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VLA Ionospheric and Transient Experiment (VLITE)


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The ionosphere analysis portion of VLITE is dedicated to the study of fine-scale (~1-10 km) ionosphere dynamics and the relationship to larger structures (hundreds of km). The VLA low-band systems have virtually unmatched sensitivity to fluctuations in the ionosphere total electron content (TEC), the integrated density of free electrons along a line of sight. When observing a bright cosmic source, these systems can be used to characterize TEC fluctuations more than two orders of magnitude weaker than those detectable with similar GPS-based methods. Such fluctuations are prevalent on smaller scales, making the VLA an excellent instrument for probing fine-scale ionosphere dynamics. Many continuously operating GPS receivers within New Mexico will also be used to simultaneously study larger-scale fluctuations. The (nearly) continuous data stream that will be yielded by VLITE, when combined with this GPS data, will constitute a singular data set for the study of coupling mechanisms among fine-, medium-, and large-scale ionosphere dynamics. In addition, such a continuous flow of data will allow for the characterization of the fine-scale ionosphere response to relatively rare atmospheric and/or seismic events such as large storms, earthquakes, and explosions that would be missed by proposal-based, low-band observing.

Example of VLITE ionospheric data
Example of antenna-based TEC gradients from November 11, 2014 observation of the Galaxy cluster Abell 2052 (A2052). The upper panel shows the δTEC time series for the V1*V4 antenna baseline (black points) with the values from a polynomial fit to all baselines used to determine the TEC gradients (red). The north-south and east-west components of the gradient are shown in the remaining panels for antennas V1 and V4.

The ionosphere pipeline is optimized to sense fluctuations on small temporal (~seconds), spatial (~few km), and amplitude (~10-3-10-4 TECU km-1) scales. Because the δTEC values represent antenna-based effects that dominate on short time scales (~minutes or less), the general approach to signal processing is as follows:
  • Extract good visibility phases from the raw data, while flagging obviously aberrant data.
  • Unwrap the phase time series and de-trend to remove slowly varying instrumental and/or source contributions.
  • Determine and remove contributions from baseline-based errors.
  • Use final δTEC time series to compute TEC gradients.

Modified on Monday, 16-Oct-2017 13:50:47 MDT