Accuracy Analysis of Gagan for Different Types of Surveying Applications

With the advancements of technology, the use of GNSS technology in all the surveying applications are significantly growing due to its many several advantages over conventional techniques. However, in most of all surveying applications, the preservation of reliability and positional accuracy should be according to the national surveying standards published by Survey Department of Sri Lanka. Therefore, the uses of GPS augmentation systems with local and wide area differential positioning capabilities have increased demand. Considering the facts, two networks of Continuously Operating Reference Stations (CORS) were established in Sri Lanka, covering a part of Colombo district for real-time augmentation as a paid local area service. While it provides higher accurate differential service the users should have mobile internet with additional hardware, limited coverage and has a cost for the service as well. Satellite-Based Augmentation Systems (SBAS) are being developed worldwide due to their unique advantage of wide area coverage. Similarly, along with Airports Authority of India (AAI), Indian Space Research Organization (ISRO) has worked out a joint project to implement the Satellite Based Augmentation System using GPS, called GAGAN (GPS Aided Geo Augmented Navigation). With the free use and availability of GAGAN in Sri Lanka, this study focuses on validating the applicability of GAGAN in various surveying methods in Sri Lanka. In order to test its performances, Control Surveying, Boundary Surveying and Road Surveying have done with a GAGAN active GNSS receiver by comparing with uncorrected standard positioning. Further, 24 hours of static observations were also collected with GAGAN active GNSS receiver to check the reliability of its use at any time of the day. It is found that accuracy in those applications has improved significantly in SBAS receiver due to real-time GAGAN corrections except in urban and forest areas (disturbing conditions). Further, 24-hour observations confirmed that GAGAN is capable of giving 92.6% of below 1-meter 2D positional accuracy at any time of the day . KEYWORDS: GNSS, GAGAN, Field Surveying, Accuracy