1. METimage Calibration Pepe Phillips GSICS Data & Research Working
Groups Meeting, 24 March 2014

2. Contents Introduction to EPS-SG Introduction to METimage
METimage performances
Calibration of the solar channels
Calibration of the thermal channels
Plans for in-orbit monitoring

3. EPS-SG (Second Generation) Payload
Satellite-A Missions
Instrument (and Provider)
Predecessor on Metop
Infrared Atmospheric Sounding (IAS)
IASI-NG (CNES)
IASI (CNES)
Microwave Sounding (MWS)
MWS (ESA)
AMSU-A (NOAA) MHS (EUM)
Visible-infrared Imaging (VII)
METImage (DLR)
AVHRR (NOAA)
Radio Occultation (RO)
RO (ESA)
GRAS (ESA)
UV/VIS/NIR/SWIR Sounding (UVNS)
Sentinel-5 (Copernicus, ESA)
GOME-2 (ESA)
Multi-viewing, -channel, -polarisation Imaging (3MI)
3MI (ESA)
-/-
Satellite-B Missions
Instrument (and Provider)
Predecessor on Metop
Scatterometer (SCA)
SCA (ESA)
ASCAT
Radio Occultation (RO)
RO (ESA)
GRAS (ESA)
Microwave Imaging for Precipitation (MWI)
MWI (ESA)
-/-
Ice Cloud Imager (ICI )
ICI (ESA)
Advanced Data Collection System (ADCS)
Argos-4 (CNES)
A-DCS

4. Introduction to METimage

5. VII primary observations
Products to be derived from the VII mission are:
Cloud observations including microphysical analysis
Water-vapour imagery
Aerosol observations
Polar Atmospheric Motion Vectors (AMVs)
Earth surface albedo
Vegetation
Cryosphere (snow, sea and land ice imagery)
Fire detection
Surface temperature (land and sea)

6. Cloud Observations
Cloud optical thickness: 670 nm over land, 1.24 µm over snow and sea ice, 865 nm over ocean.
Cloud drop/particle effective radius: 2.25 µm and 3.75 µm.
Cloud imagery: red (670 nm) / green (555 nm) / blue (443 nm) /near infrared (NIR) (865 nm) / thermal infrared (TIR) (10.8 µm) cloud imagery composites.
Cirrus clouds: 1.37 µm (land during daytime) and 8.5 µm (nighttime).
Snow/cloud discrimination: 1.6 µm and 3.75 µm.
Cloud phase at the cloud top: 1.6 µm, 8.5 µm and 10.8 µm.
Cloud top temperature, 763 nm oxygen-A band channels (daytime), µm and 13.3 µm (CO2 absorption) in combination with infrared sounding data at µm.
Cloud vortices, MODIS RGB imagery (courtesy NASA)

7. VII performance specifications
The need for more sophisticated parameterisation of clouds and surface boundary conditions drives the spectral and spatial resolution of the VII.
In comparison to AVHRR on EPS:
Number Channels
Spatial resolution
AVHRR 6
1 km
VII 20
500 m
Comparison between AVHRR (left) and MODIS (right) imagery (courtesy NASA)

8. VII Spectral Channels  (nm) Δ (nm) Cloud Cloud top height Water
vapour
Aerosol
Cirrus
Vegeta-tion
Surface
temp
Primary observations
443 30 X
Clouds and aerosol
555 20
Clouds, aerosol and vegetation
670
752 10
Cloud and aerosol height assignment
763
865
914 50
Water vapour
1,240
1,365 40
High level clouds and aerosol and water vapour imagery
1,630
Cloud phase and surface properties
2,250
Cloud microphysical analysis
3,740
180
SST
3,959 60
SST and fire
4,040
6,725
370
Water vapour imagery and polar winds
7,325
290
8,540
Cirrus clouds
10,690
500
Split window for clouds and surface parameters
12,020
13,345
310
Cloud top height.

9. Performance specifications (cont)
Bias error
< 5% (solar), < Ttyp (thermal)
Stability
< 1% (solar), < Ttyp (thermal)
Inter-spatial homogeneity
< 1% (solar), < 280 K (thermal)
Inter-channel homogeneity
MTF
> Nyquist
Geolocation accuracy
Sub-pixel nadir)
Polarisation sensitivity
< 5% (solar), < 11% (thermal)
Channel co-registration
> 80% all channels

10. METimage calibration concept
Calibration concept addresses accuracy, stability and spectral and spatial homogeneity. Accuracy is achieved using on-board 2-point linear calibration by viewing cold space as the low dynamic range reference and a target at known temperature/radiance for the high dynamic range reference -> solar diffuser (solar channels) and black body (thermal channels). Non-linearity corrections shall also be considered (TBC). Thermal channels: Offset and gain corrections performed by viewing cold space and a black body at instrument temperature every scan line - > recalibration interval of approx 3 s. Solar channels: Offset and gain corrections performed by viewing cold space once per scan line and a solar diffuser once per orbit - > recalibration interval of approx 100 mins.

11. Solar diffuser monitor
Due to the main diffuser degradation, METimage shall carry a second diffuser plate that shall be used only periodically to monitor the degradation of the main solar diffuser.
The diffuser monitor shall be deployed at regular intervals (approx once every 2 weeks). Else it remains hidden away to reduce UV exposure and contamination which are the main sources of diffuser degradation.
At end of mission, the degradation of the monitor shall be small enough that the lifetime stability requirement (1%) for the solar channels is met.

12. METimage Calibration – Lunar calibration
Lunar calibration has been successfully used for MODIS and VIIRS to monitor in-orbit performance including:
Channel dependant degradation of the solar diffuser
Reflection versus scan angle (RVS) correction of primary scan mirror
Band to band registration
Cross-talk
MTF
The role of the moon for stability monitoring is currently being considered for METimage. To use lunar calibration we need:
Lunar visibility without platform manoeuvres (except during commisioning)
Regular incidences of (full) lunar intrusions (several times per year)
Bright enough (and as constant as possible) lunar phase angle

13. Lunar calibration METimage – way forward
Plan for as many lunar calibrations as possible during commisioning/start of operation (helps curve fit to stability trending as decay steepest at start of mission).
Ensure the space view is:
Large enough to view the full moon
Where possible, optimise position of space view (simulations ongoing)
Ensure lunar intrusions suitable for calibration are achievable without spacecraft manoeuvres (no operational outage).