Simulations of Seasonal and Latitudinal Variations in Leaf Inclination Angle Distribution: Implications for Remote Sensing

Abstract

The leaf inclination angle distribution (LAD) is an important characteristic of vegetation canopy structure affecting light interception within the canopy. However, LADs are difficult and time consuming to measure. To examine possible global patterns of LAD and their implications in remote sensing, a model was developed to predict leaf angles within canopies. Canopies were simulated using the SAIL radiative transfer model combined with a simple photosynthesis model. This model calculated leaf inclination angles for horizontal layers of leaves within the canopy by choosing the leaf inclination angle that maximized production over a day in each layer. LADs were calculated for five latitude bands for spring and summer solar declinations. Three distinct LAD types emerged: tropical, boreal, and an intermediate temperate distribution. In tropical LAD, the upper layers have a leaf angle around 35˚ with the lower layers having horizontal inclination angles. While the boreal LAD has vertical leaf inclination angles throughout the canopy. The latitude bands where each LAD type occurred changed with the seasons. The different LADs affected the fraction of absorbed photosynthetically active radiation (fAPAR) and Normalized Difference Vegetation Index (NDVI) with similar relationships between fAPAR and leaf area index (LAI), but different relationships between NDVI and LAI for the different LAD types. These differences resulted in significantly different relationships between NDVI and fAPAR for each LAD type. Since leaf inclination angles affect light interception, variations in LAD also affect the estimation of leaf area based on transmittance of light or lidar returns.

Efficiency of chlorophyll in gross primary productivity: A proof of concept and application in crops

“…The likely reason for this is the different canopy structures of these crops. Canopy structure/leaf angle distribution strongly affects fAPAR (e.g., Huemmrich, 2013). Unlike the maize canopy that is "open" to incident light (spherical), allowing a significant fraction of incident light to penetrate directly inside the canopy, the soybean canopy is more "closed" to light penetration (planophilic).…”

Effects of Crop Leaf Angle on LAI-Sensitive Narrow-Band Vegetation Indices Derived from Imaging Spectroscopy

“…Other studies have also shown the relationship between VIs and LAI to vary across vegetation types (canopy architecture) and the correlations to improve when analyzing the relationship between VIs and LAI for each vegetation type separately [48,49]. The leaf angle distribution, and thus MTA, affects the spectral properties of a canopy [50] to a degree that confuses LAI estimation algorithms based on simple VIs [50]. …”

Joint leaf chlorophyll content and leaf area index retrieval from Landsat data using a regularized model inversion system (REGFLEC)

“…θ l may exhibit greater intra-class variability dependent on phenological stage (Huemmrich, 2013;Ross, 1981) and information on θ l in space and time should ideally come from independent sources such as multi-angular satellite imagery. However, such information is currently not available.…”