Characterization of lava-flow degradation in the Pisgah and Cima volcanic fields, California, using Landsat Thematic Mapper and AIRSAR data

Abstract

Digital Landsat Thematic Mapper (TM) observations, multi-frequency polarimetric AIRSAR radar data, microtopographic profiles derived from helicopter-borne photography, and field measurements were analyzed over the Pisgah and Cima volcanic fields, and Lavic Lake playa, Mojave Desert, California. Surface radiance factors were extracted from TM data using radiative transfer procedures to model the atmosphere and surface simultaneously. AIRSAR data were calibrated to backscatter specific cross sections using corner reflectors deployed at a number of locations. Analyses focused on the use of key field sites to understand compositional and textural controls on TM band-5 (1.55 to 1.75 μm) radiance factors and C- (5.6 cm), L- (24 cm), and P- (68 cm) band specific cross sections. For the Pisgah and Lavic Lake sites, the TM data are explained using a linear mixing model of basalt and fine-grained sediment (clay to sand-sized grains of clay minerals, quartz, feldspar, carbonate, and lithic fragments) radiance factors, with the addition of shadows for the rough a9a flow. On the other hand, AIRSAR data are shown to be primarily controlled by surface roughness, as there is a strong correlation between specific cross section and surface height standard deviation. For the elongate flows at the Cima volcanic field, which exhibit a mix of pahoehoe and a9a properties, we find a positive linear relationship between TM band-5 radiance factors and flow ages for the 3 m.y. age range represented. Specific cross sections remain constant until about 0.14 Ma and then decrease with age up to about 0.56 Ma. On the other hand, data for the two older flows (0.70 and 0.85 Ma) show increasing specific cross sections with increasing age. We interpret the increase in TM band-5 radiance factors (from 0.05 to 0.25) with increasing flow age and the decrease in specific cross sections (8 dB change at 35° incidence angle for L band) for flows up to 0.56 Ma in age as due to smoothing by mass wasting and infill by fine-grained aeolian deposits. The increased specific cross sections for older flows are interpreted to be a consequence of surface roughness generated by fluvial dissection.