Speaker
Description
A hyperspectral imaging instrument has been developed for the purpose of mapping air pollution in the urban environment, in particular nitrogen dioxide (NO2), a molecule responsible for respiratory diseases. The instrument is based on a large aperture commercial TeO2 acousto-optic tuneable filter (AOTF). In nominal operations, the instrument acquires spectral images of the light-diffusing atmosphere at a number of wavelengths in the 430-490nm domain, building a hypercube. The sub-nm spectral resolution of the AOTF, combined with good imaging performances, allow to detect the spectral signatures of NO2 in the light spectrum collected in every pixel.The method to retrieve the 2D distribution of NO2 from the hypercube relies on fitting each pixel-recorded spectrum with the absorption cross sections of the light-interfering species (NO2, O4, H2O, O3) convolved by the spectral response function (SRF) of the instrument (largely driven by the AOTF). Due to RF chain constraints, a too large acoustic power is sometimes injected in the crystal, taking the effective SRFs away from nominal shapes (sinc^2), and making them vary across the aperture. With the help of lasers and spectral lamps, the SRFs were characterised. The impact on the remote sensing application is discussed.