case study of windstorm effects on zenith tropospheric
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where:โข ๐ is the tropospheric
gradient (N,E)โข ๐ is the distance
vector in the 2D plane (N,E)โข ๐น is a clockwise rotation matrix of 90ยฐโข t is the interpolation timeโข t โ x is the reference time of the
gradients
INTRODUCTION
Tropospheric refraction is one of the major error sources in satellite-basedpositioning. The dependency of the troposphere on physical quantities suchas temperature, pressure and humidity makes troposphere modelingchallenging in severe weather conditions. One such severe weather event wasthe Xavier windstorm that occurred in northern Germany at the beginning ofOctober 2017. 41 GNSS stations of the LGLN-SAPOS network in LowerSaxony are used for the analysis which is based on the tropospheric productsof the Geo++ยฎ GNSMART (GNSS - State Monitoring And RepresentationTechnique) software. The variations of the Zenith Tropospheric Delay (ZTD)are compared with the variation of published weather data of DWD and withZTDs obtained from integration of the physical quantities available from theECMWF data archive. Different approaches for interpolation of ZTDsbetween reference stations have been analyzed, including a utilization of theestimated horizontal gradients. The quality of the interpolation has beenevaluated by rover tests, performed with GNSMART RTK modules .
Case study of windstorm effects on zenith tropospheric delay
for RTK networking in northern Germany
Francesco Darugna1,2, Jannes Wรผbbena1, Martin Schmitz1, Steffen Schรถn2
1Geo++ GmbH 2 Institut fรผr Erdmessung Leibniz Universitรคt Hannover
ZENITH TROPOSPHERIC DELAY (ZTD)
GROUND BASED WEATHER DATA
.
โข surface based weather data fails to detect some significant ZTD changesโข information of atmospheric parameters at different heights is required
ECMWF NUMERICAL WEATHER MODEL (NWM)
SPATIAL CORRELATION
SUMMARY AND FUTURE WORKSโข ZTD information cannot reliably be extracted from surface weather data aloneโข variation of ZTD reconstructed from ECMWF is in good agreement with GNSS
ZTD variationโข during periods with large ZTD variation, interpolation should only consider
stations close to the interpolation point improving the performance up to 1cmโข gradients information might be valuable only during a weather front
improving the interpolation up to 7mmโข implementation of the closest stations interpolation in GNSMARTโข use of NWM to predict when to use the gradients into the interpolation
process
N
E
Time: t - x
๐๐๐๐๐ก๐๐ =
(๐น ๐) โ ๐๐๐
+ 1
2
โข good agreement betweenvariation of the reconstructedZTD from NWM and GNSMARTproducts
โข the shape of the variation ismostly given by the contributiondepending on h/๐2
โข here, p is the atmosphericpressure, T the absolutetemperature and h the specifichumidity
INTERPOLATION OF ZTD REDUCTED TO HEIGHT=0
โข DOY considered with the two large slants in ZTDโข larger effect before the windstorm: there is no evident impact on the
positioning during the windstorm
ROVER TEST WITH GNSMART
AKNOWLEDGEMENTSData provided by: Landesamt fรผr Geoinformation und LandesvermessungNiedersachsen (LGLN-SAPOS), Deutsche GeoForschungsZentrum (GFZ), GermanMeteorological Office (Deutscher Wetterdienst - DWD) , European CenterMedium โ Range Weather Forecast (ECMWF)
โข GNSMART zenith troposphericmodel: UNB3, based on the Saastamoinen model
โข GNSMART slant delay model: Neill with DOY dependentmapping function
ZTD COMPARISON GNSMART, GFZ, IGS GREF STATIONS
โข good agreement in the ZTD variation but with differences up to 2.5 cmโข accurate comparison difficult due to different time-step and noise
โข Kalman filter used for the interpolation with four different ways to interpolate changing:
1.number of stations, all or stations within a maximum distance of 43 km
2.the weight, 1
๐2 or ๐๐๐๐๐ก๐๐
๐2
โข the use of the closest stations might improve the interpolation performance
โข the info from the gradients seem to be valuable when there is a weather front
โข hypotesis: the process is stationary
โข semivariogram: ๐ ๐ =๐
๐๐๐ป๐ซ ๐ + ๐ โ ๐๐ป๐ซ(๐) ๐
โข covariogram: ๐ช(๐) = ๐๐ โ ๐ ๐โข considering all the days: max correlation length ๐๐๐๐ โ ๐๐๐ ๐๐โข considering only DOY 275 (with high ZTD variations):
max correlation length ๐๐๐๐ โ ๐๐ ๐๐โข correlation with the impact of humidity contribution on the ZTD variation
TREASUREhttp://www.treasure-gnss.eu /
Geo++ GmbHfrancesco.darugna@geopp.dejannes.wuebbena@geopp.demartin.schmitz@geopp.de
Institut fรผr Erdmessung, Leibniz Universitรคt Hannoverschoen@ife.uni-hannover.de
๐๐๐๐๐ก๐๐ = 0
๐๐๐๐๐ก๐๐ = 1
๐๐๐๐๐ก๐๐ = 0.5
๐๐๐๐๐ก๐๐ = 0.5
๐๐ป๐ซ = ๐๐โ๐ ๐๐
๐๐. ๐๐
๐ปโ ๐๐. ๐๐
๐
๐ป
๐
๐.๐๐๐+ ๐๐๐๐๐๐
๐
๐ป๐
๐
๐.๐๐๐
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