Orbit Visualization Tool User Guide

version 2.3

Contents:

• What is OVT?
• Operating system and graphics
• Coordinate systems
• Models
• Satellite orbits and attitude
• User interface

• Actors and scene
• The bow shock and the magnetopause
• Magnetic Models
• Magnetospheric Structure
• Fieldline mapping
• Ionospheric Electric Potential
• Data Visualization
• Time Control
• Orbit Monitor
• Dumping of orbit data
• Footprints
• CLUSTER configuration
• View Control
• Printing
• Miscellaneous 

The Orbit Visualization Tool is a software for visualization of satellite orbits in the Earth's magnetic field. The program can display satellite orbits in five coordinate systems (GEI, GEO, GSM, SMC, GSE), satellite footprints projected on the Earth's surface and shown in either geographic (GEO) or geomagnetic (SMC) coordinates. In addition to satellite orbits the software computes and displays various models of magnetospheric structures, magnetopause, bow shock and electric potential, geomagnetic activity, and interplanetary field conditions. The models are time-dependent through user-editable activity files, which control models structure and properties. The program can be used to plan operations or interpret measurements from scientific satellites, to prepare ground-based satellite coordination, or as educational tool in astronomy and geophysics.

OVT can be installed on any Unix or Windows 95/98/2000/ME/XP/NT. The graphics used in this program is based on a Visualization Toolkit (VTK), which uses 3D accelerating hardware if present, but will still work with a simple 2D graphics card.

The graphics is mouse maneuverable: left mouse button to rotate the picture, right mouse button to zoom in and out, and SHIFT+left mouse button to move the focus.

The graphics window shows objects in one of five geocentric Cartesian coordinates described below. Let us denote the unit vector toward the Sun by S and the unit vector along the magnetic dipole axis by D (positive northward).

• GEI: Geocentric Equatorial Inertial
  
  • X-axis pointing toward the first point of Aries (the position of Sun at vernal equinox).
  • Z-axis points toward geographic north.
  
  
• GEO: Geographic
  • Z-axis along the geographic north pole.
  • X-axis in the equatorial plane at the Greenwich meridian (longitude=0).
  
  
• GSM: Geocentric Solar Magnetospheric
  • X-axis pointing toward the Sun.
  • Y-axis perpendicularto the Earth magnetic dipole and the Sun direction (Y=DxX).
  
  
• SMC: Solar Magnetic Coordinates
  • Z=D
  • Y=ZxS

  The difference between GSM and SMC is rotation around the common Y axis by the dipole tilt angle.

  
  
• GSE: Geocentric Solar Ecliptic.
  • X-axis points toward the Sun.
  • Z-axis points toward the ecliptic north.

  In all coordinates the third axis, not mentioned above, completes the right handed Cartesian triad (X,Y,Z).

The footprint projections on the Earth are shown at an altitude of 100 km above the average sphere of 6373.2 km in two coordinates system: geographic GEO (longitude and latitude), and magnetic SMC (magnetic local time and magnetic latitude). Field line tracing is done with the selected magnetospheric model (internal + external). Please note that in SMC coordinates  footprints are shown as MLT (magnetic local time) and MLAT (magnetic latitude) that are equivalent to dipole geomagnetic coordinates. The corrected geomagnetic coordinates are not used for display purposes because they do not represent an orthogonal transformation and therefore cannot be included in the global coordinate transformation matrices.

• The magnetic field models include standard internal field model IGRF 1950-2000 and Tsyganenko models of the external magnetospheric field: T87, T89, T96 and T2001.
• The bow shock model is according to Farris et al, GRL, v. 18, p.1821, 1991, and Cairns et al., JGR, v.100, p.47,  1995
• The magnetopause model is according to Shue et al., JGR, v. 103, p. 17691, 1998.
• The electric potential model is according to D. Weimer, GRL,  23,  2549,  1996.

All these model implementations have user-editable time-dependent parameter data.

The orbital module includes a standard ESOC program for computing position and velocity of Cluster, Double Star or any other s/c with the orbital parameters defined in Long Term Orbit File (LTOF). For orbits defined by TLE (two-line elements) SGP4/SDP4 orbit propagator is used.

OVT distribution contains Cluster, Double Star, Polar, Fast and Astrid-2 satellites. To add another satellite - download the .tle or .ltof orbit file and click on the menu Satellites -> Import Satellite...

Latest Cluster orbit files can be downloaded from http://jsoc1.bnsc.rl.ac.uk/pub/fd_files/ltof/, orbital elements for civilian satellites used can be obtained from CelesTrak or NASA ftp.

The information about s/c start and stop time as well as it's approximate revolution period is availabe in satellite's Info window.

If a spin data file (e.g SatelliteName.spin) is present in the odata directory under OVT installation directory, it is used to compute orientation of the spin axis in respect to the magnetic field, velocity vector, and the sun direction. The .spin files must be in the format required for CLUSTER project, i.e.

1 P 1994-09-01T00:00:00Z 1994-09-07T12:30:00Z 341.00 77.00 14.ffffff 333.800 776.1 0.0 0.0 0.00 0.00 1994-09-01T01:10:00Z

User interface consists of one visualization window integrated with a tree-like control panel. Objects in the visualization window are mouse maneuverable: use left button to rotate the picture and right button to zoom in and out. To change the focus of the viewing scene one can use the middle button on Unix systems and Shift + left mouse button.

The picture shows orbit of the Cluster1 satellite in GSM coordinates, current satellite position at time 2001-03-02T21:00:00Z and the magnetic field line passing through the satellite at this position. The footprints are shown in GEO coordinates. The position and size of the labels can be controlled by the user.

The left-side panel shows list of actors that can be displayed on the right-hand side scene. Each actor has some editable properties and can be shown/hidden on the scene. This popup menu is activated with right-side mouse button, after a selection click with left-side button.

The bow shock and the magnetopause have editable properties that control their shape and positions. SWP is the solar wind pressure (nPa) and IMF stands for Interplanetary Magnetic Field.

Magnetic field models are controlled by the window shown in the left. Each model has an associated set of parameters which can be edited by the user. At present we have four version of the Tsyganenko models, which can be combined with IGRF or dipole internal field models. Tsyganenko 2001: The two IMF-related indices G1 and G2 take into account the IMF and solar wind conditions during the preceding 1-hour interval; their exact definition is given in the paper by N.A.Tsyganenko "A new data-based model of the near magnetosphere magnetic field. 2. Parameterization and fitting to observations". The paper is available online from anonymous ftp-area www-istp.gsfc.nasa.gov, /pub/kolya/T01 The checked MP clipping means that the terrestrial magnetic field lines are not allowed to go outside the model MP surface (more than 0.5 Re).

Each activity data can be edited by the Data Editor. The data record with the time earlier or equal to the requested time is taken from the Data Editor. If the requested time is earlier then the time of the first record - the first record is used.

Magnetospheric structure represents a shell of outermost field-lines which are determined from current magnetic field model. If MP clipping is set, the field lines are not permitted to extend outside the MP model. If the MP clipping is off, then the field-lines derived from the magnetospheric model can extend significantly beyond the MP model. However in such a case their footprint is very narrow and corresponds to the topological magnetic cusp (for models T87, T89). Fieldline thickness can be specified (view the image).

View from -Y    View from Z

On this pictures you can see magnetopause, in a wireframe representation, and a surface created from two fieldlines, starting form the Earth.

Electric potential.

To visualize data click on the satellite with the right mouse button and choose "Load Data..." Load Data Wizard will apear. The data file should contain two columns: 1-st - Time 2-nd - Magnitude Time can be specified as DATE-TIME pair or in days/hours/minutes/seconds. In the last case you will be asked by OVT to specify the offset time. DATE format: YYYY-MM-DD or YYYY/MM/DD or YYYY/DDD TIME format: hh:mm or hh:mm:ss or hh.hhhh or sssss.ss Data file example: # comment - this is a Polar current magnitude data 2001-12-30 12:00:00 4.5 2001-12-30 12:01:00 5.6 .........

The time setting (left) is self-explanatory. "<<" and ">>" buttons are used to shift the start time by the interval.

Orbit Monitor can be accessed by Sat's pop-up menu. Orbit Monitor shows the current satellite position, velocity, distance from the center of the earth, magnetic field conditions, derived from the magnetic field model, and footprint coordinates. The footprints are shown for both hemispheres, if exist. In addition, the orbit monitor shows the estimated radial distance to the current model of the magnetopause and the angle of the satellite spin axes with respect to the magnetic field vector, satellite velocity, and the sun direction. The later data require presence of the spin axis attitude file in the ODATA directory. The spin attitude file has suffix .spin and must be in the format required by the CLUSTER project. The .spin files included in the distribution contain artificial data for demonstration purposes. They should be removed or replaced by real data. Dumping of orbit data Dumper panel is expanded if "Dump >>" is pressed; "Log" will dump the data specified in the Dumper Settings Window to a selected file. "Log All" will dump the data for the whole orbit. "Settings" button pops-up dumper settings window. Data available for dumping: data from the orbit monitor, Bx, By, Bz, Dipole Tilt angle.

The picture shows footprint of CLUSTER1 over northern polar regions with time lables. The tic marks are every 5 minutes. Footprints can be shown either in GEO or in SMC coordinates.

Zooming at the CLUSTER spacecraft shows the spacecraft trajectories (red, black, green, magenta) and the threading field-lines (green). The satellite is depicted as a sphere or as cylinders with a small pyramid, depending on the absence or presence of the spin attitude files. In the later case, the pyramid shows the actual orientation of the spin axis. The color convention: Cluster 1 - red Cluster 2 - black Cluster 3 - green Cluster 4 - magenta

The CLUSTER configuration window shows configuration parameters of the four spacecraft. XYZ box shows the minimum box size in current coordinates that will confine all four spacecraft. Ellipsoid shows three axes of an ellipsoid that will confine all spacecraft. FAC box shows a box in local field-aligned coordinates around the gravity centre that will confine four spacecraft: dB-along the field-lines, dA-in the azimuthal (LT) direction, and dR-in the dBxdA, pseudo-radial direction. The configuration parameters are automatically saved in file ovt/userdata/clusters.conf.

The new version has useful control of the viewer position which can be selected as a top of any of the axes X, Y, Z, or the direction perpendicular to the orbit. The focal point can be a particular satellite, center of the Earth, or a given geographic point. Projection method can be parallel or perspective.

When printing or saving image make sure that the graphics is not covered by other window. The resolution of the hard copy corresponds to the resolution of screen objects. One can export image to a file and print or edit it with another program.

Time advance arrows < and > change time by one step within the requested interval. Double arrows << and >> move to the start or end points, respectively.

The Earth can be shown either as continents, or as geographic/polar grid.
The axis XYZ can be hidden/shown and refer to the current selection of space coordinates.
Frame grid in three space planes can be also shown in the picture. Frame properties are editable.
Caption text can be included in the graphics window. Font and size of the text can be changed by the user.

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Copyright © OVT Team, 2000-2002.