Differential absorption LIDAR for profiling temperature
Inventors
Stillwell, Robert • Spuler, Scott • Hayman, Matthew • Repasky, Kevin S.
Assignees
Montana State University Bozeman • University Corp for Atmospheric Research UCAR
Publication Number
US-12061287-B2
Publication Date
2024-08-13
Expiration Date
2038-11-30
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
A beam transmitter, a receiver, and a LIDAR, along with methods to operate each are provided. The beam transmitter comprises a first and a second transmission channel (201a, 201b), each transmission channel including a first online laser, a first offline laser, and a first laser transmission selection switch operable to toggle between including the first online laser signal and the first offline laser signal in a first transmission beam. The beam transmitter further includes at least one light redirection device operable to coalign the first transmission beam with the second transmission beam. The receiver comprises a first splitter (402a, 402b), a first filter (404a, 404b), a first detector channel (406a, 406b), a second splitter (408a, 408b), a second filter (410a, 410b), and a second detector channel (412a, 412b). The LIDAR includes the beam transmitter, the receiver, and a shared telescope.
Core Innovation
The invention provides a differential absorption LIDAR (DIAL) system designed for atmospheric profiling, specifically to measure water vapor concentration, oxygen absorption, and temperature profiles with improved accuracy. The system comprises a beam transmitter with at least two transmission channels, each incorporating an online laser, an offline laser, and a laser transmission selection switch to toggle between the online and offline signals. A light redirection device coaligns the output beams from these channels to generate a combined transmission beam suitable for probing multiple molecular species simultaneously.
The LIDAR also features a specialized receiver system that employs splitters, filters, and detector channels to separate and detect the online and offline return signals for each species. Advanced filtering, using combinations of narrow band filters and etalons, allows isolation of the desired wavelengths, while photon counting modules facilitate the detection of low-intensity return signals. Some embodiments further incorporate atomic cells, such as rubidium or potassium filters, to enable high spectral resolution LIDAR (HSRL) backscatter measurements and separation of aerosol and molecular components.
The system addresses the limitations of previous DIAL approaches, which incurred errors due to variability in atmospheric oxygen mixing ratios and challenges in Doppler broadening corrections. By combining simultaneous measurements of water vapor (for O2 mixing ratio correction), oxygen absorption (temperature sensitivity), and HSRL (aerosol/molecular separation), the described LIDAR provides a robust and cost-effective means of obtaining accurate atmospheric temperature data, overcoming shortcomings such as the high uncertainty in traditional inversion methods.
Claims Coverage
The patent contains several independent claims that define inventive features covering novel aspects of the beam transmitter, receiver, and associated methods for atmospheric LIDAR systems.
Differential absorption LIDAR beam transmitter with dual transmission channels and coalignment
A beam transmitter comprising: - A differential absorption LIDAR transmission channel operable to provide a water vapor concentration signal using a first online and a first offline laser, and a first transmission selection switch. - A high spectral resolution LIDAR/temperature sensitive differential absorption LIDAR transmission channel operable to provide an aerosol backscatter/oxygen absorption signal using a second online laser and a second offline laser, and a second transmission selection switch. - At least one light redirection device operable to coalign the first and second transmission beams to generate a combined transmission beam.
Method for transmitting a combined LIDAR beam for atmospheric profiling
- Generating a first transmission beam for water vapor using a pair of online/offline lasers and toggling switch. - Generating a second transmission beam for aerosol backscatter/oxygen absorption, again using online/offline lasers and a toggling switch. - Using at least one light redirection device to coalign the beams, creating a combined transmission beam.
LIDAR receiver utilizing sequential signal splitting, filtering, and detection for multiplexed species measurement
- A receiver with a first splitter to separate a differential absorption LIDAR return signal and a high spectral resolution LIDAR/temperature sensitive absorption laser signal from the combined return, with subsequent dedicated filtering and detection channels for each. - Second splitter to further separate temperature sensitive and high spectral resolution return signal components, each with their own filtering and detection pathway.
Receiver with potassium cell filtering for high spectral resolution backscatter signal
Addition of a potassium cell to filter the high spectral resolution LIDAR return component, with a third detector channel to distinguish the elastic backscatter signal filtered for clouds and aerosols.
Receiver design for use of narrow band filters and etalons in sequence
Either the first or second filter includes a first narrow band filter, an etalon, and a second narrow band filter to provide strong spectral isolation and noise suppression.
Photon counting module for sensitive LIDAR detection channels
At least one detector channel (first or second) includes a single photon module counting module, enhancing detection sensitivity for low-return signals.
Multi-channel scaler for coordinated detection readout
Inclusion of a multi-channel scaler to receive signals from at least the first or second detector, enabling synchronized acquisition across multiple LIDAR channels.
Beam transmitter for triple-channel species and backscatter LIDAR measurements
A transmitter with three distinct channels: for water vapor (DIAL), oxygen absorption (DIAL), and a high spectral resolution channel (HSRL) using a rubidium-locked laser. The system includes at least two light redirection devices to coalign all three transmission beams.
Receiver and method with rubidium filtering and fourth detection channel
A receiver system that includes: - Sequential splitting and filtering of DIAL and HSRL return signals. - A rubidium cell to filter the HSRL signal. - Third and fourth detector channels to detect elastic backscatter signals filtered and unfiltered for clouds and aerosols, enabling direct backscatter ratio calculation.
The inventive features encompass a multiplexed beam transmitter for differential absorption and high spectral resolution LIDAR, sophisticated receiver architectures with advanced filtering and detection for multiple species, and methods for integrating, splitting, and analyzing LIDAR return signals. Design aspects such as atomic cell filters, photon counting modules, and multi-channel scalers further enhance the system's capability for precise and robust atmospheric profiling.
Stated Advantages
The system provides accurate temperature measurements calibrated for the oxygen mixing ratio in the atmosphere by simultaneously measuring water vapor and oxygen absorption.
It allows correction of O2 DIAL-derived temperature errors due to Doppler broadening and water vapor mixing ratio, enabling robust temperature retrieval accuracy.
Combining HSRL with DIAL enables direct measurement of the aerosol to total backscatter ratio while also measuring water vapor and oxygen absorption.
The device offers a low-cost, simpler temperature measurement solution by using shared optical components and minimizing the number of lasers, switches, and amplifiers required.
Embodiments using DBR or DFB laser diodes provide a more affordable DIAL instrument while enabling a narrow linewidth source.
The use of atomic cell filtering (rubidium or potassium) enables low-maintenance HSRL capable of quantitative LIDAR data products.
The shared optics and telescope design provides improved opto-mechanical stability and eye safety for the transmission beam.
Documented Applications
Detection and profiling of atmospheric water vapor.
Atmospheric temperature profiling through oxygen absorption line measurements.
Determination of aerosol and molecular background scattering in the atmosphere.
Quantitative measurement of cloud and aerosol backscatter for meteorological and climate studies.
Interested in licensing this patent?