultation by Using an Improved Harmony Search Algorithm

Chiou¹,

Kiang²

2016

PIER M

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Abstract-A ground-based radio occultation (RO) technique is proposed to retrieve the atmospheric refractivity profile around a specific region at a higher sampling rate than conventional space-based RO techniques, making it more suitable for regional weather studies. A harmony search (HS) algorithm with ensemble consideration (HS-EC) based on atmospheric physics is proposed to retrieve the refractivity profile more efficiently without being trapped in suboptimal solutions. The highest altitude of profile is extended to 95 km from 40 km adopted in conventional ground-based RO techniques, leading to more accurate results.

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“…Although modern mapping functions like VMF1 (Boehm et al, 2006b) and GPT2/VMF1 (Lagler et al, 2013) are derived from numerical weather models (NWM), most of these mapping functions ignore the azimuth dependency, which is usually introduced by two horizontal gradient parameters -in the northsouth and east-west directions -estimated directly from observations (Chen et al, 1997). More recently, the use of raytraced delays through NWM directly at observation level has shown an improvement in geodetic results (Hobiger et al, 2008;Nafisi et al, 2012;Zus et al, 2012). The adaptive mapping functions (AMF) are designed to fit most of the information available in NWM -especially the azimuth dependency -preserving the classical mapping function strategy.…”

Section: Adaptive Mapping Functionsmentioning

confidence: 99%

Simulations of direct and reflected wave trajectories for ground-based GNSS-R experiments

et al. 2014

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Abstract. The detection of Global Navigation Satellite System (GNSS) signals that are reflected off the surface, along with the reception of direct GNSS signals, offers a unique opportunity to monitor water level variations over land and ocean. The time delay between the reception of the direct and reflected signals gives access to the altitude of the receiver over the reflecting surface. The field of view of the receiver is highly dependent on both the orbits of the GNSS satellites and the configuration of the study site geometries. A simulator has been developed to determine the location of the reflection points on the surface accurately by modeling the trajectories of GNSS electromagnetic waves that are reflected by the surface of the Earth. Only the geometric problem was considered using a specular reflection assumption. The orbit of the GNSS constellation satellites (mainly GPS, GLONASS and Galileo), and the position of a fixed receiver, are used as inputs. Four different simulation modes are proposed, depending on the choice of the Earth surface model (local plane, osculating sphere or ellipsoid) and the consideration of topography likely to cause masking effects. Angular refraction effects derived from adaptive mapping functions are also taken into account. This simulator was developed to determine where the GNSS-R receivers should be located to monitor a given study area efficiently. In this study, two test sites were considered: the first one at the top of the 65 m Cordouan lighthouse in the Gironde estuary, France, and the second one on the shore of Lake Geneva (50 m above the reflecting surface), at the border between France and Switzerland. This site is hidden by mountains in the south (orthometric altitude up to 2000 m), and overlooking the lake in the north (orthometric altitude of 370 m). For this second test site configuration, reflections occur until 560 m from the receiver. The planimetric (arc length) differences (or altimetric difference as WGS84 ellipsoid height) between the positions of the specular reflection points obtained considering the Earth's surface as an osculating sphere or as an ellipsoid were found to be on average 9 cm (or less than 1 mm) for satellite elevation angles greater than 10 • , and 13.9 cm (or less than 1 mm) for satellite elevation angles between 5 and 10 • . The altimetric and planimetric differences between the plane and sphere approximations are on average below 1.4 cm (or less than 1 mm) for satellite elevation angles greater than 10 • and below 6.2 cm (or 2.4 mm) for satellite elevation angles between 5 and 10 • . These results are the means of the differences obtained during a 24 h simulation with a complete GPS and GLONASS constellation, and thus depend on how the satellite elevation angle is sampled over the day of simulation. The simulations highlight the importance of the digital elevation model (DEM) integration: average planimetric differences (or altimetric) with and without integrating the DEM (with respect to the ellipsoid approximation) were found to...

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Comparison of Ray-Tracing Packages for Troposphere Delays

Cited by 66 publications

References 26 publications

Inter-technique validation of tropospheric slant total delays

Inter-technique validation of tropospheric slant total delays

Retrieval of Refractivity Profile With Ground-Based Radio Occultation by Using an Improved Harmony Search Algorithm

Simulations of direct and reflected wave trajectories for ground-based GNSS-R experiments

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