Abstract
The present study evaluates the L band Vegetation Optical Depth (L-VOD) derived from the Soil Moisture and Ocean Salinity (SMOS) satellite to monitor Above Ground Biomass (AGB) at a global scale. Although SMOS L-VOD has been shown to be a good proxy for AGB in Africa and Tropics, little is known about this relationship at large scale. In this study, we further examine this relationship at a global scale using the latest AGB maps from Saatchi et al. and GlobBiomass computed using data acquired during the SMOS period. We show that at a global scale the L-VOD from SMOS is well-correlated with the AGB estimates from Saatchi et al. and GlobBiomass with the Pearson’s correlation coefficients (R) of 0.91 and 0.94 respectively. Although AGB estimates in Africa and the Tropics are well-captured by SMOS L-VOD (R > 0.9), the relationship is less straightforward for the dense forests over the northern latitudes (R = 0.32 and 0.69 with Saatchi et al. and GlobBiomass respectively). This paper gives strong evidence in support of the sensitivity of SMOS L-VOD to AGB estimates at a globale scale, providing an interesting alternative and complement to exisiting sensors for monitoring biomass evolution. These findings can further facilitate research on biomass now that SMOS is providing more than 10 years of data.
Highlights
Ground Biomass (AGB), while a key component of the Earth’s Surface, plays a major role in the carbon cycle [1,2,3] and is considered an essential climate variable
The two fits are similar except around L band Vegetation Optical Depth (L-Vegetation Optical Depth (VOD)) values of 0.9 where Saatchi Above Ground Biomass (AGB) are slightly lower than GlobBiomass AGB with values around 220 Mg/ha and 250 Mg/ha respectively
The agreement between L-VOD and the two AGB maps is similar as shown by the correlation coefficients R = 0.91 for Saatchi and R = 0.93 for GlobBiomass (Table 2)
Summary
Ground Biomass (AGB), while a key component of the Earth’s Surface, plays a major role in the carbon cycle [1,2,3] and is considered an essential climate variable. It is essential to monitor its evolution globally on a timely scale. In this respect, satellite remote sensing is an essential tool as it provides observations for the entire Earth surface with regular revisits depending on the characteristics of the sensor. Monitoring dense biomass is challenging and existing datasets sometimes differ on their AGB estimates [13] This is true for dense tropical forests where optical and radar measurements tend to saturate [10,14]. Future missions such as BIOMASS [15] and NASA-ISRO
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