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Comparison of C n 2 Estimations Using Ship, Rawinsonde, and Model Data

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  1. Comparison of Cn2 Estimations Using Ship, Rawinsonde, and Model Data LCDR Richard M. Murphy, USN 14 MAR ’05 Operational Oceanography/OC2570

  2. Outline • Review Cn2 (little bit of math) • Data Collection • Analysis/Results • Conclusions

  3. Index of Refraction • index of refraction (n), f(p,T,q) • for optics n more dependent on T fluctuations, for RF propagation more dependent on q fluctuations • importance of gradient wrt height

  4. Types of Refraction

  5. Scintillation 300 200 Height (m) Propagating Waves 100 0

  6. Cn2 • Monin-Obukhov Similarity Theory (physical quantities scaled w/ turbulent fluxes of heat & momentum, sfc layer assumed horizontally homogeneous & stationary, fluxes assumed constant, can specify at single height) • Cn2 = A2 CT2 + AB CTq + B2 Cq2 (where A & B are fcn’s of ∂n/∂T and ∂n/∂q, respectively) • Cx2 = [x’(0) - x’(d)]2/d2/3 • scaled parameters u*, T* & q* are f(w’,u’,T’,q’)

  7. Data Collection • u* = uk/[ln(zu/L) – “stuff”] (“stuff” depends on atmospheric stability), similar eqn’s for T*&q* • modified Matlab code from Prof. Guest to calculate optical Cn2 (runbulk.m, bulkland.m): changed zveg=0, CDn10 decrease by ½, iterative scheme to 0.5% • one run w/ measured data (from rawinsonde z/u/Tair/press/RH, from UDAS SST/RHsfc) • another run using combination of measured data & assumed 100% RHsfc (press from model or sat sounding [1000 or 1010 mbars])

  8. Data Collection • Rawinsondes: balloon-mounted RS80-15L’s recording time, wind dir/speed, temp, dew point, RH, pressure, height, ascent rate, refractivity, modified refractivity, & vapor pressure • 10 launches over 4-day cruise logging lat/long • used for simple plots of T&Td/ vs press & RH&NI/MI vs height • data points for Prof. Guest’s Cn2 Matlab functions (zu, u, Tair, RH, press) [2nd data pt 15-23m]

  9. Data Collection • UDAS Ship data: continuous data feed from RV Pt Sur; recording date, GMT, lat/long, COG/SOG, T, press, RH, SST w/ IR & boom probe, and salinity • used for SST & RHsfc data points for Prof. Guest’s Cn2 Matlab functions

  10. Data Collection • Model data: provided by Prof. Creasey; MM5 & 3km COAMPS(thanks Tara) soundings • used lowest data points for Tair & press for Prof. Guest’s Cn2 Matlab functions

  11. Data Collection • Satellite data: GOES-15/16 Tair soundings (provided by Billy Roeting) • used lowest data points for Tair & press for Prof. Guest’s Cn2 Matlab functions

  12. Data for2/5/05at 19 Z COAMPS 6hr fcst, T0 OK, T should incr at 950mb, Td high MM5 12hr fcst, high T0, no sfc inversion, opposite Td trend at sfc

  13. Data for2/6/05at 00 Z COAMPS Analysis, T & T0 OK, Td low MM5 6hr fcst, slight elev. inversion not on balloon, Td OK

  14. Data for2/6/05at 10 Z MM5 6hr fcst, T high, Td starts OK but high COAMPS Analysis, good T0, moist layer at 950mb at 910mb on balloon

  15. Data for2/6/05at 17 Z MM5 12hr fcst, high T0, Td trend OK to 950mb COAMPS 6hr fcst, T0 OK, T high, Td only good to 950mb

  16. Data for2/6/05at 23 Z COAMPS Analysis, T0 OK, T OK to 920 mb, Td OK to same MM5 6hr fcst, T0 good, Td good trend but high initial value

  17. Data for2/7/05at 12 Z MM5 18hr fcst, T0 good trend but high, Td follows COAMPS Analysis, similar to MM5

  18. Data for2/7/05at 21 Z MM5 15hr fcst, T0 good but high T, Td same COAMPS 9hr fcst, T0 good, high T values, Td high

  19. Data for2/8/05at 03 Z MM5 21hr fcst, T0 good, T high, Td good trend but high COAMPS 3hr fcst, T high, dry layer at 950mb not on balloon

  20. Data for2/8/05at 11 Z MM5 18hr fcst, T0 high, T high, Td high COAMPS Analysis, T0 high, Td high

  21. Data for2/8/05at 21 Z COAMPS 9hr fcst, T high, Td high MM5 15hr fcst, T0 OK but T high, Td high

  22. Data Trends Balloon/Ship Data 2/5 at 19Z 2/6 at 00Z 2/7 at 21Z 2/6 at 23Z 2/6 at 10Z 2/7 at 12Z 2/8 at 03Z 2/6 at 17Z 2/8 at 21Z 2/8 at 11Z

  23. Data Trends Balloon/Ship Data 2/6 at 17Z 2/8 at 11Z 2/5 at 19Z 2/7 at 21Z 2/7 at 12Z 2/8 at 03Z 2/6 at 10Z 2/6 at 23Z 2/8 at 21Z 2/6 at 00Z

  24. Data Trends

  25. Data Trends

  26. Data Trends

  27. Data Trends

  28. Data Analysis • MOS theory uses sfc layer bulk/avg. parameters, sfc layer should be approx. 10% of MBL (≈ 40-50m) • trend in RH difference most closely approximated Cn2 trend • lowest MM5 data points too high in atmosphere (1000 mbars [≈ 100-150m], i.e. outside sfc layer) • some COAMPS data points probably within sfc layer (lowest reading 1010 mbars, [≈ 17-82m]) • lowest satellite data points too high in atmosphere (1000 mbars) • good agreement between balloon/ship+measured sfc RH and balloon/ship+assumed sfc RH of 100%

  29. Data Analysis • somewhat good agreement (discounting outlier) of balloon/ship data & balloon/ship/sat data (measured sfc RH) • MM% & COAMPS model runs not same fcst times, should parallel as closely as possible - spatial comparison skewed due to different dates/times, need line of buoys/balloons for time series, would also show Cn2 spatial trends toward shore (cross-coast?) • could utilize ship-mounted scintillometer as baseline instead of measuring specific parameters and then calculating in an equation (along a linear path to/from shore - ship limited to visual range though)

  30. Applications • communications to units inland (ranges, interference) • coastal radar coverage on small boats • lasing targets inland (SpecOps)

  31. References Abahamid, A., Jabiri, A. et al, 2003: Optical Turbulence Modeling in the Boundary Layer and Free Atmosphere Using Instrumented Meteorological Balloons. Astronomy and Astrophysics, 416, 1193-1200. Davidson, K.L., Schacher, G.E., Fairall, C.W. and A.K. Goroch, 1981: Verification of the Bulk Method for Calculating Overwater Optical Turbulence. Applied Optics, 20, no. 17, 2919-2923. Davidson, K.L. and C. H. Wash, 1998: Describing Coastal Optical Properties with In Situ and Remote Measurements. Naval Research Reviews, Two, 2-7. Frederickson, P.A. and K.L. Davidson, 1999: Estimating the Refractive Index Structure Parameter (Cn2) Over the Ocean Using Bulk Methods. Journal of Applied Meteorology, 39, 1770-1783. Hutt, D.L., 1999: Modeling and Measurements of Atmospheric Optical Turbulence Over Land. Optical Engineering, 38, no. 8, 1288-1295. Porch, W.M., Neff, W.D. and C.W. King, 1987: Comparisons of Meteorological Structure Parameters in Complex Terrain Using Optical and Acoustical Techniques. Applied Optics, 27, no. 11, 2222-2228. Rachele, H. and A. Tunick, 1993: Energy Balance Model for Imagery and Electromagnetic Propagation. Journal of Applied Meteorology, 33, 964-975. Raj, P.E., Sharma, S., Devara, P.C.S. and G. Pandithurai, 1992: Study of Laser Scintillation in Different Atmospheric Conditions. Journal of Applied Meteorology, 3, 1161- 1167.