Fuqi Si

Effect of AO/UV/RD exposure on spaceborne diffusers: a comparative experiment.

The environmental measuring instrument (EMI) is a nadir-viewing wide-field imaging spectrometer, which adopts spaceborne diffusers in in-flight calibration systems, including an aluminum diffuser and a quartz volume diffuser. Spaceborne diffusers, are the key components of in-flight calibration systems, and are used to introduce sunlight into the EMI. Hemispheric reflectance and bidirectional reflectance distribution function were experimentally measured to analyze spaceborne diffuser performance. Radiation exposure experiments on atomic oxygen, UV, and radiation dose of the spaceborne diffusers were performed at ground level because the EMI works in low Earth orbit space environments. Effects of radiation exposure on spaceborne diffusers were discussed in detail. Protective methods were introduced to reduce the effects of the space environment, and an in-orbit monitoring method was also proposed.

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet (UV) spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands (320-335 nm) using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model (Tracy). The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.

Observation of tropospheric NO2 by airborne multi-axis differential optical absorption spectroscopy in the Pearl River Delta region, south China

An airborne multi-axis differential optical absorption spectroscopic (AMAX-DOAS) instrument was developed and applied to measure tropospheric NO2 in the Pearl River Delta region in the south of China. By combining the measurements in nadir and zenith directions and analyzing the UV and visible spectral region using the DOAS method, information about tropospheric NO2 vertical columns was obtained. Strong tropospheric NO2 signals were detected when flying over heavilly polluted regions and point sources like plants. The AMAX-DOAS results were compared with ground-based MAX-DOAS observations in the southwest of Zhuhai city using the same parameters for radiative transport calculations. The difference in vertical column data between the two instruments is about 8%. Our data were also compared with those from OMI and fair agreement was obtained with a correlation coefficient R of 0.61. The difference between the two instruments can be attributed to the different spatial resolution and the temporal mismatch during the measurements.

Preflight Evaluation of the Performance of the Chinese Environmental Trace Gas Monitoring Instrument (EMI) by Spectral Analyses of Nitrogen Dioxide

The Environmental trace gas Monitoring Instrument (EMI) onboard the Chinese high-resolution remote sensing satellite GaoFen-5 is an ultraviolet–visible imaging spectrometer, aiming to quantify the global distribution of tropospheric and stratospheric trace gases and planned to be launched in spring 2018. The preflight calibration phase is essential to characterize the properties and performance of the EMI in order to provide information for data processing and trace gas retrievals. In this paper, we present the first EMI measurement of nitrogen dioxide (NO2) from a gas absorption cell using scattered sunlight as the light source by the differential optical absorption spectroscopy technique. The retrieved NO2 column densities in the UV and Vis wavelength ranges are consistent with the column density in the gas cell calculated from the NO2 mixing ratio and the length of the gas cell. Furthermore, the differences of the retrieved NO2 column densities among the adjoining spatial rows of the detector are less than 3%. This variation is similar to the well-known “stripes-pattern” of the Ozone Monitoring Instrument and is probably caused by remaining systematic effects like a nonperfect description of the individual instrument functions. Finally, the signal-to-noise ratios of EMI in-orbit measurements of NO2 are estimated on the basis of on-ground scattered sunlight measurements and radiative transfer model simulations. Based on our results, we conclude that the EMI is capable of measuring the global distribution of the NO2 column with the retrieval precision and accuracy better than 3% for the tested wavelength ranges and viewing angles.

Measurement of Ammonia by a Portable UV-DOAS Gas Sensor Based on Multi-Pass Cell

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.

Electronic correction method for environment monitoring instrument

The space-borne Environment Monitoring Instrument detects the Earths 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.

Research and Application of Air Mercury Measurement Based on Transverse Zeeman Background Correction

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.

Simultaneous measurements of atmospheric NO2 and HONO using IBBCEAS with a near-ultraviolet LED

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.

Measurement of tropospheric SO2 by airborne MAXDOAS in Pearl River delta region in China

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.