CN114112964B - A Fourier transform infrared spectrometer multi-field automatic measurement system and method - Google Patents

Abstract

The invention discloses a multi-field automatic measurement system and method for a Fourier infrared spectrometer. The system includes: a blackbody radiation source: generating incident radiation; an optical chopper: realizing frequency modulation of the incident radiation; a slit and an electric three-dimensional platform : Slit scanning traverses the field of view area; parallel light tube: converts the light passing through the slit into parallel light and enters the instrument under test; normal temperature detector: used for photoelectric conversion at normal temperature; multi-channel weak signal processing system: realizes Phase-locked amplification and collection of weak signals from the detector; collaborative processing software: used for automatic control of slits, drawing of field of view response curves and calculation of field of view parameters. This invention uses slit scanning to replace the traditional rotation of the instrument under test to generate displacement of the field of view. Through collaborative control and data collection of software, it uses high-precision phase-locked amplification to obtain the response curve of signal strength with the field of view, and calculates field of view parameters, which is effective The assembly and calibration efficiency and accuracy of the cold optical system of the Fourier spectrometer at room temperature are improved.

Description

A Fourier transform infrared spectrometer multi-field automatic measurement system and method

Technical areas:

The invention relates to the field of optical detection, and specifically to a multi-field automatic measurement system and method for a Fourier transform infrared spectrometer.

Background technique:

The Fourier transform infrared spectrometer uses interference spectroscopy to detect infrared spectral radiation, which effectively solves the contradiction between the instrument's high sensitivity and high spectral resolution. It has a series of significant advantages such as high luminous flux, high spectral resolution, and wide spectral coverage. , is the main development direction of space remote sensing instruments. The United States has been developing spatial interference spectrum detection devices since the 1960s. Atmospheric detectors based on interference spectroscopy were carried on the "Nimbus" test satellite around the 1970s. Over the past few decades, Europe and the United States have developed a variety of space-based high spectral resolution atmospheric detection instruments. Research on polar-orbiting satellite platforms includes the Interferometric Thermal Sounder (ITS), the Infrared Atmospheric Interferometer Sounder (IASI) and the Cross-orbit Infrared Atmospheric Sounder (IASI). CrIS), etc., research on geostationary satellite platforms includes high-resolution infrared sounder (GHIS), imaging spectrometer (GIFTS) and hyperspectral environmental detection component (HES). my country's polar-orbiting meteorological satellite Fengyun-3D is equipped with a hyperspectral infrared atmospheric sounder (HIRAS) for the first time, and the new generation of geostationary-orbiting meteorological satellite Fengyun-4A is also equipped with a vertical atmospheric sounder (GIIRS). Vertical structure observation of temperature and humidity parameters improves detection accuracy, improves the vertical resolution of meteorological observations, provides input data for numerical weather forecasting, and serves disastrous weather monitoring and atmospheric chemical composition detection.

Field angle measurement is to obtain the actual optical field of view of each channel pixel of the instrument, which provides a basis for the optical calibration and registration of the instrument in a room temperature laboratory. It is also an important step in the calculation of the instrument's line function and spectral calibration. parameter. For Fourier transform infrared spectrometers, it is usually necessary to cool the optical path and detector to reduce background interference and improve detection performance. Since the optical field of view under radiation cooling and low temperature conditions can only be obtained during vacuum testing, and the assembly and calibration of optical components are carried out at room temperature in the laboratory, it is necessary to obtain the field of view angle at room temperature in the laboratory, also at low temperatures. Provides reference for field of view measurement and performance verification.

The traditional laboratory field of view measurement method realizes scanning of different areas within the field of view by adjusting the movement of the optical turntable. Most of the current lock-in amplifiers are single-channel, and only a single pixel can be measured for each direction of scanning. The sampling of detection signals and the movement of the field of view all rely on manual operations, lacking coordination and automation, resulting in low measurement efficiency. At the same time, due to the long test time, the thermal radiation accumulated by the detector causes the signal background to gradually increase, affecting the test accuracy and field of view calculation. At present, for the field of view measurement of Fourier transform infrared spectrometer at room temperature in the laboratory, it has not been able to achieve a high degree of collaborative automation and meet the simultaneous measurement of multiple pixels.

Contents of the invention:

In view of the limitations of existing means, the purpose of the present invention is to provide a multi-field automatic measurement system and method for a Fourier transform infrared spectrometer.

Fourier infrared spectrometer multi-field automatic measurement system, including: blackbody radiation source 1, optical chopper 2, slit and electric three-dimensional platform 3, parallel light tube 4, Fourier spectrometer optical system to be measured 5, normal temperature detection 6, preamplifier 7, multi-channel weak signal processing system 8 and collaborative processing software 9.

The blackbody radiation source 1 generates blackbody infrared radiation and is incident on the optical chopper 2. After its frequency modulation, it is incident on the slit and the electric three-dimensional platform 3. The radiation energy passing through the slit enters the parallel light tube 4 and is converted into parallel light. Entering the optical system 5 of the Fourier spectrometer to be measured, after systematic light splitting and collimation, it is finally focused on the normal temperature detector 6. The weak electrical signal after photoelectric conversion is amplified by low noise through the preamplifier 7, and then is phase-locked amplified and collected by the multi-channel weak signal processing system 8. Finally, the collaborative processing software 9 communicates through the serial port and the multi-channel weak signal processing system 8 , control the collaborative work of slit movement and data collection. Each time it moves to a field of view position, the collection of infrared detection signals is started, the signal intensity changes curve with the displacement distance is drawn, and the size and center position of the field of view are calculated.

The temperature range of the blackbody radiation source 1 is 0-500°C, and the temperature stability is 0.1K.

The modulation frequency of the optical chopper 2 is 17.46Hz.

The width of the slit and the slit of the electric three-dimensional platform 3 is 0.5mm, and the corresponding field of view resolution is 2". The width of the slit can be adjusted according to the focal length of the system under test and the required field of view resolution. The slit can be scanned horizontally and vertically with the motor. When moving in the horizontal direction, the slit is installed vertically, and when moving in the vertical direction, the slit is installed horizontally. The step distance, starting point, end point, and dwell time of the slit scanning can be set through the software.

The multi-channel weak signal processing system 8 includes a 9-channel phase-locked amplifier circuit, a phase-locked reference signal generator, an AD sampling circuit and an FPGA data processing and transmission circuit.

The invention also provides an automatic measurement method for multiple fields of view of a Fourier transform infrared spectrometer. The steps are as follows:

Step 1: Adjust the blackbody temperature to a suitable state and achieve stability;

Step 2: Move the horizontal slit outside the field of view and start sampling and recording data;

Step 3: Move the slit in the vertical direction according to the step distance of 2" corresponding to the field of view. Each time it moves to a position, the detection signal is collected until the field of view scanning of all pixels in the vertical direction is completed;

Step 4: Replace the horizontal slit with a vertical slit, move outside the field of view, and start sampling and recording data;

Step 5: Move the slit in the horizontal direction according to the step distance of 2" corresponding to the field of view. Each time it moves to a position, the detection signal is collected and recorded until the scanning of the field of view of all pixels in the horizontal direction is completed;

Step 6: According to the recorded data and the focal length of the instrument, convert the horizontal and vertical slit movement distances into angles, and draw the curves of the vertical and horizontal detection signal strengths as a function of the scanning angle;

Step 7: Based on the field of view response curve of each pixel, calculate its field of view size and center position.

Based on the characteristics of the optical system and detector of the Fourier transform infrared spectrometer, this invention converts the movement of the instrument's field of view into the movement of the target source slit to achieve scanning of the field of view. It achieves multiple lock-in amplifiers by developing a multi-channel lock-in amplifier with up to 10 channels. Synchronous testing of pixels. Light source modulation, field of view scanning and detection signal acquisition are coordinated and controlled through software to achieve automatic measurement, display and calculation. It can greatly improve the efficiency and accuracy of optical system assembly, registration, and testing.

Picture description:

Figure 1 is a schematic structural diagram of a multi-field automatic measurement system for a Fourier transform infrared spectrometer provided by an embodiment of the present invention.

in:

1. Blackbody radiation source;

2. Optical modulator;

3. Slit and electric three-dimensional platform;

4. Parallel light tube;

5. The optical system of the Fourier spectrometer to be tested;

6. Normal temperature detector;

7. Preamplifier;

8. Multi-channel weak signal processing system;

9. Coordination and processing software.

Figure 2 is a schematic diagram of the theoretical field of view and slit scanning principle of the Fourier transform infrared spectrometer. Among them (1) is the theoretical field of view arrangement and slit scanning principle of 9 pixels; (2) is the change curve of the signal of 9 pixels with slit scanning.

Figure 3 is a flow chart of an automatic measurement method for multiple fields of view of a Fourier transform infrared spectrometer provided by an embodiment of the present invention.

Figure 4 is the pixel field of view response curve obtained by the method of the present invention. Among them (1) is the field of view response curve of pixels 1, 2, and 3 during vertical scanning with a transverse slit; (2) is the field of view response curve of pixels 4, 5, and 6; (3) is the field of view response curve of pixels 7, 8, and 9 The field of view response curve of the pixel.

Figure 5 is an optical field of view obtained by the method of the present invention.

Detailed ways:

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

As shown in Figure 1, it is a schematic structural diagram of a multi-field automatic measurement system for a Fourier infrared spectrometer provided by an embodiment of the present invention, including: a blackbody radiation source 1, an optical chopper 2, a slit and an electric three-dimensional platform 3, Collimator 4, Fourier spectrometer optical system to be tested 5, room temperature detector 6, preamplifier 7, multi-channel weak signal processing system 8 and collaborative processing software 9.

The radiation emitted by the blackbody radiation source 1 is focused on the incident focal plane of the optical system. The focal plane is an adjustable slit. A set of optical choppers 2 are placed between the slit and the light source to achieve modulation of the light source. The length of the slit ensures that it can cover a total field of view of 3 × 3, and the slit width is set to 1 mm. In order to traverse the nine instantaneous fields of view distributed in 3×3, the chopper and slit are placed on the motorized three-dimensional platform, and the start and end points and step distance are set through the software to control the movement of the slit. Here the step distance is set to 0.5mm and the system focal length is 850mm, so the angular resolution tested is 2".

Since the normal temperature detector 6 is used to replace the refrigerated detector in the Fourier transform infrared spectrometer, its performance differs by several orders of magnitude, and normal temperature optics also has larger background noise than cold optics. In order to ensure the output signal-to-noise ratio, the core is to develop a 9-channel lock-in amplifier to measure the weak signals of the infrared detector. The integrated 9-channel high-performance lock-in amplifier enables simultaneous observation of all pixels.

The field of view of the Fourier transform infrared spectrometer is shown in Figure 2. Each working band has a 3×3 9-pixel field of view distribution, which corresponds to a 3×3 small area array infrared detector. Single-pixel instantaneous field of view design The value is 1°. In Figure 2, the field of view angle is measured using slit scanning. By moving the horizontal and vertical slits in the horizontal and vertical two-dimensional directions, the relationship between the signal intensity received in the field of view and the scanning angle is obtained.

Figure 3 shows the flow chart of the multi-channel automatic measurement method of the field of view angle of the spaceborne Fourier transform infrared spectrometer. After completing the system construction and test preparation, first set the blackbody temperature to an appropriate temperature according to the working band and dynamic range of the Fourier spectrometer, move the horizontal slit vertically out of the field of view, and set the starting point of the movement of the horizontal slit through the software. The end point and step distance are then controlled, and the three-dimensional mobile platform is controlled to drive the horizontal slit to move vertically. The phase-locked signal is sampled at each position and then averaged as the detection signal value at that position. The signal intensity is recorded, stored and plotted with the movement distance. Change the curve until the vertical scan of the entire 9-element field of view ends. Then switch to the vertical slit and scan horizontally in the same way.

Figure 4 is the obtained pixel field of view response curve. Find the signal peak for each pixel response curve:

DNMax＝Max(DN _i ,i＝1,2...M) (1)

In formula (1), DN is the signal digital quantity of each sampling point, M is the number of sampling points, and DNMax is the signal peak value. Then the intensity of the infrared detection signal received by the detector and amplified by phase lock-in was normalized. According to the ratio of the area of the field of view intercepted when the center of the slit is at the edge of the circular field of view and the center of the field of view is 0.241, then the intersection position of the field of view response curve and 0.241×DNMax is obtained, thereby determining the center and size of the field of view:

Z0＝k,DN _k ＝DNMax (2)

Z1＝i,DN _i ＝0.241×DNMax,i＜k (3)

Z2＝j,DN _j ＝0.241×DNMax,j>k (4)

IFOV _center =(Z1+Z2)/2 (5)

IFOV _size ＝Z2-Z1 (6)

Among them, Z0 is the signal peak position, Z1 and Z2 are the intersection positions of the field of view response curve and 0.241×DNMax respectively, IFOV _center is the center position of the field of view, and IFOV _size is the size of the field of view. According to the above formula, the center and size can be obtained in the horizontal and vertical directions respectively. As shown in Figure 5, an optical field of view with 9 pixels in the band was finally obtained through this method.

Claims (6)

1. A fourier infrared spectrometer multivariate field of view automatic measurement system comprising: blackbody radiation source (1), optical chopper (2), slit and electronic three-dimensional platform (3), collimator (4), fourier spectrometer optical system (5) that awaits measuring, normal atmospheric temperature detector (6), preamplifier (7), weak signal processing system of multichannel (8) and collaborative processing software (9), its characterized in that:

the blackbody radiation source (1) generates blackbody infrared radiation, the blackbody infrared radiation is incident to the optical chopper (2), is modulated in frequency and then is incident to the slit and the electric three-dimensional platform (3), the radiation energy passing through the slit enters the collimator (4) to be converted into parallel light, then enters the optical system (5) of the Fourier spectrometer to be detected, and finally is focused on the normal temperature detector (6) after the light splitting and collimation of the system; the weak electric signal after photoelectric conversion is amplified in low noise through a preamplifier (7), then phase-locked amplification and acquisition are carried out by a multichannel weak signal processing system (8), finally cooperative processing software (9) communicates with the multichannel weak signal processing system (8) through a serial port, the cooperative work of slit movement and data acquisition is controlled, the acquisition of infrared detection signals is started every time the slit movement is moved to a view field position, and a change curve of signal intensity along with displacement distance is drawn; searching a signal intensity peak value through acquired detection signals and slit displacement distance data, and calculating the light passing area ratio of a slit at the edge of a pixel view field and the center of the pixel view field, wherein the light passing area ratio is multiplied by the signal intensity peak value to be used as pixel edge signal intensity; and calculating an intersection point of a change curve of the signal intensity along with the displacement distance and the edge signal intensity, wherein the center of the two intersection points is the center of the field of view of the pixel, the width between the two intersection points is the size of the field of view, and the slit movement distance is converted into an angle value through a measuring system.

2. The fourier infrared spectrometer multivariate viewing field automatic measurement system of claim 1, wherein the blackbody radiation source (1) has a temperature in the range of 0-500 ℃ and a temperature stability of 0.1K.

3. The fourier infrared spectrometer multivariate viewing field automatic measurement system of claim 1, wherein the modulation frequency of the optical chopper (2) is 17.46Hz.

4. The automatic measuring system for the multi-view field of the Fourier infrared spectrometer according to claim 1, wherein the width of the slit and the width of the slit in the electric three-dimensional platform (3) are 0.5mm, the corresponding view field resolution is 2', and the width of the slit can be adjusted according to the focal length of the measured system and the required view field resolution; the slit is scanned horizontally and vertically along with the motor, the slit is installed vertically when moving in the horizontal direction, the slit is installed horizontally when moving in the vertical direction, and the step distance, the starting point, the end point and the residence time of the slit scanning are set through software.

5. The system for automatically measuring the multiple fields of view of the Fourier infrared spectrometer according to claim 1, wherein the multi-channel weak signal processing system (8) comprises a 9-channel phase-locked amplifying circuit, a phase-locked reference signal generator, an AD sampling circuit and an FPGA data processing and transmitting circuit.

6. The method for automatically measuring the multi-element view field of the Fourier infrared spectrometer is characterized by comprising the following steps of:

step 1: adjusting the proper temperature state of the blackbody radiation source (1) and stabilizing the blackbody radiation source;

step 2: the cooperative processing software (9) controls the slit and the electric three-dimensional platform (3) to enable the horizontal slit to move outside the field of view, and the multichannel weak signal processing system (8) starts to sample and record data;

step 3: according to the step distance of the slit corresponding to the field of view 2', moving in the vertical direction, after entering the field of view, moving to one position, enabling radiation emitted by the blackbody radiation source (1) to enter the collimator (4) through the slit after being modulated by the frequency of the optical chopper (2) to be converted into parallel light, entering the optical system (5) of the Fourier spectrometer to be detected, and focusing on the normal-temperature detector (6) to perform photoelectric conversion; the weak electric signal is amplified with low noise through a preamplifier (7), and then the multichannel weak signal processing system (8) collects detection signals until all pixel visual fields in the vertical direction are scanned;

step 4: changing the horizontal slit into a vertical slit, moving out of the view field, and starting sampling and recording data;

step 5: according to the step distance of the slit corresponding to the field of view 2', moving in the horizontal direction, and collecting and recording detection signals when moving to one position until all pixel field of view scanning in the horizontal direction is finished;

step 6: converting slit movement distances in the horizontal direction and the vertical direction into angles according to recorded data and focal lengths of instruments, and drawing a change curve of detection signal intensity in the vertical direction and the horizontal direction along with a scanning angle;

step 7: calculating the size and the center position of the field of view of each pixel according to the field of view response curve of the pixel;

searching a signal intensity peak value through acquired detection signals and slit displacement distance data, and calculating the light passing area ratio of a slit at the edge of a pixel view field and the center of the pixel view field, wherein the light passing area ratio is multiplied by the signal intensity peak value to be used as pixel edge signal intensity; and calculating an intersection point of a change curve of the signal intensity along with the displacement distance and the edge signal intensity, wherein the center of the two intersection points is the center of the visual field of the pixel, and the width between the two intersection points is the size of the visual field.