Pre-launch Characterization of the CERES Flight Model 5 (FM5) Instrument

on NPP

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

Hampton, Virginia

Earth Radiation Budget Components

Kiehl & Trenberth

1997

CERES CERES

Top of Atmosphere

CERES Instruments

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 SpacecraftSun synchronous polar orbit with 1:30 PM equatorial crossing.Altitude: 825 KMProposed Launch: October 2011

Four Sets are Operational on EOS Spacecraft  Flight Models 1 & 2 (FM1 & FM2) – TERRA Flight Models 3 & 4 (FM3 & FM4) - AQUA

CERES INSTRUMENT

Total: 0.3 - >100 micronShortwave: 0.3 – 5.0 micronWindow: 8.0 – 12.0 micron

• 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

• CDR Measurement Stability Goals - 0.02%/yr LW, 0.03%/yr SW

FLIGHT CALIBRATIONSYSTEMS

Internal Calibration ModuleTotal & Window: Anodized Aluminum Blackbody sourcesShortwave: Evacuated Quartz Tungsten Lamp

Mirror Attenuator Mosaic (MAM)Total & SW Sensors: Solar Diffuser PlateNickel substrate with Aluminum coated spherical cavities

CERES Radiance Equation

Filtered Radiance

: Sensor Gain : Sensor Counts : Sensor counts viewing space

Filtered Radiance

: Unfiltered Radiance

Spectral responsivity

τf : 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.

March1999

February2000

October2006

Sept. –Oct.2008

Completed hot acceptance tests. During cold acceptance testing, calibration was stopped due to carousel problems.

Tests done inhot and cold acceptancetemperatures.

Calibration tests done only inhot acceptancetemperatures.

Full calibration testsin hot and cold acceptancetemperatures.

14 days 9 days 11 days 33 days

Ground Calibration Tests

• Longwave Responsivity

• Shortwave Responsivity and Spectral Characterization

• Linearity in Sensor Responsivity

• Calibrations using on-board sources

• Point Response Function Test

• Solar MAM Characterization

Radiometric Calibration Facility

IR Bands

• Narrow Field of View Blackbody (NFBB) is primary standard (Emissivity of greater than 0.9999)

• 12.5 cm Wide Field of View Blackbody (WFBB)

• Cold Space Reference (CSR) blackbodies

Reflected Solar Bands

• SW reference source (SWRS) with minimum LW variations and spectral characterization capability

• 13 discrete bands between 420 and 1960 nm

• 5 cm integrating sphere with associated optics

• 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 312 K.

• 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 0.3μm.

CERES Spectral Response FunctionFlight Model 5 (FM5) Instrument

Calibrations using On-board SourcesSensor 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.

CONCLUSIONThe 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 pre-launch determined radiometric gains to flight.

BACK-UP SLIDES

NFBB Residuals