[1] Volcano observatories and researchers are recognizing the potential usefulness of thermal imaging cameras both before and during volcanic eruptions. Obvious applications include measurements of the surface temperatures of active lava domes and lava flows to determine the location of the most active parts of these potentially hazardous features. If appropriate precautions are taken, the new generation of thermal imaging cameras can be used to extract quantitative as well as qualitative information on volcanic activity. For example, they can be used to measure the temperature of lava on eruption and to reveal how the crust cools during flow emplacement. This is important for the validation of lava flow models. To ensure that meaningful temperatures are collected, thermal imaging data must be corrected for instrumental errors, emissivity of the surface being imaged, atmospheric attenuation, viewing angle and surface roughness. Controlled laboratory experiments have been undertaken to determine the emissivity of smooth and rough samples and the effects of viewing angle and to quantify the errors. Measured emissivities range from 0.973 ± 0.002 for smooth samples of basalt and 0.984 ± 0.004 for rough samples. Errors in emissivity-corrected temperatures are within ±15°C for lava at 1100°C. Variations from individual sensor receptors, which provide individual pixel temperature data, were found to be 0.6% and instrumental errors of the cameras used were 0.1%. Apparent temperatures were found to vary by less than the instrumental error for viewing angles up to 30 degrees from normal to lava, and thereafter increased by $1°C per degree. By increasing the apparent viewing distance of a small vent on Mount Etna from 1.5 to 30 m, the maximum temperature is shown to decrease by 53°C due to integrated averaging of radiance over increased pixel areas. At a viewing distance of 250 m the maximum temperature decreased by $200°C with a further 75°C decrease due to atmospheric attenuation for a relative humidity of 50%. However, errors in relative humidity measurements can lead to atmospheric attenuation correction inaccuracies up to 200°C at viewing distances of 1 km. We show how temperatures measured using thermal imaging cameras can be corrected to give improved estimates of temperature distributions on the surface of active lava flows.

A wide variety of Earth and planetary materials are very good recorders of paleomagnetic information. However, most magnetic grains in these materials are not in the stable single domain grain size range but are larger and in nonuniform vortex magnetization states. We provide a detailed account of vortex phenomena in geologic materials by simulating first‐order reversal curves (FORCs) via finite‐element micromagnetic modeling of magnetite nanoparticles with realistic morphologies. The particles have been reconstructed from focused ion beam nanotomography of magnetite‐bearing obsidian and accommodate single and multiple vortex structures. Single vortex (SV) grains have fingerprints with contributions to both the transient and transient‐free zones of FORC diagrams. A fundamental feature of the SV fingerprint is a central ridge, representing a distribution of negative saturation vortex annihilation fields. SV irreversible events at multiple field values along different FORC branches determine the asymmetry in the upper and lower lobes of generic bulk FORC diagrams of natural materials with grains predominantly in the vortex state. Multivortex (MV) FORC signatures are modeled here for the first time. MV grains contribute mostly to the transient‐free zone of a FORC diagram, averaging out to create a broad central peak. The intensity of the central peak is higher than that of the lobes, implying that MV particles are more abundant than SV particles in geologic materials with vortex state fingerprints. The abundance of MV particles, as well as their single domain‐like properties point to MV grains being the main natural remanent magnetization carriers in geologic materials.

Modern meteorite classification schemes assume that no single planetary body could be source of both unmelted (chondritic) and melted (achondritic) meteorites. This dichotomy is a natural outcome of formation models assuming that planetesimal accretion occurred nearly instantaneously. However, it has recently been proposed that the accretion of many planetesimals lasted over ≳1 million years (Ma). This could have resulted in partially differentiated internal structures, with individual bodies containing iron cores, achondritic silicate mantles, and chondritic crusts. This proposal can be tested by searching for a meteorite group containing evidence for these three layers. We combine synchrotron paleomagnetic analyses with thermal, impact, and collisional evolution models to show that the parent body of the enigmatic IIE iron meteorites was such a partially differentiated planetesimal. This implies that some chondrites and achondrites simultaneously coexisted on the same planetesimal, indicating that accretion was protracted and that apparently undifferentiated asteroids may contain melted interiors.

Digital images from hand-held cameras are increasingly being acquired for scientific purposes, particularly where non-contact measurement is required. However, they frequently consist of oblique views with significant camera-to-object depth variations and occlusions that complicate quantitative analyses. Here, we report the use of oblique photogrammetric techniques to determine ground-based thermal camera orientations (position and pointing direction), and to generate scene information for lava flows at Mount Etna, Sicily. Multiple images from a consumer grade digital SLR camera are used to construct a topographic model and reference associated groundbased thermal imagery. We present data collected during the 2004-2005 eruption and use the derived surface model to apply viewing distance corrections (to account for atmospheric attenuation) to the thermal images on a pixelby-pixel basis. For viewing distances of~100 to 400 m, the corrections result in systematic changes in emissive power of up to ±3% with respect to values calculated assuming a uniform average viewing distance across an image.

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