Citizen Science, Secchi Disks & Ocean Optics

Tomorrow I’m off to the Ocean Optics conference, which has taken place every two years since 1965 and brings together specialists united by light in the ocean; this year the conference has topics as varied as environmental management, fluorescence, remote sensing, phytoplankton, sediments and underwater imaging.

Secchi disk measurements, as of mid October 2014

Secchi disk measurements, as of mid October 2014

I first came to Ocean Optics in 2006, when it was held in Montreal, Canada. I enjoyed it so much I’ve attend every one since, which have been in Castelvecchio (Italy), Anchorage (USA) and Glasgow (Scotland), and this time we are in Portland, in Maine USA. One of the things I really like it is, unlike large conferences, there are no parallel sessions, and so I don’t have to make any difficult decisions on which speakers I can, and those I can’t, see. Conferences can reinforce the silo approach, with the Ocean Colour group meeting in one room and the land remote sensors meeting in another. I think the Ocean Optics format promotes a more collaborative atmosphere, where you see a more diverse range of presentations and people. The collaborative approach to research and innovation is at the centre of my philosophy of working, and so Pixalytics is also one of the conference sponsors.

Next Tuesday, I’m giving a keynote presentation on Crowdsourcing Ocean Optics. My presentation will bring together the topics of Citizen Science, collaborative research that includes members of the public in any one of a variety of way, and Earth observation (EO) data acquired via ocean colour satellites; one example of this is the Secchi Disk project.

A Secchi disk, originally created in 1865 by Father Pietro Angelo Secchi – who was the
Pope’s astronomer, is a flat white disk 30cm in diameter, attached to a tape measure or a rope and also weighted from below. The Secchi Disk is lowered vertically into the water from the side of a boat, and the point at which the disk just disappears from sight is recorded. This depth measures the turbidity of the water, which is influenced by the amount of phytoplankton in the water column.

The Secchi Disk project developed smartphone Apps to allow participants to use a homemade Secchi disk and their smartphone / tablet to record and upload depth data alongside positional information. Through everyone uploading their measurements we are building up a global map of Secchi depths.

The project is a collaboration between Dr Richard Kirby who leads the project and publicity, with Dr Nicholas Outram and Dr Nigel Barlow (Plymouth University) as the App developers, and myself for the online database and EO linkages. The Apps were released at the end of February 2013, and since then 481 Secchi disk measurements have been collected globally; see the figure at the top that shows the global distribution of the uploaded data with the coloured Secchi disks indicating the values recorded.

The Secchi Disk project data is being compared to ocean colour satellite measurements as a cross-validation exercise and, in the longer term, to contribute to our understanding of phytoplankton dynamics. Why don’t you become part of the growing citizen science movement, go on take a measurement and upload it!

The UK Space industry is healthy, but is it understood?

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

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

Last week the UK Space Agency released the Executive Summary of its biennial report into the Size and Health of the UK Space Industry. It gives a positive overall picture with the industry having a turnover of £11.3bn in 2012/13; it’s growing at an average annual rate of 7.3%, exports are expanding and we are on track to achieve the aim of having a £40bn UK space industry by 2030. Despite all the positive news, the report raised questions on how well understood the industry is.

The industry is generally split into two sectors, upstream and downstream. Where upstream refers to the part of the industry that build and launch satellites and sensors into space; whilst downstream encompasses the products and services that use the data those objects collect. However, according to the report there is a growing belief that this definition is no longer fit for purpose as it doesn’t reflect the whole industry. Instead the report has split the industry into three sectors: upstream (infrastructure and technology), downstream (direct space services) and the new sector, the wider space economy – which covers space-enabled value added applications.

Evolving definitions is something that happens as industries, technologies and knowledge matures, but we would questions whether providing this split within the downstream activity is helpful. Pixalytics is an Earth observation company; we develop products and services from space data, offer consultancy support and undertake image processing. According to the new definitions our products and services are considered downstream activities, whereas our consultancy and image processing are part of the wider space economy. It’s rarely, if ever, true, that using space data alone can be used to answer customer’s questions. Instead it’s about integrating that data with other information and knowledge, to create a product that adds value for the customer. Hence, a huge part of our work will always span the downstream and wider space economy sectors. So do these new changes create more definition or confusion?

The report is based, amongst other things, on an industrial survey. Invitations to participate in the survey were sent to 228 companies who were judged to be part of the wider space economy. Only 12 replied, that’s a response rate of just 5.26%! We need to understand why there is such a poor response rate, is it apathy, a lack of understanding that they use space services or do they not consider themselves defined by their data sources? If a company uses satellite data, overflights, in-situ measurements and scientific modelling to deliver their services, are they part of the wider space economy? We use desks and bookshelves in our office, but it doesn’t make us a furniture business.

Like many things, communication is the key. If we are evolving our definition of the industry we can’t do it alone. We need to engage with the companies within the industry, and crucially with those we are trying to bring in. Inclusive discussion, education and understanding at all levels are vital, if we want to develop a vibrant and participative wider space economy.

Celebrating World Space Week!

Did you know this is World Space Week? In 1999, the United Nations declared that World Space Week would occur between the 4th and 10th October each year. It chose these two dates because:

  • On 4th October 1957 the first human-made Earth satellite, Sputnik 1, was launched; and
  • On 10th October 1967 The Treaty on Principles Governing the Activities of States in the Exploration and Peaceful Uses of Outer Space, including the Moon and Other Celestial Bodies was signed – which was discussed in last week’s blog.

This annual international celebration supports events in countries around the world to educate people about space, encourage everyone to benefit from the space industry and inspire young people to get involved in science, technology, engineering and maths.

Space: Guiding Your Way is the theme for 2014 and focuses on all aspects of satellite navigation, from the GPS in your smartphone, though road navigation, shipping and disaster recovery. According to the World Space Week website there are over 700 events in over 60 countries taking place during this week’s celebration: everywhere from Afghanistan to Venezuela has an event, supported by a number of global events. The events vary from educational presentations, conferences and demonstrations through to water rocket competitions, training like an astronaut or even having coffee with an astronomer. The UK Space Agency has a ‘Tweet the Expert 2014’ event running between 2pm and 3pm each day this week.

Rumple Quarry in Plymbridge Woods

Rumple Quarry in Plymbridge Woods

Here at Pixalytics, we didn’t want World Space Week to go by without getting involved, and so we’ve taken part in the EarthCache Virtual 5K. Although, don’t let the word virtual fool you as there has been running! EarthCache aims to teach people about the world by highlighting interesting geologic or geographic phenomenon or features you can visit, and there are almost eighteen thousand such sites worldwide. To participate in the Virtual 5K run, you have to run at least 5K starting or ending at a registered EarthCache site.

Sam Lavender at the start of her 5K run

Sam Lavender at the start of her 5K run

Our closest EarthCache site is a quarry site in Plymbridge Woods, pictured above. Records indicate it has been worked as far back as 1683, and slate from here was reportedly used in the building of Devonport Dockyard. In addition to the quarry site, there is also a viaduct and ruins of a waterwheel and quarry workers cottages. To the right is the picture of Sam at the start of her 5K run.

Are you going to join in World Space Week? Have a look at the website and see if you can find an activity, or join us in the virtual run. Whatever you decide to do, remember you’re celebrating space and your part in this industry.

Do you know legal framework for working in space?

Ignorance is no defence in law. Business owners must know all the legal requirements for running a business from financial regulations, through human resources issues to waste disposal. If you work in the vehicle industry, you have to know the legal minimum requirements for having vehicles on the road, insurance and maximum driving hours. Every industry has its own legal framework; do you know requirements for the space industry?

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

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

Space Law begins within discussions at the United Nations at their Office for Outer Space Affairs (OOSA), and it’s associated Committee on the Peaceful Uses of Outer Space. Through these bodies a number of international agreements are approved covering how space and space activities should be operated. There have been five treaties agreed:

  1. The 1967 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (known as the Outer Space Treaty).
  2. The 1968 Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space (known as the Rescue Agreement).
  3. The 1972 Convention on International Liability for Damage Caused by Space Objects (known as the Liability Convention).
  4. The 1975 Convention on Registration of Objects Launched into Outer Space (known as the Registration Convention.
  5. The 1979 Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (known as the Moon Agreement).

Once a treated has been agreed, there is a two stage process to adopt the treaty into law in by individual countries. A country needs to first sign the treaty, then they must create their own national law to enact it – known as ratifying the treaty. Once a country has signed a treaty, it becomes binding on them. According to OOSA, of the 193 members of the United Nations at the 1st January 2014:

  • 128 countries had signed the Outer Space Treaty, although 25 still have to ratify it.
  • 118 countries had signed the Rescue Agreement, 24 still to ratify it.
  • 113 countries had signed Liability Convention, 22 still to ratify it.
  • 64 countries had signed the Registration Convention, although 4 still to ratify it.

Only 19 countries had signed the Moon Agreement, and 4 of those still have to ratify it.
Interestingly the UK has only signed the first four treaties, we have not signed the Moon Agreement. Other nations like the UK who have only signed the first four treaties include China, Germany, Italy, Japan, Russia and the United States of America. There are 13 countries that have signed and implemented all five treaties: Australia, Austria, Belgium, Chile, Kazakhstan, Lebanon, Mexico, Morocco, Netherlands, Pakistan, Peru, Turkey and Uruguay; in addition France and India have signed the treaty, but not yet ratified it.

In previous blogs we’ve highlighted that in the UK the 1986 Outer Space Act is the piece of legislation which contains enacts these treaties. It contains details about who the act applies to, the licensing requirements for operating in outer space, registration of space objects, actions that can be taken to prevent people operating in outer space and offences that can be committed. The offences can be committed both by individuals, and by corporate bodies. Other countries have their own legislation, it’s important that you read, and are aware of, the law in any country you are operating. Remember, ignorance is no defence.

Can Earth Observation answer your question?

The opportunities and challenges of utilising Earth observation (EO) data played out in microcosm in our house over the weekend. On Sunday afternoon, I was watching highlights of the Formula One Singapore Grand Prix which takes place on the harbour streets of Marina Bay and is the only night race of the season. To ensure the drivers can see, there are over 1,500 light projectors installed around the circuit giving an illumination of around 3,000 lux.

Whilst watching I wondered aloud whether we’d be able to see the track from space with the additional floodlights. My idle wondering caught Sam’s interest far more than the actual race and she decided to see if she could answer the question. The entire circuit is just over five kilometres long, but it’s a loop and so an approximate two kilometre footprint; any imagery would need a spatial resolution less than this. The final difficulty is that the data needed to be this weekend, as the circuit is only floodlit for the racing.

Within a few laps Sam had identified free near real time night data available from United States National Oceanic & Atmospheric Administration (NOAA) which covered the required area and timeframe. This was from the Visible Infrared Imaging Radiometer Suite (VIIRS) using it’s Day/Night band with a 750m spatial resolution – this resolution meant we would not be able to see the outline of the track as it would be represented by only three or four pixels, but it would be interesting to see if we could identify the track feature. By the end of the race Sam had selected and downloaded the data, and so we could answer my question. However, it turned out to be not quite that easy.

VIIRS Singapore night time imagery, data courtesy of NOAA

VIIRS Singapore night time imagery, data courtesy of NOAA

NOAA data uses a slightly different format to the image processing packages we had, and we couldn’t initially see what we’d downloaded. Sam had to write some computer code to modify the packages to read the NOAA data. For anyone thinking this is an odd way to spend a Sunday evening, to Sam this was a puzzle to solve and she was enjoying herself! After some rapid coding we were able to view the image, but unfortunately the Saturday data wasn’t useful. On Monday we tried again, the Sunday race took place on a clear night and we’ve got a good image of the area, which you can see above. On the larger image you can clearly the Indonesian Islands with Jakarta shining brightly, up through the Java Sea where the lights of some ships are visible and then at the top of the image is Singapore; the zoomed in version of Singapore is the inset image.

Despite the floodlights used for the race, Singapore and some of the surrounding Malaysian cities are so bright at night that the additional lights simply contribute to the overall illumination, rather than making the track stand out. Hence the answer to my question is that the 2014 floodlit Singapore F1 street circuit can’t be distinguished from the surrounding area at this spatial resolution. Of course if we purchased high resolution imagery we may be able to see more detail, but we thought that was going a bit far for my idle wondering!

EO can answer questions like these quickly; and whilst we know not many businesses are dependent on whether the Singapore Grand Prix can be seen from space, but change this to what is the light pollution in your area, what is happening in terms of deforestation in the middle of the jungle, what phytoplankton are doing in the middle of the ocean or whatever question you might have, then EO might be able to provide the answer in a short space of time.

However, there are two main difficulties in getting the answer. Firstly, you’ve got to know where to find the data and secondly, what do with it when you get it. Currently this can be challenging without specialist knowledge, making it inaccessible for the general population. In the coming weeks, we’re going to write some blogs looking at the freely EO data available, and the easiest way of viewing it. Hopefully, this may to help you answer your own questions. In the meantime if you have questions you want answered, get in touch, we’d be happy to help.

What the UK has launched into space

Yesterday NASA announced its ambition to launch astronauts into space from American soil by 2017, and here the Government is currently assessing eight potential sites – including one in Cornwall – to be a UK spaceport by 2018. This nationalistic view of launch pads got me wondering about what the UK has previously launched in space and crucially, where from?

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

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

Under the United Nations Convention on the Registration of Space Objects 1976 a country is deemed to have launched something into space if it does so from its own soil, or it organises someone else to launch it on its behalf. This convention also places obligations on each signatory country, and the UK is one, to make information about all such launches readily available. Details are on the UN website, and in June the UK Space Agency released the UK Registry of Outer Space Objects which makes interesting reading.

According to these sources the UK has launched 67 objects, mostly satellites, into space, beginning in April 1962 with the Ariel 1 satellite. At the time, the United Kingdom was the third country to operate a satellite, after the Soviet Union and the USA. Sadly Ariel 1 had a short four month operational lifespan as it was damaged by the Starfish Prime high-altitude nuclear test. Of all the UK’s launches 63% are still operational; a further 22% are in orbit, but non-operational; while the remaining 15% have decayed and returned to earth.

Ariel 1 was launched from the Cape Canaveral Air Force Station and since then another 17 launches have occurred from American soil, although the most popular UK launch site is French Guiana spaceport with 30 launches. We’ve also launched from Kazakhstan, Russia, Australia, India, Kenya and one even from a floating platform in the Pacific Ocean.

We’ve not launched objects every year; our last fallow year was 2004 and 2013 was the most prolific year with eight launches. Perhaps unsurprisingly a third of the satellites have been launched for telecommunications purposes, with another 18% for military communications. The vast majority of the remainder are for scientific, technological or engineering research purposes. Of the current operational satellites, 56% are in geosynchronous orbits, 30% in low earth orbits and the remaining 14% in medium earth orbits.

This doesn’t give quite the full picture of the UK’s space activities. There are an additional forty five satellites where the UK was not the launching country, but has issued an Outer Space Licence (described in our recent blog) which are listed in the Supplementary Registry of Space Objects on the UK Space Agency website.

The UK has a significant, and growing space sector, and who knows in a few years we may see satellites launched from our shores in Cornwall, Wales or Scotland. Exciting times ahead!

Current Work in Remote Sensing and Photogrammetry

Last week the annual Remote Sensing and Photogrammetry Society (RSPSoc) conference was held in Aberystwyth. Now I’ve stepped down as RSPSoc Chairman I could relax and enjoy this year’s event as a delegate.

Arriving on Wednesday morning, the first session I attended was organised by the Technology and Operational Procedures Special Interest Group (TOPSIG), which was focused on Operational Earth observation. There were a great range of presentations, and I particularly enjoyed the user insights by Andy Wells on how customers are really using imagery. Recent developments in on-the-fly importing, georeferencing and autocorrelation means bringing data together from different sources isn’t a time consuming chore. Users can therefore spend more time analysing data, extracting information and adding value to their organisations or research. In addition, as highlighted by other presentations, open software repositories continue to grow and now include complex algorithms that were once only available to specialists. Finally, Steve Keyworth reminded us that what we do should be seen as a component of the solution rather than the specification; the ultimate aim should be on solving the customer’s problem, which in the current climate is often financially motivated.

Landsat 7 image showing features in the Baltic, data courtesy of ESA

Landsat 7 image showing features in the Baltic, data courtesy of ESA

On Thursday I co-chaired the Water and Marine Environments session alongside Professor Heiko Balzter, on behalf of the Marine Optics Special Interest Group (SIG). My presentation was focused on the European Space Agency (ESA) Landsat archive that’s been acquired via the ESA ground stations. This data is being reprocessed to create a consistent high resolution visible and infrared image dataset combining the three primary sensors used by the series of Landsat satellites; MSS (Multi-spectral Scanner), TM (Thematic Mapper), and ETM+ (Enhanced Thematic Mapper Plus). Although historical Landsat missions are not ideally suited to observing the ocean, due to a low signal-to-noise ratio, features can be clearly seen and the new processing setup means images are being processed over the open ocean.

Mark Danson’s keynote lecture on Friday morning described the application of terrestrial laser scanners to understanding forest structure. He showcased his post PhD research which has led to the development of the Salford Advanced Laser Canopy Analyser, a dual-wavelength full-waveform laser scanner. The presentation also showed the importance of fieldwork in understanding what remote techniques are actually sensing, and in this case included a team of people cutting down example trees and counting every leaf!

Mark also made me feel less guilty that I am still working on a component of my PhD – atmospheric correction. In research your own learning curve, and the scientific process, mean you gain new insights as you understand more, often explaining why answers are not as simple as you might have assumed. It’s one of the reasons why I love doing research.

Overall, I had a great time at RSPSoc, catching up and seeing what’s new in the field. My next conference event is Ocean Optics, in the US, at the end of October where I’ll be discussing citizen science in a marine science context.

Can we launch a satellite?

We’ve written a number of blogs about satellites being launched, and it got me wondering if anybody can launch one – in case Pixalytics ever wants to go into space. I know we’re a micro business, but we think big! Unsurprisingly, it turns out that you can’t just launch a satellite.

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

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

In order for any UK company, or individual, to launch any object into space, operate a space object or engage in any activity in outer space, you need to have a licence. The licensing arrangements are detailed in the Outer Space Act 1986, which brought into UK law the provisions of the 1967 United Nations Outer Space Treaty.

The UK Space Agency manages the licencing procedure on behalf of the UK Government, and in order to start the process you need to fill in an application form. This requires:

  • Details of the applicant applying for the licence
  • The nature of the space activity, including technical details about the mission, the satellite, the launch arrangements, ground receiving stations and emergency arrangements.
  • Orbital details including nodal period, inclination, apogee and perigee.
  • Radio frequencies to be used to ensure they won’t cause interference issues.
  • Financial details including mission costs and the applicant’s financial standing to ensure that they can meet their licence obligations.
  • Insurance arrangements – The standard requirement is to have insurance of at least €60 million against third party liabilities arising during both launch and operational phases of the mission. However, if there are any proven third party costs resulting from the launch or operation, the licensees are liable for unlimited damages!
  • End of life disposal arrangements.

In addition, you need to send a non-refundable licence fee of £6,500; although interestingly, educational institutions carrying out activities for the purpose of scientific research or teaching don’t have to pay this fee. This starts to explain why a number of Universities have launched satellites, which we highlighted in an earlier blog.

Once submitted a variety of Government organisations will assess the application including the UK Space Agency, Department for Business Innovation and Skills, OFCOM and any third party technical experts. A licence will only be issued if it’s clear that the activities will not jeopardise public health or the safety of persons or property, will be consistent with the UK’s international obligations and will not impact on our national security.

Once a licence has been granted, the licensee has a number of ongoing obligations; including these two intriguing ones:

  • Preventing the contamination of outer space or adverse changes in the environment of the earth; and
  • Avoid any interference with the activities of others in the peaceful exploration and use of outer space.

The guidance suggests that you should submit your application at least six months before launch, although to me given the time, and cost, of building and launching a satellite, six months seems a little late in the day.

Whilst satellite technology may be getting smaller and cheaper with the development of cubesats and nanosats, the requirements around launching them are the same as any other satellite. The UK Government acknowledged this in response to the 2012 consultation on the Outer Space Act in 2012, by noting that the regulations for smaller satellites needed reviewing.

Pixalytics is a few years away from getting into space, our first job is work out what paradigm shifting Earth observation data we’d collect, but it’s useful to have an understanding of the steps we’d have to take. Anyone else thinking of taking one small step?

Controlling the Space Industry Narrative

The narrative of the satellite industry over the last week had all the components of a blockbuster novel or film: with new adventures beginning, dramatic challenges to overcome, redemption and an emotional end.

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

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

Like lots of good stories, we start with those characters setting off on new adventures. Firstly, China launched its most powerful imaging satellite, Gaofen-2. It carries a High Resolution Optical Imager capable of providing images with a spatial resolution of 80cm in panchromatic mode and 3.2m in multispectral mode, and has a swath width of 48km. It is the second in series of seven Earth observation (EO) satellites, following Gaofen-1 launched in April 2013, which will provide environmental monitoring, disaster management support, urban planning and geographical mapping. The Long March 4B rocket launched Gaofen-2, redeeming itself following a failure last December causing the loss of the CBERS-3 EO satellite. The second significant launch was from the International Space Station on the 19th August, when the first pair from the twenty-eight constellation satellites of Flock 1B were launched; with further pairs sent on the 20th, 21st and 23rd. Flock 1B is part of three earth imaging nanosat constellations from Plant Labs, providing images with a spatial resolution of between 3 – 5m.

ESA’s Galileo satellites, Doresa and Milena, provided the drama by failing to reach their planned altitude of 29.9km, reaching an orbit of 26.9km; in addition, their inclination angle is 49.8 degrees to the equator, rather than 55 degrees. They were the fifth and sixth satellites in Europe’s version of the American GPS satellite navigation system, launched on the Soyuz rocket. Getting the satellites to the correct position is likely to require more fuel than they carry. Like Long March 4B, Soyuz will get its chance of redemption in December with the launch of the next two Galileo satellites.

The Tropical Rainfall Measuring Mission (TRMM), a joint mission between NASA and Japan Aerospace, provides the emotional end to our story with the announcement last week that it had run out of fuel. Launched in 1997, TRMM had a three year life expectancy, but will now provide an incredible nineteen years worth of data. It will continue collection until early 2016, when its instruments will be turned off in preparation for re-entry.

It’s interesting to see how this news has been reported in the mainstream media, little mention of China’s progress, or the second Flock constellation or the amazing longevity of TRMM; instead, the focus was the failure of the Galileo satellites. There is rarely widespread coverage of the successful launches of satellites, but there is a push within the UK for the community to celebrate our successes more so the full range of space activities can be seen.

Earth observation is all about data and images, and whilst these may interest people, it’s only through the power of storytelling that we can describe the positives of the industry motivating and inspiring people. Remember to create stories for your industry, and your company, or someone else will dictate the narrative.

Why understanding spatial resolution is important?

Spatial resolution is a key characteristic in remote sensing, where it’s often used to refer to the size of pixels within an acquired image. However this is a simplification as the detector in the satellite doesn’t see the square suggested by a pixel, but rather it sees an ellipse due to the angle through which the detector receives the signal – known as the instantaneous field of view. The ellipses are turned into square pixels by data processing in creating the image.

The area of the port of Rotterdam shown using a Landsat image (background) at 30m resolution and MERIS full resolution image (inset image) at 300m resolution; data courtesy of the USGS and ESA. Example used within Hydrographic Academy eLearning material.

The area of the port of Rotterdam shown using a Landsat image (background) at 30m resolution and MERIS full resolution image (inset image) at 300m resolution; data courtesy of the USGS and ESA. Example used within Hydrographic Academy eLearning material.

Therefore, for example, when viewing an image with 1km resolution not only will you not be able to see anything that is smaller than 1km in size, but objects needs to be significantly larger than 1km for any detail to be discernable. Whilst this might be fine if you looking at changes in temperature across the Atlantic Ocean, it won’t be much use if you are interested in suspended sediment blooms at the mouth of a small river.

Any image with a spatial resolution of between 50m and 1km, is described as having low spatial resolution. For example, MODIS operates low spatial resolutions ranging from 250m to 1000m as the primary focus is global mapping rather than capturing detailed imagery for local regions.

If you want to look for smaller objects, you’ll need use images with medium spatial resolutions of between 4m to 50m. There is quite a lot of freely available imagery within this range. For example, NASA’s Landsat 8 operates at 15, 30m and 100m resolution and ESA’s Sentinel-1A operates at the three resolutions of 5m, 20m and 100m. If you want go even finer, you will require high spatial resolution images that go down to resolutions of between 4m and 1m, or very high spatial resolution images which cover the 0.5m – 1m range. Commercial organisations tend to operate satellites with these higher levels of resolution, and they charge for making the images available. It’s likely that military satellites offer imagery down to 0.15m, but there are regulations in place to prevent the sale of extremely high resolution imagery as it’s considered to be a potential danger to security.

Spatial resolution was in the headlines last week with launch of the DigitalGlobe’s WorldView-3 satellite that can produce spectral images with a resolution down to 0.31m. Technologies to produce images at this resolution have been around for some time, but as reported by Reuters in June, DigitialGlobe has only recently received a license from the US Commerce Department to start selling images with a resolution of up to 0.25m; without this licence they wouldn’t be able to sell this higher resolution imagery.

Regulatory involvement in very high resolution imagery was also demonstrated earlier this year, when in January, the UK government blocked the European Commission’s effort to set common European regulations on the sale of high-resolution satellite imagery. The UK government currently controls access to data through export licencing conditions on the satellite hardware, and they felt regulations would impact on UK’s ability to export space technology.

Therefore, spatial resolution is an important term, and one every remote sensing client should understand. Different services require different spatial resolutions, and selecting the most appropriate resolution for your needs will not only ensure that you get exactly what you want, but could also save you money as you don’t want to over-specify.