Impact of Wavelength Shift in Relative Spectral Response at High Angles of Incidence in Landsat-8 Operational Land Imager and Future Landsat Design Concepts

The Landsat program plays an important role in providing continuous long-term multispectral moderate resolution observations of the earth’s surface. There is an interest by the community to improve the temporal sampling in future generations of the sensors. One way to achieve higher sampling is to collect imagery with a wider swath. For future instruments using multilayer dielectric filters for band selection, this has the further implication that light may enter the filters on the detectors at a higher angle of incidence, which will shift the center wavelength of the spectral bandpasses. Through simulation of a forest environment this paper explored the impact of this effect on measured spectral radiance and the normalized vegetation difference index. The effect is quantified both for angles of incidence seen in the current Landsat-8 Operational Land Imager as well as for pushbroom designs with up to 13° off-axis imaging. Results indicate the effect will be significant compared to instrument noise and comparable to the limit of current requirements on filter manufacturing tolerances.