Global Navigation Satellite Services Research Articles

Out-of-Band Fibre-Optic Time and Frequency Transfer Using Asymmetric and Symmetric Opto-Electronic Repeaters.

Signal repeaters for fibre-optic communication can be realized with back-to-back connected transceivers. This configuration can provide high gain (≈30 dB) at low cost, and the needed semiconductor lasers and modulators can be realized for practically any relevant wavelength. Unfortunately, for time and frequency transfer the uncorrelated wavelength drifts in the transceiver lasers can compromise transfer stability, and device replacement due to failure may result in large time offsets that have to be measured via global navigation satellite services. This work demonstrates that good results can nevertheless be obtained with standard telecom DWDM tranceivers over long time periods (years). More importantly, a simple wavelength-symmetric repeater is proposed that can be used to cancel the detrimental effects of wavelength drifts and which lessens the need for link re-calibrations after transceiver replacements. In a proof-of-concept test setup, timing drift due to wavelength drift of a repeater laser is reduced by approximately two orders of magnitude.

Evaluation of the Performance of Online GPS/GNSS Data Processing Services for Monitoring the Land Deformations and Movements

In recent years, the Global Navigation Satellite Services (GNSS) technology has been frequently employed for monitoring the Earth crust deformation and movement. Such applications necessitate high positional accuracy that can be achieved through processing GPS/GNSS data with scientific software such as BERENSE, GAMIT, and GIPSY-OSIS. Nevertheless, these scientific softwares are sophisticated and have not been published as free open source software. Therefore, this study has been conducted to evaluate an alternative solution, GNSS online processing services, which may obtain this privilege freely. In this study, eight years of GNSS raw data for TEHN station, which located in Iran, have been downloaded from UNAVCO website on a daily basis. Furthermore, TEHN GNSS observations are processed with CSRS-PPP, which is based on Precise Point Positioning (PPP) algorithm, and OPUS, which is based on double difference (DD) algorithm, to compare between these two techniques in terms of station velocity estimation and Earth deformation. On the other hand, TEHN station solutions that produce via scientific software, GIPSY-OSIS, are obtained from Nevada Geodetic Laboratory (NGL) website for data validation. Eventually, the results show that both GNSS online processing services (CSRS-PPP and OPUS) are credibly efficient to estimate station velocities, while CSRS-PPP trustworthy service for monitoring the Earth deformation. 

Potential impact of global navigation satellite services on total power H i intensity mapping surveys

Future total-power single-dish HI intensity mapping (HI IM) surveys have the potential to provide unprecedented insight into late time ($z < 1$) cosmology that are competitive with Stage IV dark energy surveys. However, redshifts between $0 < z < 0.2$ lie within the transmission bands of global navigation satellite services (GNSS), and even at higher redshifts out-of-band leakage from GNSS satellites may be problematic. We estimate the impact of GNSS satellites on future single-dish HI IM surveys using realistic estimates of both the total power and spectral structure of GNSS signals convolved with a model SKA beam. Using a simulated SKA HI IM survey covering 30000 sq. deg. of sky and 200 dishes, we compare the integrated GNSS emission on the sky with the expected HI signal. It is found that for frequencies $> 950$ MHz the emission from GNSS satellites will exceed the expected HI signal for all angular scales to which the SKA is sensitive when operating in single-dish mode.

Analysis of Seismogenic Perturbations using Bartlett Method for Earthquake Signatures on GPS TEC

Background/Objectives: Earthquakes are the most unpredictable natural disasters in nature. Spectral analysis of seismoionospheric perturbations will be helpful in understanding the source mechanisms of the earthquakes. Seismogenic perturbations observed in ionosphere for an earthquake occurred on 19th December 2013 are investigated. The earthquake peaked at 4.6 on Richter scale. It took place at 16:41 hour's green which mean time. International global navigation satellite services data for the station BAKO is considered for the analysis. Methods/Statistical Analysis: In present work Bartlett method is implemented on the vertical total electron content data on the earthquake day. Findings: Earthquake signatures in the ionosphere are indentified. It is also observed that the power spectral density of the perturbations has a giant initial value and abated slowly. Application: These findings will aid us to develop early warning systems for earthquakes.