Simulating satellite infrared sounding retrievals in support of Observing System Simulation Experiments (OSSEs)

A new set of Observing System Simulation Experiments (OSSEs) are underway to assess the impact of higher spatial and temporal resolution sounding on hurricane forecast accuracy. To support these studies, we have developed an OSSE retrieval simulation system. The system uses a simulated satellite orbit track to provide sample locations and footprint area of the infrared sounder configuration to be simulated over the region of interest. The data to be sampled are an OSSE nature run developed by the NOAA Atlantic Oceanographic Meteorological Laboratory (AOML) and the University of Miami (UM). The nature run is sampled at the sounder locations and integrated over the sounder footprint area. The resulting averaged profiles are smoothed vertically with simulated averaging kernels for the Atmospheric Infrared Sounder (AIRS) using a linear retrieval simulation to produce calculated temperature and water vapor profiles. With reasonable fidelity, the sampled and smoothed profiles simulate the retrievals we can expect from a sounder like AIRS for the orbit and sampling configurations under test. Three instruments were simulated corresponding to the AIRS 45x45km footprint in LEO, a hypothetical sounder at 2x2km footprint in LEO, and a hypothetical GEO sounder at 5x5km regional and 10km x 10km full disk footprint sizes. RMS error relative to the nature run is calculated to demonstrate the error characteristics of the simulation system. The simulated retrievals as a result of this effort are currently being assessed by NOAA AOML in an OSSE study to determine the impact of advanced hyperspectral infrared sounders on hurricane forecast improvement.