Research On The Relationship Between The Typical Structure Of Granite And The Dichroism Of Reflection Spectrum

To solve the problem of "same object with different spectrum" and deepen the application of remote sensing in geology,one of the effective ways is to establish a rock BRDF model.In this study,widely distributed granites were used as the research object.8 monzonitic granites samples with similar composition,different structure and surface morphology were selected based on field sampling and indoor identification.Systematic BRDF measurement and surface morphology measurement were carried out to explore the BRDF characteristics of granite and their relationship to the typical structure and surface morphology.In the experiment,the BRDF measuring device independently developed by the National Key Laboratory of Remote Sensing Information and Image Analysis Technology was used to measure the BRDF of main reflection plane and three-dimensional surface of the sample's polished and natural surface and a binocular stereo vision system was used to mapping the natural surface morphology.Then,the wavelength characteristics of granite's BRDF was explored by the the auther proposed method of quantitatively analyzing the strength of BRDF and selecting the best bands,the variogram and multifractal spectrum was used to describe rock structures.After that,the BRDF characteristics of granite were described,and the relationship between granite structure,natural surface morphology and BRDF was explored.Finally,a empirical formula between structure and BRDF was obtained by polynomial fitting,and the parameters of structure granularity are determined.The main achievement and results are as follows:(1)The variogram can effectively distinguish the granite structure and porphyritic structure,while the multifractal spectrum can further classify the granite structure.(2)Two parameters are proposed to evaluate best BRDF bands:normalized extremum difference of spectral channel BRDF and dispersion degree of standard deviation set of reflectance at each reflection Angle.It was found that the difference of granite's BRDF decreases with the increase of wavelength,indicating that the shorter the wavelength is,the more obvious the BRDF is.Through data fitting,it was found that the greater the incident zenith Angle is,the more sensitive the granite's BRDF is to the wavelength change.Finally,600-900 nm was selected as the best BRDF band.(3)The measurement and processing results of the BRDF in main reflection plane showed that the main reflection planes of all polished surface have obvious cosine characteristic.The characteristic of the main reflection plane of the natural surface is different,the middle and fine grains granite structure still show the characteristic of cosine,while the middle and coarse grains granite structure do not show the cosine characteristic,but show the characteristic of reduced forward reflection.(4)The results of measurement and processing results of the BRDF in three-dimensional reflecting surface showed that both BRDF of the polished surface and the natural surface showed the "bowl edge effect"-low middle and high surrounding.But the medium coarse grain granite structure showed the difference of "bowl edge rolling" compared with the fine grain.Both the main reflection plane and the three-dimensional BRDF bear obvious directional reflection characteristics,and the larger the incident zenith Angle,the higher the reflectance.(5)The statistical analysis of the relationship between the BRDF and structure of granite showed that: at the same incident Angle,the smaller the particle size,the higher the BRDF of granite.Moreover,the BRDF curves of different samples are very similar at the same particle size,showing a stable characteristic.The effect of particle size variation on BRDF is similar at different incident angles.(6)The statistical analysis of the relationship between the BRDF and the surface morphology showed that the natural surface is rougher than the ground surface,with stronger Lambert property and weaker duality characteristics.The high morphology in the forward scattering direction leads to the decrease of the intensity of forward scattering radiation.Small protrusions lead to increased reflectivity in a specific direction,thus showing abrupt directional reflection characteristics on the BRDF curves.The main problems in this paper are as follows: due to the limited time and the complicated and slow measurement process,the number of measured samples was limited.At the same time,the mathematical expression model of rock structure is not deep enough,so the relationship model between structure and BRDF characteristics is only limited to the polished surface,and the quantitative relation model between the natural surface and BRDF has not been established.