Hyperspectral data in numerical weather prediction

From the early 1970s satellite sounding data have formed a vital part of the meteorological database, particularly in the data sparse southern hemisphere. First, the NOAA Vertical Temperature Profile Radiometer (VTPR) Data and then the NOAA High Resolution Infrared Radiometer Spectrometer (HIRS), the Microwave Sounding Unit (MSU) and the Advanced Microwave Sounding Unit (AMSU), provided invaluable data for numerical weather analysis and prediction. The global beneficial impact of these instruments was facilitated by strong international collaboration. In 2002 the NASA Atmospheric Infrared Sounder (AIRS) was launched on AQUA, the second of the EOS polar-orbiting satellites. It was followed in 2006 by the EUMETSAT IASI instrument on MetOp. The AIRS was the first of a new generation of meteorological advanced sounders able to provide hyperspectral data for operational and research use. The improved spectral resolution it provided compared to earlier passive infrared sounders, led to a significant increase in vertical resolution and accuracy in determining thermal and moisture fields, increased accuracy in the determination of the concentrations of absorbers such as ozone and considerably improved numerical weather prediction (NWP), (Le Marshall et al. 2006). Experiments which showed the first significant benefits from AIRS data in NWP are described. It is shown in these experiments that the benefits resulted from an expanded use of the information content of infrared hyperspectral radiance data. Experiments which have shown the benefit of improved spatial coverage, spectral coverage and the use of moisture channel data, are summarised in this paper. Also shown is the benefit available to NWP from using hyperspectral radiance data from fields of view containing clouds. Again it has been demonstrated that a more complete use of the information content in the observations available from hyperspectral sounders has resulted in improved benefits to numerical weather prediction. This conclusion is also supported by experiments reporting the benefits from using IASI data. Overall, the results indicate the significant benefits already derived from hyperspectral data assimilation and the benefits yet to be gained from an enhanced use of the information content contained in hyperspectral radiance observations.