Determining metrics of a cloud atmosphere using time-difference measurements

A method for determining a metric of a cloud atmosphere near a flying aircraft equipped with a system for performing the method, the method comprising:

• projecting, via a light projector, a pulse of light into a cloud atmosphere;
• detecting, via a light sensor, a detected portion of the projected pulse of light backscattered by the cloud atmosphere;
• determining, via a peak detector, a peak amplitude of the detected portion;
• generating, by a sub-peak threshold generator, first and second sub-peak thresholds based on the peak amplitude of the detected portion, the first and second sub-peak thresholds are predetermined fractions of the peak amplitude determined by the peak detector, the first sub-peak threshold having a greater amplitude than the second sub-peak threshold;
• determining, via a timer, a time difference between a first post-peak reference time and a second post-peak reference time, the first post-peak reference time corresponding to a time at which the amplitude of the detected portion equals or crosses the first sub-peak threshold, and the second post-peak reference time corresponding to a time at which the amplitude of the detected portion equals or crosses the second sub-peak threshold;
• calculating, based on the peak amplitude of the detected portion via a processor, a backscatter coefficient;
• calculating, based on the time difference between the first post-peak reference time and the second post-peak reference time via a processor, an optical extinction coefficient;
• calculating, based on the calculated backscatter and optical extinction coefficients via a processor, the metric of the cloud atmosphere;
• and
• communicating the cloud metric to the flying aircraft.

A system for determining a metric of a cloud atmosphere near a flying aircraft equipped with the system, the system comprising:

• a light projector configured to project a pulse of light into a cloud atmosphere;
• a light sensor having a detection surface aligned with the laser projector so as to detect a portion of the projected pulse of light backscattered by the cloud atmosphere, the light sensor further configured to generate, at an output port of the light sensor, a detection signal indicative of the detected portion;
• a logarithm amplifier having an input port electrically coupled to the output port of the detector so as to receive therefrom the detection signal, the logarithm amplifier configured to generate, at an output port of the logarithm amplifier, an amplified signal indicative of a logarithm of the detection signal;
• a peak detector having an input port electrically coupled to the output port of the logarithm amplifier so as to receive therefrom the amplified signal, the peak detector configured to generate, at an output port of the peak detector, a peak signal indicative of a peak amplitude of an amplified signal;
• a sub-peak threshold generator that generates, based on the peak amplitude of the detected portion, first and second sub-peak thresholds that are predetermined fractions of the peak amplitude determined by the peak detector, the first sub-peak threshold having a greater amplitude than the second sub-peak threshold;
• a timer configured to determine a time difference between a first post-peak reference time and a second post-peak reference time, the first post-peak reference time corresponding to a time at which an amplitude of the logarithm signal equals or crosses the first sub-peak threshold, the second post-peak reference time corresponding to a time at which the amplitude of the logarithm signal equals or crosses the second sub-peak threshold;
• and
• a cloud metric calculator configured to:
• calculate, based on the peak signal, a backscatter coefficient;
• calculate, based on the determined time difference between the first post-peak reference time and the second post-peak reference time, an optical extinction coefficient;
• calculate, based on the calculated backscatter and optical extinction coefficients, the metric of the cloud atmosphere;
• and
• communicate the cloud metric to the flying aircraft.