Climate data records with past, present and future hyperspectral infrared sounders: information content and continuity

Climate change is largely determined by the strong correlation between atmospheric chemistry (e.g., trace gas composition) and structure (e.g., vertical temperature and humidity gradients). Satellite measurements have been key in characterizing trends in cloud properties and top of atmosphere radiance, for example. Their unbiased global coverage and sampling rate make them ideal sources of information for global trend analysis. Hyperspectral infrared sounders measure the atmospheric column with high vertical resolution. Four sounders are operational in polar-orbit at present; the Atmospheric Infrared Sounder (AIRS) launched in 2002 on Aqua, Infrared Atmospheric Sounding Interferometer (IASI) launched in 2006 on Metop-A, the Cross-track Infrared Sounder (CRIS) launched on NPP in 2011, and IASI launched in 2013 on Metop-B. The Dual-Regression (DR) retrieval algorithm (released under the University of Wisconsin-Madison Community Software Processing Package, CSPP) was developed to retrieve coincident vertical atmospheric profiles, surface and cloud properties from all four sounders. With more than a decade of high-resolution vertical information available about the atmospheric column and a single retrieval algorithm to apply to all of them, we can investigate the information content of each instrument with respect to geophysical atmospheric properties. The question is whether retrieved geophysical information from these instruments can be used to construct climate data records, i.e., a continuous global record of geophysical parameters that are instrument independent. The objective is to achieve comparable signal-to-noise ratios (SNR) in retrieved information from each instrument to facilitate information continuity. We will investigate the retrieval accuracy and SNR for each instrument with respect to temperature and humidity profiles, trace gases (e.g., CO2, O3 and CO) as well as cloud top height and optical thickness. An analysis of the bias each instrument introduces will help determine whether multi-instrument decadal data records can be constructed, e.g., AIRS + IASI, followed by CrIS + IASI in future (AIRS and CrIS are on PM orbits, and both IASI instruments are on AM orbits). It will also give insight into the potential for data continuity among past, present and future hyperspectral sounders. These instruments have the potential to make a significant contribution to the understanding of long-term global trends in atmospheric chemistry and structure.