Nathan B. Higbie
Larson Davis Systems, 131 Middlesex Trpk., Burlington, MA 01803
The agreements negotiated for the new Denver Airport present an interesting example of how legal considerations can govern how noise measurements are made. The agreements stipulate certain noise limits on communities surrounding the airport. These limits are expressed in aircraft Leq(24), and are placed at 102 points, some over 15 miles away. There are financial penalties if any values are exceeded for a year. A signal-to-noise measurement problem resulted since modeled values of the aircraft Leq(24) were lower than measured Leq(24) community noise. The problems that needed solving were detection and quantification of aircraft noise in low signal-to-noise, and assignment of each noise event to its source. Arrays and other spatial techniques were proposed, but were too costly and would not meet Type 1 measurement requirements. A floating threshold was implemented so that noise events could be detected for any ambient condition. To date, all airport monitoring systems have used a fixed threshold since signal-to-noise is not a problem. The events are then correlated with the flight track data using a statistical pattern recognition algorithm whose parameters are optimized for each monitor location.