Photogrammetry is an image analysis that produces a 3D model of on object using a set of images taken from different positions. We tested this technique using a digital camera to produce a 3D model of 1m2 of Sahelian rangeland grass. In 2019 we made measurements on 3 squares of 1m2 (images capture and biomass measurement) in each of 10 days in the wet season and each month during the dry season. We analysed the images using PIX4D software. We extracted the volume and the colour indexes from the pix4D output. We used a random forest to predict the dry and fresh mass of the grass. The percentage of variance was 46.31% for the fresh mass and 40.46 % for the fresh mass. This tool could be used to monitor grass biomass during both wet and dry seasons and implemented in a grass observatory.