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

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

Instrument Background 2-sided Paddle Wheel Scan Mirror (10km by 2330 km swath per 1.478 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 Page 3

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 Page 4

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).

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.

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

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

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.

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

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

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)

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

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”

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

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

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

Spatial Uncertainty

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

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

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.

Back-up Slides

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

APRIL 01, 2001

November 21, 2002

April 9, 2004