Jet transport overflight (NASA photo)

2003 Mather Field noise studies:
Community noise (CNEL) measurements
In this page:
Site 3 CNEL graph thumbnail
Site 3 CNEL noise chart
CNEL summary thumbnail
CNEL
summary

Environmental sound levels thumbnail
Representative
CNEL examples

Community Noise Equivalent Level (CNEL) measurements are a weighted average of sound levels gathered throughout a 24-hour period. This is essentially a measure of ambient noise.  Different weighting factors apply to day, evening, and nighttime periods. This recognizes that community members are most sensitive to noise in late night hours and are more sensitive during evening hours than in daytime hours. CNEL depends not only on the noise level of individual approaches, but also on the number of approaches during the measurement period.

A different noise measure is SENEL, Single Event Noise CNEL, Community Noise Exposure Level. This concerns the loudness of a single event -- in this case, a single overflight by a jet freighter on approach to Mather Field.. See Single event (SENEL) noise measurements for more information and measurements.

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


Site 3 CNEL components, February 2003

The graph below shows three graphs measured during the February measuring period at site 3, beneath the ILS approach in El Dorado Hills. The graphs are:
During one morning in this test period noise from a rainstorm raised the measured CNEL by about 20 dB. This occurred on a Sunday, when no freighter flights operated and the approach noise contribution was 0.

CNEL contributions at site 3

Also see note about slant distance


Summary of freighter CNEL noise levels under ILS approach

CNEL noise at site 3, below ILS approach


Context:  Representative CNEL examples

Representative CNEL examples

Note:  August measurement period for VOR/DME tests showed low CNEL values at the two measurement sites in El Dorado Hills. However, the meaning of these results is questionable because of the high dispersion of approach paths on the VOR/DME approach and on visual approaches, leading to a much smaller number of arrivals passing over the noise measurement sites. Noise complaints during this period may be more significant; many reflect higher single-event noise levels due to aircraft descending to and holding at 2,000 feet while setting up for the nonprecision VOR/DME approach. For comparison, traffic on the ILS glide slope crosses the El Dorado Hills measuring point at about 3,800 feet.

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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