ABSTRACT
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 180ï½880 nm, the observing view of -70°ï½+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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
A new monitoring method of NO2 concentration near ground with the target difference absorption spectrum technology (Target DOAS) is introduced in the present paper. This method is based on the passive difference absorption spectrum technology. The instrument collects solar reflection spectrum of remote objectives, such as wall of building and mountain, and a specific reference spectrum is chosen to subtract the influence of trace gases from the target to atmospheric top, then integrated concentration of NO2 along the path between the target and instrument can be calculated through the differential absorption spectra inversion algorithm. Since the distance between the instrument and target is given, the mean concentration of NO2 can be derived. With developed Target DOAS instrument, NO2 concentration measurement was carried out in Hefei. And comparison was made between the target DOAS and long path difference absorption spectrometer. Good consistency was presented, proving the feasibility of this method.
ABSTRACT
The multi-axis differential optical absorption spectroscopy (MAX-DOAS), one of the remote sensing techniques for trace gases measurements, is sensitive to the lower atmosphere by eliminating the influence of stratosphere retrieved from zenith-sky spectroscopy. Ground-based MAX-DOAS measurements were carried out to observe NO2 at Ny-Alesund, Arctic from 5th Jul to 1st Aug 2011. The differential slant column densities (DSCDs) of NO2 at four off-axis angles showed typical pattern of tropospheric absorbers. Based on the assumption that NO2 was well mixed in 0-1 km of the troposphere, the mean mixing ratio of NO2 during the measurement period was 1.023E11 molec x cm(-3). The fluctuation of NO2 might be related to the fossil fuel combustions and the photochemical reactions. The vertical distribution of NO2 at 0-3 km showed that NO2 was mainly originated from boundary layer of sea surface.
ABSTRACT
A method of copper converting process determination based on PbO/PbS emission spectrum analysis was described. According to the known emission spectrum of gas molecules, the existence of PbO and PbS was confirmed in the measured spectrum. Through the field experiment it was determined that the main emission spectrum of the slag stage was from PbS, and the main emission spectrum of the copper stage was from PbO. The relative changes in PbO/PbS emission spectrum provide the method of copper converting process determination. Through using the relative intensity in PbO/PbS emission spectrum the copper smelting process can be divided into two different stages, i.e., the slag stage (S phase) and the copper stage (B phase). In a complete copper smelting cycle, a receiving telescope of appropriate view angle aiming at the converter flame, after noise filtering on the PbO/PbS emission spectrum, the process determination agrees with the actual production. Both the theory and experiment prove that the method of copper converting process determination based on emission spectrum analysis is feasible.
ABSTRACT
An appropriate reference spectrum is essential for the direct-sun differential optical absorption spectroscopy (DS-DOAS). It depends on the real reference spectrum to retrieve the total vertical column density (VCD). The spectrum detected at the time with minimum sun zenith angle under the relative clear atmospheric condition in the measurement period was conventionally selected as the reference spectrum. Because there is still untracked NO2 absorption structure in the reference spectrum, the VCD retrieved based on the above spectrum is actually relative VCD, which results in larger error. To solve this problem, a new method was investigated. A convolution of extraterrestrial high-precision solar Fraunhofer spectrum and the instrumental function of the spectrometer was computed and chosen as the reference spectrum. The error induced by NO2 absorption structure in the reference spectrum was removed. Then the fitting error of slant column density (SCD) retrieved by this method was analyzed. The correlation between the absolute SCD and the differential slant column density (dSCD) was calculated. The result shows that the error of SCD retrieved by this new method is below 1.6 x 10(16) molecules x cm(-2) on March 7, 2011, while the error generated by the normal method is about 4.25 x 10(16) molecules x cm(-2). The new method decreased more than 62% error. In addition, the results throughout the day were compared to the troposphere VCD from MAX-DOAS and they are in good agreement. It indicates that the new method could effectively reduce the VCD error of the common way.
ABSTRACT
The study of comparison of NO2 SCD between two ground-based multi axis DOAS is introduced. The slant columns of NO2 from JAMASTEC are compared with those of AIOFM during the period from November to 31 December 2009. It says that the more signal to noise ratio is obtained by using the adjusted integral time rather than fixed settings; Two instrument show good accordance in the lower viewing angles, with the correlation coefficient of 0.995, but it becomes bad with higher viewing angles. The low deviation between the two instruments was achieved during the period from 9am to 17pm, the results in the 20 degree direction show best agreement with a deviation of 12%, but in other period the deviation becomes larger. The results in the visible range are better than those in the UV range, the residual in the fit decreases by more than 60%, and the results in the visible range show good agreements with those of AIOFM in the UV range during the whole day.
ABSTRACT
Space-borne differential optical absorption spectrometer is used for remote sensing of atmospheric trace gas global distribution. This instrument acquires high accuracy UV/Vis radiation scattered or reflected by air or earth surface, and can monitor distribution and variation of trace gases based on differential optical absorption spectrum algorithm. Spectral calibration is the premise and base of quantification of remote sensing data of the instrument, and the precision of calibration directly decides the level of development and application of the instrument. Considering the characteristic of large field, wide wavelength range, high spatial and spectral resolution of the space-borne differential optical absorption spectrometer, a spectral calibration method is presented, a calibration device was built, the equation of spectral calibration was calculated through peak searching and regression analysis, and finally the full field spectral calibration of the instrument was realized. The precision of spectral calibration was verified with Fraunhofer lines of solar light.
ABSTRACT
The present paper describes how to measure OH radicals in the flame of alcohol burner flame by using XeCl excimer laser. The instrument consists of a XeCl excimer laser as light source, a multiple-reflection cell with whole path length of light achieving 2 560 meters, and a double pass high resolution echelle spectrometer with resolution 3.3 pm. This paper describes the reason for using the XeCl excimer laser without spectral etaloning and how to get rid of the water in reactor chamber. The results of the experiment get some absorption peak of OH radicals from 308.145 to 308.175 nm. By choosing the appropriate fit area and fitting, the results contrast with the measure data by using Xe lamp as light source.
ABSTRACT
The cloud effect correction is very significant to satellite remote sensing of atmospheric trace gases from near-infrared spectrum, even with a small amount of cloud, the remaining effects can still cause retrieval error even reaching up to 100%. Atmospheric carbon monoxide (CO) is one of the most important pollutants in the troposphere. This study, takeing CO as the example, described the cloud effect and the cloud correction on retrieval result from SCIAMACHY measurement. To validate the correction method, we compared both corrected and uncorrected results with the independent ground based FTIR measurements. After the correction, the agreement between satellite observations and FTIR measurements further improves.
ABSTRACT
Based on the scanning differential optical absorption spectroscopy (DOAS) system, field measurement of vertical profiles of HONO and NO2 was performed continuously from Aug. 27, 2007 to Sep. 4, 2007 in Chaoyang District of Beijing, and their vertical profiles were analyzed. Based on the acquired data, the typical vertical variation characteristics of HONO, NO2 and the ratio HONO/NO2 were discussed, and the possible formation sources of HONO were studied. The results indicated that the decrease of HONO with height was faster than the decrease of NO2. The study found good correlation between NO2 and HONO, as well as between the ratio HONO/NO2 and vapor, respectively. Therefore, the authors' conclusion is that HONO was formed by heterogeneous conversion of NO2 on surfaces or near ground and then transported to higher altitudes.
ABSTRACT
Daily ozone column densities were monitored by Passive DOAS (differential optical absorption spectroscopy) from December 10th, 2008 to Feb 19th, 2009 at Zhongshan Station, Antarctic (69 degrees 22'24" S, 76 degrees 22'14" E). Considering the absorption of O3, OClO, NO2, O4, BrO and the Ring effect, ozone slant column densities were retrieved using the zenith scattered sunlight as the light source. The results showed that there was no obvious "ozone hole" during the monitoring period, but ozone VCD (vertical column density) had greatly changed within short time scale, especially in middle December and early February. The analysis of passive DOAS and Brewer measurements of ozone VCD showed good agreement with the correlative coefficient of 0.863, while satellite board OMI measurements with the correlative coefficient of 0.840, which confirmed the validity of the monitoring of Passive DOAS.
ABSTRACT
Formaldehyde (HCHO) is the most abundant carbonyl compounds that play an important role in atmospheric chemistry and photochemical reactions. Formaldehyde is an important indicator of atmospheric reactivity and urban atmospheric aerosol precursors. In the present paper, the emission of formaldehyde from chemical area was measured using the mobile differential optical absorption spectroscopy (DOAS). This instrument uses the zenith scattered sunlight as the light source with successful sampling in the area loop. Vertical column density was retrieved by this system, combined with the meteorological wind field and car speed information, the emission of formaldehyde in the area was estimated. The authors carried out the measuring experiment in one chemical plant in Beijing using this technology. The result showed that the average value of the flux of formaldehyde in this area was 605 kg x h(-1) during the measuring period.
ABSTRACT
The present paper describes a new developed high resolution differential optical absorption spectroscopy instrument used for the measurement of OH radicals in flame. The instrument consists of a Xenon lamp for light source; a double pass high resolution echelle spectrometer with a resolution of 3.3 pm; a multiple-reflection cell of 20 meter base length, in which the light reflects in the cell for 176 times, so the whole path length of light can achieve 3 520 meters. The OH radicals'6 absorption lines around 308 nm were simultaneously observed in the experiment. By using high resolution DOAS technology, the OH radicals in candles, kerosene lamp, and alcohol burner flames were monitored, and their concentrations were also inverted.
ABSTRACT
A method of retrieving NO2 in troposphere based on multi axis differential optical absorption spectroscopy (MAX-DOAS) was introduced. The differential slant column density (dSCD) of NO2 was evaluated by differential optical absorption spectroscopy (DOAS), removing the Fraunhofer structure and Ring effect. Combining the results of different observing directions, the tropospheric NO2 differential slant column density (deltaSCD) was evaluated, and the air mass factor (AMF) was calculated with the radiative transfer model SCIATRAN and the tropospheric NO2 vertical column density (VCD) was retrieved. To ensure the accuracy of the results, it was compared with the results of long path differential optical absorption spectroscopy (LP-DOAS), a good accordance was shown with the correlation coefficients of 0.94027 and 0.96924.
ABSTRACT
Due to heavy air pollutants and aerosols in our country, the model for simultaneous evaluation of aerosol parameters and trace gases based on differential optical absorption spectroscopy is developed in the present paper. The spectra were used to get the concentrations of many trace gases and mean geometrical diameter, total number concentration and total volume of aerosol simultaneously over the same air volume. Retrieval of aerosol parameters was performed by the "table look-up" method based on total extinction coefficient. Experimental results show that trace gases and aerosol parameters can be successfully retrieved using this model.
ABSTRACT
Ozone (O3) often serves as the benchmark for the overall pollution level of a given airshed and it is critical that the measurement technique be accurate and precise, In the DOAS measurement, the accuracy of O3 concentration is determined by the selected spectral range. The present paper focuses on the effect of spectral range on the detected characteristic absorption structure of O3, and the variation of differential cross section of O3 with the change in spectral range and the source of interference in different spectral range. The effect of practical atmospheric light extinction on the light intensities of different spectral ranges was deduced; the effect of spectral range on the accuracy was determined by detecting the standard gases at different concentration and different spectral resolution. The optimized spectral range was determined for O3, which can yield high sensitivity, good selectivity and a reasonable time resolution for the accurate qualitative and quantitative analysis of O3.
ABSTRACT
Based on the differential optical absorption spectroscopy (DOAS) technology, the measurement of air pollutants (SOz, NO2, HONO and HCHO) was performed continuously from Jan 19, 2007 to Feb 8, 2007 in Peking University campus. The typical diurnal variation characteristic of SO2 concentration, the main source and the meteorological factors that influence the pollutants were analyzed. The results indicated that the typical diurnal variation of SO2 concentration has the same shape as the letter "V" when wind speed was low, and in the afternoon the SO2 concentration was the lowest, while in other time it was high. Coal-burning made prominent contribution to the concentration of atmospheric various pollutants in the heating period of Beijing. Wind speed played a leading role and other meteorological factors also have some effect, which resulted from the influence of the meteorology on diffusion, transmission, elimination of air pollutants.
ABSTRACT
The concentration of HONO, NO2, O3 and other atmospheric pollutants were observed continuously by using differential optical absorption spectroscopy (DOAS) from 2007-08-14 to 2007-08-24 in Beijing, China. Diurnal variation characteristics of HONO and NO2 were analyzed. The HONO levels originated from the nocturnal direct emission were discussed. And the correlation between the heterogeneous formation of HONO and its related factors (BC, RH, and so on) was studied. The results showed that HONO had two peaks at about 01:00 and 06:00, respectively, while two peaks of NO2 concentrations appeared at about 01:00 and 07:00. The highest HONO(em)/HONO ratio of 31.3% was observed at about 20:00 between 19:00 to 07:00, and the average ratio was 15%. Good correlation of HONO(corr)/NO2 ratio with BC and RH at night was obtained. The correlation suggested that heterogeneous NO2 to HONO conversion processes may occur on BC surfaces by reaction with absorption water, and the average nighttime conversion frequency from NO2 into HONO (HONO/NO2) was calculated about 0.8% x h(-1). At the same time, the results showed that heterogeneous formation of HONO was increased with RH and inhibited at RH > 80%, and the hypothesis was further supported by detailed analysis of selected case.
