PASSIVE ACOUSTIC LOCALIZATION ENHANCED WITH TOMOGRAPHY AND ACOUSTIC THERMOMETRY IN THE OCEAN

Passive localization has application for assessing the spatial distrib utions of calling animals. Improved localization is demonstrated in th e atmosphere when the sound speed and wind fields are simultaneously e stimated from sounds recorded on eight microphones spread over a 30 m by 20 m region. Localization errors in the horizontal and vertical dim ensions are 15 cm and 40 cm respectively, at two standard deviations. The accuracy degrades by a factor of three if the sound speed and wind fields are not estimated. Two other subjects are discussed. First, a Surface Suspended Acoustic Receiver (SSAR) is under development for st udying climatic temperature changes in the ocean. The SSAR's theoretic al range limit for detecting many marine mammal calls is about 100 km. Second, techniques are suggested for minimizing the possible impact o f low-frequency sounds from acoustic thermometry transmissions on the marine ecosystem. The simplest technique involves placing sound source s on autonomous moorings in nutrient depleted regions.