Original Date: 07/20/1998
Revision Date: 01/18/2007

As part of its munitions demilitarization mission, SIAD has a contract with the U.S. Navy to destroy large missile rocket motors, such as Poseidon C-3 second stage motors. The motors contain large quantities of highly explosive materials, and can produce a high level of atmospheric noise when detonated. Depending on atmospheric conditions, this noise can propagate for more than 100 miles. To lessen the environmental impact and reduce the number of complaints from surrounding communities, SIAD is adapting and implementing a Sound Intensity Prediction System (SIPS) developed by the Navy.

SIPS is an acoustic ray tracing computer code that calculates the locations of both noise enhancements and noise reductions from the conduct of explosive operations. Originally, both the code and operational procedures for program interpretation were developed in the mid-1970s to manage noise generated by explosive operations at the Naval Surface Warfare Center in Dahlgren, Virginia. The original code was written in FORTRAN and required a mainframe computer to run. Now the program has been adapted to run on a personal computer, and modified to incorporate advancements in weather data sampling and the topography of the area of interest.

Monitoring atmospheric conditions involves a meteorological data collection system employing either radiosondes or Sonic Detection and Ranging Device (SODAR) technology to collect the upper air parameters. Radiosondes are carried aloft by helium-filled balloons so the scalar quantities of wet and dry bulb temperatures and atmospheric pressures can be retrieved. Since the balloon rides with the wind, radio-navigation LORAN-C or the Global Positioning System must be employed to determine the balloon’s location as a function of time, and subsequently render the upper air wind speed and direction as a function of altitude. SODAR has the advantage of less time between atmosphere soundings and describes the atmosphere directly above the unit, rather than at the balloon’s location, but is limited to altitudes less than 20,000 feet. The atmospheric parameters needed as input to SIPS are collected by a single atmospheric sounding as near as possible to the noise event site. These parameters are considered valid for approximately one hour. Upon retrieval of the physical parameters, a model of the atmosphere is created as a series of stratified layers with constant horizontal properties. Each layer of the model represents a different linear sound speed gradient.

The output of the model includes ray trace diagrams showing atmospheric propagation paths, sound velocity profiles showing sound propagation velocity as a function of altitude, and geographic topography charts showing predicted sound intensity in decibels by geographic location. Figure 3-1 is an example of a sound velocity profile printout.

For more information see the Point of Contact for this survey.