Calibration of SeaWiFS after two years on orbit
Calibration of SeaWiFS after two years on orbit
复制标题
SeaWiFS 在轨运行两年后的校准
DOI：
10.1117/12.373189
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
C. McClain
中科院分区：
文献类型：
--
作者：
R. Barnes;C. McClain
1997年8月1日发射了海洋观测宽视场传感器，1997年9月4日拍摄了第一批地球图像。1997年9月9日开始通过机载扩散器对太阳进行定期的每日测量，1997年11月14日开始对月球进行定期的每月测量。这些月球测量首次在EUROPTO'98上报告，为确定SeaWiFS辐射灵敏度的变化提供了一种高度灵敏的方法。SeaWiFS使用的发射前辐射校准是1997年春季在航天器制造商的设施中进行的。校准测量是由美国国家标准与技术研究所（NIST）和SeaWiFS项目的一个团队进行的。对于八个SeaWiFS波段，这种校准的不确定性范围为2%至3%。此外，1993年11月，就在向航天器制造商交付SeaWiFS之前，在仪器制造商的设施对太阳进行了一系列室外测量。这些太阳测量，使用仪器的漫射器，与一套单独的太阳辐射计测量相结合，以确定大气的透射率。在SeaWiFS开始在轨测量时，该仪器再次进行了太阳测量。这两组测量构成了转移到轨道的实验。根据地面测量结果，预测了SeaWiFS波段在轨道上的输出。对于每个波段，初始在轨测量结果与预测值的一致性小于21/2%，转移到轨道实验的不确定度约为3%~ 4%。从1997年11月14日至1999年6月29日，海洋WiFS对月球进行了20次测量。这里介绍的月球测量分析对EUROPTO'98上介绍的分析有微小的修改。从目前的分析中得出的趋势线是从1997年11月14日至1997年9月4日推算出来的，以说明在地球测量的头662天中辐射灵敏度的变化。这些趋势线的不确定性约为1%。根据这些来源，我们估计SeaWiFS辐射的总体不确定性约为4%。基于从SeaWiFS之前的海洋颜色计划中吸取的经验教训，SeaWiFS计划在夏威夷群岛附近使用浮标为SeaWiFS提供“海洋真相”。浮标提供离开海洋表面的光谱辐射的测量。这些测量结果进行了比较，从“仪器/大气算法系统”的SeaWiFS，因为大气模型是用来链接的光谱辐射在大气层的顶部，在海洋表面。使用MOBY，SeaWiFS的替代校准为仪器的实验室校准系数提供了3.2%或更低的修正。这些校正应用于光谱的可见光部分的波段。MOBY不提供近红外波段的替代校准。
The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was launched on 1 August 1997, and the first Earth images were taken on 4 September 1997. Regular, daily measurements of the sun, via the onboard diffuser, started on 9 September 1997 and regular, monthly measurements of the moon on November 14, 1997. These lunar measurements, as first reported at EUROPTO'98, provide a highly sensitive method for determining the change in the radiometric sensitivity of SeaWiFS. The prelaunch radiometric calibration used by SeaWiFS was performed in the Spring of 1997 at the spacecraft manufacturer's facility. The calibration measurements were made by a team from the National Institute of Standards and Technology (NIST) and the SeaWiFS Project. The uncertainties in this calibration range from 2% to 3% for the eight SeaWiFS bands. In addition, a set of outdoor measurements of the sun were made at the instrument manufacturer's facility in November 1993, just before the delivery of SeaWiFS to the spacecraft manufacturer. These solar measurements, using the instrument's diffuser, were combined with a separate set of solar radiometer measurements to determine the transmittance of the atmosphere. At the start of on-orbit measurements by SeaWiFS, solar measurements were made again by the instrument. These two sets of measurements make up the transfer-to-orbit experiment. From the ground measurements, the outputs of the SeaWiFS bands on orbit were predicted. For each band, the output from the initial on-orbit measurements agree with the predicted values by 21/2% or less. The uncertainties for the transfer-to-orbit experiment are estimated to be approximately 3% to 4%. From 14 November 1997 to 29 June 1999, SeaWiFS has made 20 measurements of the moon. The analysis of lunar measurements presented here has minor modifications to that presented at EUROPTO'98. The trend lines from the current analysis have been extrapolated back from 14 November 1997 to 4 September 1997 to describe the changes in the radiometric sensitivity over the first 662 days of Earth measurements. The uncertainties in these trend lines are approximately 1%. From these sources, we estimate the overall uncertainty in the SeaWiFS radiances to be about 4%. Based on the lessons learned from the ocean color program that preceded SeaWiFS, the SeaWiFS Program uses a buoy near the Hawaiian Islands to provide 'sea truth' for SeaWiFS. The buoy provides measurements of the spectral radiances leaving the ocean surface. These measurements are compared with those from the 'instrument/atmospheric algorithm system' for SeaWiFS, since an atmospheric model is used to link the spectral radiances at the top of the atmosphere to those at the ocean surface. Using MOBY, the vicarious calibration of SeaWiFS has provided corrections of 3.2% or less to the laboratory calibration coefficients for the instrument. These corrections are applied to the bands in the visible portion of the spectrum. MOBY does not provide a vicarious calibration for the bands in the near infrared.