Instrumentation to track the southern elephant seal

Abstract

Marine mammal researchers at the University of Tasmania actively study the southern elephant seal each year by attaching electronic instruments to the animal and recording environmental variables experience during their time spent at sea. When the animals return to land the instruments are recovered and the data downloaded. To further this research effort a companion instrument capable of recording magnetic bearing, pitch and roll and has been designed and constructed in prototype. The instrument measures and logs the earth's magnetic field in three axis and the direction of gravity in two axis. Measuring the vector magnetic field strength is accomplished using a three axis (x,y,z) magnetoresistive device which produces analogue voltage outputs X*,Y* and Z* representing its direction with respect to the earth's magnetic field. Measurement of orientation in terms of pitch and roll is achieved by using an analogue two axis (x,y) micromachined accelerometer. The analogue signals are then converted to digital using a 10 bit analogue to digital converter. The data logging instrument is microcontroller controlled and incorporates flash memory capable of storing over 4 million bytes of information. This represents 97 days of directional data if sampled every 10 seconds. To link the data from the instrument with data gathered from other instruments, accurate timing is used, facilitated by a precision clocking oscillator with accuracy in the order of plus/minus 1 minute per year.