Orthogonal Tunable Spatial Heterodyne Spectroscopy For Solar Hyperspectral Remote Sensing

The sun is the earth's only source of energy.For the study of solar physics,the solar spectrum describes the outer layer of the sun,and its long-term changes can be used to study the life evolution of stars.For atmospheric physics,solar spectrum can be used to verify the temperature,composition,and density of the solar atmosphere.In terms of climate physics,the accurately measured solar spectrum is not only conducive to more accurate inversion of atmospheric and aerosol concentration and distribution but also can be used to explain the variation of atmospheric parameters driven by solar activity.Therefore,the long-term stable and high-precision measurement of Solar Spectral Irradiance(SSI)is of great scientific value and practical significance.Existing SSI remote sensing instruments are based on dispersion to obtain spectrum,spectral resolution is generally low,while SSI has more spectral lines in ultraviolet and visible bands,energy changes dramatically,so the spectral resolution of remote sensing instruments put forward higher requirements.Compared with the traditional dispersive spectrometer,Fourier transform spectroscopy has the characteristics of high light flux and high spectral resolution.Tunable spatial heterodyne spectroscopy(TSHS)is a kind of Fourier transform spectroscopy.Based on spatial heterodyne spectroscopy(SHS),the tunable rotating axis is introduced to expand the measured spectral range while maintaining the ultra-high spectral resolution of SHS.However,on the one hand,the existing TSHS structure design can not consider the high spectral resolution,single tuned rotating shaft,single dispersion element,and symmetrical optical path design,which will affect the spectral performance of the system,and bring difficulties in engineering implementation and calibration.On the other hand,the existing SHS structures are all based on the grating,and the transverse interference region is greatly limited due to the separation of diffraction light wavefront and energy front,which is particularly prominent when the target spectrum is continuous,resulting in lower spectral resolution than expected.In contrast,orthogonal tunable spatial heterodyne spectroscopy overcomes these problems existing in the existing TSHS technology and is a new Fourier transform spectroscopy technology with an ultra-high spectral resolution,wide spectral range,high light flux,and high stability.Compared with the existing TSHS technology,this technology adopts the orthogonal optical path design in TSHS design for the first time.The design simplifies the mechanical design,reduces the difficulty of calibration and installation,and has engineering feasibility while maintaining the high spectral resolution and wide spectral range.Meanwhile,for the first time in SHS and TSHS design,"prism+plane mirror" is used to construct the form of spatial heterodyne.This modification not only avoids the separation of grating diffraction light wavefront and energy front,resulting in limited transverse interference but also significantly improves the light flux level and spectral range of the system.Compared with the existing SSI remote sensing equipment,this technology significantly improves the spectral resolution of ultraviolet and visible bands without sacrificing the spectral detection range,and the theoretical spectral resolution is better than 2500 within the spectral range of 10000cm-1?24691cm-1(405nm-1000nm).In the visible light band,the maximum spectral resolution of existing SSI remote sensing equipment is 400?800(SSIM,CIOMP).And this technology does not need a slit and has the characteristics of high light flux.In this paper,the new quadrature tunable spatial heterodyne spectroscopy is studied systematically.The main contents include:1.Based on the analysis of the demand for solar spectral irradiance remote sensing,the development status and trend of existing in-orbit SSI spectral remote sensing instruments and tunable spatial heterodyne spectral technology are summarized.The basic theories of Fourier transform spectroscopy,spatial heterodyne spectroscopy,and tunable spatial heterodyne spectroscopy are introduced in detail,the basic ideas and principles of orthogonal tunable spatial heterodyne spectroscopy are proposed and elaborated,and the basic theoretical system of orthogonal tunable spatial heterodyne spectroscopy is established.2.The idea and principle of constructing spatial heterodyne by diffraction grating are analyzed in-depth,and the equivalent spatial heterodyne form is constructed by"dispersion prism+reflector",and the selection basis of dispersion element is discussed in detail.Aiming at this new spatial heterodyne,the function expressions of important parameters of the system and the matching relation between key components are calculated,the optimization algorithm of "ghost line" removal is given,and the nonlinear mapping relation between spatial frequency and incident light wave number is established.3.For orthogonal spatial heterodyne spectroscopy can be tuned on optical system model,through the simulation model of system main components of the position and Angle error tolerance for the perfect analysis,to guide the system with tuning scheme is determined,the final design and building of orthogonal type tunable spatial heterodyne spectroscopy principle prototype.Combined with Talbot spectrometer and power spectrum estimation method,a spectral calibration method with accuracy better than 3pm was established.The calibration mercury spectral lamp was used to perform high-precision spectral calibration on the orthogonal TSHS experimental prototype proposed by us,and the external stray light level of the system was analyzed.4.A complete data processing process was established,and spectral reconstruction experiments were carried out for the linear spectrum of 405nm?600nm mercury lamp and the continuous spectrum of 600nm?1000nm xenon lamp by using the theoretical prototype.The reconstructed line spectral position of the mercury lamp is the same as the theoretical position,and the spectral resolution is in line with the expectation.The reconstructed continuous spectrum data of the xenon lamp is consistent with the measurement results of Ocean USB4000,a Marine optical shelf product.It shows that the orthogonal tunable spatial heterodyne spectroscopy has the feasibility of SSI spatial remote sensing application.