A new, low-cost ground-based NDVI sensor for manual and automated crop monitoring

Abstract

Ground-based normalized difference vegetation index (NDVI) sensors are vital for accurate, localized crop condition and growth assessments, but their high cost and labor-intensive operation limit accessibility. To close this gap, this study presents a low-cost NDVI sensor priced under €250, offering an affordable yet high-accuracy crop monitoring tool. The device has dual functionality, operating in both manual (handheld) and automatic (standalone) modes, enabling continuous crop monitoring with higher temporal resolution and reduced labor costs. This study also identified and corrected the underestimation of measurements at higher NDVI values through sensor calibration. Subsequent field validation proved the accuracy of the low-cost sensor, showing a generally good overall agreement with results obtained with the reference sensor (r² = 0.99) after applying the derived calibration function. Extended field trials in Benin and the Philippines demonstrated the reliability of the device to adequately monitor treatment differences in various crop development and biomass accumulation. Further customization into automatic mode enabled continuous, high-frequency NDVI measurements, showing its ability to monitor crop phenological changes, such as senescence, in an additional field testing in Germany. Overall, this study demonstrates that the developed NDVI sensor device, made from affordable, off-the-shelf components, can be adapted into a scientifically usable NDVI sensor that is accurate, reliable, and cost-effective. It offers a viable alternative to expensive in-field monitoring systems and promotes accessibility to ground-based crop monitoring solutions, especially for research in the Global South.