【正文】 orectification of the thermal images and hence geo referencing of the data. An example is shown in Fig. 3. Note that, for this image, some important regions of the flow are occluded by the irregular topography of flow areas closer to the camera. This could be avoided by using less oblique images (. data acquired from a helicopter) or by bining images from different terrestrial positions. Some distortion is evident in the uppermost area of the imaged channel (to the north), where rectification errors from problems at the edge of the surface model are pounded by the oblique viewing angle.Although these issues will be addressed in future work, flow features can be easily identified in the current rectified data. For example, using the parallel lineations of elevated exitance to delineate the active regions of the channel (as opposed to the levees), at a viewing range of ~310 m, the western channel branch has a width of m, which narrows to ~9 m as the flow passes over a region of steeper gradient at a range of ~260 m (Fig. 3). This pares with an average channel width of 17 m and maxima and minima of 37 and 2 m respectively, determined from laser altimeter data collected earlier in the eruption (Mazzarini et ). For this channel section, the exitance measured from the central region of the flow is ~700–1,700 W m?2(corresponding to a black body temperature of 200–290176。 some large (~50 cm) flat targets were augmented by smaller (~5 cm) ‘ball’ targets to improve precision at short viewing distances. Target positions were coordinated using GPS (ProMark X) augmented, for relatively close targets, with targettotarget slope distances made using a tape measure. These measurements were included as observations in the photogrammetric network adjustment along with the GPS data.Fig. 2 Visible (a) and thermal (b) images of the active flow front and channels on 27 September 2004, looking approximately north. For scale, the active flow front is ~35 m wide. The visible image shows an inactive flow front and partially drained channel (which had been active during the previous day) to the right of the active front. The thermal image is overlain with a perspective view of the triangulated surface model derived from the visible images.Photogrammetry and resultsThe photogrammetric software employed (VMS, Robson and Shortis, ) provides a general case geometric solution, suitable for application to networks of convergent oblique imagery. Measurements of each identifiable control target image are used along with the threedimensional target coordinate data, to provide camera orientation starting values for each image. These initial values are then refined by least squares based resection. If required (. to generate topographic data),additional homologous points can be generated in order to increase the density of the measurement network, before a network or bundle adjustment (Granshaw 1980) is carried out. Registration of the thermal images can be achieved either by using this targetbased photogrammetric approach with thermally identifiable targets, or, where a camera position can be ascertained from a visible image taken at the same location, by calculation of relative camera rotation angles only.Postprocessing of the photogrammetric data was carried out using Matlab. A relatively coarse DEM was obtained by interpolating a 4m triangulated mesh between the topographic data points acquired. Under a suitable projective transformation, the surface can be overlain onto the thermal imagery (Fig. 2b). Obscuration of any part of the surface is handled by depthordering the triangulation and considering the closest triangle ‘viewed’ by each pixel to be the one observed.In Fig. 2b, temperature data collected with the camera set to a scale of 0–500176。 Burton et al. 2005), the channelfed flows were cooling limited (Guest et al. 1987) and (during the period of fieldwork) were km long, with active flow fronts at the break in slope on the valley floor, south of Monte Centenari (Fig. 2a).Whilst a considerable portion of the flow field developed on steep topography exposed to rock fall hazard, the flow fronts were relatively accessible. Hence, ground based images could be acquired of the flow front and distal channel regions and the data used in this paper were collected on 27 September 2004.Visible images were acquired with a Canon EOS 300D (30722048 effective pixels) fitted with a fixedfocus 28 mm lens, the imaging geometry of which had been precalibrated in a laboratory (Robson et al. 1999). Thermal images were obtained with a FLIR ThermaCAM S40 which provides a horizontal field of view of 24176。 Kerle 2002) or, more recently, from satellite data (Stevens et al. 2004). On a smaller scale, closerange and oblique photogrammetry has been successfully used for geomorphological research (. Chandler and Brunsden 1995。 Donegan and Flynn 2004。pp 105108Oblique photogrammetry with visible and thermal images Of active lava flowsMike R. James. Stuart Robson.Harry Pinkerton. Matthew BallAbstract Digital images from handheld cameras are increasingly being acquired for scientific purposes, particularly where noncontact measurement is required. However,they frequently consist of oblique views with significant cameratoobject depth variations and occlusions that plicate quantitative a