Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Landsat Looks to the Moon

14.07.2014

Every full moon, Landsat 8 turns its back on Earth. As the satellite’s orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting land-cover information of the sunny side of Earth below.

These monthly lunar scans are key to ensuring the land-imaging instrument aboard Landsat 8 is detecting light consistently. For this, engineers need a consistent source of light to measure.


Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting information on Earth.

Image Credit: NASA's Goddard Space Flight Center

And while there are some spots on Earth – like the Sahara Desert or other arid sites – that reflect a relatively stable amount of light, nothing on our planet beats the moon, which lacks an atmosphere and has an unchanging surface, barring the odd meteorite.

We really wanted something we could trust for Landsat 8,” said Brian Markham, leader of the calibration team for Landsat 8, which was built and launched by NASA and is now operated by the U.S. Geological Survey.

“We do have Earth sites we look at for calibration. But the precision with which you can track things by using the Earth, because of the atmosphere, is not as good as the moon.”

Landsat 8’s Operational Land Imager, or OLI, collects information on the visible, near infrared and shortwave-infrared light reflecting off Earth’s surface. Each wavelength of light provides information about the ground surface below.

OLI has 14 detector modules, each of which contains hundreds of individual detectors that record different spectral bands. The calibration team at Goddard and the U.S. Geological Survey’s EROS facility in South Dakota is tasked with making sure each of those detectors register light consistently over time.

Aboard the spacecraft, lamps provide light to calibrate OLl’s detectors, but the lamps aren’t perfect.  On the Landsat 7 satellite, the lamps started to fade before the detectors did.  Another option, solar diffusers, which use indirect sunlight, can darken as well.

“Everything else we’ve tried to use to monitor the stability of our instruments has often not been as good as the instruments themselves,” Markham said. But the moon is a steady, not-too-bright light in the sky. "As long as we know what its illumination conditions are, we can trend our instrument performance to it because we trust its stability.”

So Landsat 8 planners designed this latest satellite to image the moon as a baseline calibration. If, during these lunar tests, the OLI detectors indicate that the moon is getting slightly duller or brighter, then the Goddard scientists will know the instrument –not the moon – is off. With that data, they can adjust the algorithms that calculate land cover information during Landsat’s regular Earth-observation orbits.

It’s a fairly complicated operation to scan the moon each month, said Susan Good, a flight dynamics engineer at Goddard who works with Landsat 8.

“There are 14 detector modules,” Good said, “each of these has to scan the same path along the moon, so that you collect exactly the same data on each sensor.”

The flight dynamics software determines precisely where the spacecraft will need to point during a lunar calibration. The timing is set for just after the moon is completely full. Then, as Landsat 8 passes over Antarctica and heads north in Earth’s shadow, the spacecraft maneuvers to the precise location to start the first scan across the lunar surface.

It executes tiny and precise scans to take seven or eight passes across the moon – each one angled so that a different detector is centered on the moon. This takes about 18 minutes, by which time the spacecraft has almost reached the Arctic. So it maneuvers back to point at Earth, and complete its day-lit imaging. Then, Landsat 8 pivots to face the moon again, completing additional passes to test the remaining detectors. After two orbits, the lunar calibration is complete.

In Landsat 8’s first year, the lunar calibration tests show that the detectors are stable, Markham said, within a fraction of a percent. If the lunar calibrations and other tests show the detectors are off, the scientists can adjust the calculations that turn the raw Landsat data into information on land cover brightness, maintaining their accuracy.

Since the regular checks on Landsat 8’s performance, Good jokes that she will never look at the full moon the same. “I think oh, we’re having a lunar calibration,” she said. “I always know what Landsat' 8’s doing when the moon is full.” 

Kate Ramsayer
NASA Goddard Space Flight Center

Kate Ramsayer | Eurek Alert!
Further information:
http://www.nasa.gov/content/goddard/landsat-looks-to-the-moon/

Further reports about: Antarctica Earth Flight Geological Moon NASA Sahara atmosphere meteorite satellite wavelength

More articles from Physics and Astronomy:

nachricht Scientific achievements during the operation of Lomonosov satellite
18.12.2017 | Lomonosov Moscow State University

nachricht Quantum memory with record-breaking capacity based on laser-cooled atoms
18.12.2017 | Faculty of Physics University of Warsaw

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Error-free into the Quantum Computer Age

A study carried out by an international team of researchers and published in the journal Physical Review X shows that ion-trap technologies available today are suitable for building large-scale quantum computers. The scientists introduce trapped-ion quantum error correction protocols that detect and correct processing errors.

In order to reach their full potential, today’s quantum computer prototypes have to meet specific criteria: First, they have to be made bigger, which means...

Im Focus: Search for planets with Carmenes successful

German and Spanish researchers plan, build and use modern spectrograph

Since 2016, German and Spanish researchers, among them scientists from the University of Göttingen, have been hunting for exoplanets with the “Carmenes”...

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Single-photon detector can count to 4

18.12.2017 | Information Technology

Quantum memory with record-breaking capacity based on laser-cooled atoms

18.12.2017 | Physics and Astronomy

How much soil goes down the drain -- New data on soil lost due to water

18.12.2017 | Agricultural and Forestry Science

VideoLinks
B2B-VideoLinks
More VideoLinks >>>