MEIDEX – Crew Tutorial Calibration of IMC-201 Adam D. Devir, MEIDEX Payload Manager

1. MEIDEX – Crew TutorialCalibration of IMC-201Adam D. Devir, MEIDEX Payload Manager MEIDEX - Crew Tutorial - Calibration

2. Calibration of Xybion IMC-201 • Camera Parameters • Filters • FOV • The Required Radiometric Accuracy for Dust Measurements • Dust Measurements • Radiometric Accuracy – Requirements • Radiometric Accuracy – Calibration Aspects • Radiometric Calibration of Xybion IMC-201 • Xybion IMC-201 – Absolute Radiometric Camera • Temperature Effect on the Absolute Calibration • Flat Field Calibration • Pixel-to-Pixel Non-uniformity • The Moon Calibration • An Example • Radiometric Images of the Sky MEIDEX - Crew Tutorial - Calibration

3. The IMC-201 Parameters MEIDEX - Crew Tutorial - Calibration

4. Filters • The IMC-201 is equipped with a filter wheel with 6 filters • Filter #1: CWL= 339.7nm, FWHM=4.1nm • Filter #2: CWL= 380.6nm, FWHM=4.4nm • Filter #3: CWL= 472.1nm, FWHM=25.1nm • Filter #4: CWL= 558.2nm, FWHM=26.5nm • Filter #5: CWL= 665.4nm, FWHM=48.3nm • Filter #6: CWL= 855.5nm, FWHM=53.0nm MEIDEX - Crew Tutorial - Calibration

5. The FOV of the IMC-201 • The total FOV of the IMC-201 was measured to be 13.93o (H) x 10.66o (V). • The total FOV was measured to be 699 (H) x 481 (V) pixels. • The dimensions of each pixel are 0.33mrad (H) x 0.37mrad (V). • At flight altitude of 300km, each pixel will cover 0.1 km (H) x 0.11 km (V). • The PSF of the IMC-201 was measured to be ~3pixels (see next slide). • Correspondingly, from radiometric point-of-view, the minimal area that can be measured (in the nadir) will be ~ 0.3 x 0.3 km2. MEIDEX - Crew Tutorial - Calibration

6. Filter 6 The FOV of the IMC-201 – The PSF MEIDEX - Crew Tutorial - Calibration

7. The Required Radiometric Accuracy forDust Measurements MEIDEX - Crew Tutorial - Calibration

8. Dust Radiance Dust Radiance as Measured for Rural Aerosols (over sea surface) with OD ~ 0.8, 0.3, 0.2 and 0.1 MEIDEX - Crew Tutorial - Calibration

9. Radiometric Accuracy • In order to be able to calculate the aerosol parameters from the radiometric measurements of the solar radiance reflected from the dust (above the Mediterranean sea surface), two measurements have to be done: • Measurement of the radiance of the sea surface – free from the dust. • Measurement of the radiance of the dust above the sea. • Both measurements have to be done with accuracy of  1%/. • For this we need to have an accurate calibration of the Xybion camera that will enable us to calculate the radiance with that accuracy. • The main factors that affect the calibration accuracy are: • Radiometric Calibration – Absolute calibration • Calibration of the Temperature Effects on the Calibration • Flat Field Calibration • Pixel-to-Pixel Non-uniformity MEIDEX - Crew Tutorial - Calibration

10. Radiometric Accuracy – Calibration Aspects MEIDEX - Crew Tutorial - Calibration

11. Absolute Radiometric Calibration • The radiometric calibration of the Xybion camera is based on measuring the radiance (R) of an aperture of an integrating sphere (*) with different exposure times – t [msec] and for all filters. • The product of the (N x t) is shown as a function of the Level of the video signal of the aperture expressed in gray-level units – GL0. • The polynomial dependence – N x t = f3(GL0) allows to show that such fit has a residuals <1% over most of the dynamic range of the camera for all filters. • Normalizing this polynomial dependence for all filters shows that the radiometric response of the camera is the same for all filters.(*) An integrating sphere is a device that has a rather large aperture with a constant spectral radiance – N [Watt/str/cm2/nm] all over its aperture. MEIDEX - Crew Tutorial - Calibration

12. Radiometric Calibration of Xybion IMC-201 MEIDEX - Crew Tutorial - Calibration

13. Xybion IMC-201 – Absolute Radiometric camera MEIDEX - Crew Tutorial - Calibration

14. Filter Slope %/degree 1 -0.21 2 -0.30 3 -0.27 4 -0.27 5 -0.30 6 -0.11 Temperature Effect on the Absolute Calibration • System sensitivity decreases with an increase in its temperature (this is characteristic of all bi-alkali photo-cathodes. • Correctable to 0.5% level after initial warm-up period of ~25 minutes. MEIDEX - Crew Tutorial - Calibration

15. Fitted poly-surface Grayscale is 0.8 – 1.0 Difference of flat-field and fitted surface gives the Pixel-to-pixel correction. Scale is +/- 4% Sphere illuminated flat-field response Uncorrected sphere illumination Corrected sphere illumination Flat field Calibration by Integrating Sphere • Slowly varying component is removed via polynomial surface fit. • Residual variations are due to fiber optic and pixel gain variations. MEIDEX - Crew Tutorial - Calibration

16. Pixel-to-Pixel Non-uniformity Fitted surface images • The 20% variation of the center-to-edge asymmetry is mostly apparent in channel 6 and probably is due to internal scattering. • Residual non-uniformity. • Fiber bundle variations and pixel gain variations are +/- 4% and are similar for all the channels. MEIDEX - Crew Tutorial - Calibration

17. Pixel-to-Pixel Non-uniformity MEIDEX - Crew Tutorial - Calibration

18. The Moon Calibration MEIDEX - Crew Tutorial - Calibration

19. The Moon Calibration The long-term stability of the calibration was tested. The variations in the stability were found to originate in Gain changes of the MCP (due to the use of unregulated voltage supply) and to aging of the integrating sphere. MEIDEX - Crew Tutorial - Calibration

20. The Moon Calibration • In-flight calibration is the only indication that the Xybion calibration was not affected by any deposition on the window of the canister. • The MEIDEX payload has no internal calibration sources to be used for such in-flight on-board radiometric calibration of the Xybion camera. • The only in-flight calibration options are: • Using calibration sites on the earth (that depend on their exact albedo and the sun attenuation through the atmosphere). • Using moon calibration. • Two Moon calibrations made in-fight as part of MEIDEX primary mission (one at the beginning of the mission and one towards its end) will give us the indication that the Xybion calibration was not affected during the mission. • Since the moon diameter is rather small (~8.7mrad) and the PSF of the camera (~1mard ) is not very small compared to it, it was decided to test the accuracy of the moon calibration by placing a variable iris (with known angular diameter) in front of the aperture of an integrating sphere. MEIDEX - Crew Tutorial - Calibration

21. The Moon Calibration MEIDEX - Crew Tutorial - Calibration

22. The Moon Calibration MEIDEX - Crew Tutorial - Calibration

23. The Moon Calibration • The radiometric calibration of the moon was found to be good. The deviation from normalized response of one are reasonable since: • There was no flat-field correction and especially no pixel-to-pixel correction. Such correction will affect very much the radiometric response of the camera especially for small targets. • There is some jitter in the Run Mode exposure time MEIDEX - Crew Tutorial - Calibration

24. Radiometric Accuracy – An Example MEIDEX - Crew Tutorial - Calibration

25. Radiometric Images of the Sky 1 6 5 Filter # Exposure time (msec) Gain (%) CCD Temp. (Co) Date (mm/dd/yy) Time (hh:mm:ss) Coded data 1 3 2 4 MEIDEX - Crew Tutorial - Calibration

26. Clear Sky Radiance Measurements • Modeled with Rayleigh atmosphere. • Radiance data show SZA dependence in comparisons. MEIDEX - Crew Tutorial - Calibration

27. Sky with small amount of Aerosol • Better SZA agreement is obtained by adding 0.05 optical depth aerosol. • Both measured 340nm and 380 nm radiance values are lower with respect to the model which is consistent with stray light in the calibration. MEIDEX - Crew Tutorial - Calibration

28. ENDCrew Tutorial – Calibration of IMC-201 MEIDEX - Crew Tutorial - Calibration