Harnessing LEO and CubeSat constellations for ionospheric irregularity detection

Abstract

Low-earth orbiting (LEO) satellite missions are frequently using the Global Navigation Satellite System (GNSS) Radio Occultation (RO) technique for atmospheric and ionospheric remote sensing. The application of GNSS RO technique has increased manifolds with the advent of CubeSat technology. In this study, we investigated the simultaneous occurrence of local nighttime F-layer ionospheric irregularities and amplitude scintillations in low-latitude equatorial regions using 1 Hz COSMIC-2 electron density profiles (ionPrfs) and high rate 50 Hz ionospheric profiles (conPhs) from Spire’s CubeSat constellation, respectively. Both datasets are accessed from the University Corporation for Atmospheric Research (UCAR) repository. An ionospheric irregularity detection algorithm is developed using a digital non-recursive finite impulse response (FIR) high-pass filter and applied on both the electron density (Ne) and total electron content (TEC) profiles from COSMIC-2 mission. The filter operates in the s domain, where s is defined as the distance between the highest and lowest tangent point heights. If the fluctuations in Ne and TEC exceed a set threshold, the corresponding COSMIC-2 profile is identified as having irregularities. In case of Spire GNSS-RO profiles, scintillation events are identified when the amplitude scintillation index (S4) at GPS L1 frequency exceeds the set threshold. COSMIC-2 and Spire datasets from September 2021 until May 2023 (20 months) are used in this long-term comparative study. We observe a good agreement in the statistics of number of Spire and COSMIC-2 profiles detecting (showing possible signature of) scintillations/ ionospheric irregularities. Both Spire and COSMIC-2 data show that the scintillation occurrence rate is much higher during the equinoxes (spring and autumn seasons) agreeing well with existing scintillation literature. From the COSMIC-2 data alone, we also notice a direct relation with the solar activity, i.e., the number of irregularity events slowly increases as we approach the solar maximum. This study indicates the capability of LEO satellites and CubeSat missions, especially in GNSS-RO configuration, for providing an important contribution to scintillation monitoring.