"Why build one when you can have two at twice the price?" So goes the famous line (and government potshot) in the sci-fi film "Contact." But sometimes, having two of something in space is far, far better than one.
Image: picture-alliance/dpa/ESA/ATG medialab
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Launched from the northern Russian cosmodrome Plesetsk, the Sentinel-3b will traverse a stable orbit 814.5 kilometers (just over 500 miles) above our Earth.
As the "b" in its name suggests, it is the second of two Sentinel-3 satellites and forms a part of the European Space Agency's Copernicus earth observation program. It will follow its twin, the Sentinel-3a, as it circles around the earth – each following the other with an even delay. Every two days, they can cover the entire surface of the planet.
The most important tool in the Sentinel-3 satellites' kit? Their Sea and Land Surface Temperature Radiometers (SLSTR). As you might expect, they measure radiation and heat on the land and sea.
In addition, they'll use an Ocean and Land Color Instrument - another spectrometer that can track any changes of other details on the surface of our planet.
Both satellites have also got an altimeter, which, beyond measuring the sea level, can even determine the size of waves or plant growth.
Finally a dual-channel microwave radiometer will detect atmospheric disturbances and will use those readings to correct and ensure the calibration of other instruments onboard.
So far the EU's Copernicus program has sent three Sentinel satellites to observe Earth - 1A, 2A and 3A. But they're just the first halves. Enter Sentinel-1B, and the first mission becomes whole.
Image: ESA/Copernicus Sentinel data 2015
From the French Riviera
It may be among the strangest places on Earth, but this is where a lot of the European Union's Sentinel satellite equipment is being built for the Copernicus Earth Observation program. In Cannes, Thales Alenia Space is responsible for the Sentinel-1 satellites and a few of the others, too. The contractors include Airbus and many more. Sentinel-1B launches this week, making the first mission whole.
Image: ESA/Copernicus Sentinel data 2015
The story so far
Sentinel-1A was the first to launch on April 3, 2014. Since then, two have followed - Sentinel-2A on June 23, 2015 and Sentinel-3A on February 16, 2016. This shot from Sentinel-3A is one of its earliest. It shows the River Nile and Delta and parts of the Middle East. Using a sea and land surface temperature radiometer (SLSTR), the satellite measures the energy radiating from Earth's surface.
Image: ESA/modified Copernicus Sentinel data 2016
In spectacular true color
This incredibly sharp image shows Red Sea coral reefs off the coast of Saudi Arabia. It was captured by Sentinel-2A on June 28, 2015. The quality of the Sentinel images is a vast improvement on previous satellite missions, such as Envisat. The Sentinel-2 mission is for land monitoring. It provides images of vegetation, soil and water cover, inland waterways and coastal areas.
Image: ESA/Copernicus Sentinel data 2015
In spectacular false color
This false color image of south Khartoum in Sudan was one of the first from Sentinel-2A, captured five days after it arrived in orbit. In the top right corner you can see a bit of the Blue Nile River. The scattered red blotches along the river banks indicate dense vegetation, which is one of the things the satellite monitors. It's a false color image, as color was added to aid interpretation.
Image: ESA/Copernicus Sentinel data 2015
Harbor under threat
This is another great shot from Sentinel-2A, showing Sierra Leone in West Africa. The country's capital, Freetown, is on the peninsula at the bottom of the image. Its economy depends on the natural deep water harbor. But ESA says the estuary is "threatened by a growing population [and] unauthorized housing development," which has caused the removal of many hectares of mangrove vegetation.
Image: ESA/Copernicus Sentinel data 2015
The 'Yuma checkerboard'
Many of the Sentinel images are like works of art. You don't really have to know what's going on to appreciate them. But scientists, policymakers and authorities charged with national security rely on satellite imagery. And given the tools and skills, normal folk can benefit too. The Copernicus program is driven by a principle of Open Data. This shows Yuma in southwestern Arizona.
Image: ESA/Copernicus Sentinel data 2015
Tracking change in the Aral Sea
This is the Aral Sea as captured by Sentinel-1A. It's a composite of three radar scans taken between 2014 and 2015. ESA says the Aral Sea is a "striking example of humankind's impact on the environment and natural resources. [...] It has lost around 90 percent of its water volume since 1960 because of Soviet-era irrigation schemes." The different colors show the changes between the scans.
Image: ESA/Copernicus Sentinel data 2014/2015
Meanwhile, Back in Berlin…
Captured by Sentinel-2A, this image shows a vibrant Berlin, the German capital, in exquisite detail. It shows how green the city is, with the Tegeler See and Wannsee on the western side. There's also the former airport, the Tempelhofer Feld, in the lower center of the image, which in summer blooms with people, kites and bikes. All these images can be seen in full: www.esa.int/spaceimages/Images
Image: ESA/Copernicus Sentinel data 2015
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Neat gadgets, but so what?
The Sentinel-3a and b will collect data that can be used to improve meteorological forecasts and to research weather phenomena. They can help, for example, in understanding the mechanics of the periodical weather patterns of El Nino or La Nina. Also, the satellites will provide valuable data about the emergence of hurricanes and other tropical storms.
And the identically built Sentinel satellites can do even more: They can measure algae growth in the oceans by detecting pigments in the water. Such changes in the oceans have a direct impact on fish and other sea animals, and this data can help provide valuable information to fisheries and ecologists alike. It is also possible to detect marine pollution from space or to measure changes in the thickness of the ice cover in the polar regions.
As for the data the Sentinel-3 collects over land, it can, for example, be used to measure drought or localized islands of heat. And with its color spectrometer, the satellite can detect changes in vegetation. The instrument does so by computing the amount of photosynthetic active radiation absorbed by the leaves, which is not only relevant to calculate the development of natural habitat and forests, but is also of high relevance to farmers and agriculture scientists.
For them, it can help yield better crops.
Natural disasters as seen from outer space
How do satellites see the Earth? And what do they find out about what's happening down here? Check out these impressive photos of natural disasters to discover for yourself.
Image: NASA
Only tears of sand remain
Earth observation satellites such as the European Space Agency's Proba-V collect daily images that allow for the tracking of environmental changes over time. The images above - taken in April 2014, July 2015 and January 2016 (left to right) - offer crystal-clear insight into the gradual evaporation of Lake Poopo, once Bolivia's second largest lake - due at least in part to climate change.
Image: ESA/Belspo
The beast has awoken
No matter how long volcanoes sleep, they're always in a bad mood when they wake up. The International Space Station was passing overhead when the Sarychev volcano, located in the Kuril Islands of Russia, erupted in 2009. Astronauts were able to snap a picture through a hole in the clouds. From dense ash to clouds of condensed water, virtually all natural phenomena can be examined from outer space.
Image: NASA
Don't play with fire
Every year, wildfires devastate the landscape - and ecology - in numerous countries around the world. Too often, these are caused by humans. This was also the case in Indonesia, where farmers burned peat rainforest areas for agriculture. On the island of Borneo and Sumatra, satellites detected fire hot spots in September 2015, and the plume of grey smoke that triggered air quality alerts.
Image: NASA/J. Schmaltz
German kids misbehaved
In Germany, parents warn their children that if they don't finish their meals, it's going to rain. And indeed, in 2013 it rained, so much that some of central Europe's major rivers overflowed their banks. As shown in this image from 2013, the Elbe burst its banks following unprecedented rainfall. In the photo, muddy water covers the area around Wittenberg, in the German state of Saxony-Anhalt.
Image: NASA/J. Allen
At the eye of the hurricane
A strong storm can cause irreparable damage through intense winds and storm surges from the sea. Space-based information is crucial in following development of such storms: intensity, the direction it's moving, wind speed … in the eastern Pacific Ocean near Mexico, this satellite image helped determine how tropical storm Sandra reached winds of 160 kilometers per hour by November 25, 2015.
Image: NASA/J. Schmaltz
Melting away from under us
Satellites also play a key role in monitoring climate change and, inevitably, the process of melting ice. From space, scientists were able to document how several glaciers around the globe have receded - as well as the subsequent rise in sea level. This photograph, taken from the International Space Station, shows the retreat of the Upsala glacier in Argentine Patagonia from 2002 to 2013.
Image: NASA
Hold your breath!
Dust often covers remote deserts - however, in September 2015, satellites offered this impressive view of Middle East areas enveloped by a dust storm, or haboob, affecting large populated regions. What satellites can observe from space supports air quality sensors on the ground to understand patterns on how the storms start and develop. These findings can improve forecasting methods.
Image: NASA/J. Schmaltz
'Naked mountain'
These are the words NASA used to describe the lack of snow on California's Mount Shasta, a crucial source of water for the region. Images documenting drought over the past years have consistently been showing brown mountains that should be white, and bare earth where people seek water. As ice melts, drought grows.
