Gate time

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In the transit time measurement method, the gate time is the short period of time after which, at the earliest , the reflected signal is expected. Occasionally one speaks of echo time.

The gate time calculated in advance from the approximate position of the transmitter and receiver is entered into the program of the interval counter in the receiver and ignores all (presumably false) echoes that arrive before it expires. The term takes its name from this indirectly restricted opening time for the recipient.

A realistic gate time is particularly important for laser distance measurements to earth satellites, because at greater distances (from around 5,000 km) only a few light quanta come back that have to be detected with certainty. The problem is even more serious with daytime observations , where daylight is a million times brighter than the echoes to be measured from the satellite.