Roy Yaniv Department of Geophysics and Planetary Science, Tel Aviv University, Israel Yoav Yair, Open University of Israel, Ra’anana, Israel Colin 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 ( nm). 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

Camera Calibration set-up GL=0GL=255 T c =400C T c =460C T c =430C T c =490C

GL analysis Example: For T c =450C the mean Gray Level is =164 ROI

Calibration and image analysis

Where: K’ – Calibration constant [GL/(ph/sec/mic)] IFOV – Instantaneous FOV of a camera pixel [str] A opt – Clear aperture of the CCD lens [cm 2 ] P(,T c ) – Planck’s function at wavelength and cal. temp. T c [W/str/cm 2 /mic]  c – Atmospheric transmittance during the calibration (=1) F( ) – Filter transmittance QE – Quantum efficiency of the CCD Calibration and image analysis (cont.)

But we need From these equations we get Where: N( ) – The radiance of the TLE [ph/sec/str/cm 2 /mic]  m – atmospheric transmittance during the measurements (~1) Calibration and image analysis (cont.)

Assuming the atmospheric transmittance -  m is almost 1, then we get: Where It should be noted that N is expressed in Rayleigh units 1R = 10 6 /4  [ph/sec/str/cm 2 ] Calibration and image analysis (cont.)

470 C K 450 C K 420 C K 400 C K Radiance [Rayleigh] Gray Level mean value (std) Black Body Temp[C 0 ]Black body Image Calibration and image analysis (cont.)

In our CCD the calibration constant K’ has quadratic dependence on the GL

Measuring TLEs - GL of different ROIs

GL distribution - definition of TLE pixels in the ROI 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 – GL bckg-max 3.For all GL>GL bckg-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

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 Thank You