Apparatus and method for determining precision reflectivity of highway signs and other reflective objects utilizing an optical range finder instrument

A method of remotely determining a coefficient of retroreflectance of an unknown retroreflective surface comprising:

• providing a signal transmitting and receiving range finder for transmitting a signal toward a target and receiving a return signal from said target, said range finder having a processor for determining distance from said range finder to said target and including a return relative measurement of return energy determining circuit therein and an attenuation factor database containing power attenuation factors for various return relative measurements of return energy;
• transmitting a first signal toward a standard target having a known coefficient of retroreflectance;
• receiving a first return signal from said standard target;
• determining a first relative measurement of return energy for said first return signal;
• determining a distance from said range finder to said standard target from a time of flight of said transmitted signal to and from said target;
• determining a first power attenuation factor for said return signal from said first relative measurement of return energy and said power attenuation factor database;
• calculating a reference reflectance factor for said standard target from said distance to said standard target, said known coefficient of retroreflectance and said first power attenuation factor;
• transmitting a second signal toward an unknown target;
• receiving a second return signal from said unknown target;
• determining a second relative measurement of return energy for said second return signal from said unknown target;
• determining a distance from said range finder to said unknown target;
• determining a second power attenuation factor for said return signal from said unknown target;
• and
• calculating an absolute coefficient of retroreflectance for said unknown target from said reference reflectance factor, said second power attenuation factor and said distance to said unknown target.

A method of remotely determining a coefficient of retroreflectance of an unknown retroreflective surface comprising the steps of:

• providing a signal transmitting and receiving range finder for transmitting a signal toward a target and receiving a return signal from the target, said range finder having a processor for determining distance from said range finder to said target and including a return relative measurement of return energy determining circuit therein, an attenuation factor database containing power attenuation factors for various return relative measurements of return energy and a reference reflectance factor database for various target retroreflective surfaces;
• recalling from said reference reflectance factor database a reference reflectance factor for an unknown target;
• transmitting a signal toward said unknown target;
• receiving a return signal from said unknown target,
• determining a relative measurement of return energy for said return signal from said unknown target;
• determining a distance from said range finder to said unknown target;
• determining a power attenuation factor for said unknown target from said relative measurement of return energy and said power attenuation factor database;
• and
• calculating an absolute coefficient of retroreflectance for said unknown target from said reference reflectance factor, said power attenuation factor and said distance to said unknown target.

An apparatus for determining an absolute coefficient of retroreflectance of a retroreflective surface comprising:

• a signal transmitter operable to transmit a signal toward a target;
• a signal receiver operable to receive a reflected signal from said target;
• a processor connected to said transmitter and receiver for determining a distance to said target from a time of flight of said transmitted and reflected signals to and from said target;
• a relative measurement of return energy determining circuit connected to said receiver and said processor for determining a relative measurement of return energy of said reflected signal;
• and
• a power attenuation factor database connected to said processor storing power attenuation factor data for various reflected relative measurements of return energy.

A signal transmitting and receiving range finder adapted for use in determining coefficients of retroreflectance of retroreflective target surfaces, said range finder comprising:

• a signal transmitter for transmitting a signal toward a target;
• a signal receiver for receiving a return signal reflected from said target;
• a microprocessor operably connected to said transmitter and said receiver programmed to compute coefficients of retroreflectance;
• a relative measurement of return energy measuring circuit coupled to said microprocessor for measuring a relative measurement of return energy of a return signal;
• and
• a power attenuation factor database operably coupled to said microprocessor for determining a power attenuation factor (Ka) for a relative measurement of return energy, wherein said microprocessor utilizes measured return signals and power attenuation factors from said database to calculate a coefficient of retroreflectance (RA) for said target.