VTD a priori files management. Computation of VLBI time delay depends on values of a priori parameters. They are gathered in a priori files. A priori files belong to three categories: 1) Constants -- never changed 2) Infrequently updated, 2-3 times a year 3) Regularly updated on a daily basis. This document contains suggestions how the files with a priori parameters should be managed. I. Constant files. ================== 1) DE_EPHEMERIDES. The files supplied with VTD distribution is valid for the range of dates [1950, 2050] 2) STATION_ECCENTRICITIES Should updated for new stations. You can edit this file yourself. 3) AEM_FILE 4) ANTENNA_DEFORMATIONS_FILE May be updated for new stations. 5) HYDROSTATIC_MAPPING_FUNCTION/WET_MAPPING_FUNCTION: (MMF) 6) Ocean loading May be updated for new stations. 7) Loading due to atmospheric stations. May be updated for new stations. 8) SLANTED_PATH_DELAY_BIAS_FILE May be updated for new stations. II. Infrequently updated files: =============================== 1) LEAP_SECOND You check http://tycho.usno.navy.mil/leapsec.html and when a new leap second epoch is announced, edit the file accordingly. 2) STATION_DESCRIPTION You can edit this file and add a new station. You can ask for an apriori value of antenna axis offset. Antenna axis offset length can be found from VLBI solutions at http://astrogeo.org/gsol/ or http://astrogeo.org/rfc 3) SOURCE_COORDINATES The best source of source coordinates of known calibrators is http://astrogeo.org/rfc, which is updated 2-3 times a year. You can download the apriori file from there and then to add your sources to the bottom. NB: if a source is defined more than once in the file, the last definition will take effect. 4) STATION_COORDINATES You can download the latest solution, updated 2-3 times a year from http://astrogeo.org/rfc 5) STATION_VELOCITIES You can download the latest solution, updated 2-3 times a year from http://astrogeo.org/rfc III. Regularly updated files: ============================= 1) EOP_SERIES This file is updated daily. The Earth orientation parameters are derived from analysis of dedicated VLBI observations. There may many ways to generate a priori EOP file. The file provided with VTD distribution is generated at NASA GSFC by processing USNO EOP data file and applying rotations that make it consistent with a priori station and source catalogues. The file can be downloaded from http://gemini.gsfc.nasa.gov/500/oper/solve_save_files/last.erp Bash-program for updating EOP files is supplied in support/update_eop_series.sh 2) Atmospheric pressure loading These files is updated daily. Visit http://astrogeo.org/aplo for further information where to find data files. For example, here: http://lacerta.gsfc.nasa.gov/aplo/aplo_bds.tar.bz2 Bash-program for updating atmospheric pressure loading files is supplied in support/update_aplo_bds.sh Size of aplo_bds data is 320Mb 4) IONOSPHERE_DATA_FILE These files is updated daily. There are several data centers that update ionosphere data in the ionex format. You need to download them and then transform from ionex format to viono format. This is done by an auxiliary program gti_update. Bash-program for updating ionosphere data files is supplied in support/update_viono.sh Date size: data in ionex format: 720 Mb, data in viono format: 320 Mb 5) EXTERNAL_DELAY_DIR In 2010 this files were updated once a month. These file may be updated daily in the future. The data can be downloaded from http://astrogeo.org/spm Size of data in SPD_3D format: 114 Gb Size of data in SPD binary format: 14 Gb