Comparison between a low-light-level visible channel and an IR channel for spaceborne night imaging.

摘要

Aiming at night time spaceborne imaging, we compare the expected performances of a low-light-level visible sensorwith a conventional IR sensor. The low-light-level visible sensor, an electron multiplier CCD (EMCCD), is a close toideal photon counting device, with possibly negligible dark current noise and negligible readout noise. This fact, alongwith the significant improvement of diffraction (about an order of magnitude), suggests an interesting competitionbetween the two technologies. In essence, this is a tradeoff between noise and optical performances (favoring the visiblechannel) and basic target radiance (favoring IR). Other factors such as reliability and cost can also play an important role.While we consider two different spectral ranges with different imaging content, we are able to conduct a cautioustheoretical comparison based on standard targets in various lighting conditions. We show that for a given set of systemparameters, even when lighting conditions are favorable, i.e. a night with a full moon, the low-light-level visible channelperformances are inferior to those of an IR channel. We also comment on the significance of the system working pointregarding performances under varying condition.