Methods of, and systems for, detecting an airborne material. In a first preferred embodiment, a method is provided that includes deploying a cloud of optical sensors, illuminating at least a portion of the cloud with a flare, and detecting the cloud using the illumination provided by the flare. Preferably, the illumination is in the infrared, near infrared, or visible spectral range. Also, the sensors can be porous silicon sensors for measuring the concentration of either a chemical or biological agent. Moreover, the method may include deploying the flare while remaining concealed. Preferably, the spectrum of the flare is compared with the spectrum from the cloud of sensors.