The cost of ‘free data’

False Colour Composite of the Black Rock Desert, Nevada, USA.  Image acquired on 6th April 2016. Data courtesy of NASA/JPL-Caltech, from the Aster Volcano Archive (AVA).

False Colour Composite of the Black Rock Desert, Nevada, USA. Image acquired on 6th April 2016. Data courtesy of NASA/JPL-Caltech, from the Aster Volcano Archive (AVA).

Last week, the US and Japan announced free public access to the archive of nearly 3 million images taken by ASTER instrument; previously this data had only been accessible with a nominal fee.

ASTER, Advanced Spaceborne Thermal Emission and Reflection Radiometer, is a joint Japan-US instrument aboard NASA’s Terra satellite with the data used to create detailed maps of land surface temperature, reflectance, and elevation. When NASA made the Landsat archive freely available in 2008, an explosion in usage occurred. Will the same happen to ASTER?

As a remote sensing advocate I want many more people to be using satellite data, and I support any initiative that contributes to this goal. Public satellite data archives such as Landsat, are often referred to as ‘free data’. This phrase is unhelpful, and I prefer the term ‘free to access’. This is because ‘free data’ isn’t free, as someone has already paid to get the satellites into orbit, download the data from the instruments and then provide the websites for making this data available. So, who has paid for it? To be honest, it’s you and me!

To be accurate, these missions are generally funded by the tax payers of the country who put the satellite up. For example:

  • ASTER was funded by the American and Japanese public
  • Landsat is funded by the American public
  • The Sentinel satellites, under the Copernicus missions, are funded by the European public.

In addition to making basic data available, missions often also create a series of products derived from the raw data. This is achieved either by commercial companies being paid grants to create these products, which can then be offered as free to access datasets, or alternatively the companies develop the products themselves and then charge users to access to them.

‘Free data’ also creates user expectations, which may be unrealistic. Whenever a potential client comes to us, there is always a discussion on which data source to use. Pixalytics is a data independent company, and we suggest the best data to suit the client’s needs. However, this isn’t always the free to access datasets! There are a number of physical and operating criteria that need to be considered:

  • Spectral wavebands / frequency bands – wavelengths for optical instruments and frequencies for radar instruments, which determine what can be detected.
  • Spatial resolution: the size of the smallest objects that can be ‘seen’.
  • Revisit times: how often are you likely to get a new image – important if you’re interested in several acquisitions that are close together.
  • Long term archives of data: very useful if you want to look back in time.
  • Availability, for example, delivery schedule and ordering requirement.

We don’t want any client to pay for something they don’t need, but sometimes commercial data is the best solution. As the cost of this data can range from a few hundred to thousand pounds, this can be a challenging conversation with all the promotion of ‘free data’.

So, what’s the summary here?

If you’re analysing large amounts of data, e.g. for a time-series or large geographical areas, then free to access public data is a good choice as buying hundreds of images would often get very expensive and the higher spatial resolution isn’t always needed. However, if you want a specific acquisition over a specific location at high spatial resolution then the commercial missions come into their own.

Just remember, no satellite data is truly free!

Copernicus ready for lift off!

The first satellite of the European Union’s Copernicus project, Sentinel-1A, is due to be launched next Thursday, April 3rd. The project aims to create a constellation of satellites providing a range of Earth Observation data to aid our understanding, and management, of the planet and its resources.

Sentinel-1 is a two-satellite mission, with a second identical satellite, Sentinel-1B, due to be launched in 2016.  The two satellites will orbit the earth 180° apart, allowing the entire globe to be covered every six days, although the Artic will be revisited every day and Europe, Canada and main shipping routes every three days.

The Sentinel-1A satellite weighs 2,300kg and carries a 12m long C-band Synthetic Aperture Radar (SAR) instrument; this is an advanced radar system that transmits microwave radiation that allows it to capture images of the earth twenty four hours a day, in addition it get images through cloud and rain. This is particularly useful when providing imagery for emergency response during extreme weather conditions. The satellite also has a pair of 10m solar wings to provide independent power, the deployment sequence can in be seen in this European Space Agency video.

Over land Sentinel-1 will capture data in an Interferometric Wide swath mode, which means it takes three scans and then combines them into a single image. Each scan has a width of 250km and a spatial resolution of 5m x 20m, which means each pixel on the image represents a 5m x 20m area. It works slightly different over the oceans, operating on a 5m x 5m spatial resolution enabling the direction, wavelength and heights of waves on the open oceans to be determined.

Image of the port of Maracaibo (Venezuela) using ASAR imagery; courtesy of ESA

Image of the port of Maracaibo (Venezuela) using ASAR imagery; courtesy of ESA

This satellite will replace the ASAR (Advanced Synthetic Aperture Radar) C-band instrument that was on-board the Envisat mission which had a resolution of 150m; until contact was lost in April 2012. The image on the right is of Lake Maracibo in Venezuela, and was  acquired in ASAR Image Mode Precision with a spatial resolution of 12.5 m. The varying colour is created by assigning a different RGB (Red, Green, Blue) colour to different acquisition dates (8 Sep 2004 is red, 26 Feb 2004 is green and 17 Jun 2004 is blue) with the brightness being linked to surface texture, so the rougher the surface the brighter the image

Lake Maracaibo itself is also really interesting.  It was formed 36 million years ago and is the largest natural lake in South America; although it has a direct connection to the ocean and so could be called an inland sea. The port of Maracaibo, located on the west side of the strait (large bright area on the image), is the second city of Venezuela and the lake is also a petroleum-producing region supplying two-thirds of the total Venezuelan petroleum output. However, its biggest claim to fame is atmospheric phenomenon of a semi-permanent lightning storm where the Catatumbo river flows into the lake; making it a magnet for stormchasers the world over.

An EO conference roundup: RSPSoc 2013 and the ESA Living Planet Symposium

It’s conference season! I’m at my 2nd conference in 2 weeks, both in Scotland.

Last week was the Remote Sensing & Photogrammetry Society Annual Conference, #RSPSoc2013, hosted in Glasgow. It included a broad range of sessions and scientific output within the ‘family’ atmosphere that you find within societies.

The conference started off with a keynote from Dr. Stewart Walker (BAE Systems and President-Elect of the American Society for Photogrammetry and Remote Sensing)
reviewing the history and innovations in photogrammetry. I was fascinated to find out that in the early days of remote sensing (1960’s) US military satellites ejected cans of photographic film, picked up by aircraft as they fell to Earth, to get high resolution data.

He also showed that since then the number of high resolution optical satellites and the capacity of those satellites to capture information has continuing to increase; in addition to the speed at which an end user can receive captured data. Today Autonomous Unmanned Vehicles (AUVs) have the capability to take very high resolution video that can see objects as small as a songbird.

For me the most incisive comment he made was when he was summarising his own career, where he said that leaders don’t only develop science, but also develop people who develop science. Something worth remembering by every scientific business.

The second keynote was by provided by Craig Clark MBE (Clyde Space), which showcased the growth of the company that is leading the UK Space Agency’s programme to design and launch a cubesat; UKube-1 which is due for launch in December.

Cubesats are small satellites, built in units of 10 cm cubes, with Ukube-1 being 3u i.e. 3 cubes in size (length). These are not the smallest satellites to be launched, but offer the potential to provide scientific quality missions at a much lower cost than conventional satellites; allowing developers to be more innovative with technologies and off the potential for constellation, rather than single, missions. This won’t be the end of conventional larger satellites, as they are still needed for the capture of complex high quality data sets. But these two technologies will give greater flexibility for data capture.

This week I’m at European Space Agency’s Living Planet Symposium Still a ‘family’ atmosphere, but a much larger family with around 1,700 attendees in Edinburgh. The conference has showcased ESA’s historical, current and future missions including SWARM that will be launched in November and the first Copernicus mission (Sentinel 1) that will launch in 2014.

The SWARM constellation (3 satellites) will measure the Earth’s magnetic field which protects us from cosmic radiation and charged particles arriving from the Sun. Whereas Sentinel 1 is a radar mission, which has many different applications as it provides a view of the surface roughness – a rough surface will reflect strongly while a smooth surface will reflect weakly – which is available during the day and night irrespective of cloud cover. Examples include tracking vessel movements at sea, monitoring forests and looking at the growth of mega-cities.

The last week has reminded me that remote sensing and photogrammetry are changing and fast moving fields; new technologies are offering us greater opportunities and flexibilities. But as Dr Walker reminded us, behind all these developments are some amazing people.

End of the Envisat Era

MERIS Envisat Image from 28 March 2012

The Envisat satellite sent its last data to earth on the 08 April 2012 after an onboard anomaly; still under investigation. Recent images taken from the ground and Pleiades satellite show it probably tried to enter safe mode, which would have been the first time, but failed to do so.

Since then communication has not been re-established and the European Space Agency (ESA) have informed the world that no new data will be acquired although communication attempts continue in the short-term. This is an unexpected, but not unsurprising, as the satellite has significantly exceeded its design life. In addition, it leaves behind a 10 year archive that will be worked on for the next 5+ years as Phase F of the mission.

This end to an era has been reported negatively (e.g. article in the Economist on the 12 May 2012), but can also be seen as the push that the future needs. The European Commission (EC) and ESA are developing the future GMES missions with first planned to be launched in 2013 assuming ongoing budgetary discussions are resolved.