Development of a Narrow Field Auroral CCD Imager for the AMISR Observatory

Development of a Narrow Field Auroral CCD Imager for the

AMISR Observatory

Mike J. TaylorCenter for Atmospheric and Space

SciencesUtah State University

Present at: The First AMISR Science Planning Meeting at the Asilomar Conference Grounds, Oct. 11-13, 2006

Special thanks: Jeff Baumgardner, Rick Doe, Dirk Lummersheim, Josh Semeter, Betty Lanchester, Craig Heinselman, and Keo Consultants.

Outline• AMISR at PFRR.• Auroral imagery information.• Examples of coordinated radar and

optical research.• “Straw man” camera requirements and

design.• Data acquisition needs.• Infra-red imager for high latitude MLTI

research.

AMISR

•Solid state phased array radar.•Rapid pulse to pulse beam steering

capability.•3-D imaging of ionospheric properties.

Two new facilities: •Resolute Bay, Canada.•Poker Flat, Alaska.

~ 5

80 k

m

AMISR at PFRR

Pointing: 74° elev., Azi. 15° EField of view: ±25° (steerable)Full beam width: 1° (half power)Co-aligned optics: narrow field monochromatic auroral imager and CCD spectrometer.

Complimentary Imaging Capability

•Essential context “big picture” information to aid and complement the interpretation of radar data.

•High-resolution 2-D morphology and dynamics over a broad range of auroral forms.

•Comparative measurements of different auroral emissions (energetics) using broad and narrow filters.

•“Post-hoc” temporal-spatial photometry on selected narrow band auroral emissions.

•Real-time data with “in field” pointing capability to enhance the selection of radar measurement volume.

North

Wide Angle: 64° x 86°

(90x160 km)cut-off filter1 frame/3s Electric field at 3s resolution

30 Jan 1995:

Ele

ctro

n D

en

sity

Time (minutes) after 18:00 UT

West

position of field-aligned beam

electric field vector

Coordinated Radar and Optical Observations

EISCAT Mainland Radar E-region:

(Courtesy B. Lanchester, Univ. of Southampton)

EISCAT Movies Showing Electric Field Flip as Arc Crosses Radar

Higher spatial resolution~ 1 min 20 sec.

N

W

20 km

Fine detail in electric field(3 second resolution)

Summary

EISCAT Svalbard Radar CoordinationField-aligned beam (0.7°)

complicated spatial structure (<1 km)

fast temporal variations (<1 second)

17 Jan 2002

White light dataFOV: 23° x 31°25 fps (40 ms

exposure)

Coherent scatter from ion acoustic waves Structure size under 300 m at 500 km altitude Varying on 0.2 second time scale

(Courtesy B. Lanchester, Univ. of Southampton)

Auroral Arc Fine Structure

examples of discrete auroral structures 0.1 to 1 km wide T.Trondsen (Univ of Calgary)

Few instruments can measure it well Few theoretical models can account for it (Courtesy B. Lanchester, Univ. of Southampton)

Vortex Structures

From “NSF Passive Optical Report, 2005”

• Arc widths much less than 1 km

• Lengths from several km to 100s or 1000s km

• Multiple (parallel) curtains or filaments

• Large field-aligned currents and magnetic

perturbations

• Strong velocity shear near discrete aurora

• Large amplitude “spiky” electric fields in the

acceleration

region

• Time scales between fractions of seconds and

minutes

Observations: Properties of Discrete Aurora

Multi-Spectral Imaging of Discrete Aurora (<1keV el)

Semeter et al., 2001

4278

7325

AMISR Auroral Camera CapabilitiesScience Drivers:•High spatial resolution, <100-200 m (auroral fine structure).

•Large dynamic range (discriminate faint auroral structures)

•Broad spectral range (energetics of different emissions)

•Low noise (high quality imagery of faint emissions)

•Variable integration time (several frames per second to several seconds to accommodate broad range of auroral emissions)

CCD Imagers:•Best option to achieve (most of) these goals.•High sensitivity, broad spectral range, low noise data.

Imager Field of View

Circular FOV ?Uses all light butno all CCD

Square FOV ?All CCD used but some light lost.

Shape:

Size:For 30x30° rectangular fieldZenith foot print at 100 km = 52 x 52 kmCCD: 1024x1024 = 50 m/pixel resolution (at 100 km)

AMISR Poker Flat

100, 200, 300,400 km FOV

Auroral Spectrum (From Space) Courtesy L. Broadfoot

Potential Emissions: 427.8 nm N2+ (1NG) 486.1 nm H-

beta (need to select 6) 520.1 nm NI 557.7 nm OI

589.3 nm NaI 630.0 nm OI656.2 nm H-alpha 732/3 nm OII750 nm N2 1PG (4-2,3-1) 844.6

nm OIOthers? Help Please…….

QE-Bare CCD

•Back thinned CCD: High QE over spectral range 400-850 nm

•Excellent for narrow band imaging (<2nm) at visible wavelengths

•Emission longer than ~700 nm will surfer etlonging effects (which

may be possible to remove later in software but not in real time).

Andor iKon-M Bare CCD Imager

DU934N

Active pixels: 1024x1024Pixel size: 13x13 mImager area: 13.3x13.3 mmBack thinned peak QE: 95%Min. operating temperature: -80°C air,

-100°C water Pixel well depth: 80,000 e-Pixel read-out rate: 2.5 MHz, 1MHz, 50 kHzRead-out noise: 2.5e-@ 50kHz

10 e-@ 2.5 MHzDigitization: 16-bitDark Current: 0.0002 e-/pix/sec (-100°C)PC interface: USB 2.0

Max sustained data rate: ~ 2 images/sec at full resolution(~ 4 images/sec @ 512 x512 pixel resolution)

Andor iXon-EMCCD ImagerActive pixels: 1024x1024Pixel size: 13x13 mImager area: 13.3x13.3 mmBack thinned peak QE: 92.5%Min. operating temperature: -80°C air,

-90°C water Linear EM gain: 1-1000 timesPixel well depth: 80,000 e-Pixel read-out rate: 10 MHz, 5MHz, 3MHz, 1MHzRead-out noise: 49e-@ 10MHzDigitization: 14-bit, 16-bit @ 1MHzDark Current: 0.001 e-/pix/sec (-100°C)PC interface: PCIMode (switchable): EMCCD or conventional

Frame rate: 9 images/sec. (frame transfer with potential smearing of bright objects). LARGE DATA RATES!!!

DU-888

Typical Telecentric Imager Design

Courtesy Trond Trondsen

Straw man Design Requirements

Telecentric lens system (for narrow band imaging)• FOV: 30x30° (to best match AMISR FOV)

(Option 20x20° for higher spatial resolution)• Six position computer controlled filter wheel.• Three inch diameter, ~ 2 nm bandwidth interference filters.iKon camera: DU934N (1024x1024 pixel).• Spectral range: 400-900 nm.• Spatial resolution: 50 m at 100 km.• Frame rate: 2 images/sec. full resolution (normal operation: 4

images/sec.)• Investigating possibility of suppressed etalonging detector

from E2V company.

Acquisition Software

Summary• Basic camera design based on well-proven airglow (and

auroral) bare CCD imagers.• Primary role to provide high resolution imagery co-

aligned with AMISR at PFRR.• System will be mount on steerable ALT-AZI tripod

together with spectrometer.• Remote controlled operation of camera with onsite

computer for data storage and real-time display.• Suggest this DU934 back thinned CCD as best option for

a broad range of research with AMISR (typically operating at 512x512, 100 m resolution and frame rates ~ 4 per second to several second exposures)

• Currently etalonging will limit NIR (>700 nm) narrow band imagery.

• Future upgrading to EMCCD possible.