LAUSR

Abstract Tropical forest disturbance (such as selective logging and fire) along with deforestation have significant contributions to the carbon source due to land-use change and anthropogenic CO2 emissions, and thus envisioned by United Nation's REDD+ programme. In previous work, spaceborne single-pass InSAR phase-center height has been shown to have the capability of accurately monitoring the subtle height change due to forest growth and degradation (with meter or even sub-meter level RMSE about the regression curve fit to time). In this paper, a new approach using spaceborne SAR interferometry has been developed to detect and quantify selective logging events. In particular, a quantitative indicator of forest disturbance is first defined, namely disturbance index (DI; from 0 “no disturbance” to 1 “deforestation”). A numerical field data-based InSAR simulation is then performed to study the functional relationship between the field-measured DI and InSAR relative phase-center height change from a modeled perspective. A selective logging event (October 2015 through January 2016) over the Tapajos National Forest in Brazil is used for experimental validation. The InSAR-inverted DI estimates derived from DLR's TanDEM-X time-series data were compared with those measured from a field work over 32 quarter-hectare stands at Tapajos with relative RMSE of 30% for DI up to 0.3 and the disturbance epoch can be determined with an average accuracy of 13 days (constrained by the satellite repeat interval usually on the order of 2 weeks). As a comparison, the repeat-pass InSAR coherences from the concurrent JAXA's ALOS-2 data are shown to qualitatively correspond to the TanDEM-X results, confirming both the location and the epoch of the disturbance event. This new method is anticipated to contribute to the range of tools being developed for large-scale forest disturbance assessment and monitoring (for UN's REDD+ programme) through using spaceborne single-pass InSAR missions (e.g., DLR's TanDEM-X and in the future, TanDEM-L).