1. Operational Oceanography: Modeling EM Propagation Characteristics
LT Erin O’Marr
7 Sept 2007

2. Purpose of the Study
Compare and contrast upper air sounding TDA inputs for the purpose of modeling EM propagation characteristics
In situ
Model
Identification of trapping layers and ducting layers affecting shipboard sensor propagation characteristics
Surface Search Radars

3. Operational Significance
As a Navy METOC Officer, we will be assigned to/support various deployable assets
Critical decisions about variations in capabilities of platform sensors, as well as, counter-detection
Fire Control Systems
Surface Search Radars
Communications
OPTEMPO in the littoral battlespace
Coastal region is becoming evermore important
Criticality of ship-to-ship and ship-to-shore radar and communications
The environment effects system performance
Proper characterization of the environment

4. Advanced Refractive Effects Prediction System (AREPS)
Tactical Decision Aids (TDA)
Qualitative assessment of system performance given existing environmental conditions
AREPS is most widely used TDA for the prediction of radar ranges and signal propagation characteristics
Advanced Propagation Model (APM)
Extreme sensitivity to model inputs such as SST and RH
Quality input = quality output
Critical area of research:
Obtain an understanding of typical duct height values
Understand procedures for accurately estimating duct heights from routine measurements

5. Review: Refraction Categories
Davidson, K.L., “Assessment of Atmospheric Factors in EM/EO Propagation, Department of Meteorology”, Naval Postgraduate School, Monterey, CA.
Figure and Table courtesy of: Davidson, Assessment of Atmospheric Factors in EM/EO Propagation, pp

6. Review: Types of Ducting
Davidson, K.L., “Assessment of Atmospheric Factors in EM/EO Propagation, Department of Meteorology”, Naval Postgraduate School, Monterey, CA.
Figure and Table courtesy of: Davidson, Assessment of Atmospheric Factors in EM/EO Propagation, pp 3-21.

7. Evaporation Duct
The ED is one of an operator’s primary concerns over water
Can significantly enhance the range and strength of signal propagation
Radar
communications
The rapid, vertical decrease in relative humidity, at the surface, results in a simultaneous rapid decrease in the refractive index.
Primarily concerned with water vapor content; however, RH is readily measured and representative of the amount of water vapor (pressure/specific humidity) present and coincident gradient
The gradient of the refractive index causes significant bending of the ray geometry
The EDH fluctuates throughout the day and is highly dependent of Tair, Tsea, q, and the wind component(s)
Local mixing above the sea surface
Surface-based duct with typical depths of 2-30m
EDH 10m+ is significant for surface radars with frequencies above 5GHz
Ducts 30m+ are significant for almost all radar frequencies

8. Data and Methodology First leg of the Operational Oceanography cruise
Standard meteorological observations
Rawinsondes were launched to collect upper air soundings
Regional AF MM5 vertical profile forecasts
15km horizontal resolution, 25mb vertical resolution, and 3-hr time step.
Vertical sounding data was extracted at or as close as possible to the soundings times and on the precise location of the in situ sounding launch point.
Calculated Evaporation Duct Height (EDH) and it added to environmental profile
Paulus/Jeske (P/J) model
In situ SST
Organic SWS, SWD, pressure, and Tair
AREPS standard project
Platform: R/V Point Sur with standard 10GHz (X-band) radar at 15ft height.
Target: R/V Cypress Sea (small/medium sized vessel) with a regular ESM receiver

9. layer once SST is added (31.53ft thick).
Rawinsonde
MM5
Ship rawinsonde: ZJUL07
MM5 Upperair forecast: ZJUL07
Evidence of a shallow ED (17.98ft thick) present at time of ship sounding. MM5
does not reflect the ED; however, does forecast the presence of a subrefraction
layer once SST is added (31.53ft thick).

10. No extended near-surface ranges.
MM5 Upper air forecast: ZJUL07
Ship rawinsonde: ZJUL07
Range-height cross section of probability of detection (Pd) using a near surface radar against a small/medium-sized vessel target. Pd is indicated by the color scale on the bottom. Extended near-surface ranges due to ED.

11. Rawinsonde
MM5
Ship rawinsonde: ZJUL07
MM5 Upper air forecast: ZJUL07
Evidence of an ED layer at surface (30.2ft) and various elevated ducts on the in situ sounding. MM5 forecasts a deeper ED (58.12ft); however, no elevated ducts.

12. Extended near-surface ranges due to ED.
MM5 Upper air forecast: ZJUL07
Notice extended near-surface detection ranges
ED almost 2x as thick as 18JUL
Ship rawinsonde: ZJUL07
Range-height cross section of probability of detection (Pd) using a near surface radar against a small/medium-sized vessel target. Pd is indicated by the color scale on the bottom. Extended near-surface ranges due to ED.

13. Model has little to no skill in predicting ED when observed SST is used for extrapolating the ED. No further statistics were looked at.

14. Quality of input into TDA- APM is very sensitive to SST and RH
Quality of input into TDA- APM is very sensitive to SST and RH. Graphic shows in situ/model RH differences.
My hypothesis: Observed SST (not shown) created a discontinuous profile and erroneous model predictions of propagation characteristics.

15. Discussion
Value of observed surface variables added to rawinsonde/model
Knowledge of near surface atmosphere significantly aids the modeling of the existence, depth, and intensity of ducts
Need either both measured or both modeled to yield proper coupling between the SST and Air T
If adding obs SST to model sounding, must pay attention to the temperatures measured
If the SST is warmer than the lowest levels, the atmosphere would be “less stable” than it actually is
If model RH is off, the ED will be off
Underprediction or overprediction!
Appending an ED profile to an upper air profile takes manipulation
Gradients at the top of the EDH profile and the first gradient of the upper air profile cannot be too discontinuous
Focused on surface ranges, but no ducts shown in model
Model uses significant levels
Could be important for ducting situations at height and range

16. What do we do??? Vertical high resolution model fields
Use a model with SST fields
Make in situ SST observations to use
2m wind and Air T/another level and extrapolate down
In Situ or land vertical sounding
Need to remove levels/add levels for ED over water (smoothing)
Climo?
AREPS has the capability to automatically append the EDH profile to upper air refractivity profiles from COAMPS files
COAMPS has the surface parameters to compute EDH profiles using bulk models (P/J, NPS)

17. Current Research-Models
Models of similar resolution proved to be useful in predicting the spatial distributions and diurnal variations of refractivity, but missed the fine vertical structure (which is critical)
In the case of our AO, the model resolution is not fine enough to accurately depict the localized processes caused by the San Nicolas islands
Further manipulation of vertical profile
The sfc obs represent the lower 1km and the profile above
Experiment have shown improvement using the technique.
Atkinson, B. W., J.G. Li, and R.S. Plant, 2000: Numerical Modeling of the Propagation Environment in the Atmospheric Boundary Layer over the Persian Gulf, Journal of Applied Sciences, 40,
Courtesy of: Atkinson et al, 2000.

18. Current Research-Predicting EDH
Cannot be determined by rawinsondes (near-surface resolution is too coarse)
Atmospheric surface layer theory
Nomogram (TA, TS, RH, WS)
Model predictions of path losses
ED models developed that use bulk atmospheric measurements at a single altitude to blend with refractivity data measured at higher altitudes
As many measurements as possible at levels 10m and less
Minimum of two levels to extrapolate
AREPS
Automatically append the EDH profile to upper air refractivity profiles from COAMPS files
Babin, S.M, G.S. Young, J.A. Carton, 1996: A New Model of the Oceanic Evaporation Duct, Journal of Applied Meteorology, 36,
Courtesy of: Babin et al, 1996.

19. Questions?