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Technical Note – All-Sky Kite HDR IMAGING AND FAST EVEN TRACKING FOR ASTRONOMY October 2012, Northern Ireland
Traditionally, Astronomers use CCD camera with a combination of cooling and low readout speed to achieve the long integration times necessary to detect faint objects. However, this approach has two limitations, the dynamic range is limited by the electron well depth of the pixel, and long exposure times are not suitable for tracking fast occurring events such as falling asteroids or space debris. In addition, since where or when asteroids or debris will fall cannot be known, tracking these kind of objects requires a unique combination of wide field of view, very high sensitivity and speed.
Driving CCD camera at 20 frames per second greatly reduces its sensitivity and the amount of collected photons. Only EMCCDs are capable of achieving fast frame rates required for this application, while maintaining good sensitivity levels thanks to the embedded on-chip Electron Multiplication (EM gain) which eliminates the readout noise. See Figure 1 and Figure 2, EMCCD allows a gain of sensitivity of up to 4 stellar magnitudes compared to a traditional CCD.
Figure 1: 50ms exposure time WITHOUT EM gain. 20mm, F/1 lens.
Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
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Technical Note – Solar Cell Inspection
Figure 2: 50ms WITH EM gain enabled. 20mm, F/1 lens.
The removal of the readout noise and resulting added sensitivity can be used in two ways: • Lifting the limitation of the pixel well depth and obtain ultra-high dynamic range images. This is achieved through a combination of negligible readout noise and accumulation of short exposure images. • Increasing acquisition frame rate in order to capture faint and fast transient events.
Ultra HDR with All-Sky Kite
Figure 3: Single 100ms exposure time, EM gain enabled, fisheye lens f=1.8mm with Kite. Magnitude 3 stars can be detected Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
Technical Note – All-Sky Kite
Figure 4: 1500x 100ms exposure time fisheye lens with Kite. Ultra HDR in only 2m30s!
Figure 3, shows how a single 100ms exposure allows the detection of stars down to stellar magnitude 3 with 16 bit dynamic range. Figure 4 shows a stack of 1500 images, equivalent to 2min30s cumulated exposure. The resulting image exhibits Ultra-High Dynamic Range (UHDR) from the windows house light and light pollution nearby to the horizon up to the faint Milky Way and many constellations. Summing images without EM gain doesn’t result in the same increase in dynamic range or sensitivity because of the higher readout noise; see comparison on Figure 5 and Figure 6.
Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
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Technical Note – Solar Cell Inspection
Figure 5: 500x 50ms exposure time WITHOUT EM gain, 20mm, f/1 lens with Kite
Figure 6: 500x 50ms exposure time WITH EM gain, 20mm, f/1 lens with Kite
Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
Meteor falling detection
Technical Note – All-Sky Kite
With a little luck, the combination of wide angle lens, high sensitivity and fast frame rate detector, the capture of falling meteor into earth’s atmosphere is possible. See Figure 7. The camera high sensitivity allows detecting quick changes of the meteor shape and the way it degrades throughout its entry into the earth’s atmosphere. Moreover, this kind of sequence can tell if meteor remains can be retrieved into the ground.
Figure 7: Meteor, 100ms exposure time, 10mm, f/1.8 lens with Kite.
EM camera performance can also provide with this kind of time capture sequence, information on satellites reentry into earth’s atmosphere, and what and where can be recovered from it on the ground.
Conclusion
Raptor Photonics’ Kite, Figure 8, and Alcor System’s All-Sky, Figure 9, combination offers the possibility to study random and fast occurring events in the earth’s atmosphere as well as obtaining ultra-high dynamic range images within very short accumulated exposure, all within a proven compact and rugged package. Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
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Technical Note – Solar Cell Inspection
About Raptor Photonics
Figure 8: Kite EMCCD camera • • • • • • • •
658 x 596, 10x10µm EMCCD sensor. Enables optimum image resolution in low light imaging applications B/W EMCCD technology. Enables high sensitivity imaging with up to 1000x onchip gain. 16 bit CameraLink output. Provides wide dynamic range 53% QE from Virtual Phase sensor. Optimum Photon collection No Image intensifier. Optimum B/W image sharpness in ALL light conditions Interlined. No mechanical shutter required, vibration-less CCD readout Realtime Imaging. Optimum image sharpness in ALL light conditions XCAP software compatible. Ready-to-Run powerful Image Analysis Software
Figure 9: All-Sky camera • • • •
185°x185° fisheye lense. Enables ultimate light collection over the widest possible field of view Active dome defrost and camera autoiris. Enable all night reliable data acquisition Anodized aluminum casing, water tight box and connectors. To endure the harshest conditions maintenance free. Dedicated software. For easy automated acquisition and processing
Raptor Photonics Limited is a global leader and manufacturer of high performance, industrial-grade and extremely rugged ultra-low light digital & analogue cameras. Raptor specializes in complete cameras and core engine solutions using CCD, EMCCD, Scientific CMOS and SWIR sensor technology. The extreme low light capability of Raptor’s cameras makes them ideal for day/night surveillance, homeland security and scientific markets. Raptor Photonics Ltd is a registered ISO 9001:2008 company and is headquartered in Larne, Northern Ireland. Raptor Photonics Ltd Telephone: +44 28 2827 0141
[email protected] www.raptorphotonics.com
About Alcor System
Alcor System was created in 2009 to design and manufacture cutting edge software and instrumentation for astronomical applications. PRISM is a powerful software suit for automated astronomical image acquisition and processing. The “ALL-SKY” outdoor camera range is designed to offer wide angle (180°x180°) continuous surveillance of the sky for a wide range of applications from fast meteors and slower satellites tracking to the observation of aurora and nightglow. Alcor System has already delivered products and services to almost 500 customers including individuals (amateurs/professionals) as well as institutes such as ESO, CEA, IMCEE and many other worldwide class observatories. Alcor System
[email protected] www.alcor-system.com
Raptor Photonics Limited. Willowbank business Park, Larne, Co Antrim, BT40 2SF, Northern Ireland Registered in Northern Ireland No NI 60799, VAT Reg No: 906 1385 35
