Flood occurrence mapping of the middle Mahakam lowland area using satellite radar

Abstract

Abstract. Floodplain lakes and peatlands in the middle Mahakam lowland area are considered as ecologically important wetland in East Kalimantan, Indonesia. However, due to a lack of data, the hydrological functioning of the region is still poorly understood. Among remote sensing techniques that can increase data availability, radar is well-suitable for the identification, mapping, and measurement of tropical wetlands, for its cloud unimpeded sensing and night and day operation. Here we aim to extract flood extent and flood occurrence information from a series of radar images of the middle Mahakam lowland area. We explore the use of Phased Array L-band Synthetic Aperture Radar (PALSAR) imagery for observing flood inundation dynamics by incorporating field water level measurements. Water level measurements were carried out along the river, in lakes and in peatlands, using pressure transducers. For validation of the open water flood occurrence map, bathymetry measurements were carried out in the main lakes. A series of PALSAR images covering the middle and lower Mahakam area in the years 2007 through 2010 were collected. A fully inundated region can be easily recognized on radar images from a dark signature. Open water flood occurrence was mapped using a threshold value taken from radar backscatter of the permanently inundated river and lakes areas. Radar backscatter intensity analysis of the vegetated floodplain area revealed consistently high backscatter values, indicating flood inundation under forest canopy. We used those values as the threshold for flood occurrence mapping in the vegetated area.

Monitoring of an Indonesian Tropical Wetland by Machine Learning-Based Data Fusion of Passive and Active Microwave Sensors

“…However, even taking this effect into account, there still seems to be uncertainty associated with the approach discussed here. One of the potential error sources is the effect of inundated vegetation [14], which may create double-bounce backscatter or volume backscatter [18], thereby increasing the backscatter coefficient and resulting in the omission of water under the vegetation. As this effect seems to relate to complex factors (e.g., microwave incident angle, vegetation structure, density, and water levels), completely removing the effect is difficult when solely using the backscatter intensity.…”

“…On the other hand, many studies have reported the utility of horizontal transmitting and horizontal receiving (HH) polarization images of L-band SAR in wetland studies [12,13]. These studies include the mapping of the water extent or water depth in the Indonesian Mahakam lowlands [14], the Amazon River floodplain [15], and the Congo River in Africa [16], all of which have utilized phased array type L-band SAR (PALSAR) HH images. Manjusree et al [11] concluded that HH has the greatest potential for accurate water mapping.…”

Sharp bends associated with deep scours in a tropical river: The river Mahakam (East Kalimantan, Indonesia)

“…In the upstream reach several lakes and peat domes have formed. The lakes play an important role in regulating water and sediment discharge eventually issued to the delta [Storms et al, 2005;Sassi et al, 2011Sassi et al, , 2012Hidayat et al, 2012]. Small channels connecting the lakes to the river (termed tie channels by Rowland et al [2009]), regulate the exchange and, depending on the hydrograph of the river, carry water from the lakes into the river or vice versa, functioning as a discharge buffer [Hidayat et al, 2011].…”

A Review of Wetland Remote Sensing

“…Based on the comparison of notably different backscatter responses of the two large flood cases, they concluded that the backscatter signal is affected by many factors, such as the water level, vegetation density, and biomass, and shows complex changes. Hidayat et al [264] used PALSAR data to derive the flood extent and flood occurrence information in tropical wetlands. They incorporated water level measurements in lakes and peatlands in their study and revealed that the flood under forest canopy corresponds to high backscatter values.…”