Niell A E, Barrett J P, Cappallo R J, Corey B E, Elosegui P, Mondal D, Rajagopalan G, Ruszczyk C A, Titus M A
Massachusetts Institute of Technology Haystack Observatory, Westford, MA USA.
Institute of Marine Sciences, ICM-CSIC, Barcelona, Spain.
J Geod. 2021;95(6):65. doi: 10.1007/s00190-021-01505-9. Epub 2021 May 27.
We measured the components of the 31-m-long vector between the two very-long-baseline interferometry (VLBI) antennas at the Kokee Park Geophysical Observatory (KPGO), Hawaii, with approximately 1 mm precision using phase delay observables from dedicated VLBI observations in 2016 and 2018. The two KPGO antennas are the 20 m legacy VLBI antenna and the 12 m VLBI Global Observing System (VGOS) antenna. Independent estimates of the vector between the two antennas were obtained by the National Geodetic Survey (NGS) using standard optical surveys in 2015 and 2018. The uncertainties of the latter survey were 0.3 and 0.7 mm in the horizontal and vertical components of the baseline, respectively. We applied corrections to the measured positions for the varying thermal deformation of the antennas on the different days of the VLBI and survey measurements, which can amount to 1 mm, bringing all results to a common reference temperature. The difference between the VLBI and survey results are 0.2 ± 0.4 mm, -1.3 ± 0.4 mm, and 0.8 ± 0.8 mm in the East, North, and Up topocentric components, respectively. We also estimate that the Up component of the baseline may suffer from systematic errors due to gravitational deformation and uncalibrated instrumental delay variations at the 20 m antenna that may reach ± 10 and -2 mm, respectively, resulting in an accuracy uncertainty on the order of 10 mm for the relative heights of the antennas. Furthermore, possible tilting of the 12 m antenna increases the uncertainties in the differences in the horizontal components to 1.0 mm. These results bring into focus the importance of (1) correcting to a common reference temperature the measurements of the reference points of all geodetic instruments within a site, (2) obtaining measurements of the gravitational deformation of all antennas, and (3) monitoring local motions of the geodetic instruments. These results have significant implications for the accuracy of global reference frames that require accurate local ties between geodetic instruments, such as the International Terrestrial Reference Frame (ITRF).
我们利用2016年和2018年专用甚长基线干涉测量（VLBI）观测的相位延迟可观测量，以约1毫米的精度测量了夏威夷科基公园地球物理观测站（KPGO）两个甚长基线干涉测量天线之间31米长向量的各分量。KPGO的两个天线分别是20米的传统VLBI天线和12米的VLBI全球观测系统（VGOS）天线。美国国家大地测量局（NGS）在2015年和2018年使用标准光学测量方法对两天线之间的向量进行了独立估计。后一次测量在基线水平和垂直分量上的不确定度分别为0.3毫米和0.7毫米。我们针对VLBI测量和测绘测量不同日期天线热变形的变化，对测量位置进行了校正，热变形可达1毫米，从而将所有结果统一到一个共同的参考温度。VLBI测量结果与测绘结果在东、北和上天顶分量上的差异分别为0.2±0.4毫米、-1.3±0.4毫米和0.8± 0.8毫米。我们还估计，基线的上分量可能会受到引力变形和20米天线未校准仪器延迟变化的系统误差影响，这两种误差可能分别达到±10毫米和-2毫米，导致天线相对高度的精度不确定度约为10毫米。此外，12米天线可能的倾斜会使水平分量差异的不确定度增加到1.0毫米。这些结果凸显了以下几点的重要性：（1）将场地内所有大地测量仪器参考点的测量校正到共同的参考温度；（2）获取所有天线引力变形的测量值；（3）监测大地测量仪器的局部运动。这些结果对于需要大地测量仪器之间精确局部联系的全球参考框架（如国际地球参考框架（ITRF））的精度具有重大意义。
