GERB Ground Calibration Overview and Status J. Rufus CERES-GIST 21 Meeting Boulder, March 29th – April 2rd 2004 © Imperial College London
Vacuum Calibration Chamber GERB Ground Calibration Overview and Status Vacuum Calibration Chamber Cryogenically pumped high vacuum chamber capable of 10-9 Torr. Earth Orbital Calibration Facility Cleanroom (~60m3) maintained to better than class G (equivalent - class ISO6, 1000) and controlled to 2% relative humidity and 1C. © Imperial College London
GERB Ground Calibration Overview and Status © Imperial College London
GERB Ground Calibration Overview and Status © Imperial College London
How is the instrument modeled? GERB Ground Calibration Overview and Status How is the instrument modeled? Designed to be linear with respect to incoming power. where and This is tested during calibration. © Imperial College London
What are the instrument gains? GERB Ground Calibration Overview and Status What are the instrument gains? We need to measure gains in both channels over all pixels, And since LF(off) ~ 0, © Imperial College London
How is the instrument used? GERB Ground Calibration Overview and Status How is the instrument used? Differences measured to avoid external offset and increase instrument flexibility. A full characterization of the IBB source is important for GERB’s accuracy. Where is GERB ‘looking’? Need and accurate picture of the influence of GERBs optics on the field of view. Crucial to Geolocation of observations. © Imperial College London
Summary of Calibration Aims Check Instrument Linearity. GERB Ground Calibration Overview and Status Summary of Calibration Aims Check Instrument Linearity. Produce Gains for TOT and SW channels. Also measure T, filter response and use these three measurements to determine B, Gain Ratio = A, Long Wave Correction Factor = Characterize IBB Source for all pixels. Measure Instrument FOV Response (PSF, cross talk.) Perform Unit Level Spectral Response Spot Checks. Linearity Gsw GTOT IBB FOV R s (%) 0.05 0.53 0.38 0.2 0.1 PP © Imperial College London
GERB Ground Calibration Overview and Status Linearity Assumption of linear response tested for all GERBs. Results shown for 2 & 3. For total channel WBB-IBB output measured for a range of WBB temperatures, 280 – 345K © Imperial College London
GERB Ground Calibration Overview and Status © Imperial College London
GERB Ground Calibration Overview and Status © Imperial College London
GERB Ground Calibration Overview and Status Measurement of Gains Ground calibration sources have limited spatial extent, 6o E-W across the EV (24o) ~ 60 pixels N-S Measurement at 4 angles and 5+ heights. GTOT Measured using the WBB and CBB with QF out GSW Measured using the VISCs source with QF in. © Imperial College London
Gerb-3 Total Gains GERB Ground Calibration Overview and Status © Imperial College London
Gerb-3 Short Wave Gains GERB Ground Calibration Overview and Status © Imperial College London
IBB Characterization - Method GERB Ground Calibration Overview and Status IBB Characterization - Method © Imperial College London
Produce IBB filtered radiance for all pixels at TIBB. GERB Ground Calibration Overview and Status Produce IBB filtered radiance for all pixels at TIBB. Use linear fit to produce lookup table of data for all pixels and at all temperatures. Over Gerb-3 pixels, © Imperial College London
Setup for FOVR Measurement GERB Ground Calibration Overview and Status Setup for FOVR Measurement © Imperial College London
Setup for FOVR Measurement GERB Ground Calibration Overview and Status Setup for FOVR Measurement © Imperial College London
Normalised response profile of a center Pixel GERB Ground Calibration Overview and Status Normalised response profile of a center Pixel © Imperial College London
Contour profile of a typical center Pixel GERB Ground Calibration Overview and Status Contour profile of a typical center Pixel © Imperial College London
Contour Response of an end Pixel GERB Ground Calibration Overview and Status Contour Response of an end Pixel © Imperial College London
Pixel Viewing Angle GERB Ground Calibration Overview and Status GERB2 Pixel Pointing E-W Pixel Pointing E-W Pixel Pointing N-S Pixel Pointing N-S © Imperial College London
Awaiting return of GERB-3 for pre-launch recalibration. GERB Ground Calibration Overview and Status Calibration Status: Awaiting return of GERB-3 for pre-launch recalibration. Expected after Easter. Investigating correction to LIBB processing Conducting refurbishment VISCS Calibration Source. New lamps and stabilization detectors. Employ detectors to ensure greater IR stability. Planning Refit of the EOCF. © Imperial College London
GERB Ground Calibration Overview and Status Calibration Status: Resolved change in detector alpha’s effect on FOVR measurement – negligible. © Imperial College London