Validation studies performed on Clouds and the Earth`s Radiant
Transcript Validation studies performed on Clouds and the Earth`s Radiant
Pre-launch Characterization of the
CERES Flight Model 5 (FM5) Instrument
S. Thomasa, K. J. Priestleyb ,
M. Shankara, N. P. Smitha, M. G. Timcoea
a. Science Systems and Applications Inc (SSAI)
b. NASA Langley Research Center
Earth Radiation Budget Components
Broadband scanning Radiometers measuring Reflected
Solar and Emitted Longwave Radiation.
Six CERES Instruments built by Northrop Grumman
Aerospace Systems (NGAS) at Redondo Beach, CA.
FLIGHT MODEL 5 (FM5): NPP Spacecraft
Sun synchronous polar orbit with 1:30 PM equatorial
Altitude: 825 KM
Proposed Launch: October 2011
Four Sets are Operational on EOS Spacecraft
Flight Models 1 & 2 (FM1 & FM2) – TERRA
Flight Models 3 & 4 (FM3 & FM4) - AQUA
• Contains three sensor assemblies with cassegrain
optics and thermistor bolometer detectors
• Sensors measure thermal radiation in the near-visible
through far-infrared spectral region
• Three sensor channels are coaligned and mounted on
a spindle which rotates about the elevation axis
• Sensor Assembly Unit rotate about the azimuth axis
providing hemispherical sampling of data
• Pre-launch Calibration Accuracy Requirements 0.5% LW, 1.0% SW
Total: 0.3 - >100 micron
Shortwave: 0.3 – 5.0 micron • CDR Measurement Stability Goals - 0.02%/yr LW,
Window: 8.0 – 12.0 micron
Internal Calibration Module
Total & Window:
Anodized Aluminum Blackbody sources
Evacuated Quartz Tungsten Lamp
Mirror Attenuator Mosaic (MAM)
Total & SW Sensors:
Solar Diffuser Plate
Nickel substrate with Aluminum coated
CERES Radiance Equation
: Sensor Counts
: Sensor Gain
: Sensor counts viewing space
: Unfiltered Radiance
: Filter Transmittance
ρm : Mirror Reflectance
αb : Paint Absorbtance
CERES Pre-Launch Calibration
Pre-launch Calibrations were performed at the Northrop
Grumman Radiometric Calibration Facility (RCF).
Four calibrations were performed on CERES FM5 instrument
after it was fabricated.
stopped due to
Tests done in
hot and cold
done only in
Full calibration tests
in hot and cold
Ground Calibration Tests
• Longwave Responsivity
• Shortwave Responsivity and Spectral
• Linearity in Sensor Responsivity
• Calibrations using on-board sources
• Point Response Function Test
• Solar MAM Characterization
Radiometric Calibration Facility
• Narrow Field of View Blackbody
(NFBB) is primary standard (Emissivity
of greater than 0.9999)
• 12.5 cm Wide Field of View Blackbody
• Cold Space Reference (CSR)
Reflected Solar Bands
• SW reference source (SWRS) with
minimum LW variations and spectral
• 13 discrete bands between 420 and
• 5 cm integrating sphere with
• Cryogenically cooled Transfer Active
Cavity Radiometer (TACR)
CERES Longwave Calibration
Total and Window Sensors
• Narrow Field of View Blackbody
(NFBB) is operated at 12 discrete
temperature setting between 205 K and
• Sensor drifts are corrected with Cold
Space Reference (CSR) measurements.
• Relative Spectral Response of the sensor
is determined from Fourier Transform
Spectrometer (FTS) measurements.
• Radiometric gain of the sensor is
calculated through regression of the
filtered radiance from NFBB source and
the corrected sensor measurements.
CERES Shortwave Calibration
Shortwave and SW/Total Sensor
• Short Wave Reference Source (SWRS) with
13 narrow band-pass filters between 0.4μm
and 2μm are used as calibration points.
• Transfer Active Cavity Radiometer (TACR)
act as the transfer standard to place the
SWRS on same radiometric scale as the
Narrow Field of View Blackbody (NFBB).
• Sensor gains are determined from the
alternate measurements of SWRS by the
CERES sensor and the TACR.
• Optical component measurements of witness
samples are used to complete the spectral
response between the narrowband SW
sources and to extend the response below
CERES Spectral Response Function
Flight Model 5 (FM5) Instrument
Calibrations using On-board Sources
Sensor performance was evaluated using Internal calibration module
sources (ICM) throughout test period.
The response changes between ground and start-of-mission calibrations
will be used as Ground to Flight corrections for radiometric gains.
The final pre-launch vacuum characterization of CERES FM5
instrument was performed in September 2008.
Total and Window sensor gains determined by the NFBB is
8.577 counts/Wm-2 and 10.495 counts/Wm-2 respectively.
The shortwave sensor gain derived using the SWRS and
TACR is 10.105 counts/Wm-2.
Spectral response for sensors were derived using the
SWRS/TACR and optical component measurements in < 3
micron and FTS measurements in > 3 micron region.
ICM calibrations provide a transfer standard for the prelaunch determined radiometric gains to flight.