Prototype earth observing system using image slicer mirrors persist
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Prototype Earth observing System using Image Slicer Mirrors PERSIST . David Lee, Andy Vick, Peter Hastings, David Atkinson, Martin Black and Sandi Wilson STFC, UK Astronomy Technology Centre James Barlow and Paul Palmer Department of GeoSciences , University of Edinburgh.

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Prototype earth observing system using image slicer mirrors persist

Prototype Earth observing System using Image Slicer MirrorsPERSIST

David Lee, Andy Vick, Peter Hastings, David Atkinson, Martin Black and Sandi Wilson

STFC, UK Astronomy Technology Centre

James Barlow and Paul Palmer

Department of GeoSciences, University of Edinburgh


Presentation overview
Presentation overview

  • Introduction & Background

  • PERSIST concept

  • Description of PERSIST hardware

  • PERSIST test results

  • GHOST

  • Summary & Conclusions


Hyperspectral imaging
Hyperspectral Imaging

  • Measurement of the concentration of atmospheric gases, such as Carbon Dioxide or Methane, is often performed using a hyperspectral imager.

  • Hyperspectral imagers typically use two technologies:

    • Push-broom spectrometers.

    • Fourier transform spectrometers.


Push broom spectrometers
Push-Broom Spectrometers

  • Push-broom spectrometers use satellite motion to scan a single slit across the scene.

  • Observation of multiple wavelength channels requires multiple spectrometers and multiple detectors.

  • Increased observing efficiency can be obtained by simultaneously observing multiple channels with one spectrometer.


Layout of a t ypical push broom spectrometer
Layout of a Typical Push-Broom Spectrometer

  • Single input slit and relay optics to sort light into three channels, e.g. O2 A-band, CO2 (weak), CO2 (strong).

  • 3 spectrometers and 3 detectors.


Layout of persist
Layout of PERSIST

  • Input field of view is 3 slits.

  • Image slicer mirror optical system relays the light to the spectrometer.

  • Band-pass filters are used to define three wavelength channels.

  • Multiple order spectrometer simultaneously observes all wavelength channels.


Persist operational concept
PERSIST operational concept

  • Push-Broom spectrometer with along track scanning.

  • Multiple slits sample the field of view.

  • Spectrometer operates with multiple diffraction orders to simultaneously observe 3 wavelengths of interest.

  • Alternatively can observe same scene 3 times to obtain a higher signal.


Jwst miri heritage
JWST MIRI heritage

  • James Webb Space Telescope has two instruments with image slicer technology

    • MIRI – image slicers designed at UK ATC

    • NIRSPEC (Astrium)

James Webb Space Telescope

MIRI Image Slicer Mirror with 21 slices

MIRI at STFC RAL Space


Persist objectives
PERSIST objectives

  • The purpose of the PERSIST project is to build a bench mounted prototype image slicer spectrometer with a SWIR detector system.

  • The system will demonstrate the ability to simultaneously capture three wavelength ranges (via three slices) on one detector.

  • The prototype will demonstrate the feasibility of the technology for use in an Earth Observation instrument to measure atmospheric CO2.

  • Increase TRL of multiple-order spectrometer.


Persist optical layout
PERSIST optical layout


Optical layout of persist ifu
Optical layout of PERSIST IFU

Entrance Aperture

Fold Mirror

Reimaging Lenses

Image Slicer

Collimator

Bandpass Filters

Slits

Zemax optical ray trace diagram


Persist image slicer
PERSIST Image Slicer

  • Diamond machined aluminium.

  • Off-axis spherical slices.

  • Component includes input aperture.

  • Area surrounding slice will have a black mask.


Integral field module
Integral Field Module

Integral-Field

Module

external view

195 mm

40 mm

square


Integral field module with image slicer
Integral Field Module with Image Slicer

entrance aperture

Integral-Field

Module

cross-section

of hardware

slicing mirror

mirror unit

central housing

fold mirror

lens unit

collimating lens

field-imaging lens

order-sorting filter

pupil-imaging lens

slit mask


Integral field module hardware
Integral Field module hardware

IFU housing components

Pupil baffle

Masks

Spacer tubes

Output Slit

Filters

Image Slicer

Fold Mirror

Collimator Lens

Re-imaging Lenses

Pupil Lenses


Fully assembled ifu module
Fully Assembled IFU module

Fold Mirror

Image Slicer

Lens Barrel

Output Slit

White Light Input

Output three pass bands

150 mm


Layout of output slit
Layout of output slit

Picture of IFU output slit showing the three wavelength channels

Reverse illumination to demonstrate field of view


Layout of bench spectrometer
Layout of bench spectrometer

  • Simple bench spectrometer using COTS components

  • Operates in diffraction orders 8, 5, 4.

  • Raytheon VIRGO SWIR detector.

Fold Mirror

Grating

Camera

Collimator

Input Slit

Window

Blocking Filter

Bandpass Filter

Detector

Zemax optical ray trace diagram


Persist fully assembled
PERSIST – Fully Assembled

Monochromator

Telescope Simulator

IFU module

Detector

Collimator Lens

Diffraction Grating


Persist layout on bench
PERSIST – Layout on Bench

Monochromator

Light Source

IFU

Telescope Simulator

Cryostat

Cooling System


Integration and test
Integration and Test

  • A wavelength scan was performed with the monochromator to look for out of band stray light.

  • Arc Lamp illumination to perform image quality checks from spectral line width.

  • IFU illuminated with white light via an integrating sphere to generate three spectra. Check area between spectra for scattered light.

  • Measurement of atmospheric spectrum.


Illumination with monochromatic light
Illumination with Monochromatic Light

Full frame image at

1600 nm

Enlarged view of the spectrum showing the spatial structure of the lamp filament


Simultaneous capture of three spectral bands
Simultaneous Capture of Three Spectral Bands

Illumination with a Filament Lamp

Uniform Illumination

1600 nm

1020 nm

2000 nm


Measurement of scattered light
Measurement of Scattered Light

Contrast enhanced image showing scattered light between spectra

Plot of intensity along a column, scattered light level is < 2 % of peak intensity



Example atmospheric spectrum
Example atmospheric spectrum

Test set-up

Plot of 1020 nm spectrum

  • Small telescope located outside lab

  • Telescope pointed directly at sun

  • Optical fibre feed to PERSIST

  • Spectrum formed shown below


Technology highlights
Technology Highlights

  • The imager slicer technology provides a compact design that may benefit future instruments.

  • Overall PERSIST performs well – low level of scattered light and no light leaks.

  • Technology applicable to a variety of wavelengths simply by changing the filters.

  • High resolution multiple order spectrometer is being built for GHOST


Ghost
GHOST

  • GHOST – Green House Observations of the Stratosphere and Troposphere.

  • Multiple order SWIR spectrometer is being built for use on a NASA global hawk UAV.

  • High resolution SWIR hyper-spectral imager for CO2 and CH4 measurement.


Summary conclusions
Summary & Conclusions

  • PERSIST has demonstrated the feasibility of using image slicers and multiple order spectrometers for remote sensing.

  • Performance gains are possible compared with conventional push-broom systems.

  • Enables construction of smaller instruments.

  • Technology is well suited to observation of modest swath widths and 3 – 5 wavelength channels, e.g. atmospheric CO2and CH4 observation.


Contact information
Contact Information

  • David Lee

  • Science & Technology Facilities Council

    • www.stfc.ac.uk

    • www.atcinnovations.com

  • Centre for Earth Observation Instrumentation

    • www.ceoi.ac.uk


End of presentation

PERSIST

End of presentation


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