A terahertz ice cloud airborne detection system
By employing a receiving method combining a rotating plane mirror and a quasi-optical feed network with variable-speed circular scanning, an integrated terahertz airborne ice cloud detection system was designed. This system solves problems such as narrow detection swath, limited effective data volume, and large system size, achieving flexible adaptation and efficient data acquisition, and is suitable for various aircraft platforms.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAN INSTITUE OF SPACE RADIO TECH
- Filing Date
- 2023-10-27
- Publication Date
- 2026-07-03
AI Technical Summary
In the existing technology, airborne terahertz ice cloud detection systems have problems such as narrow detection swath, small amount of effective data, large system size and weight, and lack of adaptability. In particular, the large distance between the reflector surface and the feed array aperture of the ISMAR system leads to a narrow scanning swath, a small effective observation area, and complex data preprocessing.
An integrated terahertz airborne detection system for ice clouds was designed, employing a receiving method using a rotating plane mirror and a quasi-optical feed network, combined with a variable-speed circular scanning system. The system includes an antenna subsystem, a multi-band terahertz receiving subsystem, a calibration subsystem, and a comprehensive processing and control distribution unit. The system performs 360° variable-speed circular scanning via a rotating plane mirror, performs signal processing using the multi-band terahertz receiving subsystem, and employs a two-point calibration technique to achieve flexible system adaptation and efficient data acquisition.
It achieves a wider detection swath, increases the amount of effective observation data, reduces the difficulty of data preprocessing, and has the ability to adapt to different aircraft platforms, thereby improving the system's flexibility and data acquisition efficiency.
Smart Images
Figure CN117537927B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of space microwave remote sensing technology and relates to the design of a terahertz ice cloud airborne detection system. Background Technology
[0002] In the Earth observation system, clouds are one of the most important and most difficult meteorological elements to determine, especially ice clouds in the upper troposphere, which have a high coverage of the Earth's surface and have a significant impact on the Earth's energy balance, climate change and weather evolution.
[0003] To date, extensive theoretical and experimental research has been conducted abroad on terahertz ice cloud detection technology, including flight tests of airborne verification payloads. The International SubMillimeter Airborne Radiometer (ISMAR) is an airborne terahertz ice cloud detector jointly developed by the UK Met Office and ESA. ISMAR employs a reflector antenna and feed array receiver, performing airborne observations via circular scanning along the flight direction. The payload dimensions are approximately 1.1 x 0.4 x 0.5 m, and it weighs approximately 90 kg. Due to the feed array receiver method, the distance between the reflector and the feed array aperture is relatively large, and the swath width of the circular scan along the trajectory is narrow, resulting in a small effective observation area and even fewer effective observations, making data preprocessing complex.
[0004] Extensive theoretical research has been conducted in China on terahertz ice cloud radiation transfer simulation, but there are no publicly reported airborne terahertz ice cloud detection systems in China. Summary of the Invention
[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a terahertz ice cloud airborne detection system. It adopts a receiving method of rotating plane mirror and quasi-optical feeding network, an integrated structural design, and a vertical flight direction variable speed circular scanning system. This fills the technological gap of no airborne terahertz ice cloud detection system in China. At the same time, it solves the problems of narrow detection swath, small amount of effective data, and large size and weight of the ISMAR system, making the system more flexible and adaptable to various manned and unmanned aircraft platforms.
[0006] The technical solution of this invention is: a terahertz airborne detection system for ice clouds, comprising an antenna subsystem, a multi-band terahertz receiving subsystem, a calibration subsystem, and a comprehensive processing and control distribution unit, wherein:
[0007] Antenna Subsystem: Under the control of the integrated processing and control power distribution unit, the target area is detected by 360° variable speed circular scanning to obtain terahertz radiation signals within the field of view. The terahertz radiation signals are distinguished according to polarization direction and frequency to obtain multiple radio frequency signals, which are then sent to the multi-band terahertz receiving subsystem.
[0008] Multi-band terahertz receiving subsystem: adopts direct mixing double-sideband receiving method, mixes, filters, amplifies and detects each radio frequency signal to obtain each detected signal, and sends it to the integrated processing and control distribution unit;
[0009] Calibration subsystem: Under the control of the integrated processing and control distributor, the detection system is calibrated;
[0010] Integrated processing and control power distribution unit: provides power to the antenna subsystem, multi-band terahertz receiving subsystem, and calibration subsystem; and retrieves ice cloud information of the observation area based on the transmitted detection signals.
[0011] Furthermore, the antenna subsystem includes a plane mirror, a scanning mechanism, a quasi-optical feed network, and a servo controller. The plane mirror is mounted on the scanning mechanism. Under the control of the integrated processing and control distributor, the servo controller drives the scanning mechanism to move the plane mirror to perform variable-speed circular scanning along the central axis of the plane mirror. The plane mirror reflects the terahertz radiation signal within the field of view into the quasi-optical feed network. The quasi-optical feed network uses a polarization grid to polarize the terahertz radiation signal received by the plane mirror. The signals of different frequencies and polarization directions obtained by the separation are reflected by an ellipsoidal mirror into the feed horns of each branch, resulting in multiple radio frequency signals that are sent to the multi-band terahertz receiving subsystem.
[0012] Furthermore, the signals with different frequencies and polarization directions include H polarization directions of 664 GHz and 243 GHz, and V polarization directions of 664 GHz, 448 GHz, 325 GHz, 243 GHz and 183 GHz.
[0013] Furthermore, the multi-band terahertz receiving subsystem includes seven receivers, each corresponding to receive signals of different frequencies with different polarization directions.
[0014] Furthermore, the calibration subsystem includes two terahertz calibration sources, namely a room temperature source and a thermal calibration source. The room temperature source is maintained at -30°C and placed at a position perpendicular to the observation field of view at 126.2° to 143.8°. The thermal calibration source is maintained at 40°C and placed at a position perpendicular to the observation field of view at 216.2° to 233.8°.
[0015] Furthermore, the aperture of the calibration source is larger than the size of the plane mirror, ensuring that two-point calibration is achieved by providing two high and low radiation brightness temperatures required for observation, namely the thermal calibration source and the room temperature source.
[0016] Preferably, the inversion to obtain ice cloud information of the observation area includes: using a priori database and a Bayesian inversion algorithm to obtain the ice cloud height, ice water path, and effective radius of the ice cloud in the observation area.
[0017] The advantages of this invention compared to existing technologies are as follows: For terahertz ice cloud detection, this invention proposes, for the first time in China, an airborne terahertz ice cloud detection system. It employs a combination of rotating plane mirrors and a quasi-optical feed network, solving the problems of narrow swath width, large system size, heavy weight, and poor adaptability associated with ISMAR systems. This allows for the acquisition of more effective observation data and reduces the difficulty of data preprocessing. Furthermore, the detection system of this invention is adaptable to different aircraft platforms and has been experimentally verified. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the system's working state according to the present invention;
[0019] Figure 2 This is a schematic diagram of the calibration temperature range of the system of the present invention;
[0020] Figure 3 This is a schematic diagram of the scanning scheme of the system of the present invention;
[0021] Figure 4 This is a block diagram illustrating the composition principle of the system of the present invention;
[0022] Figure 5 This is a schematic diagram of the quasi-optical feed network of the system of the present invention;
[0023] Figure 6 This is a schematic diagram of the two-point calibration principle of the system of the present invention. Detailed Implementation
[0024] This invention proposes a terahertz airborne ice cloud detection system. The system adopts a receiving front-end design with a plane mirror and a quasi-optical feed network, and achieves the observation of ice crystal particles in the cloud by rotating the plane mirror and performing variable-speed circular scanning.
[0025] The terahertz airborne ice cloud detection system is a periodically calibrated full-power terahertz radiometer that detects the microphysical characteristics of ice clouds by receiving the radiation or scattered energy radiated from the observed scene. When the system's main antenna beam is pointed at the ice cloud, the antenna receives radiation flux from the ground or sea surface, low-level clouds, ice cloud radiation, scattering, and atmospheric radiation, causing changes in the antenna's apparent temperature. The received signal is amplified, filtered, detected, and re-amplified, and then presented as a voltage. After two-point calibration of the system's output voltage, establishing the relationship between the output voltage and the antenna's apparent temperature, the brightness temperature of the observed target can be determined. This brightness temperature contains some physical information about the radiator and the propagation medium. By establishing a radiation transfer model and inversion, ice cloud parameters such as ice water paths, ice crystal particle sizes, and cloud height in the observed area can be determined.
[0026] Due to the significant challenges in ice cloud detection, this invention employs variable-speed circular scanning to increase the detection probability, taking into account the cruising altitude of domestic calibration aircraft. This not only increases the swath width but also yields observational data from multiple angles, providing more research data for terahertz radiative transfer theory studies, improving the accuracy of terahertz radiative transfer models, addressing the insufficient swath width of the ISMAR system, and increasing multi-incident angle observation data, such as... Figure 1 As shown, the airborne system uses circular scanning instead of the conical scanning used on the spaceborne system. Except for the observation angle, all other receiving links are shared, further verifying the sensitivity of ice cloud radiation detection to the observation angle and meeting the adaptability and flexibility requirements of airborne installation.
[0027] To address the integrated design of the system and the errors introduced by the uncertainty of the observation field of view, two sets of terahertz calibration sources are used, placed perpendicular to the observation field of view at angles of 126.2°–143.8° and 216.2°–233.8° respectively. Figure 2 As shown. During flight, the calibration source controller sets the default operating state, and the ambient temperature of the normal temperature calibration source is controlled at -30°C by the high-altitude ambient temperature (outside the cabin temperature is about -50°C). The thermal calibration source is kept at 40°C by internal heating elements and insulation measures, which further improves the system calibration.
[0028] Existing data indicates that the fastest cruising speed of an aircraft (manned and unmanned) is approximately 580 km / h. Considering system versatility, the system adopts the fastest cruising speed for its scanning scheme design. Using a 3dB beamwidth in the 664GHz band as the minimum beamwidth to avoid missed scans, calculations show that the system's scanning observation overlap is greater than 35%, the observation period is 3 seconds, and the constant rotation speed is 68.75° / s. (Specific details are as follows...) Figure 3 As shown.
[0029] Based on the radiation characteristics of ice clouds, the terahertz airborne ice cloud detection system selected the highly sensitive 183–664 GHz frequency band for detection, comprising a total of 13 detection channels. The system features an integrated design, employing a receiving front-end scheme with a plane mirror and a quasi-optical feed network. Variable-speed circular scanning is achieved through rotating the plane mirror, increasing the flexibility of the system layout and facilitating two-point calibration of the antenna aperture.
[0030] like Figure 4 As shown, the terahertz airborne detection system for ice clouds of the present invention mainly consists of the following functional modules: antenna subsystem (including plane mirror, scanning mechanism, quasi-optical feed network, servo controller), multi-band terahertz receiving subsystem, calibration subsystem (including calibration source controller, ambient temperature source, thermal calibration source), and integrated processing and control distribution unit.
[0031] The antenna subsystem includes a plane mirror, a scanning mechanism, a quasi-optical feed network, and a servo controller. The plane mirror employs a high-precision gold-plating process to ensure the accuracy of its surface profile. It receives terahertz radiation signals within the observation field and reflects them into the quasi-optical feed network. The quasi-optical feed network uses a polarization grid to polarize the terahertz radiation signals received by the plane mirror. The H-polarized wave is split into high-frequency and low-frequency branches by frequency divider FSS#1. The high-frequency branch separates into 664 GHz H-polarized detectors, and the low-frequency branch separates into 243 GHz. The V-polarized wave is split into high-frequency and low-frequency branches by frequency divider FSS#2. The high-frequency branch separates into a 664 GHz detector branch, while the low-frequency branch is separated into 448 GHz, 325 GHz, 243 GHz, and 183 GHz branches by frequency dividers FSS#3, FSS#4, and FSS#5, respectively. These branches are reflected by ellipsoidal mirrors into the feed horns of their respective frequencies. Detailed design is available in [link to design details]. Figure 5 As shown. The servo controller controls the drive scanning mechanism to enable the plane mirror to perform variable-speed circular scanning along the central axis of the plane mirror (parallel to the flight direction), and feeds back the antenna rotation angle data in real time to the integrated processing and control distribution unit via a 422 synchronous angle bus. Details of the control strategy can be found in [link to relevant documentation]. Figure 3 As shown.
[0032] The multi-band terahertz receiving subsystem consists of 7 receivers, with 3 channels per receiver at 183GHz, 325GHz, and 448GHz, for a total of 13 receiving channels. A direct mixing double-sideband receiving method is employed. The RF signals from the optical feed network, frequency-divided to each detection branch of the multi-band terahertz receiving channel, are mixed, followed by intermediate frequency filtering, amplification, and square-law detection to obtain the final detected signals for each detection branch, which are then sent to the integrated processing and control distribution unit.
[0033] The integrated processing and control distribution unit includes an integrated processing unit and a control distribution unit. The control distribution unit supplies power to the servo controller, multi-band terahertz receiving subsystem, and calibration subsystem, and controls the on / off status of these components. The integrated processing unit receives remote sensing and telemetry information, including detection signals from the multi-band terahertz receiving subsystem and angle remote sensing information from the servo controller; telemetry information includes on / off status information, temperature information, and rotational speed information from the antenna subsystem, multi-band terahertz receiving subsystem, and calibration subsystem. The integrated processing unit is the system's processing hub. Based on the angle data provided by the servo controller, it generates a start signal for receiving remote sensing information, completes the acquisition and processing of detection signals from 13 receiving channels, receives remote sensing data from each observation point, and after receiving and processing the remote sensing data for each observation area, records the next received angle value. Simultaneously, it records the current telemetry data from the servo controller and calibration source controller, and fills the remote sensing data packet according to the required format.
[0034] The calibration subsystem includes a calibration source controller, a thermal calibration source, and a room-temperature source. The calibration source controller controls the source temperature through heating and collects the source temperature data via a temperature sensor. During each scan cycle, the temperature telemetry data of the calibration source is sent to the integrated processing and control distribution unit. The integrated processing and control distribution unit can also change the temperature threshold of the calibration source. By default, the calibration source controller maintains the thermal calibration source at 40°C, while the room-temperature source is maintained at -30°C through thermal equilibrium with the external cryogenic temperature. The source aperture is larger than the size of the plane mirror, ensuring that the thermal calibration source and the room-temperature source provide the two stable high and low radiation brightness temperatures required for observation, enabling two-point calibration. A schematic diagram of the observation and calibration process is shown below. Figure 2 As shown.
[0035] The working process of the terahertz ice cloud airborne detection system of this invention can be described as follows: The servo controller controls the scanning mechanism to drive the rotating scanning mirror to perform a clockwise 360° variable speed circular scan. The integrated processing and control distributor receives the angle information provided by the servo controller and interprets the angle data from the servo controller's synchronous 422 bus. If at least two of the three consecutively received angle data satisfy (starting angle ≤ current angle ≤ starting angle + 0.5°), the multi-band receiving channel is started, with the starting angle set at 55° for the observation area, 233.8° for the heat source, and 143.8° for the ambient temperature source. Similarly, if at least two of the three consecutively received angle data satisfy (ending angle ≤ current angle ≤ ending angle + 0.5°), the multi-band receiving channel is stopped, with the ending angles being 305° for the observation area endpoint, 216.2° for the heat source endpoint, and 126.2° for the ambient temperature source endpoint, and the multi-band receiving subsystem data is then started. During each rotation cycle, observations are made at a constant speed to the target area, the thermal calibration source, and the room temperature source, achieving two-point calibration of the cycle. The principle of two-point calibration is described in [link to documentation]. Figure 6 As shown, the plane mirror reflects the terahertz radiation signal into the quasi-optical feed network, separating the received signal according to polarization and frequency. The signal then passes through the feed horns of each branch and enters the multi-band receiving channel for processing before being sent to the integrated processing and control distribution unit for signal processing. Simultaneously, it receives data from the servo controller and calibration source controller, arranges, packages, and stores it. The integrated processing and control distribution unit can achieve autonomous control and storage, as well as human-machine interaction. The aircraft provides one +28V primary power supply to the integrated processing and control distribution unit; the +28V power required for the operation of other individual units and thermal control is transferred by the integrated processing and control distribution unit. The integrated processing and control distribution unit has multiple bus interfaces to meet the bus communication requirements of various aircraft models. After data acquisition and preprocessing, positioning and calibration are completed. Then, based on the prior database and Bayesian inversion algorithm, the ice cloud height, ice water path (IWP), and effective ice cloud radius (Dme) of the observation area are obtained.
[0036] The contents not described in detail in this specification are common knowledge to those skilled in the art.
Claims
1. A terahertz ice cloud on-board probing system, characterized in that: It includes an antenna subsystem, a multi-band terahertz receiver subsystem, a calibration subsystem, and a comprehensive processing and control distribution unit, among which: Antenna Subsystem: Under the control of the integrated processing and control power distribution unit, the target area is detected by 360° variable speed circular scanning to obtain terahertz radiation signals within the field of view. The terahertz radiation signals are distinguished according to polarization direction and frequency to obtain multiple radio frequency signals, which are then sent to the multi-band terahertz receiving subsystem. Multi-band terahertz receiving subsystem: adopts direct mixing double-sideband receiving method, mixes, filters, amplifies and detects each radio frequency signal to obtain each detected signal, and sends it to the integrated processing and control distribution unit; Calibration subsystem: Under the control of the integrated processing and control distributor, the detection system is calibrated; Integrated processing and control power distribution unit: provides power to the antenna subsystem, multi-band terahertz receiving subsystem, and calibration subsystem; retrieves ice cloud information of the observation area based on the transmitted detection signals; The antenna subsystem includes a plane mirror, a scanning mechanism, a quasi-optical feed network, and a servo controller. The plane mirror is mounted on the scanning mechanism. Under the control of the integrated processing and control distributor, the servo controller drives the scanning mechanism to move the plane mirror to perform variable-speed circular scanning along the central axis of the plane mirror. The plane mirror reflects the terahertz radiation signal within the field of view into the quasi-optical feed network. The quasi-optical feed network uses a polarization grid to polarize the terahertz radiation signal received by the plane mirror. The signals of different frequencies and polarization directions obtained by the separation are reflected by ellipsoidal mirrors into the feed horns of each branch, resulting in multiple radio frequency signals that are sent to the multi-band terahertz receiving subsystem. The signals of different frequencies with different polarization directions include H polarization directions of 664 GHz and 243 GHz, and V polarization directions of 664 GHz, 448 GHz, 325 GHz, 243 GHz and 183 GHz; The multi-band terahertz receiving subsystem includes seven receivers, each corresponding to receive signals of different frequencies with different polarization directions; The calibration subsystem includes two terahertz calibration sources: a room-temperature source and a thermal calibration source. The room-temperature source is maintained at -30°C and positioned at 126.2°~143.8° perpendicular to the observation field of view. The thermal calibration source is maintained at 40°C and positioned at 216.2°~233.8° perpendicular to the observation field of view. The aperture of the calibration source is larger than the size of the plane mirror, ensuring that two-point calibration is achieved by providing two high and low radiation brightness temperatures required for observation, namely the thermal calibration source and the room temperature source. The inversion to obtain ice cloud information in the observation area includes: using a priori database and a Bayesian inversion algorithm to obtain the ice cloud height, ice water path, and effective radius of the ice cloud in the observation area.