| 摘要 |
A ceilometer operating according to a gating method integrates output signals from a light receiver. The output signals are passed by analog gating means during consecutive time slots following each other at the transmitter frequency and being phase shifted relative to transmitted light pulses. The phase shift of the time slots is varied stepwise after preset time intervals. Signals integrated during a time interval are digitalized, processed n a microprocessor and stored in a memory according to height values determined by respective phase shifts of the time slots. The micro-processors forms a smooth function of the signals accordint to height values, differentiates the smooth function, computes maxima and minima, determines maxima differing from a preset threshold value, and selects a maximum which with increasing height value is followed by a minimum. Then the smooth function is modified by substituting the function interval corresponding to the maximum/minimum pair by a linear function interval and the modified smooth function is integrated. If the integral of the modified function exceeds a preset constant value, a precipitation warning signal is displayed. If the selected maximum sufficiently exceeds a predetermined noise level, the height corresponding to the maximum is indicated as a cloud height. |
