Advanced Microslice Technologies for Hyperspectral Imaging of the

Report
A novel hyperspectral imager
based on microslice technology
Ray Sharples, Danny Donoghue, Robert Content
Colin Dunlop, David Nandi, Gordon Talbot
Durham University
UAV Workshop
7th July 2011
Outline of Presentation
• Background
• Methods for simultaneous 3D
spectroscopy
• Operating principles of a microslice
hyperspectral imager
• First laboratory results from a CEOIfunded prototype sensor
• Future Plans
Project Background
Divides the field in two dimensions
Telescope
focus
Lenslet
array
Spectrograph
input
Spectrograph
output
Overlaps must be avoided
 less information density
in datacube
Pupil
imagery
Datacube
slit
Fibre
array
Fibres
y
x
Image
slicer
Micromirrors
1 2 3 4
1
slit
2
3
4
Both designs maximise the spectrum length and allows
more efficient utilisation of detector surface.

Only the image slicer retains
spatial information within each
slice/sample
 high information density
in datacube
Project Background
A New Approach to
Hyperspectral Imaging
• Fully exploit modern large-format 2D detectors
to obtain faster survey speeds.
• Longer exposures in stare-mode to allow higher
SNR in finer pixels for radiometry, meteorology
& and atmospheric composition studies particularly important for low reflectivity targets
such as water, forestry and shallow marine
environments.
• Enable smaller, more compact devices than
other comparable platforms. Compact designs
using state-of-the-art sensors to reduce
mass/volume requirements.
• Step-change in the imagery available to assist
in meeting NERC targets for Earth observation
with applications in many areas: not in the least
vegetation, geology and pollution monitoring.
• CEOI Seedcorn Project: budget £50k.
Dwell time = x/V
V km/sec
x
Instrument Concept: Microslice IFU
Camera
Instrument Layout
(cover omitted)
Image slicer
Dimensions 33 cm x 15 cm x 12 cm
Mass ~5 kg (excl baseplate)
GRISM
Pick-off
mirror
Collimator
Fore-optics
Baseplate
CEOI Mid-Term Review Meeting 12 Jan 2011
Hyperspectral Imaging Using
Microslice Technologies
• Novel application of microlens resampling optics to deliver
unprecedented field-of-view sampling over multiple spectral channels
simultaneously.
• Addresses current spectral resolution and sensitivity limitations with
available airborne/spaceborne instruments.
• Enables high spectral resolution observations to characterise and quantify
ecosystem and land/water surface properties.
• Allows spectral fingerprinting to be scaled up to address whole Earth
system processes.
Prototype Microslice Spectrograph
• NERC Centre for Earth Observation Instrumentation Seedcorn
Project started April 2010.
• 330 x 20 “spaxels” (spatial pixels each giving a spectrum) so 6,600
spectra.
• Spectra 180 pixels long
• Resolution of 5-7 nm (slice images 3 pixel wide) over 400 nm to
700nm
• Dimensions 33 cm x 15 cm x 12 cm
Microslicer Assembly
Microslice Optical Performance
Foveon CCD
Flatfield Performance
475-650 nm
Spectral Performance
Hg
Hg
H alpha
H beta
Application Tests
• Lab set up Microslicer & ASD FieldSpec Pro
• Objectives:
–
–
–
–
Test spectral resolution
Test signal / noise ratio
Ability to extract spectra
Use Spectralon standard
Calibration and Testing
Calibration and Testing
565 nm Fagus sylvatica leaf
Source: David Nandi
Extracting spectra from datacube
Source: David Nandi
Advantages of Microslice
Hyperspectral Imagers
• Rapid survey speeds with options for multiple viewing geometries.
• High spatial resolution with no limitations due to scanning speed on a
single overpass as with pushbroom techniques.
• High spectral and spatial resolutions.
• Longer exposures in stare-mode to allow higher SNR in finer pixels for
radiometry, meteorology and atmospheric composition studies.
• Signal strength is also particularly important for low reflectivity targets
such as water and shallow marine environments.
• Compact design using state-of-the-art sensors to reduce mass/volume
requirements.
Summary
• Knowledge transfer from astronomy to remote sensing is opening up new
concepts for hyperspectral imaging of the environment.
• Extreme multiplex microslice technologies offer a new approach to obtain
high spatial and spectral resolution simultaneously over a 2D FoV.
• The use of step and stare modes offer the potential for 2-3 orders of
magnitude increase in S/N compared with pushbroom or whiskbroom
approaches and also allows monitoring of time-dependent processes.
Further Details:
Prof. Ray Sharples - [email protected]
Prof. Danny Donoghue - [email protected]

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