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The satellite UV NO-O2-O3 robust integrating spectrometer experiment (SUNRISE) will develop highly sensitive spectrometers for satellite solar limb measurements. The first of our satellites will be launched in mid-2000, and will carry a test spectrometer called OPUS-1 which will accurately monitor the solar Lyman (alpha) during a period its normal coverage will be otherwise disrupted. It will be mounted alongside a series of more complex spectrometers, called OPUS-2 . . .. These will measure oxygen photolysis with the sun as an occulted UV light source. Inverse Abel transforms produce vertical target profiles in 3 km bins each sunrise and sunset. Our system can resolve the Schumann-Runge lines because we have devised ways to reduce greatly the systematic errors in our measurements with excellent systematic checks and system redundancies: Perhaps the most importantly, we get exoatmospheric spectra obtained immediately after sunrise and before sunset to give an excellent spectral calibration. We aim to measure O2 photolysis down to approximately 43 km. The SUNRISE collaboration has taken a fast, simple and robust route to the important measurements we have targeted. The satellites are in eccentric equatorial orbits at 800 km, with severe constraints on payload and power availability. The expected lifetimes of these satellites (8 - 15 years) offers unprecedented opportunities in UV-measurements and in ozone monitoring (for example, in spanning a sun-spot cycle) but places great demands on the robustness of our equipment. Our OPUS technology reflects that. Given that ozone has such a central role in atmospheric science, and that recent uncertainties (based on HALOE observations) in actual ozone deficits about 40 km have led to great uncertainties in atmospheric models, the precise measurement of O3 production and O3 sinks is very important. Our spectral range extends from 120 nm to 124 nm, in OPUS-1, and so we also will target the Lyman (alpha) line, which will allow real-time measurements of solar variability, and will in any case provide an excellent built in calibration, and 175 - 225 nm in OPUS-2. We can make significant measurements of NO absorption in the altitude range 40 km upwards with vertical resolution approximately 3 km and accuracies of approximately 10%. By establishing the levels of absorption in ozone, and comparing with the exoatmospheric measurements, we furthermore measure actual concentrations of ozone. SUNRISE therefore offers a unique tool making the simultaneous measurement of ozone production, concentrations, and a major mechanism of its loss, through the NO cycle. SUNRISE introduces an innovatory range of technologies, individually well-understood, the combination of which results in potentially large improvements in sensitivity and spectral selectivity.
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