11:30 〜 11:45
[G01-6-05] The leveling net adjustment with a correction for altitude variations obtained from GNSS-based control stations data
Geospatial Information Authority of Japan (GSI) has been maintaining longitude, latitude, and altitude of control points. As for the altitude reference system, we conduct leveling surveys all over Japan, the statistical calculation (net adjustment), and revise the altitude. However, the policy of administrative efficiency leads to a decrease in leveling survey distance. Thus, it takes more time to conduct surveys, and seems likely that gaps between calculated altitude and the current situation get larger because of crustal movement.
Since the 1990s, GSI has been developing GNSS Earth Observation Network System (GEONET). GEONET has two advantages: (1) observation stations exist uniformly, and (2) we can conduct a real-time observation. Focusing on these points, we investigated the potential to reduce the gaps of altitude by utilizing GEONET to correct altitude variations.
We conduct a new method for net adjustment as follows: (1) we apply curve fitting to GEONET time-series data to obtain altitude variations between the observation days for surveys and the reference day. (2) We apply Kriging method to create grid data of altitude variations for every observation day. (3) We apply bilinear method to estimate altitude variations by the grid data at each benchmark to correct relative elevations. (4) We conduct a net adjustment by using corrected relative elevations.
We evaluated the validity by comparing between altitude obtained by surveys and altitude estimated from GEONET data in the areas where we recently conducted surveys twice. From the studies, we found that (1) it was possible to estimate altitude with 1 cm accuracy on average, and (2) it was impossible to estimate local variation. These imply that we should compensate for GEONET's weakness. Fortunately, GSI has InSAR technique that has an advantage to detect local variation economically. If time allows, we will show the validation of Kumamoto earthquake with a combination of GEONET and InSAR.
Since the 1990s, GSI has been developing GNSS Earth Observation Network System (GEONET). GEONET has two advantages: (1) observation stations exist uniformly, and (2) we can conduct a real-time observation. Focusing on these points, we investigated the potential to reduce the gaps of altitude by utilizing GEONET to correct altitude variations.
We conduct a new method for net adjustment as follows: (1) we apply curve fitting to GEONET time-series data to obtain altitude variations between the observation days for surveys and the reference day. (2) We apply Kriging method to create grid data of altitude variations for every observation day. (3) We apply bilinear method to estimate altitude variations by the grid data at each benchmark to correct relative elevations. (4) We conduct a net adjustment by using corrected relative elevations.
We evaluated the validity by comparing between altitude obtained by surveys and altitude estimated from GEONET data in the areas where we recently conducted surveys twice. From the studies, we found that (1) it was possible to estimate altitude with 1 cm accuracy on average, and (2) it was impossible to estimate local variation. These imply that we should compensate for GEONET's weakness. Fortunately, GSI has InSAR technique that has an advantage to detect local variation economically. If time allows, we will show the validation of Kumamoto earthquake with a combination of GEONET and InSAR.