Transcript On-orbit Cross-calibration of AM Satellite Remote Sensing

On-orbit Cross-calibration of AM Satellite
Remote Sensing Instruments Using the Moon
International Workshop on Radiometric & Geometric
Calibration
Grand Casino Gulfport Hotel
Gulfport, MS 39501
December 4, 2003
Jim Butler
NASA’s GSFC
Code 924
Laser Remote Sensing Branch
Greenbelt, MD 20771
Phone: 301-614-5942
Fax: 301-614-6744
E-mail: [email protected]
• Acknowlegements
–
–
–
–
Tom Stone-USGS Flagstaff
Hugh Kieffer-USGS Flagstaff (emeritus)
Bob Barnes-SAIC
Bob Kozon-NASA’s GSFC Mission Ops and his entire
team
– Carol Johnson, Steve Brown, Ted Early-NIST
– Stu Biggar, Kurt Thome-U of Arizona
The Moon as an On-orbit Calibration Target
The Moon has advantages (+) and disadvantages (-) when used as a
satellite instrument calibration target.
• Advantages:
+Appropriate radiance range
for Earth-viewing
instruments
+Photometric properties are
virtually invariant (<10-8/yr)
+Spectrally bland (from
returned Apollo samples)
+Accessible to spacecraft
regardless of orbit
+Useful as a common transfer
source between spacecraft
• Disadvantages
-Non-uniform reflectance and
complex photometric
behavior
-Satellite instrument lunar
views may require a
spacecraft attitude
maneuver
•MISR, ASTER, ALI,
Hyperion, SeaWiFS, &
MODIS (Earth view port) on
4/14/03
•MODIS (Space view port) 8 to
12 times a year w/ no maneuver
The Moon is equivalent to a 6 km target from a 705 km orbit
On-orbit Lunar Viewing by AM Constellation
Instruments on April 14, 2003
AM Constellation Spacecraft & Instruments
Satellite
Optical
Instruments
Altitude (km)
Orbital
Inclination (deg)
Equatorial
Crossing Time
(LST)
EO-1
ALI
Hyperion
Atm. Corrector
705
98.2
10:01
Landsat-7
ETM+
705
98.2
10:05
SAC-C
MMRS
HRTC
HCS
702
98.2
10:15
Terra
MODIS
MISR
ASTER
MOPITT
CERES
705
98.1
10:30
SeaStar
SeaWiFS
705
98
12:00
i
h
g
f
Terra Event
a. Maneuver start
e
d
c
a
b
Elapsed time (min)
0
b. Zero pitch accel.
3.03
c. Nadir at Earth’s limb
7.37
d. Nadir at Moon
11.90
e. Midpoint of maneuver
17.95
f. Nadir at Earth’s limb
28.53
g. Maneuver end
35.54
h. Terra enters sunlight
41.6
On-orbit Lunar Viewing by AM Constellation
Instruments on April 14, 2003
• Instrument Lunar Viewing Times (UT)
1. ALI MS/Pan 1
2. ALI MS/Pan 2
3. ALI MS/Pan 3
4. Hyperion
5. MISR Df camera
6. MISR Cf camera
7. MISR Bf camera
8. MISR Af camera
9. MODIS
10. MISR An camera
11. ASTER SWIR
12. ASTER VNIR-nadir
13. MISR Aa camera
14. ASTER VNIR-aft
15. MISR Ba camera
16. MISR Ca camera
17. MISR Da camera
18. SeaWiFS
21:39:47
21:44:34
21:49:19
21:54:31
22:01:38
22:02:33
22:04:05
22:06:23
22:09:24
22:09:34
22:09:34
22:09:34
22:12:46
22:13:22
22:15:04
22:16:37
22:17:33
22:34:14
EO-1 Lunar Maneuver
X spacecraft
End
Hyperion
1
Start
MS/PAN3
MS/PAN2
MS/PAN1
1.26°
41.5°
Pitch
Roll
0.75°
Yspacecraft
ASTER 560nm Band
MODIS 645.5nm Band
MISR 672nm Band
Robotic Lunar Observatory (ROLO) and the Lunar
Irradiance Model
•
•
Goal: provide on-orbit stable and
accurate radiometric calibration at
solar reflectance wavelengths
using the Moon
Two 20 cm, 1m focal length
Richey-Chretien telescope
systems
– VNIR:
• 512 square Si-CCD
• 23 filters
– SWIR:
• 256 sq. HgCdTe
• Identical to NICMOS on Hubble
• 9 filters
•
Calibration (absolute accuracy is
TBD)
– 12” sq Spectralon™ panel +
1000W irradiance standard lamp
– Irradiance of spectrophotometric
standard star Vega
– External 0.4 m dia. collimator +
light source calibrated for radiance
Robotic Lunar Observatory (ROLO) Irradiance
Model
•
The ROLO Irradiance Model is used to
compare on-orbit lunar measurements
made by satellite instruments over a
wide range of lunar phase and
libration.
– Empirical model based on 5+ years of
lunar observations
• ~85,000 lunar images; >106 star
images
• 32 bands: 23 VNIR, 9 SWIR
• ±90º lunar phase coverage14
coefficients for each band, 4 are
wavelength coupled.
•
•
Typically 14 coefficients and >1000
data points per band.
Smooth wavelength interpolation.
NOTE: The ROLO lunar image database
is unique and extensive. The
substantial spatial, phase angle, and
wavelength coverage are far beyond
any published prior work.
Applications of the ROLO Lunar Irradiance Model
– The irradiance model has been used to:
• Determine relative differences in the radiometric scales of
satellite instruments ()
• Determine long-term degradation in the radiometric
responsivity of satellite instruments ()
• Determine band to band radiometric differences in satellite
instruments ()
• Validate the absolute radiometric scales of satellite
instruments (accuracy is TBD)
Determining Relative Radiometric Differences
Between Instruments Using the Moon
April 14, 2003 AM Instrument Lunar Comparison
% Difference from ROLO Model
25
20
15
10
5
0
-5
-10
300
600
900
1200
1500
1800
2100
2400
2700
Wavelength (nm)
MODIS
MISR (9 camera avg.)
SeaWiFS
Hyperion
ALI
-Absolute accuracy of ROLO measurements is TBD
-Relative differences between instruments due to
1. Use of different solar irradiance spectra
2. Different approaches in calculating integrated lunar radiances from
instrument lunar images
3. Inherent differences/uncertainties in instrument calibrations
Determining Relative Radiometric Differences
Between Instruments Using the Moon
MODIS Terra/Aqua Lunar Comparisons
% Difference from ROLO Model
18
16
14
12
10
8
6
4
2
0
300
400
500
600
700
800
900
1000
Wavelength (nm)
MODIS Terra 4/14/03 (-27.7 deg.)
MODIS Terra (-55 deg.)
MODIS Aqua (+55 deg.)
-Comparison of MODIS instruments at three different lunar
phases.
1. MODIS Terra: 1 through Earth view port +
25 through Space view port (2 angles of inc. on scan mirror).
2. MODIS Aqua: 10 through space view port.
Determining Relative Radiometric Differences
Between Instruments Using the Moon
% Difference from ROLO Model
AM Instrument Lunar Comparisons
20
18
16
14
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
300
600
900
1200
1500
1800
2100
2400
Wavelength (nm)
MODIS Terra
SeaWiFS
MISR
ALI
Hyperion
-Average of all lunar views for each instrument: SeaWiFS (70);
ALI (29); MODIS Terra (26); Hyperion (9); MISR (1)
2700
Determining Long-term Degradation in the
Radiometric Responsivity of Satellite Instruments
SeaWiFS
-Correcting for correlated time jitter (left), a clear asymptotic degradation trend is seen in Bands 7
and 8 (right).
-Degradation information determined through repeated lunar views is used in the generation of
SeaWiFS standard data products.
Determining Long-term Degradation in the
Radiometric Responsivity of Satellite Instruments
ALI
ALI Radiometric Stability -Band 3
1.075
Solar Calibration
Ground Truth
1.05
Lunar Calibration
Relative Response
Lamp
1.025
1
0.975
0.95
0.925
0
100
200
300
400
Mission Day Number
500
600
700
Determining Band-to-band Differences in Satellite
Instruments
MODIS Terra & Aqua Band-toband Differences
MISR An Camera Band-to-band
Differences
18
12
16
10
14
8
12
6
10
4
8
2
6
0
4
-2
2
-4
0
300
400
500
600
700
800
900
% Difference from U
of Arizona
% Difference from
ROLO Model
MODIS Terra/Aqua Band-to-band Differences
-6
1000
Wavelength (nm)
MODIS Aqua
-Results from 5 VC expts. + 1 lunar
view (4/14/03)
-Normalized VC and lunar results
show identical band-to-band trends
MODIS Terra
MODIS Aqua (U of A)
MODIS Terra (U of A)
-Lunar and U of A results show similar
band-to-band trends
-Absolute scale not established in lunar
case
Summary and Conclusions
•
On-orbit satellite instrument calibration/characterization using the Moon
complements current on-board and vicarious calibration approaches.
– Effective in long-term trending of degradation of instrument radiometric response
– Useful in determining relative radiometric differences between instruments
– Useful in determining band-to-band radiometric differences within instruments
•
Absolute calibration of lunar system needs additional work
– Analysis of calibration/characterization data obtained in Sept/Oct at Flagstaff
– Detailed analysis of atmospheric correction codes
•
•
The lunar irradiance model is currently running at GSFC
The Moon (i.e. lunar views + model) is a viable prospect for meeting
NPP/NPOESS global change/climate monitoring goals
“All you have to do is look at the Moon.”
Hugh Kieffer
“Once you look at the Moon, you may see amazing things.” Hugh Kieffer