Superconducting Gravimeter Data from Sutherland - Level 1

The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy IAG. IGETS continues the activities of the Global Geodynamics Project (GGP) between 1997 and 2015 to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. As part of this network, the South African Geodynamic Observatory Sutherland (SAGOS) was established by the GFZ German Research Centre for Geosciences during the years 1998 and 2000 based on an Agreement on Cooperative Activities between the National Research Foundation (NRF) and GFZ signed in August 1998. Continuous time-varying gravity and atmospheric pressure data from the SGs at SAGOS are integrated in the IGETS data base hosted by GFZ. The SAGOS observatory is located at the site of the South African Astronomical Observatory (SAAO) approximately 350 km northeast of Cape Town (longitude: 20.81 E, latitude: 32.38 S, height above MSL: 1755 m). The operation and maintenance of the SAGOS instrumentation is jointly done by staff of SAAO and GFZ. The shortest distance to the South Atlantic coastline is approximately 200 km. The area is located in a tectonically quiet zone far away from the African rift. Geologically, the setting is a huge dolerite plateau with a several kilometres thick layer of dolerite. This bedrock allows a good coupling of the SG pillars to the ground. The environment is a remote area with no industry and low seismicity. The climate at this place is determined by the border between summer and winter rainfall zones so that temperature fluctuations are not too rough. The observatory is built into the ground to protect it against environmental effects like strong winds and temperature changes. All rooms are thermally insulated. An air-conditioning system controls the temperature inside the measurement chamber, which is equipped with three concrete pillars embedded into the dolerite bedrock. Two of the pillars are constructed for SGs or other geophysical instruments. The third pillar is dedicated for absolute gravimeters for the calibration of the SGs. In the vicinity of the observatory four further pillars were set up for various other geodetic antennas and instrumentation. SAGOS is a high precision geodynamic observatory comprising space techniques and ground instruments. Presently, the observatory is equipped with one SG manufactured by GWR Instruments (SG D037). The second SG operating in parallel until September 2017 was installed at mountain Zugspitze in September 2018 (Voigt et al. 2019, http://doi.org/10.5880/igets.zu.l1.001). The time series of gravity and barometric pressure from the dual sensor gravimeter SG D037 starts in February 2000 and is interrupted from July 2008 to November 2009 due to an upgrade of the electronics package. The time series of SG 052 begins in August 2008 and ends in September 2017 without interruption. The SG D037 is active and the time series is kept up to date regularly with a time delay of a few months. The time sampling of the raw gravity and barometric pressure data of IGETS Level 1 is 1 minute. Starting in January 2016, raw data with a time sampling of 1 second is provided additionally. For a detailed description of the IGETS data base and the provided files see Voigt et al. (2016, http://doi.org/10.2312/GFZ.b103-16087). In addition, SAGOS is equipped with auxiliary data supporting the interpretation of the SG measurements, which is, however, not provided in the IGETS data base due to their complexity. These are a local network of hydrological and meteorological sensors as well as a permanent GNSS (Global Navigation Satellite Systems) station as a core station of the International GNSS Service (IGS) with the ID SUTM.

国际地球动力学与地球潮汐服务（International Geodynamics and Earth Tide Service, IGETS）由国际大地测量协会（International Association of Geodesy, IAG）于2015年创立。IGETS延续了1997年至2015年间全球地球动力学计划（Global Geodynamics Project, GGP）的工作，依托国际联网的超导重力仪（superconducting gravimeter, SG）数据，为大地测量与地球物理研究活动提供支持。作为该联网计划的组成部分，南非萨瑟兰地球动力学观测台（South African Geodynamic Observatory Sutherland, SAGOS）由德国地球科学研究中心（GFZ German Research Centre for Geosciences, GFZ）于1998年至2000年间建成，其建设依据为1998年8月南非国家研究基金会（National Research Foundation, NRF）与GFZ签署的《合作活动协议》。SAGOS观测台获取的超导重力仪连续时变重力与大气压力数据，已集成至GFZ托管的IGETS数据库中。SAGOS观测台坐落于南非天文台（South African Astronomical Observatory, SAAO）台址内，距离开普敦东北方向约350公里（经度：东经20.81°，纬度：南纬32.38°，平均海平面以上海拔高度：1755米）。其运行与维护由SAAO与GFZ的工作人员共同完成。该观测台距南大西洋海岸线的最短距离约为200公里，所处区域为远离非洲裂谷的构造稳定带。地质上，该区域为厚达数公里的辉绿岩高原，这种基岩可使SG的仪器支柱与地面实现良好耦合。观测台周边为无工业活动、地震活动性低的偏远区域。当地气候受夏冬降雨带交界影响，气温波动相对平缓。观测台主体建于地下，以抵御强风、气温变化等环境影响，所有房间均做了隔热处理。观测台内设有温控系统调节测量室温度，测量室内置三根嵌入辉绿岩基岩的混凝土支柱：其中两根用于安装SG或其他地球物理仪器，第三根专供用于校准SG的绝对重力仪使用。在观测台附近，还架设了四根额外支柱，用于搭载各类其他大地测量天线与仪器设备。SAGOS是集成空间技术与地面仪器的高精度地球动力学观测台。目前，该观测台配备一台由GWR仪器公司（GWR Instruments）生产的SG（型号为SG D037）。曾于2017年9月前并行运行的第二台SG，于2018年9月安装在楚格峰（Voigt等，2019，http://doi.org/10.5880/igets.zu.l1.001）。SG D037的重力与气压时间序列始于2000年2月，因电子设备升级，于2008年7月至2009年11月间中断。SG 052的时间序列始于2008年8月，于2017年9月结束，无中断记录。目前SG D037仍在运行，其时间序列会以数月的延迟定期更新。IGETS一级数据（Level 1）的原始重力与气压数据的时间采样率为1分钟；自2016年1月起，额外提供时间采样率为1秒的原始数据。关于IGETS数据库与所提供文件的详细说明，可参见Voigt等（2016，http://doi.org/10.2312/GFZ.b103-16087）。此外，SAGOS还配备了辅助数据以辅助SG观测数据的解译，但由于数据复杂度较高，这些辅助数据并未纳入IGETS数据库。辅助数据包括本地水文与气象传感器网络，以及作为国际GNSS服务（International GNSS Service, IGS）核心站的永久全球导航卫星系统（Global Navigation Satellite Systems, GNSS）台站，其台站编号为SUTM。