Data format for site displacements caused by loadings
Introduction
This document contains specifications of file formats of the intermediary
information which is the output of the mass loading computation programs and
is the input of the analysis software. These formats were developed in hope
that they will appear useful not only for users of VLBI Calc/Solve software who
can utilize the output of Goddard software for computing ocean and atmosphere
pressure loading, but also to other users.
Representation of ephemeris site position displacements caused by
a quickly varying phenomena, like atmosphere pressure loading, is rather
voluminous. Data organization which is convenient for computing site
displacements may be prohibitively expensive for data analysis software
which requires more efficient data organization for fast processing.
Therefore, two formats for ephemeris site position displacements are proposed.
The binary format is intended for using directly by data analysis software.
It is optimized for efficiency, but may not be convenient for viewing and
editing for unexperienced users. ASCII format has different organization which
makes it a little bit more convenient for visualization of the results,
but it is not optimal for data analysis software.
Representation of a harmonic model of site displacements is rather compact,
so the file can be organized in such a manner that it will be convenient for
both parsing software and for visualization for unexperienced users.
ASCII format for ephemeris site position displacements:
EPHEDISP
Purpose: to model site displacements caused by the phenomena which
currently cannot be predicted with sufficient accuracy and, therefore,
are computed from the measurements of some geophysical parameters or
data assimilation models. Examples: atmosphere pressure loading,
hydrology loading.
EPHEDISP file contains all 3-D site position displacements for all station
within the specified time range. This file is
NOT DESIGNED for using in a data
analysis software. In order to make use of these data, the file should be
converted into the BINDISP format.
Binary format for ephemeris site position displacements:
BINDISP
A file in binary format for ephemeris site position displacements
contains three components of the displacement vector of a specific
station, equally sampled within a certain time range. File organization
is very compact. This file is indented for using in data analysis software.
Analysis software can read the file using direct record
access. There is no necessity to read the files for the stations which did
not participate or to read the records for the data outside the required
time range.
Format for harmonic site position displacements:
HARPOS
Purpose: to model site displacements with the spectrum which consists of
a finite number of sharp peaks. Example: ocean loading, empirical annual
variations, diurnal site position variations, etc.
Leonid Petrov
( pet@leo.gsfc.nasa.gov )
12-DEC-2002 15:45:05