In the Global Navigation Satellite System （GNSS） positioning on the ship，a GNSS antenna fixed on the ship receives radio waves from GNSS satellites, and the position of the antenna is estimated. Although the antenna is fixed on the ship, the ship itself is propelled, and due to changes in sea level, the shipʼs hull violently oscillates vertically and horizontally （pitch, roll, and heave）. There have been few studies that have experimentally and quantitatively investigated the effects of ship body motion on GNSS ranging. We conducted the experiments utilizing a cart mounted on a GNSS antenna subjected to 21 distinct motion patterns, to effectively capture the response of GNSS measurements to controlled ship-like movements. Equipment utilized comprised the GNSS antenna and NetR9 base station receiver made by Trimble Inc., capturing signals from the GPS, GLONASS, and Galileo on various frequencies including L1, L2, and L5. The experiments were conducted atop buildings at the Institute of Industrial Science of the University of Tokyo, with the cart movements restricted along the one-dimensional axis and the antenna pivoting within the plane perpendicular to the direction of the cart movement. Obtained GNSS data were initially recorded in Trimbleʼs proprietary T02 format and subsequently converted to the Receiver Independent Exchange Format （RINEX） version 2.11 using Trimbleʼs RINEX converter. We introduced some results of the positioning analysis under various conditions, performed by the kinematic precise point positioning using the open source software for GNSS positioning （RTKLIB）.

　In June 2023, we carried out absolute gravity measurements at the Matsushiro station, Japan, with an FG5 absolute gravimeter. Thanks to the good weather conditions, we succeeded in obtaining very high-quality data over a total of four days. The drop-to-drop scatter for the whole experiment was 4.25 μGal, and the gravity acceleration at 130 cm above the floor was estimated to be 979,772,780.451±0.027 μGal. Using this data, we made calibration of the sensitivity for two superconducting gravimeters （CT #036 and iGrav #028） currently operating simultaneously at Matsushiro. Special care was taken in the treatment of the system delay of the superconducting gravimeters as well as the timing of absolute gravity measurements. Detailed analysis of the data from both types of gravimeters revealed that the absolute gravimeter recorded, though imperfectly, 20-s-period surface waves after a teleseismic earthquake. The final estimates of the scale factors（expressed as positive values） were 1134.65±0.69 μGal/V for CT #036 and 2043.05±1.23 μGal/V for iGrav #028, respectively, achieving a relative accuracy of approximately 0.06% for both gravimeters. These results were further verified by comparing amplitude of tidal signals derived from tidal analysis of the data from the two superconducting gravimeters.

　We determined soil parameters of the Van Genuchten’s model for the soil of Mizusawa VLBI Observatory, National Astronomical Observatory of Japan (NAOJ Mizusawa), utilizing the continuous data of superconducting gravity and soil moisture observed at the observatory. We calculated time variations in soil moisture and hydrological gravity change using the G-WATER [1D] software, and searched for optimal values of three soil parameters (θ_min, α, and n) by comparing the calculated time series with the observed ones. The optimal values of the parameters θ_min and n derived from the gravity data were 0.0 m³/m³ and 1.50, respectively, and they agreed with those derived from the soil moisture data independently. In contrast, the optimal value of the parameter α was inconsistent between the gravity and soil moisture data, mainly because the gravity change has a low sensitivity to the α’s variation. Instead, we determined the α’s optimal value so as to minimize an evaluation function, which was defined based on residuals for gravity and soil moisture. The α’s optimal value was obtained to be 0.45, and then the root-mean-square residuals for soil moisture and gravity were 0.0159 m³/m³ and 0.644 μGal, respectively. The optimal values of the three parameters correspond to typical values for silty soils, as did the actual value of the saturated permeability (K_s) which was measured in a previous study.

　2013 年にGGOS ワーキンググループとして発足して以来10年間，GGOS Japanは，地球システム監視の基盤としてのグローバル測地学の重要性を認識しつつ，日本の宇宙測地関係機関と関係者を結び付ける場を提供してきた．日本の宇宙測地分野の観測および研究を推進するため，各種会合の設定，測地学会誌特集号の企画，注力すべきテーマの設定，多様なアウトリーチ，など非常に多岐にわたる活動を行っている．あわせて，GGOSの最初のAffiliateとしての位置づけを通して，世界の測地関係機関に対する窓口としての役割を果たしてきた．

　This article introduces the tsunami records measured by the GPS buoys that were developed in Japan. Based on an idea that a GPS buoy placed offshore could enable for coastal people to evacuate against tsunami, the GPS buoy system for detecting tsunami in real-time has been developed since around 1996. Real-time kinematic (RTK-GPS) method was used to obtain coordinate solution in real-time manner and the obtained records were stored as the so-called PTNL, GGK format. The developed GPS buoy systems were able to detect five tsunamis due to large earthquakes; they are 2001 Peru earthquake (Mw8.4), 2003 Tokachi-Oki earthquake (Mw8.2), 2004 Kii-Suido-Oki earthquake (Mw7.4), 2010 Central Chile earthquake (Mw8.8), and 2011 Tohoku-Chiho-Taiheiyo-Oki earthquake (Mw9.0). All of the data of several hours to two days including these tsunamis are made available through the J-Stage Data.