COMPARING A SINGLE-SENSOR CAMERA WITH A MULTISENSOR CAMERA FOR MONITORING COFFEE CROP USING UNMANNED AERIAL VEHICLES

ABSTRACT There exist two options for digital cameras that can capture the near-infrared (NIR) band. Conventional red–green–blue (RGB, visible bands) cameras with a single sensor provide NIR band visibility based on the removal of the internal NIR-blocking filter. Alternatively, multisensor cameras exist that have a specific sensor for each band. The modified RGB cameras are of a lower price. In this context, the objective of this study was to compare the performance of a modified RGB camera with that of a multisensor camera for obtaining the normalized difference vegetation index (NDVI) in an area with coffee cultivations. A multispectral camera with five sensors and another camera with only one sensor were used. The NDVI of the coffee field was also measured using the GreenSeeker handheld NDVI sensor manufactured by Trimble. The images were calibrated radiometrically based on the targets in shades of gray made of napa, and the NDVI was calculated after image calibration. The calibration curves showed a high coefficient of determination. The NDVI value obtained with the calibrated images from the cameras showed a significant correlation with the values obtained by the GreenSeeker NDVI sensor, making it possible to obtain the variability pattern of the vegetation index. However, the NDVI obtained using the multisensor camera was closer to the NDVI obtained by the GreenSeeker NDVI sensor.

摘 要：具备近红外（near-infrared, NIR）波段拍摄能力的数码相机主要有两种实现方案。传统单传感器红-绿-蓝（RGB，可见光波段）相机可通过移除内置近红外截止滤镜，实现近红外波段成像。另一种方案为多传感器相机，为每个波段配备专属独立传感器。改装后的RGB相机成本更为低廉。本研究旨在对比改装型RGB相机与多传感器相机，在咖啡种植区域获取归一化差分植被指数（normalized difference vegetation index, NDVI）时的性能表现。实验分别采用一台五传感器多光谱相机与一台单传感器相机，并借助天宝（Trimble）公司生产的GreenSeeker手持式NDVI传感器，对咖啡田的NDVI进行实地测量。研究以纳帕材质制作的灰度靶标为基准对图像开展辐射定标，待图像定标完成后计算得到NDVI值。定标曲线的决定系数较高。经校准后的相机图像所获取的NDVI值，与GreenSeeker NDVI传感器测得的结果存在显著相关性，可据此获取植被指数的空间变异格局。不过，多传感器相机获取的NDVI值更贴近GreenSeeker NDVI传感器的测量结果。