Patent ID: RE44214

Claim:
An unmanned optical emissions sensor for sensing a gas mixture composition of an exhaust plume of a motor vehicle travelling along a road, comprising: a source for radiating a beam of light along a path across a road such that the beam passes through the exhaust plume of a passing vehicle and otherwise passes through ambient air; a receiver for sampling radiation levels at a plurality of predetermined wavelengths from the beam; a canister for emitting a puff of calibration gas in the path of the beam between the source and the receiver, said calibration gas having a known reference composition at the predetermined wavelengths; a data processing computer for computing a gas mixture composition from the sensed radiation levels in accordance with stored calibration curves; a trigger device that produces a trigger signal when a vehicle passes through the beam causing the data processing computer to record the gas mixture composition of the vehicle's exhaust plume for a period of time; an automated control computer that a) calibrates the data processing computer by directing the canister to emit a puff of calibration gas, whereby the data processing computer recomputes the calibration curves in accordance with the known reference composition; b) verifies the calibration by directing the canister to emit a puff of calibration gas, whereby the data processing computer computes a test composition from the radiation levels and accepts the calibration when the test composition is close enough to the known reference composition and otherwise rejects the calibration and initiates recalibration; and c) monitors the gas mixture composition of the ambient air to control recalibration of the data processing computer; and a vehicle identification device that responds to the trigger signal by recording a vehicle identification for the passing vehicle.