A comparison of field- and satellite-derived thermal flux at Piton de la Fournaise: implications for the calculation of lava discharge rate

Abstract

We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May-July 2003 eruption at Piton de la Fournaise (La Réunion). Multiple oblique ground-based thermal images were merged to provide full coverage of the flowfield. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless, extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from 94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface that were 6-24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge Rate (TADR) ranged between 1.5×10 8 J m −3 and 3.5×10 8 J m −3 . This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained from GPS surveys . Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements, particularly in terms of calculating discharge rate trends.

An experimental study of the surface thermal signature of hot subaerial isoviscous gravity currents: Implications for thermal monitoring of lava flows and domes

“… a Etna 1991–1993: Calvari et al [1994], Tanguy et al [1996], Wooster et al [1997], and Harris et al [1997a]; Etna 2001: Behncke and Neri [2003], Coltelli et al [2007], and Lombardo et al [2009]; Reunion Island 2003: Coppola et al [2005, 2010]. …”

Rheological control on the radiant density of active lava flows and domes

“…(5) summarises the appropriate insulation, rheological and topographic conditions during emplacement, and maintains the original proportionality between lava discharge rate and active area (Coppola et al, 2010). Therefore, any modification in T e and/or x, will be also embedded within the radiant density, which represents the amount of thermal energy that a unit volume of active lava body may loose by radiation.…”

“…During the last decade the availability of field-and remotelybased thermal images, has increased the use of thermal data in observing volcanic activity (e.g., Ramsey and Harris, 2012), particularly in studying the relationships with lava discharge rates (e.g., Wright et al, 2001;Harris et al, 2005Harris et al, , 2007aHarris et al, ,b, 2010Coppola et al, 2009Coppola et al, , 2010Dragoni and Tallarico, 2009;Harris and Baloga, 2009;Harris and Rowland, 2009;Hirn et al, 2009;Vicari et al, 2009;Ganci et al, 2012b;Garel et al, 2012;Gouhier et al, 2012). This kind of thermal analysis has been also used to detect and quantify extraterrestrial volcanism allowing to point out all the work done on Io, the innermost Galilean moon of Jupiter (e.g.…”

Effusive crises at Piton de la Fournaise 2014–2015: a review of a multi-national response model

“…This is a result of the large pixel size and mixed pixel problems, as well as pixel deformation, where pixels become increasingly large, ovoid, overlapping and rotated with scan angle (Harris 2013). Worse at high scan angles, or with extreme Earth curvature (which is the case for SEVIRI observations of Piton de la Fournaise), unreliable spectral radiances have been recorded (Holben and Fraser 1984;Singh 1988;Coppola et al 2010), so that spurious data at high scan angles tend After these photos were taken, parking next to the road was banned and cars were allowed to ascend from La Plaines des Cafres in groups of 100, as space became available in designated parking areas. A mini-bus shuttle service was also added from bases in La Plaines des Cafres and Tampon.…”

“…Following Frulla et al (1995), radiances for volcanic hot spots are deemed unreliable at scan angles of greater than 50°, where SEVIRI views Piton de la Fournaise at an angle of 63.4°. At such high scan angles, while over-estimates of spectral radiance, and hence TADR, will result from smearing of the anomaly due to extreme pixel overlap effects and point-spread-function problems (e.g., Markham 1985;Breaker 1990;Schowengerdt 2007), underestimates will result from atmospheric effects (Coppola et al 2010) and topographic shadowing of all or part of the thermal anomaly (Dehn et al 2002). Even local topographic features, such as cones, levees and skylights have been shown to play a role in shadowing the anomaly at high scan angles (Mouginis-Mark et al 1994), causing detection problems even at quite low scan angles for active lava surrounded by topographic highs (e.g., Wooster et al 1998;Harris et al 1999;Calder et al 2004).…”