The Impacts of Altitude on High-Resolution Multispectral Remote
Sensing for Hardwood Forest Species Delineation
Hardwood
forest inventory is a time consuming and expensive process, especially for
small forest owners (Butler et al., 2004). To expedite the process, satellite
remote sensing techniques have been used with limited success due to low
spatial resolution; unless expensive high-resolution satellite data is
purchased (Immitzer et al., 2012). Recent studies have shown that unmanned
aerial systems (UAS) can be a means to collect affordable high-resolution
forestry data that is as accurate as ground surveys in the Central
Hardwood Forest region of the United States (Hockridge, 2018). However, to
fully match the quality of ground surveys, UAS remote sensing methods will need
to successfully delineate species of trees in the imagery.
Our
project seeks to identify tree species through UAS multispectral imagery
utilizing the RedEdge Altum sensor integrated on the C-Astral Bramor ppX
airframe. The sensor’s access to the LWIR and NIR bands and aircraft’s low
altitude flight capability should allow for species specific spectral
signatures to be identifiable. The aircraft will be flown at forested sites
local to the West Lafayette, IN region at approximately 300 feet. It is unknown
how much flight altitude’s effect on spatial resolution will impact the
accuracy of the species delineation, so the Altum sensor will also be mounted
on a fixed wing manned airplane that will fly surveying transects at altitudes
of 2,000 and 3,000 feet so that data can be compared. The airborne datasets
will be processed into multi-band orthomosaics and then analyzed to determine
indices that can be used to identify tree species. From there, maps of tree
species will be generated for both manned and unmanned aircraft data, and the
accuracy associated with different spatial resolutions will be assessed when
compared with ground surveys of tree species. From this, an ideal altitude for
tree identification can be determined.
References
Butler, B.J., J.H. Hewes, B.J. Dickinson, et al.
2016. Family Forest Ownerships of the United States, 2013: Findings from the
USDA Forest Service’s National Woodland Owner Survey. Journal of Forestry
114: 638–647.
Hockridge E. (2018,
April). Exploring the use of unmanned aerial systems (UAS) for hardwood tree
inventory. Poster session presented at: Purdue Undergraduate Research
Conference. West Lafayette, IN.
Immitzer, M., Atzberger,
C., & Koukal, T. (2012). Tree Species Classification with Random Forest
Using Very High Spatial Resolution 8-Band WorldView-2 Satellite Data. Remote
Sensing, 4(9), 2661-2693. doi:10.3390/rs4092661
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