1. CoRP Cal/Val Symposium July 13, 2005
MODIS Thermal Band Radiance Cal/Val Chris Moeller Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin with contributions from Jack Xiong, MODIS Characterization Support Team (MCST), GSFC Dave Tobin, Cooperative Institute for Meteorological Satellite Studies Simon Hook, Jet Propulsion Laboratory (JPL, NASA)
CoRP Cal/Val Symposium July 13, 2005

2. Outline Brief MODIS background Cal/Val procedure
MODIS L1B validation findings
Contributions to Uncertainty
Summary

3. Instrument Background
2-sided Paddle Wheel Scan Mirror
(10km by 2330 km swath per sec)
Day data rate: 10.6 Mbps, night data rate: 3.3 Mbps (100% duty cycle, 50% day and 50% night)
3 Nadir Spatial Resolutions
250m (1-2), 500m (3-7), and 1km (8-36)
4 Focal Plane Assemblies (FPAs)
VIS, NIR, SMIR, and LWIR
36 Spectral Bands (490 detectors)
Reflective solar bands (1-19, and 26), thermal emissive bands (20-25, 27-36)
On-Board Calibrators (OBCs):
Solar diffuser (SD)
SD stability monitor (SDSM)
Blackbody (BB)
Spectro-radiometric calibration assembly (SRCA)
Space view (SV)
Science Applications
Land, oceans, and atmosphere
Nearly 40 science products generated and distributed
PFM
Aqua (EOS-PM):
Launched on 05/04/02 First light 06/24/02
FM1
MODIS is a global sensor!
Terra (EOS-AM):
Launched on 12/18/99
First light on 02/24/00
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4. MODIS TEB Calibration Using Blackbody
RVS: Response Versus Scan-angle
e: Emissivity
L: Spectral band averaged radiance
dn: Digital count with background corrected
Radiance (TOA), LEV
Key element to talk about here is that MODIS was different than previous sensors in that its accuracy goals were very ambitious. A high emissivity BB was built and a lot of work was done during pre-launch to try to ensure high radiometric accuracy. The task was to demonstrate that these high requirements were met by the on-orbit data set.
Calibration coefficient, b1, from BB
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6. MODIS IR Spectral Bands, MAS FWHM
MODIS has both window and atmospheric bands in the Thermal IR. Each has its challenges for validating.
Window bands include surface effects such as surface emissivity. In general, land surface temperature varies at smaller spatial scales than water surfaces. But sunglint may be a factor over water surfaces.
Atmospheric bands are challenging because the atmosphere above the ER-2 flight level may be contributing to the MODIS signal, and in general, the scene temperatures are lower (SNR is lower).

7. Why are high altitude aircraft useful for Cal/Val work?
Direct observation of integrated upwelling radiance, closely simulating on-orbit sensors.
Uncertainty dominated by airborne instruments
Mobile laboratory. Aircraft meets the satellite at a chosen time/place.
Covers several thousand km2 in 10 minutes (lots of samples).
Very little reliance on forward modelling and characterizing the atmosphere and surface.

8. TX-2002 ER-2 Payload
NPOESS Atmospheric Sounder Testbed (NAST-I)
Video Imaging System (VIS)
Dual RC-10 Camera
Scanning High Resolution
Interferometer Sounder
(SHIS)
Cloud Physics Lidar (CPL)
MODIS Airborne Simulator (MAS)
The instruments on the aircraft. Quick description of what they are?
MAS - 50 channel VIS/IR spectrometer, 50 m res., 36 km swath
SHIS - Scanning M/LWIR 0.5 cm-1 interferometer, 2 km res, 32 km swath
CPL – micropulse dual polarization lidar, 15 m res, nadir only
NAST-I – Scanning MWIR/LWIR interferometer, 2km res, 40 km swath
RC-10 - b/w and false color IR photo, 1-5 m res., 15 x 15 km coverage
VIS video imaging system - color video CCD camera; continuous

9. MODIS Emissive Band Cal/Val from the ER-2 Platform MODIS on Terra
2. Transfer SHIS calibration to MAS
1. Collect MODIS and ER-2 co-incident data
MAS, SHIS
on ER-2 q
20 km
705 km
MODIS on
Terra
Factors that complicate Cal/Val from Airborne platforms:
Clouds (highly transient)
Land surfaces (thermal variability)
Sun glint (4 um spectral region)
Airborne instrument performance
MODIS
Footprint
36 km
3. Co-locate MODIS FOV on MAS

10. 2000 2001 2002 2003 2004 2005 WISC-T2000 SAFARI-2000 TX-2001 CLAMS
Terra MODIS
2000
WISC-T2000
SAFARI-2000
2001
TX-2001
CLAMS
2002
Aqua MODIS
TX-2002
2003
2004
2005
THORpex-2003
Tahoe-2004
We’ve taken a few cracks at validating Terra MODIS, and to a lesser extent Aqua MODIS. A large effort was made after Terra MODIS first light resulting in some good findings but also raising some questions. We expected this because we knew there were some issues going to launch with Terra MODIS (electronic xtalk, optical xtalk, 5um leak). Aqua MODIS in general has performed more in line with specifications.
I’ll show a few results from SAFARI-2000, TX-2001, TX-2002, and Tahoe 2004 today.

11. MAS and SHIS data sets collected on the NASA ER-2 aircraft have been key for directly assessing Terra and Aqua MODIS L1B accuracy.
Terra
MODIS
CO2 4
CO2 wv
11 12
MODIS spec. given by box
Detector averaged
Terra
MODIS
11 um
04/01/01
Several field campaigns have used the NASA ER-2 to asses MODIS radiometric performance on Terra and Aqua. Campaigns include SAFARI-2000, TX-2001, TX-2002, and THORpex PTOST. This case from TX-2001 shows ER-2 based measurements (SHIS, MAS) match closely with Terra MODIS observations, with most MODIS bands falling within the radiometric specification envelope (open boxes in top center chart).
Along Track Profile

12. Brightness Temperature (K)
The Lake Tahoe 2004 field activity evaluated Terra MODIS radiometric performance.
Buoy Sites
April 9, 2004
0544 UTC
MODIS Band Number
MAS_SHIS - MODIS (K)
Terra
MODIS
Vertical bars represent radiometric accuracy spec.
Wavelength (um)
Brightness Temperature (K)
Predicted – Measured
SHIS
MAS_SHIS Simulated MODIS BT (K)
MODIS Observed BT (K)
3.7um
3.9um
The most recent MODIS validation field activity using the ER-2 was in April 2004, coordinated with Simon Hook (JPL) to obtain simultaneous surface based (radiometers), aircraft based (MAS, SHIS), and satellite based (MODIS, ASTER) measurements of the Lake Tahoe surface. These data have been evaluated to demonstrate radiometric accuracy of Terra MODIS and ASTER. The surface based measurements are also used to validate the radiometric accuracy of the SHIS and MAS instruments on the ER-2. SHIS is the primary airborne radiometric validation instrument for MODIS (and AIRS). The results showed that SHIS is a reliable airborne validation instrument, and that MODIS is performing within or nearly within radiometric accuracy specification for all bands except B34, 35, 36.
The MAS imagery of Lake Tahoe is shown in upper left. The MODIS comparisons with SHIS_MAS are shown in lower left and lower center panels. The SHIS comparisons with the surface buoy network are shown in the lower right.
CO2 4
CO2 wv
11 12
11um
12um
Detector averaged

13. TX-2002 Experiment Assess Aqua MODIS Cal/Val
MODIS Band Number
MODIS Residual (K)
Aqua
MODIS
TX-2002 Experiment Assess Aqua MODIS Cal/Val
Detector dependent
(atmospheric bands)
CO2 4
CO2 wv
11 12
Detector averaged
Nov. 21, 2002
1941 UTC
Aqua
Nov 21, 2002
MAS
B45 (11 um)
We also look at the biases on an individual detector basis.
Detector dependent
(window bands)

14. Uncertainties SHIS calibration uncertainty Altitude correction
Geolocation error (spatial mismatch)
Temporal mismatch
Sunglint influence

15. Blackbody Geometry AERI, NAST, S-HIS, GIFTS
SHIS Accuracy
Blackbody Geometry AERI, NAST, S-HIS, GIFTS
Aperture Diameters
AERI: 2.7”
S-HIS: 1.6”
NAST: 1.0”

16. SHIS Expected Performance
TABB = 227K, THBB = 310K SW MW
Based on a set of conditions. Nonlinearity error still under assessment. Cold chamber exercise coming. LW

17. Atmospheric Pressure (mb)
Level
MODIS B30, 9.6um (Ozone)
MODIS B33, 13.3um (CO2)
MODIS B35, 13.9um (CO2)
MODIS B36, 14.2um (CO2)
MAS B43, 9.6um (Ozone)
MAS B48, 13.2um (CO2)
MAS B49, 13.8um (CO2)
MAS B50, 14.3um (CO2)
Atmospheric Pressure (mb)
MODIS B36 and MAS B50 peak at different levels. This creates sensitivity to atmospheric correction.
There is important atmospheric contribution above the ER-2 level in MODIS Ozone (30) and CO2 bands (35 and 36).
Normalized Weighting Function

18. CO2 O3 Influence of Altitude Difference between MODIS and MAS
Atmospheric absorption above
the ER-2 altitude (20 km) is
important for O3 and CO2
sensitive bands. O3

19. Spatial Uncertainty

20. Temporal Uncertainty
The temperature difference is about 0.15 K between the two overpasses.

21. Sun Glint: magnifies spatial and temporal uncertainty in 4um region
The temperature difference is about 1.8 K between the overpasses. Big!

22. What Are We Learning?
Cal/Val of MODIS L1B is viable, even necessary, from high altitude aircraft.
MODIS meets spec in almost all bands.
Detector striping is corroborated by Cal/Val.
MODIS radiometric biases can be cautiously applied to L2 products, e.g. CO2 cloud heights.

23. Back-up Slides

24. The MODIS spatial weighting function was measured in the scan and
track directions during prelaunch testing using a 0.1 x 10 FOV slit
stepped across the MODIS focal planes. Idealized smearing was
added to the scan direction measurements to simulate the effect of the
scan mirror motion.
TRACK
SCAN

25. APRIL 01, 2001

26. November 21, 2002

27. April 9, 2004