Currently, APET includes a modified version of the Rotorcraft Noise Model (RNM, version 7). It also includes the newly developed Spectral Attenuation Method (SAM), which contains the Ray Tracing Program (RTP) and two versions of a Green's Function Parabolic Equation (GFPE) code. The third component of APET is an audibility prediction scheme initially called ICHIN (I Can Hear It Now), and further developed by Wyle as AUDIB.

APET is a unified process that brings together three standalone codes (SAM, RNM, and AUDIB) and coordinates their functionality by executive software. The version designation “A1.0” brands these codes as customizations for orchestrated use in APET. In particular, because the Wyle Release of RNM (version 7.0.3) was modified for importation of SAM output and inclusion of enhanced weather handling capability, this customization has been redesigned A1.0.

Similarly, because the input and output for AUDIB RNM v3.0 was APET-customized, it too is referred to by the A1.0 designator. The executive and SAM codes (which are new and created specifically for APET) are given the A1.0 tag as well for consistency. The executive software manages the APET process by coordinating user input and proper sequencing of SAM, RNM, and AUDIB so that execution of the component codes is transparent to the user, and interaction with APET consists of supplying the executive routine with the needed input files.

The process begins with appropriate input specification to the executive, followed by invocation of the first code SAM, which begins by creating a Cartesian grid over the user's specified terrain. SAM computes source noise attenuation at each of these locations by propagating the noise from the source location, accounting for ray bending, spreading, atmospheric absorption, ground effects, and variable weather along the noise path. The result, a two-dimensional table of ground attenuation at each grid point location, is then forwarded to RNM, which re-performs propagation of the noise from the source to the location, adding the appropriate SAM-supplied attenuations to its own computations. Finally, noise output from RNM is supplied to AUDIB, which computes probability of detection metrics at each ground point location as a function of both time and frequency.

This work was done by Dennis S. Pope of Analytical Services and Materials, Inc.; Charles D. Smith of Lockheed Martin Engineering and Science Corp.; David A. Conner of U.S. Army Vehicle Technology Center, ARL; Casey L. Burley and Stephanie Heath of Langley Research Center; and Xiao Di of the University of Mississippi. This software is available for use. To request a copy, please visit here.