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Roy YanivDepartment of Geophysics and Planetary Science,Tel Aviv University, Israel
Yoav Yair, Open University of Israel, Ra’anana, IsraelColin Price, Tel Aviv University, Tel Aviv, Israel Adam D. Devir, IARD Institute for Advanced R&D, Haifa, Israel
Contents
• Equipment
• Calibration set-up
• GL Analysis
• Calibration and image analysis
• Measuring TLEs - GL of different ROIs
• GL distribution - definition of TLE pixels in the ROI
• Radiance calculations
• Recent results
Equipment
• A Black Body for radiometric calibration (CI Model SR-20)
• A CCD camera (Watec Model 902H) with a well-defined band-pass filter (640-800nm).
• Video/Image capturing software
• Image processing software (ImageJ)
• Calibration method for CCD cameras (conversion of gray-level (GL) to radiance (or Rayleigh units)
• And…….images of Sprites or Elves
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.6 0.7 0.7 0.8 0.8 0.9
Wavelength [micron]
Tra
ns
mit
tan
ce
Camera
Calibration set-up
GL=0 GL=255
Tc=400C
Tc=460C
Tc=430C
Tc=490C
GL analysis
Example: For Tc=450C the mean Gray Level is <GL>=164
ROI
1.0E+07
1.0E+08
1.0E+09
1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
1.0E+15
0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Wavelength [micron]
Ra
dia
nc
e (
ph
/s/s
tr/c
m2
/mic
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Tra
nsm
itta
nce
/ QE
BB at 470 C 640-800nm Filter Watec 902H QE
Calibration and image analysis
d)(QE)(F)L,(
h
)T,(PAIFOV'KGLGL cc
coptoffsetc
Where:
K’ – Calibration constant [GL/(ph/sec/mic)]
IFOV – Instantaneous FOV of a camera pixel [str]
Aopt – Clear aperture of the CCD lens [cm2]
P(,Tc) – Planck’s function at wavelength and cal. temp. Tc [W/str/cm2/mic]
c – Atmospheric transmittance during the calibration (=1)
F() – Filter transmittance
QE – Quantum efficiency of the CCD
Calibration and image analysis (cont.)
d)(QE)(F)L,()(NAIFOV'KGLGL mmoptoffsetm
opt
mmm AIFOV'K
GLd)(QE)(F)L,()(N
?d)(NNpixel
But we need
From these equations we get
Where:
N() – The radiance of the TLE [ph/sec/str/cm2/mic]
m – atmospheric transmittance during the measurements (~1)
Calibration and image analysis (cont.)
Assuming the atmospheric transmittance - m is almost 1, then we get:
FQEAIFOV'K
GLd)(N
opt
m
d
d)(QE)(FFQE
Where
It should be noted that N is expressed in Rayleigh units
1R = 106/4 [ph/sec/str/cm2]
Calibration and image analysis (cont.)
BB [C] 400[R] 1.76E+05
0.002
Wvlngth BB
[mic] [W/cm2/str/mic]
300 0.300 5.5103E-25
302 0.302 8.5450E-25
304 0.304 1.3172E-24
306 0.306 2.0185E-24
308 0.308 3.0754E-24
310 0.310 4.6594E-24
312 0.312 7.0204E-24
314 0.314 1.0520E-23
316 0.316 1.5682E-23
318 0.318 2.3253E-23
320 0.320 3.4305E-23
322 0.322 5.0355E-23
Calibration and image analysis (cont.)
2751.71 10
7253.8 10
16461.16 10
245470 C0
623 K
450 C0
623 K
420 C0
698 K
400 C0
673 K
Radiance [Rayleigh]Gray Level mean value
(std)Black Body Temp[C0]Black body Image
62.33 10
Calibration and image analysis (cont.)
Calibration and image analysis (cont.)
In our CCD the calibration constant K’ has quadratic dependence on the GL
y = 3.34E+01x2 + 7.02E+02x + 1.43E+05
R2 = 9.99E-01
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
0 20 40 60 80 100 120 140 160 180 200 220 240 260
GL
Rad
ian
ce [
R]
Measuring TLEs - GL of different ROIs
GL distribution - definition of TLE pixels in the ROI
0
10
20
30
40
50
60
70
80
10 20 30 40 50 60 70 80
Gray Level
Nu
mb
er o
f p
ixel
s
Background-right
Sprite-right
Bckg-center
Sprite-left
Background-left
Pixels with GL<49 originate
from the background
Pixels with GL>49
originate from the TLE
1. From Image J ROI analysis we get for each ROI (background and TLE) a list of all gray levels and the number of pixels in each GL
2. We find the largest GL value that define the GL distribution of the backgrounds – GLbckg-max
3. For all GL>GLbckg-max in the ROI of the TLE we calculate the
radiance value [R] of the pixels with this GL using:
4. The average radiance of the TLE is calculated from the GL distribution
Measuring TLEs: Radiance calculations
FQEAIFOV'K
GLd)(N
opt
m
Recent results
Left Sprite: 269 KR*Right Sprite: 301 KR*
Elve: (“Upper part”) 5.3 MR^Elve: (“Lower part”) 4.82 MR^
Enhanced image
*Assuming the duration of the TLE is 30ms. ^Assuming the duration of the TLE is 1ms.
Conclusions: The fun is in capturing TLEs….
•We developed a reliable and accurate method for calibrating Commercial CCD camera.• This method enables radiometric measurements of TLE luminosity.• Using spectral filters enables us to Identify energy levels of ionozation in TLEs.
The End
ThankYou