Building Earth Observation Cameras

121Optomechanical Scanners

crystallographic orientation exhibit opposite electric charges in response to

temperature change. This can cause a displacement current to ow in an

external circuit, which can be detected. Pyroelectric detectors respond only

to changes in temperature. They have the maximum D* and fastest response

time compared to other thermal detectors.

Thermal detectors require a nite time to raise the temperature of the sens-

ing element to the nal value and hence a long time constant compared to

photon detectors, wherein an electronic transition is virtually instantaneous

on photon absorption. The time constant of thermal detec ...