S07071816

Operational Oceanography: Modeling EM Propagation Characteristics LT Erin OMarr 7 Sept 2007 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 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 OPTEMPO in the littoral battlespace

Fire Control Systems Surface Search Radars Communications 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 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 Review: Refraction Categories Figure and Table courtesy of: Davidson, Assessment of Atmospheric Factors in EM/EO Propagation, pp 3- Review: Types of Ducting Figure and Table courtesy of: Davidson, Assessment of Atmospheric Factors in EM/EO Propagation, pp 3- Evaporation Duct The ED is one of an operators primary concerns over water Can significantly enhance the range and strength of signal propagation

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) Radar communications

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 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

Calculated Evaporation Duct Height (EDH) and it added to environmental profile 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. 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 Rawinsonde Ship rawinsonde: 18191313ZJUL07 MM5 MM5 Upperair forecast: 18180000ZJUL07 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). MM5 Upper air forecast:18180000ZJUL07 No extended near-surface ranges. Ship rawinsonde: 18191313ZJUL07 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. Rawinsonde Ship rawinsonde: 20114219ZJUL07 MM5 MM5 Upper air forecast: 20120000ZJUL07 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. Extended near-surface ranges due to ED. ED almost 2x as thick as 18JUL MM5 Upper air forecast: 20120000ZJUL07 Notice extended near-surface detection ranges Ship rawinsonde: 20114219ZJUL07

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. Scatter Plot EDH OBS vs. EDH Model 90 80 EDH Model (ft) 70 60 50 40 30 20 10 0 0 5 10

15 20 25 30 35 40 EDH OBS (ft) Model has little to no skill in predicting ED when observed SST is used for extrapolating the ED. No further statistics were looked at. In Situ vs Model RH 120 RH (%)

100 80 In Situ RH 60 Model RH 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 16 Values 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. 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 model RH is off, the ED will be off Underprediction or overprediction! Appending an ED profile to an upper air profile takes manipulation

If the SST is warmer than the lowest levels, the atmosphere would be less stable than it actually is 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 What do we do??? Vertical high resolution model fields

In Situ or land vertical sounding Use a model with SST fields Make in situ SST observations to use 2m wind and Air T/another level and extrapolate down 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) 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. Courtesy of: Atkinson et al, 2000. Current Research-Predicting EDH Cannot be determined by rawinsondes (nearsurface 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 Courtesy of: Babin et al, 1996. Questions?

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