GOES-8 Sounder Derived Product Images

The GOES-8 sounder retrieves profiles of temperature and moisture for clear or partly clear fields of view. These retrievals are further processed to produce a derived meteorological product (e.g. total precipitable water). Images of these derived products are generated by combining the sounding product with the 11 um window radiance observed in the cloud-contaminated fields of view. The sounding value is allocated to the first half of the dynamic range of the grey scale used for image presentation, whereas the 11um cloud radiance is allocated to the second half of the grey scale range. The sounding portion of the grey scale is then color-enhanced in order to distinguish the sounding values from the cloud features. Several of the GOES-8 sounder derived products are:

• The land-sea temperature is derived with each retrieval. The algorithm combines moisture corrected window channel temperatures with NMC forecast model fields spatially and temporally interpolated to the retrieval locations, hourly surface observations, and sea surface temperature values from AVHRR.
• The lifted index, an estimate of atmospheric stability, is derived for each retrieval. It represents the buoyancy that an air parcel would experience if mechanically lifted from a mixed boundary layer to the 500-mb level . The lifted index expresses the difference in temperature between the ambient 500-mb temperature and the temperature of the lifted boundary-layer parcel. Negative values (parcels warmer than the environment) represent positive buoyancy, with large negative values indicating the potential for severe storms; positive values denote atmospheric stability. The lifted index is derived from the 500-mb temperature as well as a mean pressure, temperature, and moisture for the boundary layer (all are all available from the retrieved profile).
• The total column precipitable water vapor is obtained by integrating the retrieved moisture profile. Using the radiance measurements in the longwave split windows, the shortwave window, and the 6.5, 7.0, and 7.4 um water vapor bands, the derived product imagery is formed from pixel-by-pixel retrievals of atmospheric temperature and moisture profiles wherever the atmosphere is at least quasi-clear.
• The GOES-8 sounder is also providing an hourly cloud product to supplement the ASOS. This is required by the NWS introduction of the ASOS nationwide. ASOS is designed to support weather forecast activities and aviation operations. ASOS uses automated equipment to provide near-continuous observations of surface weather data including cloud height and amount that are currently obtained by NWS and Federal Aviation Administration observers. The cloud information from the ASOS equipment is limited to altitudes below 12000 ft, and GOES-8 provides supplemental information about cloud cover above 12000 ft at each ASOS site. The combined ASOS/satellite (ASOS/SAT) system depicts cloud conditions at all levels to 25000 ft. Because observations are required every hour, the satellite cloud product can be derived only from the geostationary spacecraft data. The satellite cloud information is derived using sounder data with the CO2 slicing technique, which calculates both cloud-top pressure and effective cloud amount from radiative transfer principles. It also reliably separates transmissive clouds that are partially transparent to terrestrial radiation from opaque clouds in the statistics of cloud cover. For a given ground observation site, the algorithm uses radiation measurements from an area of roughly 50 km x 50 km centered on the site.