On-Orbit Calibration Assessment of AVHRR Longwave Channels on MetOp-A Using IASI
On-Orbit Calibration Assessment of AVHRR Longwave Channels on MetOp-A Using IASI
复制标题
使用 IASI 对 MetOp-A 上的 AVHRR 长波通道进行在轨校准评估
DOI：
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发表时间：
2008
影响因子：
8.2
通讯作者：
C. Cao
中科院分区：
文献类型：
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作者：
Likun Wang;C. Cao
准确和精确的卫星辐射测量对于数值天气预报模式中的数据同化和气候变化检测非常重要。在成功发射红外大气探测干涉仪(IASI)后，多项研究表明，IASI辐射测量得到了很好的定标，并保持了极高的光谱和辐射定标精度。由于其高光谱性质和高质量的测量，IASI辐射度可以作为相对参考，以独立评估共享相同光谱区域的宽带或窄带仪器的辐射测量。在这篇文章中，我们展示了IASI辐射在评估先进的甚高分辨率辐射计(AVHRR)红外(IR)通道测量中的应用。对每个IASI像素内的共同配准的AVHRR像素进行空间平均。然后，我们通过将IASI测量的光谱与AVHRR光谱响应函数卷积，将AVHRR红外通道的空间平均辐射强度与IASI进行了比较。统计发现，在200K-300K的亮温范围内，从AVHRR通道4和5观测到的温度略高于IASI，平均BT差(IASI减去AVHRR)小于0.4K，标准偏差约为0.3K。对于通道4和5，IASI和AVHRR IR通道之间的BT差异都与场景温度有关，这可能是由于AVHRR探测器的非线性造成的。AVHRR通道4和5都显示出轻微的扫描相关偏差，在扫描两端的最大差异约为~0.2K(AVHRR比IASI更热)。
Accurate and precise satellite radiance measurements are important for data assimilations in numerical weather prediction models and for climate-change detection. After the successful launch of the infrared atmospheric sounding interferometer (IASI), several studies have indicated that the IASI radiance measurements are well calibrated and maintain superb spectral and radiometric calibration accuracy. Owing to its hyperspectral nature and high-quality measurements, the IASI radiance can serve as a relative reference to independently assess the radiance measurements of broad- or narrow-band instruments that share the same spectral region. In this paper, we demonstrate the utility of the IASI radiances to evaluate the Advanced Very High Resolution Radiometer (AVHRR) infrared (IR) channel measurements. The coregistered AVHRR pixels inside each IASI pixel are averaged spatially. We then compared the spatially averaged radiance from AVHRR IR channels with IASI by convolving the IASI-measured spectra with the AVHRR spectral response functions. It was found that, statistically, the temperature observed from AVHRR channels 4 and 5 is slightly warmer than that in IASI for the brightness temperature (BT) range of 200 K-300 K. The mean BT difference (IASI minus AVHRR) is less than 0.4 K with a standard deviation of ~0.3 K for AVHRR channels 4 and 5. The BT difference between IASI and AVHRR IR channels is scene-temperature dependent for both channels 4 and 5, which is probably caused by the nonlinearity of the AVHRR detectors. Both AVHRR channels 4 and 5 show slight scan-dependent bias with maximum differences of approximately ~0.2 K (with AVHRR being warmer than IASI) at both ends of the scan.