The GOES-8 sounder (see Table 1 for instrument features) has 18 thermal infrared bands plus a low-resolution visible band. The field of view is 8 km and is sampled every 10 km; 13 bit data is transmitted. The GOES-8 sounder spectral selection was mostly patterned after the High-resolution Infrared Radiation Sounder (HIRS) carried on the NOAA polar-orbiting satellite. It has six bands in the 15 um (longwave) band, a split-window pair, three midtropospheric water-sensitive bands and an ozone band (midwave), five 4 um (shortwave) bands, and a visible band. The spectral bands, some at wavelengths never obtained before in geosynchronous orbit, are sensitive to temperature, moisture, and ozone. Table 2 summarizes the spectral band performance characteristics for the GOES-8 sounder, measured in-flight. Table 3 shows the in-flight determination of noise performance of the GOES-8 sounder and compares it with the GOES-7 VAS and NOAA-12 HIRS performance. The GOES-8 sounder's design goal, like the imager's, is to provide brightness temperatures with 1.0K absolute accuracy and 0.3K relative precision. The quality of the absolute calibration is evident when collocated GOES-8 sounder and VAS radiances are compared; the brightness temperatures for the different spectral bands on each instrument are charted as a function of wavenumber. The GOES-8 sounder and VAS radiances agree within 2.0K; the GOES-8 sounder's additional spectral bands provide more atmospheric detail. The full-time availability of the GOES-8 sounder enables operational sounding products for the first time; this has the potential for contributing significantly to mesoscale forecasting over the conterminous United States, monitoring thermal winds over oceans, and supplementing the Automated Surface Observing System (ASOS) with upper-level cloud information. The GOES-8 sounder will also allow for the development of a number of advanced products.

Sounder imagery

The following imagery demonstrates the sounder's capabilities for a representative sampling of its long, mid, and short-wave spectral bands:

Long-, mid-, and short-wave imagery from the GOES-8 sounder at 1414 UTC on 6 June 1994. Carbon dioxide sensitive longwave band 4 (13.7 micrometer) sees the middle to upper level tropospheric temperature patterns. Smooth transitions showing the cooling further north are evident in clear regions; this is proof of the good signal to noise accomplished in this difficult portion of the spectrum. Water vapor sensitive midwave band 11 (7.0 micrometer) sees the middle tropospheric moisture fields. Dry pockets are obvious in Colorado/New Mexico, Texas, Louisiana/Mississippi, and Michigan. Carbon dioxide sensitive shortwave band 14 (4.5 micrometer) sees the middle to lower level tropospheric temperature field; contrast with band 4 indicates the warming in the lower atmosphere. The distribution of all GOES-8 sounder bands by spectral region and sensitivity to primary atmospheric constituents is given in the lower right panel.
Images from four of the longwave carbon dioxide bands of the GOES-8 sounder are shown for 1146 UTC on 7 October 1994 over the central United States. From the upper left panel (band 2 at 14.4 micrometers) across to the right (band 3 at 14.1), and then from the lower left (band 4 at 14.0) across to the right (band 5 at 13.4), the imagery depicts a process of progressively sensing lower and lower into the atmosphere, as the wavelengths of the sensed radiation decrease. See how the equivalent blackbody (or "radiative") temperatures increase from band 2 through band 5 in a generally cloud free region, such as the Gulf of Mexico, from gray to green to yellow to red, indicative of the general lapse of temperature with height in the troposphere. Note how the clouds along the front, extending from the western Great Lakes to the Texas Panhandle, are seen in the latter three bands, but not in band 2 (even including the convection in southwest Missouri and the Texas Panhandle). Only the highest cloud tops (along the west coast of Mexico and in the central Gulf of Mexico) are sensed with band 2. Also, note how for bands 3 through 5, the general temperature pattern shows cooler air to the northwest with warmer air to the southeast; however, for band 2, the gradient is reversed with warmer air to the northwest. Radiances in band 2 are actually sensing the lower stratosphere (just above the tropopause) where the north-south temperature fields are reversed from those below.
Midwave water vapor imagery from the GOES-8 sounder at 1146 UTC on 7 October 1994. Progressively less water vapor transparent bands (8, 10, 11, and 12) become more sensitive to middle and upper tropospheric moisture. Dry and moist tongues become obvious in the band 12 (6.7 micrometer) image as one progresses upward through the bands starting with the band 8 (10.8 micrometer) window image. It is interesting to note that band 11 (7.0 micrometer) has a factor of twelve improvement (in higher horizontal resolution and better signal) over the similar GOES-7 water vapor band.
Shortwave imagery from the GOES-8 sounder at 1146 UTC on 7 October 1994. Progressively more carbon dioxide transparent bands (13, 16, 17, and 18) see deeper into the atmosphere and sense more radiation from the earth surface. Reflected solar radiation in band 18 (3.7 micrometer) indicates cloud top and earth surface properties. Note how Lakes Erie and Ontario become more distinctive with decreasing wavelenth.

The retrieval overview.

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