Topographic analyses of Kilauea Volcano, Hawai'i, from interferometric airborne radar

We analyze digital topographic data collected in September 1993 over a simi lar to 500-km(2) portion of Kilauea Volcano, Hawai'i, by the C-band (5.6-cm wavelength) topographic synthetic aperture radar (TOPSAR) airborne interfe rometric radar. Field surveys covering an similar to 1-km(2) area of the su mmit caldera and the distal end of an similar to 8-m-thick 'a'a flow indica te that the 10-m spatial resolution TOPSAR data have a vertical accuracy of 1-2 m over a variety of volcanic surfaces. After conversion to a common da tum, TOPSAR data agree favorably with a digital elevation model (DEM) produ ced by the U.S. Geological Survey (USGS), with the important exception of;h e region of the ongoing eruption (which postdates the USGS DEM). This DEM c omparison gives us confidence that subtracting the USGS data from TOPSAR da ta will produce a reasonable estimate of the erupted volume as of September 1993. This subtraction produces dense rock equivalent (DRE) volumes of 392 , 439, and 90x10(6) m(3) for the Pu'u 'O'o, Kupa'ianaha, and episode 50-53 stages of the eruption, respectively. These are 124, 89, and 94% of the vol umes calculated by staff of the Hawaiian Volcano Observatory (HVO) but do n ot include lava of Kupa'ianaha and episodes 50-53 that flowed into the ocea n and are thus invisible to TOPSAR. Accounting for this lava increases the TOPSAR volumes to 124, 159, and 129% of the HVO volumes. Including the +/-2 -m uncertainty derived from the field surveys produces TOPSAR-derived volum es for the eruption as a whole that range between 81 and 125% of the USGS-d erived values. The vesicularity- and ocean-corrected TOPSAR volumes yield v olumetric eruption rates of 4.5, 4.5, and 2.7 m(3)/s for the three stages o f the eruption, which compare with HVO-derived values of 3.6, 2.8, and 2.1 m(3)/s, respectively. Our analysis shows that care must be taken when verti cally registering the TOPSAR and USGS DEMs to a common datum because C-band TOPSAR penetrates only partially into thick forest and therefore produces a DEM within the tree canopy, whereas the USGS DEM is adjusted for vegetati on.