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