CN114236493A

CN114236493A - Water surveying laser radar PMT dynamic gain control system

Info

Publication number: CN114236493A
Application number: CN202111444486.4A
Authority: CN
Inventors: 周国清; 徐超
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-03-25

Abstract

The invention discloses a PMT dynamic gain control system of a water detection laser radar. The system consists of a power supply module, a laser module, an optical receiving module, a detection module, an attenuator module, an acquisition module, a control module, a DA module and a POS module. After receiving POS data, the control module calculates gate control time according to elevation, controls gate control signals and controls a PMT switch; the laser echo is received by the PMT after passing through the optical receiving module and is changed into an electric signal from an optical signal, then the electric signal is attenuated by the attenuator, an analog signal is converted into a digital signal through high-speed AD acquisition, the maximum value is found and fed back to the control module, and the control module judges whether the gain voltage of the PMT needs to be adjusted through the DA module or not through analysis. The invention uses the FPGA in the high-speed AD acquisition module to control the PMT switch, selectively receives the water surface reflection or water bottom echo signal, realizes PMT gain self-adaptation, improves the detection accuracy, and avoids the problems of weak and saturated echo signal caused by cliff type and protrusion type terrains in unknown water areas.

Description

Water surveying laser radar PMT dynamic gain control system

Technical Field

The invention relates to the field of laser radars, in particular to water measuring laser radar detection, and provides a water measuring laser radar PMT dynamic gain control system.

Background

The echo signals of the laser water surveying comprise signals of water surface reflection, water body backscattering and water bottom reflection. Since the attenuation of the laser beam is much greater underwater than in air. The strength of the water surface echo signal is much larger than that of the seabed echo, and the dynamic range of the water surface echo signal can reach 56 orders of magnitude generally. When a gating technology is used for separating signals of the water surface and the water bottom, the echo of the water surface is always in a saturated state due to strong reflection of the water surface, and the optical receiving channel needs a low-gain PMT (photomultiplier tube) to reduce the sensitivity; the attenuation of the water bottom echo signal is weak, and at the moment, the optical receiving channel needs a high-gain PMT to improve the sensitivity; in unknown waters, the echoes need adaptive gain-adjustable PMTs to cope with cliff-like or protrusion-like terrain. With linear photoelectric conversion, it is difficult for existing electronics to withstand such a large dynamic range of input signals (even if such a signal can be tolerated, the signal peaks will typically exceed the dynamic range of the digitizing equipment, with the result that the echo signals at the seafloor will have much smaller amplitudes than the surface reflection and backscatter echo signals). Therefore, the laser echo signal that changes in a large dynamic range within several tens to several hundreds of nanoseconds must be compressed or separated.

In the patent with application number CN201911261237.4, the PMT gain voltage is remotely controlled by the FPGA to change the PMT gain, but the PMT gain still needs to be controlled by manually inputting parameters from the upper computer. In the design of a range-gated variable-gain photomultiplier detection system published in 2009 Liyan in optics, a high-speed circuit and a high-voltage pulse circuit are selected, so that the cost is high, the technology is complex, and the mass production is difficult.

Disclosure of Invention

Aiming at the problems that the PMT gain change needs manual parameter input, the cost is high, the technology is complex, and the mass production is difficult, the invention provides a PMT dynamic gain control system of a water laser radar. The method aims to improve the detection accuracy by a PMT gain adjustable technology; the method has the advantages that the echo is controlled within a reasonable range of high-speed AD acquisition, the problems of weak echo signals and full echo signals caused by cliff type and protrusion type terrains in unknown water areas are solved, the PMT is protected to a certain extent, the cost is low, the realization is convenient, and signals of water surface reflection, water body backscattering and water bottom reflection can be selectively received by only one optical channel. In actual measurement, functions of gate control of the FPGA, feedback data analysis and PMT gain voltage control are integrated into the high-speed AD acquisition module, so that power consumption and weight can be reduced.

The technical scheme of the invention comprises the composition of a PMT dynamic gain control system of the water measuring laser radar and the working process thereof.

The PMT dynamic gain control system of the water detection laser radar is composed of a power supply module, a laser module, an optical receiving module, a detection module, an attenuator module, an acquisition module, a control module, a DA module and a POS module.

The power supply module provides a +24V direct-current power supply for the laser module and the POS module, a +15V direct-current power supply for the detection module, a +12V direct-current power supply for the control module and the AD acquisition module, and a +5V direct-current power supply for the DA module;

the laser emits 532nm laser which can penetrate through a water body so as to form laser echo at the water bottom;

the optical receiving module is used for receiving an echo signal after the laser emitted by the laser hits a target, rejecting stray light and preventing the intensity of the echo light from being too high;

the detection module converts the optical signal into an electric signal after receiving the laser echo, can provide different gains according to different gain voltages, changes the detection range and selects to turn on or off according to the gate control signal;

one end of the attenuator module is connected with the detection module, and the other end of the attenuator module is connected with the acquisition feedback module to attenuate the electric signal to a suitable range of the acquisition feedback module;

the acquisition module converts the electric signal attenuated by the attenuator into a digital signal and finds the maximum value, and the requirement on the acquisition rate is high because the repetition frequency of the laser is high and the pulse width is narrow.

The POS module receives the satellite signal and transmits the satellite signal to the control module.

One end of the control module is connected with the acquisition module, the other end of the control module is connected with the DA module, the other end of the control module is connected with the POS module, and the other end of the control module is connected with the PMT gate control port. Judging whether the gain needs to be changed or not by comparing the maximum value with a threshold value, judging whether the gain is increased or decreased if the gain needs to be changed, then sending the judged result to a DA (data acquisition) module through an instruction, receiving POS (point of sale) data to find the elevation, calculating the gating time, and controlling a gating signal according to the gating time;

one end of the DA module is connected with the control module, and the other end of the DA module is connected with the detection module, and different gain voltages are provided for the detection module according to the instruction of the control module.

The working process of the PMT dynamic gain control system of the water detection laser radar is as follows:

firstly, after receiving a trigger signal, a laser starts to emit laser;

the optical receiving module receives the echo after the laser irradiates the water bottom and transmits the echo to the detection module;

the PMT of the detection module converts the optical signal into an electric signal after receiving the laser echo;

the attenuator module attenuates the electric signal to a range suitable for acquisition of the high-speed AD module;

the POS module receives the satellite signal and transmits the satellite signal to the control module;

sixthly, the POS module receives the satellite signal and transmits the satellite signal to the control module;

the control module finds out a maximum value by analyzing the digital signal, compares the maximum value with a threshold value, judges whether the gain needs to be changed, judges whether the gain is increased or decreased if the gain needs to be changed, then sends the judged result to the DA module through an instruction, receives POS data, finds an elevation, calculates the gating time and controls the gating signal according to the gating time;

the DA module provides different gain voltages for the detection module according to the instruction of the control module;

and ninthly, the PMT is switched on or off according to the gating signal, and corresponding gain is provided according to the gain voltage.

The invention has the beneficial effects that: firstly, the on-off of a PMT is controlled through an FPGA in a high-speed AD acquisition module, and a required water surface reflection or water bottom echo signal is selectively received; the gain self-adaptation of the PMT is realized, human factors are eliminated, the detection accuracy is improved, the echo is controlled within a reasonable range of high-speed AD acquisition, the problems of weak echo signals and full echo signals caused by cliff-type and protrusion-type terrains in unknown water areas are avoided, and the PMT is protected to a certain extent; and thirdly, the cost is low, the technology is simple, and the mass production can be realized.

Drawings

Fig. 1 is a schematic block diagram of the present invention.

Fig. 2 is a flow chart of the PMT switching process of the present invention.

Fig. 3 is a flowchart of PMT variable gain according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, preferred embodiments are described below in detail with reference to the accompanying drawings.

Example (b):

the invention is described by combining with figure 1, which is composed of a power module, a laser module, an optical receiving module, a detection module, an attenuator module, an acquisition module, a control module, a DA module and a POS module.

Referring to fig. 2, the PMT switching operation of the present invention is described as follows:

firstly, a POS module receives satellite signals and transmits the satellite signals to a control module;

secondly, the control module receives POS data to find an elevation, calculates the gating time and controls a gating signal according to the gating time;

and thirdly, the PMT of the detection module selects to be switched on and off according to the gate control signal.

Referring to fig. 3, the PMT variable gain operation flow of the present invention is described as follows:

firstly, after receiving a trigger signal, a laser starts to emit laser;

the optical receiving module receives the echo after the laser hits the target and transmits the echo to the detection module;

the control module judges whether the gain needs to be changed or not by comparing the maximum value with the threshold value, judges whether the gain is increased or decreased if the gain needs to be changed, and then sends the judged result to the DA module through an instruction;

sixthly, the DA module provides different gain voltages for the detection module according to the instruction of the control module;

and providing corresponding gain for PMT based on the gain voltage.

The above embodiments are merely illustrative, and not restrictive, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the protection scope of the present invention should be defined by the claims.

The technical contents not described in detail in the present invention are all known techniques.

Claims

1. The PMT dynamic gain control system is characterized by consisting of a power module, a laser module, an optical receiving module, a detection module, an attenuator module, an acquisition module, a control module, a DA module and a POS module;

the detection module converts the optical signal into an electric signal after receiving the laser echo, provides different gains according to different gain voltages, changes the detection range and selects to turn on or off according to the gate control signal;

one end of the attenuator module is connected with the detection module, and the other end of the attenuator module is connected with the acquisition feedback module to attenuate the electric signal to a suitable range of the high-speed AD acquisition module;

the acquisition module converts the electric signal attenuated by the attenuator into a digital signal and finds the maximum value, and the requirement on the acquisition rate is high because the repetition frequency of the laser is high and the pulse width is narrow;

the control module is designed by adopting an FPGA in the high-speed AD acquisition module, one end of the control module is connected with the acquisition module, the other end of the control module is connected with the DA module, the other end of the control module is connected with the POS module, and the other end of the control module is connected with a PMT gate control port; judging whether the gain needs to be changed or not by comparing the maximum value with a threshold value, judging whether the gain is increased or decreased if the gain needs to be changed, then sending the judged result to a DA (data acquisition) module through an instruction, receiving POS (point of sale) data to find the elevation, calculating the gating time, and controlling a gating signal according to the gating time;

2. The system of claim 1, wherein the system has a workflow as follows:

firstly, after receiving a trigger signal, a laser starts to emit laser;

the AD acquisition module converts the analog signals into digital signals;