CoSQM - a color hack to the SQM-LE for Light At Night Sensing
Color mapping of the night sky brightness over the Mont Bellevue natural reserve in Canada
<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.
Abstract
We present a methodology to map the night sky brightness in 4 spectral bands on the territory of the Parc du Mont-Bellevue natural reserve (Sherbrooke, Canada). In the long term, we aim to estimate a part of the exposure of living organisms to the indirect urban light as a function of the colors scattered in the atmosphere overhanging the natural reserve. The reserve is located near the Sherbrooke city center inside the city perimeter. If repeated regularly, the mapping technique can become an influential tool to estimate the light pollution transformation as a function of the ongoing Sherbrooke’s light fixture replacement program. In most cases, HPS are replaced by phosphor converted amber LED. Such transformation may shift the color composition of the sky, the major source for the artificial light propagating into the reserve. Our project is part of a new initiative aiming the creation of an “Urban Starry Sky Oasis”, an urban public area where we hope to give back, to the citizens, an easy access to the Milky Way. We performed the mapping with the data acquired with the CoSQM, a new portable device which aims to sample the multispectral properties of the artificial light scattered by the atmosphere.
Equipment
The measurements were made using an expedition utility sled on which is fixed a stabilizing support that holds in place the CoSQM.
Expedition utility sled
Made of high-density polyethylene
Dimensions : 114,3 cm x 50,8 cm x 20 cm
Stabilizing support
Necessary material to make the stabilizing support :
- Perforated steel strapping (3/4 IN X 10 FT)
- Plywood (3/4 IN X 2 FT X 2FT)
- Wood screw (No. 8, 3/4 IN)
- Wood screw (No. 8, 1 1/2 IN)
- 4 T HINGE (3 IN)
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Conditions of experimentation
Starting date of measurements | 2019-06-03 | 2019-07-03 | 2019-08-03 |
Distance traveled | 7,20 km | 5,52 km | 8,32 km |
Positive elevation gain | 176 m | 172 m | 223 m |
Max altitude | 330 m | 359 m | 368 m |
Elapsed time | 4:26:19 | 3:06:27 | 3:55:16 |
Average pace | 18:03/km | 18:24/km | 17:10/km |
Fastest intermediate pace | 18:08/km | 22:14/km | 18: 47/km |
Average speed | 3,3 km/h | 3,3 km/h | 3,5 km/h |
Conditions of visibility of the sky | Clear sky Viewing weather | Clear sky Viewing weather | Clear sky Viewing weather |
You can find below the work plan of the Mont-Bellevue Natural Reserve Alliance.
Distance covered over the Mont-Bellevue
![](http://obsand.org/wiki/index.php/Prof/Cosqm-Color-mapping-of-the-night-sky-brightness?action=download&upname=deplacement.png)
Maps
The maps represent the artificial light at zenith perceived in the Mont Bellevue natural reserve (Sherbrooke, Canada). The reserve is surrounded by a ski station, thus we compared the sky brightness during and after its operation times.
Night sky brightness perceived by the clear filter (SQM-LE)
Note that the magnitudes per square arc seconds decrease with increasing brightness, so the lower value is the brightest perceived.
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During ski station operation | After extinction of ski station lights |
Blue index
The blue color index (B-C) indicates the difference between the sky brightness in the blue spectral band and the SQM-LE measurement (clear filter). Note that the sky brightness decrease with increasing radiance, so the smaller B-C is, the bluer is the sky.
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During ski station operation | After extinction of ski station lights |
B-G index
The color index B-G indicates the difference between the sky brightness in the blue spectral band and the green spectral. Note that the sky brightness decrease with increasing radiance, so the smaller B-G is, the bluer is the sky.
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During ski station operation | After extinction of ski station lights |
B-Y index
The color index B-Y indicates the difference between the sky brightness in the blue spectral band and the yellow spectral band. Note that the sky brightness decrease with increasing radiance, so the smaller B-Y is, the bluer is the sky.
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During ski station operation | After extinction of ski station lights |
B-R index
The color index B-R indicates the difference between the sky brightness in the blue spectral band and the red spectral band.
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During ski station operation | After extinction of ski station lights |
Mapping methodology
Download QGIS
We used the 2.18.17 version of the software in this methodology, but you can download a newer version if you prefer.
Complete documentation about the 2.18.17 version
Install GRASS GIS plugin
The Geographic Resources Analysis Support System (GRASS) open source plugin is used as a tool with several GIS functions.
- In the top toolbar, click on Plugins.
- Click on Manage and Install Plugins....
- In the Plugins Window, search for GRASS then click on Install button.
- Click on Manage and Install Plugins....
Comma-separated values (CSV) file
Make sure to convert your data file in CSV format. This is a delimited text file representing tabular data as comma-separated values.
Adjusting the project Coordinate Reference System (CRS)
- Adjust the project CRS from the top toolbar and click on Project.
- Click on Project Properties.
- Click on the General tab.
- Under General settings :
- Project home : Set your project home path.
- Project title : Set the project name as Before Mont-Bellevue.
- Under Measurements : Leave default features.
- Under Coordinate display : Leave default features.
- Under General settings :
- Click on the CRS tab.
- Check Enable 'on the fly' CRS transformation (OTF).
- Set the Coordinate Reference System to WGS 84 / Pseudo-Mercator [EPSG:4326].
- Click on the General tab.
- Click on Project Properties.
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Adding basemaps to your QGIS project
Install QuickMapServices plugin
The QuickMapServices plugin is used to add basemaps to your QGIS project.
- In the top toolbar, click on Plugins.
- Click on Manage and Install Plugins....
- In the Plugins Window, search for QuickMapServices then click on Install button.
- Click on Manage and Install Plugins....
Add a map background
We recommend the use of Wikimedia Commons since it is a multilingual library of content (images, sounds and videos) for educational purposes in the public domain or published under free license.
- Add a map background from the top toolbar : click on Web.
- Click on QuickMapServices.
- Click on OSM.
- Click on Wikimedia Map.
- Click on OSM.
- Click on QuickMapServices.
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Creating a perimeter border of the Parc du Mont-Bellevue territory
Importing geomatics data of the Parc du Mont-Bellevue
- Download the geomatics data file of the Mont-Bellevue Park from the Sherbrooke city website and drag it into the map tab of QGIS. This file is named Aires_aménagées.zip.
Adjusting selected area (Parc du Mont-Bellevue)
- Adjust the selected area from the toolbar : click on
to select features by area or single click and then click on the Parc du Mont-Bellevue natural reserve area (or the selected region to map) and it will become yellow.
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- In the Layers panel (left side of the screen) : right click on Aires_aménagées.
- Click on Save as.
- Set the Format to Erpi Shapefile by using the scrolling bar.
- File name : Set the output shapefile by pressing Browse button. Navigate to the data folder and enter the new filename as Extend Mont-Bellevue.
- CRS : Selected CRS [EPSG:4326, WGS 84] by default.
- Check Save only selected features.
- Check Add saved file to map.
- Click on Save as.
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- In the Layers panel (left side of the screen) : right click on Aires_aménagées and then click on
to remove layer/group currently selected.
Reprojecting Extend Mont-Bellevue
To reproject and transform vector datasets to set the appropriate Coordinate Reference Systems (CRS).
- In the Processing Toolbox search bar(on the right side of the screen) : type Reproject layer.
- Set the Input layer to Extend Mont-Bellevue [EPSG:4326].
- Set the Target CRS to NAD83/Quebec Lambert [EPSG:32198] by clicking on
.
- Set the Target CRS to NAD83/Quebec Lambert [EPSG:32198] by clicking on
- Set the Input layer to Extend Mont-Bellevue [EPSG:4326].
- Adjust the style properties from the layers panel : double click on Reprojected Extend Mont-Bellevue.
- Click on the Style tab.
- Set the Outline to a black color.
- Set the Fill style to No Brush.
- Set the Outline style to Solid Line.
- Set the Outline width to 0.500000. This will be 0.5 millimeters.
- Click on the Style tab.
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Creating a layer from your color mapping data
Importing file data
You can find the data used for the map creation below, but the following methodology is performed with the data before closing the lighting of a ski station, which surrounds the Mont Bellevue natural reserve.
Data used for the color mapping - before closing the lighting
Data used for the color mapping - after closing the lighting
- Create a new layer from the top toolbar and click on Layer.
- Click on Add Layer.
- Click on Add Delimited Text Layer.
- File name : Set the output shapefile by pressing Browse button
. Navigate to the data folder and enter the new filename as before.shp.
- Set the File format to CSV (Comma-separated values).
- File name : Set the output shapefile by pressing Browse button
- Click on Add Delimited Text Layer.
- Click on Add Layer.
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Reprojecting datasets
To reproject and transform vector datasets to set the appropriate Coordinate Reference Systems (CRS).
- In the Processing Toolbox search bar type reproject layer.
- Set the Input layer to before [EPSG:4326].
- Set the Target CRS to NAD83/Quebec Lambert [EPSG:32198] by clicking on
.
- Set the Target CRS to NAD83/Quebec Lambert [EPSG:32198] by clicking on
- Set the Input layer to before [EPSG:4326].
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- In the layers panel, double click on Reprojected before.
- Click on the Style tab.
- Click on Marker.
- Click on the city symbol.
- Click on Simple Marker.
- Set the Outline to a black color.
- Set the Size to 1.000000. This will be 1.0 millimeters.
- Set the Outline style to Solid Line.
- Set the Outline width to 0.500000. This will be 0.5 millimeters.
- Click on Marker.
- Click on the Style tab.
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Fixing distance buffer
- Run the buffer process from the top toolbar : click on Vector.
- Click on Geoprocessing tools.
- Click on Fixed distance buffer.
- Set the Input layer to Reprojected before [EPSG:32198].
- Enter buffer Distance of 200. This will be 200 meters.
- Enter Segments to 100.
- Check Dissolve result.
- Buffer : Set the output shapefile by pressing Browse button
. Navigate to the data folder and enter the new filename as Buffer_reprojected_before.shp.
- Check Open output file after running algorithm and and the resulting shapefile will be added as a layer in your map view.
- Press Run to run the process.
- Click on Fixed distance buffer.
- Click on Geoprocessing tools.
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Vector overlay - Intersection
- Run the intersection process from the top toolbar : click on Vector.
- Click on Geoprocessing tools.
- Click on Intersection.
- Set the Input layer to Buffer reprojected before [EPSG:32198].
- Set the Intersect layer to Reprojected Extend Mont-Bellevue [EPSG:32198].
- Intersection : Set the output shapefile by pressing Browse button
. Navigate to the data folder and enter the new filename as Intersection_before.shp.
- Check Open output file after running algorithm and and the resulting shapefile will be added as a layer in your map view.
- Press Run to run the process.
- Click on Intersection.
- Click on Geoprocessing tools.
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Making voronoi polygons
- Run the voronoi polygons process from the top toolbar : Vector
- Click on Geometry tools
- Click on Voronoi polygons
- Set the Input layer to Reprojected before [EPSG:32198].
- Enter Buffer region of 100. This will be 100%.
- Voronoi polygons : Set the output shapefile by pressing Browse button
. Navigate to the data folder and enter the new filename as voronoi_polygons_before.shp.
- Check Open output file after running algorithm and and the resulting shapefile will be added as a layer in your map view.
- Press Run to run the process.
- Click on Voronoi polygons
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Clipping vectors
- Run the clipping process from the top toolbar and click on Vector.
- Click on Geoprocessing tools.
- Click on Clip.
- Set the Input layer to Voronoi polygons_before [EPSG:32198].
- Set the Clip layer to Intersection_before [EPSG:32198].
- Clipped : Set the output shapefile by pressing Browse button
. Navigate to the data folder and enter the new filename as clipped_before.shp.
- Press Run to run the process.
- Click on Clip.
- Click on Geoprocessing tools.
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