Jet transport overflight (NASA photo)

2003 Mather Field noise studies:
Single event (SENEL) noise measurements
In this page:
Site 3 SENEL graph thumbnail
Site 3 noise event chart
 SENEL summary thumbnail
SENEL
summary
 Site 3 data detail thumbnail
Site 3 data
detail table
 Slant distance illustration, thumbnail
Slant distance
 Environmental sound levels thumbnail
Environmental
Sound Levels

Single-event noise is the maximum sound level produced by an individual approach overflight at a particular measuring point. A related acronym is SENEL, which stands for "Single Event Noise Exposure Level". In this context it means the maximum sound level caused by a single freighter overflight over a noise measurement site. The noise level is measured in decibels (dB, or dBA).

A different noise measure is CNEL, Community Noise Equivalent Level. This is a form of measure for an average noise level occurring on a more or less continuous basis. See community noise (CNEL) measurements for measurements in the Mather Field approach studies.

Decibels measure the power or intensity of sound on a logarithmic scale.  Combining two identical sound sources produces a sound level 3 dB higher than that produced by either of them. Doubling the amplitude of a single sound source raises its sound level by 6 dB.  One good web reference for additional information is http://www2.sfu.ca/sonic-studio/handbook/Decibel.html

Single event noise levels under ILS approach

Plot of individual noise events at site 3

This graphic shows SENEL sound levels, which are numerically about 10 dB higher than Lmax measurements for the approach measurements in this test. Lmax, the maximum sound level recorded for each event. Actual maximum sound level for each event would be about 10 dB less than shown on this SENEL graph.

SENEL represents the event's mean energy level and involves the time duration of the event. Data tables show both measurements in their SENEL dB and LMAX dB columns.

Also see note about slant distance
Summary of single event maximum noise level
 under ILS approach

Single-event noise levels, ILS approach

This graphic shows  measured ranges and medians of Lmax, the maximum sound level recorded for each event. A different measurement of single-event noise is SENEL, also expressed in dB but with a somewhat different meaning.  SENEL describes the event's mean energy level and involves the time duration of the event. Data tables show both SENEL dB and LMAX dB measurements.

Site 3 (El Dorado Hills ILS approach site) data table
February noise measurements

 Site 3 noise data detail, Feb measurements

This table is for the February, 2003 noise measurement period as reported in August.


Slant distance illustration
Most of the data reported in this file is from a measuring point located approximately under the ILS approach path. For site 3 (at elevation 1,010 feet in El Dorado Hills), slant distance for an aircraft accurately flying the ILS approach is about 700 feet more than the aircraft's altitude above ground level (agl). This is evident in the noise event chart as clustering of most reports at a single slant distance, about 3,000 feet, corresponding to ILS approaches passing this site at about 4,000 feet MSL (altitude above mean sea level).

Points to the right of this cluster on the noise event chart are produced by aircraft whose flight path is above the glide slope or is displaced horizontally from the approach path. Radar data showed that aircraft flying the ILS approach were very consistently and accurately following the approach course. This course is marked with high precision by the localizer signal from the on-field instrument landing system (ILS) navigation aid.

Flight tracks of aircraft flying the VOR/DME approach and visual approaches had much more dispersion in both altitude and lateral position. In these cases slant distance can be much larger than the aircraft's altitude at its closest approach to the measurement site. This is apparent in the August data points on the noise event chart, which show high slant distances for non-ILS approaches.

Context:  Environmental sound levels
Note that "your mileage may vary" (sound levels will vary) among specific devices. For example, this chart cites 70 dB for a vacuum cleaner at 10 feet, 89 dB for a blender at 3 feet. This editor has a vacuum cleaner and a blender that reverse this relationship -- the vacuum at 20 feet is louder than the blender at 3 feet.

Environmental sound levels

Information on this page is based on these public documents, from the Sacramento County Airport System:
August, 2003 report on noise measurements    84 pages, 2.5 MB.pdf file
December, 2003 noise study updates    25 presentation slides, 769 KB .pdf file
VOR/DME Test Jet Cargo Correlated Complaint Summary   6 pages, 790KB .pdf file

Most of the graphics in this set of web pages are extracted from these documents, with permission from and thanks to SCAS. In many cases portions of them have been highlighted to emphasize portions relating directly to El Dorado Hills.
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