Interpretation is the Key to Remote Sensing

Landsat 8 Image, acquired on 19 May 2014. Data courtesy of NASA/USGS.

Landsat 8 Image, acquired on 19 May 2014. Data courtesy of NASA/USGS.

Landsat 8 Image, acquired on 20th May 2015. Data courtesy of NASA/USGS.

Landsat 8 Image, acquired on 20th May 2015. Data courtesy of NASA/USGS.

Remote sensing just produces pretty satellite images doesn’t it? Whilst remote sensing can produce fantastic looking images, the interpretation of the imagery is important. Take the two images at the top of the blog, both are from South America and were acquired by Landsat 8; although they were taken on different days.

In the centre of each image is a white landscape feature; the question is, what are the features and are they the same thing? White colour patches on satellite images can represent a number of things. It could indicate a snow or ice feature like a glacier, or sunglint off the ocean or other body of water, it could be fog or simply be showing that there were clouds on the day that the image was acquired.

The top image with the white feature along its length is the Perito Moreno Glacier, located in the Santa Cruz Province of Argentina. It is a 250 square kilometre glacial formation that’s 30 km in length, and interestingly it is one of three Patagonian glaciers that is currently growing.

The second image is a completely different type of landscape feature, although it might be familiar to remote sensing experts! It shows the world’s largest salt flat known as Salar de Uyuni, which is located in the Daniel Campos Province in southwest Bolivia. It has a salt crust a few metres thick over a pool of brine. It’s an extremely flat area, with the altitude varying less than one meter over its 10,582 square kilometres; the flatness of the surface is used to calibrate altimeters on Earth observation satellites.

Remote sensing produces images, and these can be freely sourced from places such as NASA’s Landsat archive or the EU’s Copernicus programme; or images can be purchased from a variety of commercial providers. However getting an image is only the starting point, you need to ensure that you know what you are looking at. This is where the skill in remote sensing, whether it is in the interpretation of the actual image or in the application of scientific theory to create new data derived from the image data.

Remote sensing experts often prefer to work with the data underlying images rather than the images themselves; whereas, novices often work with the images. It’s important to realise that imagery can require interpretation and to not simply accept the face value of what is on the image.

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