Ionospheric Range Error Correction Models

Transcription

1 Folie 1 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Ionospheric Range Error Correction Models N. Jakowski and M.M. Hoque Institute of Communications and Navigation

2 Folie 2 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Outline - Introduction - Ionospheric Correction Models - The GPS model - The NeQuick model - The DLR model NTCM-GL - Comparison of Model Outputs - Summary and Conclusions

3 Folie 3 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Radio wave propagation through the ionosphere Ionosphere vertical structure TECV ne ( h) dh Transionospheric radio waves are refracted and diffracted by the ionospheric plasma Height / km Night Day f 1 f 2 LoS s Refraction Ray path f 1 > f 2 All radio systems operating at frequencies < 10 GHz are concerned The ionosphere is a dispersive and anisotropic propagation medium Effects - delay of signal travel time - rotation of polarisation plane - attenuation - scintillations of signal strength and phase (loss of lock) Electron density n e

4 Folie 4 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Determination of Ionosphere Related Range Errors by Dual Frequency GNSS measurements TECV ne ( h) dh Receiver n e (h) e h I R E Center of Earth GNSS d I K f 2 TEC ionospheric range error d I up to about 100 m along ray path Due to the dispersive ionosphere TEC can be derived from dual frequency GNSS measurements. 2 2 f1 f 2 P P2 P1 K TEC 2 off f f Single frequency measurements need range error correction information from: TEC monitoring data (map) or TEC model computations

5 Folie 5 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 TEC Monitoring range error correction maps 16 GPS Stations TEC map Error (vertical) m Range error is proportional to TEC - Near real time ground based GNSS measurements enable the computation of TEC maps over certain areas (e.g. Europe, Japan, USA or globally) - Maps of vertical TEC enable the correction of single frequency GNSS measurements by mapping the vertical TEC information to slant radio links - Ionosphere is the biggest error source in single frequency applications

6 Folie 6 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Use of TEC models - Much more simpler than the use of actual TEC maps, requiring a permanent ionospheric monitoring, is the use of model data. - Empirical models of the ionosphere provide a climatological estimation of the ionospheric ionisation. - Storm models capable to describe severe perturbations of the electron density and its distribution are not yet available. - For estimating the transionospheric time delay or range error, several ionospheric models are currently available e.g.: - GPS correction model or Klobuchar model used for GPS - NeQuick 3 D model planned to be used for Galileo. - International Reference Ionosphere (IRI) - Family of models developed in DLR Neustrelitz TEC Models (NTCM-EU, -NP,-SP, -GL)

7 Folie 7 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 The GPS or Klobuchar model - Simple cosine function approach for the delay of L1 signals propagating through the ionosphere in vertical direction - The maximum delay is fixed at daytime at 2 pm local time (LT) - At night times the delay is set to a constant value of 5 ns. - Amplitude and period of the cosine function depend on the geomagnetic latitude of the piercing point at 350 km height - The time delay, range error or TEC can be computed by using 8 coefficients - Coefficients are uploaded regularly to the GPS satellites and broadcasted via the GPS satellite s navigation message - User may convert the vertical delay to the link related slant delay

8 Folie 8 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 The NeQuick model Global TEC derived frpm NeQuick for 4 April 2004, 13:00 UT CCIR*: Comité Consultatif International des Radiocommunications - Quick-run 3D electron density model - Has been developed at the International Centre for Theoretical Physics (ICTP) in Trieste and at the University of Graz - Solar activity level is introduced by the Zurich sunspot number R 12 or by the solar radio flux index F Vertical electron density profile is given by a sum of several Epstein layers. The shape parameters of the electron density profile are deduced from the CCIR* coefficients of ITU. - NeQuick is foreseen as the ionospheric correction model for single frequency Galileo users

9 Folie 9 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Data Base - For estimating coefficients and parameters of the global TEC model, TEC maps generated by the Center for Orbit Determination in Europe (CODE) at Astronomical Institute of the University of Bern ( ilnat/aiub/content/e15/e59/e440/in dex_eng.html) are used. - Former estimations have shown that the accuracy of CODE maps is comparable with NTCM based reconstructions over Europe - CODE TEC maps obtained from 1998 to 2007, F10.7 < 200 have been used as input data..

10 Folie 10 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Formula approach General Approach TEC vert NTCM-GL F1F2F3F4F5 F 1 F 2 F 3 F 4 F 5 Diurnal variation, solar zenith angle Seasonal Variation Geomagnetic dependence Latitudinal dependence Solar activity dependence

11 Folie 11 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Diurnal and Seasonal Variation V D V LT LT 2 24 SD LT 2 12 D Components of formula for diurnal variation and dependence from solar irradiance V TD LT coefficients cos sinsin coscos F2 1c cos( V ) c cos( V ) 6 A 7 SA Annual and semiannual variation 2 coefficients

12 Folie 12 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Geomagnetic / latitudinal dependence F3 1c8cos m Dependence on geomagnetic latitude 1 coefficient F 1c exp EC c exp EC EC EC 2 m c c1 2 m c c2 Description of crest regions north and southward of the geomagnetic equator 2 coefficients

13 Folie 13 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Solar activity dependence F c c F Strong relationship between solar activity level and TEC 2 coefficients Total number of coefficients: 12 Coefficients are determined by a least squares fitting procedure Model description and coefficients available in: Mothly mean of F10.7 from and corresponding TEC at 50N/15E at daytime Jakowski N, Hoque MM, Mayer C (2011) A new global TEC model for estimating transionospheric radio wave propagation errors, Journal of Geodesy, 85 (12), Springer. DOI: /s ISSN

14 Folie 14 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 NTCM-GL: Main aspects The empirical approach describes functions on local time/solar irradiance, season, geographic/geomagnetic location and solar activity conditions Input TEC data from CODE maps cover a full solar cycle ( ) Histogram of NTCM-GL model residuals (input data model values) Mean: Std: RMS: 0.3 TECU 7.5 TECU 7.5 TECU (1 TECU=1x10 16 m -2 ) Approach needs only 12 coefficients for describing the main ionospheric features, therefore NTCM-GL is well suited for operational applications. Solar activity input via F10.7 index

15 Folie 15 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Comparison with TOPEX altimetry data - Comparison of daytime ionospheric range error estimations (TEC units) derived from models GPS, NeQuick and NTCM-GL with TEC estimations from dual frequency satellite altimetry data at TOPEX/Poseidon. Data samples are from May 2002 at high solar activity (right panel) and from December 2006 at low solar activity conditions (left panel).

16 Folie 16 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Comparison with DLR TEC maps over Europe Comparison of TEC estimations obtained from three ionospheric models: GPS (Klobuchar) model, NeQuick, and NTCM-GL in comparison with TEC computed at DLR Neustrelitz for 65 N; 15 E for daytime (left) and nighttime (right) conditions from

17 Folie 17 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Comparison with DLR TEC maps over Europe Comparison of TEC estimations obtained from three ionospheric models: GPS (Klobuchar) model, NeQuick, and NTCM-GL in comparison with TEC computed at DLR Neustrelitz for 50 N; 15 E for daytime (left) and nighttime (right) conditions from

18 Folie 18 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Comparison with DLR TEC maps over Europe Comparison of TEC estimations obtained from three ionospheric models: GPS (Klobuchar) model, NeQuick, and NTCM-GL in comparison with TEC computed at DLR Neustrelitz for 35 N; 15 E for daytime (left) and nighttime (right) conditions from

19 Folie 19 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Solar Cycle Variation of TEC at 50N;15E, nighttime Monthly means of TEC from DLR maps, GPS and NeQuick models and NTCM-GL

20 Folie 20 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Comparison of 6 Correction Models HSA Latitudinal dependence of daytime TEC obtained from different models and reconstructions along 0E meridian Good agreement of NTCM-GL with TPX and GIM at low latitudes under high solar activity conditions in 2002 and with NeQuick at middle to high latitudes (upper panel) LSA Good agreement of all models at low solar activity conditions in 2007 (lower panel) TPX: TOPEX / Poseidon Altimeter, JPL, CNES GIM: Global Ionospheric Model, generated via data assimilation from JPL CODE: Maps generated from Center for Orbit Determination in Europe, University of Bern IRI: International Reference Ionosphere, NASA + international team NEQ: NeQuick model, ICTP Triest + Univ. Graz

21 Folie 21 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Summary and conclusions - Global TEC model NTCM-GL has been discussed primarily in comparison with single frequency GNSS correction models such as the GPS or Klobuchar model and the NeQuick model. - TEC estimations of NTCM-GL and NeQuick are similar. - The performance of NeQuick and NTCM-GL is significantly better than the performance of the GPS or Klobuchar model. - NTCM-GL is easy to handle and needs only 12 fixed coefficients. - NTCM covers a full solar cycle using only the F10.7 radio flux index as solar activity proxy. - NTCM-GL could easily be used in single frequency mass market applications requiring ionospheric time delay or range corrections.

22 Folie 22 >Ionospheric Range Error Correction Models> N. Jakowski and M.M. Hoque 27/06/2012 Thank you for your attention! Contact: Dr. N. Jakowski Institute of Communications and Navigation Kalkhorstweg 53 D Neustrelitz