Monitoring seasonal changes of a mixed temperate forest using ERS SAR observations

Temporal variations of environmental research satellite (ERS)-1/2 backscatt ering coefficients acquired over a mixed deciduous forest are analyzed with an aim toward relating the observed radiometric variations to changes eith er in the vegetation seasonal cycle or in the structural parameters. Overal l, the results are somewhat pessimistic. Temporal sigma(o) plots show chaot ic variations, which are difficult to relate to the seasonal changes of for est parameters and particularly to the foIiage dynamics. Furthermore, no di stinction between stand types or between deciduous species is found to be p ossible, and nearly identical temporal plots are observed for all the stand s, suggesting that the radar signatures are partly under the influence of n onforest parameters. Besides, the effect of meteorological events are diffi cult to evaluate. Discrimination between deciduous stands and conifers is n evertheless possible, since the radiometric difference between the two spec ies is about 1 dB. With an overall sensitivity to standing biomass of about 0.1 dB/50 tons per hectare, ERS SAR's can be considered as almost insensit ive to biomass variations. For the young stands, the C-band response is fou nd to be dominated by stand structure, whereas the backscattering coefficie nt saturates for biomass values higher than 50 and 80 t DM ha(-1) for decid uous and conifers, respectively.