Longer wavelengths can see deeper into the atmosphere than shorter wavelengths. Comparisons of the absorption signals of the same molecule in GOME's different wavebands give an impression of the agent's distribution by height. Clouds help too. The clouds also hide low-lying oxygen. The reduced absorption by oxygen enables GOME scientists to judge the clouds' extent and height and so tell how far down into the atmosphere the satellite is looking, at each place.
Scientists use many instruments to detect ozone and other ingredients of the atmosphere.
When they operate them from ground stations, aircraft and balloons, the measurements are more accurate than from space, but they are confined to particular places and times. Prolonged global observations like those of GOME are essential for discovering how the whole atmosphere works, as a chemical system, and for distinguishing natural changes from those due to human activity. It created an archive of polar ozone data spanning many years. GOME can emulate Nimbus-7's observations, and so record continuing changes in the ozone. But GOME's measurements look more deeply and more sensitively into the atmosphere's chemistry.