NAME
setdne - sets dnorth and deast fields in a css3.0 database site table
SYNOPSIS
setdne db refsta
SUPPORT
Contributed code: NO BRTT support.
THIS PIECE OF SOFTWARE WAS CONTRIBUTED BY THE ANTELOPE USER COMMUNITY. BRTT DISCLAIMS ALL OWNERSHIP, LIABILITY, AND SUPPORT FOR THIS PIECE OF SOFTWARE.
FOR HELP WITH THIS PIECE OF SOFTWARE, PLEASE CONTACT THE CONTRIBUTING AUTHOR.
DESCRIPTION
In array processing the dnorth and deast fields of a css3.0 database
are required to compute plane wave moveout corrections. Modern
broadband networks/arrays of stations often don't fill in these
fields as when the aperture is large the use of dnorth and deast
is usually viewed as a bad approximation of geometry. However,
array processing routines still require these fields because the
full spherical geometry calculation is cumbersome and, in fact,
requires an assumed origin before it can be done correctly.
Thus, some programs like dbap and mwap need this field to be
set even if it is an approximation. mwap actually computes
plane wave statics that correct the moveout for wavefront curvature
but still needs dnorth and deast to simplify the moveout computation.
This program uses a simple approximation in using the dist(3) function
of Datascope to compute a great circle path distance and bearing from
the specified origin. It then uses a simple trigonometric conversion
to convert these to distance north and distance east in kilometers.
COMMAND LINE ARGUMENTS
-
db
This is the input database. Only the site table is accessed, but the
database must be accessible for updating. Note it is common practice
to disable write permission on this table in a master database, so it
is a good idea to copy the master site table and give it write permission
before running this program.
-
refsta
This should define a valid station code of the station that is to
be used as the reference station. That is, the origin is set to the
coordinates of this master station. The program will die with an
error message if the named station does not exist in the site table.
FILES
Only the site table of the named database is accessed.
DIAGNOSTICS
Should be self explanatory.
SEE ALSO
mwap(1), dist(3)
BUGS AND CAVEATS
The appoximation of dnorth and deast gets progressively worse with
array aperture. The authors experience is that the moveout computed
for teleseismic P waves is accurate to better than 0.1 s for an
array with an aperture of about 100 km. This depends on epicentral
distance as well as total aperture.
Strangely enough the algorithm used should work
even if an array spans the pole.
AUTHOR
Gary L. Pavlis
Antelope User Group Contributed Software