Synergetic of PALSAR-2 and Sentinel-1A SAR Polarimetry for Retrieving Aboveground Biomass in Dipterocarp Forest of Malaysia

Abstract

Space borne synthetic aperture radar (SAR) data have become one of the primary sources for aboveground biomass (AGB) estimation of forests. However, studies have indicated that limitations occur when a single sensor system is employed, especially in tropical forests. Hence, there is potential for improving estimates if two or more different sensor systems are used. Studies on integrating multiple sensor systems for estimation of AGB over Malaysia's tropical forests are scarce. This study investigated the use of PALSAR-2 L-band and Sentinel-1A C-band SAR polarizations to estimates the AGB over 5.25 million ha of the lowland, hill, and upper hill forests in Peninsular Malaysia. Polarized images, i.e., HH-HV from PALSAR-2 and VV-VH from Sentinel-1A have been utilized to produce several variables for predictions of the AGB. Simple linear and multiple linear regression analysis was performed to identify the best predictor. The study concluded that although limitations exist in the estimates, the combination of all polarizations from both PALSAR-2 and Sentiel-1A SAR data able to increase the accuracy and reduced the root means square error (RMSE) up to 14 Mg ha −1 compared to the estimation resulted from single polarization. A spatially distributed map of AGB reported the total AGB within the study area was about 1.82 trillion Mg of the year 2016.

Refugee Camp Monitoring and Environmental Change Assessment of Kutupalong, Bangladesh, Based on Radar Imagery of Sentinel-1 and ALOS-2

“…Consequently, the combination of both sensors allows for the ability to analyze backscatter mechanisms of both surfaces and covered structures. This complementary use was already successfully demonstrated for biomass estimation [68,69], deforestation monitoring [70,71], the mapping of flooded vegetation [72], and rice or palm oil cultivation [73,74]. However, it has to be denoted that, while Sentinel-1 data can be freely accessed within the Copernicus Programme, ALOS-2 data is commercially distributed by the Japan Aerospace Exploration Agency (JAXA).…”

Above-ground biomass estimates based on active and passive microwave sensor imagery in low-biomass savanna ecosystems

“…[38][39][40] One way to make use of the sensitivity of microwaves toward different scattering mechanisms is the utilization of sensors that employ different frequencies. 41 While combinations of short and long microwaves have been successfully applied for forest biomass estimates, 42,43 only Srivastava et al 44 and Herold et al 45 confirmed their potential for thin vegetation layers. Integrating passive radar for large-scale mapping is mostly limited to soil moisture 46 or surface temperature.…”

Time-series maps of aboveground biomass in dipterocarps forests of Malaysia from PALSAR and PALSAR-2 polarimetric data

“…Radar backscatter from the canopies of forests is normally different from other vegetation and agricultural crops. However, it is often confused with rubber plantations because the backscatter from this crop is identical to that from forest canopies on both HH and HV polarizations [11]. To overcome this problem, several image variables were produced from the original HH and HV polarizations.…”

“…Therefore, the applications of SAR data for forest cover identification, deforestation detection and forest monitoring have been explored extensively in recent years. To some extent, SAR data are also used for landuse classification, forest stratification, stand and canopy structure studies and other biophysical predictions, including AGB [11]. …”