<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">Dear colleagues,</span></div><div><br data-mce-bogus="1"></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">As announced in <a data-mce-href="https://lists.igs.org/pipermail/igsmail/2024/008538.html" href="https://lists.igs.org/pipermail/igsmail/2024/008538.html">IGSMAIL-8542</a>, a first update of ITRF2020 called ITRF2020-u2023 was released last week. The IGS intends to adopt this update, in the form of a new IGS reference frame called IGb20, for the alignment of its products, starting with the products of GPS week 2352 (2 February 2025).</span></div><div><br data-mce-bogus="1"></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">IGb20 is a simple extract from ITRF2020-u2023. It includes reference coordinates for 343 stable, well-performing, operational and historical IGS stations. The same 332 stations as in the current IGS reference frame, IGS20, were retained. 11 new stations were added in areas currently sparsely covered by IGS reference frame stations.</span></div><div><br data-mce-bogus="1"></div><div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">The IGb20 files are available for download at <a href="ftp://igs-rf.ign.fr/pub/IGb20" data-mce-href="ftp://igs-rf.ign.fr/pub/IGb20">ftp://igs-rf.ign.fr/pub/IGb20</a>:</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">- IGb20.snx.gz : IGb20 SINEX file (gzip compressed)</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">- IGb20.ssc : IGb20 SINEX file without covariance matrix</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">- psd_IGb20.snx : post-seismic deformation models to be used with IGb20</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">- soln_IGb20.snx : discontinuity list to be used with IGb20</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">- IGb20_core.txt : list of "core" stations recommended for the alignment of global solutions to IGb20</span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;"><br data-mce-bogus="1"></span></div><div><span style="font-family: "courier new", courier, monaco, monospace, sans-serif; font-size: 10pt;" data-mce-style="font-family: 'courier new', courier, monaco, monospace, sans-serif; font-size: 10pt;">Since ITRF2020-u2023 is aligned in origin, scale and orientation to ITRF2020, IGb20 should not be considered as a complete new reference frame, but rather as an update to individual IGS20 station coordinates. This alignment implies that t</span><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">he </span></font><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">transformation parameters between ITRF2020 (IGS20) and ITRF2020-u2023 (IGb20) </span></font><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">are all zero. It also implies that the switch from IGS20 to IGb20 will not introduce any significant "datum" change in the IGS products. On the other hand, the precision and accuracy of the alignment of the IGS products to the reference frame will benefit from the adoption of updated reference station coordinates.</span></font></div><div><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;"><br data-mce-bogus="1"></span></font></div><div><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">More details on the usage of the IGb20 reference frame may be found in the comment section of the SINEX file.</span></font></div><div><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;"><br data-mce-bogus="1"></span></font></div><div><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">Best regards,</span></font></div><div><font face="courier new, courier, monaco, monospace, sans-serif"><span style="font-size: 13.3333px;">Paul Rebischung, on behalf of the IGS Reference Frame Committee</span></font></div></div></div></body></html>