Mangroves from space: 30 years of satellite images are helping us understand how climate change threatens these valuable forests

Travel Sourced, Pixabay.
Travel Sourced, Pixabay, CC BY-SA

Nicolás Younes Cárdenas, James Cook University; Karen Joyce, James Cook University, and Stefan W Maier, James Cook UniversityAustralia is home to around 2% of the world’s mangrove forests and is the fifth most mangrove-forested country on Earth. Mangroves play a crucial role in the ecosystem thanks to the dizzying array of plants, animals and birds they feed, house and protect.

Mangrove forests help protect coastal communities from cyclones and storms by absorbing the brunt of a storm’s energy. They help our fight against climate change by storing vast amounts of carbon that would otherwise be released as greenhouse gases.

In other words, mangroves are some of our most precious ecosystems. Despite their importance, there is much we don’t know about these complex wetland forests. For example, when does their growing season start? And, how long does it last?

Usually, answering these types of questions requires frequent data collection in the field, but that can be costly and time-consuming. An alternative is to use satellite images. In the future, this will allow us to track the impacts of climate change on mangroves and other forests.

Mangroves play a crucial role in the ecosystem thanks to the dizzying array of plants, animals and birds they feed, house and protect.
Nicolas Younes

What is phenology?

Our research used satellite images to study the life cycles of mangrove forests in the Northern Territory, Queensland, and New South Wales. We compared the satellite images with field data collected in the 1980s, 1990s and 2000s, and found a surprising degree of variation in mangrove life cycles.

We’re using the phrase life cycle, but the scientific term is “phenology”. Phenology is the study of periodic events in the life cycles of plants and animals. For example, some plants flower and fruit during the spring and summer, and some lose their leaves in autumn and winter.

Phenology is important because when plants are growing, they absorb carbon from the atmosphere and store it in their leaves, trunks, roots, and in the soil. As phenology is often affected by environmental conditions, studying phenology helps us understand how climate change is affecting Australian ecosystems such as mangrove forests.

So how can we learn a lot in a short amount of time about mangrove phenology? That’s where satellite imagery comes in.

How we use satellites to study mangrove phenology

Satellites are an excellent tool to study changes in forest health, area, and phenology. Some satellites have been taking images of Earth for decades, giving us the chance to look back at the state of mangrove forests from 30 years ago or more.

You can think of satellite images much like the photo gallery in your smartphone: you can see many of your family members in a single image, and you can see how everyone grows and “blooms” over time. In the case of mangroves, we can see different regions and species in a single satellite image, and we can use past images to study the life cycles of mangrove forests.

For example, satellite images depicted below, which use data from the Australian government’s National Maps website, show how mangroves forests have changed in the Kimberley region of Western Australia between 1990 and 2019. You can see how the mangrove forest has reduced in some areas, but expanded in others. Overall, this mangrove forest seems to be doing pretty well thanks in large part to the fact this area has a reasonably small human population.

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Images: NationalMap/Data61

Our study of satellite images of mangrove forests in the Northern Territory, Queensland, and New South Wales – and how they compared with data collected on the ground – found not all mangroves have the same life cycles.

For instance, many mangrove species grow new leaves only once per year, while other species grow new leaves twice a year. These subtle, but important differences will allow us to track the impacts of climate change on mangroves and other forests.

Satellite images of mangrove forests reveal not all mangroves have the same life cycles. Here we see mangroves at different growth stages.
Nicolas Younes

How climate change affects mangrove phenology

Climate change is changing the phenology of many forests, causing them to flower and fruit earlier than expected.

Science cannot yet tell us exactly how mangrove phenology will be affected by climate change but the results could be catastrophic. If mangroves flower or fruit earlier than expected, pollinators such as bats, bees and birds may starve or move to a different forests. Without pollinators, mangroves may not reproduce and can die.

The next step in our research is to figure out how climate change is affecting the life cycles of mangroves. To do this, we will use satellite images of mangroves across Australia and factor in data on temperature and rainfall.

We think rising temperatures are causing longer periods of leaf growth, a theory we plan to test by studying data from now with satellite images from the 80s and 90s.

The next step in our research is to figure out how climate change is affecting the life cycles of mangroves.
Shutterstock

Satellite monitoring can’t do it all

Satellites can tell us a lot about how a mangrove forest is faring. For example, satellite images captured a dieback event (depicted below, using data from the Australian government’s National Maps website) that happened between 2015 and 2016, when around 7,400 hectares of mangroves died in the Gulf of Carpentaria due to drought and unusually high air and sea temperatures.

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Images: NationalMap/Data61

But satellite monitoring is not enough on its own and cannot capture the detail you can get on the ground. For example, satellites cannot capture the flowering or fruiting of mangroves because flowers are often too small and fruits are often camouflaged. Also, satellites cannot capture what happens under the canopy.

It is also important to recognise the work of researchers on the ground. Ground data allows us to validate or confirm the information we see in satellite images. When we noted some mangrove forests were growing leaves twice per year, we validated this observation with field data, and confirmed with experts in mangrove ecosystems. Field data is crucial to understand the life cycles of ecosystems worldwide and how forests are responding to changes in the climate.

Wetlands, including mangroves, are some of our most precious ecosystems.
Shutterstock

Nicolás Younes Cárdenas, Postdoctoral research fellow, James Cook University; Karen Joyce, Senior Lecturer – Remote sensing and spatial information, James Cook University, and Stefan W Maier, Adjunct Research Fellow, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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The dingo fence from space: satellite images show how these top predators alter the desert

The dingo fence in the Strzelecki Desert.
Mike Letnic

Adrian G. Fisher, UNSW; Charlotte Mills, UNSW; Mike Letnic, UNSW; Mitchell Lyons, and Will Cornwell, UNSW

As one of the longest structures in the world, the dingo fence is an icon of Australia. It stretches more than 5,600 kilometres across three states, including 150 kilometres that traverses the red sand dunes of the Strzelecki Desert.

Since it was established in the early 20th century, the fence has had one job: to keep dingoes out. The effect of this on the environment has been enormous — in fact, you can see it from outer space.

Our research has, for the first time, used satellite imagery to show the effects of predators on vegetation at a vast scale.

Dingoes eat kangaroos, and kangaroos eat grass. So on the side of the fence where dingoes are rare, there are more kangaroos, and less grass cover between sand dunes. This has important flow-on effects for the ecosystem in the region.

Similar changes to vegetation may have occurred throughout the world, where other large predators, such as wolves or big cats, have been removed. But these aren’t visible without the stark contrast boundaries like the dingo fence provide.

Reshaping the landscape

The fence was built to stop dingoes moving into sheep grazing land in southeastern Australia. As Australia’s largest terrestrial predator, dingoes pose a big threat to livestock.

Today, dingoes “inside” the fence continue to be killed by various means (not all of them humane), including poison baits, trapping and shooting.

Where dingoes are removed, increasing populations of kangaroos can lead to overgrazing.
Nick Chu

It has long been understood that removing large predators can drive changes in ecosystems across large areas. A well-known example is the removal of wolves in Yellowstone National Park in the 1920s, which saw an elk grazing increase, limiting the growth of tree and shrub seedlings.

Where dingoes are removed, increasing populations of kangaroos can lead to overgrazing. This, in turn, damages the quality of the soil, making the landscape more vulnerable to erosion.

Less vegetation can also leave small animals, such as the vulnerable dusky hopping mouse, exposed to other threats like cat predation. Indeed, 2019 research showed dingoes “outside” the fence keep cat and fox populations down in the Strzelecki Desert.

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Like cats and dogs: dingoes can keep feral cats in check

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And research from 2018 showed dingo removal could even reshape the desert landscape, as changes to vegetation alter wind flow and sand movement.

Changes this large can’t be seen from the ground

Often, however, the effects of removing predators have gone unnoticed. There are two main reasons why.

First, many large predators were removed before scientists monitored ecosystems. For example, wolves were hunted to extinction in Britain during the 17th or 18th century (although there are now proposals to reintroduce them).

Second, changes occur over such large areas, so it’s difficult to spot any differences when researching from the ground.

So to gauge the impact of the fence, we used images captured by sensors on the NASA Landsat satellites, which have been regularly observing the Earth since 1972.

We looked at a section of the fence that follows the state border of New South Wales through the Strzelecki Desert, and used this to analyse the effects of removing a top predator.

32-year time lapse of dead vegetation cover for the Strzelecki Desert.

Capturing the impact

We used images processed for Australia by the Joint Remote Sensing Research Program, which are publicly available.

Using thousands of field measurements, each satellite image was converted into an image of “fractional cover”. This splits the landscape into three core components: bare soil, green vegetation and dead or dry vegetation.

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Kangaroos (and other herbivores) are eating away at national parks across Australia

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The dead vegetation fraction, which includes all non-photosynthetic material such as dry leaves and twigs, is particularly useful in the desert. It’s a more reliable indicator of vegetation cover, as green vegetation only sticks around for three months or so after rain.

Viewing “natural colour” satellite images of the Strzelecki Desert, as our eyes see the world, doesn’t show the differences across the dingo fence very well. But when we view images of dead vegetation cover a few months after rainfall, we can see the stark effect kangaroo grazing has on the landscape, where dingoes are rare.

You can see these effects in the images below.

A natural colour Landsat image from winter in 2011 after a large rainfall event (left) does not show the dingo fence, though it does when converted to dead vegetation cover (right).
Adrian Fisher

When we analysed dead vegetation cover images for each season between 1988 and 2020, we found obvious differences between the maximum dead vegetation cover and the variability of dead vegetation cover through time, as the images below show.

The differences in vegetation cover across the dingo fence become most apparent after satellite images are converted to dead vegetation cover and analysed over time.
Adrian Fisher

The results from satellite images were supported by ground surveys. This included repeated nighttime counts of kangaroos and dingoes seen with powerful spotlights.

We also fenced off plots and observed how the vegetation changed. After five years, the kangaroo-free plots in the dingo-free areas looked like islands of grass in an otherwise bare desert.

One of the fenced plots excluding kangaroos in Sturt National Park, western NSW, showing a clear difference in vegetation cover due to grazing pressure where dingoes are rare.
Mike Letnic

What do we do about dingoes?

So, should we tear down the fence to reintroduce dingoes back into landscapes for the biodiversity benefits, like wolves in Yellowstone?

There are no simple answers to this question. Allowing dingoes to return to the landscape inside the fence will reduce kangaroo numbers and increase grass growth — but will also devastate sheep farming.

Conservationists, farmers and other land managers need to start discussing where and how we can safely return dingoes to landscapes, finding a balance between restoring ecosystems and protecting farms.

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Read more:
Living blanket, water diviner, wild pet: a cultural history of the dingo

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Adrian G. Fisher, Lecturer in Remote Sensing, UNSW; Charlotte Mills, Visiting Fellow, UNSW; Mike Letnic, Professor, Evolution and Ecology Research Centre, UNSW; Mitchell Lyons, Postdoctoral research fellow, UNSW, and Will Cornwell, Associate Professor in Ecology and Evolution, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Genome and satellite technology reveal recovery rates and impacts of climate change on southern right whales

University of Auckland tohorā research team, Department of Conservation permit DJI

Emma Carroll

After close to a decade of globe-spanning effort, the genome of the southern right whale has been released this week, giving us deeper insights into the histories and recovery of whale populations across the southern hemisphere.

Up to 150,000 southern right whales were killed between 1790 and 1980. This whaling drove the global population from perhaps 100,000 to as few as 500 whales in 1920. A century on, we estimate there are 12,000 southern right whales globally. It’s a remarkable conservation success story, but one facing new challenges.

A southern right whale calf breaches in the subantarctic Auckland Islands.
University of Auckland tohorā research team, Author provided

The genome represents a record of the different impacts a species has faced. With statistical models we can use genomic information to reconstruct historical population trajectories and patterns of how species interacted and diverged.

We can then link that information with historical habitat and climate patterns. This look back into the past provides insights into how species might respond to future changes. Work on penguins and polar bears has already shown this.

But we also have a new and surprising short-term perspective on the population of whales breeding in the subantarctic Auckland Islands group — Maungahuka, 450km south of New Zealand.

Spying on whales via satellite

Known as tohorā in New Zealand, southern right whales once wintered in the bays and inlets of the North and South Islands of Aotearoa, where they gave birth and socialised. Today, the main nursery ground for this population is Port Ross, in the subantarctic Auckland Islands.

Adult whales socialise at both the Auckland and Campbell Islands during the austral winter. Together these subantarctic islands are internationally recognised as an important marine mammal area.

In August 2020, I led a University of Auckland and Cawthron Institute expedition to the Auckland Islands. We collected small skin samples for genetic and chemical analysis and placed satellite tags on six tohorā. These tags allowed us to follow their migrations to offshore feeding grounds.

It matters where tohorā feed and how their populations recover from whaling because the species is recognised as a sentinel for climate change throughout the Southern Hemisphere. They are what we describe as “capital” breeders — they fast during the breeding season in wintering grounds like the Auckland Islands, living off fat reserves gained in offshore feeding grounds.

Females need a lot in the “bank” because their calves need a lot of energy. At 4-5m at birth, these calves can grow up to a metre a month. This investment costs the mother 25% of her size over the first few months of her calf’s life. It’s no surprise that calf growth depends on the mother being in good condition.

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I measure whales with drones to find out if they’re fat enough to breed

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Females can only breed again once they’ve regained their fat capital. Studies in the South Atlantic show wintering grounds in Brazil and Argentina produce more calves when prey is more abundant, or environmental conditions suggest it should be.

The first step in understanding the relationship between recovery and prey in New Zealand is to identify where and on what tohorā feed. The potential feeding areas for our New Zealand population could cover roughly a third of the Southern Ocean. That’s why we turn to technologies like satellite tags to help us understand where the whales are going and how they get there.

Where tohorā go

So far, all tracked whales have migrated west; away from the historical whaling grounds to the east near the Chatham Islands. As they left the Auckland Islands, two whales visited other oceanic islands — skirting around Macquarie Island and visiting Campbell Island.

It also seems one whale (Bill or Wiremu, identified as male using genetic analysis of his skin sample) may have reached his feeding grounds, likely at the subtropical convergence. The clue is in the pattern of his tracks: rather than the continuous straight line of a whale migrating, it shows the doughnuts of a whale that has found a prey patch.

Migratory track of southern right whale Bill/Wiremu, where the convoluted track could indicate foraging behaviour.

The subtropical convergence is an area of the ocean where temperature and salinity can change rapidly, and this can aggregate whale prey. Two whales we tracked offshore from the Auckland Islands in 2009 visited the subtropical convergence, but hundreds of kilometres to the east of Bill’s current location.

As Bill and his compatriots migrate, we’ve begun analysing data that will tell us about the recovery of tohorā in the past decade. The most recent population size estimate we have is from 2009, when there were about 2,000 whales.

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I am using genomic markers to learn about the kin relationships and, in doing so, the population’s size and growth rate. Think of it like this. Everybody has two parents and if you have a small population, say a small town, you are more likely to find those parents than if you have a big population, say a city.

This nifty statistical trick is known as the “close kin” approach to estimating population size. It relies on detailed understanding of the kin relationships of the whales — something we have only really been able to do recently using new genomic sequencing technology.

Global effort to understand climate change impacts

Globally, southern right whales in South Africa and Argentina have bred less often over the past decade, leading to a lower population growth rate in Argentina.

Concern over this slowdown in recovery has prompted researchers from around the world to work together to understand the relationship between climate change, foraging ecology and recovery of southern right whales as part of the International Whaling Commission Southern Ocean Research Partnership.

The genome helps by giving us that long view of how the whales responded to climate fluctuations in the past, while satellite tracking gives us the short view of how they are responding on a day-to-day basis. Both will help us understand the future of these amazing creatures.

Emma Carroll, Rutherford Discovery Fellow

This article is republished from The Conversation under a Creative Commons license. Read the original article.

‘It is quite startling’: 4 photos from space that show Australia before and after the recent rain

National Map

Sunanda Creagh, The Conversation

Editor’s note: These before-and-after-images from several sources –NASA’s Worldview application, National Map by Geoscience Australia and Digital Earth Australia – show how the Australian landscape has responded to huge rainfall on the east coast over the last month. We asked academic experts to reflect on the story they tell:

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Warragamba Dam, Sydney

Stuart Khan, water systems researcher and professor of civil and environmental engineering.

This map from Digital Earth Australia shows a significant increase in water stored in Lake Burragorang. Lake Burragorang is the name of water body maintained behind the Warragamba Dam wall and the images show mainly the southern source to the lake, which is the Wollondilly River. A short section of the Coxs River source is also visible at the top of the images.

The Warragamba catchment received around 240mm of rain during the second week of February, which produced around 1,000 gigalitres (GL) of runoff to the lake. This took the water storage in the lake from 42% of capacity to more than 80%.

Unlike a typical swimming pool, the lake does not generally have vertical walls. Instead, the river valley runs deeper in the centre and more shallow around the edges. As water storage volumes increase, so does the surface area of water, which is the key feature visible in the images.

Leading up to this intense rainfall event, many smaller events occurred, but failed to produce any significant runoff. The catchment was just too dry. Dry soils act like a sponge and soak up rainfall, rather than allowing it to run off to produce flows in waterways.

The catchment is now in a much wetter state and we can expect to see smaller rainfall events effectively produce further runoff. So water storage levels should be maintained, at least in the short term.

However in the longer term, extended periods of low rainfall and warm temperatures will make this catchment drier.

In the absence of further very intense rainfall events, Sydney will lapse back into drought and diminishing water storages.

This pattern of decreasing storage, broken only by very intense rainfall, can be observed in Sydney’s water storage history.

It is a pattern likely to be exacerbated further in future.

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Wivenhoe Dam, Brisbane

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Stuart Khan, water systems researcher and professor of civil and environmental engineering.

Lake Wivenhoe is the body of water maintained behind Wivenhoe Dam wall in southeast Queensland. It is the main water storage for Brisbane as well as much of surrounding southeast Queensland.

This image from National Map shows a visible change in colour from brown to green in the region around the lake. It is quite startling.

This is especially the case to the west of the lake, in mountain range areas such as Toowoomba, Warwick and Stanthorpe. Many of these areas were in very severe drought in January. Stanthorpe officially ran out of water. The February rain has begun to fill many important water storage areas and completely transformed the landscape.

Unfortunately, this part of Australia is highly prone to drought and we can expect to see this pattern recur over coming decades.

Much climate science research indicates more extreme weather events in future. That means more extreme high temperatures, more intense droughts and more severe wet weather.

There are many challenges ahead for Australian water managers as they seek to overcome the inevitable booms and busts of future water availability.

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Read more:
Bushfires threaten drinking water safety. The consequences could last for decades

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Australia-wide

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Grant Williamson, Research Fellow in Environmental Science, University of Tasmania

It’s clear from this map above, from NASA Worldview, the monsoon has finally arrived in northern Australia and there’s been quite a lot of rain.

On the whole, you can see how rapidly the Australian environment can respond to significant rainfall events.

It’s important to remember that most of that greening up will be the growth of grasses, which respond more rapidly after rain.

The forests that burned will not be responding that quickly. The recovery process will be ongoing and within six months to a year you’d expect to see significant regrowth in the eucalyptus forests.

Other more fire-sensitive vegetation, like rainforests, may not exhibit the same sort of recovery.

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‘This crisis has been unfolding for years’: 4 photos of Australia from space, before and after the bushfires

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Grant Williamson, Research Fellow in Environmental Science, University of Tasmania

This slider from National Map shows both fire impact, and greening up after rain.

On the left – an area west of Cooma on December 24 – you can see the yellow treeless areas, indicating the extent of the drought, and the dark green forest vegetation. This image also shows quite a lot of smoke, as you’d expect.

On the right – the area on February 22 – a lot of those yellow areas are now significantly greener after the rain. However, some of those dark green forest areas are now brown or red, where they have been burnt.

It’s clear there is a long road ahead for recovery of these forests that were so badly burned in the recent fires but they will start resprouting in the coming months.

Grant Williamson is a Tasmania-based researcher with the NSW Bushfire Risk Management Research Hub.

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Sunanda Creagh, Head of Digital Storytelling, The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

I made bushfire maps from satellite data, and found a glaring gap in Australia’s preparedness

Image courtesy of Greg Harvie, Author provided

Wallace Boone Law, University of Adelaide

On the night of January 9 2020, my wife and I secured our Kangaroo Island home and anxiously monitored the South Australian Country Fire Service (CFS) website for bushfire advice.

After many horrific weeks of bushfires, the winds had again shifted, and the fire front began a slow, nightmarish march eastward into the island’s central farmlands. Official warnings advised that the entire island was potentially under threat.

Landsat-8 false colour image of southwest Kangaroo Island, showing active bushfires on January 9, 2020.
Landsat-8, Author provided

As my good neighbours and volunteer firefighters headed off to battle the flames elsewhere on the island, I desperately wanted to find a way to help. With no firefighting training, I felt I physically had little to offer. But I reasoned that my skills and training in remote sensing and spatial science could potentially turn satellite information into useful maps to track the fires, in more detail than those provided by the Country Fire Service and Geoscience Australia.

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‘This crisis has been unfolding for years’: 4 photos of Australia from space, before and after the bushfires

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While I was ultimately successful, it wasn’t quite as straightforward as I thought. And what I learned about access to good-quality and up-to-date satellite bushfire information surprised me.

Free satellite imagery is abundant; useful information is not

In principle, there are many good sources of free satellite imagery. But selecting, sourcing, understanding and processing a multilayered satellite image into an accurate burnt area map takes technical know-how that is beyond the reach of the people who need it the most.

We are fortunate to live in a time where satellite images are constantly uploaded to the web, often within hours of acquisition. There are many reputable sources for this information, including NASA Worldview, USGS Earth Explorer, USGS LandLook Viewer, and the Sentinel EO Browser.

These websites are gateways to the world of “big satellite data”, and I quickly found myself on a steep learning curve to efficiently navigate them and find recent imagery.

Once downloaded, the next hurdle I faced was how to process a data-rich satellite image into a meaningful and accurate map of the bushfire area. I scoured the internet for “how to” blogs, academic articles, spatial algorithms, and processing codes; these too are the products of much intellectual investment by global scientists, openly and freely available.

As a spatial scientist, I naturally found all this fascinating. But as a resident of an island under assault from bushfires, I also found it frustratingly time-consuming. I crashed my computer testing algorithms. I maxed out my hard drive. I spent hours on possibilities that turned out to be dead ends.

True colour satellite imagery is often the most accessible and easily understood, but it often lacks sufficient detail to clearly identify burnt areas. In this Sentinel-2 true colour image, approximately 210,000 hectares are burnt, but bushfire-impacted areas are barely visible without advanced image processing.
Sentinel-2, Author provided

Maps help to fight fires and recover from them

In the end, I produced burnt area maps from Sentinel and Landsat satellite images captured during the fires. I learned that this kind of information can indeed help firefighting and ecological recovery efforts, both during and after bushfires.

Initially I gave the maps to a group of farming friends who had been fighting fires around their properties for weeks. They told me the maps helped save time in assessing which areas had already burned, allowing them to focus on defending unburnt areas, and to make decisions on where to move livestock and install firebreaks.

The positive feedback inspired me to customise my processing techniques, so I could provide updates more quickly when new satellite images became available.

I embedded appropriate safety disclaimers into the maps and released them on Twitter and Spatial Points, a blog site managed by my research group at the University of Adelaide.

Within hours, I received messages that the maps were being used for ecological recovery efforts. The maps successfully highlighted remaining patches of habitat where endangered and vulnerable species had found refuge. Several government agencies even contacted me for burnt area information, which I’m told was used to assess infrastructure damage and habitat loss.

Processed Sentinel-2 satellite image. Red areas suggest burnt vegetation. Variation in red hues are caused by dominant vegetation type and soils.
Sentinel-2/W. Boone Law, Author provided

National knowledge gap

My experience shows there is a swag of free and regularly updated satellite imagery available, which when interpreted and presented appropriately can potentially be hugely helpful to firefighting and recovery efforts.

However, I am concerned that neither the general public nor decision-makers seem fully aware of the range of satellite information on offer. Nor is there a good understanding of the advanced technical skills needed to access and process imagery into useful map data.

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Read more:
Yes, the Australian bush is recovering from bushfires – but it may never be the same

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This leads me to wonder whether I have stumbled upon a glaring knowledge gap in Australia’s bushfire preparedness.

How can we overcome this technological and information bottleneck? I don’t propose to have all the answers, but I do believe it would be sensible for governments, industry and research agencies to invest in the kind of capabilities that I developed while trying to protect my own local community.

As Australia faces a future of more frequent and extreme bushfires, there will doubtless be many people who would be glad of this kind of information when they need it most.

Wallace Boone Law, PhD Candidate, University of Adelaide

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Satellite measurements of slow ground movements may provide a better tool for earthquake forecasting

The 2016 Kaikoura earthquake shattered the surface and twisted railway lines.
Simon Lamb, CC BY-ND

Simon Lamb, Victoria University of Wellington

It was a few minutes past midnight on 14 November 2016, and I was drifting into sleep in Wellington, New Zealand, when a sudden jolt began rocking the bed violently back and forth. I knew immediately this was a big one. In fact, I had just experienced the magnitude 7.8 Kaikoura earthquake.

Our research, published today, shows how the slow build-up to this earthquake, recorded by satellite GPS measurements, predicted what it would be like. This could potentially provide a better tool for earthquake forecasting.

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Shattering the landscape

The day after the quake, I heard there had been huge surface breaks in a region extending for more than 170 km along the eastern part of the northern South Island. In some places, the ground had shifted by 10 metres, resulting in a complex pattern of fault ruptures.

In effect, the region had been shattered, much like a fractured sheet of glass. The last time anything like this had happened was more than 150 years ago, in 1855.

Quite independently, I had been analysing another extraordinary feature of New Zealand. Over the past century or so, land surveyors had revealed that the landscape is moving all the time, slowly changing shape.

These movements are no more than a few centimetres each year – but they build with time, relentlessly driven by the same forces that move the Earth’s tectonic plates. Like any stiff material subjected to excessive stress, the landscape will eventually break, triggering an earthquake.

I was studying measurements made with state-of-the-art global positioning system (GPS) techniques – and they recorded in great detail the build-up to the 2016 Kaikoura earthquake over the previous two decades.

A mobile crust

GPS measurements for regions at the edges of the tectonic plates, such as New Zealand, have become widely available in the last 15 years or so. Here, the outer part of the Earth (the crust) is broken up by faults into numerous small blocks that are moving over geological time. But it is widely thought that even over periods as short as a few decades, the GPS measurements still record the motion of these blocks.

New Zealand straddles the boundary between the Australian and Pacific tectonic plates, with numerous active faults. Note the locked portion of the underlying megathrust.
Simon Lamb, CC BY

The idea is that at the surface, where the rocks are cold and strong, a fault only moves in sudden shifts during earthquakes, with long intervening periods of inactivity when it is effectively “locked”. During the locked phase, the rocks behave like a piece of elastic, slowly changing shape over a wide region without breaking.

But deeper down, where the rocks are much hotter, there is the possibility that the fault is slowly slipping all the time, gradually adding to the forces in the overlying rocks until the elastic part suddenly breaks. In this case, the GPS measurements could tell us something about how deep one has to go to reach this slipping region, and how fast it is moving.

From this, one could potentially estimate how frequently each fault is likely to rupture during an earthquake, and how big that rupture will be – in other words, the “when and what” of an earthquake. But to achieve this understanding, we would need to consider every major fault when analysing the GPS data.

Invisible faults

Current earthquake forecasting “reverse engineers” past distortions of the Earth’s surface by finding all the faults that could trigger an earthquake, working out their earthquake histories and projecting this pattern into the future in a computer model. But there are some big challenges.

The most obvious is that it is probably impossible to characterise every fault. They are too numerous and many are not visible at the surface. In fact, most historical earthquakes have occurred on faults that were not known before they ruptured.

Our analysis of the GPS measurements has revealed a more fundamental problem that at the same time opens new avenues for earthquake forecasting. Working with statistician Richard Arnold and geophysicist and modeller James Moore, we found the GPS measurements could be better explained if the numerous faults that might rupture in earthquakes were simply ignored. In other words, surface faults seemed to be invisible when looking at the slow movements recorded by GPS.

There was only one fault that mattered – the megathrust that runs under much of New Zealand. It separates the Australian and Pacific tectonic plates and only reaches the surface underwater, about 50 to 100km offshore. Prior to the Kaikoura earthquake, the megathrust was locked at depths shallower than about 30km. Here, the overlying Australian plate had been slowly changing shape like a single piece of elastic.

Slip at depth on the megathrust drives earthquakes in New Zealand, including the M7.8 Kaikoura Earthquake.
Simon Lamb, CC BY

The pacemaker for future quakes

In the conventional view, every big fault has its own inbuilt earthquake driver or pacemaker – the continuously slipping part of the fault deep in the crust. But our analysis suggests that these faults play no role in the driving mechanism of an earthquake, and the pacemaker is the underlying megathrust.

We think the 2016 Kaikoura earthquake provides the vital clue that we are right. The key observation is that numerous ruptures were involved, busting up the boundary between the two plates in a zone that ran more-or-less parallel to the line of locking on the underlying megathrust. This is exactly what we would anticipate if the slow build-up in stress was only driven by slip on the megathrust and not the deeper parts of individual crustal faults.

I remember once watching a documentary about the making of the Boeing 777 aircraft. The engineers were very confident about its design limits under flying conditions, but the Civil Aviation Authority wanted it tested to destruction. In one test, the vast wings were twisted so that their tips arced up to the sky at a weird angle. Suddenly, there was a bang and the wings snapped, greeted by loud cheering because this had occurred almost exactly when predicted. But the details of how this happened, such as where the cracks of metal fatigue twisted the metal, were something that only the experiment could show.

I think this is a good analogy for realistic goals with earthquake prediction. The Herculean task of identifying every fault and its past earthquake history may be of only limited use. In fact, it is becoming clear that earthquake ruptures on individual faults are far from regular. Big faults may never rupture in one go, but bit by bit together with many other faults.

But it might well be possible to forecast when there will be severe shaking in a region near you – surely something that is equally as valuable.

Simon Lamb, Associate Professor in Geophysics, Victoria University of Wellington

This article is republished from The Conversation under a Creative Commons license. Read the original article.

An artist’s surreal view of Australia – created from satellite data captured 700km above Earth

Infrared and visible light satellite data is recoloured to produce striking images of Australia.
Grayson Cooke , Author provided

Grayson Cooke, Southern Cross University

There are more than 4,800 satellites orbiting Earth. They bristle with sensors – trained towards Earth and into space – recording and transmitting many different wavelengths of electromagnetic radiation.

Governments and media corporations rely on the data these satellites collect. But artists use it too, as a new way to image and view the Earth.

I work with Geoscience Australia and the “Digital Earth Australia” platform to produce time-lapse images and video of Australian landforms using satellite data.

My Open Air project, produced through a collaboration with Australian painter Emma Walker and the music of The Necks, features macro-photography of Emma Walker’s paintings set against time-lapse satellite imagery of Australia.

Open Air will be launched in Canberra on September 20, 2018.

Trailer: Open Air – showing Lake Gairdner in South Australia with turquoise desert, red salt lakes and pink clouds (Grayson Cooke 2017).

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Read more:
Curious Kids: How do satellites get back to Earth?

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Open access to satellite data

We see satellites as moving pin-pricks in the night sky, or occasionally – as with the recent return to Earth of the Chinese Tiangong space station – as streaks of light. And most us would have heard about satellite data being used for surveillance, for GPS tracking and for media broadcasting.

But artists can divert satellite data away from a purely instrumental approach. They can apply it to produce new ways of seeing, understanding and feeling the Earth.

Of course satellites are expensive to launch and maintain. The main players are either powerful corporate providers like Intelsat, enormous public sector agencies like NASA and the European Space Agency (ESA), or private sector startups with links to these groups.

Luckily, many of these agencies make their data freely available to the public.

The NASA/US Geological Survey Landsat program makes 40 years of Earth imaging data available through Earth Explorer. The ESA provides data from their Sentinel satellites to users of the Copernicus Open Access Hub.

In Australia, Geoscience Australia‘s Digital Earth Australia platform provides researchers and the public with access to Australian satellite data from a range of agencies.

Landsat 8 image acquired in Australia in May 2013 over Cambridge Gulf and the Ord River estuary in Western Australia. Visible light bands highlight the different types of water within the estuary. Shortwave and near infrared bands highlight the mangroves and vegetation on the land.
Geoscience Australia, Author provided

Understanding and processing the data

Making satellite imaging data accessible, though, is not the same thing as making it usable. There is considerable technical know-how required to process satellite data.

The Landsat and Sentinel satellites are used by scientists and the private sector to monitor environmental change over time, using what is known as “remote sensing”. They travel in the low Earth orbit range, around 700km above the Earth and circle the Earth in around 90 minutes. After numerous orbits, they return to the exact same spot every 16 days.

Landsat and Sentinel satellites are equipped with sensors that record reflected electromagnetic radiation in a range of wavelengths. Some of these wavelengths fall within the visible light part of the spectrum (between 390-700 nanometers). In that sense, satellites image the Earth in a way comparable to a digital camera.

This image shows the percentage of time since 1987 that water was observed by the Landsat satellites on the floodplain around Burketown and Normanton in northern Queensland. The water frequency is shown in a colour scale from red to blue, with areas of persistent water observations shown in blue colouring, and areas of very infrequent water observation shown in red colouring.
Geoscience Australia, Author provided

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Read more:
A sports car and a glitter ball are now in space – what does that say about us as humans?

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But the satellites also record other wavelengths, particularly in the near and shortwave infrared range. Vegetation, water and geological formations reflect and absorb infrared light differently to visible light. Recording these wavelengths allows scientists to track, for instance, changes in vegetation density or surface water location that indicate drought, flood or fire.

A single satellite image is made up of numerous bands recording data in very specific wavelengths. Getting a full-colour image requires processing in a GIS application to combine them, and assign the bands to either red, green or blue in an output image.

Images collected over 12 months at the Gulf of Carpentaria – 2016.
Grayson Cooke, Author provided

Bringing creativity to the data

This is where creativity can enter the picture. Being able to create false colour images that combine infrared and visible light in different ways allows me to produce beautifully surreal images of Australian landforms.

The image below shows the variance in environmental conditions over 12 months in 2016 at the Stirling Range National Park in WA.

A false colour image of Stirling Range National Park created by combining data relating to infrared and visible light.
Grayson Cooke, Author provided

Because geoscientists need clear images of the earth’s surface to analyse, they filter clouds from the data. I chose to take the opposite approach, highlighting the incredible array of meteorological conditions experienced by the country.

Clouds passing over the Eyre Peninsula in 2016.
Grayson Cooke, Author provided

There are many other artists working with satellite data. Clement Valla’s Postcards from Google Earth focuses on glitches in Google’s mapping algorithm, and bio-artist Suzanne Anker uses satellite imaging to produce extruded 3D environments in petri dishes.

Working with the Nevada Museum of Art, photographer Trevor Paglen will launch the Orbital Reflector satellite as an inflatable, visible sculpture, a prompt for wonder and reflection.

Artists place satellite data and usage in new contexts. They question surveillance practices and expose scientific tools and representations to new audiences outside science and the private sector.

The thousands of satellites winging their way around the Earth represent power and possibility, a chance to look again at the intersection between humankind and a changing planet.

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“Open Air” will be officially launched at the National Film and Sound Archive in Canberra on September 20. It will also screen at the Spectra conference in Adelaide in October.

Grayson Cooke, Associate Professor, Deputy Head of School (Research), Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

South Sudan: Satellite Tracking Elephants

Article: Papua New Guinea – Bagana Volcano Eruption

The following link is to an article reporting on the eruption of the Bagana Volcano in Papua New Guinea. The photo from a satellite in the article is brilliant.

For more visit:
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=77975