Remote nocturnal bird classification by spectroscopy in extended wavelength rangesLundin, Patrik; Samuelsson, Per; Svanberg, Sune; Runemark, Anna; Åkesson, Susanne; Brydegaard, Mikkel General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We present optical methods at a wide range of wavelengths for remote classification of birds. The proposed methods include eye-safe fluorescence and depolarization lidar techniques, passive scattering spectroscopy, and infrared (IR) spectroscopy. In this paper we refine our previously presented method of remotely classifying birds with the help of laser-induced β-keratin fluorescence. Phenomena of excitation quenching are studied in the laboratory and are theoretically discussed in detail. It is shown how the ordered microstructures in bird feathers induce structural "colors" in the IR region with wavelengths of around 3-6 μm. We show that transmittance in this region depends on the angle of incidence of the transmitted light in a species-specific way and that the transmittance exhibits a close correlation to the spatial periodicity in the arrangement of the feather barbules. We present a method by which the microstructure of feathers can be monitored in a remote fashion by utilization of thermal radiation and the wing beating of the bird.

A challenging task in ornithology lies in identifying high-altitude nocturnal migrating bird species and genders. While the current approaches including radar, lunar obscuration, and single-band thermal imaging provide means of detection, a more detailed spectral or polarimetric analysis of light has the potential for retrieval of additional information whereby the species and sex could be determined. In this paper, we explore remote classification opportunities provided by iridescent features within feathers in the mid-infrared region. Our approach first involves characterizing the microstructural features of the feather by using rotation and straining, and a scheme for their remote detection is proposed by correlating these microstructural changes to spectral and polarimetric effects. Furthermore, we simulate the spectral signature of the entire bird by using a model that demonstrates how classification would be achieved. Finally, we apply infrared hyperspectral polarization imaging, showing that the net iridescent effect persists for the bird as a whole.

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A new scheme for NH detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH-air flames and on NH radicals generated through NH photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH AA←XB transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH. A general conclusion was that fluorescence interferences need to be carefully considered for NH diagnostics in this spectral region. Excitation for laser irradiances up to 0.2GW/cm did not result in NH fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH at around 630nm, excitation at 385.7nm showed a factor of ~15 higher NH signal. The improved signal allowed for single-shot NH LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000ppm, suggesting a detection limit around 700ppm. Thus, the presented approach for NH detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.

We report the observation of photoluminescence emission from airborne gold, silver, and copper nanoparticles. A continuous wave 532 nm laser was employed for excitation. Photoluminescence from gold nanoparticles carried in a nitrogen gas flow was both spectrally resolved and directly imaged in situ using an intensified charge-coupled device camera. The simultaneously detected Raman signal from the nitrogen molecules enables quantitative estimation of the photoluminescence quantum yield of the gold nanoparticles. Photoluminescence from metal nanoparticles carried in a gas flow provides a potential tool for operando imaging of plasmonic metal nanoparticles in aerosol reactions.