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テレスコープアレイ計画63
大気モニタR&D
Atmospheric Monitoring
for TA
M Chikawa, J Kaku，
T Benno, T Nishikaze Kinki Univ.
N Hayashida
ICRR
and TA group
30th March 2004 : JPS @ 福岡
Air Fluorescence
I0∝E
I
A
 R
exp
  
4R 2
I 0  I i , EEAS  Ei ,    Raileigh   Mie
I 0  EEAS
 : attenuation length, 1/ : extinctioncoefficient
Atmospheric structure
change its transmittance in spatial and vary with time
→ important to know its structure and time variation
→ back scatt., side scatt., sunphoto meter etc.
z
scattering process
atmosphere
Rayleigh(molecule)
depends on ρ(z)
density ρ(z)
cloud
Mie(aerosol)
depends on aerosol
wide and local area
time
wind
aerosol
dust,
vapour,
mist, fog
Estimate of Mie effect near ground surface (simulation by Ogio(TIT))
EAS
Fluorescence light
3km
TA
without any
cut for the data
cut data w/i 3km
above ground
generated events = 100, arrival zenith angle : uniform
energy =10^20 eV (fixed)
Atmospheric Monitoring
- lidar system : transparency of atmosphere as far as possible
 fluorescence light correction factor : I ⇒I0∝EEAS
 feasibility study at AKENO suggests aspect
to determine extinction coefficient by 20km : steerable Lidar
How to… shoot, DAQ, analyze，and calibrate, etc.
- cloud monitoring : fiducial volume
 IR(infra red) camera
Observe all sky region
→ IR camera + convex mirror
- astro dome
 will be settled on the roof of each three stations
in order to install Liar systems
These are the issues that Japanese Atmospheric WG is going to do for TA.
back scattering (LIDAR method)
&
side scattering (phase function method)
d  180
A
T
4R 2
d
 R

T  exp 2  (r ' )dr'
 0

P  P0 (l )
d R
 const  (1  cos2  )
d
8
total :  R ( ) 
  
3
θ=180
0<θ<180
θ
Laser
Horizontal Measurement
Assumption for analysis
To evaluate the extinction coeff. from Lidar data,
Simple & convenient assumption for structure of atmosphere is applied.
1, only Rayleigh Scattering>10km
Assume this behaviour,
develop a new Lidar system
Inclined Laser shots
2, Atmosphere
Almost Uniform
In Horizontal
direction
Lidar
3, Measure Horizontal: Rayleigh+Mie
Typical examples
Akeno data 15/Oct/2003
Observed at Akeno
2003/10/16
2
path length v.s. P ×R
2
2
10
P×R
• Lidar exp’t at Akeno
• Typical sample of
good results
• Corrected intensity of
scattered light PxR2
vs. light path length
1
10
0
2
4
6
path length(km)
8
Extinction length vs.
height from ground
surface
horizontal
  const  k
 : back scattercoefficient
 : extinctionlength
k : empirical constant
Lidar exp’t
R&D @ Akeno w/ steerable system
Mirror diameter 15cm, laser power 5mJ
3-dimension measurement : ≦10km in vert. & horiz.
condition
fine
hazy
cloudy
α ± Δα
0.0639 ± 0.0005
0.1394 ± 0.0005
0.1645 ± 0.0010
0.3254 ± 0.0016
⇒ should be measured far distance ～20km
solution : install larger mirror, higher power laser
1/2
parameters of the lidar system
to determine extinction
coeff. approx. 20km
with few % error
Off-line analysis :
analyze Lidar data from
each station independently
required specification for Lidar system
Nd/YAG
laser
355nm, 4 mJ
5ns pulse laser
mirror
30cmφ
PMT
3/4”
Gain ～106
FADC 12bit
ADC
→ spatial resol.: few 10m
New LIDAR system
透過率測定
Energy meter
telescope
UV透過率測定
35
30
25
20
Energy meter
T1=4752±290
31000
29500
28000
26500
25000
23500
22000
20500
19000
17500
16000
14500
13000
11500
8500
10000
7000
5500
4000
15
10
5
0
T0=128940±798
補正板＋主鏡＋副鏡
R = T1/T0 = 0.17±1%
Nd:YAG Laser
5 mJ / pulse
IR Camera
Cloud monitoring
Sensitivity : 8 -14μm
FOV：25.8゜（H）×19.5゜（V）
-20 ゜～ 300 ゜
320×236 pixel
digital value  temperapure
IR Camera
Cloud monitoring
• IR camera on a steerable system:
Akeno Lidar system
• IR camera
use 2-dimensional cloud monitor
and measure distance by Lidar
 3-dimensional cloud monitoring
• option : VTR(visible light) for allsky waether monitor
IR camera on AKENO lidar system
calculates of edge of the cloud
differential coeff.
threshold cut
digitize: B&W
Astro dome
• settle an astrodome nearby
the telescope station on the
ground
install a new LIDAR system
inside astrodome
Discussion
•
Range of extinction length : 20km  may be OK, but enough?
 feasibility study at Akeno supports 20km measurement:
realistic limit value for our Lidar system
 during laser shooting to measure
 might be serious problem for DAQ of E>1018eV, EAS rate from AGASA
★ ext. length α has large dependence of
the empirical parameter k (=0.6 to 1.3) in the model
 feasibility study to measure absolute light intensity by PMT
free from model dependence for Rayleigh scattering
•
LIDAR : steerable system
 need to establish robust system using commercial product
•
Astro dome : settle on the ground nearby the TA station
•
IR camera
 all sky monitoring and off-line data analysis can be available

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