Suggestions for Now casting of the optical environment. Ove Gustafsson, FOI

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1 Suggestions for Now casting of the optical environment Ove Gustafsson, FOI

2 Abstract The use of optical och electro-optical system within society both the military part and the civil society are expanding continuously. The environmental influence on the optical signals are evinced as reduction of the signal and turbulence disturbance, with data loss, enlarged nominal optical hazard distances (NOHD) and disturbed images as consequences. The signal reduction due to absorption and scattering for active and passive system can be deduced out of weather parameters as humidity, temperature, wind, visual range etc. The important of the influence on atmospheric attenuation and optical turbulence on laser propagation and images as function of weather parameters as for instance the structure parameter of refractive index will be discussed. With the use of mesoscale numerical weather prediction methods there are also possibilities to deduce for instance the structure parameter for refractive index (C n ) as function of heights.

3 Introduction Lidar measurement Nominal Ocular Hazard Distance, NOHD Atmospheric influence on NOHD OHD Examples of effects due to turbulence Turbulence influence on laser safety range Structurfunction of refraction, C n Cloud characterization Discussion and conclusions

4 Lidar instrument Receiver: APD module diam. 1 mm (Licel S ) focal length of 615 mm FOV of 1.6 mrad filter FWHM 1 nm Licel TR40: sample rate 40 MHz Laser: 30 mj, 1064 nm, pulse length 5 ns, PRF 10 Hz, beam divergence 0.5 mrad beam diameter 3 mm

5 Altitude [m asl] (resolution 75 m) Altitude [m asl] (resolution 75 m) IR-lidar measurement and comparison Lidarsondering (lokal tid) kl 10:8:4-10:33:45 Hm: 6975 Su: 50, H1: 000, Sm: 50, H: 10000, So: 50, ak: 8/ Lidar sounding (local time) 15:30-16: µm 355 nm Aerosol backscatter [1/(m sr)] x Aerosol backscatter [1/(m sr)] x 10-7

6 Nominal Ocular Hazard Distance, NOHD E = 4P o π a + θ r a 16,43 3,75 NOHD = 1 θ 4P o π MPE a r 331,96 NOHD NOHD Gustafsson etal. Visual appearance of wind turbine tower at long range measured using imaging system SPIE8891Y, 013 Laser Energy [J] Divergence [mrad] MPE [J/m ] NOHD [km] Designator Laser, single pulse 0,180 0,08 0,050 6,5 Designator Laser, pulse train 0,180 0,08 0,013 51,6

7 Lambert W Influence of atmospheric attenuation on laser safety range E = 4P o e µ dx π a + θ r = 4P o e µ r π a + θ r Lambert W function ωe ω = z W(z)e W(z) = z 10 Lambert W function y = z 10 1 W(z) 10 0 Steinvall, 009 Coreless, et al 1996 Valluri et. al 000 Chapeua-Blondeau et. al, W(z)/z Parameter z

8 Laser Safe Range [km] Atmospheric influence on laser safety range, NOHD OHD OHD μ = μ a + θr a + θr exp( W(μ θ θ μ ) ) a θ 60 Extinction coefficient [km -1 ] Inf NOHD-multiple OHD-multiple 30 0 NOHD-single OHD-single Visibility [km]

9 Exemple of laser spots

64 pixel image selections b Visual images, range 18.

10 Turbulence, effects on image high low high turbulence low turbulence a Intensity distributions in two 64 x 64 pixel image selections b Visual images, range 18.6 km Från Baltic 99 mätningarna FOA-R SE

11 Radiant exponering (irradians) [J/m ] Sannolikheten för skada [-] Turbulence influence on laser safety range, horizontal path Irradians vs avstånd, NOHD = 161 m Sannolikheten för skada vers avstånd, NOHD = 161 m C n =e-15 m -/3 C n =e-14 m -/3 C n =e-13 m -/ Avstånd [km] Avstånd [km] Nd:YAG laser Laser Energy 5 mj Puls frequence 0 Hz, Laser divergence 0,5 mrad Gustafsson etal. Lidar measurement as support to the ocular hazard distance calculation using atmospheric attenuation SPIE, Toulouse, 015.

12 Radiant exponering (irradians) [J/m ] Sannolikheten för skada [-] Turbulence influence on laser safety range, slant path Irradians vs avstånd, NOHD = 48 km Sannolikheten för överskrida MTE vers avstånd, NOHD = 48,4 km 1 C 0.9 n =5e-17 m -/3 C n =5e-16 m -/3 0.8 C n =e-15 m -/ Avstånd [km] Avstånd [km] Nd:YAG laser laser Energy J puls frequence 11.5 Hz, laser divergence 0,08 mrad

13 Structurfunction of refraction, C n, is influenced by weather and environment Sun time on the day season Cloud cover Meteorological parameters temperature humidity wind pressure Latitude Altitude convection wind shear Ground characteristics Breddgrad absorption och reflection vegetation buildings Strålnings flöde Tid på dygnet och året C n Brytningsindex fluktuationer Täthets fluktuationer Temperatur fluktuationer, Temperatur gradient, Höjd över marken, z Ytegenskaper Molnighet Luftfuktighet Markegenskap Marktäckning Ytan råhetsstruktur, z o Vertikal Vindhastiget Vindhastighet

14 Strukturfunktionen, C n Strukturfunktionen, C n, mått på statistiska medelvärdet C n (r 1 ) = n 1 n r 1 3 Kolmogorov spektrum och gäller for skalära vågtalet, k, inom området mellan inre och yttre skallängden. Φ n (κ) = 0,00330C n κ 11 3

15 Modeller av C n Tatarskiimodell C n (z) = C no z x Fried s och Brookner s modeller C n (z) = C no z b e z z o där x = 4/3, dagtid x = /3, natt Fried s modell, b = 1/3, z o = 300 m samt C no = 4, m -1/3 Brookner s modell, z o = 30 m samt C no = 3, m -1/3 b = /3, vid soluppgång och solnedgång b = 5/6, vid sol och dag klart väder b = 1, nattetid

16 forts. Modeller av C n Kaimal/Walters-Kunkels modell C n z = z 0 C no z z z, z 0 0,7z i 0,5z i z ,5z i z 0,7z i,9 0,5z i z z z i 3 0,7z i z z i Kukharets-Tsvangs modell (K-T) C n z C = 0,046 z z i no z ,6 exp 1 z z i 1,1 0,046 z o z i 4 3

17 forts. Modeller av C n Similaritetsmodeller C n = n T C T n T = P T Ri = g T Θ z U z C T = z 4 3 Θ z f 3 Ri

18 forts. empiriska modeller av C n Hufnagel modellen C n z = 8, U z 10 e z z o1 +, e z z o Hufnagel-Valley modellen C n z = 8, U z 10 e z z o1 +, e z z o + Ae z z o3

19 forts. parametermodeller av C n Sadot och Kopeika C n = 3, w T +, RH +, RH 1, RH 3, WS 1, WS 8, WS 3 5, Viktsfunktion, w temporal tid, th

regn Lidar med 1,5 µm laser kopplat till IR ev.

20 Moln karaktärisering Karaktärisering - moln fördelning - molnbas - molntjocklek - molntäthet - optisk täthet - regn Lidar med 1,5 µm laser kopplat till IR ev. i kombination med avståndsmätare. Studien Lidaranvändning för EO system

21 Exempel på lidarmätningar vågformer < 3 min 10 km Avståndskompenserat Elevation, steg

22 Other examples Visibility from pointmeter at the laser site Cloudy day (stratus) with ligh drizzle, T = +14 C, RH = 60 %, Vis. about km Haze close to ground Cloudy day (Cumulus) T = +14 C, RH = 60 %, Vis km. Cloudy day (stratus) with ligh drizzle, T= 13 C, RH = 74 %, Vis. about 0 km Clear, sun no clouds. T= 17 C, RH = 55 %, Vis km Clouds /8 cumulus. T= 0 C, RH = 50 %, Visibiility 5 40 km.

23 Diskussion - 3D beskrivning av atmosfärsturbulens, C n sfa höjden, med numeriska modeller, ex SAF-WRF (Masciadri et al. 1999) - Mängden aerosol sfa höjd med NWP + CTM (Kahnert 008) - Molntäckning, molnbas och tjocklek med NWP

24 Tack för uppmärksamheten!

25 Lidar station Vidsel 69 CALIPSO markspår

Latitud 66.5 JAS markspår vid, 014-11-1 1:34:11-13:57:18 66.

6 18.8 19 19. 19.4 19.6 19.8 0 0. 0.4 Longitud 66.19 66.18 66.17 66.

26 Latitud 66.5 JAS markspår vid, :34:11-13:57: CALIPSO markspår Longitud

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