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Near-Infrared Spectrometer (NIRS)

Near-Infrared Spectrometer (NIRS) is the shortest wavelength instrument of the IRTS forcal-plane instruments. It is grating spectrometer. The grating and two linear detector arrays (12 pixels each) cover the wavelength range from 1.4 to 4 micron. The NIRS has been designed as an instrument to carry out the absolute spectrophotometry of the diffuse celestial sources, such as the near-infrared cosmic background radiation, interstellar UIR band emission at 3.3 micron, and the zodiacal light. Fairly large beam size, 8' by 8', and moderate wavelength resolution, ΔΛ~0.13 μm, were adopted to get large throughput. The NIRS actually reached very high sensitivities for those diffuse emissions. This database includes the images at 24 wavelengths.


Size135 x 154 x 102 mm3 (over all)
Weight1.18 kg
Entrance aperture1.4 x 1.4 mm2
Field of view8 x 8 arcmin2
Temperature1.8 K

Detection system

Element size1 x 0.5 mm2 (per element)
Number of elements24 (2 x 12 elements)
Wavelength coverage1.43-2.54 micron, 2.88-3.98 micron
Resolution0.12 (0.10 at channel 1)
Total capacitance~50 pF
Readout methodCharge-integrated amplifier
Temperature of J-FETs~70 K
Photograph of the NIRS assembled
NIRS assembled
Photograph of the NIRS detector & J-FET
NIRS detector & J-FET


For more details, refer to the following documents.

NIRS Explanatory Supplement [PDF]

"Flight performance of the Near-Infrared Spectrometer (NIRS)"
M. Noda, T. Matsumoto, M. Tanaka, H. Murakami, and M. Kawada
1996, in SPIE Proc.2817, Infrared Spaceborne Remote Sensing IV ed. M. S. Scholl and B. F. Andresen, p.248-257 [ SPIE ] [ ADS ]
"Near-Infrared Spectrometer on the Infrared Telescope in Space"
Manabu Noda, Toshio Matsumoto, Shuji Matsuura, Kunio Noguchi, Masahiro Tanaka, and Mark L. Lim
1994, The Astrophysical Journal, vol.428, p. 363-369 [ ADS ]

Last Modified: 20 July 2023