Normalized Difference Vegetation Index Determination in Urban Areas by Full-Spectrum Photography

Abstract

(1) Background: The NDVI (Normalized Difference Vegetation Index) is a basic indicator of photosynthetic activity frequently employed in landscape and urban ecology. However, the high-resolution determination of NDVI requires an expensive multi-spectral digital camera. (2) Methods: In the present work, we are developing a general procedure that converts a Nikon D50 into a full-spectrum camera. We also use a red Hoya A25 filter to separate red (R) and infrared (NIR) radiations. Afterward, we calibrate the camera using the reflectance information of a Macbeth Color Checker. Additional procedures include a custom white balance (CWB), histogram equalization and exposure control. (3) Results: Our results indicate high correlations over 90% for R and NIR channels, which allow us to determine the NDVI with precision. Even it is possible to observe the NDVI differences between soil, water, rocks, algae, lichens, shrubs, grasses and trees in different environmental conditions and (4) Conclusions: The methodology described in this work allows a more economical analysis of high-resolution NDVI in landscape and urban areas adapting a modified camera to airborne or drone systems.