The Hyper-Cam in an advanced infrared hyperspectral imaging system which has been developed by TELOPS company (Figure 1). This remote sensing instrument operates in the thermal infrared band: 850-1300 cm-1 (i.e. 7.7 – 11.8 µm). It combines an infrared camera as well as a FTIR (Fourier Transform InfraRed spectroscopy) providing high spatial, spectral and temporal resolution images. The Hyper-Cam acquisition software “Reveal Pro 5” was used to record the data.
Each recorded file is called datacube, which corresponds to an infrared image with an infrared spectrum for each pixel. Along with the datacube acquisition, a visible image of the scene is taken as well as a broadband image.
The field of view of the instrument is 6.4 × 5.1°, projected on a 320 × 256 pixel Focal-Plane Array (FPA) detector. Additional optics can be adapted to increase the field of view. The spectral resolution of the imager can go from 0.25 to 150 cm-1. There is a tradeoff between the high spectral and high spatial resolution to acquire images with the desired temporal resolution.
Figure 1 – The HyperCam LWIR from Telops company
The IMAGETNA campaign (Huret et al., 2019) was held from 21 to 26 June 2015 at Mount Etna in Sicily. The hyperspectral infrared imager was deployed at Pizzi De Neri Volcano observatory located on the North side of Mount Etna at an altitude of 2,850 m. The Mount Etna plume was typical of a quiescent stage of activity of the volcano and situated at roughly 2 km from the HyperCam (Figure 2).
The measurements were carried out early in the morning to get maximum thermal contrast between the plume and the clear sky and to avoid the presence of convective clouds which usually forms in the afternoon. To keep a track of the topography of the scene, the field of view of the images measured with the HyperCam included part of the ground, but also part of clear sky as can be seen on the different spectral signatures presented on Figure 3.
Figure 3– Examples of radiance spectra from different pixels depicting the variety of spectral signatures of the measured scene on 26 June 2015 at 08:25:44 UTC.
Figure 2 – The HyperCam deployed during the IMAGETNA campaign at Mount Etna capturing the gas plume
The large spectral range of the HyperCam encompasses the spectral absorption band of SO2, centered around 1150 cm-1 (i.e. ~ 8.6 µm), which is one of the main chemical specie emitted by volcanoes. The retrieval of the SO2 SCD of the provided datacube is presented in Figure 4.
Figure 4 – SO2 SCD image retrieved from the HyperCam datacube measured during IMAGETNA campaign.