Utilizing high-rate GNSS radio occultation open loop tracking records from commercial small satellites for ionosphere TEC estimation and scintillation monitoring

Abstract:

GNSS radio occultation (RO) signals can provide measurements of the ionosphere electron density and scintillation indices that are complementary to the ground-based measurements and with a global coverage. For existing constellations such as COSMIC and COSMIC II and commercial small satellites in the low-Earth orbits launched by GeoOptics Inc. and Spire Inc., etc., carrier phase and pseudorange measurements from conventional closed-loop (CL) tracking are used to estimate the ionospheric total electron content (TEC) and scintillation indices. During strong scintillation, these CL tracking loop generated carrier phase measurements are vulnerable to cycle slips and fluctuations, which may lead to significant errors in the TEC and phase scintillation index estimation.

However, these RO systems also record high-rate (e.g., 50 Hz or 100 Hz) carrier phase and signal-to-noise ratio (SNR) estimates using open-loop (OL) tracking when the RO signal tangent point altitude is low (e.g., lower than ~150 km). Though primarily intended for retrieving the atmospheric profiles such as temperature, pressure, humidity, etc., these OL tracking records can also be used to estimate the ionosphere TEC and scintillation indices.

This presentation discusses an algorithm that can simultaneously reduce cycle slips and noise in the OL tracking carrier phase measurements during strong scintillation. The algorithm implements a close loop filter which dynamically tunes its filtering parameters based on the real-time SNR estimation. In the presentation, we will highlight the implementation details and share the processing results of data recorded by commercial small satellites launched by GeoOptics Inc. and Spire Inc. A quantitative analysis of the estimated ionosphere TEC and scintillation indices (i.e., S4 and sigma-phi) using high-rate OL tracking records and comparisons with ground-based measurements will also be included.