Using airborne lidar to predict Leaf Area Index in cottonwood trees and refine riparian water-use estimates

Airborne lidar point clouds of vegetation capture the 3-D distribution of its scattering elements, including leaves, branches, and ground features. Assessing the contribution from vegetation to the lidar point clouds requires an understanding of the physical interactions between the emitted laser pulses and their targets. Most of the current methods to estimate the gap probability ( P gap ) or leaf area index (LAI) from small-footprint airborne laser scan (ALS) point clouds rely on either point-number-based (PNB) or intensity-based (IB) approaches, with additional empirical correlations with field measurements. However, site-specific parameterizations can limit the application of certain methods to other landscapes. The universality evaluation of these methods requires a physically based radiative transfer model that accounts for various lidar instrument specifications and environmental conditions. We conducted an extensive study to compare these approaches for various 3-D forest scenes using a point-cloud simulator developed for the latest version of the discrete anisotropic radiative transfer (DART) model. We investigated a range of variables for possible lidar point intensity, including radiometric quantities derived from Gaussian Decomposition (GD), such as the peak amplitude, standard deviation, integral of Gaussian profiles, and reflectance. The results disclosed that the PNB methods fail to capture the exact P gap as footprint size increases. By contrast, we verified that physical methods using lidar point intensity defined by either the distance-weighted integral of Gaussian profiles or reflectance can estimate P gap and LAI with higher accuracy and reliability. Additionally, the removal of certain additional empirical correlation coefficients is feasible. Routine use of small-footprint point-cloud radiometric measures to estimate P gap and the LAI potentially confirms a departure from previous empirical studies, but this depends on additional parameters from lidar instrument vendors.

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Comparative Performances of Airborne LiDAR Height and Intensity Data for Leaf Area Index Estimation

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing ◽

10.1109/jstars.2017.2765890 ◽

2018 ◽

Vol 11 (1) ◽

pp. 300-310 ◽

Cited By ~ 9

Author(s):

Shezhou Luo ◽

Jing M. Chen ◽

Cheng Wang ◽

Alemu Gonsamo ◽

Xiaohuan Xi ◽

...

Keyword(s):

Leaf Area Index ◽

Leaf Area ◽

Airborne Lidar ◽

Intensity Data ◽

Area Index ◽

Index Estimation

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ACTUAL EVAPOTRANSPIRATION IN RELATION TO LEAF AREA

Hydrology Research ◽

10.2166/nh.1974.0012 ◽

1974 ◽

Vol 5 (3) ◽

pp. 173-182 ◽

Cited By ~ 29

Author(s):

K. J. KRISTENSEN

Keyword(s):

Water Balance ◽

Leaf Area Index ◽

Leaf Area ◽

Water Use ◽

Actual Evapotranspiration ◽

Potential Evaporation ◽

Area Index

The ratio of leaf area to ground area required for maintaining potential evaporation has been studied in a 4-year investigation, and the influence of leaf area index on the water use and the actual water balance is discussed.

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Defoliation, leaf area index, and the water use of four temperate pasture species under irrigated and dryland conditions

Australian Journal of Agricultural Research ◽

10.1071/ar9730783 ◽

1973 ◽

Vol 24 (6) ◽

pp. 783 ◽

Cited By ~ 14

Author(s):

GG Johns ◽

A Lazenby

Keyword(s):

Soil Moisture ◽

Leaf Area Index ◽

Leaf Area ◽

Water Use ◽

Leaf Senescence ◽

Late Spring ◽

Stomatal Control ◽

Area Index ◽

Autumn Period ◽

Dry Conditions

Measurements were made over a 12-month period of the water use and leaf area index (LAI) of both dryland and irrigated monoculture swards of four temperate pasture species under two defoliation regimes. All four species used similar quantities of water on the dryland plots despite large differences in their ability to grow under such conditions. Even though very dry conditions prevailed during part of the study, the dryland swards generally failed to exploit reserves of soil moisture below a depth of c. 120 cm. The water use of the irrigated swards was sensitive to the manipulation of LAI by defoliation, while in contrast, dryland water use was not. On the irrigated swards, at an LAI of 1, a 1% decrease in LAI was associated with a 1% decrease in water use. This sensitivity of water use decreased as LAI increased until, at an LAI of 3 and above, water use appeared to be insensitive to charges in LAI. During the late spring to early autumn period both irrigated and dryland water use were significantly related to LAI. In this period, those irrigated and dryland swards which had common values of LAI generally used similar quantities of water. This finding indicated that stomatal control was ineffective in reducing water use per unit of leaf area. The quantity of dead herbage present in the swards suggests that pronounced leaf senescence (and hence reduction of leaf area) may have been a consequence of ineffective stomatal control of transpiration.

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Morphological and Ecophysiological Indicators for Coriander Under Irrigation Depths and Nitrogen Levels

Journal of Agricultural Science ◽

10.5539/jas.v11n3p549 ◽

2019 ◽

Vol 11 (3) ◽

pp. 549

Author(s):

Fábio Teixeira Delazari ◽

Mariane Gonçalves Ferreira Copati ◽

Gustavo Henrique da Silva ◽

Ronaldo Silva Gomes ◽

Derly José Henriques da Silva ◽

...

Keyword(s):

Water Use Efficiency ◽

Leaf Area Index ◽

Leaf Area ◽

Water Use ◽

Area Index ◽

Nitrogen Levels ◽

High Soil Moisture ◽

Randomized Design ◽

Irrigation Depth ◽

Use Efficiency

Nitrogen fertilization and supplying of water are crucial factors for quality and quantity produces of coriander. The objective of this study was to evaluate morphological and ecophysiological characteristics for coriander under five irrigation depths and two doses of nitrogen (N). Experimental layout was completely randomized design in a split plot scheme with five replications. The irrigation depths (plot) was 25, 50, 75, 100 and 125% of crop evapotranspiration (ETc). The doses of N (subplot) corresponded to 35 and 70 kg ha-1. The cultivation of coriander (“Vedete”) was in a protected environment. The ratio between the aerial part and roots linearly increased with the increment of the irrigation depths and was highest under 70 kg ha-1 of nitrogen. The leaf area index linearly increased with the increment of the irrigation depths at both doses of N. The leaf index of chlorophyll “a” was highest under irrigation depths of 87 and 75% of ETc for 35 and 70 kg ha-1 of N, respectively. The leaf index of chlorophyll “b” decrease linearly with the increase of irrigation depths in both doses of N. The nitrogen use efficiency was maximized with high soil moisture conditions. The water use efficiency decreases linearly with increasing of irrigation depth. The best irrigation depth and nitrogen dose obtained in this study was 125% of ETc and 70 kg/ha. The leaf index of chlorophyll “a” and “b” are important indicators of hydric stress. The leaf index of chlorophyll “b” are negatively correlated with leaf area index. N supply increase the water use efficiency.

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