A high-precision pulsed laser altimeter and a measuring method thereof

Abstract

The application discloses a high-precision pulsed laser altimeter and a measuring method, and mainly solves the problem of poor accuracy and reliability in the prior art. The high-precision pulsed laser altimeter comprises a shell assembly, a laser transceiver module, a digital signal processing board and a filter. The laser transceiver module comprises a laser emission assembly, a laser receiving assembly and a time measurement system; the shell assembly comprises a side panel, a bottom cover panel and a top cover mirror panel. The laser transceiver module calculates the radial distance between a target and the laser altimeter by measuring the time interval between the time of emitting a laser pulse and the time of receiving a laser echo signal. The digital signal processing board uses an Soc control chip, and is surrounded by level conversion chips to realize data processing, filtering, format conversion and transceiving. The filter filters multiple power supply signals and transmits 422 interface signals. The application improves the accuracy and reliability of measurement, and can be used for real-time height measurement of an aircraft in a complex environment such as sand, snow, grass and mud.

Description

Technical Field

[0001] This invention belongs to the field of instrumentation technology, specifically designing a laser altimeter and measurement method, which can be used to measure the distance from the ground in the normal direction of an aircraft. Background Technology

[0002] Laser altimeters are primarily used for altitude measurement on military and civilian aircraft and helicopters to ensure flight safety. They determine distance by calculating the time difference between the emission and reception of a laser pulse, enabling rapid and high-precision measurements. They are an indispensable key piece of equipment in the aviation field. With increasing awareness of aviation safety and continuous technological advancements, modern laser altimeters are gaining increasing attention from airlines and aircraft manufacturers, and are evolving towards greater accuracy, efficiency, and reliability, becoming a future market trend.

[0003] Currently, helicopters fly over uneven terrain such as sand, snow, grass, and mud. These complex terrain environments make it impossible for digital altimeters and radio altimeters to achieve high-precision measurements, resulting in certain errors that affect flight safety.

[0004] Patent document CN202510564578.8 discloses a radio altitude simulation device, which includes a laser emitting unit, a laser receiving unit, a lens unit, a digital signal processing unit, and an EMI power filtering unit. It is mainly used for helicopters to fly at low altitudes or close to the ground and for point-to-point landings. However, this altimeter is highly susceptible to external environmental influences, resulting in poor measurement accuracy.

[0005] Patent document CN200620049336.8 discloses a single-antenna radio altimeter, which includes an antenna, a circulator, a microwave transmitting unit, a microwave receiving unit, an intermediate frequency filter, a main amplifier, a microprocessor, and a triangular wave generator. Because this single-antenna radio altimeter places the antenna outside the altimeter housing, it is susceptible to interference, resulting in low altitude measurement accuracy and large errors. Furthermore, the susceptibility of the antenna to interference further reduces its altitude measurement accuracy.

[0006] Patent document CN201911406206.3 discloses a radio altimeter, which includes a transceiver antenna assembly, a microwave transceiver assembly, and a signal processing module. In actual altimeter measurement, temperature is collected and temperature compensation is performed by a temperature sensor on the signal processing module. Although the altimeter can solve the problem of decreased accuracy caused by external temperature drift, it still has two problems: First, its temperature sensor is affected by the heat generated by other components inside the transceiver, causing a large temperature drift and resulting in a large altimeter measurement error; second, the heat generated by other components inside the altimeter transceiver can interfere with the sensor's collection of temperature information, resulting in weak environmental adaptability and low altimeter measurement accuracy.

[0007] Furthermore, during helicopter flight and takeoff and landing, the altimeter with a single antenna cannot eliminate the accuracy error caused by the antenna installation spacing near the ground due to the still immature technology. The problem of tracking the external sling during helicopter acceleration or deceleration cannot be completely eliminated. The slant range error, multipath interference and tracking harmonics caused by dual antennas have not been completely solved. All of these factors will cause errors in the altimeter's measurement of the actual altitude distance to the ground, posing a hidden danger to the safe flight of helicopters or drones. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the prior art by providing a high-precision pulsed laser altimeter and its measurement method, thereby improving the accuracy and reliability of measurements and ensuring the safety of aircraft.

[0009] The technical approach to achieving the objective of this invention is as follows: adopting the overall design of a pulsed laser altimeter system, and improving altimeter accuracy through measures such as laser echo signal amplification, constant ratio timing discrimination, automatic gain control technology, altimeter adaptation technology for uneven ground, and data filtering.

[0010] Based on the above ideas, the technical solution of this invention is implemented as follows:

[0011] 1. A high-precision pulsed laser altimeter, comprising a digital processing signal board, a laser transceiver module, and a housing assembly, wherein the input terminal of the digital processing board is connected to the laser transceiver module, and the laser transceiver module is fixed on one side of the housing assembly, characterized in that:

[0012] The input terminal of the digital processing signal board is also connected to a filter to achieve data filtering and signal transmission. The filter is fixed on the other side of the housing assembly to improve shock resistance.

[0013] The housing assembly includes a top cover mirror panel, side panels, and a bottom cover panel, all of which are equipped with conductive rubber strips and form a hexahedral structure of an aluminum alloy shielding shell. The top cover mirror panel is designed with a laser viewing window to form an electromagnetic shielding cage, thereby reducing electromagnetic leakage and preventing the laser altimeter from being affected by external electromagnetic interference.

[0014] The laser transceiver module is used to generate a narrow pulse signal with a repetition frequency of 1kHz and a pulse width of only 10ns.

[0015] 2. Preferably, the filter includes a short-circuit protection circuit, a spike suppression circuit, and a reverse connection protection circuit, which are connected in sequence to protect the filter (1). The filter (1) performs EMI filtering on the input power supply to prevent mutual interference between the helicopter power supply and the onboard equipment, improves the electromagnetic compatibility of the system, and preprocesses the input power supply to meet the power supply characteristics requirements.

[0016] Preferably, the digital signal processing board includes:

[0017] The SoC chip, as a control chip, mainly completes the reception, transformation, and transmission of external input data, as well as the generation of control signals required by other circuits. It also completes subsequent data peak detection, amplitude limiting filtering, and moving average filtering to ensure the stability and effectiveness of the output data.

[0018] The differential level conversion chip is used to receive the raw height data transmitted from the laser transceiver module and send the data to the SoC chip.

[0019] Transceiver level conversion chip, used to control the conversion of IO signals of SoC chip and RS44 bus data;

[0020] The power supply module converts the filtered power supply voltage into the voltage required by each chip and the laser transceiver module, and provides voltage to the SoC chip, differential level conversion chip, transceiver level conversion chip and laser transceiver module.

[0021] Preferably, the laser transceiver module includes:

[0022] The laser emitting component is used to control the laser emitted by the emitting module. After being collimated and expanded by the emitting antenna, the laser beam is projected onto the target under test and the signal is sent into the time system.

[0023] The time measurement system calculates the radial distance between the target and the laser altimeter by measuring the time interval between the moment the laser pulse is emitted and the moment the laser echo signal is received;

[0024] The laser receiving component is used to receive the laser pulses reflected back from the diffuse reflection of the target and send the processed signal to the time measurement system.

[0025] 3. A method for measuring altitude using the pulsed laser altimeter of claim 1, characterized in that it comprises:

[0026] When the laser altimeter is turned on, the short-circuit protection circuit, spike suppression circuit, and reverse connection protection circuit of the filter perform EMI filtering and preprocessing on the power supply voltage. Then, the power supply module supplies power to the laser transceiver module, SoC control chip, differential level conversion chip, and transceiver level conversion chip. The SoC chip controls the narrow pulse generation circuit to generate a pulse signal that enters the laser drive circuit, causing it to drive the semiconductor laser to emit a very strong and narrow laser pulse.

[0027] The laser pulse is expanded by the emitting lens to reduce its divergence angle. At the same time the laser pulse is emitted, a very small portion of the light is split and used as a reference signal for the emission to enter the time measurement system to calibrate the time of laser emission. The other portion of the light is reflected back from the original path and enters the receiving lens. Subsequently, the photoelectric detection circuit converts the optical signal into an electrical signal.

[0028] The electrical signal, after being amplified by the amplifier circuit, passes through the comparison and shaping circuit to reach the time measurement system, causing the pulse counter in the time measurement system to stop timing. The time measurement system calculates the raw data of the radial distance between the target and the laser altimeter by the time difference between the emitted laser pulse and the received laser echo pulse. The raw data is then sent to the differential level conversion chip for format conversion before being sent to the SoC chip to complete the data processing.

[0029] The processed data is sent to a transceiver level conversion chip to be converted into RS422 bus data, and finally output to the flight control and management system.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] Firstly, because the present invention has a filter connected to the input end of the digital processing signal board, the filter can perform EMI filtering and preprocessing on the power supply to obtain a low-voltage DC power supply that meets the requirements of each power supply object, thus avoiding mutual interference between the helicopter power supply and onboard equipment and improving the electromagnetic compatibility of the system. At the same time, because the filter is designed with short-circuit protection circuit, reverse connection protection circuit, and spike suppression circuit, it can not only avoid damage to the altimeter caused by power supply short circuit, reverse connection, and excessive current and voltage, but also ensure the safety of the altimeter in the face of various complex environments and emergencies.

[0032] Secondly, this invention uses four planes to form a circle around the side panel of the housing assembly, which, together with the top mirror panel and the bottom cover panel, constitutes a hexahedron of aluminum alloy shielding housing. A laser transceiver module is installed on one side of the side panel, and a filter is installed on the other side. A digital processing board is connected between the laser transceiver module and the filter module, forming a unified structure that ensures its shock resistance. Furthermore, conductive rubber strips are installed on the top mirror panel, side panels, and bottom cover panel, and the top mirror panel has a laser viewing window, forming an electromagnetic shielding cage that reduces electromagnetic leakage and further improves the product's electromagnetic compatibility.

[0033] Thirdly, this invention generates only a narrow pulse signal with a repetition frequency of 1kHz and a pulse width of only 10ns through the laser transceiver module. Since the narrower the pulse laser, the more accurate the time recorded by the time measurement system, thus improving the measurement accuracy and precision of the altimeter and the reliability of the data, thereby further improving the safety of the aircraft.

[0034] Fourth, because the cavity space of this invention is more concentrated in its structural layout, the utilization rate is higher, which is beneficial to the design of printed circuit boards, especially the arrangement of taller and larger components.

[0035] Test results show that the measurement accuracy of this invention can reach up to 100ps, making the distance measurement accuracy of the laser altimeter no more than 0.05 meters within 2 meters, which can meet the requirements for normal height measurement on uneven ground such as sand, snow, grass, and mud. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the laser altimeter according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the filter structure in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the signal processing board in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the laser transceiver module structure in an embodiment of the present invention;

[0040] Figure 5 This is a diagram of a narrow pulse generation circuit in an embodiment of the present invention;

[0041] Figure 6 This is a semiconductor driving circuit diagram in an embodiment of the present invention;

[0042] Figure 7 This is a circuit diagram of the amplifier in an embodiment of the present invention;

[0043] Figure 8 This is a comparison shaping circuit diagram in an embodiment of the present invention;

[0044] Figure 9 This is a physical diagram of the housing assembly structure in an embodiment of the present invention;

[0045] Figure 10 This is a diagram showing the height measurement results under a cement floor environment test according to an embodiment of the present invention;

[0046] Figure 11 This is a diagram showing the height measurement results under land surface environment testing according to an embodiment of the present invention;

[0047] Figure 12 This is a diagram showing the height measurement results under grassland ground environment testing according to an embodiment of the present invention. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort should all fall within the protection scope of the present invention.

[0049] Example 1: High-precision pulsed laser altimeter

[0050] Reference Figure 1 The laser altimeter in this example includes: filter 1, digital signal processing board 2, laser transceiver module 3, and housing assembly 4. The digital signal processing board 2 is connected to filter 1 and laser transceiver module 3 through connectors, so that the three are combined into a whole. Filter 1 and laser transceiver module 3 are respectively installed on opposite sides of the inner side of housing assembly 4 to improve the product's shock resistance.

[0051] Reference Figure 2 The filter 1 in this example includes a short-circuit protection circuit 11, a spike suppression circuit 12, and a reverse connection protection circuit 13. These three circuits are connected in sequence and are used to perform EMI filtering and preprocessing on the 28VDC input power supply, improving the electromagnetic compatibility and safety of the system. Specifically, when the short-circuit protection circuit 11 detects that the current exceeds a set threshold, it immediately cuts off the power output to protect the altimeter from damage caused by a short circuit. The spike suppression circuit 12 can suppress the rapid changes in the reverse recovery current of the diodes in the circuit, thereby reducing and suppressing noise in the circuit. The reverse connection protection circuit 13 is used to prevent damage to components in the circuit caused by reverse polarity of the power supply.

[0052] Reference Figure 3The digital signal processing board 2 in this example includes: a SoC chip 21, a differential level converter chip 22, a transceiver level converter chip 23, and a power supply module 24. The differential level converter chip 22 receives the raw altitude data transmitted from the laser transceiver module 3, converts the data format, and then sends it to the SoC chip 22. The SoC chip 21 serves as the control chip, using, but not limited to, a domestically produced HWD32F103ELQFP64 ARM chip. One of its functions is to use data filtering algorithms to process, eliminate, or reduce measurement errors caused by terrain undulations, thereby improving the measurement accuracy of the laser altimeter. Another function is to receive control commands, report the working status of the laser altimeter, complete data format conversion, and output the altitude data in the required format after data processing. The data processed by the SoC chip 21 is sent to the transceiver level converter chip 23 to be converted into RS422 bus data, and finally output to the flight control and management system in RS422 interface form. The power module 24 is responsible for converting the power supply voltage after passing through the filter into the operating voltage required by each module, and transmitting the voltage to the laser transceiver module, the SoC chip 21, the differential level conversion chip 22, and the transceiver level conversion chip 23.

[0053] Reference Figure 4 In this example, the laser transceiver module 3 includes a laser emitting component 31, a time measurement system 32, and a laser receiving component 33. The laser emitting component 31 consists of an emitting lens 311, a narrow pulse generating circuit 312, a laser driving circuit 313, and a semiconductor laser 314. The laser receiving component 33 consists of a receiving lens 331, a photoelectric detection circuit 332, an amplification circuit 333, and a comparison and shaping circuit 334. The pulse signal generated by the narrow pulse generating circuit 312 controlled by the SoC chip 21 enters the laser driving circuit 313, which drives the semiconductor laser 314 to emit a very strong and narrow laser pulse. After the laser pulse is expanded by the emitting lens 311, it is directed toward the altimeter target. At the same time, the time measurement system 32 starts timing. A part of the light is reflected back from the original path and enters the receiving lens 331. The photoelectric detection circuit 332 converts the light signal into an electrical signal. After the electrical signal is amplified by the amplifier circuit 333, it passes through the comparison and shaping circuit 334 to stop the timing in the time measurement system 32. The time measurement system 32 calculates the original data of the radial distance between the target and the laser altimeter based on the time difference.

[0054] The transmitting lens 311 uses a reverse Galilean telescope system to collimate and expand the emitted laser beam. The effective aperture of the transmitting lens is Φ13.5mm and the transmittance is 90%.

[0055] Reference Figure 5The narrow pulse generation circuit 312 in this example includes an oscillator and a pulse generation circuit, used to generate a continuously adjustable pulse signal with a frequency range of 0.5kHz to 1kHz and a pulse width range of 10ns to 500us. The oscillator generates a continuous signal with an adjustable frequency, which can be adjusted by adjusting the adjustable resistor Rv1 in the circuit. The pulse generation circuit generates a pulse signal under the action of an external trigger signal, and the output pulse width can be changed by adjusting Rv3 in the circuit. Under the trigger action of the oscillator signal, the pulse generation circuit generates a pulse signal. By adjusting the values ​​of Rv1 and Rv3, a narrow pulse modulation signal with a repetition frequency of 1kHz and a pulse width of 10ns can be obtained. According to the principle of pulsed laser ranging, the narrower the pulse width, the higher the ranging accuracy.

[0056] Reference Figure 6 In this example, the pulse drive circuit 313 employs energy compression technology, using a capacitor as an energy storage element. It stores energy with relatively low instantaneous power in the capacitor over a certain period, releasing it instantaneously at an appropriate moment to generate a large current excitation signal. This circuit can generate a maximum instantaneous peak current signal of 15A, with a rise and fall time of 25ns. The entire circuit features electrostatic discharge (ESD) protection, preventing damage from electrostatic discharge, and boasts a wide input voltage range (4.5V–18V), short delay (30ns), low required input current (450uA), and low output impedance (1Ω). This circuit design must provide the necessary high-current, narrow-pulse modulation signal for semiconductor laser operation while also meeting the overall design requirements of narrow pulse width, steep rise time, and high power.

[0057] The semiconductor laser 314 used in this example is, but is not limited to, the 905PLD-25W-MCL model. It can achieve high peak output power with low drive current, and the output signal has a narrow pulse width and high power. It can also maintain a good temperature operating range and a small output beam divergence angle, which can ensure the strength of the received signal in the laser receiving system.

[0058] In this example, the receiving lens 331 uses a Galilean telescope system to converge the reflected laser beam, which is then focused by a converging lens after passing through a narrowband filter. The receiving lens has an effective aperture of Φ17.5mm and a transmittance of 85%.

[0059] In this example, the photodetector circuit 332 selects a silicon avalanche diode photodetector as the optical signal detection device. The diode model is, but is not limited to, GD5210Y-2-5-LCC3. This device has a high responsivity of Resp=55A / W (T=22℃, M=15, λ=900nm) for light in the 800nm~950nm wavelength band, and is not sensitive to temperature changes within the range of -45℃~70℃. It can easily receive echo signals without temperature compensation, making it a relatively ideal photodetector.

[0060] Reference Figure 7 The amplifier circuit 333 in this example is divided into a preamplifier circuit (a) and a main amplifier circuit (b). The preamplifier circuit mainly uses a low-noise-figure amplifier circuit to amplify the useful signal without increasing the noise figure. The main amplifier circuit amplifies the signal output by the preamplifier circuit again until the subsequent circuit can correctly identify it. Both the preamplifier circuit and the main amplifier circuit designed in this invention use transistor-type transimpedance amplifier circuits. The preamplifier circuit adopts a common-collector configuration, which amplifies only the current without voltage amplification. The main amplifier circuit adopts a common-emitter configuration, which can amplify both voltage and current simultaneously.

[0061] Reference Figure 8 In this example, the comparison shaping circuit 334 uses a comparator of model number ER3490, but not limited to ER3490. This device features differential input and TTL compensated output, with a propagation delay of 10ns and very low supply current. Furthermore, its output remains stable throughout the entire linear region, resolving the instability issue of high-speed comparators caused by using low-speed input signals as drivers.

[0062] Reference Figure 9 In this example, the housing assembly 4 includes: a top cover mirror panel 41, a side panel 42, and a bottom cover panel 43. The side panel 42 is a non-removable tetrahedron formed by four flat surfaces surrounding it. It has threaded holes at its connection points with the top cover mirror panel 41 and the bottom cover panel 43, facilitating repeated disassembly and assembly and improving connection reliability. The threaded holes are fitted with cadmium-plated steel wire thread inserts. The connection between the side panel 42 and the top cover mirror panel 41 and the bottom cover panel 43 adopts a non-contact lap joint structure with sealing grooves and sealing strips, and is then secured with screws to improve the altimeter's sealing and waterproofing. The top cover mirror panel 41, side panel 42, and bottom cover panel 43 are all milled from aluminum alloy plates, and the fasteners used are all made of stainless steel.

[0063] Example 2: A method for measuring altitude using the aforementioned pulsed laser altimeter.

[0064] The implementation scheme of this example is as follows:

[0065] First, the laser altimeter is turned on. Filter 1 performs EMI filtering and preprocessing on the 28V DC power supply voltage, and its short-circuit protection circuit 11, spike suppression circuit 12, and reverse connection protection circuit 13 protect the circuit. Then, the power module 24 converts the filtered power supply voltage into the low voltage required by the laser transceiver module 3, the SoC control chip 21, the differential level conversion chip 22, and the transceiver level conversion chip 23, and supplies them with power. At the same time, the SoC chip 21 controls the narrow pulse generation circuit 312 to generate a pulse signal that enters the laser drive circuit 313, causing it to drive the semiconductor laser 314 to emit a laser pulse through the emitting lens 311 towards the altimeter target. When the laser pulse passes through the emitting lens 311, it is expanded, reducing its divergence angle.

[0066] Next, simultaneously with the emission of the laser pulse, a very small portion of the light, after beam splitting, enters the time measurement system 32 as a reference signal to calibrate the laser emission time. The other portion of the light is reflected back along the original path and enters the receiving lens 331. Subsequently, the photoelectric detection circuit 332 converts the weak reflected light signal into an electrical signal. The amplification circuit 333 further amplifies the electrical signal, enabling subsequent circuits to identify the useful signal from the noise. Finally, the amplified electrical signal returns to the time measurement system 32 via the comparison and shaping circuit 334, stopping the pulse counter in the time measurement system 32. The time measurement system 32 calculates the raw data of the radial distance between the target and the laser altimeter using the time difference between the emitted laser pulse and the received laser echo pulse. The raw data is then sent to the differential level conversion chip 22 for format conversion before being sent to the SoC chip 21 for data processing. The processed data is then sent to the transceiver level conversion chip 23 to convert it into RS422 bus data, and finally output to the flight control and management system.

[0067] The effectiveness of this invention can be further illustrated by the following experimental results:

[0068] I. Testing Environment: Including cement environment, soil environment, and grassland environment.

[0069] II. Test Content

[0070] Test 1: Testing a drone carrying an altimeter on a concrete surface:

[0071] The drone, equipped with a laser altimeter and differential GPS, takes off from the ground and hovers at an altitude of 100 meters above the concrete surface for a period of time before beginning its descent. The drone hovers again approximately every 20 meters during the descent until it returns to the ground. Throughout the entire ascent, hovering, and descent, the drone collects real-time data from the altimeter and differential GPS, and verifies the validity of the laser altimeter data using the differential GPS. The results are as follows: Figure 10 As shown.

[0072] Test 2: Testing of a drone carrying an altimeter in a land environment:

[0073] The drone, equipped with a laser altimeter and differential GPS, takes off from the ground and hovers at an altitude of 100 meters above the ground for a period of time before beginning its descent. The drone hovers again approximately every 20 meters during the descent until it returns to the ground. Throughout the entire ascent, hovering, and descent, the drone collects altimeter and differential GPS data in real time and verifies the validity of the laser altimeter data using differential GPS. The results are as follows: Figure 11 As shown.

[0074] Test 3: Testing a drone carrying an altimeter in a grassy environment:

[0075] The drone, equipped with a laser altimeter and differential GPS, took off from the ground and hovered at an altitude of 100 meters above the grass for a period of time before beginning its descent. The drone hovered again approximately every 20 meters during the descent until it returned to the ground. Throughout the ascent, hovering, and descent, the drone collected real-time data from the altimeter and differential GPS, and verified the validity of the laser altimeter data using the differential GPS. The results are as follows: Figure 12 As shown.

[0076] from Figures 10-12 It is evident that this invention can achieve accurate real-time height measurement relative to the ground in complex environments at a height of 100 meters.

[0077] The above description is merely a specific example of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A high-precision pulsed laser altimeter, comprising a digital processing signal board (2), a laser transceiver module (3), and a housing assembly (4), wherein the input end of the digital processing board (2) is connected to the laser transceiver module (3), and the laser transceiver module (3) is fixed on one side of the housing assembly (4), characterized in that: The input terminal of the digital processing signal board (2) is also connected to a filter (1) to achieve data filtering and signal transmission. The filter (1) is fixed on the other side of the housing assembly (4) to improve the shock resistance. The housing assembly (4) includes a top cover mirror panel (41), a side panel (42), and a bottom cover panel (43), all of which are equipped with conductive rubber strips and form a hexahedral structure of an aluminum alloy shielding housing. The top cover mirror panel (41) is designed with a laser window to form an electromagnetic shielding cage, thereby reducing electromagnetic leakage and preventing the laser altimeter from being affected by external electromagnetic interference. The laser transceiver module (3) is used to generate a narrow pulse signal with a repetition frequency of 1kHz and a pulse width of only 10ns.

2. The pulsed laser altimeter according to claim 1, characterized in that: The filter (1) includes a short-circuit protection circuit (11), a spike suppression circuit (12), and a reverse connection protection circuit (13). These three circuits are connected in sequence to protect the filter (1). The filter (1) performs EMI filtering on the input power supply to prevent mutual interference between the helicopter power supply and the onboard equipment, improve the electromagnetic compatibility of the system, and preprocess the input power supply to meet the power supply characteristics requirements.

3. The pulsed laser altimeter according to claim 1, characterized in that: The digital signal processing board (2) includes: The Soc chip (21), as a control chip, mainly completes the reception, transformation, and transmission of external input data and generates control signals required by other circuits, and completes subsequent data peak detection, amplitude limiting filtering, and moving average filtering to ensure the stability and effectiveness of the external output data. The differential level conversion chip (22) is used to receive the raw height data transmitted from the laser transceiver module (3) and send the data to the Soc chip; Transceiver level conversion chip (23) is used to control the conversion of IO signals of the SoC chip and RS44 bus data; The power module (24) converts the filtered power supply voltage into the voltage required by each chip and the laser transceiver module (3), and provides voltage to the SoC chip (21), differential level conversion chip (22), transceiver level conversion chip (23) and laser transceiver module (3).

4. The pulsed laser altimeter according to claim 1, characterized in that: The laser transceiver module (3) includes: The laser emitting component (31) is used to control the laser emitted by the emitting module, which is then collimated and expanded by the emitting antenna and projected onto the target under test, and the signal is sent into the time system (32). The time measurement system (32) calculates the radial distance between the target and the laser altimeter by measuring the time interval between the time of emitting the laser pulse and the time of receiving the laser echo signal; The laser receiving component (33) is used to receive the laser pulses returned by diffuse reflection from the target and send the processed signal to the time measurement system (32).

5. The pulsed laser altimeter according to claim 4, characterized in that, The laser emitting component (31) includes: The emitting lens (311) uses a reverse Galilean telescope system to collimate and expand the emitted laser beam; Narrow pulse generation circuit (312) is used to generate a continuously adjustable pulse signal with a frequency range of 0.5kHz to 1kHz and a pulse width range of 10ns to 500us. A laser driving circuit (313) is used to drive a semiconductor laser; A semiconductor laser (314) is used to generate laser light under the drive of a laser driving circuit; The narrow pulse generating circuit (312), the laser driving circuit (313), and the semiconductor laser (314) are all located on the upper part of the emitting lens (311), forming an integrated laser emitting assembly.

6. The pulsed laser altimeter according to claim 4, characterized in that, The laser receiving component (33) includes: The receiving lens (331) uses a Galilean telescope system to reduce the reflected laser beam; The photoelectric detection circuit (332) is used to convert weak light signals into current signals; The amplifier circuit (333) is used to amplify the weak current signal; The comparison shaping circuit (334) is used to compare and shape the pulse signal generated by the narrow pulse generating circuit (312); The photoelectric detection circuit (332), the amplification circuit (333), and the comparison and shaping circuit (334) are all located on the upper part of the receiving lens (331), forming an integrated laser receiving assembly.

7. A method for measuring altitude using the pulsed laser altimeter of claim 1, characterized in that, include: When the laser altimeter is turned on, the short-circuit protection circuit (11), spike suppression circuit (12) and reverse connection protection circuit (13) of the filter (1) perform EMI filtering and preprocessing on the power supply voltage. Then, the power supply module (24) supplies power to the laser transceiver module (3), the SoC control chip (21), the differential level conversion chip (22) and the transceiver level conversion chip (23). The SoC chip (21) controls the narrow pulse generation circuit (312) to generate a pulse signal that enters the laser drive circuit (313), so that it drives the semiconductor laser (314) to emit a very strong and narrow laser pulse. The laser pulse is expanded by the emitting lens (311) to reduce its divergence angle. At the same time the laser pulse is emitted, a very small part of the light is split and used as a reference signal for the emission to enter the time measurement system (32) to calibrate the time of laser emission. The other part of the light is reflected back from the original path and enters the receiving lens (331). Then, the photoelectric detection circuit (332) converts the optical signal into an electrical signal. The electrical signal is amplified by the amplifier circuit (333) and then passed through the comparison and shaping circuit (334) to reach the time measurement system (32), causing the pulse counter in the time measurement system (32) to stop timing. The time measurement system (32) calculates the original data of the radial distance between the target and the laser altimeter by the time difference between the emitted laser pulse and the received laser echo pulse. The original data is then sent to the differential level conversion chip (22) for format conversion and then sent to the SoC chip (21) to complete the data processing. The processed data is sent to the transceiver level conversion chip (23) to convert it into RS422 bus data, and finally output to the flight control and management system.

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