地物光谱仪测量中的温湿度影响

地物光谱仪在遥感领域的应用日益重要，可用于研究不同地物条件下可见和红外的光谱辐射特性，从而获得地表的光谱辐射亮度、光谱辐射照度或方向反射因子等信息。地物光谱特性的准确测量是光学遥感定量分析的基础，对于航天传感器定标、遥感数据反演等具有极其重要的意义。地物光谱仪在测量前必须进行光谱辐射定标，一方面定标过程中地物光谱仪的光谱响应特性可能发生漂移，另一方面测量时的环境与定标环境可能差异较大，都会影响测量的准确性。在恒温恒湿条件下，实验采用谱线灯光源和积分球光源考察了地物光谱仪波长和光谱响应度随探测器温度的变化。数据显示当光谱仪内部硅阵列探测器温度上升时，波长位置并未发生改变；而光谱仪的光谱响应度随着温度上升明显增大。当硅探测器温度从28.3 ℃升至35.2 ℃时，光谱仪在380～990 nm的光谱响应度变化达到1.8%～7.3%；同时近红外1 000～1 800 nm的平均变化约3.0%，2 000～2 500 nm的变化约1.9%。当改变环境温度和湿度时，测量数据表明湿度影响主要在大气中水分子的吸收峰附近波长，对其他波长影响很小；光谱仪光谱响应度与内部探测器的温度近似存在一一对应关系，环境温度的影响可以近似根据内部探测器温度变化予以表征。理论上当环境条件改变时，根据光谱响应度随温度的变化和探测器的监测温度，可以进行光谱数据修正。最后，实验测量了一组探测器温度下对应的光谱响应度，采用多项式拟合和最小二乘法建立了地物光谱仪光谱响应度与温度的函数关系。根据函数关系插值得到的光谱响应度修正因子和直接测量得到的数据基本一致，全谱段的差异几乎都小于0.2%，表明光谱响应度与温度的对应关系可用于解决不同环境条件下的测量准确性。

Temperature and Humidity Influence in Field Spectroradiometer Measurement

Field spectroradiometer is becoming more and more important in the remote sensing area.It is used to investigate the spectral radiometric characteristics of different geographic environment,such as spectral radiance,spectral irradiance or spectral directional reflectance factor from visible to infrared wavelengths.The accuracy of the spectral measurements plays an important role in space sensor calibration and remote sensing data inversion.It is the basis of quantitative analysis in optical remote sensing.Field spectroradiometer must be calibrated before use.On the one hand,the spectral responsivity may change during the calibration process.On the other hand,the field measurement environment may be totally different from the calibration conditions.The measurement accuracy cannot be guaranteed.The experiment is designed to investigate the influence of the environmental conditions on spectral responsivity.At constant temperature and humidity,spectral line lamp,and integrating sphere lamp are used to test whether the wavelength and spectral responsivity change or not when the silicon array detector’s temperature is changed.Results show that the wavelength is nearly unchanged when the silicon array detector’s temperature rises.However,the spectral responsivity rises as the temperature rises.When the silicon array detector’s temperature rises from28.3 to 35.2℃,the spectral responsivity increases by 1.8%to 7.3%from 380 to 990 nm,3.0%from 1000 to 1800 nm and1.9%from 2000 to 2500 nm.When the environment humidity and temperature are changed,results show that humidity only affects the spectral responsivity near the water molecules’absorption peaks.Also,results show that the spectral responsivity has nearly one to one correspondence with detector temperature.The influence of environment temperature can be nearly characterized according to the detector temperature change.When a group of detector temperature and corresponding spectral responsivity is measured,the relationship between the detector temperature and spectral responsivity can be obtained using the least square method.The spectral responsivity at other temperature can be calculated by interpolation.The measurement data at different environmental conditions can be corrected as long as the detector temperature is measured.The spectral responsivity difference between the calculated and measured results is less than 0.2%when the detector is 35℃,which show that the relationship between the detector temperature and spectral responsivity can be used to solve the environment problem.