Specular, diffuse, and polarized light scattered by two wheat canopies

Vanderbilt, V. C.; Grant, Lois; Biehl, L. L.; Robinson, B. F.

doi:10.1364/ao.24.002408

Cited by 96 publications

(29 citation statements)

References 8 publications

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“…The main features in the near-and the mid-IR correspond to four major absorption peaks of water at c. 975, 1175, 1450 and 1930 nm. Secondly, a layer of wax on the upper side of the leaf may actually cause a high specular reflectance (Vanderbilt et al, 1985).…”

Section: mentioning

confidence: 99%

Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves

1999

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Leaf anatomical parameters such as leaf mass per area (LMA) and biochemical composition can be used as indicators of leaf photosynthetic capacity. The aims of this study are to evaluate the potential of reflectance spectroscopy of fresh leaves for assessing and predicting various parameters, anatomical (LMA and tissue thickness) and biochemical (nitrogen concentration). This paper describes results obtained with fresh leaves of holm oak (Quercus ilex), an evergreen oak that is widely distributed from mesic to xeric habitats in the Mediterranean. Fresh leaves (560) were collected over 3 yr at six different sites, from the top to the bottom of the canopy. The reflectance of each leaf was obtained within 1 h of sampling with an NIRSystems 6500 spectrophotometer over the range 400-2500 nm. LMA was determined for all samples ; biochemical and anatomical measurements were conducted over representative subsample populations of 92 and 87 leaves, respectively. Stepwise regression calibrations and partial least squares (PLS) calibrations were developed and compared with different spectral regions and mathematical treatments. Calibration equations had high coefficients of determination (r# ranging from 0.94 for nitrogen to 0.98 for LMA and tissue thickness). The PLS regressions gave better results than stepwise regressions for all parameters studied. Compared with regressions calculated on raw spectral data, calculations on second derivatives of spectra improved results in all cases. The use of scatter corrections also improved results. These results show that visible and near-infra red reflectance can be used for accurately predicting anatomical parameters and the nitrogen concentration of fresh holm oak leaves. The results support the suggestion that high spectral resolution imaging spectrometry can be a useful tool for assessing functional processes in forest ecosystems.

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Section: mentioning

confidence: 99%

Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves

1999

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“…Tn addition to the diminished shadowing in the nearinfrared, another likely reason for the difference is a much weaker specular reflection in the near-infrared in comparison with the visible. Measurements of the linear Downloaded by [McGill University Library] polarization of reflection were used to calculate the specular reflection from wheat canopies by Vanderbilt et al (1985). They found a decreasing specular portion of the .…”

Section: Canopy Reflectance Changes Due To Hazy Sky Conditionsmentioning

confidence: 99%

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

Deering

Eck

1987

International Journal of Remote Sensing

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A field experiment was conducted to determine whether changes in atmospheric aerosol optical depth would effect changes in bi-directional reflectance distributions of vegetation canopies. Measurements were made of the directionally reflected radiance distributions of two pasture grass canopies (same species, different growth forms) and one soya bean plant canopy under different sky irradiance distributions, which resulted from a variation in aerosol optical depth. The reflected radiance data were analysed in the solar principal plane in two narrow spectral bands, one visible (662 nm) and one infrared (826 nm). The observed changes in reflectance for both wavelengths from irradiance distribution variation is interpreted to be due largely to changes in the percentage of shadowed area viewed by the sensor for the incomplete canopies (pasture grass). For the complete coverage vegetation canopy (soya bean) studied, the effects of specular reflection and the increased diffuse irradiance penetration into the canopy are concluded to be primary physical mechanisms responsible for reflectance changes. Observed reflectivities were found to be lower on a hazy day (higher optical depth with a greater diffuse fraction) than on a clear day, with solar zenith angles at about 58°on both days, for full-coverage soya bean canopies. The reduced reflectance most likely results from a diminished specular reflection and a greater diffuse radiation penetration into the canopy, which effects an increased energy absorption at large solar zenith angles. The opposite was true for fractional coverage grass canopies at solar zenith angles of about 56°since the shadowing was less on the hazy day and, therefore, the soil/litter background was more fully illuminated. In the nearinfrared waveband the changes in reflectance are much less than in the visible and, therefore, normalized difference vegetation index values differ substantially under clear and hazy sky conditions for the same vegetation canopy conditions. Thus, the influence of atmospheric optical depth must be considered for accurate remote sensing and in situ data interpretation.

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“…Polarized reflectance of natural surfaces (such as the epicuticular wax coating the surfaces of leaves or the mineral facets of exposed rock) will be dominated by interactions at the surface, as bulk scattering within the material tends to be weakly polarized. Fresnel reflectance off surface facets is thus an appropriate basis for modeling the polarized surface reflectance (Vanderbilt et al, 1985;Grant, 1987;Vanderbilt and Grant, 1991;Breon et al, 1995;Nadal and Breon, 1999;Cairns, 2003;Elias et al, 2004;Waquet et al, 2009). Since Fresnel polarized reflectance depends mainly on geometry and the real component of the refractive index, it exhibits little spectral variance.…”

Section: The Radiative Transfer Modelmentioning

confidence: 99%

Combined retrievals of boreal forest fire aerosol properties with a polarimeter and lidar

et al. 2011

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Abstract. Absorbing aerosols play an important, but uncertain, role in the global climate. Much of this uncertainty is due to a lack of adequate aerosol measurements. While great strides have been made in observational capability in the previous years and decades, it has become increasingly apparent that this development must continue. Scanning polarimeters have been designed to help resolve this issue by making accurate, multi-spectral, multi-angle polarized observations. This work involves the use of the Research Scanning Polarimeter (RSP). The RSP was designed as the airborne prototype for the Aerosol Polarimetery Sensor (APS), which was due to be launched as part of the (ultimately failed) NASA Glory mission. Field observations with the RSP, however, have established that simultaneous retrievals of aerosol absorption and vertical distribution over bright land surfaces are quite uncertain. We test a merger of RSP and High Spectral Resolution Lidar (HSRL) data with observations of boreal forest fire smoke, collected during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). During ARCTAS, the RSP and HSRL instruments were mounted on the same aircraft, and validation data were provided by instruments on an aircraft flying a coordinated flight pattern. We found that the lidar data did indeed improve aerosol retrievals using an optimal estimation method, although not primarily because of the contraints imposed on the aerosol vertical distribution. The more useful piece of information from the HSRL was the total Correspondence to: K. Knobelspiesse (kirk.d.knobelspiesse@nasa.gov) column aerosol optical depth, which was used to select the initial value (optimization starting point) of the aerosol number concentration. When ground based sun photometer network climatologies of number concentration were used as an initial value, we found that roughly half of the retrievals had unrealistic sizes and imaginary indices, even though the retrieved spectral optical depths agreed within uncertainties to independent observations. The convergence to an unrealistic local minimum by the optimal estimator is related to the relatively low sensitivity to particles smaller than 0.1 (µm) at large optical thicknesses. Thus, optimization algorithms used for operational aerosol retrievals of the fine mode size distribution, when the total optical depth is large, will require initial values generated from table look-ups that exclude unrealistic size/complex index mixtures. External constraints from lidar on initial values used in the optimal estimation methods will also be valuable in reducing the likelihood of obtaining spurious retrievals.

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Specular, diffuse, and polarized light scattered by two wheat canopies

Cited by 96 publications

References 8 publications

Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves

Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

Combined retrievals of boreal forest fire aerosol properties with a polarimeter and lidar

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