Dual-polarization vegetation indices for the Sentinel-1 sar sensor and its correlation to forest biomass from Atlantic Forest fragments

ABSTRACT

Background:

Vegetation indices have recently been proposed for remote sensing SAR (synthetic aperture radar) sensor measurements to monitor vegetation. However, they still lack validation studies on different vegetation types for their correct application. Thus, the objective of this study was to test the applicability of the Dual-polarization SAR Vegetation Index (DPSVI) and the modified DPSVI (DPSVIm) as indicators of aboveground biomass (AGB) from dense forest fragments.

Results:

Three forest fragments, comprising 54 forest plots with AGB ranging from 12 up to 220 Mg ha^-1, were studied. These forest fragments belong to the Brazilian Atlantic Forest biome, and were located within the Doce river hydrographic basin in the state of Minas Gerais, Brazil. AGB was compared with the DPSVI and DPSVIm indices, computed from dual-polarization Sentinel-1 images, using Spearman’s rank correlation test through two approaches. In the first approach (A1), correlation tests were performed using all forest plots; in the second approach (A2), samples were taken from plots on flat to undulating terrain slopes. The correlation of AGB with DPSVI presented no significant correlation (p-value >> 0.05). In contrast, for DPSVIm, the correlation with AGB was significant and positive, with coefficients ranging from 0.4 in approach A1 to 0.7 in approach A2.

Conclusion:

While the DPSVI index did not show a correlation with the AGB of the studied forests, even though it is a C-band index, the DPSVIm was found to be a good indicator of the amount of AGB in forests and therefore has potential for applications in future studies, particularly in areas with reasonable slope or flat terrain.

Keywords:
aboveground biomass; forest inventory; microwave remote sensing; semi decidual forest; slopes.

HIGHLIGHTS

Radar remote sensing provides important data for forest monitoring. We tested the dual-polarization SAR vegetation indices (DPSVI and modified DPSVI). Modified DPSVI (DPSVIm) showed to be correlated with forest aboveground biomass. C-band SAR data can be utilised in forest monitoring.