On-satellite calibration device and method for multispectral polarization remote sensing instrument

Abstract

The invention discloses an on-satellite calibration device and method for a multispectral polarization remote sensing instrument. The device comprises a light source module, a dodging 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 reflecting mirror, a second reflecting mirror and a third reflecting mirror; the emergent light of the light source is dodging through the dodging module, then is reflected by the first reflector, passes through the central hole of the second reflector, reaches the third reflector, is reflected by the third reflector, and finally enters the multispectral polarization remote sensing instrument to be calibrated. According to the on-satellite calibration device, the calibration lamp is combined with the orthogonal reflector, free switching between an on-satellite calibration mode and an imaging mode is achieved, the orthogonal reflector is plated with a metal film, it is guaranteed that the polarization performance in the calibration light beam propagation process is not changed, and meanwhile the device has the advantages of being simple in structure, free of moving parts and high in reliability.

Description

Technical Field

[0001] The 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 the application of optical remote sensing technology in various fields deepens, the precise acquisition and analysis of target information has put forward higher requirements for satellite remote sensing data. As the spatial resolution and temporal resolution continue to improve, how to improve the quantitative application ability of remote sensing data is a major problem that needs to be solved in all fields of remote sensing. High-precision on-orbit radiation calibration is the premise and foundation for the quantitative application of optical remote sensing data.

[0003] On-board calibration is an important means of on-orbit radiation calibration. It uses an on-board calibration system carried by a satellite to achieve on-orbit radiation calibration. The calibration light sources used for on-board calibration include sunlight, standard lamps, black bodies, etc. Since the sun is a highly stable radiation source, the current mainstream on-board calibration method uses "diffuse reflector + sun" as a radiation reference benchmark. The position of the diffuse reflector is accurately positioned by 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, etc. However, due to the complex environment of space, the self-degradation of the diffuse reflector is difficult to control, and the calibration device is large in size, making it difficult to apply to platforms with high volume and weight requirements. Using a standard lamp as a calibration light source can avoid the above problems. In the prior art (such as CN103207017), a prism is used in combination with a semi-transparent and semi-reflective dichroic film to introduce the calibration light path into the main light path to achieve on-board calibration of the interference spectrometer. The calibration device has stable performance and high space utilization, but does not take into account the change in polarization performance of the light beam during transmission, and 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 multi-spectral polarization remote sensing instrument, so as to realize the free switching of 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 solution:

[0006] The on-board 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 comprises: a light source control unit and a calibration light source;

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

[0009] The first reflector is orthogonal to the second reflector in space, the second reflector is orthogonal to the third reflector in space, a center hole is provided at the center of the second reflector, and the second reflector and the third reflector are plated with the same metal film; the second reflector and the third reflector are both located in the converging light path of the multi-spectral polarization remote sensing instrument;

[0010] When the multi-spectral polarization remote sensing instrument is in the on-board 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, and is reflected by the third reflector before entering the multi-spectral polarization remote sensing instrument.

[0013] When the multi-spectral polarization remote sensing instrument is in the on-board 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 on-board 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 any one of a barium sulfate coating and a polytetrafluoroethylene coating, or is plated with a metal film layer consistent with that of the second reflector.

[0015] Furthermore, the on-board 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 multi-spectral 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 on-board calibration time as the observation target of the multi-spectral polarization remote sensing instrument is the sky above the dark side of the ocean on the earth, and making the light source control module 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 row and column of the detector 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 on-board 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 equation (1) to obtain the on-board calibrated 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] Using formula (2), we can obtain the uniformity correction coefficient of the multi-spectral 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 multi-spectral polarization remote sensing instrument at time t :

[0030] (3)

[0031] Step 7: Use equation (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 radiation calibration coefficient of 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, so as to realize free switching between the calibration mode and the imaging mode at the same time, which is beneficial to improving the frequency of on-orbit calibration.

[0036] 2. The on-board calibration device of the present invention has a simple structure, no moving parts, occupies few resources, has high reliability, and 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 convergent optical path of the instrument to be calibrated, and the light beam has a certain solid angle. Therefore, there is a certain deviation in the incident angle of the light beams of the two reflectors. By coating the orthogonal mirrors with metal films, the phase difference between the S light and the P light is guaranteed to be constant, thereby ensuring that the polarization characteristics of the light beams in the main optical path of the instrument to be calibrated and the calibration optical path do not change during the transmission process. It is particularly suitable for on-board calibration of polarization remote sensing optical instruments with high polarization detection accuracy requirements. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2 It is a structural schematic diagram of the orthogonal mirror assembly of the present invention;

[0040] Figure 3 This is a schematic diagram of the calibration optical path of an onboard calibration device for a multi-spectral polarization imager according to a 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 multi-spectral polarization imager according to the second embodiment of the present invention;

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

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

[0044] Embodiment 1, taking the on-board calibration device of a satellite-borne multi-spectral polarization imager with a focal length of 200mm and a working band of 490-910nm as an example, a multi-spectral polarization remote sensing instrument on-board calibration device, such as Figure 1 As shown, it is applied to the visible light to near infrared band, and includes: a light source module, a light homogenization 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 on and off of the calibration light source, and at the same time provide a constant current to the calibration light source to ensure the stability of the brightness of the calibration light source. When the multi-spectral polarization remote sensing instrument is in the on-board 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.

[0046] In order to prevent the calibration light source from overheating and affecting the instrument performance, a heat sink is installed on the light source module, and forms a detachable structure with the calibration light source. In order to ensure that the radiance of the calibration light source is within the dynamic range of the detector, the calibration light source is an OSRAM model 64258 low-voltage halogen lamp without a reflector, and the quantity is 2.

[0047] 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 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 multi-spectral polarization imager when the multi-spectral 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 multi-spectral polarization imager is in the imaging mode, a center hole is opened in the center of the second reflector, and the opening diameter is 3mm.

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

[0051] In order to miniaturize the structure size, 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 on-board calibration optical path. The light emitted by the light source module 1 is first homogenized by the integrating sphere of the homogenizing module 2 to obtain a homogenized light beam, then reflected by the first reflector of the orthogonal mirror assembly 3, then passes through the central hole of the second reflector to the third reflector, then reflected by the third reflector, and finally enters the multi-spectral polarization remote sensing instrument 4;

[0053] When the multi-spectral polarization remote sensing instrument is in the on-board 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, a satellite calibration method for a multi-spectral polarization remote sensing instrument is applied to the above-mentioned satellite calibration device and is performed according to the following steps:

[0055] Step 1: Set the onboard calibration time as the observation target of the multi-spectral polarization remote sensing instrument is the sky above the dark side of the ocean on the earth, and let the light source control module control the calibration light source to power on, so that the calibration light source is turned on and preheated to be stable;

[0056] 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 row and column of the detector 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 equation (1) to obtain the on-board calibrated 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] Using formula (2), we can obtain the uniformity correction coefficient of the multi-spectral 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 multi-spectral polarization remote sensing instrument at time t :

[0067] (3)

[0068] Step 7: Use equation (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 radiation calibration coefficient of 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] Embodiment 2: Taking the on-board calibration device of a certain type of multi-spectral polarization detector with a focal length of 198mm and a working band of 950-1610nm as an example, the calibration light source selects two LEDs with central wavelengths of 1380nm and 1610nm respectively. The uniform light module adopts the Kohler illumination structure to achieve uniform illumination. The first reflector is coated with a diffuse reflective barium sulfate coating, and the second and third reflectors are coated with the same film system, both of which are metal Al films. A small hole is opened in the center of the second reflector, and the diameter of the hole is 2mm.

[0072] like Figure 4 The figure shows a schematic diagram of the 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 light beam, then reflected by the first reflector of the orthogonal mirror assembly 3, and then passes through the central hole of the second reflector to the third reflector, and then reflected by the third reflector, and finally enters the multi-spectral polarization detector 4. When the multi-spectral polarization detector is in the on-board imaging mode, the light source control module controls the light source to be turned off and the imaging mode to be turned on.

Claims

1. An onboard calibration device for a multi-spectral polarization remote sensing instrument, characterized in that: include: Light source module, light homogenization module, 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 first reflector is orthogonal to the second reflector in space, the second reflector is orthogonal to the third reflector in space, a center hole is provided at the center of the second reflector, and the second reflector and the third reflector are plated with the same metal film; the second reflector and the third reflector are both located in the converging light path of the multi-spectral polarization remote sensing instrument; When the multi-spectral polarization remote sensing instrument is in the on-board 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, and is reflected by the third reflector before entering the multi-spectral polarization remote sensing instrument. When the multi-spectral polarization remote sensing instrument is in the on-board 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 multi-spectral polarization remote sensing instrument according to claim 1, characterized in that: The surface of the first reflector is coated with any one of a barium sulfate coating and 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 multi-spectral 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 on-board calibration device for a multi-spectral polarization remote sensing instrument according to claim 1, characterized in that: The light source module is provided with a heat dissipation device, and forms a detachable structure with the calibration light source.

5. A method for on-board calibration of a multi-spectral polarization remote sensing instrument, characterized in that: It is applied to the on-board calibration device described in claim 1 and is performed according to the following steps: Step 1: setting the on-board calibration time as the observation target of the multi-spectral polarization remote sensing instrument is the sky above the dark side of the ocean on the earth, and making the light source control module 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 row and column of the detector 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 on-board 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 equation (1) to obtain the on-board calibrated 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; Using formula (2), we can obtain the uniformity correction coefficient of the multi-spectral 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 multi-spectral polarization remote sensing instrument at time t : (3) Step 7: Use equation (4) to obtain the absolute responsivity of the multispectral polarization remote sensing instrument at time t : (4) In formula (4), represents the absolute radiation calibration coefficient of 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.

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