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GNSS Augmentations and Other Navigation Satellite Systems
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
Although primarily meant for civil aviation, it is also beneficial for other government agencies. The space segment of GAGAN is designed to have three operational geosynchronous satellites. On the ground, the GPS data is received and processed in the 15 Indian reference stations (INRES), located at Ahmedabad, Bengaluru, Bhubaneswar, Kolkata, Delhi, Dibrugarh, Gaya, Goa, Guwahati, Jaisalmer, Jammu, Nagpur, Porbandar, Portblair, Trivandrum. The Indian Master Control Centre (INMCC), composed of two sites and located in Bangalore, processes the data from the INRESs to compute the differential corrections and estimate its level of integrity. The SBAS message generated by the two INMCC is uplinked to the satellites through its corresponding Indian Land Uplink Station (INLUS). GAGAN-enabled GPS receivers, with the same technology as WAAS receivers, are able to use the GAGAN signal. GAGAN uses GPS type modulation on L2 and L5 frequencies. One essential component of the GAGAN project was the study of the ionospheric behaviour over the Indian region. This was specially taken up in view of the rather uncertain behaviour of the ionosphere in the equatorial region. However, ISRO has successfully modelled the ionospheric correction. GAGAN ionospheric algorithm, known as ISRO GIVE Model-Multi-Layer Data Fusion (IGM-MLDF), is operational in the implemented GAGAN system. The accuracy standard of GAGAN is less than 7.6 m both horizontally and vertically 100% of the time. However, the position standard deviation of latitude, longitude, and altitude were found to be less than 4 meters, which indicates that the position accuracies of the GAGAN are well within the 7.6 m requirement. These position accuracies can be further enhanced with ground-based augmentation systems.
Global navigation satellite systems
Published in Francis Lyall, Paul B. Larsen, Space Law, 2017
Other countries are also establishing systems to augment GPS and other GNSS systems as necessary.85 The Japanese Multi-functional Transport Satellite-based Augmentation System (MTSAS) augments GPS accuracy in the Asian and Pacific Ocean regions.86 The Indian GAGAN system augments GPS accuracy in the Indian region.87
On land-use and land-cover changes over Lidder Valley in changing environment
Published in Annals of GIS, 2018
Mohammd Rafiq, Anoop Kumar Mishra, Mohammad Suhail Meer
Finally, a field survey was carried out to validate the results using the Cohen’s Kappa (k) statistics (Smits, Dellepiane, and Schowengerdt 1999; Dymond and Johnson 2002). We have collected a total no of 60 GPS points using the random sampling method. Trimble Juno SB (hand-held) GPS was used to collect the spatial data from the various features in the Lidder Valley. The GPS accuracy was improved with GAGAN signal to minimize the positional error (±1.5 m). After that, GPS points were overlaid on the image in order to identify the various tones in the LU/LC classes generated to check for digitization errors using Kappa coefficient (Equation I). It is a statistical measure of inter-rater agreement or inter-annotator agreement for qualitative (categorical) items (Lillesand, Kiefer, and Chipman 2014) and is widely used accuracy assessment technique.
Case Study: Performance Observation of NavIC Ionodelay and Positioning Accuracy
Published in IETE Technical Review, 2021
Mehul V. Desai, Shweta N. Shah
The GPS Aided GEO Augmented Navigation (GAGAN) system developed by ISRO and Airport Authority of India (AAI) together to provide high accuracy and precision in civil aviation [9–11]. The Ionospheric effect in GAGAN for the low latitude Indian subcontinent is mitigated based on different regional grid models such as Minimum Mean Square Error [11], Kriging, Inverse Distance Weighted (IDW) with the Klobuchar model and planar fit model [12]. Similarly, the local model such as Spherical Harmonic Function (SHF) model [13] modified the Klobuchar model for two shell model [14], Taylor Series Expansion (TSE) [15]. In the future, the NavIC receiver will be used as a reference station in GAGAN to transmit the correction to the aircraft.