In-orbit calibration (TOTAL channel)
Vspace-VIBB
Raw Earth V (counts) Raw IBB V (counts)
=
)(tL
VVG
FIBB
IBBspace
1)()(spaceIBB
IBBsceneFIBB
FIBB
IBBsceneFscence VV
VVtLtL
G
VVL
In-orbit calibration
1()(
)()()()(
TOTVTOTV
TOTVTOTVTOTLTOTL
spaceIBB
IBBsceneFIBB
Fscence
)(
)(
)()(
)()()(
SWLVV
VV
B
TOTL
SWLTOTBG
SWVSWVSWL
FIBB
spaceIBB
IBBsceneFIBB
FIBB
IBBsceneFscence
B : ground calibration measurement of G(SW source) / G(LW source)
LFIBB : ground calibration measurement of the filtered internal black body radiance
In-orbit calibration monitoring
• SW response monitored via CALMON solar diffuser sphere
Quartz filter transmission: [Vsw(light) – Vsw(dark)]/ [VTOT(light) – VTOT(dark)]
SW response: [VCALMON(light) – VCALMON(dark)] / GTOT
In-orbit calibration monitoring
• Internal black body behaviormonitored as by temperature variation
Calibration table updates 1: spectral response
• Updated reprocessed visible (0.4-2.5µm) detector spectral response received
• In the absence of infrared data this was ‘stitched’ to the witness sample infrared data (starting at 2.5µm)
• Updated calibration parameters have been produced from this (B, A, T)
Reprocessed Average Detector Spectral Response
and witness sample data
Reprocessed measured average detector and witness sample response
250
270
290
310
330
350
370
390
410
430
450
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
wavelength (um)
No
rmal
ize
d r
es
po
ns
e
`
Reprocessed Average Detector Spectral Response
and witness sample data
Reprocessed measured average detector and witness sample response
250
270
290
310
330
350
370
390
410
430
450
0 2 4 6 8 10 12 14 16
wavelength (um)
No
rmal
ize
d r
es
po
ns
e
`
Effect of reprocessed data on calibration
Ratio of Gain calculated from a SW source to that calculated from a LW source
Would be 1 for perfect knowledge of spectral response and instrument linearity
Green: old SR, Red: reprocessed SR
Calibration table updates 2: internal black body table
• Pixel to pixel variability in the filtered internal black body radiances determined from ground calibration has been found to be due to pixel offset drift during the calibration measurements
• This drift can and has been illuminated for the central pixels, a decision needs to be made about how the issue is dealt with for the other pixels in the array
• An update to the internal black body table will result after such a decision.
Variation of black body and detector temperatures
Detector temp. variation 0.4C
Implies G(TOT) variation ~ 0.008 (0.04%)
Gain variations 28/4/03 – 03/03/04
Pixel 123 (noisy)
Gain variations Scan means 28/4/03 – 03/03/04
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