圆形渐变滤光片光谱辐射计辐射定标

Radiometric Calibration of Circular Variable Filter Type Spectroradiometer

基于分区线性法对圆形渐变滤光片型光谱辐射计开展辐射定标研究,以解决温度范围大、工作波段宽的测量目标对该类型光谱辐射计造成的非线性问题。所提光谱辐射计的主要技术原理是将待测目标的温度区间分为多个子区间,采集目标温度区间内多个不同温度黑体对应的测量光谱,并计算各个温度下的响应度函数。在进行红外光谱测量时,将目标光谱与区间内记录的不同温度点光谱进行比对,从而确定待测目标所属温度子区间的上下限。根据子区间计算的响应度函数,通过线性插值求得待测目标的响应度函数并进行辐射定标。基于该方法的实验结果表明,待测目标理论辐亮度与使用分区线性法进行辐射定标得到的辐亮度在波长范围内的平均偏差小于1%。通过定标结果反演测量黑体的等效温度,等效温度误差小于2%。

Objective Spectroradiometers are used to determine the spectral characteristics and brightness of radiation sources,which are widely used in many different fields.This study is based on the circular variable filter type spectroradiometer,where the wavelength transmitted by the main spectroscopic component,the circular variable filter is linearly related to the angle,and the spectroradiometer is constructed with a unit detector.This type of spectroradiometer has the advantages of a wide spectral range and a wide temperature range for the target,so it has a wider range of applications.However,there are fewer studies on circular variable filter spectroradiometers in China and abroad,and the development of domestic machines for circular variable filter spectroradiometers is gradually being carried out in China.Radiation calibration is the process of converting the original signal measured by the instrument into a physical quantity with practical significance.The main methods of radiation calibration for infrared spectroradiometers are currently the single point method,the two points method,and so on.The single point method is suitable for cases with low resolution and a small amount of spectral measurement data.The two-point method is suitable for situations where the instrument has good linearity,and the number of measurement points is high.Due to the wide operating band of the circular variable filter type infrared spectroradiometer and the wide range of the target temperature,which causes non-linearity problems,the traditional two-point calibration method cannot achieve accurate radiation calibration.In this paper,a divisional linearity-based responsivity radiometric calibration method is proposed to solve this problem.Methods The radiometric calibration of circular variable filter spectroradiometers is based on the divisional linearity method,which is used to solve the non-linearity problem of this type of spectroradiometer due to the large temperature range of the measurement target and the wide operating band.The main technical principle is to divide the temperature interval of the target to be measured into several subintervals,collect the measured spectrums corresponding to several different temperature blackbodies in the target temperature interval,and calculate the responsivity function at each temperature.During the infrared spectroscopy measurements,the target spectrum is compared with the spectrums of different temperature points recorded in the interval to determine the upper and lower limits of the temperature subinterval to which the target to be measured belongs.Based on the responsivity function calculated for the subinterval,a linear interpolation is performed to find the responsivity function of the target to be measured for radiometric calibration.In addition,external ambient temperature variations,atmospheric disturbances,and the instrument's thermal radiation are taken into account in the calibration process.Results and Discussions In this paper,we propose a divisional linearity-based responsivity radiometric calibration method,which can effectively solve the non-linearity problem caused by the wide wavelength range and wide temperature range of the target measurement by zoning the target temperature into sub-regions.We compare the difference between the measured calibration data and the theoretical Planck curve at different temperatures.Figure 12 shows the relative deviation of the radiometric calibrations of two detectors at different blackbody temperatures.Figure 12 shows that the relative deviations of the radiometric calibrations are better than 1%for most of the band intervals for both detectors.The large relative deviations in some bands are due to two reasons:1)the low responses of the InSb detector in the 2.4-3μm region and the MCT detector in the 13.5-14.3μm region are due to the low signal-to-noise ratio of the collected signals in this region,which affects the calibration accuracy;2)the InSb detector in the 4.2-4.5μm region is due to the interference of CO_(2) atmospheric absorption in this band.The interference of CO_(2) atmospheric absorption exists.The experimental results show that this method can effectively meet the radiometric calibration requirements,and the calibration results are in good agreement with the theoretical values,with an equivalent temperature deviation of less than 2%.Conclusions The large temperature range and the wide operating band of the circular variable filter spectroradiometer make for a significant non-linear response in the radiometric calibration process. Different temperature targets also have different degrees of responsiveness, so the traditional two-point method does not work well for radiometric calibrations. In addition, external ambient temperature variations, atmospheric disturbances, and the instrument's thermal radiation are taken into account in the calibration process. In this paper, a divisional linearity-based radiometric calibration method is proposed, which can effectively solve the non-linearity problem caused by the wide wavelength range and temperature range of the target measurement by zoning the target temperature into sub-regions. The experimental results show that the method can effectively meet the radiometric calibration requirements, and the calibration results are in good agreement with the theoretical values, with an equivalent temperature deviation of less than 2%. The zoned linear radiometric calibration method in this paper is also applicable to other spectroradiometers of the spectral type to solve the non-linearity problem caused by the measurement of targets with a wide wavelength and temperature range.