Study On Data Correction Of Environmental Trace Gas Monitoring Instrument

As the environmental problems on the earth become severe increasingly,the atmospheric trace gas monitoring has attracted more and more attention.And the monitoring methods have evolved from ground-based and air-borne monitoring to satellite remote sensing.Based on the advantages of satellite remote sensing,such as,high viewpoint and wide field of vision,fast data collection,and repeatable continuous observation,it has played a significant role in atmospheric monitoring.The Environmental trace gas Monitoring Instrument(EMI)is an imaging spectrometer with a 4-channel back-illuminated frame transfer CCD detector.It is used to measure the scattered and reflected radiation from the sun,to retrieve atmospheric trace gases(O3,NO2,SO2,etc)and obtain the formation and transport process of the regional trace gases.So it can be employed in the composition detection and warning technical system of regional atmospher.In order to improve the spectral data of EMI and achieve accurate inversion of trace gas concentration,this paper analyzes the noise characteristics of the CCD from the characteristics of the CCD detector,including dark current,smear and pixel response non-uniformity(PRNU).By establishing EMI forward data model,the data process of 0-lb level was obtained.And through the process flow,the electronic correction method of EMI spectral image was analyzed and confirmed.It provides an effective processing algorithm and theoretical basis for obtaining higher quality spectral image data.For the dark current noise,a CCD refrigeration control system,first designed according to the principle of its temperature dependence,is to suppress the CCD dark current noise of ultraviolet channel and improve the system signal-to-noise ratio.Temperature stability of ±0.05? is achieved by controlling the integrated semiconductor refrigerator inside the CCD and using artificial PID method.Secondly,a dark current temperature correction algorithm is proposed by introducing the temperature correction factor,to achieve dark current correction at different temperatures.Based on CCD dark pixels,an image dark current correction algorithm is proposed to achieve dark current correction of spectral images.Finally,the dark current correction in the spatial dimension of the spectral image was completed by dark current calibration and CCD signal readout.For the pollution signal generated by the smear effect of CCD,a data model of smear signal was established based on the CCD frame transfer characteristics.An image correction algorithm was proposed by eliminating the smear signal from EMI raw data.For the stripe noise caused by the pixel-response non-uniformity(PRNU)of the CCD,the linear characteristics of the EMI radiation response was first verified through experiments.According to the linear response characteristics,a linear imaging model was established by the two-point method,to calculate the correction coefficient matrix of PRNU.The comparison result,gained by measuring spectral images,shows that PRNU has been improved greatly and it can be applied to the spectral image correction of on-orbit measurement data.The above data correction method has been applied to the ground sample gas measurement test.Spectral data is processed according to the data processing method of 0-1 b level,and NO2 gas concentration is retrieved by DO AS algorithm.The correction results has been checked and compared by the in-orbit data.The results show fitting residual is decreased by spectral image correction,improving the retrieval accuracy of EMI data greatly.