Earth Imaging

by | Mar 15, 2011

Overview of Earth Imaging
Since the dawn of time, humans have looked up at birds in flight and wondered, "What if…?"
Today, a vast global network of remote sensing aircraft and satellites image the planet thousands of times daily, providing a bird's eye view of everything from weather patterns to how many cars are parked at a shopping mall”valuable intelligence to a Wall Street retail analyst. In fact, the uses for Earth imaging data are expanding each day, fueled by the explosion of mobile devices and more powerful computer chips, along with enabling technologies such as Google Earth.

Earth Imaging Satellites
Earth imaging satellites range from scientific platforms, such as those flown by NASA and the European Space Agency, to powerful commercial optical satellites that can image home plate on a baseball field from 400 miles in Space.

One of the first major milestones in the history of Earth imaging was in 1972 when the first U.S. Landsat satellite returned images to Earth that were so vivid and rich with information that they surprised and exceeded the expectations of scientists everywhere. Landsat satellites have provided a continuous record of our planet's condition for more than 40 years, with Landsat 8 launched in Feb., 2013.

IKONOS from the Greek word for "image" was the first commercial high-resolution satellite. Launched in 1999, the U.S. IKONOS can image the ground at 1-meter resolution, which means its powerful digital camera can see things about that size from 435 miles in space. For example, park benches, cars and trucks are visible. An ingenious system of highly polished mirrors packed into a small compartment "fold" light to give IKONOS the same viewing power as a traditional 18-foot-long telescope.

Today's most powerful Earth imaging platforms include U.S. satellites GeoEye-1, WorldView-1, WorldView-2 and WorldView-3 along with France’s Pléiades 1A and Pléiades 1B. Medium-resolution platforms include France's Spot satellites with ground resolutions ranging from 2.5 meters to 10 meters. Landsat satellites have 30-meter resolution, offering a much wider view but not as detailed. As well as a growing number of smallsat constellations such as Skybox (recently purchased by Google) and Planet Labs.

More Than Meets the Eye

Satellite images also can have multispectral qualities, which means the same image can be viewed through different "bands" such as infrared or near infrared. Because every material on Earth has its own distinct reflectance quality or "signature" these bands can tell us what's actually on the ground. For instance, it's possible to image a cornfield and determine what portion of the crop is OK and what portion has disease or insect infestation, simply by comparing the reflectance values of the healthy and unhealthy vegetation. Landsat has seven bands and WorldView-2 has eight bands. Hyperspectral satellites can have hundreds of bands.

In addition to optical imaging satellites, which are limited by cloud cover, radar satellites can image Earth night or day, even through clouds. This is especially valuable for disaster response applications. Examples are Canada's Radarsat and Germany's unique TerraSAR-X and TanDEM-X satellites, which orbit Earth side-by-side only a few hundred meters apart.

Airborne Earth Imaging
In 1858 balloonist G. Tournachon made photographs of Paris from his hot air balloon. Modern airborne photography had its birth during Word War I with film cameras mounted on aircraft for military surveillance and reconnaissance.

Today's sophisticated digital aerial cameras are at the cutting edge of Earth imaging technology. They are used to create orhophotos, which are images that have been geometrically corrected and registered to real points on Earth so they can be used as maps for a useful purposes.

Modern 3-D maps are made possible by adding elevation data acquired from Light Detection and Ranging, or LiDAR technology. Mounted on an aircraft, a LiDAR unit sends thousands of laser pulses to the ground, which bounce back to the aircraft and are measured. The result is an accurate 3-D digital model of the terrain. When merged with airborne or satellite imagery, the result is a realistic, often striking 3-D image of Earth. LiDAR units also can be mounted on cars and trucks to obtain rich 3-D data at the street level.

Learn more about the companies that provide Earth imaging products and services in the latest Earth Imaging Journal Remote Sensing Market Guide.


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