| 摘要 |
Cloud altitude measurement is carried out in a step-by-step manner wherein the measuring distance is changed by a predetermined amount for each measurement step. First and second integrators respectively integrate reflected echo signals during respective first and second time intervals T1, T2 with T1<T2. The first integrator integrates reflected light pulses and noise and the second integrator integrates noise. The difference between the integrated signal outputs from the first and second integrators is determined by a summation device and a controllable level-sensing signal evaluating device emits a signal if the aforesaid difference exceeds a predetermined value. The signal evaluating device is controlled to emit the indicating signal when a number of consecutive measurement steps have been measured. The first and second integrators can be controlled to integrate over a plurality of consecutive measurement steps before being reset to zero or alternatively, integration is performed over one or more measurement steps at a time. In the latter case, the measuring apparatus further comprises an analog/digital convertor connected to the output of the summation device, an accumulator, and the digital output signal from the analog/digital convertor is transferred to the accumulator and the evaluation device after the predetermined number of measurements. The measurement apparatus can be further modified to include a shift register connected to the output of the analog/digital convertor and an accumulator having inputs respectively connected to the input and output of the shift register and wherein a timing circuit actuates the level-sensing signal evaluating device to examine the contents of the accumulator after each measurement step.
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