The Impact of Infrared Spectral Band Selection on Remotely-Sensed Thermodynamic Profile Information Content

Hyperspectral infrared (IR) sounders provide radiance measurements that are critical for both data assimilation in numerical weather prediction (NWP) models and thermodynamic retrievals for nowcasting. Historically, NWP data assimilation channel sets prioritize channels with information about the middle and upper troposphere over near-surface information, given the lower sensitivity of the IR sensors to the near surface layer from space-based platforms. Similarly, operational retrievals from IR sounders, such as the NOAA Unique Combined Atmospheric Processing System (NUCAPS) compare favorably with radiosonde profiles in the free troposphere, but differ significantly in the planetary boundary layer (PBL). The 2017 Decadal Survey highlighted these weaknesses and designated improved observations of temperature and water vapor within the PBL as a target observable for improved observations in the future.

A potential solution to improving remotely sensed soundings of the PBL is to combine space-based sounders with a network of ground-based sensors. This has previously been shown to provide significant improvements in information content, vertical resolution, and reductions in retrieval uncertainty in the lowest 1000 m above ground level compared to space-based sounding alone. A critical component of planning a new satellite mission are the sensor design decisions; with IR sounders, identifying the critical spectral band coverage is one of the major decisions. This presentation will assess information content of the thermodynamic profile across the lowest 2000 m above ground level across various spectral bands in the thermal IR from both space-based and ground-based perspectives in order to inform IR sensor design for future observing missions. Initial results suggest that the majority of information about the PBL, from a space-based perspective, is in the atmospheric window around 12.5 um. These results will be compared to the typical Cross-track Infrared Sounder (CrIS) and Infrared Atmospheric Sounding Interferometer (IASI) channel selections for NWP data assimilation to identify the key spectral regions where additional near-surface information may be gained from space-based IR sounders. Furthermore, the priority of spectral channels from a synergy of space-based and ground-based IR sensors will be shown.