Monitoring peat subsidence and carbon emission in Indonesia peatlands using InSAR time series

Abstract

The tropical peatland is one of the largest terrestrial carbon stores. However, deforestation, drainage, fires and conversion development have progressed all over this region. Through both legal and illegal logging, and conversion to agricultural use over the period of 1985∼2006, about 12.1 M ha of peatland was deforested and drained in Southeast Asia, of which 1.5 M ha were tropical peat swamp forests in Central Kalimantan, Indonesia [1]. Those progressions result in decomposition of the surface peat and losing carbon to the atmosphere as CO2, which results in reducing their strength as a current C store and their capacity for future soil C storage. However, related quantitative estimation of CO 2 emission is limited. Using field-based surveying to monitoring peatland surface height changes over the large areas typical of drained in the past, is challenging such that measurments are more likely to describe a small area and be only a snapshot in time. Upscaling and understanding the rate of change in surface height trough time may be overcome using remote sensing approaches. Our objective is to investigate the peat subsidence and carbon emission by Interferometry Synthetic Aperture Radar (InSAR) time series. Here we present data on the change in peatland surface height in Central Kalimantan, Indonesia, detected using the Interferometry Synthetic Aperture Radar (InSAR) Small BAseline Set (SBAS) approach[2, 3]. Using data from December 2006 to September 2010, we have generated a map of the rate of change of mean height, and time series of change in drained peatland. To do this we used two independent ALOS L-band tracks SAR images, as there is a lack of ground data for validation, correlation in output provides confidence the results are representative. Our analysis to date shows that (Figure 1): 1) the rate of change in surface height (decrease) can vary; 2) the decrease in surface height can be up to −7.65 cm/year; 3) the largest decrease in surface height observed was 25 cm.