Diapositiva 1

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S. Casotto, P. Zoccarato, A. Nardo, M.
Bardella CISAS University of Padua
ASI/EUMETSAT Meeting ASI Space Geodesy Center
Matera, 04-05 February 2009
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SWOrD Software purposes

• Multisatellite LEO-MEO orbit determination based
  on GPS measurements
• LEO-MEO orbit prediction
• Modeling and prediction of Radio Occultation (RO)
  events
• High precision reconstruction of SST velocities

• Adoption of HPC techniques
• Computation kernel separated from the process
  communications layer
• Low latency
• POD
• Dynamic
• Reduced Dynamic
• Kinematics

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ROSAROSSA(Research and OperationalSatelliteand
SoftwareActivities)data flow
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SWOrD Programming paradigms

• GPStk fundamental and advanced GPS processing
  algorithms
• XML input and output manipulation with data
  binding through Code Synthesis utility
• Development and debugging Eclipse 3.1, Intel
  C/Fortran compiler 11 and the software
  construction tool SCons

• Object Oriented Programming (OOP)
• Singleton pattern to restrict instantiation of a
  class to one object
• C/Fortran interoperability
• Multi threads/OpenMP parallelization
• Database on RAM for input data administration
  based on BoostMultiindex library

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OOP advantages (1/2)
UTC Coordinated Universal Time UT Universal
time ET Ephemeris Time. Was used 1960-1983 TDT
Terrestrial Dynamical Time. Was used
1984-2000 TT Terrestrial Time TAI International
Atomic Time (Temps Atomique International) GPS
time TAI - 19 seconds
An example the Time_Tag class
ET 1960-1983 TDT 1984-2000 TT 2001-
UTC 1972 -
UT1
delta-UT UT1-UTC (max 0.9 sec)
delta-T TT-UT1
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OOP advantages (2/2)
An example of inheritance usage the Ground
Station and Satellite classes
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BoostMultiindex
The Boost Multi-index Containers Library provides
a class template which enables the construction
of containers maintaining one or more indices
with different sorting and access semantics
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XML data binding
Automatic
CodeSynthesis XSD is an open-source,
cross-platform W3C XML Schema to C data binding
compiler
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Ancillary data required

• Planetary Ephemerides (JPL)
• Models of gravitational field and
  terrestrial/oceans tides (JMG3, EGM96, EG4)
• Ground station solutions (IGS)
• EOP e Leap seconds (bulletins B e C from IERS,
  bulletin A from USNO)
• Solar and geomagnetic activity indexes (NGDC)
• IGS products
• ROSA navigation data
• OCEANSAT2 attitude
• ROSA receiver multipath pattern

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L1 Input Output
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L2 Input Output
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Logical model
Two main kinds of operational blocks interface
classes and application classes. The first
called application class triggers the reading
interface classes to acquire the input
data. During this process the input data are
manipulated to obtain a complete set of
information that will be later used by the other
application classes.
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Functional model
SWOrD contains a mathematical model of the world
used to process observational data. The
functional model of the system can be decomposed
into several components, which are the
counterpart to the physical model to be developed
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Flow chart
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Kinematic POD (1/2)
There exist several kinematic orbit determination
techniques based on either undifferenced,
doubly-differenced or triply-differenced
observables, but also on time-differenced phase
observables. All of the kinematic approaches to
GPS-based LEO OD, including the one adopted here,
make use of the fundamental contribution of data
provided by the IGS. These data include GPS SVs
orbits, clock solutions for both SVs and ground
stations, EOP and tropospheric zenith delay (TZD)
solutions. All these parameters are held fixed in
the solution process.
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Kinematic POD (2/2)
The strategy adopted in the SWOrD OD system is
based on the use of a combination of pseudorange
and phase observables differenced in time. The
procedure is illustrated on the left
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THANKS FOR YOUR ATTENTION