籍利平  编译

资料来源：ITRF | Itrf2020-u2024

ITRF2020-u2024 is the second ITRF020 update, generated by adding four years (2021.0 – 2025.0) of data after the end of the ITRF2020 input data. The four Technique Centers (IDS, IGS, ILRS, IVS) who provided four years of extended time series of station positions and Earth Orientation Parameters (EOPs) were asked to use the same models and strategies as in their contributions to ITRF2020.

大意：（国际地球参考框架）ITRF2020-u2024，是ITRF020的第二次升级。在ITRF2020的最终输入数据结束后，添加了四年（2021.0 – 2025.0）的数据。提供四年站坐标序列和地球定向参数的四个技术中心（IDS, IGS, ILRS, IVS），采用了构建ITRF2020时相同的模型和策略。

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ITRF2020-u2024 keeps the same frame parameters (origin, scale and orientation) as ITRF2020. This is intended

 to avoid any “datum” change in user applications.

大意：

ITRF2020-u2024 保持与ITRF2020相同的框架参数（原点、尺度和定向）。这样做，可避免用户使用用中的“基准”变化。

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Frame Definition

ITRF2020-u2024 is aligned in origin, scale and orientation to ITRF2020 by means of no-net-translation, no-net-scale and no-net-rotation constraints. These constraints were applied to both the ITRF2020-u2024 long-term linear station coordinates and seasonal (annual and semi-annual) station motions.

A reference network of 838 stations, whose linear coordinates and seasonal motions were hardly affected by the addition of four more years of input data, was used for the alignment of ITRF2020-u2024 to ITRF2020. See a list of these stations here and their distribution below:

大意：框架定义

ITRF2020-u2024通过无网平移、无网尺度和无网旋转约束，在原点、尺度和方向上与ITRF2020对标。这些约束既应用于ITRF2020-u2024长期线性站坐标，也应用于季节性（年和半年）站位运动。

一个由838个站点组成的参考网络，其线性坐标和季节运动几乎不受四年输入数据的影响，用于ITRF2020-u2024与ITRF2020的对标。这些站点列表及其分布如下：

                         Reference stations used for the alignment of ITRF2020-u2024 to ITRF2020

                                           大意：ITRF2020-u2024 “对标” ITRF2020的参考站 

The alignment of ITRF2020-u2024 to ITRF2020 implies that there is no Helmert transformation between the two solutions, i.e., all transformation parameters between ITRF2020-u2024 and ITRF2020 are zero. Transformation parameters from ITRF2020 to past ITRFs are available here.

Unlike individual seasonal station motions, the ITRF2020 seasonal geocenter motion model was not updated with ITRF2020-u2024.

大意：

ITRF2020-u2024与ITRF2020的“对标”意味着两解之间不存在Helmert变换，即ITRF2020-u2024与ITRF2020之间的所有变换参数均为零。从ITRF2020到过去的ITRF变换参数可在此处查阅（略）。

与单个季节性站点运动不同，ITRF2020季节性地质中心运动模型未更新ITRF2020-u2024。

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Input data

Solutions from the four space geodesy techniques. The input time series of space geodesy solutions are summarized in the following table, indicating for each one, the time span and the type of constraints.

大意：

输入数据：

四种空间大地测量技术的解。空间大地测量解的输入时间序列总结如下表，标明每个解的时间跨度及约束类型。

--------Scale and geocenter time series大意：尺度与地心时间序列（略）----------------

ITRF2020-u2024 文件可通过 FTP 获取：

ftp itrf-ftp.ign.fr   cd pub/itrf/itrf2020-u2024