CCDs for Earth Observation
James Endicott
1st September 2011
7th UK – China Workshop on Space Science and Technology,
Milton Keynes, UK
Introduction
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•
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What is this talk all about?
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e2v sensors in spectrometers
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CCD and CMOS imagers
What is this talk really all about?
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MERIS (CCD25-20)
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OMI (CCD55-20)
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TropOMI (CCD275)
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CMOS hyperspectral imager
Identifying the trend in the evolution of detectors
Slide 2
MERIS on ENVISAT
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Medium Resolution Imaging Spectrometer (MERIS)
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Launched on Envisat 2002
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One of 10 instruments
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15 spectral bands, 390 - 1040 nm
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Ground resolution of ~300m
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1150km wide swath covered
by 5 identical cameras
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Global coverage every three days
Image courtesy of ESA
http://envisat.esa.int/instruments/tour-index/
Slide 3
MERIS
Medium Resolution Imaging Spectrometer
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Images the Earth in a push broom mode
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2D array is used to acquire spectral & spatial
information
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Each line samples the swath for a different band
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Frame transfer device enabling simultaneous
readout and integration
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44ms frame period (~23Hz)
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Fast frame transfer after integration
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4x4 binning is used
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Lines outside the 15 spectral bands are
dumped
Images courtesy of ESA http://envisat.esa.int/instruments/meris/
Slide 4
MERIS
CCD25-20 highlights
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Gold plated window and package
for low emissivity
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Graded AR coating to match the
wavelength dispersion of the
spectrometer
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Thick window to maintain flatness
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Non Inverted Mode Operation
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22.5 μm x 22.5 μm pixels
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780 x 576 image area
Slide 5
The Aura Mission - OMI
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NASA’s Aura mission
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Launched 2004
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Similar period to Envisat
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4 instruments
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OMI – Ozone Monitoring Instrument
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Similar to MERIS
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Push broom imaging frame by frame
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Spatial information along a row
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Spectral information in different rows
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Two channels, UV1 and UV2
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UV-1, 270 to 314 nm, UV-2 306 to 380 nm
Image courtsey of
http://aura.gsfc.nasa.gov/instruments/omi.html
Slide 6
NASA Aura Ozone Monitoring Instrument
CCD55-20
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CCD55
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New manufacturing masks
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Advance Inverted Mode Operation
Advantages
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Photolithography
New features
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CCD25 re-masked
Lower dark signal (x100)
Disadvantages
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Lower Full Well Capacity
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Slower line transfer
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Larger Point Spread Function
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Random telegraph Signal visible after
radiation (flickering pixels – bi/tri-stable
white defects)
Slide 7
NASA Aura Ozone Monitoring Instrument
CCD55-20
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Enhanced back thinning process
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Improved QE at short
wavelengths (< 450 nm)
QE:0°C
0°Cfor
foran
anInverted
InvertedMode
Modedevice
device
QE:
100%
100%
90%
90%
80%
80%
OMI – UV
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No window to maximise UV
sensitivity
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Enhanced BT process
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UV optimised AR coating
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AIMO to improve dynamic range
70%
70%
QE
QE (%)
(%)
•
60%
60%
50%
50%
40%
40%
30%
30%
20%
20%
10%
10%
EnhancedProcess
Process
Enhanced
BasicProcess
Process
Basic
0%
0%
250 400
350 500
450
300
550
600
650
700 750
800 850
900 950
1000
Wavelength(nm)
(nm)
Wavelength
Slide 8
TropOMI – Sentinel 5 precursor
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TropOMI – Tropsheric Ozone Monitoring Instrument
Aim to bridge the gap between Envisat / Aura and Sentinel 5 (2020)
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UV, VIS and NIR imagers from e2v
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CCD275
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1024 x 1024 image area with 26 μm
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square pixels
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More than double the image area of a
MERIS or OMI device
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2 phase image and store pixels with
metalisation for fast line transfer
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0.75μs per line
Slide 9
TropOMI – Sentinel 5 precursor
Comparision of the predicted fringing of the graded coating and
a single thickness coating optimised for 760nm
0.98
•
0.96
Graded AR coating
0.94
QE (%)
for the NIR channel
0.92
0.9
0.88
0.86
Modelled QE Spectral Features
with background QE removed 0.84
680
0.1
700
720
740
760
780
Wavelength (nm)
QE (%)
0.05
Graded Coating
AR coating for 760nm
0
-0.05
-0.1
660
680
700
720
740
760
780
800
Wavelength (nm)
Slide 10
TropOMI – Sentinel 5 precursor
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Fringe Suppression for the NIR channel
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Switch-able gain
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Switched in capacitance to alter the device responsivity
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Higher responsivity for lower signal spectral bands
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Lower responsivity for higher signal spectral bands
Slide 11
Summary of CCDs for Ozone Monitoring
Instruments
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MERIS
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OMI
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CCD55-20, AIMO, UV enhanced process
TropOMI
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CCD25-20, NIMO, graded AR coating, UV-VIS-NIR on each device
5 cameras to achieve a wide swath
CCD275, 2-phase imager with metalisation for fast frame transfer /
reduced smear / optical cross talk
Split readout register to achieve higher data rate
Graded AR coating and fringe suppression structure
Selectable gain (responsivity)
What is next?
Slide 12
CMOS hyper spectral sensor
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e2v have designed (in collaboration) and characterised a hyper spectral
CMOS sensor
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Manufactured at a foundry
Resolution
1024 x 256
Pixel pitch
24 µm square
Readout speed
250 frames per second
ROI, windowing
Random access in Y-direction (spectral
direction) only
100 ke- and 300 ke- (programmable)
Full Well charge for 1% linearity
Line-by-line programmable charge
conversion factor
Total noise
QE
12 fF or 13 µV/e–
36 fF or 4 µV/e–
<50 e-RMS in basic mode without CDS
<20 e-RMS with CDS
>90% in VIS
Slide 13
CMOS hyper spectral sensor
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Characterisation of the front
illuminated device has been
successful
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Characterisation of the back
illuminated device has revealed
some drawbacks in noise,
responsivity and dark signal
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2012 will see a 2nd iteration of
the device for future Earth
observation instrumentation
Thank you for your attention
Slide 14