Validating L-Band InSAR for Tropical Peat Motion Monitoring: A Transformative Approach for Peat Measurement, Reporting, and Verification

Peatlands are vital carbon stores but risk turning into carbon sources due to anthropogenic disturbance. In Southeast Asia, an estimated 65% of tropical peatlands have been drained, primarily for agriculture and plantation development. This drainage results in drying, subsidence, and oxidation of the peat, leading to substantial CO₂ emissions stemming from the belowground biomass. Quantifying carbon emissions from peatlands in this region is therefore crucial and growing in importance for peat Measurement, Reporting, and Verification (MRV). However, measurements remain sparse due to the vast, swampy, densely vegetated, and often inaccessible nature of these tropical landscapes. By measuring peat motion, which is a proxy for peat CO₂ emissions, L-band Interferometric Synthetic Aperture Radar (InSAR) offers a cost-effective monitoring solution with the ability to penetrate vegetation and cover large areas at millimeter-scale precision. Despite its potential, the accuracy of L-band InSAR has not been rigorously validated in Southeast Asia and results can vary significantly depending on the InSAR processing strategies taken.

Here, we address this gap by using a unique combination of L-band ALOS-2 InSAR and high-accuracy, high-rate ground truth data from peat cameras to assess the InSAR accuracy for measuring peat motion. We use 5-year long ground measurements from 8 peat cameras distributed across oil palm plantations, croplands, scrublands, and forests in Central Kalimantan, Indonesia, to provide unprecedented evaluation of the accuracy of InSAR both temporally and spatially. We also mitigate major noise sources in ALOS-2 InSAR time series of ground motion stemming from the ionosphere, troposphere, and closure phase bias to improve the InSAR accuracy.

Our results demonstrate consistency of InSAR with the long-term velocities of peat motion from ground truth data across all sites with a mean RMSE of < 5 mm/year. We also show high accuracy of InSAR (RMSE ~1.6 cm and Pearson’s correlation coefficient ~0.7) in detecting sub-annual fluctuations of peat displacements over plantations and croplands, and poorer performance over some scrublands and forests but that can be identified based on the InSAR coherence. The 5-year span of the InSAR and peat camera datasets also reveal subsidence trends driven by drainage and accelerated during El Niño events. These results show the suitability of L-band for both multi-annual and sub-annual monitoring of peat motion in the tropics. In addition, these findings demonstrate that L-band InSAR can be scaled up to provide regional to global coverage, especially with the advent of new and upcoming L-band satellites (e.g. ALOS-4 and NISAR). Frequent data acquisitions and accurate data processing and analysis are essential for MRV of peat carbon. Without reliable data, verifying carbon credits and restoration efforts becomes impossible, undermining market credibility and effective mitigation of climate change impact. This study thus validates InSAR as a cost-effective and scalable tool and contributes to the robust assessment of ongoing climate action.