利用空间外差光谱技术进行紫外高分辨率大气散射信号探测
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摘要
羟基OH对于人类理解中间层化学成分非常重要,它是大气光化学反应中重要的氧化剂,OH在308nm波段受到太阳能量激发,发射出OHA2Σ+-X2Π(0,0)荧光信号。为了探测中间层大气中OH自由基的紫外共振荧光发射信号,从复杂背景信号中分离目标信号,研制了中高层大气OH自由基超分辨空间外差光谱仪,光谱范围为308.2～309.8nm,光谱分辨率为0.008 25nm。临边观测主要探测大气散射信号,能量来源为大气中的粒子,包括大气分子与气溶胶、云等对太阳能量的散射作用。中高层大气OH自由基超分辨空间外差光谱仪基于空间外差光谱技术,可以在设计的闪耀波长范围内获得极高的光谱分辨率,适用于大气成分的精细探测。通过在前置或后置光学系统中加入柱面镜,总视场内的场景被分成多个视场切片,每一个视场切片的干涉图分别成像到对应的探测器行上。利用空间外差光谱仪具有空间维分层成像功能,临边观测时可以同时获取不同高度层大气吸收光谱的散射辐射信号,无需像传统临边探测遥感器在不同高度层进行扫描来获取大气高度维的廓线信息。为了验证中高层大气OH自由基超分辨空间外差光谱仪的临边散射信号探测能力与对观测几何的敏感性,进行了地面临边观测实验,探测紫外308nm波段大气散射信号。模拟临边观测几何,选取晴朗无云的一天,在空旷场地对大气散射信号进行观测。由于仪器基于空间外差光谱技术,需要对干涉数据进行干涉误差修正与光谱复原。对一段观测时间内间隔10分钟的干涉数据进行光谱复原并定标,得到最终临边观测光谱。由于散射信号的主要来源为大气分子对太阳光的散射作用,因此光谱中应包含太阳光谱高分辨率精细特征信息。从高分辨率太阳光谱中选取三个特征信息窗,分析观测光谱中对应波段,三个特征信息窗完全匹配,验证了中高层大气OH自由基超分辨空间外差光谱仪的超高分辨率光谱探测能力和光谱精细信息提取能力。将太阳辐射计实时测量获得的气溶胶光学厚度及根据观测时间计算的太阳天顶角与太阳方位角输入辐射传输模型SCIATRAN,结合对应日期与经纬度的大气廓线数据库,得到模拟光谱,将实测结果与辐射传输模型结果进行比对,两者残差较小。实测结果与模拟结果存在的残差,可能是由于大气环境参数并没有完全符合实测状态,后续可使用当地实时温湿压廓线对模拟数据库进行替换,使辐射传输模型更接近实际状态。与辐射传输模型对比的结果验证了中高层大气OH自由基超分辨空间外差光谱仪的散射信号探测能力与对观测几何的敏感性,验证了在轨探测多谱段、宽谱段大气散射光谱与OH目标信号的可行性,为在轨探测OH目标信号提供了理论与实验基础。
The hydroxyl(OH)radical is the most important oxidizing agent in the photochemical reactions which helps to understand the atmospheric components and photochemistry events in mesosphere.OH radical's solar resonance fluorescence A2Σ+-X2Π(0,0)is the excited emergent light by solar radiation around 308 nm.Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical is developed to detect OH ultraviolet solar resonance fluorescence in mesosphere and separate target signal from complex background signal.The spectral range is 308.2～309.8nm and its spectral resolution is 0.008 25 nm.Limb observation mode detects atmospheric scattering signal which consists of atmospheric molecules,aerosols and cloud scattered by solar energy.Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical is based on Spatial Heterodyne Spectroscopy technique.SHS technique receives rather high spectral resolution around Littrow wavelength and is applicable to fine detection of atmospheric components.Adding cylindrical lens front or behind the optical system results in several split-fields of view.Each split corresponds line of detector imaging plane.Limb observation can obtain limb-scattered signal at different height simultaneously using layered imaging in spatial dimension with SHS technique rather than traditional limb detector scanning at different height.In order to validate detection ability and sensitivity to observation geometry of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical,aground-based limb observation experiment is built up to detect atmospheric limb-scattered signal around 308 nm.Simulating limb mode geometry in a clear sky,limb-scattered radiation is detected in an open place.Interferogram error correction and spectrum restoration are needed due to the fact that the instrument is based on SHS.Spectrum restoration and calibration are done to a serial interferogram data at 10 min interval in a period of observation time to obtain final spectrum.The source of scattered radiation is the atmospheric molecule's scattering of sunlight,so the spectrum should contain high-resolution features information of solar spectrum.Choose 3feature windows from high-resolution solar spectrum and analyze correspond band in observation spectrum.It turns out that the feature windows match completely.The results can validate detection ability and fine spectrum extracting ability of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical.Radiative transfer model is set using real time aerosol optical thickness measured by solar radiometer,real time solar zenith and azimuth angle and atmospheric profiles with corresponding date,longitude and latitude.A comparison is taken between simulation spectrum and observation spectrum.Their residual is rather small.The residual between them due to the mismatch between atmospheric parameters setting and actual situation.Real time temperature and pressure profiles are considered to bring in radiative transfer model in the future.These results validate limb-scattered radiation detection ability and fine spectrum extracting ability and sensitivity to observation geometry of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical.The experiment results not only validate the feasibility in detecting multi-band and broad-band limb-scattered signal and OH target signal on orbit,but also provide theoretical and experimental foundation for orbital limb-scattering signal detection.
The hydroxyl(OH)radical is the most important oxidizing agent in the photochemical reactions which helps to understand the atmospheric components and photochemistry events in mesosphere.OH radical's solar resonance fluorescence A2Σ+-X2Π(0,0)is the excited emergent light by solar radiation around 308 nm.Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical is developed to detect OH ultraviolet solar resonance fluorescence in mesosphere and separate target signal from complex background signal.The spectral range is 308.2～309.8nm and its spectral resolution is 0.008 25 nm.Limb observation mode detects atmospheric scattering signal which consists of atmospheric molecules,aerosols and cloud scattered by solar energy.Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical is based on Spatial Heterodyne Spectroscopy technique.SHS technique receives rather high spectral resolution around Littrow wavelength and is applicable to fine detection of atmospheric components.Adding cylindrical lens front or behind the optical system results in several split-fields of view.Each split corresponds line of detector imaging plane.Limb observation can obtain limb-scattered signal at different height simultaneously using layered imaging in spatial dimension with SHS technique rather than traditional limb detector scanning at different height.In order to validate detection ability and sensitivity to observation geometry of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical,aground-based limb observation experiment is built up to detect atmospheric limb-scattered signal around 308 nm.Simulating limb mode geometry in a clear sky,limb-scattered radiation is detected in an open place.Interferogram error correction and spectrum restoration are needed due to the fact that the instrument is based on SHS.Spectrum restoration and calibration are done to a serial interferogram data at 10 min interval in a period of observation time to obtain final spectrum.The source of scattered radiation is the atmospheric molecule's scattering of sunlight,so the spectrum should contain high-resolution features information of solar spectrum.Choose 3feature windows from high-resolution solar spectrum and analyze correspond band in observation spectrum.It turns out that the feature windows match completely.The results can validate detection ability and fine spectrum extracting ability of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical.Radiative transfer model is set using real time aerosol optical thickness measured by solar radiometer,real time solar zenith and azimuth angle and atmospheric profiles with corresponding date,longitude and latitude.A comparison is taken between simulation spectrum and observation spectrum.Their residual is rather small.The residual between them due to the mismatch between atmospheric parameters setting and actual situation.Real time temperature and pressure profiles are considered to bring in radiative transfer model in the future.These results validate limb-scattered radiation detection ability and fine spectrum extracting ability and sensitivity to observation geometry of Hyper-spectral Resolution Spectrometer for Mesospheric OH Radical.The experiment results not only validate the feasibility in detecting multi-band and broad-band limb-scattered signal and OH target signal on orbit,but also provide theoretical and experimental foundation for orbital limb-scattering signal detection.
引文
[1] Kaiser J W,Atmospheric Parameter Retrieval from UV-Vis-NIR Limb Scattering Measurements.Bremen:University of Bremen,2001.
[2] Gattinger R L,Degenstein D A,Llewellyn E J.Journal of Geophysical.Research,2006,111:D13303.
[3] Llewellyn E J,Lloyd N D,et al.Canadian Journal of Physics,2004,82:411.
[4] Englert C R,Stevens M H,Siskind D E,et al.Journal of Geophysical Research,2010,115:D20306.
[5] Hanlander J,Roesler F L.Proceedings of SPIE,1990,1235:622.
[6] Cageao R P,Ha Y L,Jiang Y,et al.Journal of Quantitative Spectroscopy Radiative Transfer,1997,57:703.
[7] LI Zhi-wei(李志伟).Hefei:University of Chinese Academy of Sciences(合肥:中国科学院大学),2015.
[8] SHI Hai-liang,LI Zhi-wei,LUO Hai-yan,et al(施海亮,李志伟,罗海燕,等).Spectroscopy and Spectral Analysis(光谱学与光谱分析),2017,37(3):933.
[9] WANG Zi-jun(汪自军).Jilin:Jilin University(吉林:吉林大学),2011.
[10] Rozanov A,Rozanov V,Buchwitz M,et al.Advances in Space Research,2005,36:1015.
[11] Rozanov V V,Rozanov A V.University of Bremen,Germany,2013.
[12] Marc-Andre Soucy,Francois Chateauneuf,Christophe Deutsch,et al.Proceedings of SPIE,0277-786X,2002.
[2] Gattinger R L,Degenstein D A,Llewellyn E J.Journal of Geophysical.Research,2006,111:D13303.
[3] Llewellyn E J,Lloyd N D,et al.Canadian Journal of Physics,2004,82:411.
[4] Englert C R,Stevens M H,Siskind D E,et al.Journal of Geophysical Research,2010,115:D20306.
[5] Hanlander J,Roesler F L.Proceedings of SPIE,1990,1235:622.
[6] Cageao R P,Ha Y L,Jiang Y,et al.Journal of Quantitative Spectroscopy Radiative Transfer,1997,57:703.
[7] LI Zhi-wei(李志伟).Hefei:University of Chinese Academy of Sciences(合肥:中国科学院大学),2015.
[8] SHI Hai-liang,LI Zhi-wei,LUO Hai-yan,et al(施海亮,李志伟,罗海燕,等).Spectroscopy and Spectral Analysis(光谱学与光谱分析),2017,37(3):933.
[9] WANG Zi-jun(汪自军).Jilin:Jilin University(吉林:吉林大学),2011.
[10] Rozanov A,Rozanov V,Buchwitz M,et al.Advances in Space Research,2005,36:1015.
[11] Rozanov V V,Rozanov A V.University of Bremen,Germany,2013.
[12] Marc-Andre Soucy,Francois Chateauneuf,Christophe Deutsch,et al.Proceedings of SPIE,0277-786X,2002.