Thanks to data provided by Steve McIntyre and conversion skills provided by Barry Wise, we now have the first ever interactive global mapping tool for nightlight ratings and GISS stations worldwide that encompass USHCN and GHCN station locations.
Download it from the surfacestations website here
How to download: right click, save target as, then save to your disk, double click it to open in Google Earth, (free download here) and follow the instructions below for turning on the city night lights layer in the text below. In the file, the icons are set as follows:
A = dark
Yesterday I had a phone conversation with Steve Mosher. We were talking through some of the puzzlements of the GISS code and how it dealt with city nightlights, urbanization, the USA, and ROW. One of the big puzzles is why GISS uses counts of nightlights for an urbanization adjustment in the USA, but uses population data in the ROW. Why not keep everything on one method for a consistent result?
During the conversation, it occurred to me that there may be a tool available to us that will help us understand how nightlights look from space in relation to the placement of USHCN and GHCN weather stations, so we could check against the GISS lights database. My hunch paid off.
As luck would have it, Google recently partnered with NASA to include “city lights” data. With a little searching, I found I could add a layer to Google Earth (the free download program version, not the web browser version) and see what Imhoff must have seen, when he was researching his paper, except this is newer imagery. According to the source at NASA’s Earth Observatory web page, the visualization date of imagery is 10-23-2000
Here is what they say about it:
This image shows levels of light pollution across the globe. The brightest areas of the Earth are the most urbanized, but not necessarily the most populated—for example, compare western Europe with China and India.
The light pollution data used to create this image was measured by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). The OLS was originally built to view clouds by moonlight, but it is also used to map the locations of permanent lights on the Earth’s surface as shown here. This composite shows the data as processed by NOAA’s National Geophysical Data Center and artistically rendered over a false-color night version of NASA’s Blue Marble: Next Generation global map.
It turns out to be quite easy to enable this feature in Google Earth, but it is well hidden, and I only found it after doing a search of their support forums. The screencap below shows how to enable it by simply clicking on the NASA “Earth City Lights” checkbox in the layers control window by opening the “Features” folder and scrolling down.
Once I had this new layer working, it was quick work to add some USHCN stations locations and get some snapshots of what their GISS lights=”X” image actually looks like. Since we have been discussing several stations recently, I thought I’d try those first. Below are some screen captures of Lampasas, TX, Miles City, MT, Mount Shasta, CA, Cedarville, CA, and Moncton, N.B.
I used the GPS coordinates from surveys done by volunteers from surfacestations.org to position the USHCN station markers, and the NCDC MMS database published coordinate for the Moncton N.B. station.
Each image has the NASA GISS lights information added in the lower left corner.
As Steve Mosher pointed out, Moncton, N.B. is in an odd category called “urban dark”. However the picture above certainly doesn’t look “dark” though it does look “urban”. Otherwise there is good agreement between the other GISS lights ratings and the current photos.
I’m still a bit puzzled as to why any adjustments would be needed at all for Cedarville, since it is about as rural as rural can be, “dark”, and lights=0 and that data agrees with the DMSP nightlights image above. Here is the GISS raw versus GISS homogenized data plotted below. Some data is missing for 1915 and 1957 but the station continuity is good otherwise. Click for a larger graph.
Other lights =0 stations, such as Cheesman Lake, CO don’t have adjustments applied at all. It is important to determine what the code criteria is for determining why some lights=0 stations would be adjusted and others would not. There may be a valid method that I and others looking at this don’t yet understand, or it may be an oversight, data error, or bug in the code. Perhaps some of the folks from GISS that have been watching this discussion unfold can shed some “light” on the subject?
Having this Google Earth tool now will allow anyone to check the representivity of a lights=”x” and dark/dim/bright data field value in the GISS dataset. To make such work easier, I hope to update the Google Earth KML file (created by Barry Wise) of all USHCN stations with newer surveyed GPS coordinates, though given the coarseness (2.7 kilometer pixels) of the DMSP imagery, such accuracy may not be needed. Try it out and let me know.
If Steve McIntyre can assist in providing coordinates for other GISS stations for the USA and perhaps the ROW, we could add them to the KML file as well so that it becomes an easy matter to check any station. I hope to include these photos in the surfacestations.org database along with other survey photos since they are key to the GISS adjustment for each station.
Later, if such nightlight data would be useful for further study, perhaps an automated process could be created that would use Google Earth to display centered views for automated export, and the images could be run through an automated pixel histogram process to determine the number of bright/dim/dark pixels in a radius around the station for all ROW stations.
I welcome ideas and comments.