4:15 PM - 4:30 PM
[SGD02-10] Prototype of a New Precise Gravimetric geoid model using airborne gravity data and future observation plan
Keywords:Airborne gravity survey, Geoid, Gravity, Gravimetric geoid model
Introduction
We launched an airborne gravity survey project in Japan in 2019 to develop a new precise gravimetric geoid model of Japan. The accuracy of the precise gravimetric geoid model is evaluated by comparing the geoid slope with the GNSS/leveling geoid height data, and the target accuracy of the calibration should be within 3 cm standard deviation. In this project, we plan to complete the nation-wide airborne gravity survey by 2023 and develop the gravimetric geoid model by 2024.
Method and results of prototype precise gravimetric geoid model
As of December 2021, we have mostly completed observations at an altitude of 3,000 meters (5000 meters in mountain areas and Kanto district) from Tohoku to Kyushu district. The standard deviation of the crossover residual (gravity difference at the intersection of the measurement lines) of the acquired data is about 2 mGal, indicating high accuracy of observations (Nakashima et al., AGU2021). In order to evaluate the contribution of airborne gravity data to the gravimetric geoid model, we computed the gravimetric geoid models including and not including the airborne gravity data obtained so far using the method of Matsuo and Forsberg (2021) and then investigated their difference in the geoid height. As a result, large differences in geoid height of 10~20 cm were confirmed in some coastal areas such as Kashima-nada, Seto Inland Sea, and Tosa Bay. These results indicate that our airborne gravity data accurately capture the gravity field information that could not be captured by the existing gravity data (ground gravity, shipborne gravity and altimetry-derived global marine gravity model).
Future observation plan
In the areas with large geoid differences, there may be significant short-wavelength gravity components that cannot be observed by the current flight altitudes. Therefore, we are planning to perform observations at lower altitudes to improve the spatial resolution of the gravity field in such regions. Childers et al. (1999) showed that the spatial resolution of the observable gravity field is doubled by halving the observation altitude. This will allow us to observe the gravity field information in more detail.
Furthermore, it is estimated that the accuracy of the gravimetric geoid model around islands areas is low as in coastal areas because the accuracy of the altimetry-derived marine gravity model there is reduced by the influence of ocean currents such as the Kuroshio Current. We are planning to perform additional observations over islands areas that were not initially included in the plan for improvement of the gravimetric geoid model there.
We launched an airborne gravity survey project in Japan in 2019 to develop a new precise gravimetric geoid model of Japan. The accuracy of the precise gravimetric geoid model is evaluated by comparing the geoid slope with the GNSS/leveling geoid height data, and the target accuracy of the calibration should be within 3 cm standard deviation. In this project, we plan to complete the nation-wide airborne gravity survey by 2023 and develop the gravimetric geoid model by 2024.
Method and results of prototype precise gravimetric geoid model
As of December 2021, we have mostly completed observations at an altitude of 3,000 meters (5000 meters in mountain areas and Kanto district) from Tohoku to Kyushu district. The standard deviation of the crossover residual (gravity difference at the intersection of the measurement lines) of the acquired data is about 2 mGal, indicating high accuracy of observations (Nakashima et al., AGU2021). In order to evaluate the contribution of airborne gravity data to the gravimetric geoid model, we computed the gravimetric geoid models including and not including the airborne gravity data obtained so far using the method of Matsuo and Forsberg (2021) and then investigated their difference in the geoid height. As a result, large differences in geoid height of 10~20 cm were confirmed in some coastal areas such as Kashima-nada, Seto Inland Sea, and Tosa Bay. These results indicate that our airborne gravity data accurately capture the gravity field information that could not be captured by the existing gravity data (ground gravity, shipborne gravity and altimetry-derived global marine gravity model).
Future observation plan
In the areas with large geoid differences, there may be significant short-wavelength gravity components that cannot be observed by the current flight altitudes. Therefore, we are planning to perform observations at lower altitudes to improve the spatial resolution of the gravity field in such regions. Childers et al. (1999) showed that the spatial resolution of the observable gravity field is doubled by halving the observation altitude. This will allow us to observe the gravity field information in more detail.
Furthermore, it is estimated that the accuracy of the gravimetric geoid model around islands areas is low as in coastal areas because the accuracy of the altimetry-derived marine gravity model there is reduced by the influence of ocean currents such as the Kuroshio Current. We are planning to perform additional observations over islands areas that were not initially included in the plan for improvement of the gravimetric geoid model there.