EMIT Instrument Specs

EMIT Imaging Spectrometer Elements

Two-mirror Telescope

  • M1 (asphere)
  • M2 (asphere)

Dyson Spectrometer

  • Dyson block: CaF2 lens with step
  • Slit (30 μm width, 37.2 mm length)
  • Diffraction grating (structured blaze)

FPA Assembly

  • Order sorting filter (three zone)
  • Detector (HgCdTe)
    • 1280 x 480 pixel format
    • 30 μm pixel size

Key EMIT Properties

F-number F/1.8
Cross-track FOV 11°
IFOV (cross-track x along-track) 155 x 71 μrad
Focal length 193.5 mm
Entrance pupil aperture 110 mm
Spectral Range 380 – 2500 nm
Spectral Sampling 7.4 nm

Optical configuration of the EMIT imaging spectrometer instrument.

EMIT uses an advanced two mirror telescope and high throughput F/1.8 Dyson imaging spectrometer. The telescope focuses light entering EMIT on the spectrometer slit where it passed through calcium fluoride crystal refractive element to the grating. The concave grating has a structured blaze written by electron beam lithography to optimize the diffraction efficiency over the full spectral range. After being dispersed into the spectrum by the grating, light passes back through CaF2 block to the order sorting filter and detector array.

EMIT instrument config

This is the EMIT instrument configuration for operation on the ISS. The optical elements of the telescope and spectrometer are contained within the Optical Bench Assembly (OBA). The electronics are contained within the Electronics Baseplate (EB). The electronics receive, amplify, and digitize the weak analog signals from the detector array. These high rate data are compressed and stored on a digital recorder for replay to the ISS for transmission to the ground. EMIT also includes a sophisticated thermal control system that is required to measure the signals in the short wavelength (infrared) region of the spectrum and for optoechanical stability. Heat generated within EMIT is radiated to space to maintain thermal balance.

  • Calcium floride crystal used in the EMIT Dyson imaging spectrometer.
    Calcium fluoride crystal used in the EMIT Dyson imaging spectrometer.
  • image of the mercury cadnium teluride detector array
    Mercury cadmium telluride detector array that is sensitive over the visible to short wavelength infrared spectral range.
  • image of the next-generation three-zone order sorting filter
    Next-generation three-zone order sorting filter that is required to measure the full EMIT spectral range with a single imaging spectrometer.
  • image of the pollished M1 mirror for the EMIT telescope
    Polished M1 mirror for the EMIT telescope.