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 . <EOS>