Resonon (United States)

Direct solar illumination disappears in the umbra when the Moon’s shadow creates a total solar eclipse. However, the sky above an observer in the umbra is not completely dark because of light that scatters into the umbra from the penumbra (partial eclipse region) and beyond. We show that a simple 2nd -order scattering model reproduces the brightness and color within a factor of 2 relative to measurements made with a radiometrically calibrated all-sky imaging system at the total solar eclipse of 21 August 2017 observed in Rexburg, Idaho USA. The model includes a first scattering point outside the umbra and a 2nd scattering point at the center of the umbra that redirects the light downward to the observer. The simulations show that the primary zenith skylight at the center of the umbra arises from light whose first scattering point is near an altitude of 10 km, the first scattering creates an orangish ring of light symmetrically around the horizon up to approximately 10° elevation, and the second scattering creates zenith skylight that is reduced by approximately four orders of magnitude from daylight and that has a slightly higher blue-red ratio than the daylight before and after the eclipse.

An automated procedure for tolerance assignment is described. Tolerances are assigned so as to minimize manufacturing cost, subject to a constraint on minimum acceptable lens performance. A simulation evaluates the cost-effectiveness of the program.

Measuring the Modulation Transfer Function (MTF) of a hyperspectral imaging spectrometer focused at infinity requires a longer optical path than is available in a typical laboratory. We describe a technique that uses images of rooflines on buildings of opportunity in a knife-edge-based MTF measurement. This technique only measures the MTF along one dimension. However, the hyper-spectral imaging systems characterized in this paper are particularly suited to a knife-edge technique, as imaging only takes place in one dimension of the array and spectral separation takes place along the other. The sharp edges needed in these measurements were provided by dark rooftops backlit by a uniformly cloudy sky. We have applied this technique to hyperspectral imagers that operate in the visible-near infrared (VNIR) and short-wave infraRed (SWIR) spectral bands. The data presented in this paper focuses on the characterization of the SWIR imaging spectrometer developed by Resonon Inc.