Improving Detection Performance of Ionospheric Disturbances due to Earthquake by Optimization of Sequential Measurement Combination

Energy generated from earthquake (EQ) is transferred to the ionosphere and results in co-seismic ionospheric disturbances (CID). CID can be observed in the ionospheric combination using L1, L2 frequency carrier phase. As ionospheric trend due to normal conditions such as elevation angle of satellites is generally larger than disturbances, a proper measure is required to extract disturbance signals. Derivative, or sequential combination, is a simple and effective way to remove the normal trend in the ionospheric delay. When using derivative, however, disturbance signals can often be obscured by noise due to its small amplitude. In order to reduce the noise while preserving the time rate of data, and thus to improve signal-to-noise ratio (SNR), we designed a new derivative method using optimization under a couple of assumptions. With simulation data, it is found that N, the number of epochs used for sequential combination, turned out to be the best when N=160 with maximum SNR. Finally, the proposed algorithm’s SNR was compared to that of the previous study which also used derivative method. 120~260% improvements were observed for the proposed method compared to the conventional method.

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A New Method to Improve the Detection of Co-Seismic Ionospheric Disturbances using Sequential Measurement Combination

Sensors ◽

10.3390/s19132948 ◽

2019 ◽

Vol 19 (13) ◽

pp. 2948 ◽

Cited By ~ 1

Author(s):

Seonho Kang ◽

Junesol Song ◽

Deokhwa Han ◽

Bugyeom Kim ◽

Hyoungmin So ◽

...

Keyword(s):

Time Derivative ◽

Tohoku Earthquake ◽

Satellite System ◽

Detection Performance ◽

Ionospheric Delay ◽

New Method ◽

Ionospheric Disturbances ◽

The 2011 Tohoku Earthquake ◽

Sequential Measurement ◽

Global Navigation Satellite

Earthquakes generate energy that propagates into the ionosphere and incurs co-seismic ionospheric disturbances (CIDs), which can be observed in ionospheric delay measurements. In most cases, the CID has a weak signal strength, because the energy in the atmosphere transferred from the earthquake dissipates as it travels toward the ionosphere. It is particularly hard to observe at reference stations that are located far from the epicenter. As the number of Global Navigation Satellite System stations and their positions are restricted, it is important to employ weak CID data in the analysis by improving the detection performance of CIDs. In this study, we suggest a new method of detecting CIDs, which mainly uses a sequential measurement combination of the carrier phase-based ionospheric delay data, with a 1-second interval. The proposed method’s performance was compared with conventional methods, including band-pass filters and a representative time-derivative method, using data from the 2011 Tohoku earthquake. As a result, the maximum CID-to-noise ratio can be increased by a maximum of 13% when the proposed method is used, and consequently, the detection performance of the CID can be improved.

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Landsat TM image maps of the Shirase and Siple Coast ice streams, West Antarctica

Annals of Glaciology ◽

10.1017/s0260305500016773 ◽

1994 ◽

Vol 20 ◽

pp. 407-412 ◽

Cited By ~ 6

Author(s):

Jane G. Ferrigno ◽

Jerry L. Mullins ◽

Jo Anne Stapleton ◽

Robert A. Bindschadler ◽

Ted A. Scambos ◽

...

Keyword(s):

Signal To Noise Ratio ◽

Elevation Angle ◽

Single Band ◽

Landsat Tm ◽

Ice Streams ◽

Cd Rom ◽

Landsat Tm Image ◽

West Antarctic ◽

Tm Image ◽

Convolution Algorithm

Fifteen 1: 250000 and one 1: 1000 000 scale Landsat Thematic Mapper (TM) image mosaic maps are currently being produced of the West Antarctic ice streams on the Shirase and Siple Coasts. Landsat TM images were acquired between 1984 and 1990 in an area bounded approximately by 78°-82.5°S and 120°- 160° W. Landsat TM bands 2, 3 and 4 were combined to produce a single band, thereby maximizing data content and improving the signal-to-noise ratio. The summed single band was processed with a combination of high- and low-pass filters to remove longitudinal striping and normalize solar elevation-angle effects. The images were mosaicked and transformed to a Lambert conformal conic projection using a cubic-convolution algorithm. The projection transformation was controled with ten weighted geodetic ground-control points and internal image-to-image pass points with annotation of major glaciological features. The image maps are being published in two formats: conventional printed map sheets and on a CD-ROM.

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Investigation on peculiar SNR variation at TianMa radio telescope

Scientific Reports ◽

10.1038/s41598-019-55072-3 ◽

2019 ◽

Vol 9 (1) ◽

Author(s):

Qingbao He

Keyword(s):

Signal To Noise Ratio ◽

Elevation Angle ◽

Main Beam ◽

Control Software ◽

Software Update ◽

Astronomical Observations ◽

Pointing Error ◽

Long Baseline ◽

X Band ◽

Changing Rate

AbstractChinese lunar spacecraft Chang’E-3 (CE3) and Chang’E5-T1 (CE5T1) were launched in 2013 and 2014, respectively and very long baseline interferometry (VLBI) observations were performed. Signal to noise ratio (SNR) of the Tianma (TM) station experienced peculiar variation, whereas SNRs of other stations were rather stable. Further, it happened only when observing spacecraft, and showed no such variation when performing astronomical observations. Moreover, it was distinctive on X band signals, whereas it was not noticed on S band signals. Analysis showed that the SNR variation was closely related with changing rate of elevation angle. Further investigations discovered that there were two sets of antenna control software at TM station, and the SNR variation originated from a bug in elevation control software used for observing spacecraft, not for astronomical observations. The bug caused big pointing error (around ± 30 as) on elevation angle of TM, which resulted in the peculiar SNR variation. It was not noticed on S band signals due to its relatively wide and flat main beam comparing with ± 30 as pointing error. However, the bug was fixed in software update in July, 2016, and the SNR of TM showed no such variation in 2017 and 2018.

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A one year comparison of 482 MHz radar wind profiler, RS92-SGP Radiosonde and 1.5 μm Doppler Lidar wind measurements

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-7-11439-2014 ◽

2014 ◽

Vol 7 (11) ◽

pp. 11439-11479 ◽

Cited By ~ 3

Author(s):

E. Päschke ◽

R. Leinweber ◽

V. Lehmann

Keyword(s):

Signal To Noise Ratio ◽

Elevation Angle ◽

Wind Profiler ◽

Wind Vector ◽

Doppler Lidar ◽

Operational Testing ◽

Average Wind ◽

Wind Measurements ◽

One Year ◽

Scan Pattern

Abstract. We present the results of a one-year quasi-operational testing of the 1.5 μm StreamLine Doppler lidar developed by Halo Photonics from 2 October 2012 to 2 October 2013. The system was configured to continuously perform a velocity-azimuth display (VAD) scan pattern using 24 azimuthal directions with a constant beam elevation angle of 75°. Radial wind estimates were selected using a rather conservative signal-to-noise ratio (SNR) based threshold of −18.2 dB (0.015). A 30 min average wind vector was calculated based on the assumption of a horizontally homogeneous wind field through a singular-value decomposed Moore–Penrose pseudoinverse of the overdetermined linear system. A strategy for a quality control of the retrieved wind vector components is outlined which is used to ensure consistency between the retrieved winds and the assumptions inherent to the employed wind vector retrieval. Finally, the lidar measurements are compared with operational data from a collocated 482 MHz radar wind profiler running in a four-beam Doppler beam swinging (DBS) mode and winds from operational radiosonde measurements. The intercomparisons show that the Doppler lidar is a reliable system for operational wind measurements in the atmospheric boundary layer (ABL).

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Influence of the Type of the Underlying Surface Forest Cover on the Level of SNS Radio Signals Reflected from the Surface at Low-Altitude Aircraft Flight

Herald of the Bauman Moscow State Technical University Series Instrument Engineering ◽

10.18698/0236-3933-2019-6-64-74 ◽

2019 ◽

pp. 64-74

Author(s):

N.E. Zubov ◽

A.A. Eshchenko ◽

S.S. Demin ◽

G.E. Maslennikova ◽

S.V. Ivanenko

Keyword(s):

Noise Level ◽

Electromagnetic Waves ◽

Forest Cover ◽

Signal To Noise Ratio ◽

Elevation Angle ◽

Underlying Surface ◽

Multiple Reflections ◽

Aircraft Flight ◽

Radio Signals ◽

Low Altitude

The purpose of the study was to analyze the influence of the type of the underlying surface forest cover on the level of SNS radio signals reflected from the surface and, accordingly, on the aircraft user equipment efficiency at low-altitude flying. By mathematical simulation, we analyzed the dependences of the signal-to-noise ratio on the elevation angle of navigation spacecraft of the working constellation and the aircraft flight altitude for different types of forest cover. Findings of research show that the rugged barren terrain is characterized by the highest noise level, while the lowest noise level is typical for the thin forest. This can be explained by the fact that most electromagnetic waves penetrate deep into the forest, where they are absorbed due to multiple reflections. Moreover, the thicker the forest cover, the lower the degree of absorption and the higher the noise level.

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Detection and Description of the Different Ionospheric Disturbances that Appeared during the Solar Eclipse of 21 August 2017

Remote Sensing ◽

10.3390/rs10111710 ◽

2018 ◽

Vol 10 (11) ◽

pp. 1710 ◽

Cited By ~ 1

Author(s):

Heng Yang ◽

Enrique Monte Moreno ◽

Manuel Hernández-Pajares

Keyword(s):

Solar Eclipse ◽

Elevation Angle ◽

The United States ◽

Satellite System ◽

Electron Content ◽

Ionospheric Disturbances ◽

Vertical Total Electron Content ◽

Total Electron ◽

Bow Wave ◽

Cooling Effects

This work will provide a detailed characterization of the travelling ionospheric disturbances (TIDs) created by the solar eclipse of 21 August 2017, the shadow of which crossed the United States from the Pacific to the Atlantic ocean. The analysis is done by means of the Atomic Decomposition Detector of Traveling Ionospheric Disturbances (ADDTID) algorithm. This method automatically detects and characterizes multiple TIDs from the global navigation satellite system (GNSS) observation. The set of disturbances generated by the eclipse has a richer and more varied behavior than that associated with the shock wave directly produced by cooling effects of the moon shadow. This can be modeled in part as if the umbra and penumbra of the eclipse were moving cylinders that intersects with variable elevation angle a curved surface. This projection gives rise to regions of equal penumbra with shapes similar to ellipses, with different centers and foci. The result of this is reflected in the time evolution of the TID wavelengths produced by the eclipse, which depend on the vertical angle of the sun with the surface of the earth, and also a double bow wave phenomenon, where the bow waves are generated in advance to the umbra. We show that the delay in the appearance of the disturbances with the transit of the eclipse are compatible with the physical explanations, linked to the different origins of the disturbances and the wavelengths. Finally, we detected a consistent pattern, in location and time of disturbances in advance to the penumbra as a set of medium scale TIDs, which could be hypothesized as soliton waves of the bow wave. In all cases, the detected disturbances were checked visually on the detrended vertical total electron content (TEC) maps.

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Travelling ionospheric disturbance properties deduced from Super Dual Auroral Radar measurements

Annales Geophysicae ◽

10.1007/s00585-001-1550-z ◽

2000 ◽

Vol 18 (12) ◽

pp. 1550-1559 ◽

Cited By ~ 13

Author(s):

J. W. MacDougall ◽

D. A. Andre ◽

G. J. Sofko ◽

C.-S. Huang ◽

A. V. Koustov

Keyword(s):

Reasonable Agreement ◽

Ionospheric Disturbance ◽

Elevation Angle ◽

Ionospheric Disturbances ◽

Auroral Ionosphere ◽

Travelling Ionospheric Disturbances ◽

Radar Network ◽

Radar Measurements

Abstract. Based on modeling of the perturbations in power and elevation angle produced by travelling ionospheric disturbances (TIDs), and observed by the Super Dual Auroral Radar Network, procedures for determining the TID properties are suggested. These procedures are shown to produce reasonable agreement with those properties of the TIDs that can be measured from simultaneous ionosonde measurements. The modeling shows that measurements of angle-of-elevation perturbations by SuperDARN allows for better determination of the TID properties than using only the perturbations of power as is commonly done.Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions)

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Investigations into Phase Multipath Mitigation Techniques for High Precision Positioning in Difficult Environments

Journal of Navigation ◽

10.1017/s0373463307004341 ◽

2007 ◽

Vol 60 (3) ◽

pp. 457-482 ◽

Cited By ~ 17

Author(s):

Lawrence Lau ◽

Paul Cross

Keyword(s):

High Precision ◽

Signal To Noise Ratio ◽

Elevation Angle ◽

Simulated Data ◽

Satellite System ◽

Multipath Mitigation ◽

Laboratoire Central ◽

Mitigation Techniques ◽

Global Navigation Satellite ◽

Space Data

The modelling of most Global Navigation Satellite System (GNSS) errors/biases and developments of data processing techniques have been improved substantially since the birth of Global Positioning System (GPS), however, there has been much less progress in the improvement of phase multipath mitigation techniques. Multipath therefore remains one of the most important error sources in high precision GNSS positioning. This is because multipath is site-dependent and therefore cannot be eliminated by differencing techniques. Also multipath is highly dependent on satellite-reflector-antenna geometry, which usually causes rapid changes in phase multipath errors especially in Real-Time Kinematic (RTK) applications. Multipath mitigation for static antennas such as those at reference stations can be carried out by site calibration, averaging over long observation times, and through the estimation of the error using filtering based on signal-to-noise ratio (SNR) data. However, multipath mitigation for kinematic antennas is still very difficult today.Nevertheless, much research has been carried out on a particular class of phase multipath mitigation techniques: ones that can be applied within positioning algorithms (rather than incorporated into the receiver tracking loops or antennas). This paper investigates and further develops a number of state-of-the-art techniques in this category. They include phase multipath estimation using SNR data, phase multipath estimation through the use of closely spaced antennas, multipath mitigation stochastic models such as the satellite elevation angle model and SNR-based models (SIGMA-∊ model and our modified SNR-based model), and our own novel ray-tracing method. The techniques are tested with both real and simulated data, the real test datasets have been collected on the Laboratoire Central des Ponts et Chaussées (LCPC) testbed near Nantes in France, and on the campus of the University of Nottingham during SPACE data collection experiments.

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Multiple stellar systems

Symposium - International Astronomical Union ◽

10.1017/s007418090015185x ◽

1986 ◽

Vol 118 ◽

pp. 441-442

Author(s):

A. Duquennoy ◽

M. Mayor

Keyword(s):

Radial Velocity ◽

Small Amplitude ◽

Cross Correlation ◽

Signal To Noise Ratio ◽

High Signal ◽

Correlation Technique ◽

Multiple Systems ◽

Triple Systems ◽

The Cross

A spectroscopic survey of visual binaries with known orbital elements has been carried out with the radial velocity scanner CORAVEL at the Haute-Provence Observatory, since 1977, (Baranne, Mayor, Poncet, 1979). This survey of more than 100 visual systems, selected from Dommanget's catalogue (1967) (see also a new edition 1982) was first devoted to the determination of stellar masses. Several multiple systems were detected and have permitted also a study of the structure of triple systems. We have detected and measured in particular a class of triple systems with radial velocity variations of small amplitude. Taking advantage of the high resolution and high signal-to-noise ratio accessible with the cross-correlation technique, such small amplitude radial velocity curves are sometimes derived only through the change of width and shape of the cross-correlation function. Let us recall that the cc-function of a SB2 (or SB3) system is only the weighted sum of the individual cc-functions (Mayor, 1985). This property of the cross-correlation combined with the linearity of the detector allow a very simple analysis of blended dips. The full width at half depth of the cross-correlation dip is about FWHD = 16 km/s (in absence of noticeable rotation). Analysis of blended systems allows a good determination of the two individual velocities if the difference |vr1 -Vr2| is equal or larger than about 0.15 *FWHD (about 2 km/s).

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