How the Network Earth Rotation Service is working

The Network Earth Rotation Service (NERS) consists ot two segments: server and client.

NERS server segment

The NERS server segment checks every hour for updates of input Earth orientation time series and the output of numerical weather models. If no updates happens, it sleeps for an hour. If an update has happened, the server initiates re-computation of the EOP message. The EOP message consists of six parts:
  1. The NERS configuration: names of the model, URLs of input data used by the server, date of their last update etc.
  2. The table of UTC minus TAI function.
  3. The coefficients of expansion of IERS C04 time series into B-spline basis for the interval since 197.01.01 to the date of their last availability, typically 30–35 days in the past. The coefficients are computed using IERS C04 time series and provide their interpolation.
  4. The coefficients of expansion of Euler angles E1, E2, E3 into B-spline for the interval of end of IERS C04 time series availability through 48–72 hours in the future. These coefficients provide the short-term forecast. The coefficients are estimates with least square using input Earth orientation parameter and the atmospheric angular moment (AAM) time series computed from the numerical weather models in the data assimilation and the forecast modes. The contributing series of E(t) and the AAM are assigned specific weights. The weights are adjusted to provide the best quality of the forecast. The AAM dominates forecast 24–72 hours in the future, while the EOP time series dominates at scales 36 hours and further in the past.
  5. The coefficients of expansion of Euler angles E1, E2, E3 into B-spline for the interval from 72 hours to 6 months in the future. These coefficients provide the long-term prediction. The accuracy of the long-term prediction is significantly worse than the accuracy of the short-term prediction. It is assumed that the long-term prediction will be used only in emergency situation when short-term forecast is unavailable.
  6. The coefficients of small quasi-harmonic variations of Euler angles E1, E2, and E3. These are computed from analysis of space geodesy data and are updated 4–6 times a year.
The message is formatted as a binary file and is accessible for downloading via the HTTP interface.

NERS client segment

The NERS client segment provides a library that computes the Earth rotation matrix or the Earth orientation parameters from the NERS message and several executables. The client library performs three major functions: The executables provide the command-line interface to NERS library. They parse input parameters, call routines of NERS library and print out the output. These executables serve as examples or can be called from other programs or interpreters when fast execution time is not required.

NERS Internet services

The NERS supports several Internet services: These services have a web form that runs NERS executables at the server. They can be used interactively by filling the form manually, of using via wget, curl, or other tools for automatically retrieval the results of parsing form as it is explained here.
This page was prepared by Leonid Petrov ()
Last update: 2017.07.05_12:12:16