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