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SWOrD SoftWare for Oceansat2 Orbit Determination. S. Casotto, P. Zoccarato, A. Nardo, M. Bardella CISAS – University of Padua. ASI/EUMETSAT Meeting ASI Space Geodesy Center — Matera, 04-05 February 2009. SWOrD : Software purposes.

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SWOrDSoftWare for Oceansat2 Orbit Determination

S. Casotto, P. Zoccarato, A. Nardo, M. Bardella

CISAS – University of Padua


ASI Space Geodesy Center — Matera, 04-05 February 2009

SWOrD:Software purposes
  • Multi–satellite 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
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 Boost::Multiindex library
GPS 1980 -

TAI 1958 -


Leap seconds


32.184s fixed


19 s fixed

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 -


delta-UT = UT1-UTC

(max 0.9 sec)

delta-T = TT-UT1

OOP advantages (2/2)

An example of inheritance usage: the GroundStation and Satellite classes


The Boost Multi-index Containers Library provides a class template which enables the construction of containers maintaining one or more indiceswith different sorting and access semantics

XML data binding


CodeSynthesis XSD is an open-source, cross-platform W3C XML Schema to C++ data binding compiler

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
logical model
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.

Functional model

SWOrDcontains 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

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 SV’s orbits, clock solutions for both SV’s and ground stations, EOP and tropospheric zenith delay (TZD) solutions. All these parameters are held fixed in the solution process.

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