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.

　The dedicated satellite gravimetry missions that emerged at the beginning of the 21st century have paved fresh avenues for studying geodesy and geophysics. The Gravity Recovery and Climate Experiment (GRACE) has enabled precise measurement of the time-variable gravity field of the Earth, providing new insights into large-scale mass redistribution in the Earth system. The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) has enabled precise determination of the physical shape of the Earth, realizing the implementation of a global unified height reference system based on geoid. This article reviews the authorʼs studies on the Earthʼs mass balance and shape using the data from the satellite gravity missions. The following two topics are reviewed here: (1) analysis of precipitation anomaly signature associated with Arctic Oscillation using GRACE data, (2) improvement of a gravimetric geoid model for Japan using GOCE data. At the end of this article, the current status and future plans of satellite gravimetry missions are reviewed.

　2024年9月2日から5日にかけて2024年度の測地学サマースクールを実施した．本報告では，時系列順にサマースクール実施までの準備状況，講義・実習の概要をまとめた後，受講生のアンケート結果と感想，世話人の所感をサマースクールの報告として記載する．サマースクールに関する報告が測地学会誌に掲載されることはあまりないが，世話人で協議し文章化すべきと判断したため，寄稿することとした．また，サマースクール幹事で引き継がれている情報も少なく，本稿は引き継ぎ資料の意味合いも込めている．なお，本稿の文章の多くは特記した箇所を除き，主に幹事である加納の視点で記述していることをご了承いただきたい．

Crustal deformation data recorded by strainmeters and tiltmeters installed in snowy areas are often affected by snow （snowmelt and snow loads） in addition to rainfall. Specific characteristics of this effect have not been sufficiently investigated. Here, we analyzed the effect of snow on tilt data by comparing tilt changes with meteorological records at nearby stations. Our results showed that the amount of tilt changes during the snowmelt season is related to the annual amount of snowmelt. Furthermore, the observed tilt changes are synchronized with the period of meltwater infiltration into the ground. Based on these results, we improved a tank model that includes a ʻsnow tankʼ to remove the effects of rainfall and snow from the tilt data and applied this model to tilt data from two sites in snowy areas. Our model can calculate the expected crustal deformation response to snow loads, snowmelt and rainfall based on meteorological data （precipitation, air temperature, and hours of sunshine）. We determined optimal parameters for this improved model on a site-bysite basis from long-term crustal deformation data spanning approximately 5 years. As a proof of concept, we successfully retrieved long-term tilt changes by removing the effects of snow and rainfall of a few micro radians. By applying our model to other crustal deformation data, we can more reliably determine the amount of crustal deformation due to, for example, magmatic intrusions, seismic uplift and subsidence, etc.

We evaluated the reproducibility of two elastic models, by comparing forward calculation results with the coseismic data observed during the 2011 Tohoku earthquake. The two models are the halfspace model which consists of an isotropic and homogeneous half-space medium, and the spherical model which considers radial heterogeneity, surface curvature, and self-gravitation. The coseismic fault slip distribution was first inverted from the near-field GNSS data using each elastic model, and then the coseismic displacement and gravity change were calculated using two fault slip results and two elastic models. The calculated displacement of the half-space model exceeded 150% of the observed one at > 500 km epicentral distance, since the half-space model oversimplifies the real Earth. The near-field gravity change calculated using the half-space model also exceeded 200% of the observed one, although the near-field displacement data were used for the fault slip inversion. In contrast, the calculated displacement of the spherical model agreed, within approximately 30% in residual, with the one observed at all ranges of the epicentral distance in Japan, even though the far-field GNSS data was not used for the inversion. This is mainly because the far-field crustal deformation can be accurately reproduced by the existence of radial heterogeneity in the spherical model. Furthermore, the spherical model reproduced the coseismic gravity change observed in Japan at the smallest root-mean-square （15.0 μGal）, because the spherical model considers the depth-dependent structure of density and elastic parameters in the Earth. From these points of view, the spherical model should be chosen in calculating ground gravity change as well as far-field crustal deformation. In future studies, the effects of lateral heterogeneity and topography need to be considered additionally, to reduce the residual in displacement of approximately 30% which still remains in the calculation results using the spherical model.

　GNSS provides accurate positions of objects on the Earth’s surface by taking advantage of its precise ephemeris. The world’s most accurate ephemeris is provided by the International GNSS Service (IGS) and leveraged for individual applications including geodesy and geophysics. Combining precise ephemerides submitted by IGS Analysis Centers, IGS ensures accurate and reliable product generation. However, there had been neither participation of the Analysis Center nor contribution to this combination process from Japan. In July 2023, the joint collaborative initiative with GSI and JAXA led to yield precise ephemeris using the original Japanese multi-GNSS processing software “MADOCA”. Following this, GSI and JAXA became the first Analysis Center in Japan with the approval of IGS in December 2023. Our performance assessment revealed that GSI and JAXA’s products in the last year are almost as accurate as those calculated by other Analysis Centers. As one of the Analysis Centers, GSI and JAXA take charge of continuous product dissemination and serve the foundation for various applications in science and socioeconomic activities.

　The Murono mud volcano is one of three in Matsudai, Niigata Prefecture, Japan. Significant ground uplifts have been observed at least three times （2007 Niigataken Chuetu-oki Eqrthquake; 2011 Naganoken Hokubu Earthquake; 2014 Naganoken Kamishiro Fault Earthquake） in conjunction with large-scale earthquakes. The 2024 Noto Peninsula earthquake occurred on January 1, 2024. We conducted leveling surveys at the Murono mud volcano two months prior and half a year after the earthquake. The results showed that the entire Murono mud volcano experienced a maximum uplift of 162 mm during the period from November 2023 through June 2024. This uplift is considered to have been caused by the main shock of the 2024 Noto Peninsula earthquake, and the cracks are considered to have been caused by this uplift. In the future investigations, we will focus on the underground phenomena that caused this uplift.

　With the recent increase in the number of optical satellites in operation, high resolution optical images are becoming increasingly available. In this study, we applied the pixel offset analysis on optical images acquired by PlanetScope, Sentinel-2 and Landsat satellites to measure the surface fault displacements associated with the 2023 southeastern Türkiye earthquake near the epicentral zone. The results from the analysis of PlanetScope images were the most accurate, although their north-south displacements contained striping noise, indicating that the image resolution is the principal factor of the accuracy. On the southwestern part in the analyzed area, the surface fault displacements obtained from the pixel offset analysis were systematically larger than the field-measured data, indicating finite thickness of the fault. On the northeastern part of the analyzed area, large surface fault displacements were obtained on a pre-matured segment, indicating that the strongly locked fault segment, on which large slip deficit had accumulated, ruptured to cause large displacements.

　Geodetic surveying in Japan was started by the army in the late 19th century, based on German geodesy. Therefore, experience tended to be more important than theory in the implementation of surveying, and this trend continues to this day. This report discusses the recent GNSS surveying based on the numerical results of (1) observation equations based on the projection method, (2) weight of GNSS observations, and (3) quality control of geodetic surveying results.

　We detected the sub-microgal gravity change due to the air pressure change associated with the 15 January 2022 eruption of Hunga Tonga-Hunga Haʼapai volcano, by the continuous gravity observation using a spring-type portable relative gravimeter. We have been collecting the 1-Hz readout voltage value of the LaCoste & Romberg G31 gravimeter at the gravity measurement room in Kyoto University, along with the air pressure value using a MEMS pressure sensor. We obtained the time series of gravity residual on 15 January 2022, by correcting for the tidal gravity change in the gravity data which were converted from the original voltage data. We found that the gravity residual changed by approximately 0.5 and 1.2 μGal peak-to-peak in the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively, as the air pressure changed by approximately 2 hPa due to the propagation of the atmospheric Lamb waves generated by the Tonga volcanic eruption. The gravity changes can be explained by the the acoustic-gravity-wave theory within 0.1 μGal root-mean-square error, if the elastic parameters at the depths of 30 and 10 km of the PREM model were used in calculating the theoretical gravity changes for the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively.