**1. Introduction**

The ionospheric radio wave communication, especially navigation is strongly influenced by the equatorial spread-F irregularities. Therefore, it is a scientific interest to do study these irregularities and its morphology and dynamic for the better communication system. The equatorial spread-F irregularities have been studied by several investigators using number of measurement techniques (e.g., [1–3]). The ground-based measurement techniques such as all sky imager (ASI), scanning photometer, RADAR and ionosonde are mostly used to study the dynamics of these irregularities. In equatorial-low latitude F-region, the electron density is depletes or enhance with respect to the background density due to vertical dynamics of F region. This is a key factor for generation of ionospheric irregularities. The size of these domains of irregularities ranges from a few hundred of kilometers in the eastwest direction [4, 5] and a thousands of kilometers in north-south direction aligned with magnetic field lines (e.g., [6]). Basically, they occurred in the low latitude F region over an altitude 250–350 km, such irregularities have observed as dark and bright patches in the nightglow images of OI 630.0 nm emission. The dark patches are also called as equatorial plasma bubbles (EPBs) (e.g., [7, 8]) and bright patches are called as plasma blobs (e.g., [9, 10]).

Few investigators have been reported the nocturnal variations in occurrence (e.g., [7, 11, 12]) and zonal drift velocity (e.g., [8, 13]) of EPBs using OI 630.0 nm images. Many researchers have addressed generation mechanism of EPBs using different techniques (e.g., [14–16]). According to them, the EPBs are generated in the

bottom side of F-region (e.g., [9, 17]) at the equator, mainly by the nonlinear evolution of the generalized Rayleigh-Taylor (GRT) instability [18] and E × B drift [14]. After sunset, the rapid uplifting of F-region is one of the key factors in generating of EPBs [19, 20].

The first time observation of plasma blobs has made with images of OI 630.0 nm, which were taken by the ground-based ASI from Cachoeira Paulista [21]. Using the similar data from the Boston University, Arecibo, Krall et al. [22] have also reported the observations of plasma blobs. The general characteristics of plasma blobs have been studied by using measurements of total electron content (TEC) [23].

Nade et al. [10], suggested that the plasma blobs occurred with EPBs and the variations in apex height may responsible for occurrence of the plasma blobs over low latitude region. However, the generation mechanism of EPBs and plasma blobs is not yet clearly understood [24] and it is most challenging issue to study the dynamics of the low latitude F region. In addition, several questions were raised by Kil et al. [25] on the EPB-blob connection. They reported that the creation of plasma blobs is not depending on EPBs and they also mentioned that the occurrence rate of EPBs varies with solar activity while blobs occurred frequently with solar activity. Based on these results they raised the question, why the occurrence of plasma blobs shows opposite nature with solar activity? These questions are creating inspiration to do more research in the same area.

## **2. Methodology**

#### **2.1 Nightglow emission OI 630.0 nm measurement**

Based on numerous ground-based and in-situ studies, it is widely accepted that the nightglow OI 630.0 nm emissions are generated at low latitude F-region heights (250–300 km). The nightglow emission in F-region at (1D) 630.0 nm is governed by dissociative recombination between ions and electrons [26, 27]. The nightglow OI 630.0 nm images are used to study the characteristics of EPBs. Otsuka et al. [28] suggested that the ASI is an important aide towards improving the understanding of the coupling between ionosphere and thermosphere using images of nightglow OI 630.0 nm emission and OH emission. Because OH emissions are generating at around 100 km (ionosphere) while OI 630.0 nm emissions are generating at around 250 km (thermosphere).

Few methods are available in literature to analyze the all sky image data [29, 30]. Kubota et al. [31] has introduced a new method to convert the pixel images of the ASI into actual geographic coordinates for 250 km altitude, the airglow emission layer. Then to retrieve information from image data, the pixel value of images converted into corresponding latitude-longitude values by Narayanan et al. [32]. Recently, by the combination of both methods, Sharma et al. [33] has introduced the "average method" to process and analyze the image data.

**Figure 1** illustrates processed images of OI 630.0 nm, which are taken on 17-18 January, 2012, showing the time evolution and structure of the EPBs and plasma blobs. In **Figure 1**, yellow and white arrows are showing signature of EPB and plasma blobs respectively in the OI 630.0 nm images.

To retrieve the pixel intensity from images of nightglow OI 630.0 nm Taori et al. [34] has introduced "the image crop method." In this method, we have selected only a square bin of 5 × 5 pixel at the center of the image corresponding to a rectangular field of view having ~1° along the zenith. The average intensity of this square bin is considered as intensity of OI 630.0 nm emission to study the nocturnal variation in

**59**

*Study of Equatorial Plasma Bubbles Using ASI and GPS Systems*

intensity. Thus, we got the intensity data of OI 630.0 nm emission for each indi-

*Sequences of images of OI 630.0 nm obtained on 17-18 January, 2012 in IST at Kolhapur. Yellow and white* 

*arrows are showing dark and bright (EPB and plasma blob) respective structures in images.*

electromagnetic wave between the satellite and the receiver [37].

A dual frequency (L1 = 1575.42 MHz and L2 = 1227.60 MHz) GPS receiver (LEICA GRX1200GGPRO GNSS) is operating at Hyderabad (17.37°N, 78.48°E) [3]. It is a unique station to study the ionospheric irregularities because it is located at the northern crest of the equatorial ionization anomaly (EIA). A dualfrequency GPS receiver can measure the difference in ionospheric delays between the L1 and L2 of the GPS frequencies, which are generally assumed to travel along the same path through the ionosphere. Thus, the group delay can be obtained as

Up to 11 GPS satellites are in view and provide outputs in 22 receiver channels [35]. The ionosphere has an effect on the signal of GPS satellite. TEC is measured along the path from the GPS satellite to a receiver. The TEC is defined by the integral of electron density in TEC unit (TECU), where 1 *TEC unit* = 10<sup>16</sup> *electrons*/*m*<sup>2</sup> column along the signal transmission path. The dual frequency GPS receivers are used to measure the TEC, which is one of the most important methods to investigate the dynamics of ionosphere. Several research groups are showing interest in the equatorial ionospheric research using GPS data. Dow et al. [36] did an analysis of the importance of GPS data in support of the terrestrial reference frame, earth observations and research, positioning, navigation and timing as well as other applications that benefit the society. The slant TEC is the measure of the total number of free electrons in a column of unit cross section along the path of the

*DOI: http://dx.doi.org/10.5772/intechopen.85604*

vidual image with respect to time.

**2.2 TEC measurements**

**Figure 1.**

*Study of Equatorial Plasma Bubbles Using ASI and GPS Systems DOI: http://dx.doi.org/10.5772/intechopen.85604*

**Figure 1.**

*Geographic Information Systems in Geospatial Intelligence*

ing inspiration to do more research in the same area.

**2.1 Nightglow emission OI 630.0 nm measurement**

the "average method" to process and analyze the image data.

plasma blobs respectively in the OI 630.0 nm images.

of EPBs [19, 20].

(TEC) [23].

**2. Methodology**

250 km (thermosphere).

bottom side of F-region (e.g., [9, 17]) at the equator, mainly by the nonlinear evolution of the generalized Rayleigh-Taylor (GRT) instability [18] and E × B drift [14]. After sunset, the rapid uplifting of F-region is one of the key factors in generating

Nade et al. [10], suggested that the plasma blobs occurred with EPBs and the variations in apex height may responsible for occurrence of the plasma blobs over low latitude region. However, the generation mechanism of EPBs and plasma blobs is not yet clearly understood [24] and it is most challenging issue to study the dynamics of the low latitude F region. In addition, several questions were raised by Kil et al. [25] on the EPB-blob connection. They reported that the creation of plasma blobs is not depending on EPBs and they also mentioned that the occurrence rate of EPBs varies with solar activity while blobs occurred frequently with solar activity. Based on these results they raised the question, why the occurrence of plasma blobs shows opposite nature with solar activity? These questions are creat-

Based on numerous ground-based and in-situ studies, it is widely accepted that the nightglow OI 630.0 nm emissions are generated at low latitude F-region heights (250–300 km). The nightglow emission in F-region at (1D) 630.0 nm is governed by dissociative recombination between ions and electrons [26, 27]. The nightglow OI 630.0 nm images are used to study the characteristics of EPBs. Otsuka et al. [28] suggested that the ASI is an important aide towards improving the understanding of the coupling between ionosphere and thermosphere using images of nightglow OI 630.0 nm emission and OH emission. Because OH emissions are generating at around 100 km (ionosphere) while OI 630.0 nm emissions are generating at around

Few methods are available in literature to analyze the all sky image data [29, 30]. Kubota et al. [31] has introduced a new method to convert the pixel images of the ASI into actual geographic coordinates for 250 km altitude, the airglow emission layer. Then to retrieve information from image data, the pixel value of images converted into corresponding latitude-longitude values by Narayanan et al. [32]. Recently, by the combination of both methods, Sharma et al. [33] has introduced

**Figure 1** illustrates processed images of OI 630.0 nm, which are taken on 17-18 January, 2012, showing the time evolution and structure of the EPBs and plasma blobs. In **Figure 1**, yellow and white arrows are showing signature of EPB and

To retrieve the pixel intensity from images of nightglow OI 630.0 nm Taori et al. [34] has introduced "the image crop method." In this method, we have selected only a square bin of 5 × 5 pixel at the center of the image corresponding to a rectangular field of view having ~1° along the zenith. The average intensity of this square bin is considered as intensity of OI 630.0 nm emission to study the nocturnal variation in

The first time observation of plasma blobs has made with images of OI 630.0 nm, which were taken by the ground-based ASI from Cachoeira Paulista [21]. Using the similar data from the Boston University, Arecibo, Krall et al. [22] have also reported the observations of plasma blobs. The general characteristics of plasma blobs have been studied by using measurements of total electron content

**58**

*Sequences of images of OI 630.0 nm obtained on 17-18 January, 2012 in IST at Kolhapur. Yellow and white arrows are showing dark and bright (EPB and plasma blob) respective structures in images.*

intensity. Thus, we got the intensity data of OI 630.0 nm emission for each individual image with respect to time.
