Ground based photogrammetry to assess herbaceous biomass in Sahelian rangelands

This study conducted in a pastureland in Senegal aims to evaluate the herbaceous biomass from ground-based photogrammetry. Photogrammetry is an image analysis that use a set of images of an object to create a 3D model of this object. The technic used the parallaxes obtained from images taken from different points of views. We used the photogrammetry with a low cost RGB camera to predict herbaceous biomasses. We made a set of images taken with different positions of 1m² of grass on 35 plots of pastureland. The images were processed using Pix4D software. Herbaceous volume were assessed using canopy height model. Red, Green and Blue reflectance's were obtained from the orthomosaics.” We calculated normalized difference index for each combination of colours. We measured fresh and dry herbaceous biomass on the field the same day of image capturing. To test the reliability of our methods for assessing biomass, a PLS analysis between field measurements and variables obtained from the camera was performed. Around 60% of the variability of herbaceous biomass were explained by camera variables especially the volume from photogrammetry and the red reflectance. This work showed that a low cost camera could serve as useful tool for estimation of biomass.