Total column ozone measurements utilizing the backscatter ultraviolet (BUV) technique began in 1978 with the Nimbus-7 TOMS instrument and have continued with subsequent TOMS, SBUV, GOME, OMI, and OMPS instruments through the present. Though the basic ozone accuracy requirements remain largely unchanged over the intervening decades, sensor performance expectations have evolved. This evolution, driven by new ozone retrieval techniques and non-ozone products, has been accompanied by a corresponding change in sensor calibation.

One of the most important findings has been that standard calibration approaches, both pre-launch and in flight, often do not provide the radiometric accuracy needed for the science data products. In the case of pre-launch calibration, the state of the art is either insufficient or too expensive. Often, the complexity of sensor degradation in orbit outpaces the design of the calibration hardware to quantify the changes. In these situations, techniques that started out as a way to verify calibrations have become the primary source for adjustments. These "soft" calibration methods have proved so successful that they are now standard tools in the process of calibrating BUV sensors. In this presentation we will describe the basic BUV calibration approach and the adaptations that have become necessary to keep up with both science needs and sensor performance challenges.