Multi-Year CORS Solution 3 (MYCS3)

NGS completed the third reprocessing of daily RINEX data from 1996 to 2022 for all stations in the NOAA CORS Network (NCN). The reprocessed solution, called the Multi-Year CORS Solution 3, is aligned to the ITRF2020(epoch 2020) global frame.

On October 2, 2022 (GPS week 2125), the International GNSS Service (IGS) released the new coordinates and corresponding antenna calibrations in IGS20, the IGS realization of the International Terrestrial Reference Frame 2020 (ITRF2020). As part of this transition, products in the IGS14 frame are no longer updated. Instead, all the updates will be in the ITRF2020 frame.

NGS participated in the 3rd IGS reprocessing campaign, during which IGS Analysis Center reanalyzed the entire global IGS dataset using the latest models and processing methods. NGS took this opportunity to also reanalyze its GPS data holdings for the NCN. All processing conformed with the International Earth Rotation and Reference System Service (IERS) 2010 conventions (Petit and Luzum). The global (Repro3) and regional NCN data sets were combined to form the Multi-Year CORS Solution 3 (MYCS3), which is aligned to the ITRF2020 frame through a 14 parameter transformation relative to 97 globally distributed IGS stations. MYCS3 replaces our previous multi-year CORS solution (MYCS2).

NGS's 3rd Reprocessing Campaign

Since the MYCS2 IGS14 coordinates and velocities were released in 2018 an update was needed due to the following changes:

• Geophysical processes: Several large earthquakes have caused significant coseismic motion at dozens of CORS. Post seismic motion of several centimeters has continued to persist at a few stations. Subsidence at several CORS in California's central valley reached several centimeters. Additionally, volcanic eruptions and deformations have moved stations by several centimeters.
• Equipment changes: Antenna changes cause noticeable jumps in the coordinate time series creating discontinuities ranging from a few mm to several centimeters.
• New NCN stations:New NCN stations: Since the last MYCS several new stations have been installed. Additionally, stations that had a limited time series now have a long enough time series to be included in MYCS3.
• ITRF2020 released: A new international reference frame was released (ITRF2020). MYCS3 positions and velocities refer to ITRF2020, epoch 2020.00.
• Updated models: The IGS adopted updated geophysical models since the release of MYCS2. This allows us to better model post-seismic motion.

MYCS3 Processing

The processing included data spanning 1996 to 2022 (week 0834 to 2237). The processing involved around 3200 NCN, IGS Network and other (e.g., NGA) stations. This was a massive computation effort. Although NGS has NCN data from the early 1990s, the residual time series showed exceptionally noisy behavior and so those data were not included in the alignment/velocity computation stage.

The processing was done in 3 steps:

1. Global processing

   The Global processing step solves for orbits, Earth Orientation Parameters (EOPs), hourly tropospheric delay parameters and weekly global (IGS) station positions in an IGS-NNR frame.

   

2. NCN processing

   The NCN processing, or tying the remaining NCN stations to global, backbone stations holding fixed estimated orbits, troposphere, EOPs and IGS station coordinates. This leads to estimated CORS coordinates in an NNR frame.

   

3. Alignment of the estimated coordinates with ITRF2020(2020.00) and velocity estimation

   This process was done in multiple iterations to achieve rigorous quality control and discontinuity detection. Initial runs were done using University of Nevada Reno’s step file to detect known offsets. In depth quality control was done using both automated tools and manual inspection.

Criteria for Publishing Coordinates

Position of NCN stations vary over time with at least an annual and semi-annual variation. As a result, reliable velocity estimates require a minimum of 2.5 years of data - or 130 weekly solutions. Therefore, only stations with more than 2.5 years of data, or 130 weekly solutions - are included in our stacked solutions for the published positions and velocities, with a few exceptions (i.e. geophysically active regions or stations with low standard deviation). For newer stations, or those with less than 2.5 years of data, we compute a position but assign a modeled velocity.

Velocity Fields Relative to ITRF2020

Horizontal Velocity Field (50 km x 50 km gridding)

Velocities show a smooth pattern across most of North America. These minimal velocities are driven by the rotation of the North American plate. Around California and southern Alaska there are much higher velocities due to the interaction between the North American and the Pacific/Juan de Fuca plates. The color represents the magnitude of the horizontal motion in mm/yr.

Vertical Velocity Field

Vertical velocities show minimal subsidence across most of the United States. In Northeast Canada, vertical velocities of approximately 10 mm per year are observed due to glacial isostatic adjustment (GIA). This is accompanied by corresponding subsidence of a few mm/year in the north midwest.

Velocity Uncertainties

MYCS3 velocity uncertainties are based on the noise content of each station. Residuals from the CATREF solution were used to estimate velocity uncertainties simultaneously with the estimation of white noise, flicker noise and random walk amplitudes of the time series. Time correlated noise (flicker and random walk) can have a significant effect on the velocity uncertainty at longer observation time spans, making it critical to estimate these components in order to get realistic uncertainties. A scale factor is computed from a white noise only model and a model that includes time correlated noise, and this scale factor is used to scale the uncertainties of the CATREF solution. Each station is treated independently, allowing the noise characteristics of each station time series to determine its scale factor, rather than applying a single scale factor across all stations. Plots below show the horizontal and vertical velocity uncertainties that resulted from the noise analysis of each station time series.

The following plots present the vertical and horizontal velocity uncertainties as a function of observation duration:

NAD83(2011) Coordinate Changes

Coordinates and Velocities of the Antenna Reference Point (ARP) of All Processed Stations

Below are text files contain coordinates and velocities of the ARP of NCN stations processed in MYCS3. In which:

• Computed files contain stations, each of which provides equal or more than 2.5 years of solutions in our MYCS3, and provides at least 130 weekly solutions.
• Modeled file contain stations, each has operated for less 2.5yrs and/or provided less than 130 weekly solutions in our MYCS3. New NCN stations are included in these files.

In general, each file is a CSV file (ASCII format) containing several header lines and station records. Each line being a record referring to a specific station. Header lines contain station ID, coordinates and velocities of the ARP, country, state codes, and the current operational status in the NCN. The station operational status is either:

• Operational: currently providing data,
• Non-Operational: has not provided data for at least 30 consecutive days,
• Decommissioned: has stopped operating permanently or was removed from NCN,
• IGS_not_CORS: IGS stations, for which NGS does not store data on its servers.

	Computed		Modeled
	Cartesian	Geodetic	Cartesian	Geodetic
ITRF2020 All processed stations	Download	Download	Download	Download
NAD83(2011) Stations in CONUS, Alaska, Puerto Rico, U.S. Virgin Islands	Download	Download	Download	Download
NAD83(PA11) Stations in U.S. islands on the Pacific plate	Download	Download	Download	Download
NAD83(MA11) Stations in U.S. islands on the Mariana plate	Download	Download	Download	Download

Other methods to obtain NCN coordinates and velocities can also found at: NCN Data & Products page.