Multi-Constellation, Multi-Frequency Simulation of Ionospheric
Scintillation along Radio Occultation Raypaths and Potential Impacts on
Tropospheric Retrievals
Abstract
In recent years, the need for improved global terrestrial and space
weather specification and forecast has driven the development of new
commercial satellite constellations to monitor radio occultations (RO)
using Global Navigation Satellite System (GNSS) signals. These signals
interact with irregularities in the ionosphere, causing radio wave
scintillation that is known to degrade the performance of communication
and navigation systems, and may also degrade the accuracy of RO
tropospheric and stratospheric retrievals. This January, PlanetiQ will
launch the first two of its planned 20 microsatellites commercial
constellation (to be complete by 2022), focused on weather and space
weather forecasting and climate. With this constellation, PlanetiQ
intends to provide over 80 million global observations per day. The
focus of this paper concerns a simulation study we conducted to assess
possible impacts on tracking and tropospheric retreivals due to
ionospheric scintillation. We constructed a 3D, time-dependent model for
the strength, orientation, and spectral characteristics of the
irregularities. Our methodology generates representative realizations of
irregularity structure (space weather) rather than average conditions
(climatology). We integrated through the model along each RO ray-path to
determine the strength and location of an equivalent phase screen, which
we used to generate realizations of intensity and phase scintillation at
the receiver. The phase screen calculation is a generalization of our
previous algorithm (Carrano et al., Radio Sci., 2011) which now admits
propagation and scanning at arbitrary angles to the magnetic field.
There were approximately 50,000 RO events between the 20 PlanetiQ
microsatellites and the satellites of the GPS, GLONASS, Galileo, and
BeiDou GNSS constellations each day. We simulated scintillation for each
carrier frequency transmitted by each GNSS satellite for a total of 39
days. We discuss potential impacts of scintillation on satellite
tracking and the accuracy of tropospheric retrievals as a function of
season and solar activity. We compare the scintillation index (S4) along
each RO raypath with a vertical propagation path through the same
irregularities. These are compared with observations from the CORISS
instrument onboard the C/NOFS satellite and ground based observations
from the SCINDA network.