BACKGROUND

Optically detecting particulates in fluids typically utilizes a light source to illuminate a particle (or many particles), and a train of collection optics to receive the scattered light from the particles. The properties of the received light (e.g., intensity, phase, polarization, wavelength, etc.) are analyzed to derive the properties of the particles (e.g., size, shape, type, etc.).

For example, particle sensors are laser-based sensors that use a light scattering method to detect and count particles in a concentration range in a given environment, such as particles in air. In some particle sensors, as particles pass through the light beam, the light source becomes obscured, which is recorded on a light detector. The light is then analyzed and converted to an electrical signal providing particulate size and quantity.

Various air data systems are used on vehicles such as aircraft to measure airspeed. While these air data systems generally provide the air data needed for safe and efficient operation of these vehicles, there is a need for other systems that can be used to measure airspeed in order to improve reliability and safety through common mode failure avoidance.

SUMMARY

A system comprises a particle sensor assembly, which includes at least one light source configured to transmit a light beam into an external interrogation air region; a set of receive optics configured to provide at least one receive channel, the receive optics configured to collect a scattered portion of the transmitted light beam from at least one particle in the interrogation air region; and an optical detector in communication with the at least one receive channel and configured to receive the collected scattered portion of the transmitted light beam. The optical detector is operative to measure a signal intensity as a function of time from the scattered portion, with the signal intensity indicating a particle size and a signal duration indicating motion of the at least one particle through the interrogation air region. A processor is in communication with the optical detector and is operative to determine a transit time of the at least one particle through the interrogation air region based on the signal duration; and compute an airspeed based on parameters comprising the transit time and a size of the light beam.

