## 7 Recent and Future Space-Borne Satellite Missions for Biomass Estimation
The Argentinean SAtelite Argentino de Observacion Con Microondas (SAOCOM) is an L-band SAR mission, aiming to improve global observations of forests and forest biomass change by developing a consistent time series archive. It is based on a constellation of two identical satellites SAOCOM-1A and SAOCOM-1B to provide dual-polarized Interferometric synthetic-aperture radar (InSAR) coverage with a combined revisit time of 8 days [190]. SAOCOM-1A was launched in October 2018 and SAOCOM-1B was planned to be launched in March 2020. However, its launch is delayed amid the  
Figure 7: Satellite missions for biomass mapping—recently launched or planned to be launched in the near future. COVID-19 pandemic. The mission is operated and managed by Argentina's Space Agency (ASA), Buenos Aires (BA) and the Comision Nacional de Actividades Espaciales (CONAE) [191]. The Phased Array L-band Synthetic Aperture Radar 3 (PALSAR-3) onboard Advanced Land Observing Satellite (ALOS)-4 is a JAXA's follow-on mission of PALSAR -2 onboard ALOS-2 [192]. It is planned to be launched in 2021 with a designed life of 5 years. The PALSAR-3 is designed for long-term monitoring with a 3 m spatial resolution, and it will follow the orbit of the PALSAR -2 with a 14-days temporal resolution [190, 193, 194]. Earlier, observations from the PALSAR-2 are extensively used to produce an annual global mosaic of SAR images at a 25 m spatial resolution, which has been used for developing numerous tropical/global biomass estimation maps [164]. The improved resolution of the PALSAR-3 will enhance the accuracy of carbon stock assessment studies in the coming decades. The Multi-footprint Observation LiDAR and Imager (MOLI) is another biomass and canopy height mapping mission to be launched in 2022 by the JAXA. The most prominent feature of the MOLI mission is to improve the canopy height information by correcting the terrain slope error in the calculation of the canopy height using the three footprint observations. In addition to the Level 1 Waveform and multispectral image (Red, Green, NIR) products, the MOLI will provide Level 2 products of Canopy Height and Forest Biomass. The most comprehensive product of the mission will be wall-to-wall canopy height and forest biomass maps [195]. Moreover, a combination of these datasets would open new research horizons of multi-sensor data synchronization and harmonization for refined biomass measurements. For example, multi-sensor SAR time series from PALSAR-2, RADARSAT-2 and Sentinel-1 provided effective maps of selective logging in the tropical forests of Brazilian Amazon [196]. Apart from SAR time series, researchers are integrating LiDAR data from GEDI with Landsat data, that will open a new era of hindcasting forest biomass using the historic and harmonized time series of the Landsat since the late 1970s. For example, an integrated approach has been developed by combining 1607 field plots with GLAS and PALSAR-2 to estimate ABG in China at a 30 m spatial resolution [197]. Further research on integrated models will enable advanced understanding and modelling of change dynamics in the tropical forests. Besides, scientists are anticipating integration of GEDI observations with an in-orbit and near-future SAR mission to generate high-quality biomass maps. The overlapping operational lives of these satellite missions for biomass monitoring are the biggest advantage that will stimulate integration and synchronization of biomass products, for developing science-based policies to manage the tropical and/or global forest resources [23].