Direct Geocentric Realisation of the American reference frame by combination of geodetic observation Techniques (DIGERATI)

该项目将研究直接实现区域性、分时代的地心参照框架（RGRF）的可能性，而无需通常转换为全球参照系统。这种参考框架在地震活跃区特别重要，在这些地区，强烈地震（例如智利2010年）会产生大的地表变形（高达数米），损坏现有的参考系统，其台站坐标在固定时期和线性坐标变化，并使其无法使用。此外，气压和水储存的季节性变化会在厘米级上产生次年度坐标变化，并使现有参考系统在解释环境变化方面的应用复杂化。目前，区域参照基准完全是通过全球导航卫星系统的测量来实现的，由于全球地心参照系统数量众多，因此能够在当地使用这些参照系统。在本项目中，将通过将全球导航卫星系统与大地测量技术卫星激光测距（SLR）和甚长基线干涉测量（VLBI）相结合来直接计算RGRF。历元解的起源将由SLR实现，尺度由SLR和VLBI的加权平均实现。一个时代明智的实现需要一个可变的SLR网络配置从一个时代到另一个时代。这种对地心和稳定的基准实现的影响需要进行调查。该项目将实际应用于美洲地心参照框架。关于全球导航卫星系统，必须研究组合网络需要在目前的SIRGAS网络之外扩展到何种程度，以便以最佳方式将数据从SLR/VLBI传输到SIRGAS。该项目将在阿根廷-德国大地测量观测台安装项目的框架内，与阿根廷科学技术委员会的科学家密切合作实施。AGGO汇集了全球导航卫星系统、SLR和VLBI等重要的大地测量观测技术，因此将是这一组合中的一个重要的共址台站。将特别关注AGGO对SIRGAS的好处。在合作框架内，阿根廷方面将建立一个全球导航卫星系统-SLR-VLBI组合中心。DGFI将提供SLR和VLBI软件。在DGFI，将主要研究在区域参考框架中直接组合的策略。该项目完成后，将按照从该项目的研究结果中得出的组合策略，在阿根廷继续进行RGRF历元的计算。DIGERATI在研究环境变化对全球变化的影响方面具有很高的科学影响力，特别是在南美洲的局部地区，这些地区需要高度精确的参考系统。SIRGAS坐标的共同应用也有巨大的实际好处，例如，区域大地测量、地籍地理信息系统和土地测量。

The project shall investigate the possibility of realising directly and epoch-wise regional geocentric reference frames (RGRF) without the usual transformation onto a global reference system. Such reference frames are of particular importance in seismic active regions, where strong earthquakes (e.g. Chile 2010) produce large surface deformations (up to several meters), damage existent reference systems with station coordinates at a fixed epoch and linear coordinate changes, and disable their use. Also seasonal variations of air pressure and water storage produce sub-annual coordinate changes on the centimetre-level and complicate the application of existing reference systems in the interpretation of environmental changes. Regional reference frames are at present exclusively realised through measurements of the Global Navigation Satellite Systems (GNSS), which enable the local access to the global geocentric reference systems because of their large number. In this project epoch RGRF shall be computed directly by combining GNSS with the geodetic techniques Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). The origin of the epoch solutions will be realised by SLR, the scale by a weighted mean of SLR and VLBI. An epoch-wise realisation entails a variable SLR-Network configuration from epoch to epoch. This effect on geocentricity and a stable datum realisation need to be investigated. The project will be applied in practice to the geocentric reference frame for the Americas (SIRGAS). Regarding GNSS, it has to be studied how far the network for the combination needs to be extended beyond the present SIRGAS network in order to transfer the datum from SLR/VLBI optimally to SIRGAS. The project will be performed in close cooperation with scientists of the Argentine CONICET in the frame of a project for the installation of the Argentine-German Geodetic Observatory (AGGO). AGGO assembles the important geodetic observation techniques GNSS, SLR and VLBI and thus will be an important co-location station in the combination. A particular focus will be put on the benefit of AGGO for SIRGAS. In the frame of the collaboration, the Argentine side will establish an operational GNSS-SLR-VLBI combination centre. DGFI will provide the SLR and VLBI software. At DGFI, primarily the strategy of the direct combination in regional reference frames will be investigated. After completion of this project the computation of the epoch RGRF shall be continued in Argentina on a routine basis following the combination strategy derived from the findings of this project. DIGERATI has high scientific impact for investigations of the effect of environmental changes on global change, in particular in the topical regions of South America, which require highly precise reference systems. There is also a huge practical benefit in the common application of the SIRGAS coordinates, e.g., in regional geodesy, cadastre geographical information systems and land surveying.