NASA To Measure Forest Health from Above

NASA To Measure Forest Health from Above

From the ground, it could be hard to assess the scale of losses and effects disappearing trees have on atmospheric carbon dioxide levels and climate change. And now NASA help in calculating the forest loss and also its health from far above the earth.

NASA research scientist Jon Ranson is working to improve new technologies for studying trees from above, so future Earth-observing missions can more accurately assess forest health.

When measured from aircraft and satellites, the wavelengths of light reflected by plants tell scientists about the amount of photosynthesis occurring, and therefore how much atmospheric carbon dioxide trees take up and store. The current standard for studying vegetation is called NDVI, or Normalized Differential Vegetation Index, which is the average of two broad portions of the infra red spectrum. NASA’s NDVI record goes back 40 years, providing a low-resolution but accurate picture of forest health.

Trees do a huge service for the planet, in terms of sequestering carbon dioxide, taking it out of the atmosphere and putting it into wood,” Ranson said, “but trees are very sensitive to our changing climate. We’re trying to see the changes going on in forest ecosystems. If you detect things early enough, you might be able to do something about it.”

While NDVI is good at assessing vegetation quantity and vigour broadly, Ranson said, breaking down infra red and visible light into many more wavelengths, a technology called hyper spectral imaging, can provide insight on plants’ water content, chlorophyll and even changes in health.  

“Vegetation has these broad spectral properties,” said Ian Adams, Earth Sciences Division Technologist at NASA’s Goddard Space Flight Centre. “With hyper spectral imaging, you get lots of different measurements at smaller, closer together frequencies. There is a lot more information we can pull out if we can get better spectral resolution.”

By dramatically increasing the number of frequencies available for researchers to study, Ranson’s work serves the priorities of the National Academies of Science’s most recent Earth Science decadal survey, which determines the field’s long-term priorities. The survey lists “surface topography and vegetation,” including forests, as a key area of study in need of more advanced technology.

 “Strategically for NASA, and more broadly for the remote sensing community, hyper spectral is one of the areas we see as the future,” Adams said.

To make use of hyper spectral imaging by future orbital missions, data analysis techniques are first proven closer to the ground.


Ranson’s team fitted a Sky fish drone (UAV) from partner institution Virginia Tech with a visible and infra red (VIS/IR) hyper spectral camera and lidar equipment. They flew the imaging equipment over forests near Blacksburg, VA, in a region called Mountain Lake. Comparing their UAV observations with actual CO2 levels recorded by sensors on a nearby National Ecological Observatory Network tower, Ranson’s team was able to refine calculations about how much carbon the forest removed from the atmosphere.

These comparisons allowed them to further refine techniques for interpreting the hyper spectral data. For instance, Plants stressed by too much sunlight may release pigments to shield their chloroplasts, a condition his sensors can detect. If plants get too much shade, they may grow leaves with larger surface-areas, which can cause the sensor to overestimate plant productivity. Ranson wants to add short-wave infra red sensors to better distinguish reflections from leaves and other parts of plants, eliminating another possible source of error.

Scientists and engineers at Goddard have been developing a mission concept called Concurrent Artificially intelligent Spectrometry and Adaptive Lidar System, or CASALS. If selected, CASALS would send a satellite with lidar and hyper spectral cameras into space. A constellation of such satellites could take the frequent measurements necessary to assess changes in forest productivity over time, using models perfected by Ranson’s UAV flights.



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