LESIA Observatoire de Paris-PSL CNRS vopdc cdpp Sorbonne Université cnes Université de Paris

Wind/Waves flux density collection calibrated for Auroral Kilometric Radiation

Monday 19 April 2021, by Baptiste Cecconi

This collection contains post-processed datasets of Wind/Waves flux densities, calibrated with the Z antenna, and containing parameters relevant for the selection of Auroral Kilometric Radiation as described in Waters et al. 2021 (submitted to JGR)

Link to data

Description

Presented here are calibrated data from Wind/WAVES RAD1 receiver using the axial (Z) antenna only. Calibrated flux densities are given using a simplified form of equation 21 in Manning and Fainberg (1980), with source parameters set such that Auroral Kilometric Radiation (AKR) is assumed to be observed (0 angular radius, no linear polarisation, source direction at Earth’s center). Also contained in the collection is the spin-normalised standard deviation of the axial measurements; the metric used to select AKR emission from the data. In the paper, the threshold on the spin-normalised standard deviation used to select AKR is 0.1. The SNR is also given in dB.

For a full calibration of the raw data, the following steps are taken:

  • Each spin is normalised by the average intensity, and the standard deviation taken
  • Background values are computed from the 5% spectra for each day, and subtracted from each spin measurement. If a given intensity is < 0 after subtraction, the background value is stored instead.
  • The signal to noise ratio (SNR) is calculated for each spin measurement as well as the average SNR of the spin, using the background value as above.
  • Each spin measurement is calibrated to give the flux density observed by the axial antenna, and the mean is taken across the spin
  • Wind-calibrated flux densities are then multipled by the scaling spectrum described in Appendix A of Waters et al. 2021
  • Data have been resampled to the Wind sweep period (183 second). Timestamps for measurements are set at the start of the sweep period.
  • Flux densities are normalised as if observed from a distance of 1 AU
  • Missing data are stored as -1.

Significant RFI is present at 52 kHz for all data and has been removed for the related study, but is retained in the collections here to be removed at the user’s discretion.

Data Formats
The data is provided in 2 formats, containing identical content:

CSV (Comma Separated Values)
This format is a simple CSV table, with 5 columns:

  • UT date (ISO string),
  • Observation frequency (in kHz),
  • Spectrum number (within file),
  • Signal to noise ratio (in dB),
  • Calibrated flux density normalised to 1 AU (in W/m2/Hz)

The last column value is set to -1 when the Z-antenna variance is low.

CDF (Common Data Format)
This format is CDF-ISTP compliant and contains 4 Variables (of type zVariable):

  • Epoch: CDF_TIME_TT2000
  • Frequency: CDF_REAL4
  • FLUX_DENSITY: CDF_REAL4
  • SNR: CDF_REAL4

Acknowledgements

Authors acknowledge support from CNES, CNRS and Observatoire de Paris, as well as Paris Astronomical Data Centre (PADC). J. E. Water’s work was supported by the EPSRC Centre for Doctoral Training in Next Generation Computational Modelling Grant No. EP/L015382/1.

Contact

Any question or request should be addressed to contact.maser@obspm.fr

References

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