Total and profile ozone from the SBUV/2 instrument are retrieved from radiance measurements at 12 discrete wavelengths in the ultraviolet (252 to 340 nm) (Bhartia et al., J. of Geophys. Res., 1996). The SBUV/2 data has gaps between its 14 orbits and over the pole during polar night because it is a nadir-viewing instrument. Ozone maps are generated using Cressman interpolation scheme. This interpolation scheme works well but spatial smoothing can mask small-scale features and miss extrema.

The TOVS data are retrieved using radiance measurements made by the High Resolution InfraRed Sounder (HIRS) at 9.7 microns. This retrieval technique is sensitive only to ozone changes between 4 to 23 km. Latitude dependent but seasonally independent climatology is used in the mid-to-upper stratosphere to derive total ozone (Neuendorffer, J. of Geophys. Res., 1996). TOVS maps are at high spatial resolution because of its twice daily measurements (day and night) and because it is a scanning instrument. Unlike the ultraviolet based instruments TOVS can measure in the polar night. However, accuracy of its total ozone estimate is compromised when ozone changes occur in the mid-to-upper stratosphere.

TOAST is a total column ozone map generated by combining TOVS tropospheric and lower stratospheric (4 to 23 km) ozone retrievals with SBUV/2 spatially smoothed mid-to-upper stratospheric (24 to 54 km) layer ozone retrievals. In essense, we are replacing TOVS climatology with real-time SBUV/2 measurements in the mid-to-upper stratosphere.

The Ozone team continually monitors the performance of the various SBUV/2 and HIRS instruments and will vary the combination used in the distributed TOAST product to provide the best quality product.

Known limitations include problems over highly reflective cold surfaces (Antartica), during mid-stratospheric warming events, and contamination in the case of high thin cirrus clouds.

TOAST products are not archived operationally at CLASS, but most old products can be retrieved from the non-operational SaTellite Applications and Research (STAR) Ozone group TOAST FTP Site.