MULTICHARME: A modified Chernin-type multi-pass cell designed for IR and THz long-path absorption measurements in the CHARME atmospheric simulation chamber

We have developed MULTICHARME, a modified Chernin-type multi-pass cell especially designed for IR and THz long-path absorption measurements in the CHamber for Atmospheric Reactivity and Metrology of the Environment (CHARME). By measuring the output power using a near-IR diode-laser and a THz amplified multiplication chain, we have established that the effective reflectivity of MULTICHARME is better than 94 % over approximately three decades of frequency. Absorption measurements of N2O have been performed by probing highly excited rovibrational transitions in the near-IR and ground state rotational transitions at submillimetre wavelengths. In each case the linearity of the absorbance with the pathlengths was verified. Finally, we demonstrate that THz spectroscopy is able to study the isotopic composition of greenhouse polar gases such as N2O and to absolutely quantify stable (N2O) and reactive (O3) species at trace levels. Moreover, a THz monitoring at low pressure of the ozone decay in the chamber has been performed. The deduced ozone lifetime of 3.4 ± 0.1 h is shorter compared with previous measurements performed in CHARME at atmospheric pressure. For the first time, the ability of THz rotational spectroscopy to monitor, with a very high degree of selectivity, stable and reactive polar compounds at trace level in an atmospheric simulation chamber is demonstrated. However, the sensitivity of the THz monitoring needs to be improved to reach the atmospheric trace levels. For this purpose, it is necessary to figure out the baseline variations as well as possible induced by the multiple standing waves present in MULTICHARME.

Corrections for OMI SO₂ BRD retrievals influenced by row anomalies

Since June 2007, the Ozone Monitoring Instrument (OMI) Earth radiance data at specific viewing angles have been affected by the row anomaly, which causes large biases in sulfur dioxide (SO2) columns retrieved using the band residual difference (BRD) algorithm. To improve global measurements of atmospheric SO2 from OMI, we developed two correction approaches for the row anomaly effects in the northern latitudes and along the full orbit. Firstly the residual correction approach with median residual from a sliding 10° latitude range, and with that near the Equator was used to remove the anomalous high SO2 columns in the northern latitudes. Secondly, in the case of the row anomaly along the full orbit, the SO2 biases caused by the anomalous ozone (O3) column and underestimated Lambertian effective reflectivity (LER) were reduced, respectively, by using unaffected adjacent O3 column and residual correction with median residual from a sliding 10° latitude range. Comparisons with the OMI SO2 columns processed with median residual from a sliding 30° latitude range have illustrated the drastic improvements of our correction approaches under row anomaly conditions. The consistencies among the SO2 columns inside and outside the row anomaly areas have also demonstrated the effectiveness of our correction approaches under row anomaly conditions. The analyses of the underestimation and the errors caused by the O3 column and LER were conducted to understand the limitations of our correction approaches. The proposed approaches for the row anomaly effects can extend the valid range of OMI SO2 Planetary Boundary Layer (PBL) data produced using the BRD algorithm.

Properties of a-Si:N:H films beneficial for silicon solar cells applications

Amorphous silicon-nitride thin films a-Si:N:H were obtained by plasma enhanced chemical vapour deposition (PECVD) method from SiH4+NH3 at 13.56 MHz. The process parameters were chosen to obtain the films of properties suitable for optoelectronic and mechanical applications. FTIR analysis of a-Si:N:H films indicated the presence of numerous hydrogen bonds (Si-H and N-H) which passivate structural defects in multicrystalline silicon and react with impurities. The morpho-logical investigations show that the films are homogeneous. The deposition of a-Si:N:H layers leads to the decrease in friction coefficient of used substrates. Optical properties were optimised to obtain the films of low effective reflectivity, large energy gap Eg from 2.4 to 2.9 eV and refractive index in the range of 1.9 to 2.2. Reduction of friction coefficient for monocrystalline silicon after covering with a-Si:N:H films was observed: from 0.25 to 0.18 for 500 cycles.

Estimation of the Under-Surface Temperature Pattern by Dynamic Remote Sensing

The remote sensing (R/S) methods can be classified into three kinds: 1) the measurement of the reflection of sun beams (passive R/S); 2) the measurement using millimeter wave or laser radar (active R/S); and 3) the measurement of infrared radiation. By these methods, one can obtain information on a measured object concerning 1) its surface temperature, 2) its effective emissivity, and 3) its effective reflectivity. The surface temperature, in effect, contains the total information on the under-surface structure. The authors performed a fundamental experiment for extracting such under-surface information by R/S, which is known as ""dynamic remote sensing"". In the first place, we determined a special function for the medium (sand in our experiment), and then filtering the surface temperature pattern, and calculated the undersurface temperature pattern; from this data we estimated the form of the sample in the medium. In the second place, we analyzed the relation between the thermal input (the temperature in the bottom) and thermal output (the surface temperature) by analogy with electric circuits, calculated the heat capacity and ther thermal conductivity of the sample, and estimated its substance. As a result, the present study is expected to provide us with guidance to new methods for the exploration of underground water or minerals as well as non-destructive tests.