This image of the rough and highly complex ice sheets at Jacobshavn Glacier in Greenland was taken from the window of a P3 aircraft during a campaign to gather precise data on whether the ice sheets were moving up or down.
An instrument that has proven its worth many times over gathering topographical and vegetation data, has accomplished something that no one ever expected it to do: it has measured the rapidly thinning ice sheets over Greenland during an experiment aimed at proving the instrument’s viability for all types of climate change studies.
We’re processing the Greenland data now and it will be ready for release very soon,” says Principal Investigator Bryan Blair, who developed the Laser Vegetation Imaging Sensor (LVIS, which is pronounced Elvis) using Goddard R&D funds. “We wanted to see what this instrument, originally optimized for vegetation science, could do for ice science. Now that we have collected the data, we will let the scientists decide.”
In recent years, the Greenland ice sheets have captured the attention of scientists worldwide because they are melting at increasingly rapid rates — a phenomenon that could raise global sea levels and contribute to flooding along coastal regions.
Early last year, the National Academy of Sciences released its decadal survey that recommends a variety of space-based missions, which would help scientists better understand the natural and human-induced changes to Earth’s land surface, biosphere, atmosphere, and oceans. Some of those missions specifically recommend next-generation investigations of the polar ice sheets and vegetation.
What LVIS Can Do for Ice
The instrument, which can mount into any aircraft that accommodates a standard aerial camera, is a scanning laser altimeter or lidar that sends a laser beam toward a target and measures the time it takes for the signal to return. Since its development nearly 10 years ago, the instrument has become a mainstay for various government agencies and universities requiring information about Earth’s topography, the structure of tree canopies, biomass, and surface roughness.
Unlike other lidars, however, LVIS also uses the so-called waveform-based measurement technique that analyzes the shape of the returned pulse, not just the time it took for it to return. The waveform reveals the distribution of surfaces above the terrain, making it especially useful for measuring extremely rough terrain, such as ice sheets that are moving very fast or breaking up.
For the Greenland experiment this past September, Blair deployed his instrument on NASA’s P3 aircraft and flew over areas measured by NASA’s ICESat (Ice, Cloud, and land Elevation Satellite), a Goddard-developed laser altimeter mission. LVIS collected about 5,000 square kilometers or 2,000 square miles of data using 20-meter (about 66 feet) diameter footprints. The goal was to provide highly precise data on whether the ice sheets were moving up or down; in other words, whether they were melting. “We hope the data can help scientists better understand and evaluate the ICESat data,” Blair says.
Just as important, he also wanted to show that the technique was a viable contender for other types of climate change investigations, not just those addressing vegetation. “A lot of people think this is only a vegetation lidar, but this high-quality data set over the ice will expand LVIS’s application base.”
Space Application Remains the Goal
Ultimately, Blair hopes to see his swath-mapping laser altimeter fly in space. “Right now, LVIS flies at 10 kilometers (more than 6 miles) above the surface. All other airborne lidars fly at 1 kilometer (about a half mile) or lower. Due to the way the laser reflection weakens with distance, 10 kilometers is one hundred times harder to achieve than 1 kilometer. Going to an orbital altitude of 400 to 600 kilometers (250-375 miles) is even harder, but LVIS has a good lead over other sensors.”
“Everything we do in terms of technology development and science demonstrations are aimed at getting LVIS into space,” Blair says.
Goddard technologists win new work, secure follow-on funding to mature new technologies, formulate concepts, and validate new instrument concepts in flight demonstrations — successes that benefit Goddard and the scientific community as a whole.