REMOTELY RETRIEVING RELIABLE LAVA ERUPTION TEMPERATURES USING A CALIBRATED MULTISPECTRAL VNIR CAMERA: IMPLICATIONS FOR MONITORING VOLCANISM ON IO AND EARTH

Earth and Jupiter’s moon, Io, are the only two bodies in the Solar System with known active silicate volcanism. While active eruptions can be observed on both bodies, on Io one is restricted to remote sensing data from the Voyager and Galileo spacecraft and Earth-based multispectral telescopic observations. This makes it difficult to determine one of the most basic parameters of an eruption: the temperature of the molten lava. The temperature information retrieved from remote sensing measurements indicates silicate volcanism on Io, but the characteristics of the measurements yield considerable uncertainty in the retrieved lava eruption temperatures – leaving equally large uncertainties in the composition of Io’s dominant magma (e.g., mafic or ultramafic).

The problem is that remote sensing only measures the surface temperature, and newly exposed molten lava cools very rapidly. Furthermore, the cooling rate is highly dependent on the style of volcanic activity (ranging from 100 to 500 °C/s for lava flows to fine pyroclasts). Thus the observations (usually multispectral) from which the temperature is estimated must be completed very quickly. The Galileo Solid State Imaging experiment obtained data at different wavelengths, often minutes apart. Each measured channel may, therefore, may have observed lava at a significantly different temperature. Our goal is to quantify the uncertainty in temperatures derived from data collected over different time spans. The ultimate objective is to provide quantitative design constraints on a new instrument for measuring eruption temperatures on Io.

We report preliminary results from recent field work on Kilauea Volcano, Hawai’i. High speed image data of active basalt lava flows were acquired using a new multispectral visible and near infrared camera system capable of near-instantaneous wavelength separation at up to 60 frames per second. Camera calibration was established in a laboratory using a high temperature (600-1500 ᵒC) blackbody and allows the camera to be used as an optical pyrometer, converting incandescent color to temperature. By comparing color temperatures computed with different time lags between the different channels, we can quantify the increase in measurement uncertainty with increasing the time span of the observation.