Usability of Sentinel-1 C-band VV and VH SAR data for the detection of flooded oil palm

Abstract

Flooding in oil palm plantations in Southeast Asia is a common problem. The oil palm’s habitable range is restricted to lowland equatorial areas, and the high rainfall and degraded landscapes associated with oil palm cultivation leaves oil palm prone to flooding.
Flooding diminishes yields in mature palms, increases mortality in young palms, and disrupts operational processes. This reduces the economic viability of plantations, which may lead to their abandonment. Oil palm expansion is associated with environmental degradation and high carbon emissions; when expansion occurs in flood-prone areas a high environmental cost is paid for little or no economic gain. Climate change is expected to bring about more variable and extreme rainfall events in Southeast Asia, therefore the problem of inundation in oil palm plantations is set to worsen.
Improving our knowledge of flood events in plantations will inform decision-makers in the oil palm industry and policy-makers in government of the sensitivity of certain landscapes to oil palm cultivation so that the expansion of oil palm in flood-prone areas is avoided. Existing under-productive stands may be taken out of production and rehabilitated to restore the ecosystem, social, and economic functions of the peatland and forest landscapes that they replaced.
Few studies have applied remote sensing technology to the problem of inundation in oil palm plantations. To the best of the author’s knowledge, this is the first study to report the backscatter characteristics of flooded oil palm.
This study tested the ability of Sentinel-1 C-band VV and VH data to detect the presence/absence of flooding in oil palm stands of all growth stages in a study area in Jambi Province, Indonesia. Smallholdings were the predominant production system although industrial holdings were also present. Classes were defined to represent the different growth stages of oil palm in flooded and non-flooded conditions, and the backscatter characteristics and separability of the classes were determined.
C-band successfully detected the presence of flooding in very young oil palm, but not in older oil palm. C-band’s short wavelength and limited canopy penetration ability meant the signal saturated early and did not generate the double bounce effect that is characteristic of flooded forests. New SAR data (L-band and P-band) coming online in 2024 provides exciting opportunities for future research as the longer wavelengths are expected to achieve superior canopy penetration than C-band and, in the case of P-band, will permit the detection of flooding in all growth stages of oil palm.

Popular Abstract

Oil palm plantations are prone to flooding. Oil palm is grown in low-lying tropical areas with high rainfall, and the degraded landscapes that are associated with oil palm cultivation flood more readily during high rainfall events than the peatland and forest landscapes that they replaced.
Flooding reduces yields in mature palms, increases mortality in young palms, and disrupts operational processes by inhibiting access to the plantation. This reduces the economic viability of the plantations and can lead to their abandonment. As oil palm expansion is associated with environmental degradation and high carbon emissions, when plantations become unviable a high environmental price is paid for little or no economic gain.
Improving our knowledge of flood events in oil palm plantations raises awareness of the unsuitability of certain landscapes for oil palm cultivation so that oil palm expansion in flood-prone areas is avoided. In addition, existing stands of under-productive oil palm can be taken out of production and rehabilitated to restore the ecological, social, and economic functions of the landscape.
This study attempted to detect flooding in an oil palm environment in Jambi Province, Indonesia, using synthetic aperture radar (SAR) from the European Space Agency’s Sentinel-1 satellite. It uses a relatively short wavelength of microwave energy (C-band) to transmit a signal to objects on the earth’s surface, and those objects generate a return signal, known as backscatter, that is received by the sensor. SAR is a valuable tool in the detection of flooded vegetation because it can “see through” cloud cover and vegetation canopies to detect water underneath the canopy.
As no studies have reported the backscatter characteristics of flooded oil palm, this study analysed the backscatter characteristics of all growth stages of oil palm in flooded and non-flooded conditions, and analysed whether a sufficient distinction exists between the flooded and non-flooded states of the different growth stages to successfully identify the presence of flooding in oil palm stands.
Sentinel-1 C-band successfully identified flooding in very young oil palm but not in older oil palm. The short wavelength of the C-band signal meant the signal interacted with the top of the tree crowns and was unable to penetrate the canopy to detect standing water underneath. A new source of SAR data (long-wavelength P-band) will become available in 2024, which is expected to be highly effective at penetrating the oil palm canopy to detect flooding in all growth stages of oil palm, providing exciting opportunities for future research.

• author: Sienaert, Sarah Lee
• supervisor: Iris van Duren; David Tenenbaum
• organization: Dept of Physical Geography and Ecosystem Science
• course: GISM01 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Geography, GIS, Sentinel-1, SAR, C-band, VV, VH, Oil Palm, Flood
• publication/series: Master Thesis in Geographical Information Science
• report number: 162
• language: English
• id: 9128246
• date added to LUP: 2023-06-21 09:29:41
• date last changed: 2023-06-21 09:29:41