ASABE Technical Library - Abstract

Abstract.TheNormalized Difference Vegetation Index (NDVI) is one of important parameters to detect the growth of plant using spectrometer. In order to measure the NDVI efficiently and reduce the influence by the changes of sunlight, a new type NDVI measurement device based on active light source wasdeveloped. The deviceincludedfour modules: optical module, sensor module, signal processing module and power module. The optical module was designed with laser source and optical fiber. The laser diodes provided the laser light at red (650nm) and near-infrared (780nm) band. In sensor module, two kinds of photodiodes were applied and the sensor conditioning circuits was designed. In the software, a new method based on laser pulse modulationanddemodulation was presented. The MCU and laser driving circuits generateda 1Hz rectangular pulse wave. When the optical sensor detected the light signal reflected by the green plant, the signal processing module could demodulate the rectangular pulse wave by Fourier transformfrom the background light. By this way, the NDVI value of detecting plant could be calculated by acquired signals. Experiments have been done between the instrument and Shimadzu spectrophotometer. Use the instrument and the spectrophotometer to measure the corn leaf (75 samples) separately. The result is showed thatin 650nm, the R²=0.683 between the two devices and the relative error is ±5%. In 780nm, the R²=0.507 between the two devices, and the relative error is ±5%.