Portable Auroral Imager -- Instrument Description

The CNSR funded Portable Auroral Imager (PAI) was designed to be operated on a campaign basis, always attended, with the camera head located either indoors or outdoors.

PAI consists of, in the field, a Gen III Intensified CCD Camera with manual or automatic gain control, a GPS-locked SMPTE (VITC) time-code generator, a high resolution video cassette recorder, a small (5") TV monitor, as well as all the required power supplies (small, switched). This all fits into one foam fitted suitcase.

Any 1" C-mount lens system can be mounted on the camera. At the moment four different configurations are available (see separate Instrument Characteristics sheet). C-mount adapters for many non-C-mount lenses are available. Glass filters and step-up rings are also included. At this time only wideband operation is supported, but the inclusion of interference filters for monochromatic modes is planned.

Video signal is output by the camera according to the RS-170 standard. Images are produced by the TV camera thirty times per second, and each image (which consists of two interlaced fields) has been integrated for 1/60th second. The composite video signal is fed through the SMPTE time-code generator, which accurately time stamps each frame (drop-frame), before it is recorded on the VCR at the standard rate of 29.97 frames per second. The VCR has a resolution (horizontally) of about 400 (vertical) lines, which nicely matches the low light level resolution of the video signal received from the camera. The VCR also has time-base correction circuitry which minimizes pixel jitter and aids in properly digitizing images. About two hours of continuous recording is possible before the tape has to be changed. Special high-quality 30-minute video tapes are used for shorter measurement intervals, such as during rocket launches.

The PAI lab component consists of a 166 MHz Pentium PC equipped with, 32 Mb RAM, 2.1 Gb HD, Iomega Zip Drive, 100Mbs Ethernet Card and a Matrox Image-LC Image Digitizer (Frame Grabber). The PC has one Windows 95 partition and one Linux (kernel 2.0.29) partition. The Windows 95 partition is used for controlling the image digitizer through the use of Borland C++ and an image digitizer C-library (Matrox MIL). The Linux partition (on which the Windows 95 partition is VFAT mounted) is used for image processing and analysis.

The Digitizer ADC is 8 bits and has adjustable gain and offset. Frames arriving from the VCR can be summed in real-time in 16 bit frame buffers on the Digitizer, thereby increasing `integration time' and improving SNR. Also, binning can be performed to match the resolution of other instruments that was run in parallel with PAI.

The Ethernet Card provides a way of transferring image files to SGI workstations for further image analysis and production of hardcopies (publication quality, 1200 dpi). Image files can from there be stored on 4mm (DAT) tape.

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