Biomass values are predicted from the radar at various frequencies and polarizations and are compared to the actual biomass values. Predicted biomass levels are most accurate at P-band. Multiple incidence angle data also reveal that the incidence angle of the radar illumination affects the retrieval of biomass from the radar data even at HV polarizations. One consequence is that topographic information is required for mapping the biomass in areas of moderate topography. Also the inversion curve for biomass retrieval varies with season and environmental conditions.

During two different overflights (by the JPL radar polarimeter) of the Bonanza Creek Experimental Forest, the environmental conditions changed significantly with temperatures ranging from unseasonably warm (1 to 9°C) to well below freezing (-8 to -15°C), and the moisture content of the snow and trees changed from a liquid to a frozen state. Preliminary investigations have focused on the characterization of the radiometric and polarimetric signatures of the data. Significant changes (up to 6 dB in certain forest stands) were observed in the L-band radar cross sections. Features extracted from the Stokes matrices of the same stands from the thawed and frozen days also suggest the relative contribution of the different scattering mechanisms to the radar return. Comparison of the diffuse component and variance of the H-V phase (white spruce, for example) indicates a relatively higher contribution from diffuse scatterers on the thawed day than on the frozen day. These results indicate that the contribution of scattering from the crown is responsible for this appreciable increase in backscatter. Some of these preliminary L-band and P-band observations are presented.

At the Bonanza Creek Experimental Forest (BCEF), past ecological research has been directed at forest successional processes on the floodplain of the Tanana River and adjacent uplands. Research at the Bonanza Creek site continues on the mosaic of forests, shrublands, and wetlands in a wide variety of successional stages on the Tanana floodplain. This paper reviews research since 1988 into the capabilities of Synthetic Aperture Radar (SAR) for monitoring, classification, and characterization of these forests using radar remote sensing and modelling techniques. Classifications of successional stages, obtained by use of different classifiers on multi-frequency and multi-polarimetric AIRSAR data, are contrasted; these classifications have been used to predict classification accuracies obtained with ERS-1 data, and to estimate the utility of an ERS-1 and RADARSAT combination for classification. Forest classifications, used in combination with ground-truth data for more than 50 forest stands, are used to summarize the distribution of biomass on the landscape. This will allow projections of future biomass. Monitoring of forest phenology, seasonality of flooding, and freeze-thaw transitions is ongoing. Also, direct monitoring of dominant tree species is demonstrating diurnal variation and interrelationships among environmental, physiological, and backscatter measurements. © 1995, Cambridge University Press. All rights reserved.

Temporal dynamic studies of ERS-1 SAR measurements in relation to the changing environmental and phenologic state of the forest canopy and of the forest ground layers during the winter/spring and fall/winter transitions of 1993 and 1993 are conducted. During these transition, changes in radar backscatter observed by ERS-1 are correlated to freezing and thawing of the soil and vegetation in order to determine the start and end of the growing season for the forest.