In a number of field tests for Unmanned Aerial Systems (UAS) acoustic detection, we used several detection systems including a 16 microphone cross two-tier acoustic array, directional acoustic microphones (parabolic microphones and shotgun microphones), and the OptiNav ACAM 120 acoustic array. The improvement of the detection distance using direction microphones and microphone arrays was less than what was estimated based on the system directivity index. A possible limitation of the directional system performance can be due to wind noise, presence of various noise sources and atmospheric turbulence conditions. The turbulence leads to decorrelation of the acoustic signal received by various elements of a microphone array. The UAS and noise signals recorded by the cross two-tier AFRL acoustic array was used for estimation of external noise and UAS signal correlation depending of the distances between microphones. The array is shaped like a two-tier cross, with each tier spanning 3 m and pseudo-logarithmic spacing between the elements. The coherence measurements between various microphone pairs were used for the estimation of the optimal size of a microphone array for UAS detection and optimal sensor separation for the Stevens Drone Acoustic Detection System (DADS). [Work supported by Air Force Research Laboratory under Contract No. FA8750-17-C-0190.]