Research On Multispectral Light Field Camera For Phenological Observation

Originated from national major research instrument development project "China phenology network" automatic monitoring equipment.The snapshot multispectral light field camera solutions based on the statistical invariance of vegetation feature bands was proposed to solve the lack of multispectral equipment in the phenological observations of China.In this paper,the theoretical model,system design,simulation and data processing of multispectral light field camera embodied micro-lens array had been carried out.Firstly,the basic theory of light field was described by matrix method.It included 4D matrix expression on dual planes,the matrix operation involved in transmission,acquisition and recording of light field.The matrix transformation equations caused by the shifting and rotating between double planes and direction changed by lens were derivated.Matrix recording models of several kinds of light field acquisition methods included camera arrays,pinholes and mask code type and so on were given.Secondly,mathematical model of light field camera were formulated.According to the position and role of the micro-lens array in light path,the light field cameras can be divided into field type and aperture type.Respectively for the two different forms,the plane involving in light field transfer were defined,the light field transfer models were established from the 3D scene point to the detector focal plane considering all kinds of errors,the light field sampling models based on discreteness of micro-lens and detectors were established,the radiation transfer model based on information invariance of light radiation and linearity of detector response were established.The signal distributions on the focal plane of two kinds were obtained by the numerical simulation using MATLAB software.By comparing,the scheme of multispectral light field imaging was confirmed,spectral measurement model was established.Again,the important relations were discussed,included the distance between main lens and micro-lens,the distance between micro-lens and detector,the F number of main lens and micro-lens.In accordance with the needs for multispectral camera of phenology and the statistical invariance of vegetation feature bands,nine channels multispectral light field camera were designed.It consisted a telecentric optical system and focal plane assembly integration with micro-lens and detector.It is verificated by ray tracing simulation using ASAP software.In order to reduce the cost,nine channel light field spectrometer was designed.It could obtain the scene image and target spectrum by focusing.It is verified the using ASAP software simulation and prototype system.Finally,the data processing methods of multispectral light field camera were established,included model and method for light field reconstruction,multispectral reconstruction,image re-focus,three-dimensional reconstruction.The corresponding parameter calibration and simplified processing methods were discussed.Multispectral light field data simulated from hyperspectral data and raw data obtained from commercial light field camera were used to verify the relevant treatment,the clear of the multispectral image and the distance information valid the methods.