Near Infra-Red Hyper Spectral Imager version 7

Fred Sigernes^1,2, Marie Bøe Henriksen ², Sivert Bakken ², Joseph Garrett ², Eirik Selnæs Sivertsen ², Roger Birkeland ², Torbjørn Skauli ³ and Tor Arne Johansen ²

¹ The University Centre in Svalbard (UNIS), Norway
² Norwegian University of Science and Technology (NTNU), Trondheim, Norway
³ University of Oslo, Oslo, Norway

First, the source illumination in the NIR region can be identified in Figure 1. The wavelength region 700 - 1100 nm is less intens compared to the visible part of the spectrum and dominated by two atmospheric absorption bands (O₂ and H₂O).

The design is inspired [1] by the pushbroom HSI v6 onboard the HYPSO-1 satellite [2-4]. All components are off-the-shelf. Three 50 mm focal length NIR objectives from the company Edmund Optics (EO) is used in combination with a standard blazed transmitting grating from Thorlabs. The detector is a Black Silicon CMOS sensor from the company SiOnyx, LLC.

The optical diagram is shown in Figure 2. A 300 lines/mm blazed grating is the key element. Blaze angle is 31.7 degrees. The efficiency is above 55% for the wavelength region 700 - 1100 nm. The effective aperture may be set to D₀ = D₁ = 18 mm which corresponds to ~ F/2.8 The input slit width is fixed with no magnification or demagnification of the height (h = 10 mm). A slit width of w = 50 µm will result in a first order spectral bandpass (FWHM) of 3.33 nm.

The front lens focuses light from infinity onto the entrance slit plane. Light through the slit is collimated by the collimator lens to produce a parallel light beam that will illuminate the grating. These two lens objectives are chosen to be identical to preserve image quality through the system. The same mechanical solution as presented in [3] is used. See Figure 3.

The above parts are sufficient to create a prototype hyper spectral imager. All parts may now be embedded into a 3D printed design or a metal housing according to the angles and positions defined in the optical diagram. Note that a right-angle prism can be used between the collimator and the grating to make the design more compact in size. See figure below..

Item	Part / links	Description	Qty	Cost $
1	EO VIS-NIR 50 mm	50mm C VIS-NIR Series Fixed Focal Length Objective *	3	1785
2	EO 2nd order filter	M30.5 x 0.5 mounted UV/VIS Cut-Off filter	1	76
3	Thorlabs SM1A10	Adapter ring SM1 - C- mount internal	2	44
4	Thorlabs SM1M10	SM1 lens tube 1 inch long with internal threads	1	17
5	Thorlabs S50LK	Fixed high precision mounted slit	1	120
6	Thorlabs SM1RC	Slip Ring - SM1 tubes	1	27
7	Thorlabs Spacer Rings	Thorlabs C-mount 0.25-2mm space ring kit	1	119
8	Thorlabs GTI25-03A-NIR	(25 x 25) mm 2 Blazed Trans. grating (300 grooves/mm)	1	116
9	Thorlabs right-angle prism	N-BK7 Right-Angle Prism, Uncoated, L = 25 mm	1	64
10	Sionyx RD board	Black Silicon sensor (12.3 x 9.9) mm2	1	790
11	3D printer material	PRUSA Jet Black PETG filament	1	27
		Total	14	3185

Table 1. Detailed part list NIR HSI v7. *One option could be to use the KOWA 50 mm ruggedized lenses instead of the EO VIS-NIR 50 mm proposed lenses used in the HSI v6.

A pushbroom Near Infra-Red Hyper Spectral Imager design (NIR HSI v7) is described using off-the-shelf components. The spectral range is approximately 700 - 1100 nm with a spectral resolution less than 4 nm. Spatial resolution and senstivity is expected to be comparable to the HSI v6 on board the HYPSOP-1 satellite. Total part cost of prototype is estimated to be less than 4k USD.

1. Fred Sigernes, Mikko Syrjäsuo, Rune Storvold, João Fortuna, Mariusz Eivind Grøtte, and Tor Arne Johansen, Do it yourself hyperspectral imager for handheld to airborne operations, Opt. Express 26, 6021-6035 (2018), https://doi.org/10.1364/OE.26.006021
2. M. E. Grøtte, R. Birkeland, E. Honore-Livermore, S. Bakken, J. L. Garrett, E. F. Prentice, F. Sigernes, M. Orlandic, J. T. Gravdahl, T. A. Johansen, Ocean Color Hyperspectral Remote Sensing with High Resolution and Low Latency - the HYPSO-1 CubeSat Mission, IEEE Trans. Geoscience and Remote Sensing, Vol. 60, pp. 1-19 (2022), https://doi.org/10.1109/TGRS.2021.3080175
3. M. Henriksen, E. Prentice, C. van Hazendonk, F. Sigernes, and T. Johansen, Do-it-yourself VIS/NIR pushbroom hyperspectral imager with C-mount optics, Opt. Continuum 1, 427-441 (2022), https://doi.org/10.1364/OPTCON.450693
4. S. Bakken, M. B. Henriksen, R. Birkeland, D. D. Langer, A. E. Oudijk, S. Berg, Y. Pursley, J. L Garrett, F. Gran-Jansen, E. Honore- Livermore, M. E. Grøtte, B. A. Kristiansen, M. Orlandic, P. Gader, A. J. Sørensen, F. Sigernes, G. Johnsen and T. A. Johansen, HYPSO-1 CubeSat: First Images and In-Orbit Characterization, Remote sensing, 15(3), 755 (2023), https://www.mdpi.com/2072-4292/15/3/755
5. Post by Harron, All you need to know about Solar Radiation, http://synergyfiles.com/2016/05/solar-radiation/