Earth observation satellites in space in 2016

Blue Marble image of the Earth taken by the crew of Apollo 17 on Dec. 7 1972. Image Credit: NASA

Blue Marble image of the Earth taken by the crew of Apollo 17 on Dec. 7 1972.
Image Credit: NASA

Earth Observation (EO) satellites account for just over one quarter of all the operational satellites currently orbiting the Earth. As noted last week there are 1 419 operational satellites, and 374 of these have a main purpose of either EO or Earth Science.

What do Earth observation satellites do?
According to the information within the Union of Concerned Scientists database, the main purpose of the current operational EO satellites are:

  • Optical imaging for 165 satellites
  • Radar imaging for 34 satellites
  • Infrared imaging for 7 satellites
  • Meteorology for 37 satellites
  • Earth Science for 53 satellites
  • Electronic Intelligence for 47 satellites
  • 6 satellites with other purposes; and
  • 25 satellites simply list EO as their purpose

Who Controls Earth observation satellites?
There are 34 countries listed as being the main controllers of EO satellites, although there are also a number of joint and multinational satellites – such as those controlled by the European Space Agency (ESA). The USA is the leading country, singularly controlling one third of all EO satellites – plus they are joint controllers in others. Of course, the data from some of these satellites are widely shared across the world, such as Landsat, MODIS and SMAP (Soil Moisture Active Passive) missions.

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.

Who uses the EO satellites?
Of the 374 operational EO satellites, the main users are:

  • Government users with 164 satellites (44%)
  • Military users with 112 satellites (30%)
  • Commercial users with 80 satellites (21%)
  • Civil users with 18 satellites (5%)

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

Height and Orbits of Earth observation satellites
In terms of operational EO satellite altitudes:

  • 88% are in a Low Earth Orbit, which generally refers to altitudes of between 160 and 2 000 kilometres (99 and 1 200 miles)
  • 10% are in a geostationary circular orbit at around 35 5000 kilometres (22 200 miles)
  • The remaining 2% are described as having an elliptical orbit.

In terms of the types of orbits:

  • 218 are in a sun-synchronous orbit
  • 84 in non-polar inclined orbit
  • 16 in a polar orbit
  • 17 in other orbits including elliptical, equatorial and molniya orbit; and finally
  • 39 do not have an orbit recorded.

What next?

Our first blog of 2016 noted that this was going to be an exciting year for EO, and it is proving to be the case. We’ve already seen the launches of Sentinel-1B, Sentinel-3A, Jason-3, GaoFen3 carrying a SAR instrument and further CubeSat’s as part of Planet’s Flock imaging constellation.

The rest of the year looks equally exciting with planned launches for Sentinel-2B, Japan’s Himawari 9, India’s INsat-3DR, DigitalGlobe’s Worldview 4 and NOAA’s Geostationary Operational Environmental Satellite R-Series Program (GOES-R). We can’t wait to see all of this data in action!

SMAP ready to map!

Artist's rendering of the Soil Moisture Active Passive satellite.  Image credit: NASA/JPL-Caltech

Artist’s rendering of the Soil Moisture Active Passive satellite.
Image credit: NASA/JPL-Caltech

On the 31st January NASA launched their Soil Moisture Active Passive satellite, generally known by the more pronounceable acronym SMAP, aboard the Delta 2 rocket. It will go into a near polar sun-synchronous orbit at an altitude of 685km.

The SMAP mission will measure the amount of water in the top five centimetres of soil, and whether the ground is frozen or not. These two measurements will be combined to produce global maps of soil moisture to improve understanding of the water, carbon and energy cycles. This data will support applications ranging from weather forecasting, monitoring droughts, flood prediction and crop productivity, as well as providing valuable information to climate science.

The satellite carries two instruments; a passive L-Band radiometer and an active L-Band synthetic aperture radar (SAR). Once in space the satellite will deploy a spinning 6m gold-coated mesh antenna which will measure the backscatter of radar pulses, and the naturally occurring microwave emissions, from off the Earth’s surface. Rotating 14.6 times every minute, the antenna will provide overlapping loops of 1000km giving a wide measurement swath. This means that whilst the satellite itself only has an eight day repeat cycle, SMAP will take global measurements every two to three days.

Interestingly, although antennas have previously been used in large communication satellites, this will be the first time a deployable antenna, and the first time a spinning application, have been used for scientific measurement.

The radiometer has a high soil moisture measurement accuracy, but has a spatial resolution of only 40km; whereas the SAR instrument has much higher spatial resolution of 10km, but with lower soil moisture measurement sensitivity. Combining the passive and active observations will give measurements of soil moisture at 10km, and freeze/thaw ground state at 3km. Whilst SMAP is focussed on provided on mapping Earth’s non-water surface, it’s also anticipated to provide valuable data on ocean salinity.

SMAP will provide data about soil moisture content across the world, the variability of which is not currently well understood. However, it’s vital to understanding both the water and carbon cycles that impact our weather and climate.