Using Drone Imagery to Assess Impacts of the 2018 Carr Fire

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USGS WERC’s Dr. Karen Thorne and her research team are using drone imagery to understand how the 2018 Carr Fire affected ecosystems and cultural resources. The study, a collaboration with the National Park Service (NPS), focuses on Whiskeytown National Recreation Area in northern California. The drone images will help the WERC researchers identify changes in topography, cultural sites, debris flows, and vegetation recovery following the fire, and provide valuable data on fire impacts to the land managers at NPS.

Aerial view image of Whiskeytown National Recreation Area with marked locations of completed and proposed survey areas.

Aerial view image of Whiskeytown National Recreation Area with marked locations of completed and proposed drone survey areas. Survey areas are marked as priority areas because of the presence of dozer lines, debris flow potential, cultural value, or mines.

(Public domain.)

Understanding Wildfire Effects at Whiskeytown

The Carr Fire burned nearly 230,000 acres over 38 days in the summer of 2018, making it the seventh-largest wildfire in California history (as of spring 2019). The fire began in Whiskeytown National Recreation Area and spread east to nearby Redding, California. Large wildfires like the Carr Fire can have equally large effects on ecosystems and cultural resources. Post-fire impacts can be caused both by the fire itself and by erosion and debris flows during the winter rainy season, which are exacerbated by the loss of vegetation from the fire. USGS and NPS want to understand the impact of the fire at Whiskeytown National Recreation Area, with focus on 1) areas identified of concern to NPS for high potential for post-fire erosion and debris flow; 2) specific cultural resource features at risk of damage from post-fire erosion, 3) specific abandoned mines at risk to erosion, and 4) post-fire vegetation characteristics and recovery at affected areas.

 

Drone Surveys

Severe wildfires like the Carr Fire have impacts on big spatial scales that can be difficult to understand from on-the-ground field analyses alone. USGS WERC scientists are using drones to get a large picture of the fire effects. In October 2018, Dr. Karen Thorne’s research team, including drone pilot Chase Freeman, conducted drone surveys of 15 sites at Whiskeytown National Recreation Area, covering 2700 acres over 36 hours of flight time. Cameras and sensors mounted on the drones took images for topography and vegetation characteristics of the recently burned land below. The researchers will repeat their surveys in spring and summer 2019 and 2020 to assess recovery and effects of the winter rains. Watch drone video footage of the Carr Fire burn area here.

Woman kneeling in a clearing, holding a drone, man stands a few feet to her right holding a screen and drone piloting equipment.

USGS ecologist and drone pilot Chase Freeman and technician Kylie Mosher prepare for a drone flight at Whiskeytown National Recreation Area.

(Public domain.)

Orthoimagery

The images being used are orthoimages, which combine high-resolution aerial photos with the features of a map. Orthoimages correct photos to account for topography, lens distortion, and camera tilt, producing an extremely accurate picture of the Earth’s surface. The researchers can use orthoimages to measure elevation, area burned, and the amount or type of vegetation in a particular area. By comparing images taken at different times, they can assess changes over time, such as how vegetation is regrowing or changes in elevation caused by erosion.

Orthoimage (3D-appearing image) of a valley, with a road cutting through the center of two hillsides with burned vegetation.

Orthoimage of a burned valley at Whiskeytown National Recreation Area. Orthoimages combine aerial photos with elevation data to create an accurate, 3D image of the Earth.

(Public domain.)

On the Ground

WERC scientists will validate and supplement the data collected from drone imagery with data from images collected on the ground. In November 2018, 12 game cameras were set up in watersheds identified by NPS to capture possible debris flow events. Along with the game cameras, the researchers established photo point locations to ground truth areas surveyed with drones and provide a finer scale analysis of changes through time.

A series of 4 images illustrating orthoimagery, with colors representing elevation and vegetation

A series of 4 images illustrating how orthoimagery can be used to analyze elevation changes and vegetation regrowth.. 1) 3D image of valley with road running through it, 2) close up 3D image showing vegetation and structures, 3) Image 1 with color gradient to represent elevation, 4) Image 2 with color used to highlight the presence of vegetation.

(Public domain.)

 

Products and Results

The drone study will allow researchers to:

  • Measure percent area burned for each study site

    Determine extent of erosion and volume of displaced earth due to rains and debris flows

  • Monitor vegetation regrowth and recovery

  • Produce Digital Surface Models and Vegetation Index that may be used for future analyses

 

Technical Details

Drone Platform: 3DR solo platform

Cameras and Sensors:

  • Ricoh GR II (high resolution (3.42 cm horizontal resolution @ 120m above ground level [AGL]) ortho imagery, 12.7 hours over 61 flights)
  • Micasense RedEdge multispectral sensor (8 cm horizontal resolution @ 120m AGL) (23.3 hours over 119 flights)

Image Products:

  • High resolution 3 band orthoimagery layer
  • Digital surface model