Category Archives: Research

What Can You Really See From Space?

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Most people know that satellites in orbit do useful things such as collect images of the Earth’s surface. At the National Air and Space Museum I use satellite images in my job to understand changes in the Earth’s land surface. Today millions of people are acquainted with satellite imagery on internet map services. People sometimes ask me if it’s possible to see even more detail from space. In this post I’ll explore what is really visible in different types of satellite data.

There are dozens of orbiting remote sensing satellites, and the level of detail they see depends on its precise mission. “Remote sensing” just means looking at something from a distance. In this case we’re talking about viewing the Earth from at least hundreds of miles above the atmosphere.

The images on internet map servers are provided by a recent generation of satellites that collect detailed images, including the GeoEye and WorldView satellites. Objects smaller than automobiles are visible in some of these images. In the past, only military and reconnaissance satellite were capable of this kind of detail.

IKONOS

Image from the IKONOS satellite showing downtown San Francisco. This type of image shows great detail over small areas.

Other satellites observe large areas and discern things the size of agricultural fields. These spacecraft, including the Landsat satellites, are useful for mapping cities or regional changes in land cover.

Landsat 7

Image from the Landsat 7 showing the metropolitan area of Mexico City in the upper left. On the right is the volcano Popocatepetl, which appears dark red in this false color infrared image. This image covers an area about 100 miles across.

Another class of satellites orbit thousands of miles out in space. These spacecraft, including the GOES satellites, are designed to observe changing weather over an entire hemisphere of the Earth. They cannot discern small details.

GOES

View from GOES satellite showing weather systems moving across the entire globe.

In the past, it was often incorrectly stated that the Great Wall of China was the only man-made thing visible from space. Although an astronaut would probably not be able to see it with unaided eyes, the Great Wall is visible using orbiting sensors. However, plenty of other things made by humans are also visible. It was sometimes even stated that the Great Wall is visible from the Moon, but that’s definitely not possible. If you stood on the Moon, the entire Earth would appear to be about the size of a quarter held at arm’s length.

In some Hollywood films, satellites provide moving images from space. The hero immediately targets a satellite to search for evildoers. While this type of real-time imagery looks very cool, it’s not really how satellites work. Orbiting satellites pass over a particular point only every couple of weeks, and they cannot be immediately moved or collect moving images.

There is a way to get imagery like that, but it’s from unmanned airplanes. Drone aircraft can provide real-time imagery and even be equipped with weapons to attack targets.

In reality, satellite imagery is used for “before” and “after” images. These can be used for research purposes and for responses to emergencies. Recently media outlets widely used imagery from the GeoEye-1 satellite to show tsunami devastation in Japan.

Sometimes a satellite passes overhead at just the right time to capture a rapid change. The Indian Ocean tsunami on December 26, 2004 was one of those times. The QuickBird satellite just happened to pass over Sri Lanka when the wave of water crashed ashore, providing an amazing (and scary) image. In 2005 the same satellite provided images of New Orleans immediately after Hurricane Katrina. I had an opportunity to closely examine those images at the time, and I remember making a sobering calculation of how much of the city remained submerged.

So the detail visible in a satellite image all depends on the mission of each satellite and the scale of its observations. A few non-military satellites can see objects down to about half the size of a car. Some military satellites can still see even smaller things. But that does not tell us the whole story. For most applications we need to see larger areas, which requires other satellites that observe at a different scale.

For each satellite imaging project, we need to choose between seeing small details or seeing a large area. You can’t usually have both. But  increased computing power has made it possible to combine highly detailed images to cover very large areas. The seemless imagery on internet map servers actually consists of many thousands of individual images that have been combined. Scientists use the same kind of approach to view fine scale vegetation changes across continents. Methods of combining small images will continue to be valuable for making detailed observations of the Earth in the future.

Andrew K. Johnston is a geographer in the Center for Earth and Planetary Studies at the National Air and Space Museum.

MESSENGER on Final Approach to Mercury

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Today at 8:45 pm EDT (March 18, 2011, 12:45 am UTC), MESSENGER will become the first spacecraft ever to enter Mercury’s orbit. With MESSENGER on the last leg of its journey, I’m reminded how long it has taken to get there.  I watched the spacecraft launch in the early morning hours of August 3, 2004, almost six and a half years ago.  Now after one flyby of Earth, two flybys of Venus, and three flybys of Mercury, the spacecraft will catch up with Mercury again, but this time it will be captured by the planet.  You might think as one of our closest neighbors in the Solar System it would take a lot less time to get into Mercury orbit – but because Mercury is the closest planet to the Sun, at a distance where the influence of the Sun’s gravity is much greater, it is a challenge to reach and orbit.

MESSENGER

This artist's impression shows MESSENGER with its sunshade side. The sunshade shields the spacecraft from solar radiation, helping to keep the instruments from overheating. Image courtesy of Johns Hopkins University Applied Physics Laboratory.

In its three flybys of Mercury, MESSENGER imaged much of the planet’s surface. As great as the flyby images are, they vary greatly in resolution and in lighting geometry.  In orbit, MESSENGER will map the entire surface of Mercury at high resolution and with even lighting.  These first images obtained from orbit will revolutionize our understanding of Mercury.  I will be eagerly examining the new images for evidence of fault scarps, landforms created by the shrinking of Mercury’s crust causing it to break and from cliffs.  These cliffs tell us that Mercury’s interior has cooled and the entire planet has contracted.  With a new global view of Mercury, we can map all the fault scarps and estimate just how much the planet has contracted over time.  It’s an exciting time for the exploration of Mercury!

Mercury

This color image of Mercury was captured on September 29, 2009 during MESSENGER's third and final flyby. Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Tom Watters is senior scientist and geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum.

Vintage Aircraft Tool Cataloging, Re-housing and Preservation Project

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In the years following WWII the United States and her Allies conducted engineering and flight tests of many different types of captured or surrendered Axis aircraft, primarily from Germany and Japan. Many of these aircraft were acquired by Allied and US technical intelligence collection teams.  It was ordered that at least one of each type of enemy aircraft be captured and evaluated by these teams, and that each aircraft type be maintained in flyable condition for a minimum of one year. To make this possible all technical data and support materiel available (such as tool kits, parts, etc.) had to also be captured to meet this requirement.

fuselage

Fuselage of a captured German WWII FockeWulf Ta-152H-0 advanced fighter, currently stored at the Paul E. Garber Preservation, Restoration, and Storage Facility. This aircraft was surrendered to an RAF intelligence team and later transferred to the US for evaluation.

Several of these captured aircraft were donated to the National Air and Space Museum upon completion of US Air Force testing in the late 1940s and early 1950s, and much of the supporting parts and tools came along with them. At the time loose tools and toolkits were not seen as accessionable objects, merely as tools to be used for repair and possible future restoration purposes. They remained in storage for years. Today this collection of tools contains some of the very last examples of their kind to be found anywhere in the world. It is due to the historically important and unique nature of these objects that a Collections Care and Preservation Fund (CCPF) has enabled a project to catalog, re-house, and preserve these irreplaceable examples of tools and kits.

tools

One of several large crates filled with hundreds of loose tools of various types. Sorting these loose tools and beginning a comprehensive identification and inventory process has been the first priority of the 2010 CCPF Vintage Aircraft Tool project.

The  project began in July of 2010. The cataloging, condition assessment, and digital photography of this varied and unique collection was begun immediately so that a comprehensive inventory of this diverse collection could be created.

tools

Examples of sorted and inventoried tools. Upon identification it was discovered that these tools were highly specialized and potentially one-of-a-kind examples. The left tool was designed to cool large bearings with a cryogenic liquid to aid their removal during overhaul of a BMW 801 engine, like the one used to power the Focke Wulf FW-190. The right tool was designed to be used on the cylinder heads of several different types of Daimler-Benz engines, such as those used to power the He-219 Night Fighter currently being restored at the Paul E. Garber Preservation, Restoration, and Storage Facility.

One goal of the project is to create a curatorial and collections guideline for the proper and safe use of these tools, ensuring they remain in an accessible yet preserved condition. To ensure future access to restoration specialists and researchers, a series of protective storage cabinets will provide adequate space that maximizes accessibility yet minimizes unnecessary handling. This system of storage will also allow for easier transportation of the collection to the new Mary Baker Engen Restoration Hangar at the Steven F. Udvar-Hazy Center.

Additionally, it is necessary to prepare most of these tools for long-term, stable storage via thorough cleaning to remove old, soiled, or failing preservative coatings and service-related grime, and also treating areas of active surface corrosion. Once cleaned and treated each tool will then have a modern preservative coating reapplied, ensuring long-term stabilization and usability.

engines

Both engines above are from the He-219 Night Fighter being restored at the Paul E. Garber Preservation, Restoration, and Storage Facility. The left engine has already undergone restoration at the time this image was taken, while the right engine has yet to be restored. Being able to use or copy examples of purpose-built tools is important to restorers. If these necessary and unique tools are misplaced, damaged beyond usability or disappear, restoration is seriously hindered.

Copies of these tools have been made in the past to perform vital restoration work on some of the associated captured aircraft, and in some instances the tools themselves have been used. But once they are lost, then any similar restoration or stabilization work will be made much more difficult, if not impossible. This project will help ensure that these important objects are preserved.

Ray Barnett is a contractor working with the collections division of the National Air and Space Museum.

Learning to Capture the Sun

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The Public Observatory Project is just over a year old now, and in that time we’ve been  experimenting with the telescope to discover what is visible in the daytime sky and devise ways that our visitors can have the best experience possible.  One of our goals is to use our equipment to take images of the Sun, so that we can share our star’s day-to-day activities with the visiting public as well as those who can’t make it to the Mall to look through our telescopes.  We wanted to capture true-to-life images of the Sun as it appears through our telescope and make interesting features clearer and more apparent.

It would be dangerous to use a normal telescope to look at the Sun because the Sun’s concentrated and unfiltered light would damage your eyes.  One of the tools we use to look at the Sun safely is our Lunt Solar Systems hydrogen-alpha telescope that filters out all but one wavelength of red light. This makes it safe for viewing a part of the Sun’s atmosphere, called the chromosphere.  To take images of the Sun, I started out with this telescope, as well as a Lumenera SKYnyx 2-0 Color camera that fits where the eyepiece usually goes. We also have a laptop with software to control the camera, called Lucam Recorder.  With these in hand, I set off to take some of my first images of the Sun.

sun

This image of two prominences was taken on June 8, 2010.

Through some experimentation, I found out that different exposure settings revealed very different details on the Sun. First I cranked up the exposure to capture the faint prominences coming off the edge of the Sun and took a series of images. Next, I turned down the exposure to what I thought was an appropriate level to capture details on the Sun’s surface before taking a second series of images. I used a processing program called the GIMP to merge the two images by selecting the disk detail and moving it on top of the prominence image.  But, something wasn’t quite right. This didn’t look much like what I was seeing with my own eyes. So, I turned to a local amateur solar imaging expert and friend of the National Air and Space Museum: Greg Piepol.

Greg’s solar imaging work, which you can check out on his website sungazer.net, has been praised for its beauty and attention to detail. My colleague at the Observatory and fellow Sun imager, Katie Moore, and I were thrilled that he agreed to come into the Museum and show us how he captures such stunning images.

Greg taught us several things that improved our imaging. The first and most important was that we had been drastically overexposing the disk of the Sun, which washed out the details we were trying to capture. Greg also taught us how to better use an image stacking program called Registax, which takes individual frames from a movie file and stacks them together, thereby removing a lot of noise caused by Earth’s turbulent atmosphere. Astronomers call this “seeing,” which is what makes the stars twinkle. He also showed us other image processing techniques in the GIMP, such as levels adjustment and color correcting that brought out details on the Sun.

sun

This image was taken on July 28, 2010, the day after Greg Piepol came to visit. The small dark Sunspot near the top of the disk is about the same size as the Earth!

This was most certainly closer to what we had seen in the telescope. But of course, as they say, practice makes perfect. Over the next few months I took pictures as often as I could. I learned the extreme importance of making fine adjustments to the filters inside the telescope to get exactly the right details. I learned the advantages of using a double-stacked filter on top of our telescope to help make the darker wispy absorptive lines in the solar atmosphere, called filaments, truly pop out.  I also learned the importance of careful processing to coax the most detail possible out of the raw data.  It is interesting to compare the final product to one of the raw, unprocessed images to see what a difference it makes.

This is a single frame from the raw video before the image is processed

This is a single frame from the raw video before the image is processed

sun

This final processed image of a Sunspot was taken on July 30, 2010

A large prominence on the Sun, taken on September 15, 2010

A large prominence on the Sun, taken on September 15, 2010

This mosaic of 2 images highlights a large Sunspot group, as well as a dark filament in the Sun’s chromosphere.

This mosaic of 2 images highlights a large Sunspot group, as well as a dark filament in the Sun’s chromosphere.

And so, the journey continues! The Sun is always changing, and there are always more techniques to be learned and perfected. If you get the chance, come see the Sun for yourself at the Public Observatory, which is open Thursday through Sunday, 11 am to 3pm for the month of October, weather permitting.  We are ordering an upgraded camera and some new software to better process these images, so be on the lookout for new images online!

Erin Braswell is an Astronomy Educator at the National Air and Space Museum.

Seeing Beneath the Surface of the Moon

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“Remote sensing” is a term used to describe many different types of observations carried out at a distance. Aerial photos, satellite images of the Earth and planets, and telescope views of our solar system are all forms of remote sensing used to understand geology, climate, hazards, and changes over time. Not all remote observations use the wavelengths of light visible to humans; there is a wealth of information contained in how a surface reflects or emits radiation across the spectrum from radio waves to gamma radiation. Scientists at the National Air and Space Museum’s Center for Earth and Planetary Studies use radar signals, transmitted from satellites in lunar orbit or from the largest radio dishes on Earth, to probe below the dusty surface of the Moon. Radio waves, which have a much longer wavelength than visible light (the Museum’s research uses signals with 12.6-centimeter and 70-centimeter wavelengths), penetrate up to 30-40 meters into dry material and reflect from buried layers or rocks suspended in the thick dust. By carefully measuring the time between the transmitted and received radar signals, and the subtle changes in frequency caused by the rotation of the Moon, the radar “echoes” can be assembled into an image that resembles a photograph, but revealing aspects of lunar geology often hidden from optical cameras. Studies using the new radar maps trace the outlines of ancient lava flows now buried by material hurled from giant impact craters, find rocky material in resource-rich areas that might pose hazards to robotic exploration, and “light up” for the first time areas near the poles that are in permanent shadow from the Sun. Ongoing work suggests that some areas of the smooth lunar “seas,” or maria, may have very rugged, boulder-covered lava flows hidden by billions of years of overlying dust; how such rough deposits might form remains a mystery. The lessons learned from studies of the Moon are guiding efforts to design a radar sensor for Mars that will look beneath that dust-covered surface to reveal additional geologic signatures of past and present water.

Aristoteles

A 12.6-centimeter wavelength radar view of the lunar crater Aristoteles (87 km diameter). Rugged areas, such the northern interior wall of the crater, appear bright to the radar, and smooth or dusty parts of the surrounding region appear dark. The radar lighting comes from the lower left, so the walls of the crater cast "radar shadows" just as they would for illumination by the Sun. The surrounding clusters and chains of smaller craters were formed by debris ejected from the main crater.

Bruce Campbell is a geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum.