A novel application of satellite radar data: measuring carbon sequestration and detecting degradation in a community forestry project in Mozambique

Abstract

Background: It is essential that systems for measuring changes in carbon stocks for Reducing Emissions from Deforestation and Forest Degradation (REDD) projects are accurate, reliable and low cost. Widely used systems involving classifying optical satellite data can underestimate degradation, and by classifying the landscape ignore the natural heterogeneity of biomass.

Aims: To assess the ability of repeat L-band radar to detect areas of small increases or decreases in above-ground biomass (AGB) across a Miombo woodland landscape.

Methods: ALOS PALSAR L-band cross-polarised (HV) radar data from 2007 and 2009 were used to create maps of AGB, calibrated using 58 field plots. The change in AGB was assessed for land parcels with known landcover histories: (i) 500 ha of new agroforestry; (ii) 9500 ha of protected (REDD) areas; and (iii) 23 ha of land where degradation occurred between 2007 and 2009.

Results: Increases in AGB were detected in both the agroforestry and REDD areas (0.4 and 1.1 Mg C ha⁻¹ year⁻¹, respectively), while the degraded areas showed a decrease of 3 Mg C ha⁻¹ year⁻¹.

Conclusions: PALSAR data can be used to detect losses and gains in AGB in woodland ecosystems. However, further work is needed to precisely quantify the uncertainties in the change estimates, and the extent of false-positive and false-negative change detections that would result from using such a system.

Keywords:

• Africa
• above-ground biomass
• community forestry
• forest monitoring
• Miombo
• Radar
• REDD
• REDD+
• remote sensing
• SAR
• savanna
• woodland

Acknowledgements

The European Space Agency provided the ALOS PALSAR scenes for this study through a Category 1 application to Edward Mitchard. Landsat data were provided free of charge by the USGS and NASA. The radar data were originally collected and processed by JAXA. SRTM data were collected by NASA, and processed by the CGIAR Consortium for Spatial Information (http://srtm.csi.cgiar.org/). Mapready software, used for processing the radar data, was provided free of charge by the Alaska Satellite Facility. The European Development Fund, NERC and Envirotrade funded the field data collection; Envirotrade also provided logistical support. Edward Mitchard was funded by Gatsby Plants. We acknowledge the following Envirotrade employees who assisted in collecting the field data: Joao ‘Dois’ Eduardo, Manuel Francisco, Gary Goss, Alfonso Jornal, Zito Lindo, Neto Moulinho, Salomaõ ‘Baba’ Nhangue, Ramaio Saimone with the supervision of Alastair MacCrimmon, Antonio Serra, and Philip Powell. Meg Coates-Palgrave carried out the tree identification on the Permanent Sample Plots. Prof. John Grace, of the University of Edinburgh, provided invaluable support and advice.