All of Australia is burning? How maps can mislead

By Juan Pablo Guerschman

January 10, 2020

You might have seen this example, decried by some as misleading, prompting this Instagram post by its creator:

View this post on Instagram

* Didn’t realise this would go viral ???? PLEASE READ BELOW* Regarding False Information. This has occurred NOT because of this post, or my information being inaccurate. It has been Zucc’d because other people have shared this image with the caption “This is a NASA photograph”. This image has been flagged as a result. Update – this is now being corrected, finally. Should be clear in a day or so… This is a 3D visualisation of the hotspots in Australia. NOT A PHOTO. Think of this as a graph. Also note this was created as an art piece This is made from data from NASA’s FIRMS (Satellite data regarding fires) between 05/12/19 – 05/01/20. These are all the areas which have been affected by bushfires. https://firms.modaps.eosdis.nasa.gov/map/#z:5;c:137.4,-27.9;t:adv-points;d:2019-12-05..2020-01-05;l:dark_gray,firms_viirs,firms_modis_a,firms_modis_t Scale is a little exaggerated due to the render’s glow, but generally true to the info from the NASA website. Also note that NOT all the areas are still burning, and this is a compilation. This image is copyrighted by Anthony Hearsey. Please contact for usage. DONATE HERE – https://linktr.ee/lukebakhuizen?fbclid=IwAR1hxUc97BXMPIxjiJqcVW7uG8wlgkPLfyO2wVFLVRDSw5X6cXAGeBuikeM _ #bushfires #render #visualisation #data #3d #australia #climatechange #disaster #fire #infographic #cinema4d #graphic #nasa

A post shared by Anthony Hearsey (@anthony_hearsey) on Jan 4, 2020 at 10:50pm PST

As he explained, the image isn’t a NASA photo. What a satellite actually “sees” is quite different.

I’ll explain how we use data collected by satellites to estimate how much of an area is burning, or has already been burnt, and what this information should look like once it’s mapped.

Reflective images

When astronauts look out their window in space, this is what they see:

Wildfires are pictured surrounding Sydney, Australia, as the International Space Station orbited 269 miles above the Tasman Sea on Jan. 3, 2020. pic.twitter.com/XUTJLHZB8x

— Intl. Space Station (@Space_Station) January 4, 2020

It’s similar to what you might see from an airplane window, but higher and covering a wider area.

As you read this, many unmanned satellites are orbiting and photographing Earth. These images are used to monitor fires in real-time. They fall into two categories: reflective and thermal.

Reflective images capture information in the visible range of the electromagnetic spectrum (in other words, what we can see). But they also capture information in wavelengths we can’t see, such as infrared wavelengths.

If we use only the visible wavelengths, we can render the image similar to what we might see with the naked eye from a satellite. We call these “true color” images.

Note that the image doesn’t have political boundaries, as these aren’t physical features. To make satellite imagery useful for navigation, we overlay the map with location points.

From this, we can predict where the fires are by looking at the smoke. However, the fires themselves are not directly visible.

‘False color’ images

Shortwave infrared bands are less sensitive to smoke and more sensitive to fire, which means they can tell us where fire is present.

Converting these wavelengths into visible colors produces what we call “false color” images. For instance:

In this shortwave infrared image, we start to “see” under the smoke and can identify active fires. We can also learn more about the areas that are already burnt.

Thermal and hotspots

As their name suggests, thermal images measure how hot or cold everything in the frame is. Active fires are detected as “hotspots” and mapped as points on the surface.

While reflective imagery is only useful when obtained by a satellite during daytime, thermal hotspots can be measured at night—doubling our capacity to observe active fires.

This information can be used to create maps showing the aggregation of hotspots over several days, weeks, or months.

Geoscience Australia’s Digital Earth hotspots service shows hotspots across the continent in the past 72 hours. It’s worth reading the “about” section to learn the limitations or potential for error in the map.

When hotspots, which show “hot” pixels, are shown as extremely big icons, or are collected over long periods, the results can be deceiving. They can indicate a much larger area to be under fire than what is really burning.

For example, it would be wrong to believe all the areas in red in the map below are burning or have already burnt. It’s also unclear over what period of time the hotspots were aggregated.

Get smart

Considering all of the above, there are some key questions you can ask to gauge the authenticity of a bushfire map. These are:

• Where does this map come from, and who produced it?
• Is this a single satellite image, or one using hotspots overlaid on a map?
• What are the colors representing?
• Do I know when this was taken?
• If this map depicts hotspots, over what period of time were they collected? A day, a whole year?
• Is the size of the hotspots representative of the area that is actually burning?

So, the next time you see a bushfire map, think twice before pressing the share button.

Juan Pablo Guerschman is a senior research scientist at CSIRO. This article is republished from The Conversation under a Creative Commons license. Read the original article.

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