A multi-spectral polarization remote sensing instrument on-board calibration device and method

Abstract

The present invention discloses an onboard calibration device and method for a multispectral polarization remote sensing instrument. The device comprises a light source module, a light homogenization module, and an orthogonal mirror assembly. The light source module comprises a light source control unit and a calibration light source. The orthogonal mirror assembly comprises an orthogonal mirror frame, a first reflector, a second reflector, and a third reflector. The emitted light from the light source is first homogenized by the light homogenization module, then reflected by the first reflector, passes through the center hole of the second reflector to the third reflector, then reflected by the third reflector, and finally enters the multispectral polarization remote sensing instrument to be calibrated. The onboard calibration device provided by the present invention realizes free switching between onboard calibration mode and imaging mode by using a calibration lamp in combination with an orthogonal reflector. A metal film is coated on the orthogonal mirror to ensure that the polarization performance of the calibration beam does not change during propagation. The device has the advantages of simple structure, no moving parts, and high reliability.

Description

Technical Field

[0001] The present invention relates to the field of radiation calibration of spectral polarization instruments, and in particular to an on-board calibration device and method for a multi-spectral polarization remote sensing instrument, which can be used for on-board calibration of spectral polarization remote sensing instruments. Background Art

[0002] As optical remote sensing technology expands across various fields, the need for precise and accurate acquisition and analysis of target information is placing higher demands on satellite remote sensing data. As spatial and temporal resolution continue to improve, enhancing the quantitative application capabilities of remote sensing data is a critical challenge that needs to be addressed across all areas of remote sensing. High-precision on-orbit radiometric calibration is the prerequisite and foundation for the quantitative application of optical remote sensing data.

[0003] On-board calibration is an important means of on-orbit radiation calibration, and it is achieved using an on-board calibration system carried by a satellite. Calibration light sources used for on-board calibration include sunlight, standard lamps, black bodies, and others. Because the sun is a highly stable radiation source, the current mainstream on-board calibration method uses a "diffuse reflector + sun" as a radiation reference. The position of the diffuse reflector is precisely positioned using a calibration turntable and a stepper motor to achieve on-orbit calibration of optical instruments. This method is widely used in satellite-borne imaging spectrometers, radiometers, and other instruments. However, due to the complex environment of space, the inherent decay of the diffuse reflector is difficult to control, and the calibration device is large, making it difficult to apply to platforms with high volume and weight requirements. Using a standard lamp as the calibration light source can avoid these problems. In the existing technology (such as CN103207017), a prism is used in combination with a semi-transparent and semi-reflective spectroscopic film to introduce the calibration light path into the main light path to achieve on-board calibration of the interference spectrometer. This calibration device has stable performance and high space utilization, but does not consider the changes in the polarization performance of the light beam during transmission. It is not suitable for on-board calibration of multi-spectral polarization remote sensing instruments. Summary of the Invention

[0004] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides an on-board calibration device and method for a multispectral polarization remote sensing instrument, so as to realize the free switching between the on-board calibration mode and the imaging mode, thereby ensuring that the polarization performance of the calibration beam does not change during the propagation process.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The onboard calibration device of a multi-spectral polarization remote sensing instrument of the present invention is characterized in that it comprises: a light source module, a uniform light module, and an orthogonal mirror assembly;

[0007] The light source module includes: a light source control unit and a calibration light source;

[0008] The orthogonal mirror assembly includes: an orthogonal mirror frame, a first reflector, a second reflector, and a third reflector;

[0009] The first reflector and the second reflector are spatially orthogonal to each other, the second reflector and the third reflector are spatially orthogonal to each other, a center hole is defined at the center of the second reflector, and the second reflector and the third reflector are coated with the same metal film; the second reflector and the third reflector are both located in the converging light path of the multispectral polarization remote sensing instrument;

[0010] When the multispectral polarization remote sensing instrument is in the onboard calibration mode, the light source control module controls the calibration light source to turn on, so that the calibration mode is turned on, and provides a constant current to the calibration light source;

[0011] The light homogenization module homogenizes the brightness distribution of the light beam emitted by the calibration light source to obtain a homogenized light beam;

[0012] The homogenized light beam is reflected by the first reflector, passes through the central hole of the second reflector to the third reflector, is reflected by the third reflector, and finally enters the multispectral polarization remote sensing instrument;

[0013] When the multispectral polarization remote sensing instrument is in the onboard imaging mode, the light source control module controls the calibration light source to be turned off, so that the imaging mode is turned on.

[0014] The onboard calibration device for a multi-spectral polarization remote sensing instrument described in the present invention is also characterized in that the surface of the first reflector is coated with either a barium sulfate coating or a polytetrafluoroethylene coating, or is plated with a metal film layer consistent with that of the second reflector.

[0015] Furthermore, the onboard calibration device is applied to the visible light to near-infrared band.

[0016] Furthermore, a heat dissipation device is installed on the light source module, and forms a detachable structure with the calibration light source.

[0017] The on-board calibration method of a multispectral polarization remote sensing instrument of the present invention is characterized in that it is applied to the on-board calibration device and is performed according to the following steps:

[0018] Step 1: setting the onboard calibration timing to the observation target of the multispectral polarization remote sensing instrument being the sky above the dark side of the ocean, and instructing the light source control module to control the calibration light source to be powered on, so that the calibration light source is turned on and preheated to be stable;

[0019] Step 2: Let the first on-board calibration time be the initial time t0. The on-board calibration device collects multiple images at time t0 and calculates the average value to obtain the average bright field image at time t0. , where k represents the band, i and j represent the rows and columns of detectors in the multispectral polarization remote sensing instrument respectively;

[0020] Step 3: The light source control module controls the calibration light source to be turned off, and the onboard calibration device collects multiple background images and calculates the average value to obtain the average background image at time t0. ,

[0021] Will and After subtraction, the average effective image of the on-board calibration device at time t0 is obtained ;

[0022] Step 4: The current on-board calibration time is taken as time t, and the on-board calibration average effective image of the on-board calibration device at time t is obtained according to the process of steps 1 to 3. ;

[0023] Step 5: Use formula (1) to obtain the on-board calibration normalized image at time t0 ;

[0024] (1)

[0025] In formula (1), n ​​represents the number of pixels in the central area of ​​the detector, i0 represents the row where the central pixel of the detector is located, and j0 represents the column where the central pixel of the detector is located;

[0026] Use formula (2) to obtain the uniformity correction coefficient of the multispectral polarization remote sensing instrument at time t: ;

[0027] (2)

[0028] In formula (2), represents the normalized image calibrated on board at time t;

[0029] Step 6: Use formula (3) to obtain the absolute radiation correction coefficient of the multispectral polarization remote sensing instrument at time t :

[0030] (3)

[0031] Step 7: Use formula (4) to obtain the absolute responsivity of the multispectral polarization remote sensing instrument at time t :

[0032] (4)

[0033] In formula (4), represents the absolute radiometric calibration coefficient for band k calibrated by the laboratory, It represents the uniformity coefficient of band k in row i and column j of laboratory calibration; It represents the absolute temperature correction coefficient of band k at time t; It represents the nonlinear correction coefficient of band k at time t, where K is the gain coefficient.

[0034] The beneficial effects of the present invention are:

[0035] 1. The device of the present invention adopts a calibration light source combined with an orthogonal reflector, and opens a small hole in the center of the orthogonal reflector, which can realize the free switching between the calibration mode and the imaging mode at the same time, which is conducive to improving the frequency of on-orbit calibration.

[0036] 2. The onboard calibration device of the present invention has a simple structure, no moving parts, occupies few resources, and has high reliability. It is particularly suitable for satellite platforms with high requirements on volume and weight.

[0037] 3. In the device of the present invention, the orthogonal reflectors are located in the converging optical path of the instrument to be calibrated. The light beams have a certain solid angle, resulting in a certain deviation in the angles of incidence of the two reflectors. By coating the orthogonal reflectors with a metal film, the phase difference between the S- and P-light beams is maintained constant, thus ensuring that the polarization characteristics of the beams in the instrument's main optical path and the calibration optical path remain unchanged during transmission. This makes the device particularly suitable for onboard calibration of polarization remote sensing optical instruments, which require high polarization detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a structural block diagram of the onboard calibration device for the multi-spectral polarization remote sensing instrument of the present invention;

[0039] Figure 2 Schematic diagram of the structure of the orthogonal mirror assembly of the present invention;

[0040] Figure 3 This is a schematic diagram of the calibration optical path of the onboard calibration device for a multispectral polarization imager according to the first embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the calibration optical path of the onboard calibration device for a multispectral polarization imager according to the second embodiment of the present invention;

[0042] Numbers in the figure: 1-light source module, 2-light homogenization module, 3-orthogonal mirror assembly, 4-detector of the multi-spectral polarization remote sensing instrument. Specific embodiments

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] In the first embodiment, a calibration device for a multi-spectral polarization remote sensing instrument on board a satellite is used as an example. Figure 1 As shown, it is applied to the visible light to near infrared band and includes: a light source module, a uniform light module, and an orthogonal mirror assembly;

[0045] The light source module includes a light source control unit and a calibration light source. The light source control unit is used to control the calibration light source's on and off state and provides a constant current to the calibration light source, ensuring the stability of its brightness. When the multispectral polarization remote sensing instrument is in onboard calibration mode, the light source control module turns on the calibration light source, enabling calibration mode and providing a constant current to the calibration light source.

[0046] To prevent the calibration light source from overheating and affecting instrument performance, a heat sink is installed on the light source module, forming a detachable structure with the calibration light source. To ensure the calibration light source's radiance is within the detector's dynamic range, two Osram model 64258 low-voltage halogen lamps without reflectors were used.

[0047] The light homogenization module evens out the brightness distribution of the light beam emitted by the calibration light source to obtain a homogenized light beam. The light homogenization module uses an integrating sphere to achieve uniform illumination. The inner wall of the integrating sphere is coated with white diffuse reflective material barium sulfate. The aperture of the integrating sphere is 30mm, the diameter of the light outlet is 10mm, and the calibration light source is symmetrically distributed on the inner wall of the integrating sphere.

[0048] like Figure 2 As shown, the orthogonal mirror assembly includes: an orthogonal mirror frame, a first reflector, a second reflector, and a third reflector;

[0049] Among them, the first reflector is spatially orthogonal to the second reflector, and the second reflector is spatially orthogonal to the third reflector. In order to ensure that the light beam emitted by the calibration light source can illuminate the detector of the multispectral polarization imager when the multispectral polarization imager is in the calibration mode, and at the same time ensure that the light beam energy loss is as low as possible when the multispectral polarization imager is in the imaging mode, a center hole is opened in the center of the second reflector with a diameter of 3 mm.

[0050] The first reflector, the second reflector, and the third reflector are coated with the same metal film; all are coated with a metal Ag film. In a specific implementation, the surface of the first reflector is coated with either a barium sulfate coating or a polytetrafluoroethylene coating, or is coated with the same metal film layer as the second reflector.

[0051] In order to miniaturize the structure, the second reflector and the third reflector are both located in the converging light path of the multi-spectral polarization remote sensing instrument;

[0052] like Figure 3The figure shows a schematic diagram of the onboard calibration optical path. The light emitted by the light source module 1 is first homogenized by the integrating sphere of the light homogenization module 2 to obtain a homogenized beam. The light is then reflected by the first reflector of the orthogonal mirror assembly 3, passes through the center hole of the second reflector to the third reflector, and then is reflected by the third reflector before entering the multispectral polarization remote sensing instrument 4.

[0053] When the multispectral polarization remote sensing instrument is in the onboard imaging mode, the light source control module controls the calibration light source to be turned off, so that the imaging mode is turned on.

[0054] In this embodiment, an onboard calibration method for a multispectral polarization remote sensing instrument is applied to the above-mentioned onboard calibration device and is performed in the following steps:

[0055] Step 1: Set the onboard calibration timing to the observation target of the multispectral polarization remote sensing instrument as the sky above the dark side of the ocean, and instruct the light source control module to control the calibration light source to power on, so that the calibration light source is turned on and preheated to a stable state;

[0056] Step 2: Let the first onboard calibration time be the initial time t0. The onboard calibration device collects multiple images at time t0 and calculates the average value to obtain the average bright field image at time t0. , where k represents the band, i and j represent the rows and columns of detectors in the multispectral polarization remote sensing instrument respectively;

[0057] Step 3: The light source control module controls the calibration light source to turn off. The onboard calibration device collects multiple background images and calculates the average value to obtain the average background image at time t0. ,

[0058] Will and After subtraction, the average effective image of the on-board calibration device at time t0 is obtained ;

[0059] Step 4: The current on-board calibration time is taken as time t, and the on-board calibration average effective image of the on-board calibration device at time t is obtained according to the process of steps 1 to 3. ;

[0060] Step 5: Use formula (1) to obtain the on-board calibration normalized image at time t0 ;

[0061] (1)

[0062] In formula (1), n ​​represents the number of pixels in the central area of ​​the detector, i0 represents the row where the central pixel of the detector is located, and j0 represents the column where the central pixel of the detector is located;

[0063] Use formula (2) to obtain the uniformity correction coefficient of the multispectral polarization remote sensing instrument at time t: ;

[0064] (2)

[0065] In formula (2), represents the normalized image calibrated on board at time t;

[0066] Step 6: Use formula (3) to obtain the absolute radiation correction coefficient of the multispectral polarization remote sensing instrument at time t :

[0067] (3)

[0068] Step 7: Use formula (4) to obtain the absolute responsivity of the multispectral polarization remote sensing instrument at time t :

[0069] (4)

[0070] In formula (4), represents the absolute radiometric calibration coefficient for band k calibrated by the laboratory, It represents the uniformity coefficient of band k in row i and column j of laboratory calibration; It represents the absolute temperature correction coefficient of band k at time t; It represents the nonlinear correction coefficient of band k at time t, where K is the gain coefficient.

[0071] Example 2: Using the onboard calibration device for a multispectral polarization detector with a focal length of 198 mm and an operating wavelength of 950-1610 nm as an example, the calibration light source is two LEDs with central wavelengths of 1380 nm and 1610 nm, respectively. The uniform illumination module uses a Köhler illumination structure to achieve uniform illumination. The first reflector is coated with a diffusely reflective barium sulfate coating, while the second and third reflectors are coated with the same film system: a metallic Al film. A small hole with a diameter of 2 mm is opened in the center of the second reflector.

[0072] like Figure 4 Figure 1 shows a schematic diagram of the calibration optical path. Light emitted by light source module 1 is first homogenized by the integrating sphere of homogenization module 2 to produce a homogenized beam. This light is then reflected by the first reflector of orthogonal mirror assembly 3, passes through the center hole of the second reflector, reaches the third reflector, and then reflects again before entering multispectral polarimeter 4. When the multispectral polarimeter is in onboard imaging mode, the light source control module turns the light source off and imaging mode on.

Claims

1. An onboard calibration device for a multispectral polarization remote sensing instrument, characterized in that: include: Light source module, light homogenization module, orthogonal mirror assembly; The light source module includes: a light source control unit and a calibration light source; The orthogonal mirror assembly includes: an orthogonal mirror frame, a first reflector, a second reflector, and a third reflector; The first reflector and the second reflector are spatially orthogonal to each other, the second reflector and the third reflector are spatially orthogonal to each other, a center hole is defined at the center of the second reflector, and the second reflector and the third reflector are coated with the same metal film; the second reflector and the third reflector are both located in the converging light path of the multispectral polarization remote sensing instrument; When the multispectral polarization remote sensing instrument is in the onboard calibration mode, the light source control module controls the calibration light source to turn on, so that the calibration mode is turned on, and provides a constant current to the calibration light source; The light homogenization module homogenizes the brightness distribution of the light beam emitted by the calibration light source to obtain a homogenized light beam; The homogenized light beam is reflected by the first reflector, passes through the central hole of the second reflector to the third reflector, is reflected by the third reflector, and finally enters the multispectral polarization remote sensing instrument; When the multispectral polarization remote sensing instrument is in the onboard imaging mode, the light source control module controls the calibration light source to be turned off, so that the imaging mode is turned on.

2. The onboard calibration device for a multispectral polarization remote sensing instrument according to claim 1, characterized in that: The surface of the first reflector is coated with either a barium sulfate coating or a polytetrafluoroethylene coating, or is plated with a metal film layer consistent with that of the second reflector.

3. The onboard calibration device for a multispectral polarization remote sensing instrument according to claim 1, characterized in that: The on-board calibration device is applied to the visible light to near-infrared band.

4. The onboard calibration device for a multispectral polarization remote sensing instrument according to claim 1, characterized in that: The light source module is equipped with a heat dissipation device, and forms a detachable structure with the calibration light source.

5. A method for onboard calibration of a multispectral polarization remote sensing instrument, characterized in that: It is applied to the on-board calibration device described in claim 1 and is carried out in the following steps: Step 1: setting the onboard calibration timing to the observation target of the multispectral polarization remote sensing instrument being the sky above the dark side of the ocean, and instructing the light source control module to control the calibration light source to be powered on, so that the calibration light source is turned on and preheated to be stable; Step 2: Let the first on-board calibration time be the initial time t0. The on-board calibration device collects multiple images at time t0 and calculates the average value to obtain the average bright field image at time t0. , where k represents the band, i and j represent the rows and columns of detectors in the multispectral polarization remote sensing instrument respectively; Step 3: The light source control module controls the calibration light source to be turned off, and the onboard calibration device collects multiple background images and calculates the average value to obtain the average background image at time t0. ; Will and After subtraction, the average effective image of the on-board calibration device at time t0 is obtained ; Step 4: The current on-board calibration time is taken as time t, and the on-board calibration average effective image of the on-board calibration device at time t is obtained according to the process of steps 1 to 3. ; Step 5: Use formula (1) to obtain the on-board calibration normalized image at time t0 ; (1) In formula (1), n ​​represents the number of pixels in the central area of ​​the detector, i0 represents the row where the central pixel of the detector is located, and j0 represents the column where the central pixel of the detector is located; Use formula (2) to obtain the uniformity correction coefficient of the multispectral polarization remote sensing instrument at time t: ; (2) In formula (2), represents the normalized image calibrated on board at time t; Step 6: Use formula (3) to obtain the absolute radiation correction coefficient of the multispectral polarization remote sensing instrument at time t : (3) Step 7: Use formula (4) to obtain the absolute responsivity of the multispectral polarization remote sensing instrument at time t : (4) In formula (4), represents the absolute radiometric calibration coefficient for band k calibrated by the laboratory, It represents the uniformity coefficient of the band k in row i and column j of the laboratory calibration; It represents the absolute temperature correction coefficient of band k at time t; It represents the nonlinear correction coefficient of band k at time t, where K is the gain coefficient.

Images