Citation:

Iiames, J. AN EVALUATION OF TWO GROUND-BASED CROWN CLOSURE ESTIMATION TECHNIQUES COMPARED TO CROWN CLOSURE ESTIMATES DERIVED FROM HIGH RESOLUTION IMAGERY. Presented at American Society for Photogrametry and Remote Sensing (ASPRS), Baltimore, MD, March 7-11, 2005.

Impact/Purpose:

Our research objectives are to: (a) develop new methods using satellite remote sensor data for the rapid characterization of LC condition and change at regional to national scales; (b) evaluate the utility of the new NASA-EOS MODIS (Moderate Resolution Imaging Spectrometer) leaf area index (LAI) measurements for regional scale application with landscape process models (e.g., biogenic emissions and atmospheric deposition); (c) provide remote sensor derived measurement data to advance the development of the next generation of distributed landscape process-based models to provide a predictive modeling capability for important ecosystem processes (e.g., nutrients, sedimentation, pathogens, etc.); and (d) integrate in situ monitoring measurement networks with UAV and satellite based remote sensor data to provide a continuous environmental monitoring capability.

Description:

Two ground-based canopy closure estimation techniques, the Spherical Densitometer (SD) and the Vertical Tube (VT), were compared for the effect of deciduous understory on dominantlco-dominant crown closure estimates in even-aged loblolly (Pinus taeda) pine stands located in the Neuse River Basin in eastern North Carolina. Correlation of crown closure estimates for both techniques were compared to an unsupervised image crown closure classification (ICC) analysis generated from 1: 15840-scale panchromatic scanned (0.5 meter resolution) aerial photographs.

Crown closure measurements were taken prior to leaf cessation (leaf-on) and after leaf cessation (leaf -oft) between 1998 and 1999. Results indicate no significant differences occur when measuring dominantlco-dominant crown closure with the VT between leaf-on and 1eaf-offtime periods. However, significant differences were observed when comparing measurements made for that same period with the SD., The percent of the variation explained by the linear models was larger with the VT for both seasons (leaf-on and leaf-oft) than was for the SD when comparing regression results from both crown closure estimation techniques to the ICC analysis. The tighter fit to the linear regression model for the VT method was expected due to the smaller viewing angle (less than 1 degree) when compared to the 60 degree viewing angle of the SD. This larger viewing angle of the SD incorporated tree boles and the sides of tree crowns into the crown closure estimate thus causing a positive bias in the estimate (i.e., overestimation). In summary, dominant and codominant crown closure estimates ofloblol1y pine were consistent between leaf- on and leaf-offperiods for the VT, but not for the SD.

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