Abstract
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
Highlights
Satellite-Based Augmentation Systems (SBAS) is a free to air regional augmentation service where corrections are derived from a regional network of reference stations and transmitted to users via geostationary satellites
Precise Point Positioning (PPP) method was used to assign co-ordinations to the station NSG01. (This point was used as the base station of all control point establishments)
The time periods were selected as four sets of threehour observations, (1 pm to 4 pm, 5 pm to 8 pm, 11 pm to 2 am and 4 am to 7 am) to cover up 24 hours to check the accuracy of GAGAN over the time
Summary
SBAS is a free to air regional augmentation service where corrections are derived from a regional network of reference stations and transmitted to users via geostationary satellites. DGPS uses the ground reference station to determine the difference between the positions indicated by the navigation satellites. As SBAS gives free wide area coverage, it is a very useful utility than other correction methods. Professional surveying works need more accurate, reliable, continuously available and costeffective correction services. DGPS and SBAS can be used for more precise services. SBAS possesses several advantages than DGPS, such as costeffectiveness, wide area coverage and time effectiveness. India has its own SBAS (GAGAN) and it covers Sri Lankan region as well. Its applicability on surveying applications is not yet validated according to the different types of surveying methods in Sri Lanka.
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