Abstract: A method includes projecting light to obtain a reference measurement using a first photoresistor; collecting dust on a platform during a collection time interval; and projecting light across the platform to obtain a dust measurement using the first photoresistor or a second photoresistor.

Abstract: A method and apparatus for determining the position of a vessel in distress and transmitting an auditory distress message containing the position of the vessel. The apparatus obtains the position of the vessel as determined by a LORAN-C type receiver from either a cassette or directly from the LORAN-C receiver and generates a "Mayday" message including the identification of a vessel, the position of the vessel and the nature of the emergency. The "Mayday" message is synthesized into an auditory human or Morse code message. The language of the auditory message is preferably chosen to correspond with the most likely language used by a possible receiver of the "Mayday" message. Also preferably, the apparatus determines whether the primary distress radio frequency is clear; should the primary distress frequency be in use, the apparatus automatically shifts to a secondary frequency and transmits the "Mayday" message.