Geography Realm
| Maps and Cartography |
Due to excessive human activity, an Urban Heat Island (UHI) is a section of an urban or metropolitan area that has a much higher temperature than its rural counterpart. The temperature difference is most noticeable at night and when the breezes are weak.
Urban heat islands tend to affect the social, economic, and physical make-up of the environment. An excessive increase in urban temperature can cause mental and health illness of individuals. An estimation of highly heated spots in urban centers can help in the provision of well-informed futuristic techniques that will address the United Nations’ Sustainable Development Goals 2, 3, 6, 7, 9, 13, 14 and 15.
This GIS tutorial contributes to the battle against urban heat islands by making use of remote sensing and geospatial science techniques (ArcGIS Pro) to outline procedures that can be followed to assess urban heat in a Region.
Relevant factors that will be utilized in this tutorial are Normalized Difference Vegetation Index (NDVI), Proportional Vegetation Index, Brightness Temperature, Error Correction, Top of Atmosphere, and Land Surface Temperature.
Figure 1 below shows a summary of the method employed in this tutorial.
The Normalized Difference Vegetation Index (NDVI) dataset can be accessed freely from the United States Geological Survey (USGS) website after registration. The NDVI can also be calculated using the Landsat toolbox after performing line correction where necessary (Landsat 7 imagery). In order to perform scanline correction with the Landsat toolbox, this video may be useful (https://www.youtube.com/watch?v=kJGkl_Q7D3w). The Landsat toolbox can also be accessed using this link (https://drive.google.com/file/d/1FKc-G1vMVtWXi66hh15VKoj-zk3UPWgX/view).
Normalized Difference Vegetation Index can also be performed by using the raster calculator in ArcGIS Pro. In order to use this procedure, follow the steps outline below;
Note: “B10.tiff” as illustrated in figure 5 below represents band 10 of the Landsat 8 imagery.
To calculate BT from TOA in ArcGIS Pro, follow the following steps;
The following steps can be adhered to, in order to calculate PVI from NDVI;
Note: “ndvi min” and “ndvi max” can be found in the “properties tab” of the NDVI layer.
To perform error correction on proportional vegetation index of the Landsat 8 imagery, the following steps should be adhered to;
To calculate Land LST from brightness temperature and error correction in ArcGIS Pro, the following steps can be followed. (Related: How to Use ArcGIS Pro to Calculate Land Surface Temperature (LST) from Landsat Imagery)
Note: “e_c” and “bt” from the figure below represents the output of the error correction and brightness temperature calculation respectively.
Urban heat line can be generated by creating a shapefile whilst setting the geometric feature to polyline. In other words, digitizing a line across any section of the output of the LST calculation.
For more information on creating feature classes on ArcGIS Pro, the following video may be helpful (https://www.youtube.com/watch?v=L2hmTvSEK0c).
Figure 10 below shows urban heat line that has been digitized and generated with respect to the Land Surface Temperature (LST) output.
After the generation of the urban heat line, stack profile of the heat line can be generated with respect to LST. The following steps outlined below can be used;
A graph can be generated from the “First_z” values which represents the temperature values in Degree Celsius generated by the urban areas across the urban heat line from the output table generated.
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