Lava-flow characterization at Pisgah Volcanic Field, California, with multiparameter imaging radar

Geological Society of America Bulletin



Multi-incidence-angle (in the 25° to 55° range) radar data acquired by the NASA/JPL Airborne Synthetic Aperture Radar (AIRSAR) at three wavelengths simultaneously and displayed at three polarizations are examined for their utility in characterizing lava flows at Pisgah volcanic field, California. Pisgah lava flows were erupted in three phases; flow textures consist of hummocky pahoehoe, smooth pahoehoe, and aa (with and without thin sedimentary cover). Of the eight AIRSAR images used here, four were calibrated to within an accuracy of ±2 dB with trihedral corner reflectors, and data from these calibrations were used to process the additional images to a conservatively estimated ±5 dB level of accuracy. Calibrated radar backscatter data (σ°, in dB) were plotted as a function of incidence angle at three wavelengths (P-band, 68 cm; L-band, 24 cm; and C-band, 5.6 cm) and three polarizations (HH, horizontal transmit/horizontal receive; HV, horizontal transmit/vertical receive; and VV, vertical transmit/vertical receive) for eight major units at Pisgah for which multi-incidence-angle AIRSAR data were available. The eight units consist of near-vent and distal aa flows; near-vent and distal, hummocky pahoehoe flows; a mantled, hummocky pahoehoe flow; a platform pahoehoe flow; an alluvial fan; and a playa. Analyses of these backscatter data show that major unmodified volcanic units at Pisgah are readily distinguishable from each other and that they exhibit diffuse (HH, VV) and/or multiple (HV) scattering behavior typical of rough surfaces at these wavelengths. These analyses show that discrimination of smooth lavas (platform pahoehoe) from mantled units with greater primary roughness (hummocky pahoehoe) is difficult and must rely on supporting observations (such as evidence of localized weathering and/or sediment deposition, contrast with surrounding units, and superposition of flow units). L-band backscatter and image data at HV polarization show the best discrimination of Pisgah lava flows, with optimal unit separation observed between ∼40° and 50° incidence angles. Backscatter data shown as a function of relative age of Pisgah flows indicate that dating of lava flows on the basis of average radar backscatter may yield ambiguous results if primary flow textures and modification processes are not well understood.

Publication type Article
Publication Subtype Journal Article
Title Lava-flow characterization at Pisgah Volcanic Field, California, with multiparameter imaging radar
Series title Geological Society of America Bulletin
DOI 10.1130/0016-7606(1992)104<0695:LFCAPV>2.3.CO;2
Volume 104
Issue 6
Year Published 1992
Language English
Publisher Geological Society of America
Contributing office(s) Astrogeology Science Center
Description 9 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geological Society of America Bulletin
First page 695
Last page 703
Country United States
State California
Other Geospatial Pisgah volcanic field
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