Study area: Dhanmondi (ward DSCC 15), situated in Dhaka South City Corporation, was selected. It is situated between 23°44´12´´ and 23°45´22´´ north latitudes and between 90°22´ and 90°23´ east longitudes. Noise levels at 40 sample points of the study area have been collected. These points were not selected at a specific distance from each other, instead it was measured around places like shopping mall, schools, hospitals, roadsides, commercial places, etc. The surrounding neighborhood is characterized by residential houses generally comprised of 4-5 floors. It was found that 8 sample points belonged to the residential zone, 7 sample points belonged to the mixed zone, 7 sample points were in commercial area (Shopping mall, bank, other offices) and 3 sample points were in silent zone (Primary school, hospital) and 4 in recreational place (Abahoni playground, lake side park, etc.) and rest of the sample points belonged to roadside and road intersections. Many important organizations, offices, hospitals, educational institutions, residences, lakes etc. are situated in the study area. The major roads are important for urban and national connectivity and have all modern facilities.
In this study, the interpolation method was used for the study area’s spatial distribution of noise levels. Several interpolation methods include linear interpolation, Inverse Distance Weighting (IDW), Natural Neighbor Inverse Distance Weighted (NNIDW), Spline and Kriging, etc. The spatial distribution of noise levels in Dhanmondi in the years 2019 and 2021 was done with the IDW method. Based on the noise levels behavior of the locations in the study area IDW method was selected for generating noise color contour. It is one of the most commonly used techniques with higher accuracy than other interpolation methods. It weighs each point by the inverse of the distance after the reference point assigned for each measurement. It provides an exact weighted interpolated surface grid. Furthermore, IDW offers satisfactory results for predicting noise level maps.
Data standardization: Several sound level data were taken at each location point with a VOLTCRAFT digital noise level meter SL-50. Then, they were averaged to get the final sound level value. The data were collected above 1.5 meters above the ground surface to avoid the noise generated by the wind condition. The data were averaged because a place’s sound level varies due to different types of sources common in the study area, such as traffic signals, honking, crowd, etc.
Data analysis and interpretation: Arc GIS 10.4.1 software was used in data analysis and interpretation. Noise level contour map and surface were generated based on noise level data collected from the different points of the study area. Noise level color contours were produced using different intervals, which depict the spatial variation of noise. Bangladesh transverse mercator (BTM) projection system was used in this study.