From: Indian Space Research Organisation
Posted: Friday, April 20, 2018
A two-day workshop on “Satellite Navigation and Applications of GNSS/NavIC” was organised during April 5-6, 2018 at NARL, Gadanki. The aim of the workshop was to create awareness on the potential and use of Indian Regional Navigation Satellite System (IRNSS) – NavIC. The workshop was intended to impart training to develop knowledge and skill necessary for the advancement in various applications of NavIC and Global Navigation Satellite System (GNSS) in the country.
Over a decade, NARL has been actively pursuing research in ionospheric and atmospheric domains by setting-up ground network of GNSS and NavIC receivers. Since the NavIC signals pass through the ionosphere and atmosphere, remote sensing of these regions can be done using a receiver at ground. Atmospheric water vapor and ionospheric electron content can be derived using the delay of signal in the respective medium. Using differential delay on two frequencies (L5 and S-band) of NavIC signal, ionospheric electron can be directly estimated as ionosphere is a dispersive medium. Water vapor is derived by removing all other delays on the signal. The line of sight ionospheric delay on the signal can vary between 5 to 100 meters depending upon solar activity, season, place and time of the day over Indian region. The atmospheric delay remains between 0.5 to 3 meters including the delay due to dry gases and water vapor of the atmosphere that exhibit high variability during Monsoon.
NavIC receivers which are capable of measurements of carrier phase up to an accuracy of 1-2 mm on both the L5 and S-bands will be deployed as best optimised ground network to meet the science objectives. NARL plans to derive maps of precipitable water vapor and ionospheric total electron content using combined observations from NavIC and GNSS. Such maps are useful in studying the spatial as well as temporal variations in water vapor and ionosphere. The water vapor mapping can directly be applied in numerical weather prediction models which are not implemented at present. The ionospheric maps can be used for space weather monitoring and forecast at high resolution. In addition to the usability of direct NavIC signal for above mentioned probing, the reflected signal from ground can be used for derivation of soil moisture. The soil moisture is an important parameter for agriculture as well as numerical weather forecast models.
Besides these science applications, the continuous and long term observations from NavIC receiver network can yield equatorial specific "delay models" over India. Better "delay model" can improve the accuracy in position estimated using NavIC signal. At present the most utilised model for water vapor and ionospheric corrections for GNSS signals are developed for mid-latitude conditions which drastically differ from real time variations over equatorial regions like India. NavIC has implemented much improved correction models for these delays. However, the corrections for applications demanding real-time high-precision positioning needs further research, especially under conditions of equatorial plasma bubbles and Space weather Storms. Thus the workshop elucidated fundamentals of NavIC, its signal and architecture besides the role of water vapor and electron density mapping to improve future applications of NavIC. Moreover, it was stressed to improve weather forecast and space weather monitoring through ground based receiver network. The longitudinal difference in atmospheric/ionospheric gradients that could only be studied using stable satellite link provided by the regional NavIC was highlighted including the role of the new forthcoming IRNSS –1I satellite (launched on April 12, 2018) in receiving high resolution observations at 55 degree East longitude.
The workshop was attended by about 80 participants, including 42 Ph.D students, 7 post-graduate students and 30 faculties from 50 Institutes/Universities and DOS centers across the country. Scientists from ISRO and experts from universities delivered eleven lectures about the NavIC Space segment, Ground control segments of navigation satellite system, Time Standards and Positioning, GAGAN and SBAS applications, various applications of NavIC signal in different fields including the emerging technologies based upon NavIC and GAGAN. The need of our own navigation system was stressed. Science applications of the unique configuration of the constellation that can be used to map water vapor & ionospheric electron density and utility of the reflected signal for geophysical sciences were addressed. The role of water vapor and electron density mapping to improve future applications of our satellite navigation was highlighted besides improving weather forecast and space weather monitoring through ground based receiver network.
The lectures provided the scope of doable science objectives including unresolved science questions specific to the equatorial atmospheric/ionospheric regions through science results from the ongoing NARL activities on NavIC. The participants were also encouraged to visit various facilities (experimental and computational) of NARL and interact with scientist/engineer on the second day of the workshop.
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