Calibration Plan for GOSAT Sensors
Kei Shiomi and Shuji Kawakami
Japan Aerospace Exploration Agency

Workshop on the Data Utilization of GOSAT, Toranomon Pastoral, 5 Nov., 20081

Contents
FTS calibration
Calibration items
In-orbit operation
Onboard calibration
L1 processingVicarious calibration

CAI calibration (briefly)
Summary2

TANSO-FTS

3

Calibration overview ofTANSO-FTS
 Pre-flight Test (PFT) Radiometric characterization
 Spectral characterization
 Alignment

 Onboard Calibration (OBC) Dark target
 Deep space (FTS-SWIR/TIR) Bright target Solar irradiance (FTS-SWIR)
 Blackbody (FTS-TIR) Spectral calibration for ILS
 1.55μm laser (FTS-B2)

 Lunar observation

 Vicarious Calibration (VC) Radiometry
 Cross calibration – using DB and othersatellite data Cal/Val experiment – using in-situ
experimental data
 FTS-CAI relative radiance of 1.6μmband

 Geometry Pointing accuracy
 Coastlines

 Pointing stability
 Band-to-band registration
 FTS-CAI registration
 IFOV monitoring camera Spectral Quality
 Spectral accuracy
 Absorption lines

 SNR
 Desert

4

Operation of FTS
Solar Irradiance Cal.
Lunar CalFTS SWIR
Solar Flux

FTS TIR

Nominal observation(dayside land, nightside)

Sunglint observation(dayside ocean)Specific observation(calibration, validation, pipeline)5Pre-flight test characterization
Cross calibration with OCO and GOSAT X-calibration with OCO/GOSAT standard radiometers
Fixed point
blackbody(GOSAT)

Integrating Standard radiometers
sphere(GOSAT)
0.76µm
1.6 µmmonochromator

2.0 µmIntegratingsphere(OCO)•1st step @ JPL (Apr, 2008) Difference < 3%Pre-launch•2nd step @ JAXA (Aug, 2008)6

Pre-flight test characterization
 Instrument function

Band Integrated sphere (Ar lamp) Tunable diode laser

 Sensitivity (also SNR) Fixed-point blackbody and integratingsphere Blackbody cavity

 IFOV Collimator
1.2

Overwrite 520 111515-111834 B2P
Peak=6.317e-002 FWHM=0.26382 StdFWHM=6.34e-005 Position=6456.924

1Output [n.u.]

0.8

0.6

0.4

0.2

0-0.2
6452

6453

6454

6455

6456

6457

6458-1

Wavenumber [cm ]6459

64606461Instrument function
SpecResults

1P
1S
2P
2S
3P
3S

<0.6 cm-1<0.27 cm-1

0.367
0.356
0.258
0.257
0.262
0.263

SNRBand Wavenumber
Radiance
Specification
-1
2-1
[cm ]
[W/cm /sr/cm ]Result1P
1S
2P
2S
3P
3S
4345
246
322257412
287
28313050 5.5e-7
6200 5.2e-7
5000 3.8e-7
700 280K

310
--310
--310
--310

7

Pre-flight test characterization
Data sheets Although the following data are not used for L1 processing,
they are separately provided for users.
FTS

DataPre-launch

IFOV (Responsedistribution within PFT resulta pixel if exists)○

Instrument Line
Shape Function

PFT result○PFT result○

Sensitivity
calibration
coefficients

Solar Irradiance Cal.

PFT result

L+6M

L+12M

○

○

○

○

○

○

○

Lunar Cal.

○

Vicarious cal.
A model forpolarization

L+3M

○8

Onboard calibration
FTS-B10.76μmFTS-B2
1.6μm

FTS-B32.0μm

FTS-B4TIR

Frequency

Electric Calibrationxxxx

1 / month

Deep Spacexxxx

Every pass

Solar Irradiancexxx

FTS OBCxBlackbody
Lunar Calibrationxxxx

Every pass
1 / yearx

1 / monthx

1.55μm Laser for ILS(IFOV Monitoring Camera

Every passxxEvery scene) Deep space and blackbody data will be obtained 4 times
nominally, 16 times at maximum in an orbit.
 Lunar calibration will be operated at full moon once a year.
 1.55 μm ILS laser for B2 will be operated once a month.
9

FTS Level 1
Radiometric calibration
L1A

Interferogram

TIR band

SWIR band

I scene , I deep _ space _ cal , I blackbody _ cal

I scene , I Solar _ irrad _ cal※sensitivity correction (gain, non-linear, phase correction）

Uncorrected
spectrum

S (σ ) =MPD− 2πixσI(x)
edx
∫

− MPD

※sensitivity correction （reflectance、polarization、BRDF correction）

Corrected
spectrum

TIR band

SWIR band

S scene , S deep _ space _ cal , S blackbody _ cal

S scene , S solar _ irradi _ cal

2-point calibration
SWIR band

L1B Spectral
Radiance

TIR band radianceS scene , S solar _ irradi _ cal Lscene (σ ) =S scene − S deep _ space _ cal

Sblackbody_ cal − S deep _ space _ cal

ε blackbody B(Tblackbody )10Vicarious calibration
 Comparison with other spectrometers
 OCO-TANSO
 OCO spectrum is an exact reference for TANSO.

 Comparison with other imagers
 Aqua/MODIS-TANSO Comparison between Aqua/MODIS and TANSO in 1.6μm band ispossible with total radiance level.

 Comparison by using physical parameters Reflectance DB at stable or well-known site (SWIR band) Without appropriate active sensors for TANSO reference, thesimulated radiance for reference is produced if we have reflectanceDB from the analysis of past data.

 Sea surface temperature DB (TIR band) Estimated SST by split window is compared with Reynolds OI-SSTor AMSR-E microwave radiometry SST.
11

Preparation of Post-launch
Cal/Val The radiometric and geometric accuracies will be
estimated at nadir view at first.
 Scene selection for Radiance comparison with other similarsensor and DB simulation
 Geolocation
 Cal/Val locations
12

Geometric study of FTS

GCPs

CAM scene

Clear skyrate

Estimation of GCPs / scenes① Num of CAMscene (nadir)② Num of CAM sceneinc. 3 GCPs

③ ②×ISCCP clear sky rate
Estimated CAM scenes

Mar5192

12540

Jun5104

196

64

Sep5148

198

69

Dec5182

86

28

13

Comparison with OCO and GOSAT Nadir match-up of OCO and GOSAT OCO: continuous swath observation at 13:26LT GOSAT: separate pointing observation at 13:00LT
Match-up points in a day (Distance < 10km, Time < 30 min)14

TANSO-CAI

15

Operation of CAI
Lunar calCAI obs
Nightside obs

CAI onboard calibration
B1

B2

B3Offset

Nightside observation

Radiance

Lunar observation (1 / year)

B416

Geometric study of CAI

2003/8/3

South Africa

Ch1(380nm)

2003/8/3

Ch19(865nm)

BlackSea

Ch1(380nm)

Ch19(865nm)

 It is difficult to identify the land/ocean features from UV channel.
 The GLI 380nm image data is available and preliminary checked.
 The identified points is white sand shore and snowfield shore.
 GCPs of 380nm channel is estimated less than the other visible
and SWIR channels.
17

Summary TANSO calibration is conducted by PFT, OBC, and VC.
 Sensor performance is characterized in PFT and sensor
parameters are provided for development of L1 processingsystem.
 Calibration factors are optimized using OBC data in operationof L1 processing.
 Responsive gain and offset (Radiometric calibration)
 Laser wavelength (Spectral calibration) The vicarious procedures are prepared for radiometric,geometric, spectrometric calibration.
 Accuracy of L1 spectra will be evaluated by comparison withother satellite observed radiance or physical parameters.
18

backup

19

Pre-flight Test Items
Item

Configuration

Signal to Noise Ratio

Halogen lamp Integrating Sphere (SWIR)
Large Aperture Cavity Blackbody in TVT (TIR)

Instrument Line Shape Function(shape and wavelength)

Ar lamp Integrating Sphere and Tunable diode laser

Radiometric Response(Non liner correction if exists)

Fix Point Blackbody and Integrating Sphere
Large Aperture Cavity Blackbody (TIR)IFOV (Response distribution
within a pixel if exists)

Collimator with Alignment test

Diffuser BRDF

Spherical Distributed Detectors

Onboard Laser temperaturedependency

Wavelength meter

Response Stability

Halogen lamp Integrating Sphere and light source
monitoring radiometers

Stray Light

Halogen lamp Integrating Sphere and CO2 cell

Micro-vibration

Ar lamp Integrating Sphere and Shaker

20

FTS L1 processing flow of SWIR
Interferogram (FTS L1A)
Quality check (spike detection)
Low-freq correction
Corrected Interferogram
FFT
Phase correction
Corrected Spectrum
Spectral calibration
Final Spectral Radiance (L1B)
In PFT: Standard light source is calibrated by fixed-point blackbody.

Conversion (output to radiance)

In orbit: Onboard calibration and Vicarious calibration

21

Pointing and footprints
Cross- Distance Expotrack bet. points surepattern (at 30deg (sec)in latitude)1790 km
4x33260 km
4x35160 km
47110 km
2988 km
1GOSAT

FTS IFOV=10.5 km
CAI IFOV=0.5, 1.5 km

TANSO-CAI Swath
900 km88 – 260 km

SatelliteDirection(Along Track)

Cross Track
22Beam splitter(+) IGM
Bandpass filters of B1-3

Modulator

B1-3 detector

Unmodulated light

Modulated lightTargetRelations bet. input and inner radiations

IGM

Deep space

Input(3K) < Inner(265K)+Blackbody

Input(290K) > Inner(265K)-Observation

Input(270-320K) >=< Inner(265K)+-Spectrum

Dichroic filters of B1-3
B4 detector(-) IGMObs = 300K

Phase

Scene flux

Interferogram

TIR interferogram

23

TIR calibration
 Input radiance is injected by a vacuum
blackbody source of 300 K.
 The calibration is operated by 2-pointcomplex calibration using onboard
blackbody and cooled shroud for deepspace.
LObs (σ ) =SObs − S DScal
ε BB B(TBB )S BBcal − S DScal

 The phase is approximately zero after
calibration.
 The calibrated equivalent brightness
temperature is estimated around 300Kof input radiance.
24

ILS measurement by onboard laser
B2P

FWHM = 0.255cm-1

 The ILS of B2P was estimated by using the onboard 1.55μm laser afterreflection of the solar diffuser.
 Measured ILS (FWHM=0.255cm-1) satisfies the specification requirement.
25

Spectral calibration fromatmospheric absorptions
B3P

CO2 cell measurement

 The sampling laser wavelength was estimated to an accuracy of 1E-4 %.
 As a result, the spectral axis was evaluated to an accuracy of 0.004 cm-1.
 Simple procedure for spectral calibration will be implemented after
selection of effective absorption lines.
26