OCCAM A modern VLBI Software Package with a long History

burpfancyΗλεκτρονική - Συσκευές

8 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

96 εμφανίσεις

OCCAM


A modern
VLBI Software Package with a long

H
istory


H
arald

Schuh

Institute of Geodesy and Geophysics, Vienna University of Technology, Austria

hschuh@luna.tuwien.ac.at



It is a pleasure to note that with the release of the VLBI data analysis software OCCA
M
ve
r-
sion
5.0 a powerful VLBI software package is available based on a broad and very successful
international
cooperation. The n
e
w v
e
rsion

of OCCAM provides all features that are nece
s-
sary to analyz
e VLBI data with highest accuracy. Within the International V
LBI Service (IVS)
it is used by several analysis centers and is even applied by the majority of operational anal
y-
sis centers (three of five).


The roots of OCCAM go ba
ck to the seventies when James Campbell (Geodetic Institute of
the University of Bonn, Ge
rmany
) programmed software for analyz
ing
geodetic
VLBI data of
MkII type. The accuracy of the geodetic results
in that time
was in the

range
of several dec
i-
meters
(Campbell, 1979
).


Based on these first
routines
Harald Schuh (Geodetic Institute of the University of Bonn,
Germany,

today at the Institute of Geodesy and Geophysics of the
Vienna
University of Tec
h-
nology
, Austria) developed a VLBI data analysis software package called BVSS (Bonn VLBI
Software System)
i
n the beginning of the eighties
.
The
BVSS

ra
n on the IBM mainframe
computer (
under
CMS/OS) of
the
Bonn University

and a

single baseline solution needed a few

minutes of CPU
-
time
. T
he goal in that time was
to generate
a software
that

is
flexible to ha
n-
dle
,

easy to modify, and applicable
more for
special scientific investigations rather than for
routine operations. The software included most of the geodynamical models to take into a
c-
count all tidal influences on the

rotation of the Earth
,

tidal deformation, various kinds of

loa
d-
ing effects

and also

relativistic effects
. With the first MkIII data a precision of ±3 cm for inte
r-
continental baselines could
be achieved (
Schuh, 1987).


The

next one who took over the lea
d in improving the VLBI software was Nestor Z
arraoa
(Institute of Astronomy and Geodesy of
the
University of Madrid, Spain; later at Statens
Kar
t
ver
k, H
ø
nefoss, Norway)
. He implemented the software on an AT Personal Computer
under MS
-
DOS. He also did a lot of improvements in particular by ext
ending the software to a
multi
-
station, multi
-
experi
ment version
and he added new features to
the stochastical part, e.g.
by introducing the Kalman filter. It was him who

introduced the name OCCAM hono
ring
William of

Oc
kkh
am
, XIVth

century

s English philosopher
who
st
ated that from all possible
a
nsw
ers to a question, the simplest

one

is the right one

(Zarraoa et al. 1
990;

Zarraoa et al.
1992
;

Zarraoa, 1992).


Sin
ce 1993 Oleg Titov (Institute for

Applied Astronomy
, St. Petersburg, Russia; then
St. P
e-
tersburg

State University
, Russia;

now at
Australian Surveying and Land Information Gro
up,
Bruce
, Australia) has been the chairman of the growing OCCAM user group.

It i
s his merit
that OCCAM has been

considerably

improved

by incorporating the IERS
Conventions

(1996)
and
the Least S
qua
res Collocation Method

(
Titov and Zarraoa, 1997
;
Titov, 2000
). In the last
years he ha
s been mainly supported
in develop
ing OCCAM
by Volker Tesmer (Deutsches
Geodaetisches Forschungsinstitut, Munich, Germany) and by Johannes Boehm (Institute of
Geodesy and Geophysics,
Vienna
University of Technology
, Austria).
Both, contributed

to


various parts of
the new ver
sion 5.0 of OCCAM, e.g. by entering the least
-
squares parameter
estimation.


In the past two decades there were several other

users of BVSS/OCCAM, e.g.
VLBI groups
in
Canad
a,

China,
and
India

who applied the software for
standard
geode
tic and astrometric
analyses or

did particular modifications for special purposes such as
analyz
ing

geodetic
Space
VLBI

data
.


With OCCAM 5.0 a
modern,
very powerful and accurate VLBI
software is available that can
be applied for
standard
operational
VLBI analysis but that allow
s also a big variety of
special
investigations in the field of geodetic/astrometric VLBI. Already now it is evident, that further
modifications will become necessary, e
.g. by incorporating more precise
astronomical and
geodynamica
l

models according to the new IERS Conventions
(2000)
that will be published
s
oon. Also the stochastical part

needs further development, e.g.
in

the least
-
squares fit

the
problem of cho
o
sing

correct a
-
priori weights
has to b
e solved and
the cor
relation
s

between the
observations

should be taken into account
.


Thus, in

spite of its

great success the work on OCCAM will be a never
-
ending story.



References


Campbell, J.:
Die Radio
interferometrie
auf langen Basen als geodaetisches Messprinzi
p hoher
Genauigkeit. DGK Reihe C, Nr. 254, Mu
enchen, 1979.


Schuh, H.: Die Radiointerfero
metrie auf lange
n Basen zur Bestimmung von Punktverschi
e-
bunge
n und Erdrotationsparametern. Ph.D. thesis, D
GK, Reihe, C, Muenchen, 1987.


Titov, O. and N. Zarraoa: OCCAM 3.4 User

s Guide. Co
mmunications of the Institute for

A
pplied

Astronomy (IAA), St. Pete
rsburg, No. 69, 199
7.


Titov, O.: Least Squares Collocation Method f
or Space Geodetic Data Analysis. IAG Symp.
To
wards an Integrated Global G
eodetic
Observing System (IGGOS), Munich Oct. 1998, e
d.
by R. Rummel, H. Drewes, W. Bosch, H. Horn
ik, IAG Symposia,

Vol. 120, Springer, 238
-
240
, 2000.


Zarraoa, N., A. Rius, E. Sardon, H. Schuh, J. Vierbuchen: OCCAM: A Compact and Tran
s-
p
ortable Tool for the Analysis of VLBI Experiments. Proceedings of the 7
th

Working Meeting
on European VLBI

for Geodesy and Astrometry
, ed. by A. Rius,
C.S.I.C.
Madrid, 92
-
102,
1990.


Zarraoa, N., A. Rius, E.

Sardon, H. Schuh
:
Intro
duction to the
OCCAM

V2.0 Models
. Pr
o-
ceedings of the
8
th

Working Meeting on European VLBI

for Geodesy and Astrometry
,
Dwingeloo, June 1991,
ed. by
F.J.J. Brouwer
.

Report MDTNO
-
R
-
9243, S
urvey Department
of Rijkswaterstaat, Delft, T
he
Netherlands,
IV59
-
IV69
, 1992
.


Zarraoa, N.: Estudio de Movimientos Relativos

en Europa Mediante una Red de Radiointe
r-
fero
metr
ía Geod
ésica. Tesis Doctoral, Madrid, 1992.