Study On Atmospheric Imaging Instrument With Nadir And Omnidirectional Limb Fields Of View

Information on the composition of the atmosphere helps humans to study the global climate,which guides human production and life.Space-based remote sensing atmospheric detection method is a highly efficient detection method.Researching the space-based remote sensing atmospheric detection method plays an important role in the fields of climate prediction,early warning,and protection and treatment of pollution.According to actual needs,this paper deeply researches a space-based atmospheric remote sensing imaging detection method,and proposes a multi-spectral and hyperspectral atmospheric detection method with dual optical paths sharing optical elements and detector.Based on the analysis principle and feasibility,a prototype of a dual optical path and multispectral imaging system was built to verify the feasibility of this atmospheric remote sensing detection method.At present,the atmospheric remote sensing load in China only has a single detection mode,and the detection range is also small,which makes it difficult to interpret later.In order to improve the coverage of the limb view,this paper applies the principle of panoramic imaging to atmospheric limb detection.A panoramic annular lens is used to receive the omnidirectional range of limb radiation.The beam is folded back twice inside the panoramic annular lens twice.The cross-check method can improve the accuracy of limb inversion.The data from the limb detection can interpret the atmospheric profile,but not the total amount.In order to obtain the total information of the atmosphere,a front lens group is placed in front of the panoramic annular lens,and the beam of the nadir field of view enters the optical system from the front lens.For a nadir field of view,a panoramic ring lens is equivalent to a thick lens.The two light paths at the nadir and the limb are focused on the same image plane,and the focus shapes are a bright spot and a ring surrounding the bright spot.The focal length of the nadir and limb view is 4.86 mm and 5.75 mm respectively,and the field of view is 10° and 360° ×(70.32°~72.82°)respectively.When the instrument works at a 400 km orbit altitude,it can detect the atmosphere with a height range of 10-100 km from the limb zone,and the nadir coverage is 70 km.Since the ultraviolet to visible region has characteristic spectral bands of the atmosphere and aerosol molecules,six spectral bands are selected in this wavelength range,and the bands are separated using filters.In the optical design process,some key technologies have been studied,such as the method of increasing the illumination of the large field of view and the design method of the panoramic annular lens.The optical model of the remote sensing instrument shows that the design result has a good imaging quality.Given that the image plane shape of the nadir and limb fields of view isnot a long strip,a slit cannot be placed on the image plane and the solar radiation cannot be separated by using a grating or prism.This paper proposes and designs a method that uses acousto-optic tunable filter(AOTF)instead of grating or prism to perform hyperspectral imaging detection.We optimized and improved the previous multispectral detection model,and added an AOTF module and a relay lens module.This details of the design and optimization method of this optical system is described in this paper.The physical simulation model shows that the AOTF dual-field hyperspectral detection system has good imaging detection effect.The proposal of the atmospheric hyperspectral detection method fills the blank in China in related fields,and also provides a new idea for China's space-based hyperspectral detection.In order to realize the engineering of the detector with nadir and omnidirectional limb views,the sensitivity of the multispectral model based on filters was analyzed and the corresponding mechanical structure was designed.In order to meet the detection requirements of the two fields of view,the mechanical structure is frame type,and then the processing and assembly of the optical machine components of the prototype are completed.Because the limb ring-shaped field of view of the prototype is large,it is difficult to complete high-precision calibration at one time.The method of segmented field of view calibration is adopted to improve the calibration accuracy.The measured focal length of the prototype is slightly larger than the designed focal length,which guarantees the resolution requirements.The static MTF and external field test results show that the prototype works well and validates the design theory.This method of simultaneous detecting the nadir and omnidirectional limb views can improve the efficiency of space-based atmospheric detection,save the detection costs,and provide an important reference direction for future atmospheric detection.