Time series visualization tools through a Virtual Observatory in geodesy 1 DELEFLIE
1 BERTHIER
2 BARACHE
Florent Jérôme Christophe 2 2 3 Laurent SOUDARIN Christophe PORTMANN Sébastien LAMBERT 2 5 Sébastien BOUQUILLON Xavier COLLILIEUX
1-IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides / GRGS, Paris, France 2-Observatoire de Paris/SYRTE, GRGS, Paris, France 3- CLS, Toulouse, France 4- Observatoire de la Côte d’Azur, France 5- IGN/LAREG, GRGS, Paris, France Corresponding author:
[email protected]
Abstract This poster presents the context of the astronomical Virtual Observatory (VO), an ambitious international proposal to provide uniform, convenient access to disparate, geographically dispersed archives of astronomical data from software which runs on the computer on the astronomer’s desktop. The VO could be of interest for the geodetic community: we present here some of our efforts in this direction that we have recently achieved, concerning the visualization of time series obtained from the analysis of space geodetic techniques. Some of these products are now natively built and archived following the data format recommended by IVOA, the VO-Table format. We present this format, which is based on the XML format, and we list the reasons why we chose to use it. Astronomers using that Virtual Observatory are now organized within an international association called the International Virtual Observatory Alliance (IVOA). As noted on the IVOA website (http://www.ivoa.net/), IVOA was formed in June 2002 with a mission to "facilitate the international coordination and collaboration necessary for the development and deployment of the tools, systems and organizational structures necessary to enable the international utilization of astronomical archives as an integrated and interoperating virtual observatory." 1. What is the Virtual Observatory? Virtual Observatory (VO) is an ambitious international proposal to provide uniform, convenient access to disparate, geographically dispersed archives of astronomical data from software which runs on the computer on the astronomer’s desktop. The VO could be of interest for the geodetic community: we present here some of our efforts in this direction that we have recently achieved.
The first step on this development was to provide our data and products in VOTable format. GRGS Analysis Centers (ILRS AC, IVS AC, IGS AC, IVS AC) offer all the operational products and the IERS/ICRS-PC products in VOTable format, including station coordinates and Earth Orientation Parameter time series.
Astronomers using that Virtual Observatory are now organized within an international association called the International Virtual Observatory Alliance (IVOA). As noted on the IVOA website, IVOA was formed in June 2002 with a mission to "facilitate the international coordination and collaboration necessary for the development and deployment of the tools, systems and organizational structures necessary to enable the international utilization of astronomical archives as an integrated and interoperating virtual observatory."
Visit the IVOA Website ! http://www.ivoa.net/
2. Why choosing the Virtual Observatory?
? Several thousand users worldwide in the astronomical community. ? Existing standards. ? Existing self descriptive format based on these standards and XML : the VO-TABLE. ? Many tools already exist to manage, plot or analyze data supplied in VO-TABLE format (described non-ambiguously). Convert ones own data in VO-TABLE format means benefiting of all existing tools. ? Easy access to data by other scientific communities. Data that need to be distributed can be registered to a "registry". See for Figure 2: Plot of the quasars of the example http://esavo.esac.esa.int/registry/. Large Quasar Astrometric Catalogue (LQAC) of ? Successful project in Astronomy. The hisSouchay et al. (2008). Illustration of the tool torical collaboration and close foundation Aladin, freely available that manipulates VObetween Astronomy and geodesy encourTABLE. ages an adoption of VO standards by the geodetic community.
Figure 5: IVS-OPAR http://ivsopar.obspm.fr/vo/
Figure 3: Example of a VOTable formatted file: the ICRF-Ext.2 catalogue available at http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/AJ/127/3587/Such files can easily and automatically be built thanks to dedicated tools from common ASCII files, such as "stilts" and "TOPcat". We proposed in 2008 to the IVOA the new standards relevant to the Earth orientation data (polar motion, UT1-UTC, nutation etc.) and to space geodesy that have been adopted. VOPlot and TopCat are examples of software that use VOTables (data plotting). Aladin, created in 1999, is an interactive software sky atlas allowing the user to visualize digitized astronomical images in multi-wavelength, superimpose entries from astronomical catalogues or databases.
4. Geodetic products available in VOTable format and their associated services
4.1 Celestial Reference Frame
Virtual
Observatory
portal
We developed two web-tools to assist LLR observers. • The first tool offers the capability to compute predictions of topocentric and geocentric coordinates of lunar targets (as retro-reflectors or craters) and predictions of round-trip times of laser-pulses between terrestrial stations and lunar retro-reflectors. • The second tool allows observers to compute differences between their LLR observations and POLAC reduction model for LLR data. The residuals Figure 6: Lunar Laser Ranging: Support Tools for observers obtained in this way allow (http://polac.obspm.fr/PaV/) observers to have a validation of their observations. These tools can be used in already operational observatories for the laser lunar ranging but they are more particularly aimed at the new teams who begin to carry out LLR observations. A proof of the usefulness of this tool is its use by MeO station during winter 2012-2013 to obtain a signal back from the lost reflector Lunokhod 1 for the fist time since the start of LLR observations in the early eighties. north :
STATISTICS:
Station
mean
wrms
Slope
Period
TLSA ids12wd01
-63.7mm
12.38mm
13.76+/-0.71mm/year 1993/01/12-1997/08/12
TLHA ids12wd01
35.91mm
9.37mm
13.19+/-0.18mm/year 1997/08/26-2007/07/03
TLSB ids12wd01
133.15mm
7.58mm
15.4+/-0.4mm/year 2007/07/03-2011/12/25
east : Station
3. Exchanging, understanding and analyzing geodetic data: thanks to VOTable data format
mean
wrms
Slope
Period
TLSA ids12wd01
-86.91mm
18.29mm
19.14+/-0.99mm/year 1993/01/12-1997/08/12
TLHA ids12wd01
49.62mm
14.89mm
18.66+/-0.26mm/year 1997/08/26-2007/07/03
TLSB ids12wd01
177.74mm
10.79mm
17.56+/-0.56mm/year 2007/07/03-2011/12/25
up : Station
The VOTable Data Exchange Format
mean
wrms
Slope
Period
TLSA ids12wd01
1.11mm
15.96mm
0.27+/-0.86mm/year 1993/01/12-1997/08/12
TLHA ids12wd01
-0.94mm
11.58mm
0.8+/-0.22mm/year 1997/08/26-2007/07/03
TLSB ids12wd01
0.53mm
8.78mm
-0.58+/-0.46mm/year 2007/07/03-2011/12/25
VOTable is a XML-based format for representing astronomical catalogues (properties of celestial objects : celestial coordinates, brightness etc.). The VOTable has been defined in terms of XML in order to take advantage of computerindustry standards and to utilize standard software and tools. At the same time it is important not to lose the previous investment in astronomy-specific standards, such as the tables variants of the FITS (Flexible Image Transport System) format. Also, astronomical, as well as geodetic tables are rich in metadata, which in this context means annotation, interpretable by either computers or humans, both of the tables and the individual columns that they contain. It is important that these metadata should be preserved with the table and the VOTable has features to permit this. Adopting VOTable does not mean giving up of its own data format. VOTable may encapsulate existing files and simply supplies metadata to understand its content and facilitate data exchanges. VOTable is designed to describe a wide variety of physical parameters. However when it is itself not sufficient for an accurate description of complex data, it can be used conjointly with an external data model. An example of such model for reference system is the STC (Space-Time Coordinate Metadata for the Virtual Observatory) .
Figure 4: ICRF-ext2 available through the portal of the ICRF product center web site catalogue available at http://hpiers.obspm.fr/webiers/
4.2 Terrestrial Reference Frame ITRF2000 and ITRF2005 tables are provided in VOTable format for testing. XSLT ’Extensible Stylesheet Language Transformations’ stylesheets are also provided to easily visualize VOTable without XML tags (for example in major web browers). In the next release of ITRF web site (beg. of 2014), all Tables, namely ITRF solutions but also station position residual series from ITRF combinations will be provided in VOTable format. See : http://itrf.ign.fr/VO.php
4.3 GRGS Analysis Centers, in the frame of IDS, ILRS, IVS
Figure 7: Example of a coordinates time series provided by IDS @ CLS, containing as well additional information (here: satellite events)http://ids-doris.org/plottool/stcd/stcdtool.php • These tool contain utilities for selecting sites or satellites, displaying time series, editing data, changing plot appearance, specifying scaling, downloading data, plots and graph statistics in several formats. • They are equipped with statistic tools for the calculation of mean, slope and weighted rms with respect to the slope (WRSD). • Several series can be viewed and compared on the same graph. Complementary data about station and satellites events can also be displayed. •A help online is available for both tools.
5. Associated fields of research
Metrology in the Earth environment EGU General Assembly 2013, Wien, April 2013, Session GI1.5: EGU2013-13105
Trajectory Analysis
