Overview:
The example below shows a Image Juxtaposition H5P content type to help demonstrate to students how different colour composites can be used in Remote Sensing to highlight different environmental features. Click and drag the slider across the images to change the visible layer.
The activity was created within H5P’s activity builder wizard, which is a simple and intuitive system for creating these and similar interactive teaching content. The activity was designed by Dr Kristofer Chan and can be easily adapted to other Geographical concepts and with flexibility over the number of boxes and tailored responses.
Interactive content below
In this example, the image can be swapped between a ‘true colour’ composite and a ‘false colour’ composite of the Salton Sea and Alamo river valley, California.
We see light in three primary colours: Red, Green & Blue. Any colour you can see can be made by mixing some combination of these (with the exception of black, which is the absence of light). Thus, colour images as we see them can be thought of as overlaid red, green and blue images – otherwise known as a composite image.
A true colour composite show the world as we are are used to seeing: with red colours representing reflected red bands of light, and likewise for the green and blue bands. As many satellites collect many different wavelengths of light (some not visible to the human eyes), we can create what are known as false-colour composites, so-called because the bands we select do not correspond to the red, green and blue bands of a true colour image.
False-colour composite can take any band combination. The false-color composite shown below is made by showing Near Infra-Red (NIR) bands detected from a satellite in red, the red light bands shown in green, and the green light bands shown in blue. This is a very common false colour combination as it is aids differentiation of vegetation (red areas) from other surfaces. Remember that red sections of the image actually represent high amounts of NIR light reflected. Leaves on vegetation are highly adapted at selectively absorbing visible light, and reflecting NIR waves – which would otherwise cause the plant to heat up, dry out, and ultimately to wild then die. Thus, vegetated areas are shown in red (indicating high reflectance of NIR light).
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