The effect of the environment on sensor performance is twofold. Signal level and local noise level are both affected by acoustic propagation. In performance analyses, noise level is often taken to be a spatially homogeneous and temporally constant value. This paper utilizes a three-dimensional propagation model to determine the detection properties of bottom-mounted passive low-frequency sensors. The parabolic equation (PE) model is used to propagate noise from a field of surface dipole sources to the sensor location. Summation of noise from the entire area under consideration yields the local noise level. Two environments are considered. In the Adriatic Sea, the acoustic environment emphasizes local noise sources. In the Florida Straits, noise from distant sources affects local noise levels.