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