Micropulse differential absorption LIDAR
Inventors
Spuler, Scott M • Repasky, Kevin S • Nehrir, Amin R
Assignees
NASA Langley Research Center • Montana State University Bozeman • University Corp for Atmospheric Research UCAR
Publication Number
US-10605900-B2
Publication Date
2020-03-31
Expiration Date
2036-04-27
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Abstract
A shared optics and telescope, a filter, and a micropulse differential absorption LIDAR are provided, with methods to use the same. The shared optics and telescope includes a pair of axicon lenses, a secondary mirror, a primary mirror including an inner mirror portion and an outer mirror portion, the inner mirror portion operable to expand the deflected annular transmission beam, and the outer mirror portion operable to collect the return signal. The filter includes an etalon and a first filter. The micropulse differential absorption LIDAR includes first and second laser signals, a laser transmission beam selection switch, a first laser return signal switch, and a toggle timer.
Core Innovation
The invention provides a micropulse differential absorption LIDAR system with a shared optics and telescope design, configured to transmit a transmission beam and receive a return signal. Central to the design is the use of a pair of axicon lenses for shaping the beam into an annular pattern, a secondary mirror to deflect the beam, and a primary mirror with separate inner and outer mirror portions to expand the transmission beam and collect return signals, respectively. The system further incorporates a specialized optical filter composed of an etalon with free spectral range matched to the difference between two laser wavelengths and a first filter with a passband selected to include both wavelengths, enabling effective background noise suppression and stable multi-wavelength operation.
This LIDAR system can operate with two separate laser signals—an online and an offline wavelength—facilitated by a beam selection switch, synchronized counters, and a toggle timer to allow rapid and concurrent switching between signals for improved measurement of atmospheric constituents, such as water vapor. The new optical and electronics architecture addresses limitations of previous systems, particularly by improving isolation between transmit and receive paths, increasing the duty cycle, and offering enhanced mechanical and thermal stability of the transmitter and receiver components.
The system also addresses the need for daytime operation and operation under variable and cloudy atmospheric conditions through its optical filtering approach, which effectively reduces solar background without loss of relevant return signal. By synchronizing the laser switching and detection counters with a toggle timer and using multi-stage filtering, the system enables robust, high-resolution, and continuous measurements of atmospheric water vapor and similar species over an expanded set of environmental conditions.
Claims Coverage
There is one independent apparatus claim and one independent method claim covering two inventive features.
Micropulse differential absorption LIDAR with synchronized dual-wavelength selection and detection
A LIDAR comprising: - A first laser signal and a second laser signal of different wavelengths. - A laser transmission beam selection switch, operated by a toggle timer, to toggle between including either the first or second laser signal in the transmission beam. - A first laser return signal switch that toggles between a first counter (for return signals from the first laser signal) and a second counter (for return signals from the second laser signal). - A toggle timer that causes both the transmission beam selection switch and the return signal switch to toggle substantially concurrently. This configuration facilitates rapid, synchronized switching between two laser wavelengths for atmospheric differential absorption measurement.
Method for operating a micropulse differential absorption LIDAR with concurrent wavelength toggling and counting
A method including: - Receiving a first and second laser signal of different wavelengths. - Upon receiving a timing pulse from a toggle timer, toggling between including only one of the laser signals in the transmission beam via a selection switch. - Toggling between a first and second counter based on which laser signal's backscattered return signal is received. - Substantially concurrently operating both the selection switch and the return signal switch using the toggle timer. This allows concurrent and coordinated management of transmission and detection for time-resolved, dual-wavelength LIDAR measurements.
The inventive features specifically cover a micropulse differential absorption LIDAR and its method of operation, where dual-wavelength transmission selection and synchronized return-signal counting are achieved through concurrent electronic switching, enabling efficient, dual-wavelength atmospheric measurements.
Stated Advantages
Enables autonomous long-term field operation under an expanded set of atmospheric conditions, including daytime and cloudy environments.
Provides a mechanically and thermally stable design for both the beam transmitter and receiver using a shared optics and telescope approach.
Improves duty cycle and data acquisition robustness through rapid, synchronized switching of dual-wavelength laser signals and detectors.
Offers excellent isolation between transmitted and received signals, enhancing measurement accuracy.
Delivers substantial background noise suppression while maintaining constant transmission for both laser wavelengths through optimized filtering.
Achieves eye-safe operation by efficiently expanding the transmission beam.
Documented Applications
Measurement of atmospheric water vapor distributions with high vertical and temporal resolution relevant for weather forecasting and climate studies.
Direct profiling and detection of atmospheric trace gases using differential absorption LIDAR techniques.
Continuous, high-resolution monitoring of the planetary boundary layer and lower troposphere for both clear and cloudy conditions.
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