Assessment of ALOS PALSAR Polarimetric Measurements of Tropical Forest Structure and Biomass

Sassan Saatchi(1)

(1) Jet Propulsion Laboratory, 4800 Oak Grove Drive, pasadena, United States


Assessment of ALOS PALSAR Polarimetric Measurements of Tropical Forest Structure and Biomass

Measurement of the aboveground forest biomass stock and its changes through time are important for quantifying the global carbon cycle and defining the mechanisms of international carbon monitoring, accounting, and management. Radar remote sensing has been used extensively for measuring forest structure and biomass and is considered for spaceborne biomass inventory and monitoring system. In this paper, we report on a research performed as part of the ALOS principle investigators team to assess the ALOS PALSAR performance in measuring forest aboveground biomass in tropical ecosystems. We have chosen three study areas: La Selva Biological Station in Costa Rica, a forest-savanna boundary in Cameroon, and an old growth forest in Malaysia to examine the sensitivity of ALOS cross- and co-polarization measurements to forest biomass. An algorithm based on the polarimetric data has been developed to covert the radar backscatter measurements to biomass. The results show that the ALOS backscatter can measure the aboveground biomass with ± 10% precision up to 200 Mg/ha at 100 m resolution. The precision reduces gradually for higher biomass densities and improves at coarser spatial resolutions up to 500 m. The results also demonstrate the overall improved performance of HV polarization over HH because of the lower incidence angles (21-34 degrees) of radar measurements, allowing better penetration through dense forest canopy and sensitivity to the crown biomass. Comparison of ALOS data with JERS-1 measurements over the same study areas indicate that L-band sensors are capable of estimating changes of the biomass from disturbance and recovery processes. Given the relative calibration accuracy of ALOS PALSAR sensors, biomass changes from recovery may be measured with 5 Mg/ha/year on the annual time scale and resolutions of 500-1000 m. The study concludes that the L-band polarimetric or dual-mode spaceborne sensors are capable to provide biomass distribution and its changes over tropics with variable precisions suitable for global scale inventory, monitoring, management of carbon stock.


Symposium presentation


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