光谱辐射测量仪器温度修正方法的研究及验证

光谱辐射定标是光学遥感仪器研制中的关键环节。深入分析实验室定标的光谱辐射测量仪器至户外应用的不确定度来源，环境温度是限制仪器户外高精度测量的最主要因素之一。传统的光谱辐射度实验室定标通常在室温（~25 ℃）下进行，而户外光谱辐射测量处于不同温度环境，严重影响仪器测量的准确度。设计搭建实验测量系统，采用遥感辐射领域常用的光谱辐射测量仪器，研究环境温度对光谱辐射测量的影响。实验结果显示：常用光谱辐射计（CR-280）的测量结果受温度影响明显，在10～40 ℃之间变化时，仪器光谱辐射亮度测量值在400～700nm波段内的偏差为±5%左右，而700～1 050 nm内的偏差高达±15%左右。这主要由于仪器采用硅探测器，红外波段恰好与硅的带边接近，硅探测器易受温度影响，温度增加硅的带边会向长波方向移动，光谱辐射计的响应度也随之增加。基于实验数据统计分析，提出一种适用于不同类型光谱辐射计的温度修正方法，相对于传统的斜率/截距（S/B）算法适用性更广，还可由公式计算出任意温度下的修正结果。修正后CR-280红外波段的偏差（950 nm左右）由±10%降低为±1%，明显减小了因户外使用与实验室定标温度不同造成的测量结果偏差。此外，利用不同类型光谱辐射测量仪器（Avantes及SVC HR-1024）对温度修正方法进行验证。环境温度变化时光谱仪Avantes（VIS/NIR）的测量结果存在较大偏差（1 060 nm高达±17%）。通过温度修正方法运算，仪器修正值与定标值的偏差在±1%以内。光谱辐射计（SVC HR-1024）不同波段的测量值，与定标值的偏差受温度影响不同。这主要由于：仪器由Si、制冷型InGaAs及扩展InGaAs探测器组成，Si探测器受温度影响大，950～1 000 nm波段测量值与定标值的偏差高达±10%。而制冷型InGaAs可有效控制探测器温度，受温度的直接影响相对小。但随温度增加，InGaAs探测器制冷效果受限（制冷最佳工作温度为20 ℃），测量结果产生偏差（1%~3%）。同样，利用温度修正公式对不同温度下SVC HR-1024的测量结果进行修正运算，仪器因温度变化引起的偏差可降低至±1%以内。

Laboratory Calibration and Temperature Research of Spectral Radiometric Instruments

The uncertainty of laboratory calibrated spectroradiometers used in field was analyzed. Ambient temperature is one of the most important factors limiting the accuracy of outdoor measurements. Currently, the laboratory calibrations are generally performed at room temperature (25±1.0) ℃]. However, the spectrometers applied in earth observation and remote sensing is usually operated in the field under different ambient temperature conditions. The calibration coefficients determined under room temperature are not applicable to data collected in field conditions. In this paper, the experimental measurement system was set up, which was used to investigate the temperature effects. The sensitivity of spectroradiometers (CR-280) at different wavelengths was affected differently by ambient temperature. The deviation of 400～700 nm between measured and calibrated value at 40° is about ±5%. The deviation of near-infrared wavelengths (1 050 nm) is about ±15%, this spectral range is close to the band edge of the silicon, which is highly temperature sensitive, and the silicon band edge moved to longer wavelengths as increasing temperature. It is important to reduce the deviation of measured results in field after laboratory calibration. Here, a temperature correction method by matrix calculation for different kinds of spectroradiometers was proposed, which calculated the spectroradiometer response at each pixel. The correction method was also verified with a randomly selected temperature. It can reduce the deviation of CR-280 from ±10% to ±1% in the near-infrared wavelengths (about 950 nm). The temperature correction method can be easily used for spectral radiometry measurement in the field, which can be greatly improves the accuracy of spectral radiometry measurement. Also, the other two kinds of spectroradiometers (Avantes, SVC H-1024) were used to verify this correction method. The result showed the deviation of Avantes (VIS/NIR) between measured and calibrated value (about 1 060 nm) is reduced from ±17% to ±1%. At different ambient temperatures, the deviations between the measured and calibrated values of SVC HR-1024 are different. The instrument consists of three detectors: Si, cooled InGaAs and extended InGaAs. Si detector is greatly affected by temperature, and the deviation of the measured and calibrated value (950～1 000 nm) is as high as ±10%. The cooled InGaAs can effectively control the detector temperature. However, as the ambient temperature increases, the InGaAs detector is affected (the optimal working environment for cooling is about 20 ℃), and the deviation of measuredand calibrated value results is 1%~3%. The temperature correction formulas were used to correct the measured results. The deviation of SVC HR-1024 can be reduced to ±1%.