AGU 2014: Urban Areas as Seen from Space

December 18th, 2014 by Kathryn Hansen

The 2014 fall meeting of the American Geological Union (AGU) is more than halfway over. Throughout the week we’ve been enjoying a series of cartoons drawn live at the meeting by Miles Traer, a multimedia producer at Stanford’s School of Earth Sciences, inspired by various sessions. Below is a cartoon from December 16 titled: “Atlas of Global Urban Change, a compendium of Earth’s rapid urbanization.” See the full collection here.

Urban Change Atlas_0 copy

Also on December 16 at AGU, scientists presented images demonstrating an aspect of urbanization that appeared less like a cartoon and a bit more festive. The images showed that city lights shine brighter during the holidays in the U.S. when compared with the rest of the year. In central urban areas, brightness was shown to increase by 20 to 30 percent, while suburbs and outskirts of major cities saw light intensity increase by 30 to 50 percent. Read more about the holiday lights images here and here.

IDL TIFF file

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2 Responses to “AGU 2014: Urban Areas as Seen from Space”

  1. Pawan Gupta says:

    Hi

    I have two questions regarding this analysis, which show increase in night light intensity due to Holiday lights.

    1) How the particle pollution (aerosols) have been taken into account? Atmospheric aerosol loading in summer and winter is very different, which can make large differences in the calculations.

    2) Due to almost no leafs on the trees, more lights from the ground source escapes to the space during winter whereas due to thick vegetation in summer months, it is likely that less light will be escaped to the space. I am wondering if this has been taken into account while making estimations. This can make big difference in the signal satellite receives.

    Thanks, Pawan

  2. Kathryn Hansen says:

    Pawan Gupta — Great questions, thanks for posting them. NASA scientist Miguel Roman provided the following response:

    1) How the particle pollution (aerosols) have been taken into account? Atmospheric aerosol loading in summer and winter is very different, which can make large differences in the calculations.

    Yes. The MODTRAN5 radiative transfer code was used to estimate the required parameters (e.g., Path Radiance, Transmittance, etc.) for a given set of nighttime surface and atmospheric conditions. Our method is similar to that of Johnson et al., (2013), with some minor differences in the radiative transfer model and selection of input parameters.

    2) Due to almost no leafs on the trees, more lights from the ground source escapes to the space during winter whereas due to thick vegetation in summer months, it is likely that less light will be escaped to the space. I am wondering if this has been taken into account while making estimations. This can make big difference in the signal satellite receives.

    Yes, we took this effect into account. We used a modified version of the Vegetation Adjusted NTL Urban Index (VANUI) [Zhang et al., 2013] to compensate for the seasonal increase in canopy-level foliage, particularly during the summer months. We are happy to share the specifics of our retrieval method (including question 1) once our manuscript draft is accepted (it is currently undergoing peer-review).