Sentinel To Be Launched

Sentinel-2 Image of Plymouth from 2016. Data courtesy of Copernicus/ESA.

Sentinel-2B was launched at 01:49 GMT on the 7th March from Europe’s Spaceport in French Guiana. It’s the second of a constellation of optical satellites which are part of the European Commission’s Copernicus Programme.

Its partner Sentinel-2A was launched on the 23rd June 2015, and has been providing some stunning imagery over the last eighteen months like the picture of Plymouth above. We’ve also used the data within our own work. Sentinel-2B carries an identical Multispectral Imager (MSI) instrument to its twin with 13 spectral bands:

  • 4 visible and near infrared spectral bands with a spatial resolution of 10 m
  • 6 short wave infrared spectral bands with a spatial resolution of 20 m
  • 3 atmospheric correction bands with a spatial resolution of 60 m

With a swath width of 290 km the constellation will acquire data in a band of latitude extending from 56° South around Isla Hornos, Cape Horn, South America to 83° North above Greenland, together with observations over specific calibration sites, such as Dome-C in Antarctica. Its focus will be on continental land surfaces, all European islands, islands bigger than 100 square kilometres, land locked seas and coastal waters.

The satellites will orbit 180 degrees apart at an altitude of 786 km, which means that together they will revisit the same point on Earth every five days at the equator, and it may be faster for parts of southern Europe. In comparison, Landsat takes sixteen days to revisit the same point.

With all Copernicus data being made freely available to anyone, the short revisit time offers opportunities small and micro Earth Observation businesses to establish monitoring products and services without the need for significant investment in satellite data paving the way for innovative new solutions to the way in which certain aspects of the environment are managed. Clearly, five day revisits are not ‘real-time’ and the spatial resolution of Sentinel data won’t be suitable for every problem.There is joint work between the US and Europe, to have complementarity with Landsat-8, which has thermal bands, and allows a further opportunity for cloud-free data acquisitions. Also, commercial operators provide higher spatial resolution data.

At Pixalytics we’re supporters of open source in both software and imagery. Our first point of call with any client is to ask whether the solution can be delivered through free to access imagery, as this can make a significant cost saving and allow large archives to be accessed. Of course, for a variety of reasons, it becomes necessary to purchase imagery to ensure the client gets the best solution for their needs. Of course, applications often include a combination of free to access and paid for data.

Next’s week launch offers new opportunities for downstream developers and we’ll be interested to see how we can exploit this new resource to develop our products and services.

Uncovering Secrets with Remote Sensing

Artist's rendition of a satellite - mechanik/123RF Stock Photo

Artist’s rendition of a satellite – mechanik/123RF Stock Photo

Recent significant discoveries in Cambodia and Jordan have highlighted the potential offered by remote sensing and satellite imagery to help uncover secrets on Earth – a field known as satellite archaeology.

Cambodia
Helicopter mounted Lidar was used to reveal multiple cities beneath the forest floor near the ancient temples of Angkor Wat in Cambodia. Lidar, which stands for Light Detection and Ranging, is an active optical remote sensing technique that uses a laser scanner to map the Earth’s topography by emitting a laser pulse and then receiving the backscattered signal. In Cambodia, a topographic Lidar with a near infrared laser was used by Australian archaeologist Dr Damian Evans to survey beneath the forest vegetation.

The conurbations discovered, surrounding the stone temple Preah Khan Kompong Svay, are believed to be between 900 to 1 400 years old. Analysis of the survey has shown a large number of homes packed together liked terraced houses, together with structures for managing water and geometric patterns formed from earth embankments – which could be gardens.

At 734 square miles, the 2015 survey is also thought to be the most extensive of its type ever undertaken. Dr Evans work is due to be published in the Journal of Archaeological Science.

Jordan
Archaeologists using high resolution satellite imagery, drones surveys and imagery within Google Earth have discovered a huge structure buried in the sand less than a kilometre south of the city of Petra. The two high resolution satellites used were Worldview-1 and Worldview-2, operated by DigitalGlobe. Worldview-1 was launched in September 2007 and has a half-metre panchromatic resolution; Worldview-2, launched two years later, offers similar panchromatic resolution and 1.85m multispectral resolution.

The outline of the structure measures 56m x 49m, and there is a smaller platform contained inside the larger one. Nearby pottery finds suggest the platform is 2 150 years old, and it is thought that it had a ceremonial purpose. The research undertaken by Sarah Parcak and Christopher Tuttle was published in the May 2016 edition of the Bulletin of the American Schools of Oriental Research.

Benefits of Remote Sensing & Satellites
Angkor Wat and Petra are both World Heritage sites, and the benefits of using remote sensing and satellite technology to undertake archaeological investigations are evident in the statement from Christopher Tuttle who noted that they did not intend to excavate their Petra discovery as ‘The moment you uncover something, it starts to disintegrate.’

Satellite technology allows investigations to take place without disturbing a piece of soil or grain of sand, which is a huge benefit in terms of time, cost and preservation with archaeology. These two discoveries also demonstrate that the world still has secrets to reveal. As Sarah Parcak herself said in 2013, “We’ve only discovered a fraction of one percent of archaeological sites all over the world.”

Who knows what remote sensing and satellite imagery will uncover in the future?

Four reasons why 2016 will be big for Earth observation

Artist's rendition of a satellite - 3dsculptor/123RF Stock Photo

Artist’s rendition of a satellite – 3dsculptor/123RF Stock Photo

2016 has caught its first few rays of sunlight, but is already shaping up to be an exciting year for Earth observation (EO). Here are four reasons why:

Reason One
China launched the world’s most sophisticated geostationary satellite, Gaofen 4, on the 28th December – okay I know that was technically 2015, but it will begin operating in 2016! Gaofen 4 is part of the China High-Resolution Earth Observation System (CHEOS) that aims have a suite of seven high definition satellites, with varied specifications, providing real-time all day global coverage in all weathers by 2020. Unusually for EO, the Gaofen 4 high-resolution satellite is in a fixed-point 36,000 km geosynchronous orbit focusing on China and the surrounding area.

It has two optical instruments: a visible light imager with 50 m resolution, and an infrared imager with 400 m resolution. The main applications are disaster prevention, disaster relief, agricultural planning and climate change monitoring.

Reason Two
NASA awarded the contract to build Landsat-9’s Operational Land Imager-2 (OLI) instrument to Ball Aerospace & Technologies Corporation on 31st December – yes, I know that was 2015 too!

OLI will have eight spectral wavebands with a resolution of 30 m, and one panchromatic waveband with a resolution of 15 m. This will help extend the Landsat archive that has over 40 years of continuous satellite images. Interestingly despite having a similar number of optical bands as ESA’s comparable Sentinel 2 satellites; the spatial resolution is poorer as Sentinel 2 has 10 m resolution for its visible wavebands.

Reason Three
There are a number of significant EO satellite launches planned for the coming twelve months. Highlights include for:

  • Jason 3 ocean altimetry mission on January 17th
  • ESA’s Sentinel 3A on 4th February
  • Astro-H X-ray observatory on February 12th
  • ESA’s Sentinel-1B on 14th April
  • Ten SkySat Earth observation satellites for Google/Skybox Imaging over the summer
  • Worldview 4 in September
  • Geostationary Operational Environmental Satellite R-Series Program (GOES-R), a NASA/NOAA next-generation geostationary weather satellite, in October
  • Planet Labs are expected to deploy a significant number of small satellites from the International Space Station during the year, starting with Flock 2e’s twelve satellites, to enable them to provide terrestrial images for the entire Earth.

Reason Four
EO is a growing industry that had sales of $1.6 billion in 2014, up 60% from five years earlier. With the investment and development currently happening within the industry, it is anticipated that this growth will continue. Pixalytics is one example!

The focus in this, and future years, will be getting a broader user base for satellite imagery including providing more operational services using near real time imagery. This should offer potential new applications, services and markets to support the ongoing growth.

You can be part of it! Satellite imagery is no longer just for governments, space agencies or research bodies. Satellites still provide the large scale climate change, ocean and land monitoring; but there can also provide small scale support on everything from crop/field management, building and smart city planning, traffic/parking monitoring and even counting animals from space.

If you want to see how Earth observation might benefit your company, get in touch. We’d be happy to talk through what might be possible – you’ll never know unless you ask!

What do colours mean in satellite imagery?

False colour image of phytoplankton blooming off the coast of Patagonia. Acquired 2nd Dec 2014. Image Courtesy of NASA/NASA's Earth Observatory

Phytoplankton blooming off the coast of Patagonia on 2nd Dec 2014.
Image Courtesy of NASA/NASA’s Earth Observatory

Satellite images are a kaleidoscope of colours, all vying for attention. It’s important to be clear what the colours are showing, and more importantly, what they may not be showing, to interpret the image correctly. For example, a patch of white on an image might indicate snow or ice, sunglint off the ocean, fog or it could just mean it was cloudy.

On the earth’s surface different colours represent different land types:

  • Vegetation appears as shades of green from pale for grasslands to dark for forests – although some forests will progress from green to orange to brown in autumn.
  • Ocean colour is significantly influenced by phytoplankton, which can produce a range of blue and green colours. A fantastic example of this can be seen in the image at the top of the blog showing phytoplankton blooming off the cost of Patagonia.
  • Snow and ice can appear white, grey, or slightly blue.

As noted in the opening, colours can also mislead with cloud cover being the natural nemesis of optical remote sensing. However, you also have to be careful with effects such as:

  • Smoke: ranges from brown to grey to black.
  • Haze: a pale grey or a dirty white.
  • Dust: can be brown, like bare ground, but also white, red and black.
  • Shadow: Clouds or mountain shadows can look like dark surface features.

There is a good article here from NASA’s Earth Observatory giving more details on the different colours of surface land types. So far, we’ve focussed on natural colour signatures; but man-made structures also appear on imagery. Generally, urban areas tend to be silver or grey in colour; although larger objects also show up in their own right such as the bright red roof of Ferrari World in the middle of the Abu Dhabi Grand Prix Circuit – as discussed in a previous blog.

Composite Google Earth image of the entrance to the Panama Canal: Data courtesy of DigitalGlobe

Composite Google Earth image of the entrance to the Panama Canal: Data courtesy of DigitalGlobe

We tried to repeat the identification of man-made objects for this blog using the coloured roofs of the Biomuseo building, located on the Amador Causeway – at the entrance to the Panama Canal in the Pacific Ocean. Sadly, Landsat 8 pixels are too coarse; and Google Earth has fallen prey to cloud cover preventing visibility, as shown in the image on the right. What you can see though is the buildings in Panama City and the yachts in the marinas and clustered around the four islands (Naos, Perico, Culebra and Flamenco) at the end of the Amador Causeway.

The final thing to remember when considering colours, is the format of the image itself. Some images use true-colours from the red, green and blue wavelengths, which produce colours as if you were looking at the scene directly, so trees are green, sea is blue, etc. However, other images incorporate infrared light to enhance the detection of features not easily distinguished on a true-colour image; this means colours aren’t what you would expect, for example, the ocean may appear red.

Colour is central to use of satellite imagery, but you need to know the properties of the rainbow you are looking at or you may never find the pot of satellite gold.