The space-borne Environment Monitoring Instrument detects the Earth's surface radiation from ultraviolet to visible band, and it could be used to inverse the trace gas concentrations of target area. To obtain the 1b radiation data products, raw measurement data (level 0 data) should be corrected and modulated. Based on CCD detectors and payload’s characteristics, the electronic correction processing flow and data correction algorithm are proposed, and dark current, electronic offset, Smear and PRNU are also corrected. By using this algorithm, the ground level 0 test data are corrected. The result shows that the corrected data can improve the accuracy of the data; it can be used to process the data which are measured in orbit observation; it strongly guarantees the formation of further level 2 data products.
A space-borne differential optical absorption spectrometer is a high precision aerospace optical remote sensor. It obtains the hyper-spectral，high spatial resolution radiation information by using the spectrometer with CCD（Charge Coupled Device）array detectors. Since a few CCDs are used as the key detector, the performance of the entire instrument is greatly affected by working condition of CCDs. The temperature of CCD modules has a great impact on the instrument measurement accuracy. It requires strict temperature control. The selection of the thermal conductive filler sticking CCD to the radiator is important in the CCD thermal design. Besides，due tothe complex and compact structure, it needs to take into account the anti-pollution of the optical system. Therefore, it puts forward high requirements on the selection of the conductive filler. In this paper, according to the structure characteristics of the CCD modules and the distribution of heat consumption, the thermal analysis tool I-DEAS/TMG is utilized to compute and simulate the temperature level of the CCD modules, while filling in thermal grease and thermal pad respectively. The temperature distribution of CCD heat dissipation in typical operating conditions is obtained. In addition, the heat balance test was carried out under the condition of two kinds of thermal conductive fillers. The thermal control of CCD was tested under various conditions, and the results were compared with the results of thermal analysis. The results show that there are some differences in thermal performance between the two kinds of thermal conductive fillers. Although they both can meet the thermal performance requirements of the instrument, either would be chosen taking account of other conditions and requirements such as anti-pollution and insulation. The content and results of this paper will be a good reference for the thermal design of the CCD in the aerospace optical payload.
Mercury is known as a highly toxic metal, which will have a significant health hazard to the human body. To monitor the trace mercury pollution in air, the development of monitoring instruments has been conducted. In this paper the mercury analyzer is developed based on the cold atomic absorption spectrometry theory by exploiting the transverse Zeeman-Effect background correction technology. The experiments have been done to test the performance of the system. At the same time, the same experiments with RA-915 mercury analyzer have been done to compare with the results. First, zero gas was measured for an hour and high concentration mercury sample gas was measured for four days. The results of zero gas shows that the detection limit of the system is 2.19ng/m3 and the standard deviation is 0.73. The concentration fluctuation is within a tight range of ±1.5ng/m3. The results of high concentration sample gas are in good agreement with the results of RA-915, and the correlation coefficient is 0.95. Second, laboratory air was measured for 12 hours. The results compared with RA-915 are in good agreement and have the same variation trend. Additionally, the atmospheric mercury concentration near the non-ferrous metal smelter in Tongling city has been measured by the system and the RA-915. The measurement results from two analyzers have a good linear correlation with correlation coefficient of 0.98 and slope of 1.027. It indicates that the system has accurate background correction ability, low detection limit and is applicable to long-term air mercury on-line monitoring.
The multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique is being widely used in the monitoring of trace gases column density. In this paper, a retrieval method of visibility from O4 slant column density measured with MAX-DOAS is present. O4 slant column density is sensitive to the change of aerosol properties, and aerosol properties determine the atmospheric visibility. The relationship of atmospheric visibility and O4 slant column density is analyzed, and a retrieval algorithm to convert the O4 differential slant column density into visibility is described. MAX-DOAS observation is carried out, and atmospheric visibility is retrieved successfully. The visibility measured with MAX-DOAS shows good agreement with the result obtained with visibility meter, proving the feasibility of the retrieval method. This research presents a simple and effective monitoring method of visibility with MAX-DOAS, expands the application of MAX-DOAS technique.
High sensitivity simultaneous measurements of atmospheric NO2 and HONO using incoherent broadband cavityenhanced absorption spectroscopy (IBBCEAS) were developed. A near-ultraviolet light emitting diode (LED) peaked at 372 nm was used as light source of the IBBCEAS instrument to measure the absorption of NO2 and HONO in the spectral range of 361-378 nm. Concentrations of atmospheric NO2 and HONO were retrieved from the absorption spectra recorded in the absence of atmospheric aerosols and the average detection limits of 2.9 ppbv for NO2 and 1.2 ppbv for HONO with an acquisition time of 5 min were achieved. The results demonstrated high sensitivity of this measurement technique based on IBBCEAS, which is a promising technique for measurements of atmospheric trace gases.
Ammonia, the third most important abundant nitrogen compound, is a primary alkaline gas in the atmosphere. It has
strong absorption bands in the deep ultraviolet (DUV) spectral range and so can be reliably detected by the differential
optical absorption spectroscopy (DOAS) technique. A portable UV-DOAS gas sensor based on multi-pass cell has been
designed to detected trace gases, especially for ammonia, in the DUV spectral range, with good performance using a
broad-band Deuterium source and high-sensitivity spectrometer. With the optical path as long as 20m, such a sensor
could detected NH3 concentrations as low as 100ppb according to the result of in-situ measurement. Fast response time
and low measurement error of this portable gas sensor could be competent for emergency monitoring.
The tropospheric SO2 in Pearl River delta region was firstly measured by airborne Multi Axis
Differential Optical Absorption Spectroscopy in China on 10 December, 2008. The SO2 slant columns
were derived with DOAS method in the wavelength from 310~ 325nm and the vertical columns were
retrieved by radiative transfer model SCIATRAN. High values were observed near power plant regions
with the vertical column density values higher than 8x1016molec./cm2 in the measurement. Combining
with the meteorological data from local station the SO2 flux from the power plant was calculated, the
emission flux of SO2 was about 2.59x1025molec./s. Over the city of Zhuhai, the observed SO2 vertical column density was 2.46x1016molec./cm2. This is in good agreement with ground-based MAX-DOAS
of 2.62x1016molec./cm2 if the same aerosol parameter settings and a well mixed boundary layer of 1000 m is assumed.