System for detecting ice or snow on surface which specularly reflects light

Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting a pulse of polarized light onto said surface;
• means for receiving said pulse reflected from said surface;
• means for directing said reflected pulse onto a non-blocking optical path to a detector;
• means for directing said reflected pulse onto a blocking optical path to said detector;
• and
• one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated.

Apparatus for detecting on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting light over a transmitting path to said surface;
• means for receiving transmitted light;
• a receiving path for said transmitted light from said surface and from said substance to said means for receiving;
• optical means in at least one of said transmitting path and said receiving path;
• means for alternating said optical means between an optical non-isolator state and an optical isolator state;
• said means for receiving including means for measuring a first intensity of light received at said means for receiving when said optical means is in said optical non-isolator state, and means for measuring a second intensity of light received at said means for receiving when said optical means is in said optical isolator state;
• means for compensating said measured first intensity of light for effects of scattering and/or absorbing interference of said transmitted light;
• and
• means for comparing said compensated first intensity and said second intensity of light to a plurality of reference data to detect the presence of said substance on said surface.

Apparatus for detecting on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting light over a transmitting path to said surface;
• means for receiving transmitted light;
• a receiving path for said transmitted light from said surface and from said substance to said means for receiving;
• optical means in at least one of said transmitting path and said receiving path;
• means for alternating said optical means between an optical non-isolator state and an optical isolator state;
• means for measuring a first intensity of light received at said means for receiving when said optical means is in said optical non-isolator state and outputting a first signal;
• means for compensating said first signal for effects of scattering and/or absorbing interference of said transmitted light and outputting a compensated first signal;
• means for measuring a second intensity of light received at said means for receiving when said optical means is in said optical isolator state and outputting a second signal;
• means, responsive to a length of said receiving path, for range-correcting said first compensated signal and said second signal;
• means for comparing said range-corrected second signal to said range-corrected compensated first signal and outputting a ratio signal;
• means for calculating a threshold signal;
• and
• means for comparing said ratio signal to said threshold signal.

Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting a pulse of light over a transmitting path to said surface;
• means for receiving transmitted light;
• a receiving path for said transmitted light from said surface and from said substance to said means for receiving;
• means for splitting said transmitted light into a non-isolated portion and an isolated portion;
• means for delaying one of said non-isolated portion and said isolated portion relative to another thereof to produce a first-to-arrive signal and a second-to-arrive signal;
• said first-to-arrive signal being completed at an output of said means for delaying before said second-to-arrive signal arrives at said output;
• means for measuring a first intensity of said first-to-arrive signal and outputting a first signal;
• means for measuring a second intensity of light of said second-to-arrive signal and outputting a second signal;
• means for compensating said first signal for effects of scattering and/or absorbing interference of said transmitted light and outputting a compensated first signal;
• and
• means for comparing said compensated first signal and said second signal to reference data to detect the presence of said substance on said surface.

Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting a pulse of polarized light onto a surface;
• means for receiving said pulse reflected from said surface;
• means for directing said reflected pulse onto a non-blocking optical path to a detector;
• means for directing said reflected pulse onto a blocking optical path to said detector;
• one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated;
• and
• means for compensating said reflected pulse for effects of scattering and/or absorbing interference of said transmitted light.

Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

• means for transmitting a pulse of polarized light onto a surface;
• means for receiving said pulse reflected from said surface;
• means for directing said reflected pulse onto a non-blocking optical path to a detector;
• means for directing said reflected pulse onto a blocking optical path to said detector;
• one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated,
• said detector including means for measuring a first intensity of said reflected pulse directed onto one of said blocking and non-blocking optical paths not having said delay and outputting a first signal, and means for measuring a second intensity of said reflected pulse directed onto another one of said blocking and non-blocking optical paths having said delay and outputting a second signal;
• means for establishing thresholds for said first and second signals;
• and
• means, responsive to said means for establishing thresholds, for controlling an intensity of said transmitted pulse.

Apparatus for measuring horizontal visibility, comprising:

• means for transmitting a pulse of polarized light onto a reference surface;
• means for receiving said pulse reflected from said reference surface;
• means for directing said reflected pulse on a non-blocking optical path to a detector to isolate a non-blocking component of said reflected pulse;
• means for directing said reflected pulse on a blocking optical path to said detector to isolate a blocking component of said reflected pulse;
• means for measuring an amplitude of said non-blocking component and/or said blocking component;
• means for determining an attenuation coefficient by comparing said measured amplitude to a reference amplitude;
• and
• means for calculating the horizontal visibility based on the attenuation coefficient.