Scheduling VLBI satellite observations with VieVS. Andreas Hellerschmied

Transcription

1 Scheduling VLBI satellite observations with VieVS Andreas Hellerschmied

2 VLBI satellite observations Motivation for VLBI satellite observations Establish inter-technique ties in space Improve ITRF realization etc. Previous direct satellite observations with VLBI antennas e.g. Tornatore (2010a/b, 2014) G Experiment (Haas, 2014) Co-Location in Space (L. Plank, 2014). Problem: Available Scheduling Programs (SKED, SCHED, VIE_SCHED) do not support satellites as radio sources routinely Idea: Upgrade VieVS with a tool for scheduling VLBI satellite observations 5th VieVS User Workshop 2

3 VieVS satellite scheduling - Overview Vie_SCHED GUI updated with the new satellite scheduling module. 5th VieVS User Workshop 3

4 Input data NORAD Two Line Element (TLE) data: Datasets for precise satellite orbit determination by dedicated analytical models (SGP; Hoots & Röhrich, 1988) Widely available, e.g. at TLE example for GLONASS-717 (NORAD ID: 29671) Catalog files: SKED catalog files (Vandenberg, 1997) VEX catalog files VLBI Station data (Station coordinates, equipment, etc.) Configuration files To define setup of receiver/station equipment used for actual satellite observations 5th VieVS User Workshop 4

5 Find available observation periods Conditions for a valid satellite scan: Satellite visibility..... Sun distance. Antenna Slew rates... Station n 2 Station 2 1 Station 1 n n number of stations Available observation times for the station network 5th VieVS User Workshop 5

6 Satellite overpass information Configuration: 3 GLONASS satellites Wettzell, Onsala 31 Aug :00 13:00 UTC Elevation plot Determined available observation times Helps the scheduler to select satellites/observation times 5th VieVS User Workshop 6 Skyplots

7 Scheduler interface In the MATLAB Command Window User input: 1. Experiment name 2. Select Satellite 3. Observation period (t_start, t_stop) By repeating the steps 2 and 3 an arbitrary number of consecutive scans can be scheduled. Schedule files (VEX) are generated after user input is finished Scheduler interface (screenshot) 5th VieVS User Workshop 7

8 Generation of VEX files Schedule file format: VEX 1.5b1 (Whitney et al., 2002) Stepwise satellite tracking approach can be implemented directly with these VEX files Satellite positions are defined similar to quasars Satellite orbit are converted to series of distinct topocentric Ra/Dec positions Antenna is repositioned in a defined time interval (e.g. 15 sec) to follow the satellite Stepwise satellite tracking principle Cross-eyed schedule (Duev et al, 2012) Satellites orbit in the Earth s near field Topocentric view directions differ between sites Separate pointing data (topo. Ra/Dec) has to be calculated for each station 5th VieVS User Workshop 8

9 Satellite observation experiments Scheduled with VieVS Baseline Wtz O85 Onsala, Sweden: Responsible: R. Haas 25 m antenna, L-band feed Wettzell, Germany Responsible: A. Neidhardt 20 m antenna, S/X-band feed New L1-band GNSS receiver (Kodet et al., 2014) GLONASS satellites L1 signals( MHz) Four sessions, each with 1h duration 16 th January 2014: G140116a, G140116b 21 st January 2014: G140121a, G140121b 5th VieVS User Workshop 9

10 Observation results Correlations with DiFX software correlator (Deller et al., 2007) Preliminary data analysis by Rüdiger Haas 0.25 sec integration time Fringe fitted with the Astronomical Image Processing System software (AIPS, 2014) Continuous phases and strong amplitudes were found for all satellites. IF spectrum of GLONASS Data acquired during the G140121a session. Fringe plots for GLONASS Data acquired during the G140121a session. 5th VieVS User Workshop 10

11 Summary The VieVS satellite scheduling module provides a flexible tool for scheduling real VLBI satellite observations and for generating VEX files. For any satellites (LEO, MEO, etc.) and various station networks. No scheduling optimization so far. No combination with classical observations to quasars yet. Stepwise satellite tracking based on VEX files generated with VieVS is feasible for all VLBI stations without modifications in the Field System. First satellite experiments scheduled with VieVS were successfully carried out in January 2014 on the baseline Wettzell Onsala. 5th VieVS User Workshop 11

12 Outlook VieVS - Flexible tool for scheduling real VLBI satellite observations and generating VEX files. Additional experiments Larger station networks Possible observation scenario: :00 16:00 UT - ONSALA - MEDICINA - WETTZELL - ZELENCHUKSKAYA - SVETLOE Glonass-724/736/743 5th VieVS User Workshop 12

13 Questions? Contact: References: AIPS, Astronomical Image Processing System (2014), Web resource: HOOTS, F. AND ROEHRICH, R. (1980). Spacetrack Report number 3: Models for Propagation of NORAD Element Sets. Tech. rep., US Airforce Aerospace Defense Command, Colorado Springs, CO. VANDENBERG, N. (1997). sked s Catalogs - Program Reference Manual. NASA/Goddard Space Flight Center, Space Geodesy Program, ftp://gemini.gsfc.nasa.gov/pub/sked/docs/skcat.pdf, vlbi Software Documentation, Scheduling Program. DUEV D.A. et al. (2012). Spacecraft VLBI and Doppler tracking: algorithms and implementation. Astronomy & Astrophysics, 541, A43. WHITNEY A. et al. (2002). VEX File Definition/Example, Rev. 1.5b1. DELLER A.T. et al. (2007). DiFX: A Software correlator for very Long Baseline Interferometry using Multiprocessor Computing Environments. The Astr. Soc. of the Pacific, 119, pp KODET J. et al. (2014). Co-locations of Space Geodetic Techniques on Ground and in Space. 8 th IVS General Meeting, Shanghai, March PLANK, L. (2014). VLBI satellite tracking for the realization of frame ties. Geowissenschaftliche Mitteilungen, Heft 95, Geowissenschaftliche Mitteilungen, Wien. HAAS R. et al. (2014). The Wettzell-Onsala G experiment. 8 th IVS General Meeting, Shanghai, March Tornatore V. et al. (2010a). Planning of an Experiment for VLBI Tracking of GNSS Satellites, IVS 2010 General Meeting Proceedings, p Tornatore V. et al. (2010b). Tracking of Glonass satellites by VLBI radio telescopes. 5th ESA International Workshop on Tracking, Telemetry and Command Systems for Space Applications, September Tornatore V. et al. (2014), Direct VLBI Observations of Global Navigation Satellite System Signals, International Association of Geodesy Symposia, Proc. IAG General Assembly, Melbourne , 139 pp th VieVS User Workshop 13