RO Data Description

Data type: - ionPrf / - igaPrf

ionPrf is one of the data products from FORMOSAT-7/COSMIC-2 occultation observation, which includes the ionospheric electron density profiles, the calibrated TEC, geographic longitude / latitude / altitude at perigees, etc.

igaPrf is another data products derived from ionPrf, which includes corrected electron density profiles and some related observables.
The major difference between ionPrf and igaPrf is: the former is derived from the standard Abel inversion; the latter is derived from the aided-Abel inversion.

ionPrf Profile Data

• MSL_alt: Mean sea level altitude of perigee point in km
• GEO_lon：Geographic longitude of perigee point in °E
• GEO_lat：Geographical latitude of perigee point in °N
• TEC_cal：Calibrated occultation TEC below LEO orbit in TECU
• ELEC_dens：Electron density in el/cm3

igaPrf Profile Data

• MSL_alt：Mean sea level altitude of perigee point in km
• GEO_lon：Geographic longitude of perigee point in °E
• GEO_lat：Geographical latitude of perigee point in °N
• TEC_cal：Calibrated occultation TEC below LEO orbit in TECU
• ELEC_dens：Aided electron density in el/cm3
• ELEC_dens_orig：Original electron density in el/cm3 (same as ELEC_dens in ionPrf)
• ELEC_dens_bg：Background electron density in el/cm3

ionPrf Data Processing

Since FORMOSAT-7/COSMIC-2 provides dual-frequency GNSS occultation and non-occultation observables, the ionospheric electron density profile can be retrieved from two data processings: the excess phase data processing and ionosphere inversion processing.

The former data processing estimates the ionospheric excess phase by the following procedures:

• Read in 1-second sampled dual-frequency GNSS phase observables
• Derive the linear combinataion of the excess phase by linear differencing
• Identify occultation flag (rising/setting) or indicate it if it is an non-occultation event based on the orbital information of GNSS and LEO satellites

The latter processing retrieves the ionospheric electron density profile by the following procedures:

• Read in electron density profiles in ionPrf
• Reconstruct 3-dimensional global electron density field as the background field based on 45-day worth of the profiles
• Convert the calibrated TEC into the corrected (aided) electron density profiles based on the aided-Abel inversion (cf. Chou et al., 2019)

These figure shows the number of daily FORMOSAT-7/COSMIC-2 ionospheric profiles.

Reference:

Chou, M. Y., C. C. H. Lin, H.-F. Tsai, and C.-Y. Lin (2017), Ionospheric electron density inversion for Global Navigation Satellite Systems radio occultation using aided Abel inversions, J. Geophys. Res. Space Physics, 122, doi:10.1002/2016JA023027.