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.
Highlights
The Normalized Difference Vegetation Index (NDVI) is one of the most widely used indicators of photosynthetic activity in urban ecology [1]
NDVI is the difference between near infrared (NIR) and red (R) radiations emitted by vegetation divided by its sum
We have found that apertures of less than 6.1 markedly overexposed the images and above 14.3 it is impossible to capture enough infrared radiation and NDVI estimates were incorrect
Summary
The Normalized Difference Vegetation Index (NDVI) is one of the most widely used indicators of photosynthetic activity in urban ecology [1]. NDVI is the difference between near infrared (NIR) and red (R) radiations emitted by vegetation divided by its sum. This index, created by Rouse [2], is based on the spectral properties of chlorophylls a and b. Other indexes are more efficient as indicators [5], NDVI remains the most used index of photosynthetic activity in landscape ecology studies [6]. Different factors have contributed to the popularity of this index, such as easy determination, early historical origin, wide applicability in different ecological contexts and good discrimination between vegetation (from 0 to 1) and ground areas (from −1 to 0). The use of NDVI based on satellite images
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