BackForwardInstrument:  SEM/SSB/X-2 

Instrument details
Acronym SEM/SSB/X-2
Full name SEM / Special Sensor Gamma/X-ray Detector
Purpose Location and spectrometry of gamma and X rays from the Earth's atmosphere
Short description Array-based spectrometer which detects the location, intensity and spectrum of X-rays in the range 3-60 keV and gamma-rays in the range 1.2-10 MeV, emitted from the Earth's atmosphere
Background Part of the Space Environment Monitor (SEM) package. SEM/SSB/X-2 is the latest version of several SSB sensors flown on previous DMSP satellites
Scanning Technique Earth's viewing under four angles, from a sunsynchronous orbit
Resolution N/A (integration over the field of view)
Coverage / Cycle Full ionosphere in 100 min (orbital period) with sampling at 1 s intervals
Mass Power Data Rate


Providing Agency DoD
Instrument Maturity Flown on operational programme
Utilization Period: 1976 to 2015
Last update: 2022-07-25
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
  • Solar and space environment monitors
  • Space radiometer or spectrometer
WIGOS Subcomponents
  • Subcomponent 1
  • X-ray spectrograph on GEO orbit
  • X-ray spectrometer at LEO
Mission objectives
Primary mission objectives
  • Gamma-ray flux spectrum
  • X-ray flux spectrum
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
Gamma-ray flux spectrum*1 - primaryNo specific limitation.Interplanetary space viewing including the Earth's limb, extending into the X-ray field
X-ray flux spectrum*1 - primaryNo specific limitation.Interplanetary space viewing, high spectral resolution, extending into the gamma-ray field
Aurora5 - marginalNo specific limitation.Aurora imaged in X-ray observing the Earth's limb