Tunable laser spectroscopy (TLS) combined with mid-infrared imaging is a powerful tool for a sensitive and quantitative visualization of gas leaks. This work deals with standoff methane leak detection within 2 m by an interband cascade laser (3270 nm wavelength) and an infrared camera. The concept demonstrates visualization of methane leakage rates down to 2 ml/min by images and sequences at frame rates up to 125 Hz. The gas plume and leak can be localized and quantified within a single image by direct absorption spectroscopy (DAS). The HITRAN database allows a calibration-free, pixelwise determination of the concentration in ppm*m. The active optical imaging concept showed pixelwise sensitivities around 1 ppm*m.

No abstract

Since 2008, the Solar Auto-Calibrating EUV Spectrometer (SolACES) experiment monitors the solar EUV radiation. SolACES is part of the SOLAR mission, a device mounted on the COLUMBUS module on the International Space Station (ISS). The SolACES device is capable of measuring the EUV radiation of the full solar disk, with three grazing incidence spectrometers, covering the spectral range from 17 to 135 nm. Degradation and ageing effects of hardware components are a major issue in the field of EUV measurements. In addition, propellant pollution from ISS logistic vehicles strongly complicate the instrumental operation as well as the data evaluation. To correct these effects, two double ionization chambers have been mounted onto the device frame. These are considered as a primary radiometric detector standard. By refilling the ionization chambers, the absolute EUV flux can be measured. Efficiency changes, being a severe issue in the field of measurements of EUV radiation, can corrected via an in-situ auto-calibration. The use of this method requires a thorough understanding of electron multiplier degradation and processes inside an ionization chamber. Aims The main focus of this paper lies on the correction of hardware ageing effects in the spectrometer readout, as well as on the usage of ionization chamber measurements for absolute calibration. Additionally, we intend to demonstrate the long term stability of the in-orbit calibration principle of EUV spectrometers with double ionization chambers. Methods In this paper, we first briefly present the instrument and its components. Second, we list, explain, and correct various degradation effects within the spectrometer units. The core part are the adjustments between spectrometer and ionization chamber data, for calibration purposes. Results and perspectives The proof of concept of the in-orbit calibration, via ionization chambers, is given, by intercomparison of EUV data from SolACES with other experiments, over almost one decade. The presented data can be used for further investigations in climate modelling, as well as contribute to a SSI composite

Abstract. The measurement of low methane (CH4) concentrations is a key objective for safety of industrial and public infrastructures and in environmental research. Laser spectroscopy is best suited for this purpose because it offers high sensitivity, selectivity, dynamic range, and a fast measurement rate. The physical basis of this technique is infrared absorption of molecular gases. Two detection schemes – direct absorption spectroscopy (DAS) and photoacoustic spectroscopy (PAS) – are compared at three wavelength regions in the near-infrared (NIR), mid-wavelength (MWIR), and long-wavelength (LWIR) infrared ranges. For each spectral range a suitable semiconductor laser is selected and used for both detection techniques: a diode laser (DL), an interband cascade laser (ICL), and a quantum cascade laser (QCL) for NIR, MWIR and LWIR, respectively. For DAS short absorption path lengths comparable to the cell dimensions of the photoacoustic cell for PAS are employed. We show that for DAS the lowest detection limit can be achieved in the MWIR range with noise-equivalent concentrations (NECs) below 10 ppb. Using PAS, lower detection limits and higher system stabilities can be reached compared to DAS, especially for long integration times. The lowest detection limit for PAS is obtained in the LWIR with a NEC of 7 ppb. The different DAS and PAS configurations are discussed with respect to potential applications.