Ground based photogrammetry to assess herbaceous biomass in Sahelian rangelands
Résumé
This study, conducted in pastureland in Senegal, aims to evaluate herbaceous biomass from ground-based photogrammetry. Photogrammetry is an image analysis that uses a set of images of an object to create a
3D model. In this study, the technique used the parallaxes obtained from images taken from different viewing points. We used the photogrammetry with a low cost RGB camera to predict herbaceous biomass
values. We made a set of images taken with different positions on 35 plots (each of 1 m2) of grass on pastureland. The images were processed using Pix4D software. Herbaceous volume was assessed using
a canopy height model. Red, Green and Blue reflectance were obtained from the orthomosaics. We calculated normalised difference index for each combination of colours. We measured fresh and dry
herbaceous biomass on the field on 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 was 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.