COMS/MI IR channel calibration using MODIS measurements

B.J. SohnSchool of Earth and Environmental Sciences

Seoul National UniversitySeoul, Korea

Inter-calibration method for IR/WV channels- Compare the observed IR or WV radiance with

calculated radiance from well-calibrated polar orbiting satellites (here MODIS)

- Outputs : correlation coefficient, mean difference, standard deviation of the brightness temperature from GEO and LEO satellites

- Inter-calibration will serve as a monitoring tool

Background

! Determination of calibration coefficientLch = αch (C – C0)

where, Lch : expected radiance for a channel

αch : calibration coefficient C : satellite observed count C0 : offset (space view)

! Empirical relationship between Lch and TBchTBch = b/(ln Lch – a)

where, a and b are regression coefficients

Background

Determining the calibration coefficient

TBGEO’ = F (TBLEO)LGEO’ = exp (a + b/TBLEO’)αGEO ’ = LGEO’ / (C’ – C0)

whereTBLEO : LEO (MODIS channel) brightness temperatureTBGEO’ : Predicted GEO brightness temperature from the

observed LEO brightness temperature F : transfer functionCo ’ : offset count αGEO’ :calibration coefficient

Background

For MTSAT-1R IR channels

TB’(MTSAT) = a + b *TB(MODIS)

Relate observed TB(MTSAT) to estimated TB’(MTSAT)

MTSAT-1R Application

Algorithm Flowchart

MODIS Level 1B data

GEO IR/WVLevel 1B data

Scene type

Collocated data

RT model

Predicted radiance,Brightness temperature

Satellite measured radiance,Brightness temperature

Response function

Calibration monitoring(mean bias, RMSE)

clear

TOVS Initial Guess Retrieval (TIGR)

Viewing angle

Pre-calculated transfer function

-0.9498701.00357245°

-0.9174101.00344535°

-0.9339331.00350940°

-0.9559241.00360450°

-0.9000021.00337530°

-0.8855531.00332325°

-0.8738971.00327720°

-0.8628411.00323515°

-0.8586971.00322010°

-0.8524621.0031955°

-0.8505431.0031880°

y-interceptSlopeViewing angle

IR1 (11μm, ocean)

2.6186020.98959340°

2.6923500.98929845°

2.5573020.98983835°

2.7805710.98895550°

2.5080900.99003830°

2.4661620.99020925°

2.4301050.99035220°

2.4058860.99045415°

2.3865170.99053110°

2.3792410.9905625°

2.3713980.9905930°

y-interceptSlopeViewing angle

IR2 (12μm, ocean)

2.5175590.98721945°

2.6559480.98662240°

2.7220920.98633535°

2.1755260.98869850°

2.746224 0.98623030°

2.745126 0.98623525°

2.7462350.98623220°

2.7451670.98623815°

2.7413860.98625210°

2.7420740.9862515°

2.7379410.9862690°

y-interceptSlopeViewing angle

IR3 (WV, ocean)

0.7991640.99581645°

0.7260740.99616640°

0.6709850.99643335°

0.8981710.99535350°

0.633049 0.99662530°

0.605603 0.99677025°

0.5801540.99689620°

0.5642400. 99697715°

0.5558390.99702310°

0.5501110.9970565°

0.5462460.9970730°

y-interceptSlopeViewing angle

IR4 (NIR, ocean)

Transfer Function F

Collocated data sets

Data sets

" Viewing angles ≤ 50°" Viewing angle difference: ≤ |5°| " Observation time difference: ≤ 5 min" Only clear targets" MTSAT-1R / MODIS data are smoothed to 0.2° grid resolution

" MTSAT-1R & Terra/MODIS- Period: August, 2005 & 2006- Region: 40°N ~ 40°S, 100°E ~ 180°E

" MSG-1/SEVIRI & Aqua/MODIS- Period: July, 2004- Region: 40°N ~ 40°S, 40°W ~ 40°E

MTSAT-1R & Terra/MODIS

#Spectral response functions

6.5-6.9

6.5-7.0

Water Vapor CH [µm]

3.7-3.811.8-12.310.8-11.336MODS/Terra

3.5-4.011.5-12.510.3-11.35MTSAT-1R

SWIR CH [µm]

Window CH2 [µm]

Window CH1 [µm]ChsInstrument

wave length [µm]10.0 10.5 11.0 11.5 12.0 12.5 13.0

rela

tive

resp

onse

0.0

0.2

0.4

0.6

0.8

1.0

wave length [µm]4 7

0.0

0.2

0.4

0.6

0.8

1.0

MTSAT-1RMODIS/Terra

Window CH1 Window CH2 SWIR CH WV CH

TB Intercomparison for MTSAT-1R

WindowCH1 Window

CH2

WV CH SWIR CH

6.831.400.840.78RMSE

-6.69 1.310.36-0.16Mean bias

SWIR CHWV CHWindow CH2Window CH1

M e a s u re d M T S A T -1 R B rig h tn e s s T e m p e ra tu re [K ]

2 7 0 2 8 0 2 9 0 3 0 0 3 1 0 3 2 0

Pred

icte

d B

right

ness

Tem

pera

ture

[K]

2 7 0

2 8 0

2 9 0

3 0 0

3 1 0

3 2 0Y = 1 0 .4 7 + 0 .9 6 XM e a n B ia s : - 0 .1 5 5 0R M S E :0 .7 7 9 5C o rr: 0 .9 9 1 4

c o llo c a tio n : 4 6 2 6 p o in ts

a ) IR 1 (1 1 u m )

2 7 0 2 8 0 2 9 0 3 0 0 3 1 0 3 2 02 7 0

2 8 0

2 9 0

3 0 0

3 1 0

3 2 0Y = 1 0 .7 5 + 0 .9 6 XM e a n B ia s : 0 .3 6 2 9R M S E : 0 .8 4 2 0C o rr: 0 .9 9 0 1

c o llo c a tio n : 4 6 2 6 p o in ts

b ) IR 2 (1 2 u m )

2 3 0 2 4 0 2 5 0 2 6 0 2 7 0

Pred

icte

d B

right

ness

Tem

pera

ture

[K]

2 3 0

2 4 0

2 5 0

2 6 0

2 7 0Y = -7 .1 8 + 1 .0 2 XM e a n B ia s : 1 .3 0 8 8R M S E : 1 .4 0 0 7C o rr: 0 .9 9 6 5

c o llo c a tio n : 4 6 2 6 p o in ts

c ) W V (6 .7 u m )

M e a s u re d M T S A T -1 R B r ig h tn e s s T e m p e ra tu re [K ]

2 6 0 2 7 0 2 8 0 2 9 0 3 0 0 3 1 0 3 2 02 6 0

2 7 0

2 8 0

2 9 0

3 0 0

3 1 0

3 2 0Y = -4 .6 4 + 1 .0 4 XM e a n B ia s : -6 .6 9 3 3R M S E : 6 .8 3 2 8C o rr: 0 .9 7 3 8

c o llo c a tio n : 3 0 7 5 p o in ts

d ) S W IR (3 .7 u m )

(August 2005)

SWIR TB difference (Feb 14 - Feb 15, 2006)

0214.1933 UTC 0215.1933 UTC

-60 60

130 320 130 320

TB Intercomparison for MTSAT-1R

WindowCH1

WindowCH2

WV CH SWIR CH

0.981.680.950.90RMSE

-0.46 1.620.41-0.09Mean bias

SWIR CHWV CHWindow CH2Window CH1

M easu red M T S AT -1R B rig h tn ess T em p era tu re [K ]

270 280 290 300 310 320

Pred

icte

d B

right

ness

Tem

pera

ture

[K]

2 70

280

290

300

310

320

co llo catio n : 5635 p o in ts

a ) IR 1 (11 u m )

270 280 290 300 310 320270

280

290

300

310

320Y =11 .12+0 .96XM ean B ias : 0 .4082R M S E : 0 .9535C o rr: 0 .9943

co llo catio n : 5635 p o in ts

b ) IR 2 (12 u m )

230 240 250 260 270

Pred

icte

d B

right

ness

Tem

pera

ture

[K]

2 30

240

250

260

270Y =-8 .782+1 .03XM ean B ias : 1 .6178R M S E : 1 .6787C o rr: 0 .9960

co llo ca tio n : 5635 p o in ts

c ) W V (6 .7 u m )

M easu red M T S AT -1R B rig h tn ess T em p era tu re [K ]

270 280 290 300 310 320270

280

290

300

310

320Y =1.21+1 .00XM ean B ias : -0 .4576R M S E : 0 .9794C o rr: 0 .9871

co llo catio n : 3108 p o in ts

d ) S W IR (3 .7 u m )

Y =12 .96+0 .96XM ean B ias: -0 .0924R M S E : 0 .9038C o rr: 0 .9950

(August 2006)

MTSAT-1R Crosstalk Correction

$ MTSAT had a crosstalk problem in the shortwave band coming from the water vapor band

$ There may still be a problem with the calibration in very cold temperatures where the crosstalk signal overwhelms the weak signal in that band at thosetemperatures

CGMS-34, NOAA-WP-39

MSG-1/SEVIRI & Aqua/MODIS

#Spectral response functions

6.5-6. 9

5.4-7.2

Water Vapor CH1 [µm]

7.2-7.5

6.9-7.9

Water Vapor CH2 [µm]

3.9-4.011.8-12.310.8-11.3MODS/Aqua

3.5-4.411.0-13.09.8-11.8SEVIRI/MSG

SWIR CH [µm]

Window CH2 [µm]

Window CH1 [µm]Instrument

Wavelength [µm]

9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5

Spec

tral

resp

onse

func

tion

0.0

0.2

0.4

0.6

0.8

1.0Window CH1 Window CH2

Wavelength [µm]

3.0 3.5 4.0 4.5 6.0 7.0 8.0

Spec

tral

resp

onse

func

tion

0.0

0.2

0.4

0.6

0.8

1.0SWIR CH Water Vapor CHs

SEVIRIMODIS

TB comparison for MSG-1

1.92

-1.71

WV CH1

1.090.840.610.51RMSE

-0.96 0.440.310.20Mean bias

SWIR CHWV CH2Window CH2Window CH1

(July 2004)

Time series of calibration statistics

date (2004/07)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Mea

n B

ias

(K)

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

SWIR (3.9 µm)WV1 (6.2 µm)WV2 (7.3 µm)IR1 (10.8µm)IR2 (12.0µm)

date (2004/07)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

RM

SE (K

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0