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Published byKenneth Ash Modified about 1 year ago

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NASA NPP OMPS Science Team meeting August 15, 2013 P. K. Bhartia, Zhong Chen, Rob Loughman, Leslie Moy, Steve Taylor

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Evaluation of OMPS-LP radiances - stray light - altitude registration PAGE 2 OF 20

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Methodology Radiance Simulation –Higher accuracy RTM used for simulation Still has scalar code & other issues –Bass & Paur cross-sections –ZM MLS O 3, temp and GPH profiles –OMPS-NP reflectivity –NO 2 from climatology, No aerosols Measured OMPS LP data –Solar irradiances –Ungridded UV ( nm) radiances from long/short high gain, center slit images 2012 April 5 zonal means –Gridded UV 2012 Sept 14

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Topic #1 : Estimation of additive errors (e.g., straylight, dark current, air glow) Pre launch values from Ball Aerospace Radiance residuals Ideal gas law approximation**

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Ideal Gas Law approximation Technique used In the absence of absorption

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Term 1 Term 2 dlnr/dz = dlnP/dz - dlnT/dz Red = 65S Green = 5N Blue = 45N T _____ K/km MLS has 4km vertical resolution We are calculating slopes at 1km …

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65S 352 nm 5N 352 nm 45N 352nm Red = RTM dlnI/dz Blue = Measured dlnI/dz Green = /T + dlnT/dz (first term in summation)

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65S 352 nm 5N 352 nm 45N 352nm Red = RTM dlnI/dz Blue = Measured dlnI/dz

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Red = RTM dlnI/dz Blue = Measured dlnI/dz 352 nm, 50 km 352 nm, 60 km

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0 to 10N Lat Sept 14, 2012 No PreLaunch StrayLight Correction With Corrections Gridded Radiances April 14, 2012, 0-10 N NO stray light correction With stray light correction RTM measured density -Prelaunch stray light correction is ~working -Unrealistic RTM curvature at high altitudes probably due to boundary set at 80km RTM density measured

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Topic 1: Conclusions to Stray Light analysis No detectable stray light problem at 352nm below 50km RTM error above 70km probably due to boundary set at 80km Ideal gas law estimation is helpful but not a replacement for RTM calculations PAGE 10 OF 20

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Topic #2 : Altitude Registration Errors two methods 305 nm radiance residuals - requires accurate radiance/irradiance, requires MLS, not affected by aerosols “knee method” – compares the altitudes where the slope (dlnI/dz) is equal to zero (Janz et al., SPIE 1996) PAGE 11 OF 20

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Alt Registration using 305 nm No O 3 abs strong O 3 abs Strong sens to TH weak sens to TH 305 nm not affected by reflectivity

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305 nm result Using SUSIM SI Using OMPS SI 54.5 km Assuming MLS has 300m error, OMPS error is 0±200m

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“Knee method” PAGE 14 OF 20

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Altitude where slope = 0 shown here at 65deg South 300nm 310nm 305nm 315nm RTM slope = Red, Meas slope = Blue

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Altitude where slope = 0 as a function of latitude bands 300nm 305nm 315nm 310nm

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TH error as a function of latitude band TH error [300nm, 305nm, 310nm, 315nm] MLS has +300m bias in GPH and Varies by latitude ~200m

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Topic 2: Conclusions to Altitude Registration Errors Both methods show a similar orbital dependence minima at poles, peak ~20°N, but the peak is larger using the “knee method” ~500m versus ~300m. PAGE 18 OF 20

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Summary There are no show stoppers – No significant stray light error below ~50km at 352nm – TH errors vary ~500m pole to tropics

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Recommendation Keep normalization altitude at 68 km – no advantage to lowering Increase RTM boundary from 80 to 100km Begin study of aerosol using slopes of radiances Work with Rob Loughman in improving the rxfer code – Change to vector code, fix other problems

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MLS GPH uncertainties 64 km 48 km 32 km 16 km Z* If we use MLS data to estimate TH error we have to consider error in MLS GPH. NCEP/GMAO GPH may be better than MLS below 40 km, but probably not above.

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ideal gas law: r = P/RT where r is rho (density) take the first derivative with respect to z: dr/dz= (1/RT) * dP/dz - (P/RT^2) * dT/dz substitute dP/P = dlnP, dT/T = dlnT into above equation: dr/dz = (P/RT) * (dlnP/dz) - (P/RT) * (dlnT/dz) Substitude ideal gas law, r=(P/RT), dr/r=dlnr dlnr/dz = dlnP/dz - dlnT/dz R= Joules/(mol * K) (where Joule=kg*m^2/sec^2) g=9.81 m/sec^2 (can vary with latitude) molecular mass = kg/mol assuming dry air dlnP/dz = molmass * gravity / R constant = ( kg/mol) * (9.81 m/sec^2) / (8.314 kg*m^2/sec^2*mol*K) so units cancel and you get dlnP/dz = Kelvin / meter Backup slide

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RTM 290nm RTM 352nm Meas 352nm In agreement ~52 km April 5, N dlnI(290nm)/dz, dlnI(352nm)/dz dlnI(290nm)/dz - dlnI(352nm)/dz Meas Meas 290nm RTM

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