Diouf, Abdoul Aziz; Brandt, Martin; Verger, Aleixandre; El Jarroudi, Moussa; Djaby, Bakary; Fensholt, Rasmus; Ndione, Jacques Andre; Tychon, Bernard (2015). Fodder Biomass Monitoring in Sahelian Rangelands Using Phenological Metrics from FAPAR Time Series. REMOTE SENSING, 7(7), 9122-9148.

Abstract
Timely monitoring of plant biomass is critical for the management of forage resources in Sahelian rangelands. The estimation of annual biomass production in the Sahel is based on a simple relationship between satellite annual Normalized Difference Vegetation Index (NDVI) and in situ biomass data. This study proposes a new methodology using multi-linear models between phenological metrics from the SPOT-VEGETATION time series of Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) and in situ biomass. A model with three variables-large seasonal integral (LINTG), length of growing season, and end of season decreasing rate-performed best (MAE = 605 kg center dot DM/ha; R-2 = 0.68) across Sahelian ecosystems in Senegal (data for the period 1999-2013). A model with annual maximum (PEAK) and start date of season showed similar performances (MAE = 625 kg center dot DM/ha; R-2 = 0.64), allowing a timely estimation of forage availability. The subdivision of the study area in ecoregions increased overall accuracy (MAE = 489.21 kg center dot DM/ha; R-2 = 0.77), indicating that a relation between metrics and ecosystem properties exists. LINTG was the main explanatory variable for woody rangelands with high leaf biomass, whereas for areas dominated by herbaceous vegetation, it was the PEAK metric. The proposed approach outperformed the established biomass NDVI-based product (MAE = 818 kg center dot DM/ha and R-2 = 0.51) and should improve the operational monitoring of forage resources in Sahelian rangelands.

DOI:
10.3390/rs70709122

ISSN:
2072-4292