Space Based Navigation and GNSS remote sensing

Precise positioning and navigation is one of the critical components of modern day’s economic and societal well-being. The use of satellite based navigation revolutionizes many areas of day-to-day life as well very important for defence, energy, transport, flights, space activities and other areas. GPS is the forefather of space based navigation systems. However, now many such systems are now available from several countries like China, European Union, Russia, Japan etc. Indian also developed its own navigation system, called NavIC.   

Moreover, planetary exploration requires an autonomous navigation system beyond the satellite based system. The use of Pulsar for a GPS like system, but on a celestial scale are currently being explored. 

The study of ionospheric effect on navigational systems is essential in regions like India with severe ionospheric activity and also very relevant to national priorities of making Indian GPS like systems, GAGAN and NavIC. Further, atmospheric components like water vapor play a key role in precise positioning. The Understanding and modelling of ionosphere, troposphere and other parameters for GNSS systems have consequences on precise position systems and navigation. Figure 1 shows the schematic of developed two shell ionospheric model and the performance of Klobuchar Like model over Indian region. 

Fig. 1: (a) The Two Shell Ionospheric model and (b) performance of new Klobuchar-like model 

GNSS signals are also useful for remote sensing of Earth’s environment. As the number of signals are increasing with addition of new satellite constellations and new frequencies, a new opportunity emerges to study both lower atmospheric as well ionospheric phenomena. Our research is specially focusing on monitoring tropospheric variables such as atmospheric water vapour by using the signal from Global Navigation Satellite System (GNSS) network as well as our newly launched Indian Regional Navigation Satellite System, NavIC. The near real time accurate estimation of atmospheric water vapour is very much helpful to predict the extreme weather events. Figure 2 shows the TEC variation observed by our algorithm as well the water vapor. 

Figure 2: (a) The TEC variation over Kolkata and (2) performance of PWV retrieval from GPS data using our model

The impact of highly energetic lower atmospheric disturbances such as cyclones, thunderstorm generated very high intensity lightning strikes has been seen in the upper atmosphere by the interaction of generated very low frequency signals with the layers of ionosphere. The continuous monitoring of ionospheric total electron content retrieved from GNSS signal is very helpful for detection of such low frequency signals and hence the characterization of such lower atmospheric disturbances. In Fig. 4,