Net primary productivity of aquatic vegetation of the Amazon floodplain: A multi-SAR satellite approach

Field measures were combined with synthetic aperture radar (SAR) images to evaluate the use of radar for estimating temporal biomass and mapping of aquatic vegetation in the lower Amazon. A SAR-based methodology was developed for quantification of the annual net primary productivity (NPP) of aquatic vegetation. The predictable monomodal flooding cycle of the floodplain is the primary control of the growth pattern of the aquatic vegetation. The total biomass increased steadily from November to August following the hydrological cycle.; The spatial variability of the canopy biophysical properties was detectable with radar data. Significant correlation existed between backscattering coefficients and above water dry biomass, height, and percentage of canopy cover. The logarithmic relationship between backscattering coefficients and biomass suggested that (1) at low biomass, high transmissivity of the microwave radiation through the vegetation canopy occurred and the backscattering was a result of quasi-specular reflection of both C and L bands and a minor contribution of canopy volume scattering from C band; (2) at intermediate levels of biomass, moderate changes in backscattering values occurred and the backscattering saturation point was reached at 470, 660, and 620 gm−2, for C band, L band, and the index, respectively; and (3) at high biomass, the transmissivity of C and L band radiation was equally attenuated and backscattering approached similar values for both.; The combination of the mapped area of seasonal aquatic vegetation with the SAR derived-biomass estimation allowed the calculation of the seasonal total biomass. By November, the new generation of aquatic vegetation started to develop; total biomass in the area was 0.1 × 1012 g. The steady growth of vegetation yielded a total biomass of 1.5 × 1012 g in an area of 395 km2 in May. From May onwards, with the water receding, some plants detached from the sediment and were carried towards the Amazon River. Consequently, by August, both area and total biomass decreased to 281 km2 and 5 × 10 11 g, respectively. Any estimate of total biomass had a margin of error of at least 18%. After correction for seasonal biomass loss, the estimated annual NPP was 6350gm−2 or 4.1 × 1012 g for the entire area. (Abstract shortened by UMI.)...