Description

Three years after its release, the ITRS Center has initiated regular (yearly) updates of ITRF2020 motivated by a number of reasons, including:

• the stability of the ITRF long-term origin, evaluated to be at the level of or better than 5 mm and 0.5 mm/yr for its time evolution,
• the agreement in scale between VLBI and SLR, at the level of 1-2 mm, with no drift,
• the growth of extrapolation errors of the ITRF2020 coordinates beyond the end of the ITRF2020 input data,
• changes in the positions of certain ITRF2020 stations (due to, e.g., earthquakes and equipment changes) that occurred after the end of the ITRF2020 input data.

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.

ITRF2020-u2024 keeps the same frame parameters (origin, scale and orientation) as ITRF2020. This is intended to avoid any “datum” change in user applications.

The computation strategy of ITRF2020-u2024 is identical to that of ITRF2020 (see ITRF2020 computation strategy).

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.

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:

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.