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NAPS provides an estimate of the surface peak noise intensity in all directions surrounding a blast source while accounting for meteorological and topographical variations. The NAPS model defines the focusing and shadow regions in the area surrounding an airblast by generating acoustic ray traces over a sufficient range of azimuth and elevation angles. The acoustics of the model include the effects of spherical acoustic spreading, absorption, focusing, shadow zones, reflection of rays from water, interference of multiple rays arriving at the same location, and the directional asymmetry of a blast wave. The background information was taken from a paper published in September 1991 {UDR-TR-91-87, Technical Reference Guide for Noise Assessment Prediction System (NAPS)}.

The meteorological input parameters for the NAPS model include wind speed and direction, temperature, and humidity. The required blast source inputs include intensity, type, location, and height above ground. Additional requirements include a detailed map of terrain features for the surrounding area. The computational limits of the NAPS model include 5-degree increments of azimuth, increments as required in elevation, 200 meter ray-tracing increments along the radial direction, and 3000 meter height and 40,000 meter distance. A set of generic blast specifications and terrain features are currently used to initialize a set of graphics for the NAPS interface. These standards are a 20-pound blast weight detonated at 1 meter above the ground at Abbey Point. These specifications can be altered to determine the effects of specific tests and locations.

The NAPS model begins running immediately after the MM5 model completes its run to generate the Abbey Point loop. Currently, the NAPS model requires all of the MM5 model output to be available before it can run. A proposed update to the NAPS software is to allow it to run in conjunction with the MM5. The hourly incremental images that have been completed to that time are viewable, while those that have not been completed will show a "Please Stand By" image.

The NAPS output is displayed via a graphical movie interface. You can watch the loop progress in a movie-like fashion or use the control icons found on the page to control the stepping of the data images. A coded legend displays the decibel levels contained by each set of colors, shown in Figures 2 and 3. Additionally, the controls for the movie loop itself are included in this figure. The two modes for the movie loop include a continual loop and a single run of the movie frames in the forward or reverse direction. The buttons under the movie loop and to the left are links to the Skew-T movie loop page, the Raw Data page, and the Blast Specifications page. The buttons to the right are to decrease and increase the speed of the movie loop, respectively. The numbered boxes below the buttons allow you to omit specific frames of the movie loop. The content of the NAPS movie loop are a series of images created from the vertical meteorological MM5 output at each forecast hour for the current MM5 model run. The images show the acoustic effects of a standard blast as determined by the standard blast specifications. An available Skew-T movie loop allows users to see the predicted vertical structure of the atmosphere and how it affects the NAPS output. The Raw Data consists only of the meteorological data required for the model run. The Blast specifications are input as desired, and the terrain data files are considered to be static.