README Closure Plots for _Source Structure and Measurement Noise Are as Important as All Other Residual Sources in Geodetic VLBI Combined_ James M. Anderson (1) and Ming H. Xu (2,1) (1) Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany (2) Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China These data are freely available under the Creative Commons Attribution 4.0 International Licence. When using the data please cite: Anderson, James M.; Xu, Ming H. (2018): Closure Plots for "Source Structure and Measurement Noise Are as Important as All Other Residual Sources in Geodetic VLBI Combined". V. 1. GFZ Data Services. http://doi.org/10.5880/GFZ.1.1.2018.001 2018 Jun 13 Introduction This is the README file for the plots of closure delay, closure phase, and closure amplitude for the geodetic very long baseline interferometry (VLBI) observations of the Continuous VLBI Campaign 2014 (CONT14) experiment of the International VLBI Service for Geodesy and Astrometry calculated by Anderson and Xu for their article titled _Source Structure and Measurement Noise Are as Important as All Other Residual Sources in Geodetic VLBI Combined_, submitted to the Journal of Geophysical Research - Solid Earth in 2018. For details describing exactly how the closure quantities were calculated and descriptions of the plots, see that article. Abstract Plots of closure delay, closure phase, and closure amplitude are provided for the geodetic very long baseline interferometry (VLBI) observations of the Continuous VLBI Campaign 2014 (CONT14) experiment of the International VLBI Service for Geodesy and Astrometry (IVS, https://ivscc.gsfc.nasa.gov/ , see https://ivscc.gsfc.nasa.gov/program/cont14/ for a description of CONT14, and see https://ivscc.gsfc.nasa.gov/about/org/components/dc-list.html for a list of IVS data centers from which the CONT14 data can be downloaded) as calculated by Anderson and Xu for their article titled _Source Structure and Measurement Noise Are as Important as All Other Residual Sources in Geodetic VLBI Combined_, submitted to the Journal of Geophysical Research - Solid Earth in 2018. Closure quantities are insensitive to station-based calibration terms, such as station clock errors, atmospheric delay errors, phase offsets, station position errors, amplitude calibration errors, and so on, and as a result are sensitive only to source structure (the two-dimensional brightness distribution of source emission on the sky, which is typically time and frequency dependent), measurement noise, and closure errors such as bandpass mismatch and polarization leakage. We used closure quantities derived from the CONT14 data to investigate the amount of source structure present in the celestial sources observed in the CONT14 experiment. Details Three data files are included: closure_delay_Anderson_Xu_JGR_2018.tar.gz closure_phase_Anderson_Xu_JGR_2018.tar.gz closure_amplitude_Anderson_Xu_JGR_2018.tar.gz The file with the name starting with "closure_delay" contains closure delay plots, the file with the name starting with "closure_phase" contains closure phase plots, and so on. These three files are collections of files made by the UNIX tar program that have been compressed with the gzip program. To decompress and extract files on a Linux or macOS, download a data file of interest, and then extract the files by running tar zxf filename where filename is the name (including a path if necessary) of the original data file you downloaded. For example, if you downloaded the closure_delay_Anderson_Xu_JGR_2018.tar.gz file, run tar zxf closure_delay_Anderson_Xu_JGR_2018.tar.gz This will produce a directory called Anderson_Xu_JGR_2018 and inside that directory will be a number of PDF files containing closure plots. For users with Windows operating systems, if you have Windows 10 with a version at or later than 1803, support for .tar.gz files is built into Windows. Open a Command Prompt as administrator, and run (type) tar -zxf C:\PATH\TO\FILE\FILENAME.tar.gz -C C:\PATH\TO\FOLDER\EXTRACTION where C: should be replaced by the appropriate drive letter, and paths and filenames should be replaced appropriately. (See also https://blogs.msdn.microsoft.com/commandline/2018/03/07/windows10v1803/ or https://blogs.technet.microsoft.com/virtualization/2017/12/19/tar-and-curl-come-to-windows/ .) If you are using an earlier version of Windows, there are a myriad of downloadable utilities for compressing and uncompressing various file formats for Windows. The closure plots for a specific source and a specific frequency band are stored within individual PDF files, with different closure triangles or quadrangles provided on individual pages within the PDF files. For example, the first 6 files in an ASCII-sorted listing of the files generated from the closure_delay_Anderson_Xu_JGR_2018.tar.gz data file are: all_0014+813_closure_delay_S.pdf all_0014+813_closure_delay_X.pdf all_0014+813_closure_delay_iono_free.pdf all_0016+731_closure_delay_S.pdf all_0016+731_closure_delay_X.pdf The filenames contain the IVS source name (for example, 0014+813 and 0016+731 above), the type of closure plots (closure_delay in the example above) and the frequency band (S, X, and iono_free above). Note that for the frequency bands we only compute the ionosphere-free values for closure delays. For closure phases and amplitudes we only provide S and X band data individually. The plots of individual closure triangle or quadrangles are sorted alphanumerically by the IVS station names. For details of the plot layouts and symbols, see the Anderson & Xu paper referenced above. Only a brief description is provided here. Closure delays (in units of picoseconds), phases (in units of degrees, wrapped into the range -180 degrees to +180 degrees), and amplitudes (shown as the natural logarithm of the unitless closure amplitude) are plotted in the vertical axis. The horizontal axis shows Greenwich Mean Sidereal Time (GMST) in hours, with times on different days wrapped by 24 hours. Baseline orientations are to first order only a function of GMST, such that the baseline orientations at the same GMSTs on different days are nearly exactly the same, so plotting the closure quantities as a function of GMST shows the closures as a function of the closure baseline orientations. Actual CONT14 closure measurements are shown by magenta symbols. Filled points show closures for which all baselines in the closure quantity were used in the geodetic analysis performed by Anderson & Xu. Open magenta circles show closure quantities for which at least one baseline was flagged out in the official IVS version 4 datasets for the CONT14 experiment. One-sigma errorbars showing the measurement errors in the closure quantities are indicated by vertical black lines through these measured points. Closure quantities that exceed the upper or lower vertical limits of the plots are shown as large open magenta circles at the upper or lower plot boundaries, respectively. The model closure quantities, derived from images of the sources made from the CONT14 visibility data, are shown by a continuous blue line, showing the model closure value as a function of GMST, and as small blue points showing the model closure values at the specific observation times corresponding to the actual geodetic measurements in CONT14. Thin horizontal black lines are shown to guide the eye. For closure delay these lines are located at -500 ps and +500 ps for S band, -100 ps and +100 ps for X band, and -100 and +100 ps for the ionosphere-free combination. For closure phase, the horizontal lines are shown at -55 degrees and +55 degrees. For closure amplitude, the thin lines are shown at about -1.15 and +1.15 in the natural logarithm, corresponding to about 1/3.2 and 3.2, respectively, for the (regular) closure amplitude value. The IVS station names in the closure triangles and quadrangles are printed in black at the top of each plot. For closure delays and phases, the unprojected baseline lengths for each baseline in the triangle are printed in units of kilometers following the names of the three stations.