Shaw Ping-Shine, Woodward John T, Johnson B Carol, Brown Steven W, Yoon Howard W
Appl Opt. 2021 Dec 10;60(35):10935-10944. doi: 10.1364/AO.444568.
The long-term temporal stability of a spectrograph is one of the most important characteristics affecting the spectrograph's radiometric performance. For many applications, from monitoring ocean color and lunar irradiance to laboratory irradiance measurement standards, the stability of a spectrograph is a primary factor in the overall measurement uncertainty and therefore is the major criterion for the suitability of the spectrograph as an optical-scale transfer standard. Here we report a facility built for testing the long-term radiometric stability of commercial, fiber-coupled spectrographs. The facility uses tungsten quartz-halogen irradiance standard lamps, type "FEL," of the National Institute of Standards and Technology (NIST) as light sources. To ensure the highest stability of these lamps during spectrograph tests, parameters such as lamp current, lamp voltage, and signals from an independent filter radiometer were continuously recorded to monitor any possible instability caused by such effects as lamp aging. Using this facility, we report the stability study of four spectrographs with spectral coverage from the UV to short-wave infrared over an interval of two months during which the lamp irradiance was stable to better than 0.02%. The tested spectrographs show good stability in general, ranging from 0.02% to 0.1% in the visible over a span of 11 days. For a longer two-month test, the variation in spectrograph responses increases by less than 0.1% with no discernable long-term drifts. In addition, we measured the response variation of two of the test spectrographs before and after they were sent to remote field locations and subjected to adverse environmental conditions. In this case, a larger response variation of up to 1.0% dependence on the wavelength was observed. We discuss the performance of the facility and the implications for using these spectrographs for several of NIST's remote sensing projects as radiometric transfer standards based on these stability measurements.
光谱仪的长期时间稳定性是影响其辐射性能的最重要特性之一。对于许多应用，从监测海洋颜色和月球辐照度到实验室辐照度测量标准，光谱仪的稳定性是整体测量不确定度的主要因素，因此是光谱仪作为光学尺度传递标准适用性的主要标准。在此，我们报告一个用于测试商用光纤耦合光谱仪长期辐射稳定性的设施。该设施使用美国国家标准与技术研究院（NIST）的“FEL”型钨石英卤化物辐照度标准灯作为光源。为确保在光谱仪测试期间这些灯的最高稳定性，持续记录灯电流、灯电压以及来自独立滤光片辐射计的信号等参数，以监测由灯老化等效应引起的任何可能的不稳定性。利用该设施，我们报告了对四台光谱仪的稳定性研究，这些光谱仪的光谱覆盖范围从紫外到短波红外，在两个月的时间间隔内，灯辐照度稳定在优于0.02%。测试的光谱仪总体上显示出良好的稳定性，在可见光范围内11天内的变化范围为0.02%至0.1%。对于为期两个月的更长测试，光谱仪响应的变化增加不到0.1%，且没有明显的长期漂移。此外，我们测量了两台测试光谱仪在被送往偏远野外地点并经受不利环境条件前后的响应变化。在这种情况下，观察到高达1.0%的更大响应变化，其与波长有关。我们基于这些稳定性测量结果，讨论了该设施的性能以及将这些光谱仪用作NIST的几个遥感项目的辐射传递标准的意义。
