CERES-GERB Joint Science Teams The Geostationary Earth Radiation Budget (GERB) experiment GERB Status Imperial College London J E Harries (GERB PI) J E Russell (GERB Project Scientist) J Hanafin, (GERB Operations Scientist)

CERES-GERB Joint Science Teams The Geostationary Earth Radiation Budget (GERB) experiment GERB Status Imperial College London Contents: 1.Short review of the project 2.Status 3.Some early science

CERES-GERB Joint Science Teams Short review of the project  Why do we need ERB measurements? Understanding our climate and how it may change in the future is one of the scientific “Grand Challenges” of our time We make predictions about how climate might change in future using coupled, ocean-atmosphere General Circulation Models (GCMs).Ultimately the models must be tested and validated against observations of the real world. ERB variability is sensitive to climate processes on all timescales, especially those with cloud signature. Combination of CERES and GERB offers powerful new tool, building on past ERB measurements.

CERES-GERB Joint Science Teams Spatial Scale (km) Temporal scale min 1 hour 1 day 1 month 1 year 1 decade DIURNAL CYCLE Mesoscale convection complex Synoptic processes GERB TEMPORAL SAMPLING Individual clouds GERB SPATIAL SAMPLING El Nino Southern Oscillation Equatorial Wave disturbances (e.g. African Easterly waves) Intraseasonal Oscillation Hurricanes SEVIRI SPATIAL SAMPLING SEVIRI TEMPORAL SAMPLING North Atlantic Oscillation  Time and space scales of climate processes

CERES-GERB Joint Science Teams ERB (NIMBUS-6) ERBE (ERBS) - Scanner ERBE (NOAA-9) - Scanner ERBE (NOAA-10) - Scanner ScaRaB (METEOR) CERES (TRMM)  ERB Instrument timeline CERES: Clouds and the Earth’s Radiant Energy System ScaRaB: Scanner for Radiation Budget ERBE: Earth Radiation Budget Experiment Red - Sun synchronous Green- Precessing Yellow - Geostationary ERB (NIMBUS-7) CERES (TERRA) CERES (AQUA) GERB

CERES-GERB Joint Science Teams To make progress, accurate, inter-calibrated, better sampled observations are needed, to test improved models. MSG/SEVIRI/GERB is a European initiative to contribute to international effort. GERB developed by a European consortium of groups from UK, Belgium and Italy.  MSG/SEVIRI/GERB

CERES-GERB Joint Science Teams  The GERB instrument

CERES-GERB Joint Science Teams  The GERB instrument

CERES-GERB Joint Science Teams  The GERB instrument

CERES-GERB Joint Science Teams detector pixels 262 steps Satellite rotation period = 0.6 s 262 steps for full Earth disc = s Between each Earth scan, internal BB measurement taken for calibration At correct viewing geometry, calibration monitor records scattered solar light as a relative measure over time Average three scans in each channel to improve S/N Total repeat time = 157.2*6 ~ 15 min. 2 channels: Total Total+quartz filter (SW)  GERB scanning

CERES-GERB Joint Science Teams

CERES-GERB Joint Science Teams  GERB characteristics WAVEBANDS Total: 0.32 mm mm Shortwave, SW: 0.32 mm mm Longwave, LW (by subtraction): 4.0 mm mm RADIOMETRY SW LW Absolute Accuracy:< 1.0 % < 1.0 % Signal/Noise: Dynamic Range: W m -2 sr W m -2 sr -1 SPATIAL SAMPLING 44.6  39.3 km (NS  EW) at nadir TEMPORAL SAMPLING 15 minute SW and LW fluxes CYCLE TIME Full Earth disc, both channels in 5 minutes CO-REGISTRATION Spatial:3 km wrt SEVIRI at satellite sub-point Temporal:Within 15 min of SEVIRI at each pixel INSTRUMENT MASS 25 kg POWER 35 W DIMENSIONS 476 mm  275 mm  345 mm

CERES-GERB Joint Science Teams SOLAR AND TERRESTRIAL RADIATION FIELDS INSTRUMENT SIGNAL CREATION GERB FILTERED RADIANCE AT SATELLITE RECTIFICATION AND GEOLOCATION (GRIDDED FILTERED RADIANCES AT TOA) GERB UNFILTERED RADIANCES/FLUXES 15 MINUTE INTEGRATION GERB 15 MINUTE RADIANCES/FLUXES  The data processing chain On board calibration SEVIRI data ON BOARD RAL PROCESSING RMIB PROCESSING

CERES-GERB Joint Science Teams Status  Overall Instrument performance: Excellent performance; Issues being worked on include:  Scanning;  Stray light;  Geolocation;  Validation and absolute accuracy;  Spectral response.

CERES-GERB Joint Science Teams  PSF scans Measured PSF for Pixel 124

CERES-GERB Joint Science Teams  PSF scans 1400 scanlines 1800 scanlines 500 scanlines

CERES-GERB Joint Science Teams  Mirror side offset correction Observation of Earth limb with step size of 0.15’ (~1/28th NORMAL scan step) ’Optimum’ correction of ~2.7 pixels (0.4’)

CERES-GERB Joint Science Teams  Scan mirror performance Basically excellent. MSG rotation period ~600ms. GERB de-spin mirror rotation period ~1200ms synchronised to MSG rotation by spacecraft Start of Line pulse (SOL) generated by MSG sun and earth sensors. De-spin mirror provides 40msec integration on a N-S earth ‘line’ (of 256 pixels) each rotation. Line position advanced by line (pixel) width (4.2 arcmin) each rotation.

CERES-GERB Joint Science Teams  Scan mirror performance Note: the line position precision of ~1/10th not yet achieved because of systematic diurnal errors in the SOL pulse - related to the in-orbit performance of the sun-, and particularly the earth- sensor. (Knowledge of the misalignments between the MSG and GERB frames should pin this down). Note: the SEVIRI nodding mirror causes variations in the MSG rotation rate at the ~0.01% level, which if not tracked would cause ~0.5 pixel line position errors. The mirror control system, however, tracks these changes. Any remaining errors are included in the 1/10th pixel line error above.

CERES-GERB Joint Science Teams  Scan mirror performance Mirror performance Very good performance to date: No of significant individual ‘sticky events’ v. small Worst month (July 2003) had 14 instances of mirror position error > 2 pixels, but 12 within one scan Other months have seen 1-4 files affected (i.e. < 0.025% of images collected)

CERES-GERB Joint Science Teams  Geolocation Geolocation errors 24 th May 2003

CERES-GERB Joint Science Teams  Stray Light Straylight in earth view

CERES-GERB Joint Science Teams  Stray Light Straylight visible as a stripe feature along image Magnitude Increases rapidly at onset of feature, then asymptotes to ~100Wm-2 in TOTAL channel Times affected: 23:00 – 01:00 UTC Dates affected: See graph

CERES-GERB Joint Science Teams  Lunar scans Fine scans both static and moon motion tracking have been made for calibration and science applications

CERES-GERB Joint Science Teams  CERES inter-calibrations CERES PAPS scanning pattern Aqua pass at 12:39–12:47 on 06/21/2003; view from 2000km

CERES-GERB Joint Science Teams Reprocessed Average Detector Spectral Response (mean shape over ASICs)

CERES-GERB Joint Science Teams Reprocessed Average Detector Spectral Response (mean shape over ASICs)

CERES-GERB Joint Science Teams Reprocessed Average Detector Spectral Response (mean shape over ASICs) Normal incidence reflectance varies < 1% at wavelengths shorter than 2.5  m and by less than 10% at 10  m. 0.2  m  m in the visible, the reflectance of gold black < 2%. Visible to ~3  m the reflectance gradually decreases to a very low value < 0.3%” Reflectance from 100 to 500  m (40  m thick samples of gold black) was 8 and 20% at 100  m rising to 20 and 26% at 500  m for 45  and 25  incidence respectively.

CERES-GERB Joint Science Teams Effect of reprocessed data on calibration Ratio of Gain calculated from a SW source to that calculated from a LW source Would be 1 for perfect knowledge of spectral response and instrument linearity Green: old SR, Red: reprocessed SR

CERES-GERB Joint Science Teams Some early science  Definition of clear sky fluxes and cloud forcing studies (Jo Futyan)

CERES-GERB Joint Science Teams Some early science Study of the radiative properties of aerosol using GERB and SEVIRI (Dr Helen Brindley) Image courtesy NASA GERB reflected shortwave fluxes MODIS visible image

CERES-GERB Joint Science Teams Some early science  Comparison of GERB and Met Office UM broadband fluxes: SINERGEE project (Prof Tony Slingo, Dr Richard Allen)

CERES-GERB Joint Science Teams SUMMARY GERB is providing ERB from geostationary orbit with a 15 minute time resolution Instrument commissioning tests indicate very stable instrument gains and low measurement noise After correction for a mirror side offset problem, instrument pointing is accurate to within 0.1 of a pixel MSG supplied geolocation information has some artefacts that are affecting the data geolocation. These are expected to be solved in the next few months. Initial intercomparison between GERB and CERES data indicate the mean SW and LW radiances from the instrument agree to within the expected measurement accuracy. These data are now being analysed for any indication of scene dependent differences Data is expected to be released after validation later this year.

CERES-GERB Joint Science Teams