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Papers by sheetal karia

Advances in Space Research

$Research paper thumbnail of Change in Atmospheric Refractivity and GPS based TEC prior to Iran-Pakistan Border earthquake (M=7.8) in April 2013$

The paper presents the analysis of GPS TEC data and atmospheric refractivity in order to study th... more The paper presents the analysis of GPS TEC data and atmospheric refractivity in order to study the ionospheric and atmospheric perturbations prior to the Iran earthquake that occurred on 16 April 2013 in Iran (28.10°N, 62.05°E). The data of GPS based total electron content (TEC) are derived from two GPS receivers, Surat (21.16°N, 72.78°E) and Lucknow (26.91°N, 80.95°E). The GPS TEC showed variations few days prior to the earthquake. Further, the Field Of View (FOV) of GPS antenna is observed by counting number of satellite passes and results of atmospheric refractivity profile for radiosonde observation stations (Shiraz, Iran and Delhi, India) around the faultline are presented in this paper. It is seen that the number of satellite passes registering TEC increased as well as atmospheric refractivity gets modified from 8 to 6 days prior to the earthquake at Shiraz, Iran and Delhi, India. We conclude that in search of precursory signatures for an earthquake, both GPS TEC and refractiv...

Among different precursory phenomena on earthquake predictions the ionospheric ones are the young... more Among different precursory phenomena on earthquake predictions the ionospheric ones are the youngest. Anomalous behaviour of the ionosphere prior to the earthquake was reported as early as in 1982. It has been well established that strong earthquakes (M>5)preparation can cause anomalous total electron content (TEC) variations. To detect seismo-ionospheric disturbances in the TEC we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India ( Geographical Lat.21.16N , Long .72.78E) . The TEC data has been analysed corresponding to two earthquakes which occurred on 09 April, 2009 (M=5.6, Lat. 27.130N, Long. 70.769 E) and on 16 April, 2009 (M=5.5, Lat. 34.20N, Long. 70.065E). The analysis of TEC data of 09 April, 2009 shows abnormal variation in TEC during 06-09 April, 2009 from normal values followed by a large daytime enhancement on 09April 2009. Similarly, anomalous variation in TEC was also observed on...

The present study reports the analysis of GPS based TEC for IGS stations Ogaswara (27.06 N, 142.1... more The present study reports the analysis of GPS based TEC for IGS stations Ogaswara (27.06 N, 142.19 E) and Aira (31.82 N, 130.59 E) in Japan at times close to a strong Tohoku earthquake (M=9. 0) On 11 march 2011 Japan. The TEC data used in the study are obtained from IGS stations in RINEX format. TEC data have been analyzed corresponding to moderate solar and magnetic activity period. We found enhancement in peak TEC 7, 9, 10, 11 and 12 days at Ogaswara station and enhancement in peak TEC is also observed at Aira station prior to the earthquake. This enhancement in TEC is obtained daily from 8-13 days prior to an earthquake. In light of solar and magnetic indices, these enhancements in TEC may be considered as ionospheric precursor.

The present paper reports the occurrence of ionospheric scintillation (S4 > 0.2) measured usin... more The present paper reports the occurrence of ionospheric scintillation (S4 > 0.2) measured using GPS receiver (GISTM) at Surat, (21.160N, 72.780E) located near the northern crest of equatorial anomaly in India. The results are presented for data collected during di�erent levels of solar activity from Jan-2009 to Dec-2011. These long time observations phenomenon, which covers low to moderate solar activity period, have shown features such as, diurnal, monthly, seasonal, magnetic activity and solar cycle variation in scintillation occurrence. It was observed that the diurnal variation of the amplitude scintillation predominately occurred after sunset time (18:00 to 06:00 LT). Our observation shows that the duration of scintillation occurrence is found to be maximum during moderate solar activity and least during low solar activity. The seasonal variation shows that the occurrence of scintillation is observed to be maximum for equinox months, less in winter months and least in summer...

This paper investigates the features of pre-earthquake ionospheric anomalies in the total elec-tr... more This paper investigates the features of pre-earthquake ionospheric anomalies in the total elec-tron content (TEC) data obtained on the basis of regular GPS observations from the GPS receiver at SVNIT Surat (21.16 N, 72.78 E Geog) located at the northern crest of equatorial anomaly region. The data has been analysed for 5 different earthquakes that occurred during 2009 in India and its neighbouring regions. Our observation shows that for the cases of the earthquake, in which the preparation area lies between the crests of the equatorial anomaly close to the geomagnetic equator the enhancement in TEC was followed by a depletion in TEC on the day of earthquake, which may be connected to the equatorial anomaly shape distortions. For the analysis of the ionospheric effects of one of such case-the 30 September 2009 Sumatra earthquake, Global Ionospheric Maps of TEC were used. The possible influence of the earth-quake preparation processes on the main low-latitude ionosphere peculiarity---...

Geomatics, Natural Hazards and Risk, 2015

ABSTRACT The present paper studies the basic characteristics of night time scintillation: simulta... more ABSTRACT The present paper studies the basic characteristics of night time scintillation: simultaneously occurred with S4 ≥ 0.2 and enhancement of ROTI (ROTI ≥ 0.5) over Indian low latitude station Surat (21.160 N, 72.780 E) during the four year period of initial rising phase of solar activity from 2009 to 2012.

The present paper reports the modification in refractivity prior to the Iran earthquake that had ... more The present paper reports the modification in refractivity prior to the Iran earthquake that had occurred on 16 April 2013 in Iran (28.10°N, 62.05°E). The reception of over horizon GPS signal from two GPS receivers Surat (21.16°N, 72.78°E) and Lucknow (26.91°N, 80.95°E ) and results of atmospheric refractivity profile derived from Radio Occultation observations from COSMIC satellite obtained for epicenter region are presented in this paper. It is seen that atmospheric refractivity gets modified from 8 to 6 days prior to the earthquake at the epicenter.

$Research paper thumbnail of Modification in Atmospheric Refractivity and GPS Based TEC as Earthquake Precursors$

Positioning, 2014

The present paper reports the modification in GPS TEC (total electron content) and atmospheric re... more The present paper reports the modification in GPS TEC (total electron content) and atmospheric refractivity prior to the Iran earthquake that had occurred on 16 April 2013 in Iran (28.10˚N, 62.05˚E). The analysis of GPS-based TEC from two GPS receivers, Surat (21.16˚N, 72.78˚E) and Lucknow (26.91˚N, 80.95˚E ) and results of atmospheric refractivity profile for radiosonde observation stations (Shiraz, Iran and Delhi, India) around the fault line are presented in this paper. It is seen that atmospheric refractivity gets modified from 8 to 6 days prior to the earthquake at Shiraz, Iran and Delhi, India. The GPS TEC showed variations a few days prior to the earthquake. We conclude that in search of precursory signatures for an earthquake, both GPS TEC and refractivity are important parameters.

$Research paper thumbnail of Refractive index of drifting ionized plasma with variable electron collision frequency in the Earth's upper atmosphere$

The refractive index of an ionized medium in a magnetic field is complex. The formula for the ref... more The refractive index of an ionized medium in a magnetic field is complex. The formula for the refractive index is the cornerstone of the theory useful to establish the background study for radio wave propagation in uniform magneto-plasma. In the present paper, the expression for refractive index have been derived by considering Ionosphere as an anisotropic media with a constant drift so that it could be applied to any type of irregularities observed in the ionosphere. The formula has been derived taking variation in electron collision frequency with electron speed in drifting plasma. This expression is useful and helps to study the propagation characteristics of drifting plasma. The relativistic drift velocities of the plasma, generally reached by astrophysical plasma, will change the refractive index of the plasma considerably for example during re-entry of space vehicle in earth's atmosphere, the creation of high density plasma medium affects the radiated signal from the spac...

Journal of Earth System Science, 2011

In recent years, measurements of total electron content (TEC) have gained importance with increas... more In recent years, measurements of total electron content (TEC) have gained importance with increasing demand for the GPS-based navigation applications in trans-ionospheric communications. To study the variation in ionospheric TEC, we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India (21.16 • N, 72.78 • E) located at the northern crest of equatorial anomaly region. The data collected (for the low sunspot activity period from August 2008-December 2009) were used to study the diurnal, monthly, seasonal semi-annual and annual variations of TEC at Surat. It was observed that the diurnal variation at the region reaches its maximum value between 13:00 and 16:00 IST. The monthly average diurnal variations showed that the TEC maximizes during the equinox months followed by the winter months, and are lowest during the summer months. The ionospheric range delay to TEC for the primary GPS signal is 0.162 m per TECU.

International Journal of Remote Sensing, 2013

The present study includes observations of anomalies at ionospheric and ground levels using data ... more The present study includes observations of anomalies at ionospheric and ground levels using data from global positioning system (GPS)-based total electron content (TEC), ionospheric electron density by Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER), and ground-based ultra-low-frequency (ULF) emission prior to an earthquake that occurred on 12 December 2009. The analysis of the data from these three different techniques show relations with preseismic activities. The GPS-based TEC showed enhancement three days prior to the day of the earthquake. On converting the satellite azimuth into latitude and longitude, a large number of passes giving anomalous TEC values were observed covering a zone 17-23 • N and 70-74 • E (i.e. around the epicentre). Electron density and temperature as measured by DEMETER also show enhancement of the tracks around the epicentre one day prior to the earthquake. For ground-based ULF emission, we used different analysis techniques for the detection of abnormal changes in ULF emission before the earthquake. We observed changes in different parameters such as polarization ratio and fractal dimension. Clear enhancement is observed for polarization parameters (Z/X , Z/Y ) and fractal analysis (for the Z component). The results provide useful information in acquiring data prior to earthquakes.

International Journal of Remote Sensing, 2012

ABSTRACT The temporal and seasonal variations of Total Electron Content (TEC) are studied at Sura... more ABSTRACT The temporal and seasonal variations of Total Electron Content (TEC) are studied at Surat (Geographic Lat. 21.16 N, Long. 72.78 E,), India, which is in the equatorial anomaly region, for a period of 11 months from 01 February to 31 December, 2009 using a Global Positioning System (GPS) receiver. The mean TEC values show a minimum at 0500 h LT (LT = UT + 5.5 h) and a peak value at about 1400 h LT. The lowest TEC values are observed in winter whereas largest values are observed in equinox. These results are compared with the TEC derived from IRI-2007 using three different options of topside electron density, NeQuick, IRI01-corr, and IRI-2001. A good agreement is found between the TEC obtained at Surat and those derived from IRI-corr and NeQuick.

$Research paper thumbnail of Change in refractivity of the atmosphere and large variation in TEC associated with some earthquakes, observed from GPS receiver$

Advances in Space Research, 2011

The present study reports the analysis of GPS based TEC for our station Surat (21.16°N, 72.78°E) ... more The present study reports the analysis of GPS based TEC for our station Surat (21.16°N, 72.78°E) located at the northern crest of equatorial anomaly region in India at times close to some earthquake events (M P 5) during the year 2009 in India and its neighbouring regions. The TEC data used in the study are obtained from GPS Ionospheric Scintillation and TEC Monitoring (GISTM) system. The TEC data has been analysed corresponding to 11 earthquakes in low solar activity period and quiet geomagnetic condition. We found that, out of 11 cases of earthquakes (M > 5) there were seven cases in which enhancement in TEC occurred on earthquake day and in other four cases there was depletion in TEC on earthquake day. The variation in refractivity prior to earthquake was significant for the cases in which the epicentre lied within a distance of 600 km from the receiving station. By looking into the features on temporal enhancement and depletion of TEC a prediction was made 3-2 days prior to an earthquake (on 28 October 2009 in Bhuj -India). The paper includes a brief discussion on the method of potentially identifying an impending earthquake from ionospheric data.