2016 Volume 7 Issue 1 Pages 62-69
Water use facilities such as irrigation and drainage channels, water gate, hydraulic drop etc. are constructed to make water supply to paddy field and upland field. In a planning of irrigation project, it is necessary to obtain elevation value with accuracy and efficiency around project site. In generally, elevation values are obtained by the direct leveling survey with specific instruments, e.g. digital or auto level, a couple of staffs and turning plates. The direct leveling survey also needs several benchmarks, which are points of reference with high accuracy location information including latitude, longitude and elevation. There is, however, a serious problem that survey work of the direct leveling survey must begin at several benchmarks. In the case of survey work in mountainous area, surveyors must carry out the direct leveling survey over several very-long routes, because there are few benchmarks. On the other hand, in the Global Navigation Satellite System (GNSS) surveying, elevation values can be obtained indirectly by observing carrier phase from multi positioning satellites such as GPS, GLONASS since 2011. This study started to install the new benchmark on a 920 m high mountain, about 5 km away from some known benchmarks in Karuizawa Town, Nagano Prefecture. After surveying the new benchmark by the GNSS and the direct leveling, we compared its elevation values. Furthermore, a streamlined survey process, the influence on most probable value and standard deviation by the difference of using satellite, “GPS-only” and “GPS and GLONASS” were investigated in the GNSS surveying. As the results, our tests found that dramatically streamlined survey process, “GPS-only” can obtain an elevation value that is consistent with the value from the direct leveling survey. Therefore, the GNSS surveying is useful to obtain accurate elevation values over long distance like very long channels.
