Abstract:
Atmospheric turbulence degrades angle-of-arrival (AOA) estimates derived from acoustic receiver arrays by reducing mutual coherence between the array elements. This turbulent degradation becomes most important for large propagation distances and high frequencies. Theoretical array performance is assessed by calculating Cramer--Rao lower bounds (CRLB) on the AOA estimates. CRLB calculations are presented for several different turbulence models and propagation environments. The reduction in mutual coherence is found to be caused almost exclusively by wind velocity fluctuations generated by near-ground wind-shear instability (i.e., small-scale turbulence). Large-scale eddies may play an indirect role by creating regions of locally high shear, and hence locally high C[inf V][sup 2] (the structure-function parameter for velocity).