[Bidirectional Reflectance Distribution Function of Space-Borne Quartz Volume Diffuser].

Quartz Volume Diffuser(QVD) is used in the observing system of Space-Borne differential optical absorption spectrometer. The precision of observed solar spectrum directly influences the accuracy of the gas retrievals. Therefore the QVD is required for well Lambert feature to ensure the accuracy of full field solar spectrum, and it can provide uniformity source in the observing view of the instrument. Using bidirectional reflectance distribution function(BRDF) measurement instrument, adopting the powder pressboard of F4(polytetrafluoroethylene(PTFE)), QVD's BRDF is measured by choosing the relative measurement method. Four kinds of QVD's BRDF is obtained in the range of 180～880 nm, the observing view of -70°ï½ž+70°. Two kinds of QVD which has a well Lambert feature are selected by analyzing the QVD's BRDF. The diffuse sunlight measured by QVD and F4 is compared, which show that QVD has well scattering properties with regard to solar spectrum and can be selected as the measuring diffuser. That supports for next Ultraviolet irradiation measurement, atomic oxygen erosion measurement and comparison measurement.

[Two Data Inversion Algorithms of Aerosol Horizontal Distributiol Detected by MPL and Error Analysis].

Atmospheric aerosols have important impacts on human health, the environment and the climate system. Micro Pulse Lidar (MPL) is a new effective tool for detecting atmosphere aerosol horizontal distribution. And the extinction coefficient inversion and error analysis are important aspects of data processing. In order to detect the horizontal distribution of atmospheric aerosol near the ground, slope and Fernald algorithms were both used to invert horizontal MPL data and then the results were compared. The error analysis showed that the error of the slope algorithm and Fernald algorithm were mainly from theoretical model and some assumptions respectively. Though there still some problems exist in those two horizontal extinction coefficient inversions, they can present the spatial and temporal distribution of aerosol particles accurately, and the correlations with the forward-scattering visibility sensor are both high with the value of 95%. Furthermore relatively speaking, Fernald algorithm is more suitable for the inversion of horizontal extinction coefficient.

[Spectral Calibration of Space-born Imaging Spectrometers Using Spectrum-Matching Technique].

Spectral calibration of space-born imaging spectrometers based on spectrum-matching technique is presented, which adopts atmospheric absorption lines as the matching lines, and chooses correlation coefficient method as the criteria. In order to simulation the onboard spectral calibration, the spectrum-matching technique is applied on the imaging spectrometers that after the vibration test. The vibration test is able to simulation the launching. The spectral resolution, center wavelength of two-dimensional pixel is determined during onboard spectral calibration. As the calibration results show, the spectral resolution of imaging spectrometers after the vibration test is 0.40 nm, it is the same comparing to the value before the vibration, the wavelength shifts 0.08 nm towards the long wave for the spectral pixels, and the spectral smile is determined for all spatial elements, which shifts towards the short wave direction, with the max smile value is 0.96 nm, the result is similar to that before the vibration. As a result, the spectrum-matching technique is tested and verified.

Study on the Non-Uniformity Calibration of Space-Born Differential Optical Absorption Spectrometer.

Space-borne differential optical absorption spectrometer is a nadir viewing wide field imaging spectrometer, which adopts two-dimensional CCD detector arrays. The pixel response non-uniformity exists in each column of spatial dimension, which will introduce high-frequency instrument-related spectral structures in the measurement data. However, the non-uniformity calibration of space-born imaging spectrometer is difficulty due to two factors: the spectral smile effect and the large field of view. For this reason, a method of non-uniformity calibration is discussed in detail. The result shows that the spectral smile effect and non-uniformity of full FOV image are corrected effectively, and high-frequency instrument-related structures in the measurement data are removed.

[On using tunable diode laser absorption spectroscopy to determine gas fluxes over cropland].

Tunable diode laser absorption spectroscopy (TDLAS) is a compact, automated, high precision technique and fit for in-situ or field measurements. Two spectroscopy measurement systems, TDLAS and NDIR (non-dispersive infrared spectroscopy), were used to monitor trace gas emission over cropland at Fengqiu Agricultural Ecology Experimental Station for one month. The fluxes of carbon dioxide were estimated by flux-gradient and eddy covariance method, respectively. A footprint model was developed during experiment. Based on this model, the source areas of TDLAS and NDIR were investigated. The effects of different factors on the flux measurement were also analyzed. The authors concluded that the source areas for the two techniques are discrepant in most of the cases. The source areas increase with path length and detecting height. This result will help the installation of instruments.

[A new retrieval method for ozone concentration at the troposphere based on differential absorption lidar].

Aerosols interfere with differential absorption lidar ozone concentration measurement and can introduce significant errors. A new retrieval method was introduced, and ozone concentration and aerosol extinction coefficient were gained simultaneously based on the retrieval method. The variables were analyzed by experiment including aerosol lidar ratio, aerosol wavelength exponent, and aerosol-molecular ratio at the reference point. The results show that these parameters introduce error less than 8% below 1 km. The measurement error derives chiefly from signal noise and the parameters introduce error less than 3% above 1 km. Finally the vertical profile of tropospheric ozone concentration and aerosol extinction coefficient were derived by using this algorithm. The retrieval results of the algorithm and traditional dual-wavelength difference algorithm are compared and analyzed. Experimental results indicate that the algorithm is feasible, and the algorithm can reduce differential absorption lidar measurement error introduced by aerosol.

[Study of remote sensing the flux of carbon dioxide gas with tunable diode laser absorption spectroscopy].

Tunable diode laser absorption spectroscopy (TDLAS) technique is a new method to detect trace gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectra in the characteristic absorption region. TDLAS is a highly sensitive, highly selective and fast time response trace gas detection technique. In the present paper, a DFB laser at room temperature was used as the light source, wavelength modulation method was employed, and the second harmonic signal of one absorption line near 1.578 microm of carbon dioxide molecule was measured. A system was built for online monitoring of carbon dioxide concentration within the optical path of more than 700 meters at different heights. Combined with Alonzo Mourning-Obukhov length and characteristic velocity detected by large aperture scintillometer, the flux of carbon dioxide gas calculated by the experiential formula is within -60-60 mg x m(-2) x s(-1). The comparison of the datea detected by TDLAS system and the eddy covariance showed that the change of the data detected by TDLAS had a similar trend to that detected by the eddy covariance, and the best results can be produced by this method, breaking through the phenomenon of only providing the flux of trace gases near the ground at present, and making the measurement of trace gas fluxes within a large area possible.

[Ozone concentration inversion based on multi-reflected cell FTIR spectra and correlation analysis].

The stratosphere ozone plays the protective action role for human and the ground-level ozone is harmful to human health. Monitoring ozone with different ways and methods took an active part in understanding distribution and transformation of ozone, which was useful to controlling pollution emission. Spectra were got by multi-reflected white cell Fourier transform infrared (FTIR) spectrometer, inversed with nonlinear least squares (NLLSQ) method and then the concentrations of ozone were got exactly. The correlations of measured ozone concentration time series by Fourier transform infrared spectrometer, open path UV differential optical absorption spectrometer and ozone analyzer of the Thermo Corporation were significant. The results showed that the measured ozone absolute concentrations with different monitoring methods and instruments had some differences, but the concentration diurnal variations were coincident and the correlations were good. Therefore, ozone concentration inversion method, based on multi-reflected cell Fourier transform infrared spectrum and not reported in domestic articles, could be used as an effective technique to measure ozone concentration.

[Application of SOF-FTIR method to measuring ammonia emission flux of chemical plant].

In the present paper, a new method is introduced for real-time monitoring polluted gas emission flux of chemical plant, which is called FTIR based on the solar occultation flux technique (SOF-FTIR). The model to obtain background spectrum, measured spectrum and atmospheric penetration rate surrounding polluted gas under complicated conditions is also proposed. Continuous measurements were preformed at a closed loop surrounding the contaminated areas that need to be mornitored to obtain measured spectrum, and finally column concentration of polluted gas was retrieved by using the nonlinear least squares fitting algorithm (NLLS). Then the flux information combined with the meteorological data and GPS information of the time was obtained when the experiments were done. Using this method, remote sensing experiment of ammonia emission around a chemical plant was done, and the concentration distribution and its emission flux was quantitatively analyzed. Compared with traditional FTIR methods of monitoring, this method is featured by convenient operation and high maneuverability, so it has a good application prospect in pollution monitoring and other applications in regional air pollution contingency monitoring.

[Passive remote measurement of flame infrared image by a FTIR scanning imaging system].

The present paper introduced a FTIR scanning imaging system. This system is based on the combination of a FTIR spectrometer and a scanning mirror. So it has the advantage of FTIR spectrometer: non-contact, real-time, celerity, nicety and high sensitivity. Through scanning mirror, the authors can obtain the space information of targets. The authors used this system to measure the flames infrared emission spectra of three alcohol burners at a flat roof in our laboratory. According to Planck's law, the authors calculated the relative temperature of from each spectrum. These temperature data formed an array. The authors used matlab software to plot the infrared images of target and contrasted them with video image. They were consistent with each other very well. This experiment allowed us to obtain the temperature distribution of three alcohol burners' flames, and provide identification, visualization, and quantification of pollutant clouds.

[Study on the method of FTIR spectrum non linear multiple point calibration].

FTIR Technique has developed rapidly since 1980s, and has become increasingly important. It has been used in a variety of fields. In order to make sure the result is of nicety, the authors should manipulate the FTIR spectrometer accurately and study its instrument response function and calibration arithmetic. Because the instrument response of the detector of FTIR spectrometer is different at different wave band, the no-calibrated spectrum was ruleless. Without calibration, we can not obtain the absolute intensity, even relative intensity. There are two calibration arithmetics: Linear calibration arithmetic corresponding linear detector and non-calibration arithmetic corresponding non-linear detector. The present paper gave the arithmetic of linear calibration and non-linear multiple point calibration. The authors measured several blackbody spectra at some different temperatures. Some of them were used for calibration and one was used to test the result of calibration The result indicated that this method of non-linear multiple point calibration was very good. The relative arbitrary between calibrated blackbody spectrum and standard blackbody spectrum was near 0.2%, while the maximum was still lower than 0.4%.

[The study of instrument response function of FTIR detectors].

FTIR spectrometer detectors have different instrument response function in different wave band. In application, no matter absolute or relative intensity of spectrum the authors use, the authors should calibrate the instrument with standard blackbody to find the instrument response function. In the present paper, the authors study the instrument response function of detectors (InSb detector and MCT detector) in Canada MOMAN MR154 FTIR spectrometer. The authors found the law of the change in instrument response function with temperature (radiation brightness). It is important for FTIR spectrometer calibration.

[A method of eliminating the water vapor interference simultaneously in open path FTIR measurement by instrumental line shape correction].

Water vapor absorption, which exists in mid-infrared region, is an interferential element for infrared spectra analysis. A new method, which can be used to eliminate the water vapor interference in FTIR measurement, is presented. To calculate the high resolution absorbance of water vapor, a fast line by line method which computed with the HITRAN database (eg. line strength, self broadening, air broadening, etc) and meteorological parameters (eg. temperature, pressure, and relative humidity) was used. After convolving with Instrumental line shape (eg. divergence angle, resolution, etc), the absorbance of water vapor was then transferred from high resolution to low resolution, which matched the instrumental parameters. After the acquirement of water vapor absorbance spectrum, it will be subtracted from the measured spectrum to calculate the spectrum with the water vapor was eliminated. In the present work, analysis of measured data from open path FTIR is described. Only the absorbing character and noise was left in the spectrum after eliminating the water vapor interference. Consequently, this method has an ideal effect on water vapor elimination when there is no dryer can be used, especially in the case of open path FTIR measurement.

[Study on the measurement of the atmospheric extinction of fog and rain by forward-scattering near infrared spectroscopy].

In the visible and near IR, absorption is negligible so that the atmospheric extinction can be derived by atmospheric scattering which is mainly contributed by fog droplet, rain droplet, another types of droplet and small articles. The forward-scattering visibility meter (FVM) works by illuminating with near IR light a small sample volume of about 100 mL of air and measuring the intensity scattered in the angular range of 30 to 36 degrees. The scattered intensity is proportional to the extinction coefficient regardless of the article size distribution and after wavelength calibration. The ratio of scattered signal to extinction coefficient of fog and haze can be achieved by comparative test of FVM outputs and manual observations. Nevertheless, as a result of the application of the measurement during rain with the ratio of fog and haze, an unacceptable error is raised. To obtain an accuracy extinction measurement during rain, an appropriated ratio of scattered signal to extinction coefficient of rain would be found. The calculation for different size distributions of fog and rain with Mie theory has been made in this paper. And a comparison of extinction measurements made with two FVMs and manual observations during fog and rain has been made. The result shows that during rain the FVM extinction coefficient is from 20% to 60% greater than that of manual observations. This result can be used to define correction factors so that the FVM using forward-scattering near IR spectroscopy not only can be used to estimate extinction during fog and haze as well as during rain.

[Atmospheric CH4 concentrations and the correlation between CH4 and CO concentrations].

Methane (CH4) is an important greenhouse gas and a key molecule in tropospheric photochemistry, some more potent than CO2. The remote-sensing experiments of CH4 were carried out in the fall of 2 000 in Beijng. The 6-day records of the atmospheric CH4 concentrations were examined by means of a time-series analysis using a fast Fourier transform with a low-pass filter to elucidate the seasonal cycles and the long-term trends. The variation in the long-time trends of the CH4 concentrations in Beijing may be ascribed to the emission changes in the CH4 sources due to the human activities such as waste dumping and landfills and the emission from motor vehicles. The correlation between the CH4 and CO concentrations was analyzed.

[FTIR measurement and analysis based on the selection of optimized spectral band].

In active infrared remote sensing measurements, the infrared absorption caused by the presence of trace gases in atmosphere is related to the transmittance spectra in different infrared wave band. In many cases, transmittance spectra play an important role in spectsal quantitative analysis. Thus, the selection of wave band to be optimized for the measured and simulated transmittance spectra is the key in quantitative analysis. In the present paper, the optimal measurement range of transmittance is analyzed theoretically, which causes the minimum relative error of the retrieved concentration. The cross section for the measured gas based on Lorentz line shape is derived by calculation. At the same time, the transmittance spectra calibration training set is presented. The measured and analyzed band is determined for single component CO2. The optimal measurement band is determined for multi-component measurement. The simultaneous measurement of CO, CO2 and N2O with open path FTIR spectrometer system is accomplished successfully. The measured transmittance spectra are in good agreement with the reference transmittance spectra. The root mean square error of fitting results is less than 1%.

[Application of long open path FTIR system in ambient air monitoring].

A long open path fourier transform infrared spectroscopy system is described. The 250-meter-optical-path configuration is combined with a Fourier transform spectrometer of 1 cm(-1) resolution. With an active blackbody source, the transmittance spectrum of the atmosphere could be measured by the system. And then, it was fitted with the nonlinear least square algorithm to calculate the average concentrations of the constituents in the path. Measuring result of some gases such as CH4, CO, N2O and CO2 in polluted air was presented in the experiment part and the RMS of the residuals was <1%. The result shows that the system is stable and rapid, and can be easily aligned. It is suitable for research work on some infrared active important atmospheric constituents.

[Measurement of CO2 using an open-path FTIR and the factor of influence].

In the remote-sensing experiments of CO2 in Beijng, the authors found that the higher concentration of CO2 in autumn is caused by the CO2 emission by the traffic sector during the day time. During the day time, the concentratration of CO2 is comparatively lower because of the photochemistry and the transportation of troposphere. And the concentration of CO2 is about 410 microg x mL(-1). At night the fossil fuel power plants will be taken as a model for the source of CO2, so the concentration of CO2 is about 610 microg x mL(-1) or higher. The carbon increment from increased photosynthesis is greater than the increment in ecosystem carbon stocks. The higher the temperature, the lower the CO2 concentration. And the lower the rate of wind, the higher the concentration of CO2 also. Besides, the concentration of CO2 is affected by some other weather factors.

[Monitoring and analysis of CO2 and CH4 using long path FTIR spectroscopy over Beijing].

Recently, the greenhouse effect is well known and is of great worldwide concern. CO2 and CH4 are two of the main human activity-induced greenhouse gases in the atmosphere. It is important for environmental scientists to monitor their long-term variation. A Fourier transform infrared spectrometer was used to monitor the concentrations of CO2 and CH4 at a specific site in Beijing. The pollution air was passed through a long open path and the absorption spectra were collected over a period of a month. Quantitative analysis was performed by means of the nonlinear least square method using synthetically generated spectra, which was than convolved with instrumental line shape function. Ambient levels of CO2 and CH4 are reported with a time resolution of five minutes for 4-10, September 2005, and some analysis is present.

[Remote sensing of atmospheric trace gas by airborne passive FTIR].

The present article describes the details of aviatic measurement for remote sensing trace gases in atmosphere under various surface backgrounds with airborne passive FTIR. The passive down viewing and remote sensing technique used in the experiment is discussed. The method of acquiring atmospheric trace gases infrared characteristic spectra in complicated background and the algorithm of concentration retrieval are discussed. The concentrations of CO and N2O of boundary-layer atmosphere in experimental region below 1000 m are analyzed quantitatively. This measurement technique and the data analysis method, which does not require a previously measured background spectrum, allow fast and mobile remote detection and identification of atmosphere trace gas in large area, and also can be used for urgent monitoring of pollution accidental breakout.