A novel hyperspectral imager based on microslice technology

Ray Sharples, Danny Donoghue, Robert ContentColin Dunlop, David Nandi, Gordon Talbot

Durham University

UAV Workshop7th July 2011

Outline of Presentation

• Background• Methods for simultaneous 3D

spectroscopy• Operating principles of a microslice

hyperspectral imager• First laboratory results from a CEOI-

funded prototype sensor• Future Plans

Project Background

Telescopefocus

Spectrographinput

Lensletarray

Fibrearray

Imageslicer

1 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

Overlaps must be avoided less information density in datacube

Spectrographoutput

slitFibres

Pupilimagery

slit1

2

3

4

Micro-mirrors

x

y

Datacube

Divides the field in two dimensions

Project Background

• 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.

A New Approach to Hyperspectral

Imaging

V km/sec

x

Dwell time = x/V

Instrument Concept: Microslice IFU

Instrument Layout

CEOI Mid-Term Review Meeting 12 Jan 2011

Pick-off mirror Collimator

Image slicer

Fore-optics

GRISM

Camera

Baseplate

(cover omitted)

Dimensions 33 cm x 15 cm x 12 cmMass ~5 kg (excl baseplate)

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

H beta

H alpha

HgHg

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

565 nm Fagus sylvatica leafCalibration and Testing

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 - r.m.sharples@durham.ac.ukProf. Danny Donoghue - danny.donoghue@durham.ac.uk