An aircraft comprising a system, the system comprising: a particle sensor provided to one side of an external interrogation air region, the particle sensor comprising: at least one light source configured to transmit a light beam into the 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 operative to measure a signal intensity, as a function of time from the scattered portion, the signal intensity indicating a particle size and a signal duration indicating motion of the at least one particle through the interrogation air region; and a processor in communication with the optical detector, the processor operative to: determine a transit time of the at least one particle through the interrogation air region based on the signal duration; determine a size of the at least one particle based on the signal intensity; and compute an airspeed based on parameters comprising the transit time, the size of the at least one particle, and a size of the light beam. a particle sensor provided to one side of an external interrogation air region, the particle sensor comprising: at least one light source configured to transmit a light beam into the 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 operative to measure a signal intensity, as a function of time from the scattered portion, the signal intensity indicating a particle size and a signal duration indicating motion of the at least one particle through the interrogation air region; and at least one light source configured to transmit a light beam into the 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 operative to measure a signal intensity, as a function of time from the scattered portion, the signal intensity indicating a particle size and a signal duration indicating motion of the at least one particle through the interrogation air region; and a processor in communication with the optical detector, the processor operative to: determine a transit time of the at least one particle through the interrogation air region based on the signal duration; determine a size of the at least one particle based on the signal intensity; and compute an airspeed based on parameters comprising the transit time, the size of the at least one particle, and a size of the light beam. determine a transit time of the at least one particle through the interrogation air region based on the signal duration; determine a size of the at least one particle based on the signal intensity; and compute an airspeed based on parameters comprising the transit time, the size of the at least one particle, and a size of the light beam.