Evaluating the Absolute Calibration Accuracy and Stability of AIRS using the CMC SST

We compare the daily mean and standard deviation of the difference between the Sea Surface skin Temperature (SST) derived from clear Atmospheric InfraRed Sounder (AIRS) data from seven atmospheric window channels between 2002 and 2020 and collocated Canadian Meteorological Centre (CMC) SST data from the tropical oceans. After correcting the mean difference for cloud contamination and diurnal effects, the remaining bias relative to the CMC SST, is not inconsistent with estimates of the AIRS absolute accuracy based on the uncertainty of the pre-launch calibration. The time series of the bias produces trends well below the 10 mK/yr level required for climate change evaluations. The trends are in the 2 mK/yr range for the five window channels between 790 and 1231 cm-1, and +5 mK/yr for the shortwave channels. Between 2002 and 2020 the time series of the standard deviation of the difference between the AIRS SST and the CMC SST shows the effects of version changes in the CMC SST, but dropped fairly steadily to below 0.4 K in several AIRS window channels, a level previously only seen in SST models relative to the Argo buoys.

本研究对比了2002至2020年间，基于7个大气窗口通道的晴空大气红外探测器（Atmospheric InfraRed Sounder, AIRS）反演得到的海表表皮温度（Sea Surface skin Temperature, SST），与热带海域匹配的加拿大气象中心（Canadian Meteorological Centre, CMC）海表温度数据之间的差值日均值与标准差。在针对云污染与日变化效应修正均值偏差后，相较于CMC海表温度数据的剩余系统偏差，与基于发射前定标不确定性得到的AIRS绝对精度估算结果并无显著矛盾。该偏差的时间序列所呈现的趋势远低于气候变化评估所需的10毫开尔文每年（mK/yr）阈值：其中790至1231波数（cm⁻¹）区间内的5个窗口通道的趋势处于2毫开尔文每年区间，短波通道的趋势则为+5毫开尔文每年。2002至2020年间，AIRS反演海表温度与CMC海表温度差值的标准差时间序列，体现出CMC海表温度版本更新带来的影响；但多个AIRS窗口通道的标准差持续稳步下降，最终降至0.4开尔文以下，这一精度水平此前仅在与阿尔戈浮标（Argo buoys）比对的海表温度模型中被观测到。