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Session A3: QZSS

Development of Gridded-VRS in the Southern Part of the Korean Peninsula using QZSS CLAS Messages
Seong-Yeop Shin, Jeong-Min Han, Inha University; Kwan-Dong Park, Inha University, PP-Solution Inc.
Location: Prince Edward (Third Floor)
Date/Time: Wednesday, Apr. 17, 10:11 a.m.

The Quasi-Zenith Satellite System (QZSS) broadcasts Centimeter Level Augmentation Service (CLAS) to users through their satellites in the Compact State Space Representation (CSSR) format. CLAS correction messages contain augmentation information for satellite orbits, satellite clocks, and satellite code and phase biases in addition to ionospheric and tropospheric errors for the whole region of Japan. Since CLAS correction messages are transmitted through the L6 band of QZSS satellites anyone who can receive the L6 band can use CLAS correction messages. Also, as online archives for CLAS are available for post-processing, one could get CLAS L6 Data files from the CLAS archive. CLAS correction messages are utilized for Precise Point Positioning - Real Time Kinematic (PPP-RTK) services, enabling high-precision positioning results in real-time for CLAS users in Japan. CLAS was designed to serve Japan and its surrounding annexed islands including Tsushima Island adjacent to the Korean peninsula. If we use CLAS correction messages provided for Tsushima Island and its surroundings, it may be possible to enable PPP-RTK in the Korean peninsula with CLAS. However, SSR messages cannot be used as it is in general commercial GNSS receivers, so they must be generally converted into Observation Space Representation (OSR) format so that these receivers can use SSR messages. In this study, therefore, a grid-type Virtual Reference Station (VRS) on the Korean peninsula based on SSR2OSR technology using CLAS correction messages was tested to validate CLAS-based precise positioning in South Korea.
We have already confirmed in Korea that Gridded-VRS (GVRS) service could be provided and commonly used by using SSRG, a GNSMART-based SSR that is currently provided free of charge to the general public by the Korean National Geographic Information Institute. In addition, when we deliberately used the correction information provided for the SSR grids located more than 200 km away when we created VRS, the positioning accuracy was different from the results of using the correction information provided for the SSR grids located about 30km away. So, it should be possible to provide GVRS service based on CLAS if the region is close enough to Japan. To evaluate the performance of the algorithm and confirm this possibility, we used CLAS correction messages on Tsushima Island to generate VRS grids in the cities of Busan, Ulsan, and Geoje, which are located within a radius of 100 km from Tsushima Island. Using traditional RTK receivers we verified that single-baseline RTK could provide an accuracy level of 3-4 cm.
Furthermore, we applied the same GVRS algorithm in Japan and tested its performance. We confirmed positioning performance in Osaka and the results suggest that the GVRS service is, of course, feasible throughout Japan. Also, the performance of positioning results using the GVRS service based on CLAS correction messages in Daejeon and Seoul whose distances from Tsushima Island are a couple of hundred km was analyzed. Accordingly, we devised improvement strategies in terms of algorithms and application plans when the users are quite far away from the nearest CLAS grid points. In addition, the utility of the algorithm developed in this study was confirmed by measuring the effective distance that CLAS can be used on the Korean peninsula.

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