402 research outputs found
Feasibility of precise navigation in high and low latitude regions under scintillation conditions
Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes.
For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by s¿) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions.
For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large s¿), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.Postprint (published version
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CASES: A Smart, Compact GPS Software Receiver for Space Weather Monitoring
A real-time software-defined GPS receiver for the L1 C/A
and L2C codes has been developed as a low-cost space
weather instrument for monitoring ionospheric
scintillation and total electron content. The so-called
CASES receiver implements several novel processing
techniques not previously published that make it well
suited for space weather monitoring: (A) a differencing
technique for eliminating local clock effects, (B) an
advanced triggering mechanism for determining the onset of scintillation, (C) data buffering to permit observation
of the prelude to scintillation, and (D) data-bit prediction
and wipe-off for robust tracking. The receiver has been
tested in a variety of benign and adverse signal conditions
(e.g., severe ionospheric scintillation, both real and
simulated); the results are presented here. The custom
hardware platform on which the software runs is compact
while remaining flexible and extensible. The CASES
platform consists of a digital signal processor, an ARM
microcontroller, and a custom-built narrow-band dualfrequency
front end. Because the receiver is softwaredefined,
it can be remotely reprogrammed via the internet
or another communications link.Aerospace Engineering and Engineering Mechanic
Initial GPS scintillation results from CASES receiver at South Pole, Antarctica
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94940/1/rds6025.pd
GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm
The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs) from L1 signal recorded at the rate of 50 Hz. The scintillation indices S[subscript 4] and σ[subscript Φ] are stored in real time from an array of high-rate scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN). Ionospheric phase scintillation was observed at high latitudes during a moderate geomagnetic storm (Dst = −61 nT) that was caused by a moderate solar wind plasma stream compounded with the impact of two coronal mass ejections. The most intense phase scintillation (σ[subscript Φ] ~ 1 rad) occurred in the cusp and the polar cap where it was co-located with a strong ionospheric convection, an extended tongue of ionisation and dense polar cap patches that were observed with ionosondes and HF radars. At sub-auroral latitudes, a sub-auroral polarisation stream that was observed by mid-latitude radars was associated with weak scintillation (defined arbitrarily as σ[subscript Φ] 0.1 rad and DPR > 2 mm s[superscript −1], both mapped as a function of magnetic latitude and magnetic local time, are very similar.National Science Foundation (U.S.) (Grant ATM-0856093
The ionosphere prediction service prototype for GNSS users
The effect of the Earth’s ionosphere represents the single largest contribution to the Global
Navigation Satellite System (GNSS) error budget and abnormal ionospheric conditions can impose serious
degradation on GNSS system functionality, including integrity, accuracy and availability. With the growing
reliance on GNSS for many modern life applications, actionable ionospheric forecasts can contribute to
the understanding and mitigation of the impact of the ionosphere on our technology based society. In this
context, the Ionosphere Prediction Service (IPS) project was set up to design and develop a prototype
platform to translate the forecast of the ionospheric effects into a service customized for specific GNSS
user communities. To achieve this overarching aim, four different product groups dealing with solar activity,
ionospheric activity, GNSS receiver performance and service performance have been developed and
integrated into a service chain, which is made available through a web based platform. This paper provides
an overview of the IPS project describing its overall architecture, products and web based platform.PublishedA412A. Fisica dell'alta atmosferaJCR Journa
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