Soil‐Dependent Spectral Response in a Developing Plant Canopy¹

Abstract

A major problem in the use of remote sensing techniques to assess plant biomass and condition over incomplete canopies concerns the soil background contribution toward measured spectral response. An understanding of this soil signal is essential to better relate canopy spectra with plant properties. An interactive, plant‐soil radiant flux model was developed to separate spectral variations associated with soil background from those attributable to vegetation. Field measured spectra taken over n developing cotton (Gossypium hirsutum L.) canopy with four soil types (Cumulic Cryoboroll, Typic Torrifluvent, Ustollic Haplargid, and Typic Calciorthid) alternately inserted underneath were decomposed into soil and vegetation spectra by utilizing the model in a principal component analysis. The soil component included all radiation penetrating the canopy and interacting with the underlying soil. The vegetation component represented all radiation reflected directly from the plant cover with no soil interaction. The soil component was found to resemble the spectral response of green vegetation due to the scattering and transmittance properties of the overlying plant canopy. Results show how the soil signal mixes into various vegetation indices inhibiting reliable vegetation discrimination. The potential improvements in vegetation analysis that can result from filtering soil background response from plant‐canopy spectra are also discussed.

Effect of impervious surface area and vegetation changes on mean surface temperature over Tshwane metropolis, Gauteng Province, South Africa

“…Also, spectral index such as NDVI suffer from a number of limitations that include value saturation and sensitivity to soil background among others according to Huete (1987).…”

A Review on Remote Sensing of Weeds in Agriculture

“…Furthermore, soil brightness influences were found to increase with increasing canopy cover up to 60%, suggesting that soil and plant spectra collectively interact in a nonadditive, nonlinear fashion to produce a composite spectral response. In a related experiment, Huete (1987) developed a plant-soil radiant flux model to separate composite spectra into soil reflected and vegetation reflected components. Depending on the percentage of canopy cover, the soil reflected component of the model exhibited similar properties to that of the surrounding vegetation, namely a low red reflectance and high NIR reflectance.…”

“…Depending on the percentage of canopy cover, the soil reflected component of the model exhibited similar properties to that of the surrounding vegetation, namely a low red reflectance and high NIR reflectance. Huete (1987) concluded that, in the case of significant canopy coverage, only a small portion of red radiation reaches the underlying soil surface due to intense absorption by chlorophyll. On the other hand, the plant leaves readily scatter and transmit NIR radiation deep into the canopy.…”

Field Measurements of Canopy Spectra for Biomass Assessment of Small-Grain Cereals

“…Light intensity, sun position, winds or nebulosity may interfere with the way in which the interaction between solar irradiation and crop is captured (Baret & Guyot, 1991;Huete 1987;Jackson 1983;Kollenkark et al, 1982). Green biomass may be overestimated when measurements are taken on cloudy days because the increased diffuse radiation improves the penetration of light into the canopy.…”