The various Landsat datasets are a commonly used medium resolution, free, source of satellite imagery, available from the United States Geological Survey’s earthexplorer portal. I’m all in favour of free satellite imagery, but because they are free data, you’ll need to do a little processing before you can use them as a colour base map for your research. In this post, I will explain how Landsat data appears when first downloaded and how you can create a composite, true colour 3-band, raster base map from the 11 bands of Landsat-8 satellite imagery in ESRI ArcGIS.
Land(sat) salad – what you get
Landsat satellites all record a range of different wavelengths within the electromagnetic spectrum as a series of bands. They range from the four bands (red, green, blue and near infra-red) of the earliest Landsat satellites 1-3, to the 11 bands of Landsat-8. If you order Landsat satellite imagery you’ll receive a zip file containing a series of .tif files with long names which describe the images. After a long series of letters and numbers, each file ends ‘B’ and then a number, such as, ‘LC08_L1TP_176041_20191124_20191203_01_T1_B2.TIF’. The B2 refers to the band number, in this case band number 2, which is the visible ‘green’ part of the electromagnetic spectrum. There are also a couple of .txt files giving further information. The table below gives the band information for Landsat-8 sensors.
|Landsat-8 (OLI and TIR)||Micrometres||Colour|
|Band 1 – coastal aerosol||0.43 – 0.45||Ultra Blue|
|Band 2||0.45 – 0.51||Blue|
|Band 3||0.53 – 0.59||Green|
|Band 4||0.64 – 0.67||Red|
|Band 5||0.85 – 0.88||Near Infra Red|
|Band 6||1.57 – 1.65||Short-Wave Infra Red 1|
|Band 7||2.11 – 2.29||Short-Wave Infra Red 2|
|Band 8||0.50 – 0.68||Panchromatic|
|Band 9 – Cirrus||1.36 – 1.38|
|Band 10||10.60 – 11.19||Thermal Infra-Red 1|
|Band 11||11.50 – 12.51||Thermal Infra-Red 2|
‘I see your true colours . .’
Each band will appear in your GIS as a single-band greyscale raster. Which bands you use will depend on the data you need, but for my base map, I used the three bands of visible light, the red (4), green (3), and blue ( 2) bands, to create a ‘true-colour’ composite image. It’s called a ‘true colour’ image because the bands representing the three visible colours, red, green and blue, are shown as red, green and blue in the resulting composite, producing an image of the landscape that is ‘true’ to how it would actually look to a human. Because the red, green and blue bands of Landsat-8 are bands 4, 3 and 2, a Landsat-8 true colour image is described as a ‘3-band 4-3-2 RGB true colour’ composite image.
Creating a composite 3-band raster is incredibly easy to do in ArcGIS. You can do it using the ‘Composite bands’ tool in Arctoolbox>Data Management Tools> Raster> Raster Processing. Simply choose the bands you want to composite in the ‘Input rasters’ box, and provide a filepath and filename for the output in the ‘Output raster’ box. Click ‘OK’ and wait for the tool to do its thing! You can watch a video of the process on my Youtube channel or below.
At the end of the process you should end up with a raster similar to the image below.
All the images in this blog post were created using ArcGIS® software by Esri. ArcGIS® and ArcMap™ are the intellectual property of Esri and are used herein under license. Copyright © Esri. All rights reserved. For more information about Esri® software, please visit http://www.esri.com.
The satellite imagery used is Landsat 8 data from the United States Geological Survey.
The song ‘I see your true colours’ was a 1986 hit for Cyndi Lauper.
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