This paper presents a methodology to obtain the day-night average sound pressure levels DNL from continuous measurements. The methodology is used for processing data acquired during 3 days of the summer of 2011 at a point located 9,500 meters to the south of the SCEL airport in Santiago of Chile, considering the unique contribution of aircraft noise. Additionally, this measured DNL is compared with a modeling performed for the same point via the software Integrated Noise Model version 7.0b. Finally, using the model settled, a calculation was made to find values of DNL on the same points where measurements were made in 2003 under the Environmental Impact Assessment for the second runway of the SCEL Airport. The results were compared and discussed.