Image Acquisition Overview Resource Mapping -- Remote Sensing and GIS for Conservation

Multi-temporal Surveys and Biomass Estimates

Multi-temporal surveys to measure changes in the landscape and forest canopy. Duke University is studying the long-term effect of increased CO2 levels on trees in its Blackwood Forest site. Rings of towers release the gas into certain sections of the forest while researchers measure relative changes in tree growth. In collaboration with Duke University, Mt. Holyoke College, and the University of Massachusetts/Amherst, Resource Mapping is periodically flying and modeling the canopy to determine if subtle changes in spectral activity, tree height, and crown diameter can be measured from the air with our system and correlated to this growth.

Berkshire County Oblique


Each Duke Forest image set was automatically georeferenced in a bundle-adjusted block by extracting elevation data from the profiling laser altimeter to produce 3D control points on the surface of the canopy. This photogrammetric model generated a high resolution 50 cm DEM that was used to differentially rectify the imagery into an orthophoto mosaic. The resulting model was combined with the laser profiles to measure tree height and crown diameter in the existing forest stands.


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Duke Forest oblique with DEM


Laser profile Calculating tree height from the laser altimeter. The profiling laser fires 248 times per second and records alternating first and last returns from each pulse, modeling both the canopy surface from the first returns and the underlying topography whenever a last return can penetrate through to the ground.

Laser forest model

As a result, the approximate height of trees in a forest stand can be determined from a DEM of the canopy surface, even when a correspondingly accurate DEM of the ground is not available, by examining the underlying profile of laser data. Combined with DEM or Stereo Analyst measurements of crown diameter, these data produce a simple model of the forest stand that can be used to estimate growth, standing biomass, or board feet removed.


Crown detail -- Crown detail DEM
FACE site 2


50-cm DEM of a single ring site (lower left), with its corresponding 15 cm per pixel multispectral image (middle left). A combined 3D view of both (top left) shows how individual crowns can be identified and measured.

3D modeling of forest canopies to measure standing biomass or growth. At the Duke Blackwood site each tree crown is modeled in 3D, measuring changes in diameter and height, and monitoring either the growth or disappearance of individual specimens between multi-temporal coverages.




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Click on title page below to view Drs. Brown and Pearson's slide show

Click here to view this slideshow

This research follows the work of Dr. Sandra Brown, et al., who developed a methodology for determining regional carbon stocks in tropical and temperate forests using aerial measurements taken from randomly selected plots within a set of geographically distributed transects photographed with our camera system.

Every tree in each 28-m diameter plot was manually measured in Stereo Analyst, outlining the crown in a 3D shapefile and attaching two points to each polygon for maximum crown elevation and nearest ground elevation. Allometric regression equations were established between biomass carbon per individual tree and crown area/height, with enough plots measured to estimate sequestered carbon in the forests to a 95% confidence interval +/-10% of the mean. This aerial approach was compared to conventional field methods and determined to require approximately one-third the number of total person-hours needed to achieve the levels of precision necessary to qualify the tested forest as a carbon asset.

Rio Bravo Conservation and Management Area, Belize.
15 cm multispectral sampling grid with 1-kilometer spacing.

Rio Bravo
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