Evaporation Duct Profiles Lt. Charlotte A. Welsch OC 3570 19 MAR 02

Evaporation Duct Profiles Comparisons using Kites and Bulk Methods Review Evaporation Duct Results Conclusions

An over the water surface duct which increases distances of radar transmissions is likely to form when there is significant temperature and humidity gradients. Three parameters determine duct height: Pressure, Temperature, and water vapor. Relative humidity has greatest impact on evaporation ducts

Evaporation Duct Effect Effect Factor Tair = 19 C EDH = 7.6 m Wind speed = 10 kts RH = 80% SST = 20 C Tair = 21 C EDH = 14.8 m 40 30 20 10 SPS-12 1.5 GHz at 44 m Duct Height (m) SPS-10 5 GHz at 39 m 0 20 40 60 80 100 Radar Detection Range (nm) Detection range for a destroyer size target vs duct height

29 Jan 1800 29 Jan 2200 One average period fits bulk method better than smaller periods 2 Feb 2200

29 Jan 1800 One average period Bin averages: 2m 4m 8 m 0-10 10-20 20-200 1m 2m 4m 0-10 10-20 20-200 29 Jan 1800 Showing bin averages really don’t change the result when one average period 3

Edited/1st ave 29 Jan 2200 Edited/2nd ave One average Edited/3rd ave Each kite profile has many up/downs. When the kite is brought down it comes closer to the ship than any other time. When editing out the very bottom of the down segment, It is possible to improve the profiles from the overall average as seen here.

One must note it is difficult to cut out the bottom data and does not give a consistant improved profile as seen here for 29 Jan 1800

29 Jan 1800 29 Jan 1800 29 Jan 2200 29 Jan 2200 It appears that the M profile is closer to the bulk method when the relative humidity is higher in the time series. This could be because the relative humidity increase is indicating the kite is actually close enough to the surface To record the rh and temp gradients needed to have an evap duct 2 Feb 2200 2 Feb 2200

One up down was examined where rh was hi and a better profile was the result

Conclusions: Subjective Error Lower than 3-5 meters unreliable swell, kite dipping ht, sonde response Contaminated averages/uncertainty Bulk Method showed a higher duct height than kite data Shorter periods did not represent bulk method/Atmosphere variability important