Measurement of Forest Above-Ground Biomass Using Active and Passive Remote Sensing at Large (Subnational to Global) Scales

Abstract

Within the global forest area, a diverse range of forest types exist with each supporting varying amounts of biomass and allocations to different plant components. At country to continental scales, remote sensing techniques have been progressively developed to quantify the above-ground biomass (AGB) of these forests, with these based on optical, radar, and/or light detection and ranging (LiDAR) (airborne and spaceborne) data. However, none have been found to be globally applicable at high (≤30 m) resolution, largely because of different forest structures (e.g., heights, covers, allocations of AGB) and varying environmental conditions (e.g., frozen, inundated). For this reason, techniques have varied between the major forest biomes. However, when combined, these estimates provide some insight into the distribution of AGB at country to global levels with associated levels of uncertainty. Comparisons of data and derived products have, in some cases, also contributed to our understanding of changes in carbon stocks across large areas. Further improvements in estimates are anticipated with the launch of new spaceborne LiDAR and SAR that have been specifically designed for better retrieval of forest structure and AGB.

Terrestrial Laser Scanning for Plot-Scale Forest Measurement

“…It is anticipated that a major driver for large-scale plot acquisition campaigns using TLS will be the calibration and validation of these satellite-based sensors for large-area aboveground biomass mapping [82]. Existing plot inventory data will not be sufficient, since it has been shown that a major source of difference between pan-tropical biomass maps is the result of inadequate ground data and allometrics for spatial extrapolation of satellite measurements [83].…”

Remote Sensing Concepts and Their Applicability in REDD+ Monitoring

“…Steininger [31], for example, found the canopy reflectance-biomass relationship to saturate at around 150 Mg/ha, while [37] reported that the above-ground biomass, below-ground biomass and necromass estimates for the large geographical expanse of the Brazilian Amazon could vary from minimum estimates of 78 billion Mg up to a maximum of 186 billion Mg. Another approach for estimating biomass by remote sensing is based on canopy density [38,39], as presented on tree cover percentage maps. The SAR-based technologies are rather sensitive to environmental conditions on a per scene basis [40] and have many challenges in worldwide mapping campaigns. Topographic reliefs, precise viewing angles and wet conditions are difficult to control in large area SAR data mosaic processing.…”

“…TerraSAR) and processing techniques have increased the expectations towards a feasible SAR mapping concept [40]. Saatchi et al [44] have demonstrated the high sensitivity of P-and L-band airborne SAR observations to above-ground biomass (AGB) <300 Mg/ ha on a one-hectare scale.…”

“…[10]. The spaceborne sensors needed to use LiDAR approaches for large-scale wall-to-wall mapping and monitoring efforts will not be available before the end of this decade [40].…”

“…[8][9][10]. Many radar techniques have been tested for global mapping over the last few decades (see [40]), but still many organisation rely on optical remote sensing, which can indirectly indicate the amount of biomass present when Landsat ETM type of data is used from the right season [11••].…”