- This week's guest video is from a channel
based around explaining interesting things, on location,
with a style that sometimes feels like a BBC documentary from the early 2000s.
So, introducing someone who is going to have my job in a few years,
James, from Atomic Frontier,
who starts his video about bushfires and satellites
by climbing a tree.
James, take it away.
- I'm up a tree in the land of Down Under.
Not only does this perilous position give us a convenient place to hide
from the hordes of killer kangaroos down on ground level,
but it also provides a convenient vantage point
from which to look for another very Australian threat.
Since the 1930s, lookout trees have been used to spot bushfires
in the giant karri forests of Western Australia.
This one, the 65 metre tall, Dave Evans Bicentennial Tree,
is the tallest tree house in the world.
From the top we can see up to 20 kilometres in every direction.
However, to monitor something, the size of a continent,
we're going to have to climb even higher,
to the satellites orbiting far above our heads.
Here is a series of images
taken by Japan's Himawari weather satellite.
It's in a geostationary orbit where the 24-hour rotation of the Earth
is exactly matched by the satellite's own 24-hour orbit.
Such orbits are only possible at an altitude of 36,000km
and directly above the equator.
Himawari takes a photograph every 10 minutes
giving meteorologists the ability to observe weather as it develops in real time.
Between June 2019, and May 2020,
18 million hectares of Australian bush burned
in what is now known as the Black Summer.
34 people, and more than 4 billion terrestrial vertebrates
perished in the flames.
From its unique vantage point the Himawari weather satellite watched on
as cities on the eastern seaboard were smothered in the smoke.
Geostationary satellites aren't a great fire detection tool.
By the time the smoke is visible the flames beneath have grown too large
to control effectively.
We spotted the fire, but your house burned down six hours ago.
By dropping from a geostationary to low earth orbit
we can massively improve resolution.
However, this comes at the cost of no longer being able to match
the rotational period of the Earth.
To achieve live coverage we therefore need a lot of satellites,
so that as one leaves an area, the next one arrives.
Most fire services can't afford to buy multiple
290 million-dollar apiece weather satellites,
but these small cubesats come in at a fraction of that cost.
You can launch about 4,000 of them
for the same price as one weather satellite.
CubeSats were originally intended for low-cost research,
but after more than 15 years of research and development
they're now good enough for use in industry.
This one, built by Curtin University in Western Australia
will eventually be able to take photos with a resolution down to 4m across.
Rather than just looking for smoke,
at this resolution we can also spot the fire itself.
Flames are red, so by including a simple red filter
we can quickly zero in on the target.
Unfortunately, as you can see from my assorted collection
of car boot sale items, which yes, does include the obligatory red t-shirt,
we're likely to get a lot of false positives
from things that are red, but also not on fire.
To refine the search further we need to include another condition.
Fires have a characteristic flicker
growing brighter and dimmer roughly 12 times per second.
By first searching for the colour red,
and then checking that it flickers at this 12 hertz,
we can detect fires when they begin.
As the fires grow, so do their accompanying clouds of smoke.
After a point, we can't even see the flames.
This is terrible for firefighters and residents
who need to know where the fire is, and its rate of growth,
in order to stay safe.
In order to look through the smoke, we can use infrared radiation.
Now, our eyes can't see in infrared like my camera can,
but if you hold your hand close to your face,
you can feel it as heat.
Infrared radiation has a few key benefits over the visible variety.
First of all, there's a lot more infrared radiation
being produced by a fire than visible light.
Next, it has a much longer wavelength,
so it's able to pass through clouds of smoke
pretty much unaffected.
Together, this means that we can detect and then track large blazes.
Infrared cameras have quite a low resolution,
which means that small spot fires will often go undetected.
We need to monitor them, however,
because these spot fires can act as important precursors
to the larger blaze, jumping over fire breaks,
and spreading to new patches of forest.
Fortunately, there is one final fire detection technique,
which I'm going to share with you,
especially designed for these smaller blazes.
However, please, don't try this at home.
Here are three beakers, into which I've placed about 20ml of ethanol.
Into the first we have a pure solution,
and the others are mix of boric acid and potassium chloride.
We're going to see what happens when they ignite.
As you can see, ethanol burns with a clear, slightly orange-red flame,
it's quite dim and almost invisible.
That's because it's quite a clean-burning fuel
producing a minimum amount of soot.
It's the heated soot which gives a regular fire its orange-red flame,
but for our experiment that would just get in the way.
Next, we have the boron.
It burns with a bright green flame.
It's not because of some special effects or camera trickery,
it legitimately looks like the alchemists' wildfire in "Game of Thrones."
The green is actually a mix of a few very specific wavelengths,
characteristic of the electron configuration of the vaporised boron ions.
When the ions are heated,
their electrons jump up and down the energy levels
producing wavelengths specific to that jump.
Different elements have different electron configurations
leading to a range of possible colours.
Trees don't contain all that much boron,
which is why wood doesn't burn with a green flame.
However, they do contain a lot of potassium
where it's used for cell metabolism.
The potassium burns with a dim purple flame.
It's a bit disappointing in the visible spectrum,
but it doesn't only produce visible wavelengths,
it also produces infrared.
The 770 nanometer wavelength in particular is very bright.
Since potassium only produces this wavelength
during combustion, if we tune our detectors to this band,
we can be certain that it is coming from an active blaze.
With the right filters we can even identify fires smaller than a pixel
since the 770 nanometer emission is so bright.
We have come a long way from the bushfire lookout trees of the past.
With fleets of low-cost satellites tuned to specific wavelengths,
we can detect bushfires as they flare up
and then track their progress even as the plumes of smoke start to grow.
The fire service may no longer need these lookout trees,
but, they can provide visitors some spectacular views
of the forests that we're trying to protect.
The only question is: how am I going to get down from here?
This has been James Dingley from the Atomic Frontier.
Keep looking up.
- Check out Atomic Frontier!
You could start with James's video about a country-sized telescope
or about the world's deepest scuba dive. Next week,
me. But also, not me. It'll make sense, I promise.