研究目的
To test the performance of the Beer-Lambert law to retrieve crop water content from spectra with a contiguous spectral coverage around 970 nm and perform validation separately for leaves, stalks, and fruits by means of the two very different crop types: corn and winter wheat.
研究成果
The proposed PWR model based on the inversion of the Beer-Lambert law effectively succeeds in the determination of wheat EWTleaf and EWTear with consistent results over a three-year dataset (R2 = 0.72; rRMSE = 26%). For corn EWTleaf was estimated from two-year data with even better results (R2 = 0.86; rRMSE = 23%). Since the detectability of canopy water content fractions seems to be largely dependent on the crop type, its canopy structure, depth, and growth stage, it is recommended to collect EWTleaf, EWTstalk and EWTfruit data and corresponding reflectance for different crop types over all phenological stages along the growing cycle.
研究不足
The PWR model considers the 970 nm absorption to be caused solely by liquid water. In addition, since reflected radiance in the 930–1060 nm range is also affected by atmospheric water vapor, the process of accurate atmospheric correction is a critical prerequisite when the PWR model is applied to future available hyperspectral TOC reflectance acquired from space.
1：Experimental Design and Method Selection:
The Beer-Lambert law was applied to inversely determine water content information in the 930 to 1060 nm range of canopy reflectance from measured winter wheat and corn spectra. The spectral model was calibrated using a look-up-table (LUT) of 50,000 PROSPECT spectra.
2：Sample Selection and Data Sources:
Measured winter wheat and corn spectra collected in 2015, 2017, and
3：Internal model validation was performed using two leaf optical properties datasets (LOPEX93 and ANGERS). List of Experimental Equipment and Materials:
20 Analytical Spectral Devices Inc. (ASD, Boulder, CO, USA) FieldSpec3 Jr. spectroradiometer with an effective spectral resolution of 3 nm in the VIS (≤700 nm) and 10 nm in the NIR and SWIR (≤2500 nm).
4：Experimental Procedures and Operational Workflow:
Five nadir measurements were conducted per ESU at a height of 25 cm above the canopy, the same height at which the white reference panel (OptoPolymer, Munich, Germany) could be fully observed with the instruments field of view of 25°.
5：5°. Data Analysis Methods:
5. Data Analysis Methods: The Beer-Lambert law was rearranged to iteratively optimize the thickness of the optically active water layer so that an objective function—the sum of absolute residuals between the modelled reflectance and the linear connection between the descending and ascending vertices of the 970 nm absorption—is minimal.
独家科研数据包，助您复现前沿成果，加速创新突破
获取完整内容
