Drones, Multispectral Imagery Offer New View of Calif.’s Giant Sequoias

As part of a joint project, Pix4D and Parrot recently used drones and multispectral technology to create a 3D normalized difference vegetation index (NDVI) point cloud of Whitaker’s Forest in Kings Canyon National Park, located in California’s Sierra Nevada mountains.

According to Pix4D, large air purifiers – like the giant sequoia trees in California – are key for the environment and are studied to measure how much carbon dioxide they capture. By using drones and multispectral imagery, the companies gave researchers access to information that was previously undisclosed.

Multispectral images capture what human eyes cannot: information from spectral bands beyond our sight range. Even though mapping and modeling from images is increasingly commonplace, multispectral imagery has been limited to 2D map creation, explains Pix4D.

Thus, without 3D imaging, critical pieces of information may be missing. Recognizing this, Pix4D says it developed a methodology to leverage multispectral images for 3D point cloud generation.

These 3D point clouds are produced by merging radiometric information acquired from different spectral bands into a single 3D point cloud geometry. After doing radiometric corrections to obtain reflectance, the observations of a particular point in each band are weighted separately. The technology takes into account visibility constraints in order to avoid obstructed points, and a representative reflectance value for each band is obtained.

As a result, each point in the point cloud contains accurate reflectance values for each observed band, says Pix4D.

Then, the companies combine the reflectance values depending on the vegetation index formula that wants to be applied.1-UtCTJoDuWPEtb7uFS54aig Drones, Multispectral Imagery Offer New View of Calif.'s Giant SequoiasNow, vegetation can be analyzed from the top-down and also in 3D – in turn, allowing foresters, agronomists and wide range of other environmental workers to recognize problems in whole structure of the plant. For example, forest conservation organizations can document the trees with both geometric and radiometric information much faster, rather than spend days to survey and CAD-draw individual trees, says Pix4D.

The end result is a 3D NDVI point cloud, where plants can be observed and scouted in their entirety – adding a new dimension to an industry previously constrained to information from plant canopies.

Considering there are several direct implications of this breakthrough, Pix4D says it excited to see what researchers, companies and industries will do with the data.

More information on the Parrot and Pix4D project can be found here.

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