Simulations and Information Content of New Water Vapor Bands for the GeoXO Imager

The GeoXO Imager (GXI) will replace the Advanced Baseline Imager (ABI) on the next generation of geostationary NOAA satellites (GeoXO), to be launched in the early 2030s. It will contain two channels at wavelengths that are not present on ABI, one in each of the near- and thermal-infrared portions of the electromagnetic spectrum. Both of these channels aim to improve detection of water vapor in the lower atmosphere and as such will have multiple uses, including evaluation of pre-convective environments. The 0.91 µm channel is located in a water vapor absorption band and is sensitive to total precipitable water. At this wavelength, solar radiation reflected from the surface and atmosphere is attenuated by water vapor, resulting in a decrease in radiation reaching the satellite. The other channel, centered at 5.15 µm, has a weighting function (a balance between atmospheric absorption and emission) that offers peak sensitivity at a lower level in the atmosphere than any existing ABI vapor channel. As such, this channel is sensitive to low-level water vapor, including water vapor in the boundary layer.

Starting with a review of the relevant physics, this work will examine the utility of these new channels as illustrated by realistic satellite simulations driven by the 4 km National Severe Storms Laboratory (NSSL) Weather Research and Forecasting Model (WRF), and utilizing the Community Radiative Transfer Model (CRTM). These simulations, which are produced daily and publicly distributed, reveal, for example, the presence of clear-sky moisture boundaries over the U.S. Great Plains that are difficult to detect with other satellite-based methods. The simulations also illustrate some challenges to overcome, such as the need to develop methods to separate the effects of moisture on the measured radiances from contributions that are dependent on the underlying surface albedo (at 0.91 µm) or surface temperature (at 5.15 µm). Additionally, we utilize the Moderate Resolution Atmospheric Transmission (MODTRAN) to perform idealized simulations designed to help us better understand and ultimately disentangle these competing effects.