EMIT Imaging Spectrometer Elements
- M1 (asphere)
- M2 (asphere)
- Dyson block: CaF2 lens with step
- Slit (30 μm width, 37.2 mm length)
- Diffraction grating (structured blaze)
- Order sorting filter (three zone)
- Detector (HgCdTe)
- 1280 x 480 pixel format
- 30 μm pixel size
Key EMIT Properties
|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.
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.