观测角度对岩石热红外光谱解混影响的实验研究

Experimental Study on the Effect of Observation Angle on Thermal Infrared Spectral Unmixing of Rock

岩石定量遥感是矿产资源探测与地质环境监测的主要手段,光谱解混是岩矿定量遥感的重要方法。在实际应用中,由于卫星对地观测受地形起伏的影响,观测具有一定的角度,导致所测发射率光谱产生变异。但在目前的研究中,解混所采用的矿物端元光谱,是在实验室垂直试样表面观测得到的,忽略了观测角度对发射率光谱的影响,降低了光谱解混精度。因此,有必要将观测角度作为影响岩石光谱解混的因素,研究其对光谱解混精度的影响。首先,将常见的石英、正长石和斜长石矿物表面制作成一般粗糙度,并设计0°~77°共9个观测角度实测发射率光谱,分析观测角度对矿物热红外光谱特征的影响。其次,利用观测角度13°~77°的矿物端元,构建相应角度虚拟岩石光谱,并用0°的矿物端元光谱解混9个观测角度的岩石光谱,分析观测角度对岩石热红外光谱解混的影响。结果表明:(1)在0°~20°范围,观测角度对光谱影响较弱,从30°开始,影响显著。基本规律是:随着角度的增加,光谱吸收深度增加,但各波段处的情况不尽相同。CF特征在观测角度大于50°之后向短波方向移动明显;RF特征处的吸收谷在观测角度大于20°之后显著加深,且谷底位置向短波方向移动;TF特征在观测角度大于40°之后发射率显著降低。表明观测角度的变化,会引起光谱特征的明显变化。(2)在0°~20°范围内,观测角度对光谱解混影响不明显,解混误差小于5%;当观测角度大于20°时,观测角度对光谱解混有显著影响,30°~77°解混误差均大于5%,平均解混误差达到17.2%,解混精度较低。这表明,在基于光谱解混方法进行岩石矿物组分定量反演时,需要考虑观测角度的影响,这对于提高反演精度、准确确定岩石类型具有重要意义。

Rock quantitative remote sensing has gradually become the main means of mineral resources exploration and geological environment monitoring,and spectral unmixing is an important method for rock quantitative remote sensing.However,in practical application,because the satellite’s observation of the earth is influenced by topographic fluctuation,the observation has a certain angle,resulting in the variation of the measured emissivity spectrum.However,in the present study,the mineral endmember spectrum used for unmixing is obtained by vertical observation on the surface of the sample in the laboratory,ignoring the observation angle’s effect on the emissivity spectrum and reducing the unmixing spectral accuracy.Therefore,in this work,the observation angle is taken as the consideration factor to influence the unmixing spectral accuracy of rock.First,the common quartz,orthoclase and plagioclase surfaces are fabricated into general roughness,and a total of nine observation angles of 0°~77°are designed to observe the emissivity spectrum,and the effects on the thermal infrared spectral characteristics of the observation angles are analyzed.Secondly,using the mineral endmember with the observation angle of 13°~77°,the corresponding angle virtual rock spectrum is constructed,and the rock spectrum of 9 observation angles is unmixed with the mineral endmember of 0°spectrum,and the effect of the observation angle on the thermal infrared spectrum unmixing of rock is analyzed.The results show that:(1)in the range of 0°~20°,the observation angle has a weak effect on the spectrum,and the influence is significant from starting at 30°.Basic law:As the angle increases,the spectral absorption depth increases,but the situation at each band is different.The CF moves obviously to the short band direction after the observation angle is more than 50°.The absorption valley of RF is significantly deeper than 20°,and the valley bottom moves in short band direction.The emissivity of TF decreases significantly after the observation angles are greater than 40°.Therefore,the change of observation angle,will cause the obvious change of spectral characteristics.(2)In the range of 0°~20°,the effect of observation angle on spectral unmixing is not obvious,and the error of unmixing is less than 5%.When the observation angle is greater than 20°,the observation angle significantly affects spectral unmixing,the error of unmixing at 30°~77°is more than 5%,the average unmixing error reaches 17.2%,and the unmixing accuracy is low.This indicates that when the quantitative inversion of rock mineral components based on the spectral unmixing method is carried out,the influence of observation angle is considered,which is of great significance to improve the inversion accuracy and accurately determine the rock type.