Abstract
Abstract. One of the largest constraints to the retrieval of accurate ozone profiles from UV backscatter limb sounding sensors is altitude registration. Two methods, the Rayleigh scattering attitude sensing (RSAS) and absolute radiance residual method (ARRM), are able to determine altitude registration to the accuracy necessary for long-term ozone monitoring. The methods compare model calculations of radiances to measured radiances and are independent of onboard tracking devices. RSAS determines absolute altitude errors, but, because the method is susceptible to aerosol interference, it is limited to latitudes and time periods with minimal aerosol contamination. ARRM, a new technique introduced in this paper, can be applied across all seasons and altitudes. However, it is only appropriate for relative altitude error estimates. The application of RSAS to Limb Profiler (LP) measurements from the Ozone Mapping and Profiler Suite (OMPS) on board the Suomi NPP (SNPP) satellite indicates tangent height (TH) errors greater than 1 km with an absolute accuracy of ±200 m. Results using ARRM indicate a ∼ 300 to 400 m intra-orbital TH change varying seasonally ±100 m, likely due to either errors in the spacecraft pointing or in the geopotential height (GPH) data that we use in our analysis. ARRM shows a change of ∼ 200 m over ∼ 5 years with a relative accuracy (a long-term accuracy) of ±100 m outside the polar regions.
Highlights
Instruments that measure the solar radiation scattered by the Earth’s atmosphere in the limb direction provide a low-cost way of measuring trace gases, aerosol profiles, and clouds from satellites
Since aerosol contamination limits the range of latitudes and times where Rayleigh scattering attitude sensing (RSAS) can be applied, we developed the absolute radiance residual method (ARRM)
--01.155 --01.100 -0-.505 0.000 0.505 d(lndI(Cl)n/Idc)z/d(z%/km) eral variations of the RSAS technique have been developed for ozone sensors (McPeters et al, 2000; Rault, 2005; Taha et al, 2008), we find that the simplest formulation described below works as well as any other
Summary
Instruments that measure the solar radiation scattered by the Earth’s atmosphere in the limb direction provide a low-cost way of measuring trace gases, aerosol profiles, and clouds from satellites. The RSAS method works best in latitudes and months where the 350 nm aerosol extinction at 20 km is relatively small Another potential source of uncertainty in applying the RSAS technique comes from uncertainty in simulating radiances at 40 km; one needs to have accurate pressure profiles for altitudes at and above 40 km. We developed ARRM to be applicable over many latitudes and times In part this method uses radiances measured by a limb instrument near 295 nm at ∼ 65 km to determine altitude error. The knee ozone absorption becomes so large that it essentially blocks most of the Rayleigh-scattered radiation from reaching the satellite, making the radiances insensitive to atmospheric pressure This characteristic shape allows estimations of altitude registration error in a manner very similar to that www.atmos-meas-tech.net/10/167/2017/.
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