1. OC3570 Operational Meteorology
Analysis of
Refractive duct
trends during
July 2002 Pt Sur
cruise
LCDR John Daziens

2. Project Definition - Analysis of elevated & surface ducting conditions
- Propagation impacts of surface ducting conditions (AREPS)

3. Standard Atmosphere vs. Surface Ducting

4. Vaisala RS-80 specifications
Sensor Type
Range
Accuracy
Resolution
Response/Lag Time
Pressure (and Height)
capacitive aneroid
1060 to 3 hPa
0.5 hPa
0.1 hPa
Temperature
capacitive bead
-90 to 60 oC
0.2 oC
0.1 oC
<2.5 sec
Humidity
(and Vapor Pressure)
thin film capacitor
0 to 100% 2% 1%
1 sec

5. Data Analysis Part I
* 21 Rawindsonde profiles analyzed (Full & “Up Downs”)

6. What affects refractivity?
N is affected by temperature (T in degrees K), pressure (P in mbar) and humidity (vapor pressure, e, in mbar) in the following manner:

7. Modified Refractivity
Properties
Modified Refractivity
The modified refractivity (M) is used to determine how radar rays are bent relative to the earth’s curvature:
where: T is temperature in K P is atmospheric pressure in mb e is vapor pressure in mb z is height above the surface in m

8. NO SURFACE DUCTING
Elevated Duct

9. Determine Elevated Duct Trends
Data Analysis Part II:
Determine Elevated Duct Trends

10. Downward Analysis:
(14 Rawindsondes)

11. Data Smoothing Benefits
Up / Down Downward Leg
Ambiguous Elevated Duct (~800m)
SMALL Lower Level Duct

12. Elevated Duct Height Analysis

13. Elevated Duct Thickness Analysis

14. EM Frequencies Trapped by Duct

15. Propagation Modes: Atmospheric & EM Regions
Alt
(km)
GROUND WAVE SKYWAVE SCATTERING SPACEWAVE
400
300
200
150
100 50
Ionophere
Ionophere
Scatter Volume
SAT-COM
Ionosphere
Communication
Meteor scatter
Line of site microwave
Ducting(surface)
Ionoscatter 1500Km
range
D-layer Daytime
Mesosphere
Stratosphere
Troposcatter
400 km range 10
10 Mm Mm km km km m m m cm cm mm
Wavelength
radio bands
frequency
ELF VF VLF LF MF HF VHF UHF SHF EHF
30 Hz Hz KHz KHz KHz MHz MHz MHz GHz GHz GHz
CONTROLLING INFLUENCE - Number
of free electrons (N) in the IONOSPHERE
CONTROLLING INFLUENCE - Vertical variation of pressure, temperature, and humidity (P,T,e) of TROPOSPHERE
CONTROLLING INFLUENCE - Absorption by water vapor and oxygen molecues in the TROPOSPHERE

16. Trend Analysis Lowest elevation for “significant” ducting
100m = “Significant”
Thickness
190600Z Z

17. Large Thickness
High Elevation

18. Trapping Layer Formation
Initial T
After
Subsidence
Height
9.8 0K/km e
Vertical Velocity

19. Surface Duct Detection: Rawindsonde vs. Kite Methods
Elevated Duct

20. Conclusions
Surface Ducting not evident from rawindsonde data (differs from 19July02 Kite Data).
Diurnal variance of elevated duct height / thickness not indicated by analysis.
Thickness maximum / elevation minimum corresponded to period of higher subsidence.