[vc_row][vc_column][vc_column_text]This page explains the geomaps of Average Daily Noise Level (DNL) values that I have computed across the mid-peninsula area of the San Francisco metroplex. The particular set of geomaps available for view covers a one-week period from Sunday, 12/10/2017 through Saturday, 12/16/2017. For each day, DNL geomaps are computed for a 24-hour period and four 6-hour periods: 0:00 – 6:00; 6:00 – 12:00; 12:00 – 18:00; and 18:00 – 24:00. In these plots, only DNL values above 45 dBA are included.
The data are derived from a FlightAware feeder located at 31 Tevis Place, Palo Alto, and include sightings every 10 seconds over a 25 mile radius and altitudes up to 2 miles (10,560 feet). Estimated DNL values are computed using a model for the Sound Exposure Level (SEL) produced at each aircraft closest approach to a matrix of observations points separated by 1/4 mile (1,320 feet), and calibrated to sound monitor recordings collected at the feeder location. The model takes into account to first order the intrinsic noise level of the aircraft, atmospheric attenuation of sound propagation, and, as a function of time, the aircraft gps coordinates, altitude, and velocity.
The following slides shows display DNL geomaps in different orderings of days analyzed and of time cuts:
- DNL Geomap by Day — for each day, the geomaps for successive time intervals are shown: 24-hr; 0:00 – 6:00; 6:00 – 12:00; 12:00 – 18:00; and 18:00 – 24:00.
- DNL Geomap by Time Slice — for each time slice (24 hr, 0:00 – 6:00, etc.) the geomaps for successive days are shown.
Some of the things to notice in the geomap slide shows are: (a) the 24-hr DNL geomap averages out many important features of the overflight traffic variations during the day and (b) the traffic patterns change dramatically during the day and from day to day. These differences in various parts of the day and from day to day suggest why it is so hard to pin down explanations for why aircraft noise appears to abate from time to time and then returns in highly annoying clusters. In many ways these data raise more questions than they answer.
The lightbox frame in each page is the window to view the geomaps. The lightbox should launch automatically with the viewing active. Navigation is fairly straightforward. If you do nothing, the images advance every 3 seconds. To pause the slide show, put your cursor arrow over the picture. To resume automatic advance, move your cursor off the image. To move forward faster that the 3 second rate (or backward), click the forward or backward arrows in the lower right corner. The highlighted dot in the row of dots below the lightbox indicates where you are in the slide show. You can randomly move to another location by clicking any dot.
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