Determining the sensitivity of L-band synthetic aperture radar to change in miombo woodland biomass over time: Gorongosa, Mozambique.

Abstract

Significant uncertainties persist in the global carbon cycle resulting from land use change in tropical woodlands. Africa’s dry tropical “miombo” woodlands have received particular academic focus since increasing intensity of agriculture, alongside climate-induced greening could be driving opposing directional changes in the carbon stock of this broad ecoregion. L-band Synthetic Aperture Radar (SAR) is a popular tool for quantifying the above ground woody biomass (AGB) of African woodlands, and timeseries of radar acquisitions have recently been used to estimate change in woodland AGB over time. However, the sensitivity of SAR to changes in miombo AGB over time has never been determined. This project presents the results of an experiment which attempts to establish how sensitive Phased Array L-band SAR (PALSAR) is to changes in biomass over time. The change in AGB of a series of 15 in-situ plots near Nhambita, Mozambique was regressed against subsequent change in PALSAR backscatter, and it was found that PALSAR-1 has a sensitivity of 0.0003 m2/m2 Mg-1 ha-1. A second methodology is presented which measures the changing backscatter signature over time of a series of 57 abandoned and regrowing agricultural plots in the study area. Estimates of AGB were produced using the regrowth rates of similar plots from the literature, which enabled a second empirical relationship to be produced. It was found PALSAR-2 had a significantly higher sensitivity of 0.0028 m2/m2 Mg-1 ha-1 to increases in biomass of these machambas. This research has important implications for future work seeking to use SAR to monitor the changing biomass of forest and woodland ecosystems.