1. Ground Based Observatories (GBO) All Sky Imager Design Stewart Harris - UCB
_101220_ATHA

2. All Sky Imager Overview Use Camera/Lens design validated in Phase A
Cooled CCD camera
16-bit A/D, USB interface
All Sky Lens
w/ telecentric filter cell
Add USB extender
USB cable extends from 5m to 50m using CAT5 cable
Add Environmental Enclosure
Requires heating / temperature control
Provides flexible mounting interface
Add Sun Shield
Electrical Interface
Unit Test

3. All Sky Imager w/ USB I/F
Starlight Xpress MX716

4. ASI Requirements REQUIREMENT SYSTEM DESIGN
GB.ASI-1: FOV. The field of view of the ASI shall be greater than 170°, full angle.
Compliance. Yes
GB.ASI-2: Exposure Time. Shall have an exposure duration that is programmable with a maximum exposure duration of no less than 1 second.
GB.ASI-3: Spectral Response. Within passband of 400 to 700nm, shall provide detectable response when stimulated with a source radiance less than 10kRayleigh, at maximum specified exposure duration.
Compliance. Expect minimum sensitivity < 1kR (5:1 SNR)
GB.ASI-4: Spatial Resolution. Shall provide aurora onset localization with accuracy better than 100km (dMLT< 1°)
Compliance. Raw ASI image will have > 250 pixel resolution per image diameter. Thumbnails will have 0.5° binning.
GB.ASI-5: Viewport. Shall have heated dome viewport
GB.ASI-6: Cadence Shall have a programmable repetition interval, minimum interval of no less than 10 seconds
Compliance. Have demonstrated cadence of 5s, and 3s appears to be feasible

5. 20040225_132755_TEST_THEMIS00_VIS_1000ms
ASI Data Products
ASI primary image 290 pixel diameter is “binned” to 0.5° resolution (thumbnails)
Primary science data:
Level 1 (~ 1kbps) (incl GMAG, housekeeping)
• Available via SAT comm, either Telesat (Internet real-time) or Iridium (daily)
High resolution data:
Level 0 (180 kbps) recorded HDD
Selective downloads via Satellite Internet
Periodic manual collection via disk swapping
_132755_TEST_THEMIS00_VIS_1000ms

6. ASI Enclosure Specifications
Operate in external ambient –50º to +40ºC
Maintain internal temperature at 20º ± 10ºC
Requires about 150 W heating
Heat dome to clear it of snow/ice
Hermetically sealed unit w/ nitrogen purge
Dessicant used for field repair
Hermetically sealed electrical connectors
Polycarbonate/acrylic dome
Flexible mounting

7. Prototype ASI Enclosure

8. ASI Enclosure Performance
Dome:
Stayed clear
Some ice buildup on flange
Heating:
Maintain 50° T using about 35W avg. heat power
Total heating power available is 240W
3/3/2004

9. ASI Prototype Findings
“dome gunk”
Courtesy M. Greffen
What we learned:
5 second cadence produces a LOT of data
Insulation must be tolerant to sun exposure
Adopting Foil-face polyethylene air pillow wrap, multi-layer wrap
Improvement to dome heating is desirable
Sealing improvement needed
Other minor issues:
Need to reduce length of housing
Improve thermal coupling of thermistor to mounting bracket
Orient camera such that top of image is North
Various changes in fasteners / assembly

10. Production Enclosure Design
Design: Allison Park Group, Inc.

11. ASI Sun Shield Background Result
ASI must survive, without degradation, non-operating exposure to daytime sun exposure
CCD is Sony Interline Transfer device ICX249AL
Features “microlens” on each pixel, an organic material subject to deterioration due to UV exposure
All Sky Lens uses Peleng Fisheye f/3.5
A/R coating exhibited discoloration after one summer in Athabasca
Result
Need internal sun shield
Drives housing diameter and heat required

12. Retracted Position is the Fail-safe Position
Sun Shield Design
Retracted Position is the Fail-safe Position

13. Sun Shield Prototype Status: Just built Needs adjustment / balancing
Solenoid drive circuit needs test
Provides low power cont. duty drive
Needs qualification test

14. ASI Electrical Interface
ASI has two external interface connectors:
Power
Data

15. ASI Unit Test Summary Acceptance Tests: Pre-Shipment: FOV (>170°)
Exposure Time (duration at least 1 sec)
Spectral Response
Produce detectable response to source radiance < 10kR
Goal < 1kR
Passband 400 – 700nm
1 sec exposure duration
Spatial Resolution (>250 pixel image diameter)
Verify point source response
Cadence (better than 10s)
Goal < 5s
Record dark and bias images (room temperature)
Record response to standard source
Pre-Shipment:
Focus adjustment and verification
Alignment verification (top of image relative to alignment datum)
Heater control functional test (incl thermistor time response)
Solenoid functional test (#iterations TBD)
Internal mechanical inspection checklist
Final Assembly / purge and backfill
Final functional test and Imager Burn-in (duration TBD)