IVS Working Group on Satellite Observations with VLBI

Purpose
The IVS Working Group on Satellite Observations with VLBI (WG7) will study possibilities to observe Earth satellites with the VLBI ground network affiliated with the IVS. In particular the development of corresponding observing schedules, of the necessary technology at the observing stations, data correlation, and data analysis will be promoted. Experts from the various fields, who are able to perform one or more of the different tasks will be brought together to enable observations of Earth satellites by VLBI.

Justification
One of the main products of space geodesy is the ITRF. There still exists several local tie vectors with doubtful quality and there is no independent method to externally validate e.g. the VLBI–GNSS local tie vectors. An enhancement to the current ITRF combination method would be to include VLBI observations of co-location satellites, i.e. satellites that can act as space-borne co-location sites, including also GNSS satellites. It might be possible to detect systematic differences between the orientation of the related reference frames by the co-location in space and finally even to contribute to improved satellite orbits and more precise EOP.

The mandate of the WG7 comprises the following tasks:

• Task 1: Technical issues
• Technical issues concerning observations of future dedicated co-location satellites
• Technical issues concerning the observation of GNSS L-band signals with legacy and VGOS telescopes
• Necessary formulation in vex-files, interface to FS, antenna control
• Preparation of a possible test-network
• Task 2: Scheduling and simulations
  1. Implementation of scheduling of satellite observations into scheduling software
  2. Simulation of various observation scenarios and anlysis of simulated observations
  3. Once technology allows (see Task 1), corresponding R&D session shall be scheduled and observed
  4. Potential start with GNSS satellites
• Task 3: Correlation
  1. Development of strategies for the correlation of the data and to test different correlation approaches
  2. Establishment of corresponding fringe fitting and post-processing
  3. Provide feedback to the observation schedulers and the stations
  4. Involve at least one IVS affiliated correlator
• Task 4: Analysis
  1. Development of suitable post–processing data analysis strategies
  2. Goal is to derive meaningful results (e.g., to check and enhance loacal tie vectors or to achieve an improvement of the VLBI contribution to ITRF, ICRF, and EOP.)

Desired Outcomes
Memos and other publications concerning the main requirments. Initiate corresponding test sessions (once possible) to demonstrate the feasibility of the new type of cross-technique observations. Validate and possibly provide an enhancement to the VLBI–GNSS local tie vectors (once a sufficient number of observations are available). Impact on the accuracy of VLBI–GNSS combinations for the ITRF and EOP, the GNSS orbits and potentially even ICRF determinations shall be demonstrated. First experience w.r.t. co-location in space shall be gained.