1. Comparison of Aircraft Observations With Surface Observations from
R/V POINT SUR
Dominick Vincent
OC 3570
18 March 2003

2. Operational Motivation:
Naval Oceanography Program Operational Concept - Guiding Principles (2002):
“…We will employ a doctrinal Rapid Environmental Assessment (REA) process, using both dynamic and static data to characterize the battlespace environment and reflect it in the 4D Cube as part of deliberate and contingency military operations.”
- Page 6

3. Rapid Environmental Assessment Aircraft: Rapid (Synoptic)
In-situ (Atmosphere)
Remote (Surface Obs)
Ship: Slower
In-situ (Surface)
In-situ (Atmosphere)

4. Question for Investigation:
Can Aircraft provide comparable or superior observational data for environmental assessment?

5. Method of Investigation:
Compare aircraft and ship data as used in the following:
- Determining surface fluxes based on a bulk
method calculation, and
- Determining the spatial variability of wind field
over a given area.

6. Data and Methods of Collection:
Data were collected during the 8 day OC 3570 Operational Oceanography cruise from 27 Jan 2003 to 03 Feb 2003 aboard the R/V POINT SUR.
Additionally, the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) provided aircraft data collection support for 27 Jan and 1 Feb.

7. Area of Collection:
Area of investigation for the R/V POINT SUR covered a box off the coast of Central California and was bounded by California Cooperative Oceanic Fisheries Investigations (CalCOFI) line 67 to station 67-70, alongshore to station 77-70, and inshore to Port San Luis along line 77.
Additional CalCOFI Hydrography lines were covered within the outer box by both the R/V POINT SUR and the CIRPAS Aircraft.

8. Ship
Plane – 27 Jan
Plane – 1 Feb
CalCOFI Line 67
CalCOFI Line 77

9. Ship
Plane – 27 Jan
Plane – 1 Feb

10. Collection Platforms:
R/V POINT SUR
Data Collected every 54 seconds (SAIL):
Position Time (UTC)
Wind Direction Wind Speed
Air Temperature Relative Humidity
Pressure Sea Surface Temperature

11. Collection Platforms:
UV-18A “Twin Otter”
Data Collected every second:
Position Time (UTC)
Wind Direction Wind Speed
Air Temperature Relative Humidity
Pressure Sea Surface Temperature
Altitude

12. Bulk Method-derived Surface Fluxes:
Comparison of
Bulk Method-derived Surface Fluxes:
Calculated using a Matlab program, sfcfluxoc3570, by Guest (1997) using a bulk method formulation based on Smith (1990) and requiring the following inputs:
- Wind speed
- Air temperature
- Relative humidity
- Sea Surface Temperature
- Pressure

13. Bulk Method-derived Surface Fluxes:
Comparison of
Bulk Method-derived Surface Fluxes:
Measurements needed to be spatially and temporally coincident to achieve a valid comparison.
One window, approximately 15 minutes in length, was found for each day.

14. Ship
Plane

15. Ship
Plane

16. Bulk Method-derived Surface Fluxes:
Comparison of
Bulk Method-derived Surface Fluxes:
Ship Data:
- Averaged over the 15 minute window.
Aircraft Data:
- Input parameters taken at lowest altitude,
- Winds averaged over lowest 10 meters in window.

17. Data Comparison - 27 January 2003

18. Data Comparison - 27 January 2003

19. Data Comparison - 1 February 2003

20. Data Comparison - 1 February 2003

21. Results of Comparison of Bulk Method-derived Surface Fluxes:
27 January 2003:
Differing total heat flux values likely due to difference in in relative humidity and wind speed measurements.
Differing wind stress values likely due to 10-meter wind speed difference.
τ = cDu102

22. 10-Meter Normalized Parameters Bulk Method Derived Surface Fluxes
27 January 2003
Input Parameters
10-Meter Normalized Parameters
Bulk Method Derived Surface Fluxes
Ship
Plane
Air Temp
(C)
14.1
14.9
Temperature
14.8
Sensible Heat Flux
(W/m2)
-2.3
-4.3
Pressure
(mbar)
1018.7
1012.2
Potential Temp
(K)
287.4
288.0
Latent Heat Flux
3.0
20.9
Relative Humidity (%)
94.4
66.3
Wind Speed
(m/s)
5.0
3.5
Total Heat Flux
0.7
16.6
Sea Surface Temp (C)
13.8
13.6
Specific Humidity
(g/kg)
9.4
7.4
Drag Coefficient
0.0010
0.0008
5.2
4.2
Wind Stress
(N/m2)
0.0304
0.0118
Height of Ob
(m) 14
20.7

23. Results of Comparison of Bulk Method-derived Surface Fluxes:
1 February 2003:
Valid comparison impossible due to height of aircraft data.

24. 10-Meter Normalized Parameters Bulk Method Derived Surface Fluxes
1 February 2003
Input Parameters
10-Meter Normalized Parameters
Bulk Method Derived Surface Fluxes
Ship
Plane
Air Temp
(C)
12.9
12.4
Temperature
13.0
Sensible Heat Flux
(W/m2)
5.2
-6.3
Pressure
(mbar)
1015.6
985.8
Potential Temp
(K)
286.2
286.3
Latent Heat Flux
142.7
394.8
Relative Humidity (%)
77.7
39.9
Wind Speed
(m/s)
18.7
22.0
Total Heat Flux
147.9
388.5
Sea Surface Temp (C)
13.3
Specific Humidity
(g/kg)
7.2
4.3
Drag Coefficient
0.0017
0.0019
19.3
26.9
Wind Stress
(N/m2)
0.7466
1.115
Height of Ob
(m) 14 81

25. Comparison of Measured Wind Fields:
Ship Data:
- Plotted every 15 minutes
Aircraft Data:
- Plotted every minute

26. Ship
Plane

27. Ship
Plane

28. Ship
Plane

29. Ship
Plane

31. Ship
Plane

32. Ship
Plane

33. Ship
Plane

34. Ship
Plane

36. Results of Comparison of Measured Wind Fields:
- Offshore winds show clockwise turning with increasing elevation consistent with Ekman Theory as described in Holton (1992).
- Nearshore winds show terrain effects.
- Ship data likely a combination of spatial and temporal variability.

37. Recommendations for Future Studies:
- Specifically design an experiment to collect a significant amount of temporally and spatially coincident data sufficient to quantitatively describe biases.
- Ensure careful calibration of sensors before experiment.
- Ensure aircraft flies at a consistently low altitude to ensure collection of data within the surface layer.

38. Conclusions:
- Aircraft data are a powerful tool for REA but must have some ground truth.
- Biases must be carefully studied for data to have any validity for data assimilation purposes.

39. References Guest, P., sfcfluxoc3570.m, 1997. Matlab program.
Guest, P., windvector.m, Matlab program.
Holton, J. R., An Introduction to Dynamic Meteorology. Academic Press, San Diego, 1992.
Naval Oceanography Program Operational Concept, March 2002, 48 pp.
Smith, S.D. 1988: Coefficients of sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature. J. Geophys. Res, 93, 15,467-15,472.