CN114216559B - A partial aperture factor measurement method and device for on-board calibration mechanism - Google Patents

Abstract

The invention provides a method and device for measuring the partial aperture factor of a calibration mechanism on a satellite, which can accurately measure the partial aperture factor of the calibration mechanism without the need for external instruments to enter the calibration or imaging optical path of the remote sensor. The method includes: establishing a linear relationship between the response count values of the radiometer and the remote sensor when observing the same radiation source at different energy levels, and establishing the relationship between the observation direction of the radiometer and the remote sensor under the same lighting conditions based on the BRDF measurement data of the diffuse reflector laboratory. The relative proportional relationship of the BRDF in the observation direction. Under the same illumination angle, the count value of the diffuse reflection plate observed by the specific radiometer in the calibrator is used to estimate the full aperture response count value of the remote sensor at the same radiation input, combined with the remote sensor's own calibration optical path. The aperture factor is calculated from the actual measured count value.

Description

A partial aperture factor measurement method and device for on-board calibration mechanism

Technical field

The invention relates to satellite-borne remote sensor radiation calibration technology, and in particular to a partial aperture factor measurement method of a satellite-borne calibration mechanism and a device applying the method.

Background technique

With the development of society, people have higher requirements for geological survey and meteorological forecast, which leads to an urgent need for high-precision quantitative remote sensing by satellites. Radiation calibration of spaceborne remote sensors can ensure the quantification level of remote sensing data, thereby improving the performance of remote sensors.

The so-called radiation calibration is usually defined as determining the radiation performance of the instrument in the spatial domain, time domain, and spectral domain during a series of measurement processes. Its output is a value related to the actual radiation energy measurement.

Radiation calibration can be divided into pre-launch calibration and on-orbit calibration. Due to the vibration and acceleration impact of the remote sensor when it is launched, as well as the difference between the on-orbit environment and the ground environment, as the time in orbit becomes longer, the system parameters measured before launch will no longer be applicable. Therefore, on-orbit satellite calibration is required to regularly Corrected laboratory calibration coefficients.

However, the on-board calibration mechanism will be affected by many factors such as power consumption, volume, and weight. It cannot adopt an overly complex or bulky structure. Simplification of its design is very important. For example, when the calibration mechanism is configured for a large-aperture remote sensor or the overall structure of the remote sensor has limitations and cannot achieve full-aperture calibration, the partial-aperture all-optical path on-board calibration method based on diffuse reflection plates can be used to obtain the results through partial-aperture calibration measurements. Remote sensor full aperture calibration coefficient. The size of the calibration mechanism is reduced at the expense of the complexity of the on-board calibration mechanism and its physical model, so that on-board calibration can be achieved for large-aperture remote sensors or when the available space of the remote sensor itself is insufficient or limited.

The Advanced Baseline Imager (ABI) carried by the US GOES-16 and the Advanced Geostationary Radiation Imager (AGRI) of my country's Fengyun-4 multi-channel scanning radiometer have adopted a partial aperture all-optical path on-board calibration scheme. Among them, the measurement of some aperture factors is the key to determining whether the calibration scheme is feasible. At the same time, its measurement uncertainty is also the largest source of uncertainty affecting the final on-board calibration.

Contents of the invention

The technical problem to be solved by the invention

The remote sensor observes the ground imaging in full aperture mode, while the remote sensor observes the diffuse reflector calibration in partial aperture mode. Therefore, the guiding idea of measuring partial aperture is to compare the two modes to observe the same radiance source, and thereby calculate the partial aperture factor. .

Therefore, ideally, the same radiation source provides radiation input for the calibration optical path and imaging optical path of the remote sensor respectively. When the remote sensor response is linear, part of the aperture factor can be expressed as the response count value of the calibration optical path and the imaging optical path. The ratio of the response count value.

At present, part of the aperture factor measurement is mainly performed by inserting the hyperspectrometer into the calibration optical path and imaging optical path of the remote sensor and measuring the response values of the two optical paths simultaneously with the remote sensor. Using the spectral radiance measured by the hyperspectral instrument as a reference, the radiation of the two optical paths is calculated. The response is corrected for the same radiation input, and the ratio of the count values of the two optical paths in this state is the partial aperture factor of partial aperture calibration. The final measurement of some aperture factors should be performed after the remote sensor is assembled, and is a parameter that can only be obtained by system-level measurements.

However, during the measurement process, it is difficult for the hyperspectrometer to ensure that the direction of the measurement radiation source is consistent with that of the remote sensor, regardless of whether it is inserted into the calibration or imaging optical path. Moreover, after the assembly of the remote sensor, there is still a problem in the process of inserting the hyperspectral probe into the calibration optical path. Touching the optical surface of the scatterer causes the risk of calibration system failure, low measurement efficiency, poor repeatability of measurement results, and a large difference from the actual application state of the remote sensor.

In view of the problems existing in the prior art, the present invention proposes a partial aperture factor measurement method of the on-board calibration mechanism, which can accurately measure part of the calibration mechanism without cutting into the hyperspectrometer in the calibration or imaging optical path of the remote sensor. The aperture factor can improve the measurement efficiency of some aperture factors and the stability of the measurement results, bringing it closer to the real application state of the remote sensor, and ultimately contributes to improving the calibration accuracy of on-board calibration. In particular, the radiometer in the on-board calibration mechanism, which is usually used to monitor the reflectance of diffuse reflectors, can also be used for partial aperture factor measurements, which can improve stability and simplify the structure and measurement steps.

Technical means to solve problems

The invention provides a partial aperture factor measurement method of a satellite calibration mechanism. The satellite calibration mechanism is used for on-orbit radiation calibration of a satellite-borne remote sensor, and includes a diffuse reflection plate and a device for monitoring the A radiometer for the reflectivity of a diffuse reflection plate. The method includes: a first step, establishing a linear relationship between the response count values of the radiometer and the remote sensor when observing the same radiation source at different energy levels; a second step. , based on the BRDF basic data of the diffuse reflector obtained in advance, establish a relative proportional relationship between the BRDF of the diffuse reflector observation direction of the radiometer and the diffuse reflector observation direction of the remote sensor under the same lighting conditions; and Three steps: Obtain the response count value of the diffuse reflection plate under the calibration light path of the radiometer and the remote sensor under the same illumination angle, and deduce the remote sensor based on the obtained response count value of the radiometer. The partial aperture factor of the on-board calibration mechanism is calculated using the full aperture response count value when the same radiation is input, combined with the obtained response count value of the remote sensor calibration optical path.

In the partial aperture factor measurement method of the present invention, in the first step, the remote sensor is used to observe the radiation source used to simulate the reflected radiance of the diffuse reflector on the satellite, and the ratio is moved through a moving mechanism. The radiometer cuts into/out of the radiation measurement light path of the remote sensor, and while changing the energy level of the radiation source, measures the respective response count values of the remote sensor and the radiometer, based on the measured response counts. The values establish the linear relationship according to the linear regression equation.

In the partial aperture factor measurement method of the present invention, in the second step, the observation direction of the diffuse reflector plate of the radiometer in the actual on-orbit calibration state of the on-board calibration mechanism and the Based on the relationship between the observation directions of the diffuse reflector of the remote sensor, the corresponding data is extracted from the BRDF basic data to calculate the BRDF relative proportion relationship.

In the partial aperture factor measurement method of the present invention, in the third step, the radiometer and the diffuse reflection plate are used to assemble the on-board calibration mechanism, which is then integrated and assembled with the remote sensor. The diffuse reflector is illuminated by a solar simulator, and the calibration optical path of the remote sensor and the response count value of the diffuse reflector under the same incident angle observed by the radiometer are obtained.

Furthermore, using the BRDF relative proportion relationship obtained in the second step, the response count value of the diffuse reflector illuminated by the solar simulator observed by the radiometer is equivalent to the remote sensor The observation direction of the diffuse reflector plate, and use the linear relationship obtained in the first step to obtain the full aperture response count value of the remote sensor at the same radiation input, based on the calculated value of the remote sensor at the same radiation input The partial aperture factor is calculated based on the full aperture response count value when radiation is input and the response count value obtained by observing the diffuse reflection plate illuminated by the solar simulator using the calibration light path of the remote sensor.

The invention also provides a partial aperture factor measuring device for a satellite calibration mechanism. The satellite calibration mechanism is used for on-orbit radiation calibration of a satellite-borne remote sensor, and includes a diffuse reflection plate and a detector for monitoring the satellite. The radiometer of the reflectivity of the diffuse reflection plate, the device includes: a first module to establish a linear relationship between the response count values of the radiometer and the remote sensor when observing the same radiation source at different energy levels; The second module, based on the pre-obtained BRDF basic data of the diffuse reflector, establishes a relative proportional relationship between the BRDF of the diffuse reflector observation direction of the radiometer and the diffuse reflector observation direction of the remote sensor under the same lighting conditions; and the third module, obtain the response count value of the diffuse reflection plate when observing the calibration light path of the radiometer and the remote sensor at the same illumination angle, and deduce the response count value based on the obtained response count value of the radiometer. The full aperture response count value of the remote sensor when the same radiation is input is combined with the obtained response count value of the remote sensor calibration optical path to calculate the partial aperture factor of the on-board calibration mechanism.

Invention effect

Using the partial aperture factor measurement method and device of the on-board calibration mechanism of the present invention, the partial aperture factor of the calibration mechanism can be accurately measured without inserting a hyperspectrometer into the calibration or imaging optical path of the remote sensor, and the partial aperture factor can be improved. The measurement efficiency and the stability of the measurement results are closer to the actual application status of the remote sensor. It ultimately provides a solution for the realization of high-frequency on-board radiation calibration of medium and large remote sensors, and at the same time makes a contribution to improving the calibration accuracy of the on-board calibration. contribute. In particular, the specific radiometer in the on-board calibration mechanism, which is usually used to monitor the reflectance of the diffuse reflector, is also used as a reference radiometer to achieve partial aperture factor measurement, which can improve stability and simplify the structure and measurement steps.

Description of drawings

Figure 1 is a schematic diagram showing the principle of the on-satellite calibration method based on the diffuse reflection plate.

FIG. 2 is a conceptual diagram showing a scaler of the present invention that applies the on-board calibration method shown in FIG. 1 .

Figure 3 is a flow chart of a partial aperture factor measurement method of the on-board calibration mechanism of the present invention.

Figure 4 is a schematic optical path diagram showing the linear relationship used in establishing the linear relationship between the response count values of the radiometer and the remote sensor in step 301. It is a top view along the y-axis.

FIG. 5 is a schematic diagram showing the definition of BRDF.

Figure 6 is a measurement principle diagram of step 303.

FIG. 7 is a schematic block diagram of a device applying the partial aperture factor measurement method of the on-board calibration mechanism of the present invention.

Detailed ways

Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

In the following embodiments, when numbers and the like (including numbers, numerical values, amounts, ranges, etc.) of elements are mentioned, they are not referred to except when it is particularly clearly stated and when it is clearly limited to a specific number in principle. Limited to the specific number, it can be above or below the specific number. In this application, the expressions "consisting of" or "consisting of" only represent the main components and do not exclude the inclusion of other components.

In addition, in the following embodiments, the structural elements (including step elements, etc.) are not necessarily indispensable except when it is particularly clearly stated or when it is clearly understood to be necessary from a principle, and the description may also be included. elements not explicitly mentioned in .

The implementation described in this specification is only a fully described example and does not limit the protection scope of the present invention. Based on the implementation of the present invention, those skilled in the art can obtain all other implementations without exerting creative work. All belong to the protection scope of the present invention.

[Embodiment]

With the development of on-board calibration over the years, currently the calibration method of "sunlight + diffuse reflection plate" can achieve the highest calibration accuracy. This is because the sun is considered a stable light source all year round, but direct observation of the sun by a remote sensor will damage the remote sensor. The measurement accuracy of the diffuse reflector can reach a very high level due to its Bidirectional Reflectance Distribution Function (BRDF). High level, so the radiance observed by the remote sensor can be accurately calculated using "sun + diffuse reflector".

Figure 1 is a schematic diagram showing the principle of the on-satellite calibration method based on the diffuse reflection plate.

As shown in Figure 1, this calibration method uses the sun S, which is relatively stable all year round, as the light source, uses the diffuse reflection plate 101 to reflect sunlight as the standard radiance source, and the remote sensor (detector 102) observes the diffuse reflection of known radiance. The board 101 establishes the relationship between the physical quantity and the count value, and determines the radiation calibration coefficient.

In addition, the diffuse reflector 101 is affected by ultraviolet radiation and space particles in the space environment, and its reflection characteristics will decline, so that the BRDF of the diffuse reflector measured in the laboratory cannot be used to calculate the radiance of the diffuse reflector after running for a period of time. . Therefore, as shown in FIG. 1 , a solar diffuse reflector reflectance calibrator (hereinafter referred to as a specific radiometer, SDRDM) 102 for monitoring the stability of the diffuse reflector 101 is also configured.

FIG. 2 is a conceptual diagram showing a scaler of the present invention that applies the on-board calibration method shown in FIG. 1 .

In Figure 2, corresponding to Figure 1, the calibrator (i.e. on-board calibration mechanism) 200 is composed of a calibration box 201, a diffuse reflection plate 202, a radiometer 203 and a partial aperture diaphragm 204. The dotted box in the figure Representing the remote sensor optical system 205, the calibrator 200 is configured to enable the calibration box 201 to be externally mounted on the remote sensor. The specific structure of the remote sensor optical system 205 is not directly related to the present invention and will not be mentioned here.

The cross-section of the calibration box 201 is roughly in the shape of a rectangle with one corner cut off (a quasi-triangular shape). The surfaces constituting the calibration box 201 mainly include two surfaces that are perpendicular to each other in the cross-sectional view of Figure 2, namely the light-incoming surface 2011 and the light-emitting surface 2012. , as well as Bevel 2013, the inner surface of each facet is coated with a matt coating. The light entrance surface 2011 and the light exit surface 2012 are respectively provided with an entrance opening and an exit opening. The partial aperture diaphragm 204 is provided at the exit opening so that the light path enters the entrance pupil of the remote sensor with a designated aperture. The diffuse reflection plate 202 is made of polytetrafluoroethylene material, quartz material, etc., is arranged on the slope 2013 through mounting accessories inside the calibration box 201, and is installed at a predetermined angle with respect to the incident light. Therefore, the parallel incident light from the sun is incident into the scaler 200 through the incident opening. After diffuse reflection occurs on the diffuse reflection plate 202, a part of the reflected light is incident into the remote sensor optical system 205 through the partial aperture diaphragm 204.

In addition to the incident opening, the light incident surface 2011 is also provided with an opening for a radiometer. As shown in FIG. 2 , a radiometer 203 using a double-port symmetrical monitoring method is provided near the intersection of the light incident surface 2011 and the light exit surface 2012 in the calibration box 201 . The radiometer 203 has a solar observation port 2031 and a diffuse reflection plate observation port 2032. The solar observation port 2031 faces the sunlight side and can observe the incident light incident on the diffuse reflection plate 202 from the radiometer opening of the calibration box 201. For the same sunlight, the observation port 2032 of the diffuse reflector faces the side of the diffuse reflector. Therefore, the sun is observed through the solar observation port 2031 to monitor the detector response of the radiometer, and the diffuse reflector is observed through the diffuse reflector observation port 2032 to monitor the detector response of the radiometer and the reflectance product of the diffuse reflector. The monitored ratio can be used to monitor the reflectivity of the diffuse reflection plate.

Therefore, by accurately measuring the BRDF of the diffuse reflector before launch, and monitoring the reflectivity of the diffuse reflector before launch and in orbit to correct the BRDF in real time since the moment when the BRDF is measured, sufficiently high calibration accuracy can be further ensured. .

However, the structure of the scaler 200 described here is only an example and does not limit the scope of the present invention. For example, the shape of the calibration box and the material of the diffuse reflection plate are not limited to the above description.

As mentioned above, when measuring part of the aperture factor of a calibrator, the main method currently used requires cutting the hyperspectrometer into the calibration and imaging optical path. However, it is difficult to ensure that the direction of the radiation source measured by the hyperspectrometer is consistent with that of the remote sensor, regardless of whether it is inserted into the calibration or imaging light path, and some aperture factor measurements cannot be performed until the remote sensor is assembled. Cutting the hyperspectrometer into the optical path may cause the probe to touch Risk of calibration system failure due to scattering optical surfaces.

To this end, the present invention proposes a new method for measuring the partial aperture factor of the on-board calibration mechanism.

Figure 3 is a flow chart of part of the aperture factor measurement method of the on-board calibration mechanism of the present invention, including: (step 301) establishing a linear relationship between the response count values of the radiometer and the remote sensor in observing the same radiation source at different energy levels. , (Step 302) Establish the relative proportional relationship between the BRDF of the radiometer observation direction and the remote sensor observation direction under the same lighting conditions based on the BRDF measurement data of the diffuse reflector laboratory. (Step 303) Use the ratio in the calibrator under the same lighting angle. The count value of the diffuse reflector observed by the radiometer is used to estimate the full aperture response count value of the remote sensor when the same radiation is input, and the aperture factor is calculated based on the actual measurement count value of the remote sensor's own calibration optical path.

That is, the present invention simulates the full aperture response value of the remote sensor with the same radiation input based on the measured response count value of the radiometer, so that the aperture factor can be measured compared with the actual measured response count value of the remote sensor.

Therefore, by adopting the method of the present invention, partial aperture factor measurement of partial aperture full optical path calibration can be indirectly achieved without introducing external instruments to cut into the optical path to assist measurement, thereby reducing measurement difficulty and measurement risk. Among them, the present invention uses the specific radiometer originally equipped with the on-board calibration mechanism, which is usually used to monitor the reflectivity of the diffuse reflection plate, as a reference radiometer to achieve partial aperture factor measurement, especially in the above-mentioned step 303. When the calibration device and the remote sensor are integrated and assembled, there is no need to insert external instruments in the calibration optical path of the remote sensor, which can improve stability and simplify the structure and measurement steps.

The following takes the scaler (ie, the on-board calibration mechanism) 200 shown in FIG. 2 as an example to specifically describe the implementation of the partial aperture factor measurement method of the scaler.

(1) Step 301

In step 301, a linear relationship between the response count values observed by the radiometer and the remote sensor under different energy levels of the same radiation source is established.

Figure 4 is a schematic optical path diagram showing the linear relationship used in establishing the linear relationship between the response count values of the radiometer and the remote sensor in step 301. It is a top view along the y-axis.

As shown in Figure 4, a remote sensor 401, a radiometer 402 and a large-aperture integrating sphere radiation source 403 are arranged in the optical path. It should be noted that since the purpose of the present invention is to measure part of the aperture factor of the scaler 200 in Figure 2, the remote sensor 401 is the part shown as 205 in Figure 2, and the radiometer 402 is the part shown in Figure 2 Radiometer 203. However, at the stage of step 301, although the remote sensor has been assembled, the radiometer has not yet been assembled into the calibrator, so for convenience of explanation, different reference numbers are used here.

The large-diameter integrating sphere radiation source 403 is used to simulate the reflected radiance of the diffuse reflector on the satellite. In this embodiment, the interior is a cavity, and for example, a high reflectivity polytetrafluoroethylene material is integrally formed to form a diffuse reflection layer on the inner surface, and a halogen lamp 404 is used as the light source. The light emitted by the halogen lamp 404 undergoes multiple reflections in the integrating sphere, and a Lambertian surface light source with a uniform, wide spectral range and a relatively flat spectrum is obtained at the exit port (for the convenience of illustration, only the parallel emergent light is drawn in the figure) . Moreover, combined with a high-precision regulated DC power supply (not shown), the radiation source can have high stability, high uniformity and multiple energy levels.

As shown in Figure 4, the remote sensor 401 is aligned with (the exit port of) the large-aperture integrating sphere radiation source 403. At the same time, the specific radiometer 402 is configured on a moving mechanism such as a translation platform or a lifting platform (not shown) that can translate or lift in the direction shown by the arrow (perpendicular to the light emission direction of the radiation source), so that the specific radiometer 402 can move in a short period of time. Flexible switching in and out of the radiation measurement optical path within a certain time period. Moreover, the radiometer 402 is arranged in such a direction that when the radiometer 402 is cut into the radiation measurement optical path through a translation stage or a lifting stage, its diffuse reflection plate observation port can be aligned with the large-aperture integrating sphere radiation source 403.

In step 301, the optical path shown in Figure 4 is used to adjust the radiation energy level by adjusting the power supply of the large-diameter integrating sphere radiation source 403, and simultaneously obtain the response values of the remote sensor 401 and the radiometer 402 at multiple energy levels. The pure response value relationship between the two at different energy levels is established according to the linear regression equation, as shown in equation (1).

C′ _imf (B _j )＝aC _SDRDM,t (B _j )+b (1)

Since each parameter in the formula will be used in the following formula (3), its meaning is shown in the description of the following formula (3).

Here, regarding the different energy levels of the large-aperture integrating sphere radiation source 403, this embodiment does not need to be specifically limited, and it can be any energy level and number of energy levels that a person skilled in the art can think of and implement.

(2) Step 302

In step 302, a relative proportional relationship between the BRDF of the radiometer observation direction and the remote sensor observation direction under the same lighting conditions is established based on the BRDF measurement data of the diffuse reflector laboratory.

The on-board calibration technology based on the diffuse reflector uses the diffuse reflector to reflect sunlight to form a uniform surface light source that is approximately Lambertian. In order to calculate the radiance, the BRDF of the diffuse reflector needs to be used. Therefore, the accuracy of the BRDF used on the diffuse reflector satellite is a key factor in ensuring calibration accuracy.

Here, BRDF (Bidirectional Reflectance Distribution Function) is used to describe the scattering characteristics of a surface within a range of incident illumination angles and reflection angles. It is defined as shown in Figure 5. When a beam of light irradiates a surface, along θ _r , The spectral radiance of internal reflection per unit solid angle in the direction and along θ _i ,/> The ratio of the increment of reflected radiance per unit solid angle to the increment of incident irradiance. Since the sun's irradiation is considered to be stable all year round, the BFDF based on the diffuse reflector can accurately calculate the radiance observed by the remote sensor.

Before the satellite calibration based on the diffuse reflector is launched, the diffuse reflector BRDF of the solar illumination angle variation range during the on-board calibration throughout the year will be measured in the laboratory. In this implementation, the data measured in this way is called "BRDF basic data." ".

The radiometer 402 and the remote sensor 401 used in step 301 are configured in the state shown in Figure 2 when actually used on the satellite. In step 302, first, obtain the ratio in the state of actual on-orbit calibration—that is, in the state of assembling the radiometer 402 into the calibrator 200 and arranging the calibrator 200 at the entrance pupil of the remote sensor. There is a fixed geometric relationship (such as an angular relationship) between the direction in which the radiometer observes the diffuse reflector and the direction in which the remote sensor observes the diffuse reflector. Based on this relationship, the corresponding data is extracted from the BRDF basic data to calculate the relative proportion relationship BRF (Bidirectional Reflectance Factor) of the BRDF in the two exit directions at the same incident angle.

Here, regarding the fixed geometric relationship between the direction in which the radiometer observes the diffuse reflector and the direction in which the remote sensor observes the diffuse reflector, for example, the radiometer 402 can be actually assembled into the scaler 200 shown in FIG. 2 and actually configured to the remote sensor 401 The relationship is obtained above, but even if it is not actually assembled, the relationship between the two can be pre-designed, the relative proportion of BRDF can be obtained based on this relationship, and the assembly can be carried out according to the pre-designed relationship during actual assembly.

The calculated relative proportional relationship BRF between the BRDF in the above two emission directions is shown in Equation (2), which is used as a correction coefficient to calculate the difference in reflectivity of the diffuse reflection plate between the radiometer observation direction and the remote sensor observation direction.

In this formula, BRF (θ _SD ,φ _SD ,B _j ) represents the relative proportional relationship between the BRDF in the remote sensor observation direction and the radiometer observation direction BRF, f _SD,lab (θ _SD ,φ _SD ; θ _v ,φ _v ; B _j ) and f _SD,lab (θ _SD ,φ _SD ;φ _r ,φ _r ;B _j ) are respectively the BRDF values of the remote sensor observation direction and the radiometer observation direction under the same lighting conditions.

(2) Step 303

In step 303, under the same illumination angle, the count value of the diffuse reflection plate observed by the radiometer in the calibrator is used to estimate the full aperture response count value of the remote sensor when the same radiation is input, combined with the actual measurement count of the remote sensor's own calibration optical path. value to calculate the aperture factor. That is, the estimation here refers to the calculation based on one of the two emission directions (the remote sensor observation direction and the radiometer observation direction of the diffuser) at the same incident angle with respect to the diffuse reflector. The count value of the meter) is deduced from the other (the full aperture response count value of the remote sensor).

Figure 6 shows the measurement principle diagram of step 303.

As shown in FIG. 6 , the remote sensor 401 and the scaler 200 system assembled from the radiometer 402 are integrated into one body, and are arranged on the working surface of the solar simulator 601 with a small divergence angle. Adjust the posture of the remote sensor on the working surface of the solar simulator 601 so that the angle at which the diffuse reflection plate 202 of the scaler 200 is illuminated by the solar simulator 601 reaches a predetermined value. The predetermined value here is a certain angle within the specified marking time (can be arbitrary). For convenient adjustment, the predetermined value can be selected as 0° hour angle and 0° declination angle illumination. The purpose is to ensure that the radiometer and remote sensor observation directions have a known BRDF.

On this basis, the remote sensor 401 adjusts the angle of its scanning mirror 602, uses the calibration optical path and the radiometer 203 to simultaneously measure the diffuse reflector 202 illuminated by the solar simulator 601, and records the remote sensor 401 and the radiometer 203. Both instruments measure the response of a diffuse reflector at the same angle of incidence.

Based on the measured response value of the radiometer 203, the relative reflectivity is corrected according to the relative proportion of the BRDF in the two emission directions shown in equation (2) obtained in step 302, and the actual observation direction of the radiometer 203 is equivalent to the remote sensor. 401 observation direction. Then, according to the linear relationship of the response count values shown in equation (1) obtained in step 301, the full aperture response estimated count value of the remote sensor 401 and the radiometer 203 observing the same radiation source in the same direction is obtained. Finally, according to the definition of aperture factor, the actual measured response value of the calibration optical path of the remote sensor 401 is compared with the full aperture response value of the imaging optical path simulated by the radiometer, and the value of the partial aperture factor is obtained, as shown in Equation (3).

In the formula, k (B _j ) is the measured partial aperture factor; C′ _ca,p (B _j ) is the actual response count value of the diffuse reflection plate 202 measured by the calibration optical path of the remote sensor 401; C′ _im,f (B _j ) is the full aperture response count value of the remote sensor when the same radiation input is obtained based on the outgoing radiance level in the direction of the diffuse reflector observed by the radiometer and equivalently converted according to equations (1) and (2); C _SDRDM (B _j ) is the response count value of the radiometer 203 observing the diffuse reflector 202; a and b are the conversion relationship coefficients of the response count value of the radiometer and the remote sensor observing the same radiation source, the subscript j represents the band number, and B _j is used to refer to The jth band.

It should be noted that the formula (1) and formula (2) obtained in steps 301 and 302 are used in step 303, but the processing results of each other are not used in steps 301 and 302, so the order of steps 301 and 302 is not fixed. Yes, you can also perform step 302 first and then step 301.

As mentioned above, by adopting the partial aperture factor measurement method of the on-board calibration mechanism of the present invention, the partial aperture factor measurement of the partial aperture full optical path calibration is indirectly realized without introducing external instruments to cut into the optical path to assist the measurement, thereby reducing the cost. Measurement difficulty and measurement risk.

Moreover, this method uses the existing BRDF basic data and the linear change law of the response of the radiometer and the remote sensor to simulate the full aperture response value of the remote sensor's full aperture with the same radiation input by measuring the response count value of the radiometer.

In addition, the measurement process of this method is closer to the actual use state than the traditional measurement method, simplifying the measurement process and improving reliability, and the measurement uncertainty is smaller. Therefore, it can ultimately provide a solution for the realization of high-frequency sub-satellite radiation calibration for medium and large remote sensors, and at the same time contribute to improving the calibration accuracy of on-satellite calibration.

Moreover, the present invention uses the specific radiometer originally equipped with the on-board calibration mechanism, which is usually used to monitor the reflectivity of the diffuse reflection plate, as a reference radiometer to achieve partial aperture factor measurement, especially in the above-mentioned step 303. When the calibration device and the remote sensor are integrated and assembled, there is no need to insert external instruments in the calibration optical path of the remote sensor, which can improve stability and simplify the structure and measurement steps.

Figure 7 is a schematic block diagram of a device 700 that applies the partial aperture factor measurement method of the on-board calibration mechanism of the present invention.

As shown in Figure 7, the device 700 includes a first module 701, a second module 702 and a third module 703. The processing results of the first module 701 and the second module 702 are output to the third module 703 for use.

Specifically, the processing performed in the first module 701 corresponds to step 301, that is, obtaining the response values of the remote sensor 401 and the radiometer 402 at multiple energy levels of the optical path shown in Figure 4, and establishing the relationship between the radiometer and the remote sensor. Observe the linear relationship between the response count values of the same radiation source at different energy levels.

The processing performed in the second module 702 corresponds to step 302, that is, establishing the same illumination based on the pre-obtained BRDF measurement data of the diffuse reflector laboratory and the relationship between the direction of the diffuse reflector observed by the radiometer and the direction of the diffuse reflector observed by the remote sensor. The relative proportional relationship between the BRDF of the radiometer observation direction and the remote sensor observation direction under certain conditions.

The processing performed in the third module 703 corresponds to step 303, that is, obtaining the count value of the diffuse reflector observed through the radiometer in the calibrator and the calibration light path of the remote sensor itself at the same illumination angle, based on the count value of the radiometer. Calculate the full aperture response count value of the remote sensor when receiving the same radiation input, and calculate the aperture factor based on the measured count value of the remote sensor's own calibration optical path.

Therefore, by using the device 700 of the present invention, the same effect as the above-mentioned partial aperture factor measurement method can be achieved.

In addition, it should be understood that each module in the device 700 can be implemented by a computer executing a prescribed program, or can be implemented by hardware through integrated circuit design, and the present invention has no limitations on this.

Table 1

Table 1 above gives the verification experimental data of part of the aperture factor measurement method of the present invention, which is the measurement result of the aperture factor in three bands (450nm, 550nm, 750nm) of a certain remote sensor. According to the data in the table, for each band, the repeatability of the test equipment when turned on twice is better than 0.26%, which fully proves that the partial aperture factor measurement method of the present invention has the above-mentioned "improved reliability, and measurement uncertainty" "smaller" technical effect.

Industrial applicability

The invention is suitable for partial aperture factor measurement of the on-board calibration mechanism of the satellite-borne remote sensor.

Claims (9)

1. A method for measuring partial aperture factor of on-board calibration mechanism for on-orbit radiometric calibration of remote sensor comprises diffuse reflection plate and specific radiometer for monitoring reflectivity of diffuse reflection plate,

the partial aperture factor measurement method is characterized by comprising the following steps:

the method comprises the steps that a linear relation of response count values of the specific radiometer and the remote sensor under different energy level states of the same radiation source is established;

the second step, according to the pre-acquired BRDF basic data of the diffuse reflection plate, establishing a BRDF relative proportion relation between the diffuse reflection plate observation direction of the specific radiometer and the diffuse reflection plate observation direction of the remote sensor under the same illumination condition, wherein the BRDF basic data is obtained by measuring the BRDF of the diffuse reflection plate in the solar illumination angle change range in the whole-year on-satellite calibration time in a laboratory; and

and thirdly, obtaining response count values of the specific radiometer and the diffuse reflection plate observed by the calibration light path of the remote sensor under the same illumination angle, calculating the full aperture response count value of the remote sensor during the same radiation input based on the obtained response count value of the specific radiometer, and calculating partial aperture factors of the on-board calibration mechanism by combining the obtained response count values of the calibration light path of the remote sensor.

2. The partial aperture factor measurement method according to claim 1, wherein:

in the first step, the remote sensor is used for observing the radiation source for simulating the reflection radiance of the satellite diffuse reflection plate, the specific radiometer is switched into/out of a radiation measuring light path of the remote sensor through a moving mechanism,

and measuring the response count values of the remote sensor and the specific radiometer while changing the energy level of the radiation source, and establishing the linear relation according to a linear regression equation based on the measured response count values.

3. The partial aperture factor measurement method according to claim 1 or 2, characterized in that:

the radiation source is a large-caliber integrating sphere radiation source with an emergent port forming a lambertian surface light source.

4. The partial aperture factor measurement method of claim 3, wherein:

the large-caliber integrating sphere radiation source uses a halogen lamp as a light source, and adopts polytetrafluoroethylene to be integrally molded to form a diffuse reflection layer on the inner surface of the large-caliber integrating sphere radiation source.

5. The partial aperture factor measurement method according to claim 1, wherein:

in the second step, a known geometrical relationship between the diffuse reflection plate observation direction of the specific radiometer and the diffuse reflection plate observation direction of the remote sensor in the actual on-orbit calibration state of the on-satellite calibration mechanism is obtained, and based on the obtained relationship, the corresponding data is extracted from the BRDF basic data to calculate the BRDF relative proportional relationship.

6. The partial aperture factor measurement method according to claim 1, wherein:

in the third step, the on-board calibration mechanism is assembled by using the specific radiometer and the diffuse reflection plate, and then the on-board calibration mechanism is assembled with the remote sensor in an integrated way, and the diffuse reflection plate is illuminated by a solar simulator, so that a calibration light path of the remote sensor and a response count value of the diffuse reflection plate under the condition that the specific radiometer observes the same incidence angle are obtained.

7. The partial aperture factor measurement method as recited in claim 6, further comprising:

using the BRDF relative proportion relation obtained in the second step, equivalent the response count value of the diffuse reflection plate illuminated by the solar simulator observed by the radiometer to the diffuse reflection plate observation direction of the remote sensor, and using the linear relation obtained in the first step, obtaining the full aperture response count value of the remote sensor during the same radiation input,

and calculating the partial aperture factor based on the obtained full aperture response count value of the remote sensor during the same radiation input and the obtained response count value of the diffuse reflection plate illuminated by the solar simulator observed by the calibration light path of the remote sensor.

8. The partial aperture factor measurement method according to claim 1, wherein:

the on-board calibration mechanism is used for arranging the specific radiometer and the diffuse reflection plate in a calibration box, and a part of aperture diaphragms are arranged on the surface of the calibration box on the light emergent side, so that light reflected by the diffuse reflection plate enters the entrance pupil of the remote sensor in a specified aperture.

9. The partial aperture factor measuring device of the on-board calibration mechanism is used for carrying out on-orbit radiometric calibration on the remote sensor on board and comprises a diffuse reflection plate and a specific radiometer for monitoring the reflectivity of the diffuse reflection plate,

the partial aperture factor measuring device is characterized by comprising:

the first module is used for establishing a linear relation of response count values of the specific radiometer and the remote sensor under the state that the specific radiometer and the remote sensor observe different energy levels of the same radiation source;

the second module establishes a BRDF relative proportion relation between the diffuse reflection plate observation direction of the specific radiometer and the diffuse reflection plate observation direction of the remote sensor under the same illumination condition according to the BRDF basic data of the diffuse reflection plate, wherein the BRDF basic data is obtained by measuring the BRDF of the diffuse reflection plate in the solar illumination angle change range in the on-satellite calibration time of the whole year in a laboratory; and

and a third module for obtaining the response count value of the diffuse reflection plate observed by the calibration light path of the ratio radiometer and the remote sensor under the same illumination angle, calculating the full aperture response count value of the remote sensor during the same radiation input based on the obtained response count value of the ratio radiometer, and calculating the partial aperture factor of the on-board calibration mechanism by combining the obtained response count value of the calibration light path of the remote sensor.