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Tangent height verification algorithm

Tangent height verification algorithm. Chris Sioris, Kelly Chance, and Thomas Kurosu Smithsonian Astrophysical Observatory. Algorithm described in Sioris et al., JGR, in press. - find the longest median wavelength for the set of pixel that has the

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Tangent height verification algorithm

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  1. Tangent height verification algorithm Chris Sioris, Kelly Chance, and Thomas Kurosu Smithsonian Astrophysical Observatory

  2. Algorithm described in Sioris et al., JGR, in press. - find the longest median wavelength for the set of pixel that has the same knee TH on the measured TH grid such that the median is < 305 nm -compare this knee TH (e.g. ~45 km) to one produced by a limb radiative transfer model at the median wavelength for the same conditions (SZA, d, T[z], p[z], O3[z]) -algorithm takes 3 sec per limb scan (at 800 MHz) with McLinden et al. model. -this approach has been compared to one where a quadratic in  is fitted to observed and simulated knee THs (and the difference between the ‘obs’ and ‘sim’ is the TH offset)

  3. Median  used for 305 nm technique

  4. Results Orbit 3422: 282-305 nm gives wrong TH offset due to wrong mesospheric O3 in the model

  5. # of limb scans=325, # of orbits = 17, mostly from Aug. and Sep. ’02

  6. Analysis of five consecutive SCIAMACHY orbits

  7. Paired t-test: every 2nd orbit has same latitude sampling scheme, Applied to NH extratropics where algorithm is less sensitive to assumed atm orbit pairs lat range (°) p (that drift is insignificant) drift/orbit (km) 2995 vs. 2997 28-74 0.04% -0.19 2997 vs. 2999 28-51 0.93% -0.19 2996 vs. 2998 31-82 0.02% -0.24

  8. Offset statistics (km, obs - model TH) GLOBAL Average: 0.06 stdev: 1.42 maximum: 6.03 minimum: -4.38

  9. Expected error budget for spectral knee at ~305 nm 1. theoretical limit to due spectral resolution and sampling and shot noise ~40 metres 2. completely wrong surface albedo, trop. cloud info: <50 3. completely wrong temperature profile: <50 4. 10% bias in O3 column (variability for worst-case 200 latitude, for most months above 45 km) 5. interannual variability, (July=worst-case, [Keating <200 et al., 1990]) 6. Neglect of diurnal variation below 53 km ([Keating et al.]) since LT at poles is not LT at equator <50 7. Radiative transfer accuracy 200 8. planetary and gravity wave activity affecting p at 46 km [Barnett and Labitzke, 1990]: worst-case: hi lat winter 1280 best-case: equator 20-40

  10. Worst-case total error (added in quadrature): ~1300 m at the equator: ~330 m

  11. Application to Level 2:NO2 profile intercomparison with SAGE III SAGE III pointing for solar occultation is accurate to ~100 m. Vertical column (21-37 km) agreement improves marginally from 6.5% to 3.8% but profile agreement improves from 21% to 11% as sharp features are captured only after TH correction of 2.6 km

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