Sol 6.3 Solar Energy Test Review: How Does it Compare to the Other Satellites?

A couple of days ago, the world’s most advanced weather satellite, the JSC-built Suomi-VX, boosted into orbit to begin a new era of meteorological exploration. Equipped with a laser-guided imager, the world’s first-ever water-vapor satellite, and a day-night sensor, the new SPCentral has the tools to measure every aspect of our planet from space.

With the retirement of the Space Shuttle this year and the emergence of the private sector, there was no long-cherished dream of taking a stroll on the Moon with a selection of artists and filmmakers looking to capitalize on the new found popularity of outer space.

While all eyes were on the Moon, there was another satellite in orbit taking pictures of our planet that deserve our attention—the U.S. Air Force’s most advanced Earth observation satellite, the SoLiDAR, built by the Defense Advanced Research Projects Agency (DARPA).

The SoLiDAR mission’s primary goal is to map the Earth’s surface in 3D using a technique called laser-induced demodulation (LIDAR). In layman’s terms, that’s like flying over a mountain range and being able to see the topography of the entire planet in detail from space. While this may sound impossible, it’s actually been done before. And you can put a LIDAR instrument on the Moon to do it, too.

The major difference with SoLiDAR is that it collects all that data and transmits it back to Earth—no stops at the moon. This is accomplished using the Laser Communications System (LCS) between the satellite and ground stations on Earth. This is actually a critical element of the system. Without it, the whole thing becomes useless. It would be like trying to watch a TV broadcast from the Moon—if you can’t see the antenna, then it’s no good.

The Laser Communications System (LCS)

The laser communications system (LCS) is really two things: the laser and the transceiver. The laser is extremely important because it allows for the transmission of high-quality data over large distances. The transceiver, which is carried onboard the satellite, is responsible for taking the data from the laser and transmitting it to other locations on Earth for further processing. This is where things get interesting. While the laser and transceiver are the only things that matter from a technical standpoint, it’s the data that gets transmitted using them that makes the difference. This data can be used to generate 3D models of cities and continents complete with accurate topographic features. The resolution of these models can be up to 100 meters, which is considered extremely high for this type of application.

The usefulness of such an unprecedented level of detail in mapping the Earth cannot be overstated. Imagine being able to see the exact topography of any location on the planet in 3D from space. This could open up a whole new world of possibilities in just about any field of study—from natural resources to geography, meteorology, or astronomy. It’s hard to overstate the importance of this technology—it holds the promise of revolutionizing how we look at our planet from space.

The SoLiDAR Instrument Package

SoLiDAR is equipped with two powerful instrument suites—the laser altimeter and the hyperspectral imager. The former measures the height of the Earth’s surface with great precision using a laser ranging and measuring instrument called the Altimeter. It’s actually a derivative of the technology developed for the U.S. Army’s YALO targeting system and the ESA’s Copernicus satellite, which was responsible for the first-ever 3D mapping of the Earth from space. The Altimeter has a resolution of 4.5 centimeters in the horizontal plane and 3.5 millimeters in the vertical.

The hyperspectral imager takes the form of a traditional satellite imager with a variety of scientific instruments including visible light and infrared cameras, along with a 3D LIDAR scanner. The resulting images are classified with confidence levels determined by the spectra of the light detected.

The combination of the Altimeter and hyperspectral imager form the backbone of the SoLiDAR mission. While the world’s first laser-induced 3D map of the Earth was generated by the combination of these two instruments, subsequent missions to map the surface will include more sophisticated instruments which harness the power of these two technologies. Having more advanced sensors onboard is crucial to making this type of information available to decision makers on the ground—whether that’s natural resources, environmental, or economic development organizations.

How Does It Compare to the Other Satellites?

While all eyes were on the Moon, the story of the other Earth satellites has been going on beneath our very noses. The United State’s most advanced Earth observation satellite, the SoLiDAR, was successfully launched into orbit last month.

A derivative of the YALO targeting system, the Altimeter uses a laser to detect the distance to the ground surface and a micro-seismic transducer to pinpoint locations of high geophysical activity, such as volcanoes and earthquakes. This technology was originally developed for the U.S. Army’s YALO system and first flown in space in 2011 on the Copernicus Sentinel-1 satellite.

Key Differences Between SoLiDAR and other Satellites

While all satellites suffer from some degree of inaccuracy due to the effect of rounding errors and uncertainties associated with the measurements, the SoLiDAR team was able to significantly reduce these errors by using a more accurate atomic clock, more precise software for image analysis, and better design.

What’s more, SoLiDAR’s design enables it to capture images of the entire Earth every two weeks—a task which would normally require multiple missions. This is made possible by a phenomenon known as drift—the gradual change in the position of a celestial body as it orbits another (due to a combination of factors including tidal forces and atmospheric drag).

What’s Next for SoLiDAR?

With the successful completion of the SoLiDAR mission, the next step for DARPA and its colleagues at JPL is to begin working on improvements to the instrument and laser for the next generation of Earth observation satellites. This is made easier by the fact that most of the technology developed for YALO and Copernicus has been made freely available as open source software—a testament to the value of publicly funded research and development.

With an accuracy of better than 1 cm in the horizontal plane and 0.01 meters in the vertical, the SoLiDAR laser altimeter can measure changes in vegetation density with great precision—making it ideal for monitoring changes in the world’s forests and identifying which tree species are responding to climate change. Identifying and verifying the causes of environmental fluctuations in these locations is crucial to understanding global ecological dynamics.

The hyperspectral imager can identify and quantify the chemical composition of material on the ground—such as vegetation and soil—using both visible and infrared light, providing valuable information about the state of our planet’s natural resources. This makes it ideal for monitoring and tracking changes in the world’s largest lakes, oceans, and rivers as well as identifying deforestation along coastlines and in the mountainsides.

DARPA, JPL, and its partners are working together to bring this groundbreaking technology to the public as the Revolutionizing Remote Sensing Technology (RRST) program—an open-source endeavor which will enable the next generation of Earth observation satellites.

Scroll to Top