1. Measurements of Flow Distortion within the CSAT3 Sonic Anemometer T.W. Horst and S.R. Semmer National Center for Atmospheric Research Technical University of Denmark E. Dellwik, J. Mann, N.Angelou

2. Measurements of Flow Distortion within the CSAT3 Sonic Anemometer History of Sonic Development History of Sonic Development

3. Measurements of Flow Distortion within the CSAT3 Sonic Anemometer History of Sonic Development History of Sonic Development CSAT 3 Transducer Shadowing CSAT 3 Transducer Shadowing

4. Measurements of Flow Distortion within the CSAT3 Sonic Anemometer History of Sonic Development History of Sonic Development CSAT 3 Transducer Shadowing CSAT 3 Transducer Shadowing Field Tests of Transducer Shadowing Field Tests of Transducer Shadowing NCAR Comparison to ATI-K sonics NCAR Comparison to ATI-K sonics

5. Measurements of Flow Distortion within the CSAT3 Sonic Anemometer History of Sonic Development History of Sonic Development CSAT 3 Transducer Shadowing CSAT 3 Transducer Shadowing Field Tests of Transducer Shadowing Field Tests of Transducer Shadowing NCAR Comparison to ATI-K sonics NCAR Comparison to ATI-K sonics DTU Comparison to Doppler LiDAR DTU Comparison to Doppler LiDAR

6. Chandran Kaimal

7. Kaimal-designed sonic anemometers with dedicated vertical paths U. of Washington, 1960

8. Kaimal-designed sonic anemometers with dedicated vertical paths U. of Washington, 1960 AFCRL/EG&G, 1973 BAO/ATI, 1990

9. Kaimal-designed sonic anemometers with dedicated vertical paths U. of Washington, 1960 AFCRL/EG&G, 1973 BAO/ATI, 1990 Kaimal (1979): Horizontal paths require correction for transducer wakes Impinging on the acoustic paths

10. Transducer shadowing depends on wind direction w.r.t. path and d/L (Kaimal, 1979)

11. University of Washington non-orthogonal sonic anemometer, Businger and Oncley (1984)

12. CSAT3 Geometry and Coordinates

13. CSAT3 Transducer Shadowing, L/d = 18, d/L = 0.056 0.97

14. Vertical velocity statistics, such as and, are measured to be greater with a vertical-path sonic than with a non-orthogonal sonic.

15. Vertical velocity statistics, such as and, are measured to be greater with a vertical-path sonic than with a non-orthogonal sonic. CSAT3 transducer shadowing?

16. CSAT3 Transducer Shadowing, L/d = 18, d/L = 0.056 + 18 0.16

17. CSAT3 transducer shadowing measured in the NCAR wind tunnel

18. Marshall-2012 sonic anemometer field test CSAT.x (test sonic) CSAT.va (vertical a-path) ATI-K.e (reference) CSAT.w (test sonic) 5 sonics at 3m height, 0.5 m spacing ATI-K.w (reference)

22. CSAT3 intercomparison with 3-component DOPPLER LiDAR E. Dellwik, J. Mann, N. Angelou, E. Simley, M. Sjoholm & T. Mikkelsen, Technical University of Denmark

23. αα Inside Outside Technical University of Denmark Risø Wind Scanner Experiment November, 2013 o o

24. LiDARs focused 80 cm Outside of sonic LiDARs focused Inside sonic measurement volume Thin lines: Sonic; Thick lines, LiDAR (60 Hz data) u, v, w

25. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction.

26. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. Maximum effect near transducers. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. Maximum effect near center of sonic array.

27. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. Maximum effect near transducers. LiDAR and sonic data differ for the Inside case. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. Maximum effect near center of sonic array. LiDAR and sonic data agree for Inside case.

28. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. Maximum effect near transducers. LiDAR and sonic data differ for the Inside case. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. Maximum effect near center of sonic array. LiDAR and sonic data agree for Inside case. U Sonic /U LiDAR are different for Inside and Outside cases.

29. Outside case: k = U Sonic /U LiDAR, U = U Z

30. Outside case: k = U Sonic /U LiDar, U = U X,Y

31. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. LiDAR and sonic data differ for the Inside case. Maximum effect near transducers. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. LiDAR and sonic data agree for Inside case. Maximum effect near center of sonic array. U Sonic /U LiDAR are different for Inside and Outside cases.

32. Comparison between Inside and Outside cases, U = U Z

33. Comparison between Inside and Outside cases, U = U X,Y

34. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. LiDAR and sonic data differ for the Inside case. Maximum effect near transducers. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. LiDAR and sonic data agree for Inside case. Maximum effect near center of sonic array. U Sonic /U LiDAR are different for Inside and Outside cases.

35. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. LiDAR and sonic data differ for the Inside case. Maximum effect near transducers. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. LiDAR and sonic data agree for Inside case. Maximum effect near center of sonic array. U Sonic /U LiDAR are different for Inside and Outside cases.

36. Two possible causes for sonic flow distortion 1.Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. LiDAR and sonic data differ for the Inside case. Maximum effect near transducers. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. LiDAR and sonic data agree for Inside case. Maximum effect near center of sonic array. U Sonic /U LiDAR are different for Inside and Outside cases.

37. Two possible causes for sonic flow distortion Transducer shadowing: Wakes behind transducers. Strong dependence on wind direction. LiDAR and sonic data differ for the Inside case. Maximum effect near transducers. U Sonic /U LiDAR are the same for Inside and Outside cases. 2.Blocking of flow: Flow speeds up within sonic. Weak dependence on wind direction. LiDAR and sonic data agree for Inside case. Maximum effect near center of sonic array. U Sonic /U LiDAR are different for Inside and Outside cases.

38. Analysis is continuing of the DTU Wind Scanner/CSAT3 data, with the goal of directly measuring the sonic anemometer flow distortion/transducer shadowing.

39. Analysis is continuing of the DTU Wind Scanner/CSAT3 data, with the goal of directly measuring the sonic anemometer flow distortion/transducer shadowing. Results of the NCAR data analysis will be published in an upcoming issue of Boundary Layer Meteorology: Horst, T.W., S.R. Semmer and G. Maclean, Correction of a Non-Orthogonal, Three-Component Sonic Anemometer for Flow Distortion by Transducer Shadowing, Accepted, with minor revision, for publication in Boundary Layer Meteorology.