Measurement Method for Height-Independent Vegetation Indices Based on an Active Light Source.

Area of Science:

• Agricultural remote sensing
• Spectroscopy
• Plant physiology

Background:

• Traditional vegetation indices (VIs) can be affected by measurement height.
• Developing height-independent VIs is crucial for accurate crop monitoring.
• Active light sources offer controlled illumination for spectral measurements.

Purpose of the Study:

• To introduce a novel method for calculating height-independent vegetation indices (VIs).
• To design a spectrometer with an active light source to maintain a constant spectral ratio (C).
• To validate the method's effectiveness in discriminating nitrogen application levels in wheat fields.

Main Methods:

• Introduced a coefficient C (NIR/red spectral response ratio) for height-independent VIs.
• Designed a spectrometer with an active light source (730 and 810 nm central wavelengths).
• Tested Normalized Difference Vegetation Index (NDVI) and Ratio Vegetation Index (RVI) at various heights and nitrogen levels in wheat.

Main Results:

• The designed spectrometer maintained a constant coefficient C.
• Measured VIs showed significant ability to discriminate nitrogen application rate levels.
• VIs exhibited no significant correlation with measurement heights (65-105 cm).
• Low coefficients of variation (CV) for NDVI (3.85%) and RVI (2.93%) were observed.

Conclusions:

• The developed method successfully calculates height-independent vegetation indices.
• The spectrometer design ensures stability and accuracy in VI measurements.
• This approach is feasible and valid for agricultural applications, particularly for assessing crop nitrogen status.