Using IASI Observations to Resolve HIRS Spectral Response Function Induced Intersatellite Biases

摘要

There are significant challenges in making the observations from HIRS (High Resolution Infrared Radiation Sounder) on the 13+ satellites consistent for climate change detection. It is well known that for HIRS, the inter-satellite biases are significantly affected by differences in the spectral response functions (SRF) between instruments, since they often lead to observations of the atmosphere at different altitudes. The SRF dependent biases are further mixed with other effects such as the diurnal cycle due to observation time differences and orbital drifts, blackbody emissivity, and calibration algorithms. In this study, the IASI (Infrared Atmospheric Sounding Interferometer) observations are used to calculate the HIRS radiances by convolving the IASI observed radiances with the SRF of each HIRS model across different climate zones in different seasons, which separates the SRF induced intersatellite biases from other factors. It is found that the calculated radiance ratios using IASI observations for the HIRS satellite pairs form bell shaped curves that vary with the HIRS model, channel, as well as climate zones. Understanding the characteristics of these bell curves are essential for resolving the SRF dependent intersatellite biases and the development of fundamental climate data records from HIRS.