کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4459566 1621293 2011 16 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Airborne discrete-return LIDAR data in the estimation of vertical canopy cover, angular canopy closure and leaf area index
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات کامپیوتر در علوم زمین
پیش نمایش صفحه اول مقاله
Airborne discrete-return LIDAR data in the estimation of vertical canopy cover, angular canopy closure and leaf area index
چکیده انگلیسی

Remote sensing of forest canopy cover has been widely studied recently, but little attention has been paid to the quality of field validation data. Ecological literature has two different coverage metrics. Vertical canopy cover (VCC) is the vertical projection of tree crowns ignoring within-crown gaps. Angular canopy closure (ACC) is the proportion of covered sky at some angular range around the zenith, and can be measured with a field-of-view instrument, such as a camera. We compared field-measured VCC and ACC at 15° and 75° from the zenith to different LiDAR (Light Detection and Ranging) metrics, using several LiDAR data sets and comprehensive field data. The VCC was estimated to a high precision using a simple proportion of canopy points in first-return data. Confining to a maximum 15° scan zenith angle, the absolute root mean squared error (RMSE) was 3.7–7.0%, with an overestimation of 3.1–4.6%. We showed that grid-based methods are capable of reducing the inherent overestimation of VCC. The low scan angles and low power settings that are typically applied in topographic LiDARs are not suitable for ACC estimation as they measure in wrong geometry and cannot easily detect small within-crown gaps. However, ACC at 0–15° zenith angles could be estimated from LiDAR data with sufficient precision, using also the last returns (RMSE 8.1–11.3%, bias –6.1–+4.6%). The dependency of LiDAR metrics and ACC at 0–75° zenith angles was nonlinear and was modeled from laser pulse proportions with nonlinear regression with a best-case standard error of 4.1%. We also estimated leaf area index from the LiDAR metrics with linear regression with a standard error of 0.38. The results show that correlations between airborne laser metrics and different canopy field characteristics are very high if the field measurements are done with equivalent accuracy.

Research Highlights
► LiDARs produce reliable estimates of vertical canopy cover even without field data.
► Canopy closure (FOV = 150°) has a nonlinear relationship with LiDAR cover indices.
► Boreal forest LAI was best estimated using both first and last echoes with se = 0.38.
► Detailed field measurements are needed to match the inherent precision of LiDARs.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Remote Sensing of Environment - Volume 115, Issue 4, 15 April 2011, Pages 1065–1080
نویسندگان
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