A framework for national-scale predictions of forage dry mass in Senegal: UAVs an intermediate step between field measurements and Sentinel-2 images

Nungi-Pambu Maïalicah, Lo Adama, Fassinou Cofélas, Tageson Torbern, Fensholt Rasmus, Diouf Abdoul Aziz, Menassol Jean-Baptiste, Assouma Mohamed Habibou, Touré Ibra, Taugourdeau Simon. 2023. A framework for national-scale predictions of forage dry mass in Senegal: UAVs an intermediate step between field measurements and Sentinel-2 images. International Journal of Remote Sensing, 20 p.

Liste HCERES des revues (en SHS) : oui

Thème(s) HCERES des revues (en SHS) : Géographie-Aménagement-Urbanisme-Architecture

Résumé : Monitoring available feed for livestock is a key factor for developing pastoralism in the Sahel, and satellite images has proven useful in monitoring dry mass on large spatial scales. This approach requires field measurements of dry mass (herbaceous and woody plants) to calibrate such models based on Earth observation data. However, the need for representative field measurements can be a challenge when considering the low spatial resolution of available satellite data. Unmanned Aerial Vehicles (UAV) can produce very high-resolution images, so we tested UAVs as an intermediate step between field measurements and satellite images, to bridge the difference in spatial scale. We used 43 orthomosaics from a red-green-blue (RGB) UAV sensor in combination with field measurements of herbaceous and woody dry biomass at sites located primarily in the northern/central and southernmost parts of Senegal. We developed a dry mass model trained with filed observed measurements to be applied on the UAV orthomosaics. The dry mass information obtained from these UAV maps was subsequently related to vegetation indices derived from Sentinel-2 data to produce a national-scale 10 m spatial resolution baseline map of herbaceous and woody dry mass for Senegal in 2020. We obtained a high correlation between dry mass derived from UAV and Sentinel-2 indices (R² = 0.91), suggesting a robust basis for national-scale mapping. Lastly, our map was compared with a state-of-the-art annual reference map based on satellite remote sensing. This comparison showed a difference of 21 million tons of dry mass at national level. We concluded that bridging the spatial gap between field and satellite observations using spatially representative UAV data collection is a cost-effective approach for accurate mapping of dry mass at national level using freely available Sentinel-2 satellite data.

Mots-clés Agrovoc : télédétection, plante herbacée, savane, plante ligneuse, mesure (activité), biomasse, séchage, pastoralisme, cartographie, drone, parcours, forêt tropicale

Mots-clés géographiques Agrovoc : Sénégal, Sahel

Mots-clés libres : Uav, Biomass, National map, Sahel

Classification Agris : F01 - Culture des plantes
U30 - Méthodes de recherche
L01 - Élevage - Considérations générales

Champ stratégique Cirad : CTS 2 (2019-) - Transitions agroécologiques

Agences de financement européennes : European Commission

Agences de financement hors UE : Agence Nationale de la Recherche, Swedish National Space Agency

Projets sur financement : (FRA) Institut Convergences en Agriculture Numérique, (EU) Sequestration and Green-house Gas Emissions in (Agro) Sylvopastoral Ecosystems in the Sahelian CILSS States

Auteurs et affiliations

• Nungi-Pambu Maïalicah, Montpellier SupAgro (FRA)
• Lo Adama, CSE [Centre de suivi écologique] (SEN)
• Fassinou Cofélas, ISRA (SEN)
• Tageson Torbern, Lund University (SWE)
• Fensholt Rasmus, UCPH (DNK)
• Diouf Abdoul Aziz, CSE [Centre de suivi écologique] (SEN)
• Menassol Jean-Baptiste, Montpellier SupAgro (FRA)
• Assouma Mohamed Habibou, CIRAD-ES-UMR SELMET (BFA) ORCID: 0000-0002-8163-0340
• Touré Ibra, CIRAD-ES-UMR SELMET (FRA) ORCID: 0000-0002-7046-2986
• Taugourdeau Simon, CIRAD-ES-UMR SELMET (FRA) ORCID: 0000-0001-6561-3228 - auteur correspondant

Source : Cirad-Agritrop (https://agritrop.cirad.fr/607601/)

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