Gliding Across The Ice

ESA’s Earth Explorer CryoSat. Image courtesy of ESA/AOES Medialab.

ESA’s Earth Explorer CryoSat. Image courtesy of ESA/AOES Medialab.

There’s been a flurry of reports in the last couple of weeks, reporting melting ice and retreating glaciers in Greenland and the Himalayas respectively.

A paper by McMillan et al (2016), titled ‘A high-resolution record of Greenland mass balance’ and published in Geophysical Research Letters earlier this month, highlighted that Greenland’s melting ice has contributed twice as much to sea level rise than in the previous twenty years. The research used CryoSat-2 radar altimetry between 1 January 2011 and 31 December 2014 to measure elevation changes in the Greenland ice.

The main instrument on ESA’s CryoSat-2 satellite is a Synthetic Aperture Radar (SAR)/Interferometric Radar Altimeter known as SIRAL, although also carries a second version of this instrument as a back-up. The SIRAL instrument has been enhanced to detect millimetre changes in the elevation of both ice-sheets and sea-ice. It sends out bursts of radar pulses, with an interval of 50 μs between them, covering a 250 m wide strip of the Earth and measures the time of the return signal to determine the height of the satellite above the Earth. It requires a very accurate measurement of its position to calculate this, and so it also carries a Doppler Orbit and Radio Positioning Integration by Satellite (DORIS) instrument to determine its orbit.

The research team discovered that the Greenland Ice Sheet lost an average of 269 ± 51 Gt/yr of snow and ice during the investigative period, which compared well with other independent measurements from sensors such as the Gravity Recovery and Climate Experiment (GRACE) satellite and results from climate models. This snow and ice loss corresponds to a 0.75 mm contribution to global sea-level rise each year.

It was reported this week that research undertaken by the Indian Space Research Organisation, Wadia Institute of Himalayan Geology and other institutions have revealed that the majority of the glaciers in India are retreating; albeit at different rates. Using remote sensing data up to 2006, the study looked at 82 glaciers in the Bhagirathi and Alaknanda river basins and found that there had been an overall loss of 4.6% of the glaciers within the region. The Dokriani glacier in Bhagirathi is retreating between 15 and 20 metres per year since 1995, whereas the Chorabari glacier in the Alaknanda basin is retreating 9-11 metres per year.

It’s interesting to read the retreating glacial picture alongside the research published by Schwanghart et al (2016), titled ‘Uncertainty in the Himalayan energy–water nexus: estimating regional exposure to glacial lake outburst floods’, in Environmental Research Letters. Here the research team completed the first region wide risk assessment of floods from glacial lakes, even though this only covered around a quarter dams in the Himalaya’s. The study mapped 257 dams against more than 2,300 glacial lakes within the region and found that over 20% of the dams are likely to be overwhelmed with flood water as rock systems that surround glacier-fed lakes fail. Due to the hydro-electric power needs of the region, more dams have been built in recent years, putting them closer to glacier-fed lakes.

The potential danger of this issue is demonstrated by the collapse of Zhangzangbo, a glacier-fed lake in southern Tibet, in 1981 where 20 million cubic meters of floodwater damaged hydroelectric dams and roads causing damage of approximately $4 million.

These three reports also show the potential danger melting ice and glaciers pose both locally and globally. Remote sensing data, particularly from satellites such as CryoSat-2, can help us monitor and understand whether this danger is increasing.

Flooding Forecasting & Mapping

Sentinel-1 data for York overlaid in red with Pixalytics flood mapping layer based on Giustarini approach for the December 2015 flooding event. Data courtesy of ESA.

Sentinel-1 data for York overlaid in red with Pixalytics flood mapping layer based on Giustarini approach for the December 2015 flooding event. Data courtesy of ESA.

Media headlines this week have shouted that the UK is in for a sizzling summer with temperature in the nineties, coupled with potential flooding in August due to the La Niña weather process.

The headlines were based on the UK Met Office’s three month outlook for contingency planners. Unfortunately, when we looked at the information ourselves it didn’t exactly say what the media headlines claimed! The hot temperatures were just one of a number of potential scenarios for the summer. As any meteorologist will tell you, forecasting a few days ahead is difficult, forecasting a three months ahead is highly complex!

Certainly, La Niña is likely to have an influence. As we’ve previously written, this year has been influenced by a significant El Niño where there are warmer ocean temperatures in the Equatorial Pacific. La Niña is the opposite phase, with colder ocean temperatures in that region. For the UK this means there is a greater chance of summer storms, which would mean more rain and potential flooding. However, there are a lot of if’s!

At the moment our ears prick up with any mention of flooding, as Pixalytics has just completed a proof of concept project, in association with the Environment Agency, looking to improve operational flood water extent mapping information during flooding incidents.

The core of the project was to implement recent scientific research published by Matgen et al. (2011), Giustarini et al. (2013) and Greifeneder et al. (2014). So it was quite exciting to find out that Laura Guistarini was giving a presentation on flooding during the final day of last week’s ESA Living Planets Symposium in Prague – I wrote about the start of the Symposium in our previous blog.

Laura’s presentation, An Automatic SAR-Based Flood Mapping Algorithm Combining Hierarchical Tiling and Change Detection, was interesting as when we started to implement the research on Sentinel-1 data, we also came to the conclusion that the data needed to be split into tiles. It was great to hear Laura present, and I managed to pick her brains a little at the end of the session. At the top of the blog is a Sentinel-1 image of York, overlaid with a Pixalytics derived flood map in red for the December 2015 flooding based on the research published by Laura

The whole session on flooding, which took place on the last morning of the Symposium, was interesting. The presentations also included:

  • the use of CosmoSkyMed data for mapping floods in forested areas within Finland.
  • extending flood mapping to consider Sentinel-1 InSAR coherence and polarimetric information.
  • an intercomparison of the processing systems developed at DLR.
  • development of operational flood mapping in Norway.

It was useful to understand where others were making progress with Sentinel-1 data, and how different processing systems were operating. It was also interesting that several presenters showed findings, or made comments, related to the double bounce experienced when a radar signal is reflected off not just the ground, but another structure such as a building or tree. Again it is something we needed to consider as we were particularly looking at urban areas.

The case study of our flood mapping project was published last week on the Space for Smarter Government Programme website as they, via UK Space Agency, using the Small Business Research Initiative supported by Innovate UK, funded the project.

We are continuing with our research, with the aim of having our own flood mapping product later this year – although the news that August may have flooding means we might have to quicken our development pace!

Two Fantastic Remote Sensing Innovations

Aberdeenshire (Scotland) January 2016 flooding captured by Sentinel-1; Data courtesy of Copernicus/ESA

Aberdeenshire (Scotland) January 2016 flooding captured by Sentinel-1

Two academic remote sensing research announcements caught our eye this week. To be fair most remote sensing announcements catch our eye, but these two were intriguing as they are repurposing remote sensing techniques.

Remote Sensing the Human Body
Researchers at Kyoto University Centre of Innovation have developed a system based on spread-spectrum radar technology to remotely sense signals from the human body. They have focussed on heartbeats, although they acknowledge that other elements such as breathing and movement are also measured by the system. It uses a unique signal analysis algorithm to extract the beats of the heart from the radar signals, and then calculates the intervals to give the heartbeat.

Anyone who has ever needed to wear a Holter monitor for twenty-four or forty-eight hours will appreciate the advantage of having measurements taken remotely, in real time. In addition, under controlled conditions, the system has worked with a similar accuracy to an electrocardiographs (ECG). This will be music to the ears of regular ECG takers who know how much removing those sticky electrode pads can hurt!

This system is still at an early developmental stage and further testing and validation is necessary, but it offers a potential new use of remote sensing technology.

Remote Sensing & Social Media
Researchers from Pennsylvania State University have led a project developing an innovative way of combining social media and remote sensing. The research was undertaken on a flood in Boulder, Colorado in September 2013 with a particular focus on urban locations.

The team identified over 150,000 flood related tweets and used a cloud-based geo-social networking application called CarbonScanner, from The Carbon Project, to cluster the pictures from Twitter and Flickr to identify flooding hotspots. These were then used to obtain optical data, in this case from the high resolution commercial satellite Worldview 2 and the lower resolution, but freely available, Landsat 8.

A machine learning algorithm was developed to perform a semi-automated classification to identify individual pixels that contained water. As the data was optical it used the near infrared band as, due to its strong absorption, water is easily distinguishable from soil and vegetation. The researchers believe that this methodology has the potential to give emergency teams near real-time data, which could make live-saving differences to their work.

This is a particularly interesting development for us, given our current work on flood-mapping using synthetic aperture radar (SAR) data as part of the Space for Smarter Government Programme.

These two current examples show that remote sensing is an exciting, innovative and developing field, and one that is not solely related to Earth observation.

The Question of Dredging

Dredging has been a hugely contentious issue in the UK ever since the St Jude’s storm hit the country on the 28 October 2013; this marked the beginning of a relentless winter weather pattern of heavy rainfall and high winds. This severe weather coupled with coastal surges breaching flood defences led to large parts of the UK to be under water – a situation that still exists for significant parts of Somerset. Satellite data was used to map the flooded areas as part of the flood response by UK government agencies; more details can be found in our post Is the Southern UK Flooding a Disaster?

As the flooding occurred local communities bemoaned the lack of river dredging in recent times, and they felt this was a significant contributing factor for the rising water levels. In Prime Minister’s Questions on the 29th January this year, David Cameron announced that once flood waters in Somerset had drained away, rivers in the county will be dredged. Dredging itself also creates problems, releasing suspended sediment into the river water and secondly the need to get rid of the dredged material.

Image of East Devon, UK taken by Landsat 8 on 4th November 2013.  The River Exe flows from top to bottom and the River Teign from left to right. Plumes of suspended sediment are clearly visible following periods of heavy rainfall in late October and early November 2013.  Image courtesy of the U.S. Geological Survey

Image of East Devon, UK taken by Landsat 8 on 4th November 2013.

The River Exe flows from top to bottom and the River Teign from left to right. Plumes of suspended sediment are clearly visible following periods of heavy rainfall in late October and early November 2013.

Image courtesy of the U.S. Geological Survey

In addition to flood mapping, satellite data can also be used to map and monitor sediment transported. The Landsat 8 image on the right shows the plumes of sediment visible around the east Devon coastline just one week after the St. Jude’s storm. Since 1972 the Landsat mission has continuously monitoring the Earth’s surface; and makes this information freely accessible for use across a range of sectors.

This week it was announced that dredging of the River Tamar, on the border between Devon and Cornwall, will continue for the next two years in order to keep the channels clear for access to Devonport Dockyard. The silt from this process will be deposited in Whitsand Bay, Cornwall, despite the area being designated as a Marine Conservation Zone.

Dredging is a tool coming back into the UK flood defence armoury; the benefits, and potential harm, will be monitored closely in the coming months and years.

Next week’s we’ll be looking at the accelerated coastal erosion from the winter storms.

Blog produced by Bryony Hanlon, work placement student with Pixalytics, and Andy Lavender.

Is the Southern UK Flooding a Disaster?

Landsat 8 image acquired on the 23 January 2014 showing the floods within Somerset, UK, with the river Parrett flowing into the Bristol Channel in the top left corner; courtesy of the USGS and NASA.

Landsat 8 image acquired on the 23 January 2014 showing the floods within Somerset, UK, with the river Parrett flowing into the Bristol Channel in the top left corner; courtesy of the USGS and NASA.

Over the last couple of months flooding has impacted the southern half of the UK. Coastal surges affected the South East of England in early December and the Somerset levels became flooded in the middle that month; and they remain flooded. The South West was battered by huge waves and rain at start of February – you may have seen the dangling railway lines in Dawlish, which is our main rail connection to everywhere north of Plymouth! Over the last few days the flooding has impacted communities bordering the river Thames and river Severn. Further rainfall, tidal surges, river flooding and ground water flooding means parts of UK are likely to be ‘under water’ for many months to come. Is this a disaster?

The Oxford Dictionary describes a disaster as a sudden accident or a natural catastrophe that causes great damage or loss of life – the current scenario seems to fulfil this definition. In the UK the Prime Minster is taking charge by chairing COBRA Meetings. Whilst COBRA sounds really impressive, COBRA actually stands for Cabinet Office Briefing Room A; and so less impressively, it’s only referring to the room the meeting is in! However, COBRA is the emergency committee coordinating the Government and associated agencies response to the flooding situation. COBRA is meeting regularly, is it a disaster?

The Earth Observation community considers the UK is experiencing a disaster. This was recognised by the activation of the International Charter: Space and Major Disasters on the 6th February for flooding in South West England. When this charter is activated, space agencies around the world use their resources to collect satellite datasets that can be used to help mitigate the effects on human life and property.

Earth Observation offers the opportunity to see the big picture, something that is usually difficult in disaster situations, as well as what is happening at street level. It gives governments, civil protection agencies and international relief organisations key information to assist their decision-making processes. The UK Space Agency works in collaboration with DMCii (a subsidiary of SSTL that operates the Disaster Monitoring Constellation) to contribute imagery with a recent image showing the flooding in Somerset.

In 2013 there were 38 activations of the Disaster Charter. Flooding in the UK also activated the charter on the 6th January this year and the 4th December last year. Since the 6th February there have been three further activations of the charter on the 7th for Floods in Zimbabwe, on the 10th for snowfall in South Korea and on 11th for a flood and landslide in Burundi.

With weather patterns evolving around the globe, the activation frequency of this charter is likely to increase. Earth Observation supports the observation, and management, of the planet and its natural resources; and supporting disaster relief situations is one of its most beneficial uses.