Ionospheric Imprint to LOFAR

Transcription

1 Ionospheric Imprint to LOFAR Norbert Jakowski Institute of Communications und Navigation German Aerospace Center Kalkhorstweg 53, D Neustrelitz, Germany LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 1

2 OUTLINE Monitoring of the European Ionosphere in DLR Neustrelitz Space based ionospheric monitoring Ground based ionospheric monitoring Large scale TIDs Mid scale TIDs Small scale Irregularities Ionosphere weather service SWACI Radio Wave propagation through the ionosphere including LOFAR frequencies Refraction errors Absorption effects Bottomside ionosphere measurements LF and VLF measurements Summary & Conclusions LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 2

3 Space weather refers to the conditions on the sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health. (Definition NSWP, USA, 1996) GNSS Satellite NZ ACE Early warning Energetic particles In the solar wind Arrival: 2-4 days Duration: several days GNSS - Global Navigation Satellite System LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 3

4 Height / km Radio wave propagation in the ionosphere Electron density n e & Total Electron Content (TEC) are closely related to the solar irradiance TECV ne ( h) dh Night Ionosphere Day LoS s Ray path Solar Flux Index F 10.7cm Total Electron Content/ TECU Solar Flux Index F Solar Flux 10.7cm Year TEC 50 N, 15 E Total Electron Content 50 N; 15 E 13UT Ionospheric Range Error/ m f 1 f 2 f 1 > f 2 Refraction All radio systems operating at frequencies < 10 GHz are concerned Electron density n e Year Ionosphere causes Regular effects due to the presence of plasma - signal delay - rotation of polarisation plane Irregular effects due to plasma distortions, turbulences - misinterpretation of data due to horizontal gradients (HMI) - Radio scintillations 0 LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 4

5 Ground and space based ionosphere monitoring CHAMP 2 3 Monitoring of the Ionosphere by: - GNSS Ground stations 1 over a full solar cycle Europe, since 1995 North pole area, since 2001 South pole area, since Space Weather Application Center SWACI - LEO Satellites carrying GNSS receivers onboard Radio occultation 2 Topside reconstruction CHAMP since 2001 GRACE since Non-GNSS based techniques Vertical sounding + GNSS Beacon measurements 3 LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 5

6 Space Based Monitoring of the Ionosphere GNNS Satellit Sun GPS Okkultation (1Hz) Navigation (0.1 Hz) LEO Orbit IRO Profiling CHAMP, GRACE TerraSAR-X Tandem-X, SWARM LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 6

7 SWACI products Space based measurements (CHAMP) Ionospheric Radio occultation (IRO) Automatic retrieval of vertical electron density profiles (up to 150 profiles per day) Assimilation of GPS measurements into a model Operational reconstruction of the electron density in the plane of the CHAMP revolution ( D maps/day) Jakowski, N. Wehrenpfennig, A., Heise, S., Reigber, C. and Lühr, H., GPS Radio Occultation Measurements of the Ionosphere on CHAMP: Early Results, Geophysical Research Letters, 29, No. 10, /2001GL014364, 2002b Heise, S., Jakowski, N., Wehrenpfennig, A., Reigber, C., Lühr, H., Sounding of the Topside Ionosphere/Plasmasphere Based on GPS Measurements from CHAMP: Initial Results, Geophysical Research Letters, 29, No. 14, /2002GL014738, 2002 LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 7

8 Dual frequency ground based GNSS measurements Total Electron Content TECV ne ( h) Receiver R E n e (h) Center of Earth e dh hi raypath s d I K f 2 GNSS TEC Ionospheric range error up to about 100 m Estimation of ionospheric perturbation degree is a practical need Statistics and case studies required 2 f1 f P P2 P1 K 2 f f 2 TEC TEC can be derived from dual frequency GNSS measurements off GPS based TEC measurements and mapping in DLR Neustrelitz Europe post proc. (1 day) since operational (5 min) since North Pole post proc. (1 day) since LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 8

9 GNSS based TEC Monitoring in SWACI Sample: 16 Stations TEC monitoring over Europe in DLR Neustrelitz since 1995 based on dual frequency GPS measurements of IGS, EUREF, ascos networks Model assisted technique to calibrate instrumental biases and to reconstruct TEC maps from GPS measurements The project Space Weather Application Center - Ionosphere (SWACI) is established to provide actual ionospheric information and data to users. SWACI is essentially supported by the state governmant of Mecklenburg-Vorpommern. LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 9

10 European TEC maps in SWACI Near real time ground based GNSS measurements enable the computation of high resoultion TEC maps over certain areas (e.g. Europe, Japan, USA) LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 10

11 Global TEC monitoring Since July 2010 global TEC maps are routinely produced in DLR. Maps are available via SWACI every 5 min. Dat base is provided by the Real time pilot project of the International GNSS Service (IGS). LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 11

12 Propagation of TIDs during ionospheric storms Longitude: 7 E TECU Immediate propagation of the perturbation at the onset (electric field) Wavelike propagation of disturbances Ionosphärische during the main phase of the storm on 29 October 2003 (speed 400 Störungsprozesse m/s) High latitude disturbance zone (northward über Europaof the trough) moves also equatorward (speed 50 m/s) Borries et al., Ann. Geophys., 27, , 2009 LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 12

13 Enhanced E-layer ionization due to particle precipitation Particle precipitation from the magnetosphere causes enhanced ionization in the lower ionosphere LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 13

14 Ionospheric Threat model for aviation Model needed for safe aircraft landing Threat: Horizontal gradients of ionization Range error that might occur: 8.5 m Threat Model by three parameters (FAA -Stanford): Slope g Quelle: FAA GBAS CAT- I Ionosphere - Threatmodell for Germany Velocity v Width W ITMA Ionospheric Threat Model Assessment ( ) Project financed by German Air Navigation Services (DFS) Data Screening: Analysis of anomal Effects (SAPOS- Data) Future Projects: EUROCONTROL slant iono Ionospheric front Time Aircraft Links to the same GPS satellite g W v GGF distance GBAS: Ground-Based Augmentation System SAPOS: SAtelliten POSitionierungsdienst Deutschland FAA: Federal Aviation Administration LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 14

15 Mid scale TIDs by Beacon Satellite Measurements Ionospheric traces Neustrelitz (DLR) Wachtberg (FGAN) Two-station calibration method applied Differential carrier phase measurements (150/400MHz) at two stations allow calibration of TEC by two-station calibration method High sensitivity of beacon measurements (gravity wave and ionisation front detection) Snapshot character of measurements (advantage for studying spatial structures) Several satellites can be used (e.g. OSCAR, FORMOSAT) LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 15

16 Small scale irregularities - Radio scintillations Plasma turbulences High Latitudes Low latitudes Jicamarca, Peru Turbulences of Plasma density S I I I 2 1/ 2 Fluctuations of Signal strength Loss of P1, P2, L1, L2 GPS phases in a dual frequency GPS receiver requires safety concept to solve the positioning and navigation tasks by single frequency use only, complete loss also observed LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 16

17 GPS scintillation monitoring network of DLR σ φ Kiruna Update: 1 min Remote access to all stations of the network (EVNet) +Radio beacon S 4 La Laguna Data reduction on observation site by computing scintillation parameters DLR operates a network of high rate dual frequency GPS receivers (20-50 Hz) for scintillation monitoring Network provides actual scintillation data for further distribution via SWACI Extension of the network is planned towards North and South, the network includes capabilities to receive Galileo signals LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 17

18 Space weather Application Center Ionosphere The Space Weather Application Center - Ionosphere (SWACI) is a joint project of two DLR institutes - the Institute of Communications and Navigation and the German Remote Data Center. The project is essentially supported by the German State Government of Mecklenburg-Vorpommern. SWACI provides information and data to characterize the actual state of the ionosphere. This information can be used to correct ionospheric propagation errors or to estimate the performance of the radio system currently used. Country world wide access to SWACI Italien 3% others 21% Canada 3% China 5% Ukraine 6% Austria 6% Poland 14% Germany 28% USA 14% Germany USA Poland Austria Ukraine China Canada Italien others LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 18

19 Relationship to LOFAR SWACI LOFAR LOFAR area and European TEC map area overlap. Radio signals observed by LOFAR contain valuable information about the ionosphere. On the other hand knowledge about the basic ionisation level over LOFAR area should be helpful for LOFAR data processing. LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 19

20 Transionospheric Ray Path Bending Jakowski, N. et al., Ionospheric ray path bending effects in precision positioning systems, SPN 1, 6-13, 1994 LOFAR frequencies range is MHz. Strong refraction of radio waves in the ionosphere expected. In relation to space weather effects also enhanced absorption should be observed in the lower frequency range. LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 20

21 Riometer - Ionospheric absorption of radio waves Enhanced absorption of radio wave energy at frequencies below 100 MHz must be taken into account during space weather events. This effect is not measurable by GNSS techniques. Information about space weather impact on the bottomside ionosphere may be provided by propagation characteristics of LF and VLF radio waves LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 21

22 Sun & Ionosphere MONitoring Network -SIMONE Solar flare Ionosphere 24 khz Antenna EMAG Bergen NAA Cutler ca km Schools in Germany Signal strength 1 June 2007 SR Solar flare EMAG Bergen SS DLR Neustrelitz Receiver Time / hrs LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 22

23 European LF receiver network DLR plans to install a network of LF receivers in Europe to get continuous information on the actual state of the bottomside ionosphere 3 receiving sites are decided, the place for the 4 th receiver is not yet clear LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 23

24 Summary & Conclusions Principally, radio systems operating at frequencies <10 GHz should take into account ionospheric impact. Radio frequencies used in LOFAR ( MHz) are subjected to strong ionospheric refraction in particular in the lower frequency range. SWACI can provide the ionoisation background for LOFAR by TEC maps with every 5 min updates (faster possible if required) High precision ranging requires the mitigation of higher order refraction effects. Information about the behaviour of the bottomside ionosphere by using VLF and LF frequencies seems to be valuable. Investigation of small scale ionospheric irregularities important since they may cause loss of lock of signals. LOFAR has the capability to monitor horizontal fine structures of ionospheric irregularities. LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 24

25 Thank you for your attention Contact: Dr. Norbert Jakowski Kalkhorstweg 53 D Neustrelitz Germany Tel. +49 (0) Fax. +49 (0) Web: LOFAR Workshop, 8/9 November 2010, Potsdam, Germany Page 25