Assessment of ALOS-2 PALSAR-2L-band and Sentinel-1 C-band SAR backscatter for discriminating between large-scale oil palm plantations and smallholdings on tropical peatlands

Abstract

Oil palm agriculture is rapidly expanding across the tropics, particularly on peatlands to meet increasing global demand for palm oil based products. Oil palm production systems can be divided into two broad categories of management system: large-scale monoculture plantations and smallholdings. Both categories are separated by large differences in environmental and social impacts. These oil palm production systems are often characterized by different agricultural practices and vegetation characteristics and therefore land cover. To date, there are no examples of radar remote sensing studies in oil palm production landscapes assessing differences between large-scale plantations and smallholdings. Here, we investigate whether these management systems have distinct radar signatures that can be identified through backscattering intensity using ALOS (Synthetic Aperture Radar) – PALSAR (Phased Array L-band Synthetic Aperture Radar) L-band and Sentinel-1 C-band Synthetic Aperture Radar (SAR). SAR has been shown to be superior to other remote sensing sensors in the tropics for monitoring oil palm expansion due to its all-weather capabilities. In this study we measured backscattered intensity of 196 plots planted with oil palm that were established on peatland in Peninsular Malaysia. Our results indicated that backscattered intensity was significantly influenced by the management systems. We found that canopy and soil moisture was greater in smallholdings compared to large-scale plantations. With the exception of HV polarization method, season had significant effect on backscattered intensity. Irrespective of management systems, canopy and soil moisture was greater in wet months compared to dry months. Our findings suggest that ALOS-2-PALSAR-2L-band and Sentinel-1 C-band have great potential to discriminate oil palm production landscapes managed under different management systems. Further investigation is needed to determine whether the current findings are consistent for oil palm in mineral soils.