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October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 1
MEIDEX – Crew Tutorial
Calibration of IMC-201
Adam D. Devir, MEIDEX Payload Manager
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 3
The IMC-201 Parameters
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 6
The FOV of the IMC-201 – The PSF
Filter 6
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 7
The Required Radiometric Accuracy
for
Dust Measurements
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 8
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 10
Radiometric Accuracy – Calibration Aspects
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 12
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 13
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 14
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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 15
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 17
Pixel-to-Pixel Non-uniformity
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 18
The Moon Calibration
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 19
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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 21
The Moon Calibration
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)
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 22
The Moon Calibration
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 24
Radiometric Accuracy – An Example
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 25
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
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 26
Clear Sky Radiance Measurements
Modeled with Rayleigh atmosphere.
Radiance data show SZA dependence in comparisons.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 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.
October 29-30, 2001 MEIDEX - Crew Tutorial - Calibration F - 28
END
Crew Tutorial – Calibration of IMC-201