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  • Publication
    New method to calculate the angular weighting function for a scattering instrument: Application to a dust sensor on Mars
    (MDPI, 2022-12-01) Santalices, David; Castro González, Antonio Jesús de; Briz Pacheco, Susana; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
    Suspended dust above the Martian surface is an important element in Martian climatology. In the frame of the Exomars'22 mission, we developed a dust sensor instrument, designed to provide size parameters of dust particles suspended in Mars surface from the light scattered by the particles. Thus, to interpret the data of the dust sensor, we need a method to calculate the theoretical optical power dispersed by the particles and, therefore, the theoretical signal obtained by the instrument. This signal depends on the suspended particles and on the instrument configuration. In this paper, we present a new method to calculate the angular weighting function (Wf) for scattering sensors. (Wf) encompasses the scattering angles measured by the sensor and depends only on the instrument and not on the suspended particles. To calculate this (Wf), we use fundamental radiometry principles and an appropriate coordinate system, where one coordinate is the scattering angle. The method is applied to the dust sensor instrument and compared with other methods. The comparison highlights the advantages of the proposed method since it avoids using an ideal sampling volume, preserves the radiometric meaning, and avoids instrument calibration. The effectiveness of the method makes it a valuable tool for the design of scattering instruments and also for the interpretation of their data.
  • Publication
    Virtual spectral selectivity in a modulated thermal infrared emitter with lock-in detection
    (MDPI, 2022-07-02) Santalices, David; Meléndez Sánchez, Juan; Briz Pacheco, Susana; Comunidad de Madrid; Ministerio de Ciencia, Innovación y Universidades (España)
    The need for affordable low-power devices has led MEMS-based thermal emitters to become an interesting option for optical gas sensors. Since these emitters have a low thermal mass, they can be easily modulated and combined with a lock-in amplifier for detection. In this paper, we show that the signal measured by a lock-in amplifier from a thermal emitter that varies its temperature periodically can have different spectral profiles, depending on the reference signal used. These virtual emitters appear because the Fourier series expansion of the emitted radiance, as a function of time, has different coefficients for each wavelength, and this spectral signature, which is different for each harmonic, can be retrieved using a reference signal that corresponds to its frequency. In this study, the effect is first proved theoretically and then is measured experimentally. For this purpose, we performed measurements with an IR camera provided with six different spectral filters of a modulated emitter, in combination with lock-in amplification via software. Finally, we show a potential application of this effect using multiple virtual emitters to gain spectral selectivity and distinguish between two gases, CO2 and CH4.
  • Publication
    Multilayer perceptron as inverse model in a ground-based remote sensing temperature retrieval problem
    (Elsevier, 2008-02) García-Cuesta, Esteban; Galván, Inés M.; Castro González, Antonio Jesús de
    In this paper, a combustion temperature retrieval approximation for high-resolution infrared ground-based measurements has been developed based on a multilayer perceptron (MLP) technique. The introduction of a selection subset of features is mandatory due to the problems related to the high dimensionality data and the worse performance of MLPs with this high input dimensionality. Principal component analysis is used to reduce the input data dimensionality, selecting the physically important features in order to improve MLP performance. The use of a priori physical information over other methods in the chosen feature’s phase has been tested and has appeared jointly with the MLP technique as a good alternative for this problem.