ers - envisat symposium gothenburg 16-20 october, 2000 meris instrument calibration
TRANSCRIPT
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
MERIS Instrument Calibration
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
OPTICAL DESIGN
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
ON-BOARD PROCESSING
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
GEOMETRIC CALIBRATION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
•FROWN < 1/3 FR PIXEL
•DISTORTION & SKEW< 1/5 FR PIXEL
• CAMERA DEPOINTING +/- 1/3 FR PIXEL(after corrections)
• RESAMPLING METHOD = NEAREST-NEIGHBOUR ACROSS TRACK• GRID = PSEUDO-EQUAL DISTANCE PROJECTED ON WGS84 ELLIPSOID• OVERLAPING PIXELS REMOVED
GEOMETRIC PERFORMANCE
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
GEOGRAPHIC VALIDATION
METHOD
REDUCED RESOLUTION• GLOBAL COVERAGE USING CIA VECTOR SHORELINE
FULL RESOLUTION• GROUND TRUTH i.e. OIL RIGS
PLATFORM ATTITUDE CONTROL LAW• OFFSETS
OBJECTIVES
• 2000 m IN REDUCED RESOLUTION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
SPECTROMETRIC CALIBRATION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
BANDPASS
CHARACTERISATION• 9 DETECTOR
• 9 VIEWS
INSTRUMENT MODEL• 15 BANDS
• ALL PIXELS
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
759.6
760
760.4
760.8
761.2
100 200 300 400 500 600 700
Localisation of spectral line #274 (B11)
CAM FM1 spectroCAM FM2 spectroCAM FM3 spectroCAM FM4 spectroCAM FM5 spectroTheoretical pos itionLow er limitUpper limit
Pixel
Max wav 760.5 nmMin wav 759.5 nmMax-Min 1.0 nm
SMILE PERFORMANCE
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
SPECTRAL CALIBRATION
• ERBIUM DOPED “PINK” DIFFUSER
• TWO FEATURES WILL BE USED @ 520 nm & 650 nm
• ACCURACY < 1nm
SYSTEMATIC MONITORING EVERY THREE MONTHS
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
VICARIOUS CALIBRATION
OBJECTIVE• ACCURACY OF 1 A° @ 760 nm
METHOD• OBSERVATION WITH BANDS SETTINGS:
• FRAUNHOFER LINES: Ca (393 & 396nm), Na (589nm), Ca II (853 nm)
• OXYGEN ABSORPTION LINES: 15 BANDS (753 - 672nm)
• LEVEL 2 PRESSURE PRODUCTS:
• SPECTRAL SHIFT INDEX
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
RADIOMETRIC CALIBRATION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
RADIOMETRIC MODEL
• BASED ON DIFFUSER BRDF
• SOLAR IRRADIANCE = THUILLIER
• BANDPASS
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
21.127.5
35.1
-34.
3
-27.
2
-20.
7
-17.
1
-10.
1
-6.5
0.0
6.5
10.1
17.1
20.7
27.2
34.3
0.3
0.32
0.34
0.36
BR
DF
(sr
-1)
Angle in FOV (degrees)
Azimuth angle (degrees)
DIFFUSER BDRF
• ON-GROUND CHARACTERISATION (<1%)
• ROUND-ROBIN WITH NASA (<1%)
• IN-FLIGHT CHARACTERISATION:• ALONG TRACK• BETWEEN DIFFUSERS
• FEEDBACK <= VICARIOUS CALIBRATION
• BRDF MODEL
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
STRAYLIGHT
• ASAP INSTRUMENT MODEL
• INCLUDED IN CALIBRATION
• MODEL VALIDATION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
AIC counts minus linear trend
-12
-10
-8
-6
-4
-2
0
2
4
0 500 1000 1500 2000 2500 3000 3500 4000 4500
data (counts)
dev
iati
on
(co
un
ts)
NON-LINEARITY
• CHARACTERISED AT UNIT LEVEL
• CORRECTIONS APPLIED AT CCD OUTPUT
• MODEL VALIDATION
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
VICARIOUS CALIBRATION SITES
SYTEMATIC ACQUISITION & PROCESSING OVER ALL TARGETS
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
ABSOLUTE CALIBRATION RAYLEIGH
INTER-BAND CALIBRATION SUN GLINT
INTER-COMPARAISON WITH OTHER SENSORS - DESERT SITES
CALIBRATION APPROACH
442 510 560 665 705 865490 620 681 753 760 775 890 900412
CALIBRATION USING ON-BOARD DIFFUSERS
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
CALIBRATION ACCURACY
VICARIOUS CALIBRATION
• RAYLEIGH < 4% ABSOLUTE• SUN GLINT +/- 1% RELATIVE INTER-BANDS•DESERT SITES < 4%
ON-BOARD DIFFUSERS
• BRDF < 2 %• SPECTRAL DEPENDENCE < 2%
ERS - ENVISAT SYMPOSIUMGothenburg 16-20 October, 2000
MERIS
STABLE U.V. PROTECTED POLARISATION INSENSITIVE COOLED DETECTOR 2 PROTECTED DIFFUSERS
SYSTEM CALIBRATION EVERY 15 DAYS VICARIOUS DATA ACQUISITION IS CONTINUOUS
GOALS 4 % FOR THE RELEASE OF LEVEL 1B PRODUCTS 2% < BY THE END OF THE MISSION