Dobbins JLUS IMP Public Draft Light Pollution Study | Page 15
Chapter 2. Baseline Lighting Conditions
Introduction
Lighting measurements were mapped to assess the current level of light
pollution within the Dobbins ARB JLUS Light MCA. This information was
used to determine which specific geographical areas could be targeted for
mitigation recommendations.
Data used was generated from the 2017 VIIRS onboard the Suomi National
Polar‐orbiting Partnership weather satellite operated by NOAA and filtered
by the Earth Observation Group, NOAA National Geophysical Data Center to
exclude data impacted by stray light, lunar illumination, and cloud‐coverage.
These measurements were used to establish a baseline, quantifying the
current relative severity of light pollution. The data gathered from NOAA
provides a comprehensive picture of the lighting conditions throughout the
entire Light MCA.
Process
watt per steradian per centimeter, i.e., 10 ^‐9 W/cm*sr. For mapping and
analysis purposes, the output radiance values from the radiance calculation
were categorized into ranges: 3,00‐6,00; 6,00‐20,0; 20,0‐40,0; >40,0 watts
per steradian per centimeter.
To examine how light reflectivity affects the human eye, radiance ranges
were converted to the Bortle Scale developed by John E. Bortle as a method
for ranking and describing sky brightness on a scale of one (1) to nine (9).
Table 1 shows the light radiance ranges and their respective Bortle Scale
including a description of the night sky appearance at each scale. Because
the radiance values for the Light MCA are higher than 3,00, the table
excludes the Bortle Scale ratings of two (2) through four (4) which do not
occur in the Light MCA.
Nighttime lighting within the Light MCA was mapped by using light
reflectivity data published by NOAA on the website 1 , which provides the
measurement of brightness from sources generated on the earth’s surface.
Surface light reflectivity is an appropriate indicator of light pollution for this
Study because it approximates the light levels experienced by a pilot from an
elevated position in the sky reflected off the ground below them.
The light reflectivity values published by NOAA are expressed as radiance
and calculated using a mathematical formula to derive intensity values of
1 https://www.lightpollutionmap.info
March 2018
DRAFT Dobbins Air Reserve Base Light Pollution Study
Page 2‐1