1. Mini Lidar Overview
GroundWinds is based on Light Detection And Ranging (LIDAR) technology. LIDAR relies on the light scattering properties of the atmosphere. A laser is emitted into the atmosphere, and the light is scattered off of the molecules and aerosols (if present). This scattered light can be analyzed to directly determine various atmospheric properties including wind velocity, air density and temperature. The direct detection technology that Michigan Aerospace Corporation has developed differs from other techniques in several ways. More information about LIDAR technology can be found in the LIDAR FAQ.
How Michigan Aerospace Corporation Fringe Imaging Direct Detection LIDAR Differs From Coherent Doppler LIDAR:
- GroundWinds does not require the presence of aerosols in order to make a wind measurement. This is of great advantage in various parts of the world, and when probing most of the atmosphere
- The GroundWinds 355 nm laser is eye-safe.
- The receiver optics and transmission optics need not be of very high quality, reducing cost and complexity of the system.
How Michigan Aerospace Corporation Fringe Imaging Direct Detection LIDAR differs From Other Direct Detection Doppler LIDAR systems:
- The GroundWinds system images the entire laser spectrum. This provides more information about how the outgoing pulse is being affected by the atmosphere, and makes the system more robust.
- Photon recycling improves the throughput of the system, providing up to a factor of 4-10 in efficiency gains, reducing laser power and/or telescope collection area.
- Because multiple orders are used, the clear aperture of the etalon is greatly reduced over what is required of a comparable Fizeau or Double-Edge system, reducing mass, volume, and cost.
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2. Fundamental Features
- Uses high quantum efficiency CCD detector
- Uses patented CLIO optics
- Allows spectrum to be imaged onto a CCD detector
- Maximizes signal-to-noise ratio by minimizing the number of pixels used to detect the spectrum (minimizes read noise)
- Relies on molecular signal return
- Uses photon recycling to improve throughput and reduce laser power.
- Uses multiple orders to reduce size of instrument.
- Uses aerosol signal return when available
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3. General System Overview
- Laser beam is emitted
The scattered laser light is collected in the telescope
The collected light is sent through a filter etalon
The filtered light is directed to the aerosol etalon where the interferenece pattern is transformed by the CLIO and captured on a CCD camera
The reflected aerosol signal is directed to the molecular etalon and the interference pattern is transformed by the CLIO and captured on another CCD camera
GroundWinds CCD Image
By design a CCD device streaks the image across the chip during image readout and each row is
read individually by the readout register. GroundWinds takes advantage of this streaking behaviour by masking off a portion
of the CCD as the image collecting area, and then collecting data during the streaking process. This provides a time-based
image, where each row is imaged at a different point in time. The time of flight for each LIDAR return is then translated
to it representative measurement altitude.
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