Methodology

Landsat data has been used to create four different maps for each Urban Heat Island (UHI). Two of the maps depict land surface heat, and two maps show the amount of vegetation that is present/absent in each UHI. Additionally, an interactive heat map for each UHI study area was created by using the the Landsat Thermal Infrared (TIR) band to create polygons of the warmest areas within the UHI. This polygon layer is added to the OpenStreets GIS mapping system, which allows for more detailed exploration (at the street name level) of the anthroprogenic warming effect within each UHI. A second interactive temperature map has been created from the Landsat "Analysis Ready Data", provided on the USGS Earth Explorer web site. This second map also uses the OpenStreets GIS mapping system. The interactive map provides land surface temperatures (degrees Fahrenheit) for each 30 square meter area which has a temperature greater than (>) 99 ºF. The interactive temperature maps are comparable between cities, since the temperatures (and associated map colors) have been standardized between the maps.

Landsat Image Creation

Landsat satellites acquire data in several different ranges of the electromagnetic spectrum. Each of these spectrum ranges are referred to as "bands". The spectrum bands can be used individually or collectively to produce a wide range of images, which are used to identify physical features on the landscape.

Landsat-5 and Landsat-8 both have a Thermal Infrared Sensor (TIRS) that collects Land Surface Temperature (LST) data. The Landsat-5 TIRS is Band 6 and Landsat-8 has two TIRS, Band 10 & 11. The TIRS raw digital numbers were used to create thematic colored maps, which depict the LST changes within each UHI. These maps are useful for comparing temperature changes within each image, but can not be used for comparing LST changes between a different UHI location map or a different image collection date. Raw LST data needs to be standardized to a common temperature, to allow for comparisons between a different UHI location map or a different image collection date.


The Landsat band combination of 10-6-5 was used to create a false color composite image, which depicts LST. The various levels of orange to red represent warm to hot areas, and various levels of blue represent cooler areas. Surface water areas are in shades of black. This band combination for visualizing LST benifits from the higher 30 meter resolution of bands 6 & 5. The geographic features of the landscape are more distinct with the 10-6-5 combination, as compared to the the LST image created using only the 100 meter resolution data in band 10. A similar band combination was previously used for a Washington D.C. UHI project in 2009.


The Landsat band combination of 5 and 4 was used to create a Normalized Difference Vegetation Index (NDVI) which shows the proportion of vegetation present on the landscape. The NDVI scale ranges from 0.01 (dark brown, showing very little vegetation), to 0.99 (dark green, showing lush vegetation).


The Landsat band combination of 7-5-3 shows vegetation in shades of green, developed urban areas are in shades of purple and pink, water is dark blue to black. Asphalt roofs and pavement  can be colored black.


The Landsat TIR Band was used to create a polygon layer for use in OpenSteetMaps, as shown in the map below this text. The raw digital numbers which depict the higher LST values were used to create this layer. This map layer helps identify areas that have the greatest risk of endangering human health from excessive anthroprogenic heat generated within the UHI.

The interactive map legend, in the upper righ corner of the screen (see image below), can be displayed by clicking on the blue diamond. The legend items can be individually turn on or off by simply clicking in the "check box" beside each layer name. The map "zoom" tool is located in the upper left corner of the screen, represented by the + & - blue squares. The map can be moved/panned by using the mouse to click/hold/drag the map on the screen.

Click on image below to accesses the dynamic map. A new window will open for each click.

WashDC TIR Map



The Land Surface Temperature (LST) map shown below was created using Landsat Analysis Ready Data from USGS. The original Kelvin temperatures have been converted to Fahrenheit. When you move the cursor over the map, the temperature for each 30 square meter area will be displayed. Only LST values greater than (>) 99ºF are displayed, which reduces the file size from 413,978 polygons (65.9MB) to 106,089 polygons (17MB). The reduced file size takes about one minute to load into your web browser (depending on your network). Please be patient.

Note: The ambient air temperature in Washington D.C. on 7/8/2018 was: Average (75 ºF); Max (85 ºF); Min (64 ºF). See this  web site link for more details.

Click on image below to accesses the dynamic map. A new window will open for each click.