First Light Images

Mosaic image of The Netherlands created using three Sentinel-1 scans in March 2015.
Data Courtesy of Copernicus Sentinel data (2015)/ESA.

Two of the satellites launched on 12th January by the Indian Space Research Organization (ISRO) have released their first images. We wrote about the launch two weeks ago, and wanted to follow up on their initial outputs.

The first is the exciting ICEYE-X1, which is both the world’s first synthetic-aperture radar (SAR) microsatellite and Finland’s first commercial satellite. We currently use Sentinel-1 SAR imagery for some of Pixalytics flooding and water extent mapping products and so are really interested to see what this satellite produces.

One of the key advantages of radar satellites over optical ones is that they can capture images both during day and night, and are not hampered by the presence of clouds.  However, using a different part of the electromagnetic spectrum to optical satellites means that although it is black and white image it’s sometimes easier to distinguish objects within it.

Zoomed in portion of Netherlands mosaic image created using three Sentinel-1 scans in March 2015.
Data Courtesy of Copernicus Sentinel data (2015)/ESA.

For example, the image to the left is a zoomed in portion of Sentinel-1 mosaic of the Netherlands acquired in March 2015 where you can clearly see couple of off-shore windfarms.

Sentinel-1 is a twin satellite constellation and uses a C-Band SAR on board two identical satellites. Over land it captures 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 250 km and a spatial resolution of 5 m x 20 m, with a six day repeat cycle for an area of land.

In comparison, ICEYE-X1 produced its first image with a spatial resolution of 10 m, and it’s hoped to reduce this down to 3 m. It issued its first image on Monday 15th January, three days after launch, showing part of Alaska, including the Noatak National Preserve, with a ground coverage of approximately 80 km by 40 km. The image can be seen here.

ICEYE-X1 weighs in at under a 100 kg, which is less than a twentieth of Sentinel-1 which weighed in at 2 300kg. This size reduction produces a high reduction in the cost too, with estimates suggesting it only cost ICEYE around a hundredth of the €270 million price of the second Sentinel-1 satellite.

By 2020 ICEYE is hoping to establish a global imaging constellation of six SAT microsatellites that will be able to acquire multiple images of the same location on Earth each day. After this, the company has ambitions of launching 18 SAR-enabled microsatellites to bring reliable high temporal-resolution images which would enable every point on the Earth to be captured eight times a day.

Cartosat-2F also sent its first image on the 15th January. The image, which can be found here, is of the city of Indore, in the Indian state of Madhya Pradesh. The Holkar Stadium is tagged in the centre, a venue which has previously hosted test Cricket. The satellite carries a high resolution multi-spectral imager with 1 m spatial resolution and a swath width of 10 km.

It is the seventh satellite in the Cartosat series which began in 2007, the others are:

  • Cartosat 2 launched on 10th January 2007
  • Cartosat 2A launched on 28th April 2008
  • Cartosat 2B launched on 12th July 2010
  • Cartosat 2C launched on 22nd June 2016
  • Cartosat 2D launched on 15th February 2017
  • Cartosat 2E launched on 23rd June 2017

These two satellites are just at the start of their journey, and it will be interesting to see what amazing images they capture in the future.

Earth observation satellites in space in 2017?

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

Earth Observation (EO) satellites currently account for just over a third of all the operational satellites orbiting the Earth. As we described two weeks ago, according to the Union of Concerned Scientists database there were 1 738 operational satellites at the end of August 2017, and 620 of these have a main purpose of either EO or Earth Science.

This represents a massive 66% increase in the number of EO satellites from our 2016 update, and the percentage of overall active satellites is also up from one quarter. These figures demonstrate, once again, that EO is a growing industry.

What do Earth observation satellites do?
Looking more closely at what EO satellites actually do demonstrates that despite increases in satellite numbers in almost all categories, it’s clearly growth in optical imaging which is the behind this significant increase. The purposes of active EO satellites in 2017 are:

  • Optical Imaging: 327 satellites representing a 98% increase on last year
  • Radar imaging: 45 satellites, a 32% increase on last year
  • Infrared imaging: 7 satellites, no change to last year
  • Meteorology: 64 satellites, a 73% increase on last year
  • Earth Science: 60 satellites, a 13% increase on last year
  • Electronic intelligence: 50 satellites, a 6% increase on last year
  • 16 satellites with other purposes, a 133% increase on last year
  • 51 satellites simply list EO as their purpose, a 100% increase on last year

Who controls Earth observation satellites?
Despite the huge increase in EO satellites, the number of countries who control them has not seen the same growth. This year there are 39 different countries listed with EO satellites, an increase of only 15% on last year. In addition, there are satellites run by multinational agencies such as the European Space Agency (ESA).

The USA leads the way controlling over half the EO satellites, although this is largely due to Planet who account for 30% on their own! Following USA is China with 14.4%, and then come India, Japan and Russia who each have over 3%.

The USA is followed by China with about 20%, and Japan and Russia come next with around 5% each. The UK is only listed as controller on 4 satellites all related to the DMC constellation, although we are also involved in the ESA satellites.

Size of Earth observation satellites
It’s interesting to look out the size breakdown of these satellites which shows the development of the small satellite. For this breakdown, we’ve classed satellites into four groups:

  • Large satellites with a launch mass of over 500kg
  • Small satellites with a launch mass between 100 and 500 kg.
  • Microsats with a launch mass between 10 and 100 kg.
  • Nanosats/Cubesats with a launch mass below 10 kg.

For the current active EO satellites there are:

  • 186 large satellites equating to 30.00%
  • 74 small satellites equating to 7.26%
  • 100 microsats equating to 16.13%
  • 215 Nanosats/Cubesats equating to 34.68%
  • The remaining 45 satellites do not have a launch mass specified.

Who uses the Earth observation satellites?

There has also been significant movement in the breakdown of EO satellites users since 2016. The influence of small commercial satellites undertaking optical imaging is again apparent. In 2017 the main users for EO were:

  • Commercial users with 44.68% of satellites (up from 21% in 2016)
  • Government users with 30.81% (down from 44% in 2016)
  • Military users with 19.35% (down from 30% in 2016)
  • Civil users with 5.16% (approximately the same as in 2016)

It should be noted that some of these satellites have multiple users.

Orbits of Earth observation satellites
In terms of altitude, unsurprisingly the vast majority, 92.25%, of EO satellites are in low earth orbits, 6.45% are in geostationary orbits and 1.3% are in an elliptical orbits.
There is a much greater variation in type of orbits:

  • 415 in a sun-synchronous orbit
  • 125 in a non-polar inclined orbit
  • 17 in a polar orbit
  • 8 in an equatorial orbit
  • 5 in an elliptical orbit
  • 5 in a Molniya orbit (highly eccentric elliptical orbits of approximately 12 hours)
  • 45 satellites do not have a type of orbit listed

Few interesting facts about active Earth observation satellites

  • Oldest active EO satellite is the Brazilian SCD-1 Meteorology/Earth Science satellite.
  • Valentine’s Day (14th February) 2017 saw Planet launch its Flock 3P meaning that 88 active EO satellites were launched on that day.
  • Most popular launch site is Satish Dhawan Space Centre operated by Indian Space Research Organisation (ISRO) who have put 169 into space.
  • ISRO’s Polar Satellite Launch Vehicle is also the most popular launch vehicle with 114 satellites.
  • The EO satellite furthest away from the Earth is the USA’s Electronic Intelligence satellite Trumpet 3 which has an apogee of 38 740 km.

What’s next?
It’s not clear whether the rapid growth in the number of EO satellites will continue into 2018. Planet, one of the key drivers, announced earlier this month that they had successfully completed their objective to image the globe’s entire landmass every day – which is a massive achievement!

That’s not say that Planet won’t push on further with new ideas and technologies, and other companies may move into that space too. China launched a number of EO satellites last weekend and there are already a number of interesting satellites planned for launch between now and the middle of 2018 including, Cartosat-2ER, NovaSAR-S, GOES-S and Sentinel-3B to name a few. .

One thing is for certain, there is a lot collected EO data out there, and it is increasing by the day!