Sidebar

public:vievs_manual:exercises_intensive_sessions

Intensive sessions

The screenshots in this chapter still show an older VieVS version (2.1)!

Intensive sessions are 1- or 2-hour VLBI experiments which are carried out (nearly) every day with the goal of near-real time estimation of Universal Time (UT1). The stations taking part in Intensive sessions are Kokee Park, Ny Ålesund, Tsukuba and Wettzell:

Intensive sessions in NGS format usually have the suffix XK, XU or XT. In File - Set Input Files you can select session/s using the button Browse for sessions. How you can create process lists easily using the function mk_list, is described in the according Chapter.

Since we usually estimate one constant zwd per station per session, we change the estimation settings in Estimation - Troposphere:

Since we estimate piece-wise linear offsets (at least two) we use tight constraints to get 'one' constant offset. We do not estimate gradients (uncheck the boxes in the GUI). The clock estimation parametrization can be found in Estimation - Least Squares - Clock. In total we estimate a linear clock function between the two station clocks; no constraint is needed. Take care that the interval is long enough to cover the session. The clock parametrization is shown in the Fig. below:

We estimate one constant $\Delta UT1$ value per session, which means that we fix the other Earth Orientation parameters to their a priori values (see Fig. below).

Station coordinates are also not estimated but fixed to their a priori values:

The last options one has to change can be found in Run - VieVS estimation settings. There you can (de-)select the first solution (more details about the first solution can be found in the according Chapter). You could skip the first solution, but if you apply it, do not estimate more parameters than a linear clock function between the stations. An outlier test is not needed. The Fig. below shows the final options chosen in the exercise.

Optionally one can specify a subdirectory where the final output is saved into. The according GUI can be found in Run - Run options and is shown in the Fig. below. Click the Save + Run button to start the processing.

To check the obtained results, one can check the residuals plot, the number of scans as well as the $\chi^2$. The plotting tool could be used for visualizing the estimated parameters.

An example residuals plot of an intensive session is shown below. The residuals could be smaller but are ok.

If you check the command window output you find the number of scans in the current session. In this example we have 15 scans which is not that much. A $\chi^2$ of 1.6 is ok. In the parametrization given above the actual number of estimated parameters is five (one linear clock, two zenith wet delay offsets and one $\Delta UT1$ offset). The number shown in the command window output (eight) is due to the fact that we estimate piece-wise linear offsets. The standard deviation of the estimated parameters can be found in the x_ files. For an example session, this file can be loaded and the $\sigma$ value displayed using the following commands (a more convenient way to visualize parameters is shown in get results Section:

load('D:/VieVS/DATA/LEVEL3/INT/x_11APR02XK_N003.mat')
x_.dut1.mx(1)
ans = 0.0154

The formal error is 15.4~$\mu s$.

| <= back |