Greg Asner/Carnegie Institution for Science

The Sensor Revolution: Using LiDAR and Satellite Imagery to Map Drought

As California’s 2015 fire season raged, the sky was filled with planes and helicopters. Cal Fire maintains a fleet of more than 50 aircraft, including a converted 747 that can drop 24,000 gallons of flame retardant, while buzzing just 400 feet off the ground.

For 12 of those days, Cal Fire’s aerial bombardment was accompanied by a fire-fighter of a different kind. A platform called the Carnegie Airborne Observatory (CAO) — crewed by ecologists — conducted high-fidelity imaging spectroscopy in search of the state’s vanishing water.

Greg Asner, the scientist that helms the CAO, fears that California’s forests may be approaching a turning point. “We don’t know when the lack of rain will lead to runaway conditions where the forests are beyond repair,” Asner told the Los Angeles Times.

CAO scientist Robin Martin collects canopy foliage from California’s giant sequoias. After linking these ground data on canopy water to the spectra seen by CAO sensors, the plane can map drought stress over more than 100,000 hectares in a single day. Greg Asner/Carnegie Institution for Science.

The CAO’s sensors are among the best in the world for ecosystem monitoring. State-of-the art LiDAR (Light Detection and Ranging) peers into the physical structure of ecosystems, producing stunning 3D models. A short-wave infrared spectrometer — one of two carried by the Observatory — probes another dimension of ecosystems: their chemistry. By linking airborne data with information collected on the ground, CAO can map canopy water levels, a variable indicative of drought stress

The CAO crew has spent more than a decade bouncing from one biodiversity hotspot or ecological crisis to the next: Peruvian gold mines. Logging in Borneo. Landscape evolution on the slopes of Hawaiian volcanoes.

In California, Asner and his team encountered vast numbers of dead trees, with hotspots in the Sierra foothills and mountains surrounding LA. The proliferating snags are a sign that the drought has taken a toll.

Multi-dimensional data form Carnegie Airborne highlights drought stress among Giant Sequoias. Blue trees are getting water, but those shown in yellow, orange and red are increasingly drought-stressed. Greg Asner/Carnegie Institution for Science.

While Asner and his team have dramatically increased the scale of ecological monitoring, even aircraft that sample more than a hundred thousand hectares per day have limits. Carnegie Airborne is a one-of-a-kind instrument and crew, and they can only be above one jungle, mountain range or seashore at a time.

In a debut of its Ambassadors Program, Planet Labs has partnered with Asner to enhance CAO’s leading-edge work. By enabling access to Planet’s frequent coverage of the Earth’s surface, Asner’s surgical airborne data collections can be scaled up across both space and time.

Planet’s tools allow researchers like Asner to isolate changes to ecosystems on a day-to-day basis. Imagery here highlights dwindling water storage in California’s Trinity Reservoir. With such tools, Asner and his team can extend their surgical airborne data to vastly larger regions.

“The Planet Labs approach for ultra high frequency, high resolution monitoring is taking Earth science to a completely new level. For example, Planet imagery allows us to map rapid changes in California’s forest cover and health, which greatly improves our ecological models and forecasts,” Asner said.

The effort is long overdue. Amazingly, in a state with real-time, on-demand drivers and smorgasbord delivery services, keeping ecosystem monitoring and decision-making up to speed is a constant challenge.

“By combining our airborne science and Planet’s space-borne observations, we can vastly improve our scientific support for environmental conservation, management and decision-making.”

Learn more about Planet’s Ambassador program for researchers like Greg Asner.