Thursday, January 24, 2013

Landsat aims to maintain gold standard

Byrd Glacier, Antarctica
Sensor: L7 ETM+

From BBC

One of the very best ways to understand the changes taking place on Planet Earth is to make observations from space.
And to get a true sense of any trends, you really need those measurements to be long-term and unceasing.
Preferably, you use the same type of instrument to make the observations, and when, inevitably, you're required to replace aging equipment, you do so in such a way that the new system can be cross-calibrated with the old.

 Small, blocky shapes of towns, fields, and pastures surround the graceful swirls and whorls of the Mississippi River. Countless oxbow lakes and cutoffs accompany the meandering river south of Memphis, Tennessee, on the border between Arkansas and Mississippi, USA.
The “mighty Mississippi” is the largest river system in North America.
This image, taken by Landsat 7 on May 28, 2003, won 3rd place in the online “Earth as Art” competition to celebrate the 40th anniversary of the Landsat satellite program.

Few Earth observation programmes get as close to this gold standard as Landsat, the cooperative space mission run by US space agency (Nasa) and the US Geological Survey.
For 40 years now, the Nasa/USGS satellites have maintained a permanent eye on Earth.
It was during the Apollo preparations - when astronauts would also take pictures of their home planet as they tested their Moon technologies - that the idea was born for a dedicated imaging system to observe the Earth.
It led to the development of the Earth Resources Technology Satellite (ERTS), launched on 23 July 1972 and operated for six years.
Subsequent platforms picked up the baton. Today, Landsat-7 maintains the watch, with its successor, Landsat-8, being readied for lift-off next month.
The latest incarnation will go up from California's Vandenberg Air Force base on an Atlas rocket, and, after a few weeks of checks, assume the lead role of imaging the planet from an altitude of 705km.

 Along the southern coast of the Netherlands, sediment-laden rivers have created a massive delta of islands and waterways in the gaps between coastal dunes.
After unusually severe spring tides devastated this region in 1953, the Dutch built an elaborate system of dikes, canals, dams, bridges, and locks to hold back the North Sea.
Image taken on September 24, 2002, by the ASTER instrument aboard NASA’s Terra satellite.

The Landsat spacecraft view the Earth in visible and infrared wavelengths, and track details as small as 30m across.
It's true there are imaging sensors up there now that will return pictures of Earth with far better resolutions (in the tens of centimetres), but for the job Landsat is trying to do, the 30m/pixel view is perfect.

Akpatok Island lies in Ungava Bay in northern Quebec, Canada.
Accessible only by air, the island rises out of the water as sheer cliffs that soar 150 to 243 m above the sea surface. Akpatok Island is an important sanctuary for cliff-nesting seabirds.
Numerous ice floes around the island attract walrus and whales, making Akpatok a traditional hunting ground for native Inuit people.
Image taken January 22, 2001, by Landsat 7.

Over its 40-year history, Landsat has catalogued the growth of the megacities, the spread of farming and the changing outlines of coasts, forests, deserts and glaciers.
It has monitored fires and volcanic eruptions.
It has even detailed the behaviours of Antarctic penguins and North American beetles.

The Lena River, some 4,500 km long, is one of the largest rivers in the world.
The Lena Delta Reserve is the most extensive protected wilderness area in Russia.
It is an important refuge and breeding ground for many species of Siberian wildlife.
This is a false-color composite image made using shortwave infrared, infrared, and red wavelengths.
Image taken July 27, 2000, by Landsat 7.

"One [application] that we're particularly proud of is the use of something we call the thermal band," explained Matt Larsen, the associate director for climate and land-use change at the USGS.
"This is a technique by which we can estimate the temperature of the surface of the Earth from the sensors on the Landsat satellite, and from that we can measure evapotranspiration (the conversion of water to water vapour).
"Why do we care about that? That's a key part of agricultural activity, and in the western US where we have a huge amount of land in irrigated agriculture, it allows us to better understand how much water we are using, how much water we need and how that might be affected in the future because of changing stream flows because of changing temperatures," he told the BBC World Service's Science In Action programme (listen to our feature).
Landsat-8 will carry an additional thermal band that will lead to more precise measurements.

 The ParanĂ¡ River delta is a huge forested marshland about 30 km northeast of Buenos Aires, Argentina. The area is a very popular tour destination.
Guided boat tours can be taken into this vast labyrinth of marsh and trees.
The ParanĂ¡ River delta is also one of the world’s greatest bird-watching destinations.
This image highlights the striking contrast between dense forest and wetland marshes, and the deep blue ribbon of the ParanĂ¡ River.
This is a false-color composite image made using shortwave infrared, near infrared, and green wavelengths.
Image taken May 26, 2000, by Landsat 7.

The uses of Landsat data really are innumerable.
Paul Donald, a conservation scientist with the UK's Royal Society for the Protection of Birds (RSPB), gives a great example of how these pictures can be used to understand the geographical distribution of very poorly known avian species.
You cannot see the birds from space, obviously, but you can map their likely habitat.
"One of the ways we can do this is to use a modelling technique, where we take Landsat data and we match that with areas where we know the birds are; and that will then give us a very good description of where the bird may be where people have never even been to look for it," he told us.
"The results have been extraordinary. We've generated maps using Landsat imagery which have predicted areas we never thought suitable for this bird. We've gone there, and we've found the bird."

 The tongue of the Malaspina Glacier, one of the largest piedmont glaciers in the world, fills most of this image. The Malaspina lies west of Yakutat Bay in Alaska and covers roughly 3,900 sq km.
This image was acquired on August 31, 2000, by Landsat 7′s Enhanced Thematic Mapper plus (ETM+) sensor.
This is a false-color composite image made using infrared, near infrared, and green wavelengths, and has been sharpened using the sensor’s panchromatic band.

Landsat-8 is more formally called the Landsat Data Continuity Mission (LDCM).
This mouthful reflects the rather tortured route the mission had to take to get budget approval.
It's a perennial problem for Earth observation missions - getting a timely sign-off from the politicians so that an enduring presence in orbit can be maintained. Even with Landsat, it is as if each satellite was born an only child, and the next mission had to fight for justification as if there had been no heritage.

 Ephemeral Lake Carnegie, in Western Australia, fills with water only during periods of significant rainfall.
In dry years, it is reduced to a muddy marsh.
This image was acquired on May 19, 1999, by Landsat 7′s Enhanced Thematic Mapper plus (ETM+) sensor.
This is a false-color composite image made using shortwave infrared, infrared, and red wavelengths, and has been sharpened using the sensor’s panchromatic band.

Nasa, USGS and the Federal Office of Management and Budget (OMB) are now seeking a long-term solution that would see Landsat-9 and all following spacecraft arrive on a predictable track.
It is the sort of assurance Earth observation seeks in Europe, also.
At the end of this year, the European Space Agency will start to roll out the multi-billion-euro Sentinel fleet of satellites, which aim to echo the Landsat philosophy but with many more types of sensor. However, even as the first mission is prepared for launch, politicians are still arguing over how the project should be funded.

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