@article{Liu2023a,
  author = "L. Liu and Y. J. Morton",
  title = "Assessment of storm-time ionospheric electron density measurements from Spire Global CubeSat GNSS radio occultation constellation",
  year =  2023 ,
  journal = "GPS Solutions",
  volume = 27,
  number = 2,
  keywords = "pfisr, gnss, radio occultation",
  doi = "10.1007/s10291-023-01414-8",
  url = "https://doi.org/10.1007/s10291-023-01414-8"
}


@article{Liu2015a,
  author = "J. Liu and T. Nakamura and L. Liu and W. Wang and N. Balan and T. Nishiyama and M. R. Hairston and E. G. Thomas",
  title = "Formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions",
  year =  2015 ,
  journal = "J. Geophys. Res.",
  volume = 120,
  number = 8,
  pages = "6860-6873",
  keywords = "amisr, pfisr, pfrr",
  doi = "10.1002/2015JA021393"
}