NSIDC Cryosphere Seminar
Viewing passive microwave sea ice concentrations through a magnifying glass: Investigating the potential of enhanced resolution products by Walt Meier, DAAC Scientist, NSIDC
Sea ice concentrations derived from passive microwave observations are one of the longest satellite-derived climate records and changes in Arctic sea ice cover are one of the most iconic indicators of sea ice change. While passive microwave products provide a consistent long-term record and complete polar coverage, their low spatial resolution limits their ability to discern details in the ice cover and precisely map the sea ice edge. In 2016, the NSIDC NASA Snow and Ice Distributed Active Archive Center (DAAC) published a new NASA-funded gridded brightness temperature product, the "Calibrated Enhance-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperatures (CETB)”. This product combines multiple overlapping sensor footprints via signal processing techniques to obtain enhanced resolution gridded brightness temperature fields. Depending on the sensor input, the resolution enhancement is 4 to 8 times higher than the standard gridded products.
Here we derive sea ice concentrations from these enhanced resolution brightness temperatures. We investigate the potential to obtain finer-scale sea ice information, such as polynyas, and to more precisely define the ice edge. Early results indicated an improvement, but not to the full gridded resolution of the CETB product. This is a result of the resolution enhancement processing that yields a gridded resolution finer than the actual effective resolution. Further investigation has defined an approximate effective resolution and developed a method to optimally “upscale” from the CETB resolution to the optimal effective resolution. Case studies show that open water features missed by the standard resolution concentration products can be captured in concentrations derived from the CETB. The CETB also provides twice-daily fields based on local time of day, morning and evening. The concentration fields from the CETB show a clear difference between morning and evening fields near the ice edge, which yields new information on diurnal effects on sea ice. Finally, the CETB uses better calibrated input swath brightness temperatures, providing more consistency between the multitude of sensors across the 40-year record. Sea ice extent derived from these fields show good consistency, indicating that the CETB would be a suitable source for a new long-term sea ice climate record.
This project was funded by the CIRES Innovative Research Program.