Hyperspectral imagers are able to collect spectral information among a wide range of wavelength values using diffraction. Each wavelength will thus be detected by a separate row of the sensor. The spectral alignment test aims to test that the correct wavelengths are mapped onto the hyperspectral imager at the correct rows. The reference to be used is the sensor vs wavelength mapping trade-book on Architect with the correct specifications for the grating prism.
FINCH Payload Verification Plan
https://www.alluxa.com/optical-filter-specs/angle-of-incidence-aoi-and-polarization/
Ideally, we would be able to measure the spectral alignment of the entire range of the hyperspectral imager, between 0.9 -1.7 micrometers. However, this is too far out of the budget due to the need to purchase a tunable light source along with spectral filters. Since, the most important bands for capturing methane emissions are at 1610 nm, 1650 nm, and 1670 nm, we can focus on a smaller range of 1590 nm - 1690 nm instead. This can be accomplished by using a xenon lamp in conjunction with an integrating sphere to produce a uniform light source. Additionally, bandpass filters centered around the three aforementioned wavelengths can be used to direct a very small range of wavelengths onto the diffraction grating.
Furthermore, by changing the angle of incidence (AOI) of the spectral filter with respect to the light source, we can shift the wavelength of light down, at the cost of lower transmission of light. Thus, we should restrict the changing of the AOI to 30 degrees maximum, while preferably staying within 15 degrees. The new wavelength transmitted by the bandpass filter can be calculated as follows:
For the bandpass filters listed on the budget, which can be found in the following link below,
https://www.edmundoptics.ca/p/1650nm-cwl-12nm-fwhm-25mm-mounted-diameter/20313/
there is no mention of the exact material used nor the refractive index of the filter.