World Atlas 2015 data credits: Falchi, Fabio; Cinzano, Pierantonio; Duriscoe, Dan; Kyba, Christopher C. M.; Elvidge, Christopher D.; Baugh, Kimberly; Portnov, Boris; Rybnikova, Nataliya A.; Furgoni, Riccardo (2016): Supplement to: The New World Atlas of Artificial Night Sky Brightness. GFZ Data Services. http://doi.org/10.5880/GFZ.1.4.2016.001
Falchi F, Cinzano P, Duriscoe D, Kyba CC, Elvidge CD, Baugh K, Portnov BA, Rybnikova NA, Furgoni R. The new world atlas of artificial night sky brightness. Science Advances. 2016 Jun 1;2(6):e1600377.
Left click and drag the map in desired direction or slide your finger if you are using a touchscreen capable device.
Use mouse scroll wheel to change zoom or press +/- buttons on the toolbar. You can also zoom to a desired rectangle by drawing it using shift-left mouse drag. Another way to zoom in is to just double-click the map and it will zoom-in.
The right menu contains areas where you can change what is show on the map. It can be hidden or displayed by clicking on menu button.
Base layers and overlays
The “base layers and overlays” section of the right menu contains controls which enable you to select a desired radiance/sky brightness overlay and with the slider next to its name you can change its opacity. The default opacity is set at 40%. Use the vertical scroll-bar to see older overlays.
There are two base layers available, Bing Road and Hybrid which is a mix between Satellite and Road type map. These two base maps are provided by Microsoft REST service.
SQM/SQC overlay & filters
Check “SQM/SQC” to display user SQM/SQC measurements and with the slider you can change its opacity. Filters are provided to control the number of points displayed on the map. You can filter them by name, type and date (filter settings are remembered even if you close the browser!).
Shows the legend of the currently visible overlays.
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Positions the screen where the user is located. The location is provided by a HTML5 Gelocation API using GPS, GeoIP, Cell network or other means.
Measure the distance and azimuth. Left click to start the measurement, double click to end. Azimuth is available if the line is not segmented and it represents the angle from start of the line to the end. Multiple measurements are supported. To clear all measurements, click again on the ruler icon to deactivate it.
Radiance statistics per country
Displays the statistics of VIIRS data per country land and territorial waters for each year.
Prints the map to a PNG image.
Shows or hides the extended toolbar. The extended toolbar can be repositioned by grabbing it by its right side frame.
The extended toolbar contains various measurement tools and tools for adding your own measurements. You can reposition the toolbar by grabbing it by its right edge and move it.
Left clicking on the map shows a popup displaying clicked coordinates (WGS84 coordinate system in degrees, minutes, seconds format), value of the visible VIIRS/DMSP overlay and elevation in meters at clicked location. For World Atlas there is a bit more information available. If no other control is active, this is the default control when left clicking the map.
Area information using a polygon
Displays statistics of visible VIIRS/DMSP/WA layer that intersects the drawn polygon. To draw the polygon use left clicks and double left click to finish. The resulting popup can be moved by grabbing its’ frame and repositioning it. The Raw GeoTIFF button will export the original raw data clipped by the polygon. The RGB GeoTIFF button will export the RGB data clipped by the polygon. Export is not only available for World Atlas overlay.
Area information using a circle
Displays statistics of visible VIIRS/DMSP/WA layer that intersects the drawn circle. To draw the circle left click, then move mouse and then left click to finish at desired radius. The resulting popup can be moved by grabbing its’ frame and repositioning it. The Raw GeoTIFF button will export the original raw data clipped by the polygon. The RGB GeoTIFF button will export the RGB data clipped by the polygon. Export is not only available for World Atlas overlay.
Add a marker
By left clicking the map it adds a pushpin marker on the map. To remove markers, left click on them.
Add a SQM measurement
Activating this option enables you to add your own SQM measurement to the map. In the name field enter your name or place name. Date/Time field should contain your local time the measurement was taken. SQM value contains the value, while the “SQM-L” checkbox should be check if your SQM is the lens version. Comment should contain your comments about the measurement or the place. Before submitting the form, a captcha verification needs to be typed into the Verification textbox. Press submit to submit the form. If successful, closing the form will show your added measurement (make sure a filter is not active and thus hiding the added point)
Add a SQC measurement (experimental)
If you own a SQC you simply upload the info image. Name and commentary are optional.
Located on the upper left corner of the map. Enter a place and by selecting it from a dropdown menu it will reposition the map to it. It is also possible to enter coordinates manually in a “latitude, longitude” format and selecting it from a dropdown menu which will zoom to those coordinates.
Located on the bottom left corner of the map. Shows the current map scale
Located on the bottom right corner of the map. Shows the current coordinates of the mouse cursor or last touch if you are using a touchscreen device. Left click on the coordinate display toggles between decimal and degrees/minutes/seconds display modes.
Toggle right menu
Located on the upper right corner of the right menu. Shows or hides the right menu.
Share map view on social media
Located under the right menu. A quick way to share the current view of the map on certain social media web sites.
Located on the bottom left corner of the map. Shows attributions associated with visible overlays and base layers.
All due to continuous sunshine in summer/winter months for northern/southern hemisphere.
3. Why is on a 2015 map less light pollution than on 2014? Isn't it supposed to get worse each year?
There are numerous reasons for this. One could be lack of good data. For example some areas have always some clouds and as VIIRS overlay is composited monthly, it is impossible to get good quality data coverage for that month. It is also possible that the proccess used to make the global image is not perfect. It could simply be that the radiance actually decreased or that HPS lamps have been replaced by high color temperature LEDs to which VIIRS sensor isn't too sensitive.
4. Why are swath trails visible on some VIIRS maps?
Maybe because of not perfect onboard calibration? Best to direct the question to NOAA.
5. What's an SQM?
SQM stands for Sky Quality Meter. It's a small device that can measure sky quality ie. darkness. It's widely used by amateur astronomers because it's fairly cheap and gives you fast results which can be easily compared to other SQM users. Be aware that two versions exist (SQM and SQM-L) and their readings are not comparable. More about the SQM product visit the manufacturer website.
6. How can I add my own SQM data?
To add your SQM measurements click on the +SQM icon in the extended toolbar. Please note that the time entered should be your local time the measurement was taken. The only mandatory fields are time and the SQM measurement
7. What's an SQC?
SQC stands for Sky Quality Camera. It's a calibrated Canon dSLR with a fisheye lense bundled together with a software suite. It produces a 360 degree all-sky image with MPSAS (magnitudes per square arc second) or CCT (color temperature of a black-body radiator) measurements. The result adds another dimension to a standard SQM measurement. More about the SQC product contact Andrej Mohar.
8. How can I add my own SQC data?
This function is still in the experimental phase. To add your SQC measurements click on the +SQC icon in the extended toolbar. Name and comment are not mandatory. The uploaded image must be ImageType = 18 (info).
9. I have hundreds of measurements. How can I submit them all easily?
If they have at least coordinates, date/time, then contact me.
10. What is the map projection?
The original data is in a WGS84 geographic coordinate system. To have it display as overlays on top of Bing maps the data needs to be projected to a Spherical Mercator projection. When you export to raw GeoTIFF the data is in the original WGS84 coordinate system.
11. What is the resolution of the overlays?
The original VIIRS data has a resolution of 15 arc seconds, DMSP and World Atlas 30 arc seconds for each pixel. When projected the resolution is around 500m for each pixel for VIIRS and 1000m for DMSP and World Atlas.
12. How do you convert VIIRS data to MPSAS (magnitudes per square arc second) or Bortle scale? What does W/cm2 * sr mean anyway?
W/cm2 * sr is a SI radiometry unit for radiance. Radiance is radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. It sounds complicated right? Well that's because it is. Things get a bit more (actually a lot more) complicated if you want to do a simple conversion to MPSAS. I'm not even going to touch the Bortle scale issue because it is highly subjective scale. Anyway if you are still interested in a "conversion" I can try to explain the problem. Imagine you have a small light source aimed at the sky and this light source gets picked up by the VIIRS detector detector. The VIIRS detector is monochromatic and has its own spectral response curve. It has no idea of the spectral curve of the light source. MPSAS or more specific magnitude is a measure that is measured in a “specific wavelength or passband”. See the problem? That's one major issue. The other major issue is that light from the light source passes through the atmosphere and while doing this it scatters due to air molecules and aerosols. So you need to create a model of light propagation for the entire Earth taking into the account local air conditions, earth curvature, light absorption, Earth terrain and what not. You can read more about it here. If you got skills to do this and willing share the result I'll be glad to include it! If not be sure to check the World Atlas (WA 2015) overlay.
SQM/SQC layer is partially sourced from Unihedron database, the rest from lightpollutionmap.info users.
14. How can I view the raw VIIRS/DMSP data from NOAA/EOG website? The files are too big to be opened by Photoshop or similar software!
To work with this kind of data you need to have GIS software installed (QGIS, uDig, ArcGIS, etc...)
15. How should I credit the use of www.lightpollutionmap.info?
The use of data from www.lightpollutionmap.info should be credited to "Jurij Stare, www.lightpollutionmap.info".
If VIIRS/DMSP data is used or displayed it should also include "Earth Observation Group, NOAA National Geophysical Data Center".
If World Atlas data is displayed it should also include "Falchi, Fabio; Cinzano, Pierantonio; Duriscoe, Dan; Kyba, Christopher C. M.; Elvidge, Christopher D.; Baugh, Kimberly; Portnov, Boris; Rybnikova, Nataliya A.; Furgoni, Riccardo (2016): Supplement to: The New World Atlas of Artificial Night Sky Brightness. GFZ Data Services. http://doi.org/10.5880/GFZ.1.4.2016.001
Falchi F, Cinzano P, Duriscoe D, Kyba CC, Elvidge CD, Baugh K, Portnov BA, Rybnikova NA, Furgoni R. The new world atlas of artificial night sky brightness. Science Advances. 2016 Jun 1;2(6):e1600377."
16. I see the coordinate display is in a decimal format, but can you display them as degrees/minutes/seconds?
Click on the coordinates and it should toggle between those two display modes.
17. What is the precise date when VIIRS/DMPS satellite data was collected?
"layer VIIRS 2017" data was taken between dates 20170301-20170331
"layer VIIRS 2016" data was taken between dates 20160301-20160331
"layer VIIRS 2015" data was taken between dates 20150301-20150331
"layer VIIRS 2014" data was taken between dates 20140301-20140331
"layer DMSP 2010" data was taken during the whole 2010
18. VIIRS version 1 series is run globally using two different configurations. Which one are you using?
I'm using vcmcfg which excludes areas impacted by stray light.
19. Exported GeoTIFF is all black!
Exported GeoTIFF is the raw VIIRS/DMSP data. VIIRS is in a 32bit floating point while DMSP is in a 8bit unsigned integer pixel type GeoTIFF. Use GIS software (QGIS, uDig, ArcGIS, etc...) to stretch the histogram, reclassify etc...
24. What is the difference between VIIRS/DMSP and World Atlas overlays? They look so different.
VIIRS/DMSP are radiance maps while World Atlas ia a sky brightness map. VIIRS/DMSP shows you the light sources, while World Atlas tells you how dark is the zenith based on a model calculated from VIIRS/DMSP data.