Source:
This image was generated using TerraViva! Global Data ViewerTerraViva!
Global Data Viewer from ISciences.
 |
Our featured image, "Night
Lights" of America, reveals the intensity
of nighttime illumination from built-up regions of the
US - like cities, towns, urban areas, transportation
corridors, industrial centers, and offshore oilrigs. Night
light intensity is represented with a blue to red color
ramp. Black represents no light; blue tones are
low intensity night light areas and red tones high intensity
areas. Notice the bright lights emitted from large
urban areas like New York City, Chicago, and Los Angeles,
and low light levels from desert areas and poorly developed
regions in the western US, Canada, and Mexico. Data
imaging through night lights offers scientists an extraordinary
visual tool for evaluating urbanization trends, examining
energy consumption habits, and studying other critical
global phenomenon. |
The image is extracted
from the Radiance-Calibrated Lights of the World (RCLW) database
produced by the NOAA National Geophysical Data Center (NGDC) using
the Defense Meteorological Satellite Program (DMSP) Operational Linescan
System (OLS) sensor. The colors depicted correspond to relative
radiative intensity in the visible to near-infrared region of the
electromagnetic spectrum that is given off due to nighttime illumination,
and is visible at the top of the atmosphere. RCLW significantly
advances the study of nighttime illumination by revealing what its
predecessor, Persistent Lights, does not - the relative intensity
of detected light, and not just its presence. Persistent Lights
is produced by examining data collected daily over a period of months
and determining locations that are often, or persistently, lit. The
reported statistic is the percentage of days the location is found
lit over the period of analysis. This algorithm relies on sensor
settings that are unable to detect low light, and that saturate as
light intensity increases, thereby losing the ability to discriminate
brighter light readings. So, while persistent light values
had been found to relate to population density and other socioeconomic
factors, they may be inaccurate in determining correspondence to
more subtle features such as greenhouse gas emissions. RCLW,
with its greater sensitivity to light intensity, was deemed valuable
as a way to further refine types of analyses that scientists and
engineers could perform. We can expect scientists to test whether
radiance calibrated measurements may reveal more subtle information.
RCLW was computed based on data from three separate sensor collections
over the whole globe in 1997. Each collection employed a different
instrument gain setting - one sensitive to bright light, one to low
light and one to medium intensity light. NOAA then processed
the data to remove artifacts and to integrate the responses of the
three different collections into one data set. By using three
different gain settings, NOAA was able to estimate the radiance emitted
and transmitted through the atmosphere to the point of measurement
by the sensor. No attempt is made to correct for atmospheric
effects that would both attenuate the original emission and introduce
energy due to scattering in the atmosphere. Even so, the result
is approximately related to the actual energy emitted by the terrestrial
light sources and provides scientists with an important environmental
analysis tool. |
