NIRS : Near-Infrared Spectrometer

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.


Size 135 x 154 x 102 mm3 (over all)
Weight1.18 kg
Entrance aperture 1.4 x 1.4 mm2
Field of view 8 x 8 arcmin2
Temperature 1.8 K
Detection system
Element size 1 x 0.5 mm2 (per element)
Number of elements24 (2 x 12 elements)
Wavelength coverage 1.43-2.54 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
"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

Last Modified: 19 November 2018