BackForwardInstrument:  TOPCAT-II 

Instrument details
Full name TOPside ionosphere Computer Assisted Tomography
Purpose TOPCAT II derives the total electron content (TEC) of the propagation medium from the differential phase of the received GNSS signals. The calculated TEC allows for 4D mapping of the ionosphere.
Short description A triple-frequency GNSS receiver.
Background A research development.
Scanning Technique Limb view of GNSS satellites
Coverage / Cycle
Mass Power Data Rate


Providing Agency UKSA
Instrument Maturity Flown on an R&D satellite
Utilization Period: 2023 to 2025
Last update: 2022-11-07
Detailed characteristics
Satellites this instrument is flying on

Note: a red tag indicates satellites no longer operational, a green tag indicates operational satellites, a blue tag indicates future satellites

Instrument classification
  • Earth observation instrument
  • Active and radio-occultation sensor
  • GNSS radio-occultation
WIGOS Subcomponents
  • Subcomponent 1
  • GNSS radio occultation (basic constellation)
  • GNSS radio occultation sounder (basic constellation)
Mission objectives
Primary mission objectives
  • Ionospheric Vertical Total Electron Content (VTEC)
Evaluation of Measurements

The following list indicates which measurements can typically be retrieved from this category of instrument. To see a full Gap Analysis by Variable, click on the respective variable.

Note: table can be sorted by clicking on the column headers
Note: * Primary mission objective.
VariableRelevance for measuring this variableOperational limitationsExplanation
Geoid4 - fairHighly indirect.Radio-occultation processing implies precise orbitography. Geoid derived from multi-temporal analysis
Gravity field5 - marginalHighly indirect.Radio-occultation processing implies precise orbitography. Gravity field derived from multi-temporal analysis
Atmospheric density1 - primaryNo specific limitation.Measuring atmospheric density