October 29-30, 2001MEIDEX - Crew Tutorial - Calibration F - 1 MEIDEX – Crew Tutorial Calibration...

October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 1

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

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


The IMC-201 Parameters


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


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.


The FOV of the IMC-201 – The PSF

Filter 6


The Required Radiometric Accuracy

for

Dust Measurements


0.3 0.4 0.5 0.6 0.7 0.8 0.90.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0.011

Sea albedo, Rural Aerosol, Total Radiance, IVSA=0

VIS=5km VIS=15km VIS=23km VIS=40km

SP

EC

TR

AL

RA

DIA

NC

E (

W/s

r/cm

^2/m

)

WAVELENGTH (m)

Dust Radiance

Dust Radiance as Measured for Rural Aerosols (over sea surface) with OD ~ 0.8, 0.3, 0.2 and 0.1


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


Radiometric Accuracy – Calibration Aspects


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.


y = 4.2387E-08x3 + 3.2137E-06x2 + 2.1325E-02x - 3.1018E-02

0

12

3

4

56

7

8

0 50 100 150 200 250

GL0

N*t

-4.E-02

-3.E-02-2.E-02

-1.E-02

0.E+00

1.E-022.E-02

3.E-02

4.E-02

F1

Res(%)

Poly (F#1)

y = 1.1724E-09x3 + 2.1094E-06x2 + 3.5903E-03x - 1.2991E-03

00.10.20.30.40.50.60.70.80.9

1

0 50 100 150 200 250

GL0N

*t

-3.E-02-2.E-02-2.E-02-1.E-02-5.E-030.E+005.E-031.E-022.E-022.E-023.E-02

F2

Res(%)

Poly (F#2)

y = -3.7268E-11x3 + 1.0192E-07x2 + 8.5271E-05x - 3.4402E-05

0

0.005

0.01

0.015

0.02

0.025

0.03

0 50 100 150 200 250

GL0

N*t

-3.E-02

-2.E-02

-1.E-02

0.E+00

1.E-02

2.E-02

3.E-02

F3

Res(%)

Poly (F#3)

y = 2.9827E-11x3 + 3.2520E-08x2 + 4.5472E-05x - 7.9079E-05

0

0.0020.004

0.0060.008

0.01

0.0120.014

0.016

0 50 100 150 200 250

GL0

N*t

-4.E-02

-3.E-02-2.E-02

-1.E-020.E+00

1.E-02

2.E-023.E-02

4.E-02

F4

Res(%)

Poly (F#4)

y = 1.3538E-11x3 + 1.4886E-08x2 + 1.8570E-05x - 1.3633E-05

0

0.001

0.002

0.003

0.004

0.005

0.006

0 50 100 150 200 250

GL0

N*t

-3.E-02

-2.E-02

-1.E-02

0.E+00

1.E-02

2.E-02

3.E-02

F5

Res(%)

Poly (F#5)

y = 1.8949E-11x3 + 2.2680E-08x2 + 2.7429E-05x - 1.5746E-05

0

0.0010.002

0.0030.004

0.005

0.0060.007

0.008

0 50 100 150 200 250

GL0

N*t

-4.E-02

-3.E-02-2.E-02

-1.E-020.E+00

1.E-02

2.E-023.E-02

4.E-02

F6

Res(%)

Poly (F#6)

Radiometric Calibration of Xybion IMC-201


Normalized Response of Xybion IMC-201

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250

Gray-Level

No

rmal

ized

[E

xpo

sure

x R

adia

nce

]

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Total Residuals

-4%

-3%

-2%

-1%

0%

1%

2%

3%

0 50 100 150 200 250

GL0

RE

SID

UA

LS

Xybion IMC-201 – Absolute Radiometric camera


XYBION Temperature Response

0.92

0.94

0.96

0.98

1

1.02

1.04

20 25 30 35 40

Temperature [C]

No

rmal

ized

Res

po

nse Filter 1

Filter 2

Filter 3

Filter 4

Filter 5

Filter 6

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.


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.

Sphere illuminated flat-field response

Fitted poly-surfaceGrayscale is 0.8 – 1.0

Difference of flat-field and fitted surface gives the Pixel-to-pixel correction. Scale is +/- 4%

Uncorrected sphere illumination

Corrected sphere illumination


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.


Pixel-to-Pixel Non-uniformity


The Moon Calibration



XYBION Camera Long-term Stability

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

1.06

Nov 2

6th a

Nov 2

6th b

Nov 2

9th

Feb 1

7th

Apr 17

th a

Apr 17

th b

Apr 18

th a

Apr 18

th b

Apr 20

th a

Apr 20

th b

Test date

Re

spo

nse

Re

lati

ve

to

No

v 2

9th

, 199

9

Filter 1

Filter 2

Filter 3

Filter 4

Filter 5

Filter 6

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.



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.



Moon Relative Calibration with Lock_Manual Fixed Exosure for each filterResponse = (60x60 square ROI sum - 3600 Bkg)/"Moon" mask Area

0.98

0.99

1.00

1.01

1.02

1.03

1.04

3 4 5 6 7 8 9 10Moon Angular Size [mrad]

No

rmal

ize

Res

po

nse

Filter 3

Filter 4

Filter 5

Filter 6

Filter 3 (50 pixelsquare)



Moon Relative Calibration with Run-Auto ExosureResponse = (60x60 square ROI sum - 3600 Bkg)/"Moon" mask Area

0.95

0.96

0.97

0.98

0.99

1.00

1.01

1.02

1.03

1.04

1.05

3 4 5 6 7 8 9 10

Moon Angular Size [mrad]

No

rmal

ized

Res

po

nse

Filter #3

Filter #4

Filter #5

Filter #6



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


Radiometric Accuracy – An Example


Filter #

Exposure time (msec)

Gain (%)

CCD Temp. (Co)

Date (mm/dd/yy)

Time (hh:mm:ss)

Coded data

Radiometric Images of the Sky

1

1

2 43

5 6


Clear Sky Radiance Measurements

Modeled with Rayleigh atmosphere.

Radiance data show SZA dependence in comparisons.


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.


END

Crew Tutorial – Calibration of IMC-201

October 29-30, 2001MEIDEX - Crew Tutorial - Calibration F - 1 MEIDEX – Crew Tutorial Calibration...

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Transcript of October 29-30, 2001MEIDEX - Crew Tutorial - Calibration F - 1 MEIDEX – Crew Tutorial Calibration...