BEGIN:VCALENDAR
VERSION:2.0
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BEGIN:VEVENT
SUMMARY:About the extension of the coordinate parametrization of radio sou
rces in VLBI
DTSTART;VALUE=DATE-TIME:20160317T083000Z
DTEND;VALUE=DATE-TIME:20160317T084500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4568@events.saip.org.za
DESCRIPTION:Speakers: Maria Karbon (GFZ)\nUsually celestial radio sources
in the celestial reference frame (CRF) catalog are divided in three catego
ries: defining\, special handling\, and others. The defining sources are t
hose used for the datum realization of the celestial reference frame\, i.e
. they are included in the No-Net-Rotation (NNR) constraints to maintain t
he axis orientation of the CRF\, and are modeled with one set of totally c
onstant coordinates. At the current level of precision\, the choice of the
defining sources has a significant effect on the coordinates. For the ICR
F2 295 sources were chosen as defining sources\, based on their geometrica
l distribution\, statistical properties\, and stability. The number of def
ining sources is a compromise between the reliability of the datum\, which
increases with the number of sources\, and the noise which is introduced
by each source. Thus\, the optimal number of defining sources is a trade-o
ff between reliability\, geometry\, and precision.\n\nIn the ICRF2 only 39
of sources were sorted into the special handling group as they show large
fluctuations in their position\, therefore they are excluded from the NNR
conditions and their positions are normally estimated for each VLBI sessi
on instead of as global parameters. All the remaining sources are classifi
ed as others. However\, a large fraction of these unstable sources show ot
her favorable characteristics\, e.g. large flux density (brightness) and a
long history of observations. Thus\, it would prove advantageous includin
g these sources into the NNR condition. However\, the instability of these
objects inhibit this. If the coordinate model of these sources would be e
xtended\, it would be possible to use these sources for the NNR condition
as well. All other sources are placed in the “others” group. This is t
he largest group of sources\, containing those which have not shown any ve
ry problematic behavior\, but still do not fulfill the requirements for de
fining sources.\n\nStudies show that the behavior of the sources can vary
dramatically in time. Hence\, each source should be modeled individually.
Considering this\, the shear amount of sources\, in our study more than 90
0 are included\, sets practical limitations.\n\nWe decided to use the mult
ivariate adaptive regression splines (MARS) procedure to parametrize the s
ource coordinates\, as they allow a great deal of automation as it combin
es recursive partitioning and spline fitting in an optimal way. The algori
thm finds the ideal knot positions for the splines and thus the best numbe
r of polynomial pieces to fit the data. We investigate linear and cubic sp
lines determined by MARS to "human" determined linear splines and their im
pact on the CRF.\n\nWithin this work we try to answer the following questi
ons: Do we still need the categorizations in stable\, special handling and
other sources? If yes\, how can we find optimal criteria for the definiti
on of these categories? Whats the best approach to find the best fitting p
olynomials? And finally\, what can we gain by introducing this type of par
ametrization within the CRF determination?\n\nhttps://events.saip.org.za/e
vent/56/contributions/4568/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4568/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aspects of ICRF-3
DTSTART;VALUE=DATE-TIME:20160316T132500Z
DTEND;VALUE=DATE-TIME:20160316T134000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4569@events.saip.org.za
DESCRIPTION:Speakers: Chopo Ma (NASA Goddard Space Flight Center)\nThe Sec
ond Realization of the International Celestial Reference Frame (ICRF) used
dual-frequency VLBI data acquired for geodetic and astrometric purposes f
rom 1979-2009 by organizations coordinated by the IVS and various precurso
r networks. Since 2009 the data set has been significantly broadened\, es
pecially by observations in the Southern Hemisphere\, and modeling of astr
onomical\, geophysical and tropospheric effects has progressed. While the
new southern data have ameliorated the north/south imbalance of observati
ons\, they appear to cause a systematic zonal declination change in the ca
talog positions. Over the three decades of the ICRF data set the effect o
f galactic aberration may be significant. Geophysical and tropospheric mo
dels also may affect the source positions. All these effects need to be a
ddressed in preparation for ICRF-3.\n\nhttps://events.saip.org.za/event/56
/contributions/4569/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4569/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tidal atmospheric loading and VLBI
DTSTART;VALUE=DATE-TIME:20160317T130000Z
DTEND;VALUE=DATE-TIME:20160317T131500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4577@events.saip.org.za
DESCRIPTION:Speakers: Anastasiia Girdiuk (TU Wien)\nThis presentation is d
edicated to the influence of diurnal atmosphere-ocean dynamics on Earth ro
tation and loading effects as observed by Very Long Baseline Interferometr
y. The first part focuses on the rotational signals associated with atmosp
heric tides\, comprising small but non-negligible oscillations in the orde
r 5 Μas. Here\, we compare tidally analysed VLBI observations against est
imates from different providers of numerical weather models. We also discu
ss the complexity of the issue that must make allowance for indirect effec
ts due to tidal pressure variations acting on the ocean.\nIn the second pa
rt\, we are investigating loading signals caused by atmospheric tides and
the associated mass variations in the ocean. Different models of the effec
t are compared with respect to their performance in a VLBI analysis\, and
strategies how to apply consistent corrections for the atmosphere and the
ocean are discussed. Moreover\, we also show VLBI results for two gravitat
ional ocean tide models\, FES2004 and FES2012\, where the latter benefits
from a much finer horizontal resolution and an improved description of hyd
rodynamic processes.\n\nhttps://events.saip.org.za/event/56/contributions/
4577/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4577/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Status of the X/S Source Catalog
DTSTART;VALUE=DATE-TIME:20160317T071500Z
DTEND;VALUE=DATE-TIME:20160317T073000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4590@events.saip.org.za
DESCRIPTION:Speakers: David Gordon (NVI Inc./GSFC)\nThe current state of t
he X/S source catalog is presented\nand compared to ICRF2. There are curre
ntly ~60% more observations\nand ~30% more sessions than were used for ICR
F2. An ICRF made\ntoday would have ~20% more sources than ICRF2 and the av
erage inflated\nformal errors would be ~2.4 times better than ICRF2. Much
of this\nimprovement has come from the VCS-II campaign on the VLBA\, in\nw
hich the average inflated formal errors of 2062 sources were\nreduced by a
factor of 3.7 and 324 new sources were added.\nAdditional new sources hav
e come from the RDV/RV\, CRF\, AUST\, AUA\,\nand AOV sessions. In addition
to the current\nstatus\, we will present some of the additional goals\nfo
r the X/S catalog before ICRF3 in 2018. This includes\nimproving the posit
ions of a limited number of sources\nfor Gaia alignment and for X/Ka compa
risons.\n\nhttps://events.saip.org.za/event/56/contributions/4590/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4590/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vienna contribution to the ICRF3
DTSTART;VALUE=DATE-TIME:20160317T070000Z
DTEND;VALUE=DATE-TIME:20160317T071500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4595@events.saip.org.za
DESCRIPTION:Speakers: David Mayer (Technische Universität Wien)\nThe curr
ent realisation of the celestial reference frame\, the ICRF2\, was publish
ed 2009. Since then the VLBI technique evolved. New stations were implemen
ted and the amount of data from the Southern Hemisphere increased dramatic
ally. The demands on accuracy of the celestial reference frame are higher
than ever\, with the GAIA mission providing a catalogue in the visible spe
ctrum with comparable accuracy. These advances in the VLBI technique and n
ew demands on accuracy entail the necessity of a new version of the celest
ial reference frame which will be called ICRF3. We will report on the prog
ress and plans of the Vienna group to estimate such a reference frame. Fur
thermore\, we will discuss issues which arise during the estimation proces
s such as a declination bias.\n\nhttps://events.saip.org.za/event/56/contr
ibutions/4595/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4595/
END:VEVENT
BEGIN:VEVENT
SUMMARY:VLBI processing at ESOC\, the last piece for generating an indepen
dent reference frame
DTSTART;VALUE=DATE-TIME:20160316T123000Z
DTEND;VALUE=DATE-TIME:20160316T124500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4596@events.saip.org.za
DESCRIPTION:Speakers: Claudia Flohrer (ESOC - Navigation Support Office\,
Darmstadt\, Germany)\nESOC’s Navigation Support Office is providing the
geodetic reference for ESA missions and as leader of the Galileo Geodetic
Service Provider (GGSP) consortium\, also for Galileo. The Navigation Supp
ort Office has demonstrated its expertise in the processing of various spa
ce-geodetic techniques\, such as GNSS\, SLR and DORIS and their combinatio
n on the observation level. Nevertheless\, the last and vital piece missin
g for the generation of an independent reference frame is VLBI\, which is
required to define the Earth’s orientation. \nESOC’s Navigation Sup
port Office is currently extending its expertise to VLBI processing and an
alysis. We are enhancing the processing capabilities of our work horse sof
tware package NAPEOS for VLBI tracking data. \nThis capability will put us
in the position to combine all space-geodetic techniques with one single
software package at the observation level. The combination of the differen
t techniques brings together the strengths of the individual techniques.
The satellite techniques GNSS\, SLR and DORIS are able to determine the Ea
rth’s centre of mass\, the X- and Y-pole offsets and rates and the Lengt
h of Day. However\, VLBI is the only technique able to accurately determin
e universal time (UT1-UTC) and the celestial pole offsets.\nThe processing
of VLBI tracking data will complete ESOC’s capabilities in generating a
n independent reference frame for ESA missions. It will allow us to contri
bute to the IERS service for UT1-UTC and for the celestial pole offset\, w
hilst at the same time to reduce our dependency on this service. And last
but not least our software NAPEOS would become the first software combinin
g all four geodetic techniques on the observation level and thus supportin
g GGOS\, the Global Geodetic Observing System\, to get a better understand
ing of our living planet.\nWe will present an overview of the current stat
us of the VLBI processing at ESOC and will give an outlook on our future p
lans.\n\nhttps://events.saip.org.za/event/56/contributions/4596/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4596/
END:VEVENT
BEGIN:VEVENT
SUMMARY:El Nino and VLBI measured LOD
DTSTART;VALUE=DATE-TIME:20160317T121500Z
DTEND;VALUE=DATE-TIME:20160317T123000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4599@events.saip.org.za
DESCRIPTION:Speakers: John Gipson (NVI Inc/GSFC NASA)\nShort term (daily t
o annual) variations in LOD are highly correlated with Atmospheric Angular
Momentum. It has been known since the late 1980s and early 1990s that yo
u could detect the effect of El Nino in the Length of Day (LOD). I review
these results\, paying particular attention to the current El Nino which i
s still developing\, and is one of the strongest ever recorded. I look at
correlation with Modified Enso Index and VLBI measured LOD. I also discus
s the cumulative effect of the El Nino on UT1.\n\nhttps://events.saip.org.
za/event/56/contributions/4599/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4599/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The Statistic Analysis of Atmospheric Effects of Differential VLBI
DTSTART;VALUE=DATE-TIME:20160317T100000Z
DTEND;VALUE=DATE-TIME:20160317T101500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4621@events.saip.org.za
DESCRIPTION:Speakers: Shuangjing Xu (Shanghai Astronomical Observatory)\nD
uring the Chinese Lunar Mission hundreds of VLBI observations have been ca
rried\, we re-analysis all the quasar observations which used to calibrate
the satellite observables. In each observation there are two quasar scans
lasting about one hour\, we use these data by splitting them into differe
nt time intervals and doing self-calibration each other in phase-referenci
ng style to investigate the relationship of differential atmospheric delay
and different “time-switching”. In this report we will present our pr
imary result.\n\nhttps://events.saip.org.za/event/56/contributions/4621/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4621/
END:VEVENT
BEGIN:VEVENT
SUMMARY:ICRF sources: How good is the 'deep' southern sky
DTSTART;VALUE=DATE-TIME:20160317T091500Z
DTEND;VALUE=DATE-TIME:20160317T093000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4630@events.saip.org.za
DESCRIPTION:Speakers: Sayan Basu (University of South Africa and Hartebees
thoek Radio Astronomy Observatory\, South Africa)\nThe International Celes
tial Reference Frame (ICRF) are constructed using catalogs of extragalacti
c radio source (mainly quasars) positions measured at 2.3 and 8.4 GHz with
the Very Long Baseline Interferometry (VLBI) technique. Most extragalacti
c radio sources exhibit spatially extended structures on milliarcsecond an
d sub-milliarcsecond scales which are variable in both time and frequency
. These extended structures may contribute significant errors in the VLBI
measurements that will introduce uncertainty in the source position measur
ements. Therefore\, in order to define and maintain the celestial referenc
e frame with the highest accuracy\, efforts are required to map sources an
d to study their suitability as reference frame source on VLBI scales. \n
We will present multi-epoch imaging results of the ICRF sources in the sou
thern sky from the Celestial Reference Frame Deep South (CRDS) observing c
ampaign from the IVS. Source morphology as well as source quality aspects
will be discussed in the presentation which will give a better understand
ing of source behavior at 2.3 and 8.4 GHz observing frequencies with the V
LBI technique.\n\nhttps://events.saip.org.za/event/56/contributions/4630/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4630/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The XKa Celestial Reference Frame: Assessing Accuracy
DTSTART;VALUE=DATE-TIME:20160317T081500Z
DTEND;VALUE=DATE-TIME:20160317T083000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4633@events.saip.org.za
DESCRIPTION:Speakers: Christopher Jacobs (JPL/NASA)\nObservations at X/Ka-
band are motivated by their ability to access more compact source morpholo
gy and reduced core shift relative to observations at the historically st
andard S/X-band. In addition\, the factor of four increase in interferomet
er resolution at Ka-band should resolve out some wide binary black holes w
hich are a topic of concern \nfor AGN centroid stability.\n\nGiven these m
otivations\, an X/Ka-band (8.4/32 GHz) celestial reference frame has been
constructed using a combined NASA and ESA Deep Space Network. In 124 ob
serving sessions we detected 673 sources covering the full 24 hours of ri
ght ascension and the full range of declinations. The resulting XKa median
precision is now better than the ICRF-2 precision thereby raising the que
stion of which frame is more accurate. \n\nComparison of over 500 X/Ka sou
rces in common with the S/X-band (2.3/8.4 GHz) ICRF2 produced wRMS agreem
ent of about 200 microasec. There is evidence for systematic errors above
the 100 microasec level. Known errors include limited SNR\, lack of phase
calibration\, troposphere mismodelling\, and terrestrial frame distortion
s. Actions are underway to reduce all of these errors. In particular\, a
collaboration between NASA and the ESA deep space antenna in Malargüe\,
Argentina is quickly reducing weaknesses in the southern hemisphere. By l
ooking at the best observed sources\, we probe the accuracy limits of curr
ent celestial frames in an effort to understand the advantages of each fra
me.\n\nhttps://events.saip.org.za/event/56/contributions/4633/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4633/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Estimating the Celestial Reference Frame via Intra-Technique Combi
nation
DTSTART;VALUE=DATE-TIME:20160317T073000Z
DTEND;VALUE=DATE-TIME:20160317T074500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4637@events.saip.org.za
DESCRIPTION:Speakers: Andreas Iddink (Institute of Geodesy and Geoinformat
ion\, University of Bonn)\nOne of the primary goals of VLBI is the determi
nation of a CRF. Currently the third realization of the internationally ad
opted CRF\, the ICRF3\, is under preparation. In this process\, various op
timizations are planned to realize a CRF which does not only benefit from
the increased number of observations. For instance\, various campaigns hav
e been performed to sample the southern hemisphere with a better density.
Furthermore\, the VLBI Calibrator Surveys have been redone. Further optimi
zations of the ICRF3 with respect to the prior versions will be obtained o
n the analysis side. The new ICRF will benefit also from an intra-techniqu
e combination as it is also done for the TRF. Following IUGG Resolution No
. 3 (2011) this approach can then easily be extended to a consistent estim
ation of CRF\, TRF and the EOPs\, based on the observations of different g
eodetic space techniques.\n\nHere\, we aim at estimating an optimized CRF
by means of an intra-technique combination. The solutions are based on the
input to the official combined product of the International VLBI Service
for Geodesy and Astrometry (IVS)\, also providing the radio source paramet
ers. We discuss the differences in the setup between the classical TRF-EOP
combination and an extended CRF-TRF-EOP combination. Furthermore\, we inv
estigate the differences between the combined CRF and the CRFs for the ind
ividual ACs. Finally\, the impact on the TRF and the EOPs are analyzed to
demonstrate the benefits of our enhanced combination procedure.\n\nhttps:/
/events.saip.org.za/event/56/contributions/4637/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4637/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The IVS Contribution to JTRF2014
DTSTART;VALUE=DATE-TIME:20160316T120000Z
DTEND;VALUE=DATE-TIME:20160316T121500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4640@events.saip.org.za
DESCRIPTION:Speakers: Richard Gross (Jet Propulsion Laboratory)\nKALREF\,
JPL's KALman filter and smoother for REference Frames\, has been used to p
roduce JTRF2014\, a combined terrestrial reference frame determined from t
he input SINEX files submitted by the IVS\, IGS\, ILRS\, and IDS for ITRF2
014. Using a Kalman filter and smoother allows the reference frame to be d
etermined sequentially as a time series. Incorporating process noise\, det
ermined from geophysical fluid loading models\, allows the observed statio
n positions to be smoothed between discontinuities caused by earthquakes a
nd equipment changes. Non-linear and non-seasonal changes in station posit
ions\, such as postseismic displacements\, are automatically included in t
he smoothed time series. The creation of JTRF2014 will be discussed with a
n emphasis on the contribution that the VLBI observations made to it.\n\nh
ttps://events.saip.org.za/event/56/contributions/4640/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4640/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Selecting sources that define a stable celestial reference frame w
ith the Allan variance
DTSTART;VALUE=DATE-TIME:20160317T074500Z
DTEND;VALUE=DATE-TIME:20160317T080000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4642@events.saip.org.za
DESCRIPTION:Speakers: Karine Le Bail (NVI\, Inc.)\nICRF2 was adopted by th
e IAU in 2009 and was based on the position of 3414 radio sources determin
ed by VLBI. Discussions on the next realization of the ICRF (ICRF3) have b
een underway within the IAU and IVS since 2012. VLBI has made significant
advances since ICRF2.\nFrom the latest GSFC solution\, we extract a set of
sources that defines a stable celestial reference frame\, as shown by M.
Feissel-Vernier 2003 (A&A) using tools such as the Allan variance and the
drift of the position time series. This method also allows us to highlight
a set of the least "stable" sources that may need special handling.\n\nht
tps://events.saip.org.za/event/56/contributions/4642/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4642/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On the impact of different mapping functions on geodetic and tropo
spheric products from VLBI data analysis
DTSTART;VALUE=DATE-TIME:20160317T103000Z
DTEND;VALUE=DATE-TIME:20160317T104500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4646@events.saip.org.za
DESCRIPTION:Speakers: Kyriakos Balidakis (Technische Universität Berlin\,
Institute of Geodesy and Geoinformation Science\, Berlin\, Germany)\nDue
to the highly volatile character of the neutral atmosphere\, the modeling
of the related propagation delay is challenging. This poses the most promi
nent limitation in the precision and accuracy of the parameters estimated
in very long baseline interferometry (VLBI) data analysis. Hence\, it is o
f paramount importance that all parameters involved in the process to desc
ribe the atmosphere induced delay effects such as mapping functions or gra
dients are rigorously accounted for.\nIn this work\, we assess the impact
of different mapping functions (MFs) in the analysis of the 24-hour VLBI s
essions from 2002 onwards. Besides the original Vienna mapping functions (
VMF1)\, which are based on data from ECMWF operational analysis\, we apply
MFs based on this concept but utilizing data from ray tracing in CMC's GD
PS (UNB-VMF1). In addition to these we test the concept of advanced mappin
g using ECMWF's ERA-Interim reanalysis based on rigorous ray-tracing appro
ach. For the parameter estimation we use the VieVS@GFZ software applying t
he classical Gauß-Markov model. \nThe purpose of this study is twofold. W
e investigate the effect of these analysis options on the baseline length
repeatability as well as on the time series of station\, source coordinate
s and Earth orientation parameters. As far as the tropospheric products ar
e concerned\, estimated zenith wet delays and linear horizontal gradients
are compared with the ray traced ones from the aforementioned models.\n\nh
ttps://events.saip.org.za/event/56/contributions/4646/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4646/
END:VEVENT
BEGIN:VEVENT
SUMMARY:INVITED TALK: Status of the ICRF3 and Gaia activities
DTSTART;VALUE=DATE-TIME:20160316T130000Z
DTEND;VALUE=DATE-TIME:20160316T132500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4668@events.saip.org.za
DESCRIPTION:Speakers: Patrick Charlot (Laboratoire d'Astrophysique de Bord
eaux)\nThe ICRF3\, the next realization of the International Celestial Ref
erence Frame\, is going to be built within the next two years for approval
at the IAU 2018 General Assembly. This timescale is driven by the forthco
ming optical reference frame to be built by the Gaia mission and aligned a
t best with the ICRF3. The ICRF3 work is carried out by an IAU Working Gro
up set up in 2012. While the work so far was primarily focused on increasi
ng the pool of observations\, it must now concentrate on the analysis. The
Gaia mission is operational since September 2014\, observing 30-40 millio
n sources per day. It is performing largely nominally despite a few proble
ms which slightly degrade the accuracy. A first release of the Gaia data i
s planned for mid-2016 while a second release is expected by mid-2017.\n\n
https://events.saip.org.za/event/56/contributions/4668/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4668/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Images of VLBI calibrators from the BeSSeL survey
DTSTART;VALUE=DATE-TIME:20160317T094500Z
DTEND;VALUE=DATE-TIME:20160317T100000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4671@events.saip.org.za
DESCRIPTION:Speakers: Bo Zhang (Shanghai Astronomical Observatory)\nThe Be
SSeL Survey (Bar and Spiral Structure Legacy Survey) is a VLBA Key Science
project. The primary goal of the survey is to study the spiral structure
and kinematics of the Milky Way\, by measuring distances and proper motion
s to masers in regions of massive star formation across large portions of
the Milky Way. To measure the distances of masers via trigonometric parall
axes\, the relative positions between the masers and extragalactic VLBI ca
librators are determined with phase-referencing VLBI at different epochs s
panning at least 1 year. \n\nThe Masers are usually served as phase refere
nce since they are much stronger than the calibrators\, allowing several h
ours' integration times for the weak calibrators. In addition\, the calibr
ators are often observed though the whole observing program\, providing ex
cellent uv-coverage for imaging. From the BeSSeL survey\, there will be ab
out ~5000 high quality images of ~ 400 VLBI calibrators distributed near t
he Galactic plane. For each calibrator\, there are at least 4 images obtai
ned from different epochs spanning at least 1 year. In this talk\, I will
introduce the construction of the image database of these calibrators\, an
d discuss the potential application on VLBI astrometry using this image da
tabase.\n\nhttps://events.saip.org.za/event/56/contributions/4671/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4671/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Defining Sources Selection and Celestial Reference Frame Stability
DTSTART;VALUE=DATE-TIME:20160317T080000Z
DTEND;VALUE=DATE-TIME:20160317T081500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4673@events.saip.org.za
DESCRIPTION:Speakers: César GATTANO (SYRTE - Observatoire de Paris)\nIn a
previous study\, we characterized radio sources observed by Very Long Bas
eline Interferometry by different criteria in both radio and optical domai
ns (see the abstract "VLBI sources in optical\nand radio"). On the basis o
f the data derived from this study\, we constructed several celestial refe
rence frames by choosing a set of defining sources and studied their stabi
lity by two ways\, statistically and temporally\, inspired by Lambert [201
3]. In parallel\, a re-analysis of the ICRF2 was made\, in the perspective
of ICRF3 (expected date : 2018)\, to estimate its current stability and i
f it has changed since 2009\, as it was the case for ICRF1 [ Gontier et al
. 2001\, Feissel-Vernier 2003\, Lambert et al. 2008\, Lambert & Gontier 20
09 ] . Finally\, an ambitious goal will be to develop by those works an au
tomatic tool that will regularly analyse new VLBI observation sessions and
will be able to alert the community on defining sources becoming potentia
lly unstable.\n\nhttps://events.saip.org.za/event/56/contributions/4673/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4673/
END:VEVENT
BEGIN:VEVENT
SUMMARY:INVITED TALK: IVS contribution to the ITRF2014
DTSTART;VALUE=DATE-TIME:20160316T102500Z
DTEND;VALUE=DATE-TIME:20160316T105000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4676@events.saip.org.za
DESCRIPTION:Speakers: Sabine Bachmann (BKG)\nGenerating the contribution o
f the International VLBI Service for Geodesy and Astrometry (IVS) to the I
TRF2014 was the main task of the IVS Combination Center at the Federal Age
ncy for Cartography and Geodesy (BKG\, Germany) in 2015. Starting with the
ITRF2005\, the IVS contribution to the ITRF is an intra-technique combine
d solution using multiple individual contributions from different institut
ions.\nFor the ITRF2014 nine international institutions were used for a co
mbined solution. The data files contain 24h VLBI sessions from the late 19
70s until the end of 2014 in SINEX file format containing datum free norma
l equations with station coordinates and Earth orientation parameters (EOP
). All contributions have to meet the IVS standards for ITRF contribution
in order to guarantee a consistent combined solution.\nIn the course of th
e generation of the intra-technique combined solution\, station coordinate
time series for each station as well as a terrestrial reference frame bas
ed on the contributed VLBI data (VTRF) were generated and analyzed.\nThe d
ata analysis\, the combination procedure and results of the combined solut
ion for station coordinates and EOP will be presented.\n\nhttps://events.s
aip.org.za/event/56/contributions/4676/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4676/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The structure of the radio source 0642+449 detected from CONT14 ob
servations
DTSTART;VALUE=DATE-TIME:20160317T093000Z
DTEND;VALUE=DATE-TIME:20160317T094500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4677@events.saip.org.za
DESCRIPTION:Speakers: Minghui XU (Shanghai Astronomical Observatory)\nThe
CONT14 campaign features state-of-art VLBI data. Therein\, the radio sourc
e 0642+449 was observed with about one thousand observables each day durin
g the continuous observing period of fifteen days\, providing tens of thou
sands of closure delays\, the sum of the delays around a closed loop of ba
selines. The closure delay is independent of the instrumental and propagat
ion delays and provides valuable additional information about the source s
tructure. An example of the use of this new “observable” for the deter
mination of source structure is given for the radio source 0642+449. This
source\, as one of the defining sources in the second realization of the I
nternational Celestial Reference Frame (ICRF2)\, is found to have two poin
t-like components with separation of 425 milliarcseconds in right ascensio
n and 47 milliarcseconds in declination. The two components are almost equ
ally bright with the flux-density ratio up to 0.92. With the help of recen
t space VLBI observations at 1.6 GHz\, the morphology of 0642+449 could be
identified to some extent. The closure delays larger than 1 ns are found
to be caused by the source structure as well\, demonstrating the structure
effect of a source with this simple structure could reach up to tens of n
anoseconds\, at least one magnitude larger than expected. We anticipate ou
r study to be a starting point for more effective determination of the str
ucture effect in VLBI observations without the involvement of radio source
images.\n\nhttps://events.saip.org.za/event/56/contributions/4677/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4677/
END:VEVENT
BEGIN:VEVENT
SUMMARY:An Inequality Constrained Least-Squares approach as an alternative
estimation procedure for atmospheric parameters from VLBI observations
DTSTART;VALUE=DATE-TIME:20160317T101500Z
DTEND;VALUE=DATE-TIME:20160317T103000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4679@events.saip.org.za
DESCRIPTION:Speakers: Sebastian Halsig (Institute of Geodesy and Geoinform
ation\, University of Bonn)\nOn its way through the atmosphere\, the signa
ls of space-geodetic techniques\, such as GNSS or VLBI\, are delayed and a
ffected by bending and attenuation effects relative to a theoretical path
in vacuum. Changing atmospheric conditions contribute considerably to the
error budget of the observations. At the same time\, space-geodetic techni
ques play a crucial role in the understanding of the Earth's atmosphere\,
because atmospheric parameters can be linked to the water vapor content in
the atmosphere.\n\nIn the VLBI data analysis\, the tropospheric delay is
usually taken into account by applying an adequate model for the hydrostat
ic component and by additionally estimating zenith wet delays for the high
ly variable wet component. Unfortunately\, the standard Least-Squares appr
oach sometimes leads to negative estimates\, which would be equivalent to
negative water vapor in the atmosphere and does of course not reflect the
meteorological and physical conditions in a plausible way.\n\nTo cope with
this phenomenon\, we introduce an Inequality Constrained Least-Squares (I
CLS) method from the field of convex optimization and use inequality const
raints to force the tropospheric parameters to be non-negative allowing fo
r a more realistic tropospheric parameter estimation in a meteorological s
ense. The impact of the ICLS approach will be validated with regard to sta
tion positions. Since deficiencies in the a priori hydrostatic modeling ar
e almost fully compensated by the tropospheric estimates\, the ICLS approa
ch urgently requires suitable a priori hydrostatic delays. Thus\, we prese
nt strategies to deal with missing or incorrect a priori model data.\n\nht
tps://events.saip.org.za/event/56/contributions/4679/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4679/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Application of Kalman filtering for the determination of a VLBI te
rrestrial reference frame
DTSTART;VALUE=DATE-TIME:20160316T121500Z
DTEND;VALUE=DATE-TIME:20160316T123000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4680@events.saip.org.za
DESCRIPTION:Speakers: Benedikt Soja (GFZ German Research Centre for Geosci
ences)\nTerrestrial reference frames (TRF) of high quality are indispensab
le for many geoscientific and geodetic applications including very long ba
seline interferometry (VLBI) data analysis. While secular station coordina
te changes\, e.g. due to tectonic plate motion\, can be well represented b
y a linear model\, current accuracy requirements also demand modeling of n
on-linear signals such as surface deformations due to mass loading or post
-seismic deformations. The ITRF2014\, for instance\, includes coefficients
for exponential and logarithmic functions after major earthquakes. Anothe
r approach\, used for the determination of JTRF2014\, is the application o
f Kalman filtering that allows post-seismic displacements to be accounted
for in a non-parametric manner.\n\nIn this paper\, we portray a TRF soluti
on solely based on VLBI data\, employing Kalman filtering and smoothing fo
r the computation of session-wise coordinates of more than hundred VLBI ra
dio telescopes over more than 30 years. By using a random walk process\, n
on-linear coordinate changes are modeled stochastically. The noise model i
s derived from loading deformation time series that are not included in th
e model for the station motion (i.e.\, non-tidal atmosphere\, non-tidal oc
ean\, and continental water storage loading). This stochastic model alone
is not able to adapt to the large coordinate variations that can happen af
ter major earthquakes. Therefore\, we additionally increase the process no
ise in the periods following earthquakes based on the amplitude of the est
imated coordinate jumps\, introducing the epochs of the seismic events as
prior information.\n\nWe compare our Kalman filtered and smoothed VLBI-TRF
to a classical least squares VLBI solution calculated by the VieVS@GFZ so
ftware\, based on linear segments between episodic events. Additionally\,
multi-technique TRF\, such as the ITRF2014 and JTRF2014\, are included in
the comparisons\, especially for assessing the different approaches of mod
eling post-seismic deformations.\n\nhttps://events.saip.org.za/event/56/co
ntributions/4680/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4680/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Combination of the two radio space geodetic techniques with VieVS
during CONT14
DTSTART;VALUE=DATE-TIME:20160316T124500Z
DTEND;VALUE=DATE-TIME:20160316T130000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4687@events.saip.org.za
DESCRIPTION:Speakers: Younghee Kwak (Technische Universität Wien)\nUnlike
CONT11\, CONT14 does not have official information on common frequency st
andards for co-location sites. Nevertheless\, according to Kwak et al. (20
15)\, we have a possibility to find the co-located sites\, which used the
same clocks\, through comparing clock rates from single technique solution
s. Moreover\, CONT14 includes co-located VLBI radio telescopes\, i.e. HOBA
RT26 and HOBART12. Therefore\, it is a good test bed to develop the analys
is strategy for future twin/sibling telescopes.\nIn this study\, we comput
e GNSS single differences between the ranges from two stations to a satell
ite\, using phase measurements with most of the errors corrected by the c5
++ software. We estimate station coordinates and site common parameters\,
i.e. zenith wet delays\, troposphere gradients and clock parameters\, with
the Vienna VLBI Software. Common clock parameters are limited to the site
s that are sharing the same frequency standard during CONT14. Local tie ve
ctors are introduced as fictitious observations for co-located instruments
\, GNSS-VLBI and even VLBI-VLBI\, i.e. at Hobart. In this presentation\, w
e show the comparison results between the combination solutions and the si
ngle technique solutions in terms of station position repeatability during
15 days.\n\nhttps://events.saip.org.za/event/56/contributions/4687/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4687/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ultra-rapid earth rotation determination with VLBI during CONT11 a
nd CONT14
DTSTART;VALUE=DATE-TIME:20160317T123000Z
DTEND;VALUE=DATE-TIME:20160317T124500Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4689@events.saip.org.za
DESCRIPTION:Speakers: Rüdiger Haas (Chalmers University of Technology)\nI
n 2007 the Geospatial Information Authority of Japan (GSI) and the Onsala
Space Observatory (OSO) started a collaboration project aiming at determin
ing the earth rotation angle\, usually expressed as UT1-UTC\, in near real
-time. In the beginning of this project dedicated one hour long one-baseli
ne experiments were observed periodically using the VLBI stations Onsala (
Sweden) and Tsukuba (Japan). The strategy is that the observed VLBI data a
re sent in real-time via the international optical fibre backbone to the c
orrelator at Tsukuba where the data are correlated with a software correla
tor and analyzed in near-real time with the c5++ VLBI data analysis softwa
re\, thus producing UT1-UTC results with very low latency. The latency bet
ween the observation at the stations and the determination of UT1-UTC is o
n the order of a few minutes\, thus we can talk about an ultra-rapid deter
mination of UT1-UTC. An offline version of this strategy was adopted in 20
09 for the regular VLBI intensive series INT-2\, organized by the Internat
ional VLBI Service for Geodesy and Astrometry (IVS)\, that involves Wettze
ll (Germany) and Tsukuba. Since March 2010 the INT-2 is using real-time e-
transfer\, too\, and since June 2010 also automated analysis. Starting in
2009 the ultra-rapid approach was applied to regular 24 hour long IVS VLBI
-sessions that involve Tsukuba and Onsala\, so that ultra-rapid UT1-UTC re
sults can be produced already during ongoing VLBI-sessions. This strategy
was successfully operated during the 15 days long continuous VLBI campaign
s CONT11 and CONT14. In this presentation we give an overview of the ultra
-rapid concept\, present the results derived during CONT11 and CONT14\, an
d compare these ultra-rapid results to results derived from post-processin
g.\n\nhttps://events.saip.org.za/event/56/contributions/4689/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4689/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Effects on Earth Orientation Parameters caused by different analys
is options
DTSTART;VALUE=DATE-TIME:20160317T124500Z
DTEND;VALUE=DATE-TIME:20160317T130000Z
DTSTAMP;VALUE=DATE-TIME:20240329T065018Z
UID:indico-contribution-254-4690@events.saip.org.za
DESCRIPTION:Speakers: Robert Heinkelmann (GFZ Potsdam)\nThe Earth Orientat
ion Parameters (EOP) are arguments of the time-dependent rotation matrices
describing the difference in orientation between the Earth crust-fixed re
ference system\, ITRS\, and the space-fixed reference system\, ICRS. Very
Long Baseline Interferometry (VLBI) is the technique that connects the rea
lizations of ITRS and ICRS in terms of orientation directly on the observa
tion level. Many applications in spacecraft navigation\, fundamental astro
nomy\, astrometry\, and geosciences depend on the provision of the Earth O
rientation Parameters (EOP). Currently\, under the IAG/IAU Joint Working G
roup on the Theory of Earth Rotation\, activities are supported that foste
r the advance on the theory of Earth rotation. Some components of the Eart
h rotation\, such as the Free Core Nutation (FCN)\, are not well predictab
le but rely entirely on empirical determination through VLBI. In our paper
we step-by-step alternate different analysis options\, such as a priori d
ata and models\, and quantify the resulting effects on the EOP. Our approa
ch is purely empirical: we will alternate certain analysis options and ass
ess the differences with respect to the reference solution that adheres to
IERS Conventions (2010) and applies the parameterization that was used in
our contribution to ITRF2014\, the next realization of the ITRS. For demo
nstration we analyze current regular International VLBI Service for Geodes
y and Astrometry (IVS) sessions: IVS-R1 and –R4. The IAG flagship compon
ent GGOS (Global Geodetic Observing System) aims to realize EOP with an ac
curacy of 1 mm\, i.e. about 30 microarcseconds. This accuracy will be used
as a threshold to interpret the significance of the effects.\n\nhttps://e
vents.saip.org.za/event/56/contributions/4690/
LOCATION:
URL:https://events.saip.org.za/event/56/contributions/4690/
END:VEVENT
END:VCALENDAR