OfPrecipitatingSystemsAtVariousFrequencyBands … · 2013. 9. 10. · Email...
1
Simulation Of Mono And Dual-Wavelength Airborne Radar Observations Of Precipitating Systems At Various Frequency Bands V ALENTIN L OUF 1 ,O LIVIER P UJOL 1 ,H ENRI S AUVAGEOT 2 ,J ÉRÔME R IEDI 1 , AND G UILLAUME P ÉNIDE 1 1 Université Lille 1, LOA Laboratoire d’Optique Amtosphérique 2 Université Toulouse III, Observatoire Midi-Pyrénées References [1] Valentin Louf et al. Simulation of airborne radar observations of precipitating systems at various frequency bands. IEEE TGRS, 2013. [2] Valentin Louf et al. The dual-wavelength method for hailstorm detection by airborne radar. submit- ted to IEEE TGRS. Conclusion and further studies We have studied the effect of different parameters: f , θ 3dB , rainfall and hailfall rate, and DW configuration. For this, more than 400 systems (purely numerical or inspired from reality) have been computed. Due to the relation θ 3dB ∝ λ/D , decreasing θ 3dB implies decreasing λ and increasing D . The simulation presented herein on modelled precipitating systems shows that (1) S -band is the best one to distinguish hail from rain since it does not suffer attenuation, but a low θ 3dB -values implies us- ing an important antenna diameter; (2) X -band is pe- nalized by attenuation, but allows good θ 3dB -resolution; (3) C -band seems to be a good compromise. Therefore, C-X is the best couple for hail observations by dual- wavelength airborne radar. Contact Information Web www-loa.univ-lille1.fr Email [email protected] Phone +33 (0)3 20 43 43 11 Scan this QR code to download this poster and more informations about this work. 1. Introduction Meteorological hazard in civil aviation is mainly due to convective precipitating systems, and par- ticularly hail and strong turbulence areas. A radar located behind the radome, forming the noise of the plane, is the only tool used to de- tect these precipitations. The question of the most efficient couple (f , θ 3dB ) has to be set for airborne radar precipitating system observations, where f is the microwave frequency and θ 3dB the beamwidth aperture at 3 dB (θ 3dB = 70λ/D , D is antenna diameter). We also studied the interest of the dual-wavelength technic. 2. Method Figure 1: (a) System configuration. Convective tow- ers are surrounded by a stratiform background (b) Hy- drometeor normalized vertical distribution. A realistic model of precipitating systems is used to perform simulations of airborne radar ob- servations at the six meteorological frequency bands: S (f ≈ 3 GHz), C (5.5 GHz), X (10 GHz), K u (15 GHz), K a (35 GHz), and W (94 GHz). The air- borne radar is located at 10 km of altitude. Range bin spacing is set to 150 m. The electromagnetic energy is supposed to be uniformly distributed. 3. Frequency and θ 3dB comparison Figure 2: The frequency effect. (a,b) Antenna diame- ter D a = 2m, and (c,d,e,f) D a = 0.8 m. All convective towers contain hail (here R h = 40 mm h -1 ) S and C -bands, two lines of convection are clearly visible. X -band the second row is attenuated and seems to be safe. K u , K a , and W -bands, the con- vective system is unobservable. Figure 3: The θ 3dB effect. PPI view simulation of the measured reflectivity Z m in a mesoscale system at vari- ous frequency bands: S (a,d), C (b,e), X (c,f), with a radar antenna size of 2m (a,b,c) and of 4m (d,e,f). X-band presents a good improvement for D = 2m, since the convective towers are separated. For D =4m, convective towers are identifiable. 4. Dual-wavelength technic (DWT) Figure 4: Gradient of the dual-wavelength reflectivity difference relative to the distance for (a) S-X, (b) S-C, and (c) C-X. Reflectivity field for (d) S, (e) C, and (f) X- bands for θ 3dB =3 ◦ . The quantity studied is the dual-wavelength ratio (DWR) dy /dr : dy dr = d dr [Z m,λ l (r ) - Z m,λ s (r )]. (1) where Z m is the measured reflectivity at a wave- length l or s (for large or small). It requires that the two radar beams illuminate identical volumes of resolution, the same value of θ 3dB =3 ◦ has been considered at S , C , and X -bands. The use of the DWR is interesting because hail is the only non- Rayleigh scatterer at these frequency bands, and thus it implies that DWR is positive in front of a hail tower and always negative at the rear, and this can be used as . R h (mm h -1 ) Target dist. (km) a) 10 20 30 40 50 60 70 80 50 100 150 200 250 300 350 400 450 500 550 dy/dr (dB km -1 ) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 R h (mm h -1 ) Target dist. (km) b) 10 20 30 40 50 60 70 80 50 100 150 200 250 300 350 400 450 500 550 dy/dr (dB km -1 ) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 R h (mm h -1 ) Target dist. (km) c) 10 20 30 40 50 60 70 80 50 100 150 200 250 300 350 400 450 500 550 dy/dr (dB km -1 ) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Figure 5: Gradient of the dual-wavelength reflectivity difference relative to the distance for (a) S-X, (b) S-C, and (c) C-X. Reflectivity field for (d) S, (e) C, and (f) X- bands for θ 3dB =3 ◦ . dy /dr increases with R h , small variations are due to Mie modes. 5. Real mesoscale system Figure 6: PPI field of dy /dr of hailstorm for S-X (a), S-C (b), and C-X (c). Measured reflectivity in dBZ at S (d), C (e), and X -bands (f). CAPPI at 10 km of alti- tude of the mesoscale system of May 2003, 2 nd , in Al- abama (USA). R indicates airborne radar position. Data comes from NEXRAD network (S -band). Radar desig- nation is KFCC. Black contours delimite possible hail area (Z m > 45 dBZ). White zone between 30 and 50 km corresponds to an absence of data. In order to illustrate the usefulness of the DWR to determine hail areas, let consider a real mesoscale precipitating system that occurs on May 2003, 2 nd in Alabama (USA). Note that the area C does not contain hail, although it presents a reflectiv- ity which is about that of areas A and B . It illus- trates that a criteria based solely on reflectivity is not sufficient for hail detection.
Transcript of OfPrecipitatingSystemsAtVariousFrequencyBands … · 2013. 9. 10. · Email...
Simulation Of Mono And Dual-Wavelength Airborne Radar ObservationsOf Precipitating Systems At Various Frequency Bands
VALENTIN LOUF1, OLIVIER PUJOL1, HENRI SAUVAGEOT2, JÉRÔME RIEDI1, AND GUILLAUME PÉNIDE11Université Lille 1, LOA Laboratoire d’Optique Amtosphérique 2Université Toulouse III, Observatoire Midi-Pyrénées
References
[1] Valentin Louf et al. Simulation of airborne radarobservations of precipitating systems at variousfrequency bands. IEEE TGRS, 2013.
[2] Valentin Louf et al. The dual-wavelength methodfor hailstorm detection by airborne radar. submit-ted to IEEE TGRS.
Conclusion and further studiesWe have studied the effect of different parameters: f ,θ3dB, rainfall and hailfall rate, and DW configuration.For this, more than 400 systems (purely numerical orinspired from reality) have been computed. Due to therelation θ3dB ∝ λ/D, decreasing θ3dB implies decreasingλ and increasing D. The simulation presented herein onmodelled precipitating systems shows that (1) S-band
is the best one to distinguish hail from rain since it doesnot suffer attenuation, but a low θ3dB-values implies us-ing an important antenna diameter; (2) X−band is pe-nalized by attenuation, but allows good θ3dB-resolution;(3) C−band seems to be a good compromise. Therefore,C-X is the best couple for hail observations by dual-wavelength airborne radar.
Contact Information
Web www-loa.univ-lille1.frEmail [email protected] +33 (0)3 20 43 43 11Scan this QR code to download thisposter and more informations aboutthis work.
1. Introduction
Meteorological hazard in civil aviation is mainlydue to convective precipitating systems, and par-ticularly hail and strong turbulence areas. Aradar located behind the radome, forming thenoise of the plane, is the only tool used to de-tect these precipitations. The question of themost efficient couple (f , θ3dB) has to be set forairborne radar precipitating system observations,where f is the microwave frequency and θ3dB thebeamwidth aperture at 3 dB (θ3dB = 70λ/D, D isantenna diameter). We also studied the interest ofthe dual-wavelength technic.
2. Method
Figure 1: (a) System configuration. Convective tow-ers are surrounded by a stratiform background (b) Hy-drometeor normalized vertical distribution.
A realistic model of precipitating systems is usedto perform simulations of airborne radar ob-servations at the six meteorological frequencybands: S (f ≈ 3 GHz), C (5.5 GHz), X (10 GHz), Ku(15 GHz), Ka (35 GHz), and W (94 GHz). The air-borne radar is located at 10 km of altitude. Rangebin spacing is set to 150 m. The electromagneticenergy is supposed to be uniformly distributed.
3. Frequency and θ3dB comparison
Figure 2: The frequency effect. (a,b) Antenna diame-ter Da = 2 m, and (c,d,e,f) Da = 0.8 m. All convectivetowers contain hail (here Rh = 40 mm h−1)
S and C -bands, two lines of convection are clearlyvisible. X -band the second row is attenuated andseems to be safe. Ku , Ka, and W -bands, the con-vective system is unobservable.
Figure 3: The θ3dB effect. PPI view simulation of themeasured reflectivity Zm in a mesoscale system at vari-ous frequency bands: S(a,d), C (b,e), X (c,f), with a radarantenna size of 2 m (a,b,c) and of 4 m (d,e,f).
X-band presents a good improvement for D =2m, since the convective towers are separated.For D = 4 m, convective towers are identifiable.
4. Dual-wavelength technic (DWT)
Figure 4: Gradient of the dual-wavelength reflectivitydifference relative to the distance for (a) S-X, (b) S-C,and (c) C-X. Reflectivity field for (d) S, (e) C, and (f) X-bands for θ3dB = 3◦.
The quantity studied is the dual-wavelength ratio(DWR) dy/dr :
dydr = d
dr [Zm,λl (r) − Zm,λs (r)]. (1)
where Zm is the measured reflectivity at a wave-
length l or s (for large or small). It requires thatthe two radar beams illuminate identical volumesof resolution, the same value of θ3dB = 3◦ has beenconsidered at S , C , and X -bands. The use of theDWR is interesting because hail is the only non-Rayleigh scatterer at these frequency bands, andthus it implies that DWR is positive in front of ahail tower and always negative at the rear, andthis can be used as .
Rh (mm h
−1)
Targ
et dis
t. (k
m)
a)
10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
400
450
500
550
dy/dr (dB km−1
)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Rh (mm h
−1)
Targ
et dis
t. (k
m)
b)
10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
400
450
500
550
dy/dr (dB km−1
)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Rh (mm h
−1)
Targ
et dis
t. (k
m)
c)
10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
400
450
500
550
dy/dr (dB km−1
)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Figure 5: Gradient of the dual-wavelength reflectivitydifference relative to the distance for (a) S-X, (b) S-C,and (c) C-X. Reflectivity field for (d) S, (e) C, and (f) X-bands for θ3dB = 3◦.
dy/dr increases with Rh, small variations are dueto Mie modes.
5. Real mesoscale system
Figure 6: PPI field of dy/dr of hailstorm for S-X (a),S-C (b), and C-X (c). Measured reflectivity in dBZ atS (d), C (e), and X -bands (f). CAPPI at 10 km of alti-tude of the mesoscale system of May 2003, 2nd, in Al-abama (USA). R indicates airborne radar position. Datacomes from NEXRAD network (S-band). Radar desig-nation is KFCC. Black contours delimite possible hailarea (Zm > 45 dBZ). White zone between 30 and 50 kmcorresponds to an absence of data.
In order to illustrate the usefulness of the DWR todetermine hail areas, let consider a real mesoscaleprecipitating system that occurs on May 2003, 2nd
in Alabama (USA). Note that the area C does
not contain hail, although it presents a reflectiv-ity which is about that of areas A and B. It illus-trates that a criteria based solely on reflectivity isnot sufficient for hail detection.
