Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager
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MEIDEX – Crew Tutorial Calibration of IMC-201 Adam D. Devir, MEIDEX Payload Manager PowerPoint PPT Presentation


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MEIDEX – Crew Tutorial Calibration of IMC-201 Adam D. Devir, MEIDEX Payload Manager. Calibration of Xybion IMC-201. Camera Parameters Filters FOV The Required Radiometric Accuracy for Dust Measurements Dust Measurements Radiometric Accuracy – Requirements

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

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Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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

MEIDEX - Crew Tutorial - Calibration


Calibration of xybion imc 201

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


The imc 201 parameters

The IMC-201 Parameters

MEIDEX - Crew Tutorial - Calibration


Filters

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


The fov of the imc 201

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


The fov of the imc 201 the psf

Filter 6

The FOV of the IMC-201 – The PSF

MEIDEX - Crew Tutorial - Calibration


The required radiometric accuracy for dust measurements

The Required Radiometric Accuracy forDust Measurements

MEIDEX - Crew Tutorial - Calibration


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


Radiometric accuracy

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


Radiometric accuracy calibration aspects

Radiometric Accuracy – Calibration Aspects

MEIDEX - Crew Tutorial - Calibration


Absolute radiometric calibration

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


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

Radiometric Calibration of Xybion IMC-201

MEIDEX - Crew Tutorial - Calibration


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

Xybion IMC-201 – Absolute Radiometric camera

MEIDEX - Crew Tutorial - Calibration


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

Pixel-to-Pixel Non-uniformity

MEIDEX - Crew Tutorial - Calibration


The moon calibration

The Moon Calibration

MEIDEX - Crew Tutorial - Calibration


The moon calibration1

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


The moon calibration2

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


The moon calibration3

The Moon Calibration

MEIDEX - Crew Tutorial - Calibration


The moon calibration4

The Moon Calibration

MEIDEX - Crew Tutorial - Calibration


The moon calibration5

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


Radiometric accuracy an example

Radiometric Accuracy – An Example

MEIDEX - Crew Tutorial - Calibration


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

Clear Sky Radiance Measurements

  • Modeled with Rayleigh atmosphere.

  • Radiance data show SZA dependence in comparisons.

MEIDEX - Crew Tutorial - Calibration


Meidex crew tutorial calibration of imc 201 adam d devir meidex payload manager

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


End crew tutorial calibration of imc 201

ENDCrew Tutorial – Calibration of IMC-201

MEIDEX - Crew Tutorial - Calibration


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