CN114216559B - Partial aperture factor measuring method and device for on-board calibration mechanism - Google Patents
Partial aperture factor measuring method and device for on-board calibration mechanism Download PDFInfo
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Abstract
The application provides a method and a device for measuring a partial aperture factor of an on-board calibration mechanism, which can accurately measure the partial aperture factor of the calibration mechanism without cutting an external instrument into a calibration or imaging light path of a remote sensor. The method comprises the following steps: and establishing 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, establishing a BRDF relative proportion relation between the specific radiometer observation direction and the remote sensor observation direction under the same illumination condition according to BRDF measurement data of the diffuse reflection plate laboratory, calculating a full aperture response count value of the remote sensor under the same radiation input through the count values of the specific radiometer observation diffuse reflection plate in the scaler under the same illumination angle, and calculating an aperture factor by combining the actual measurement count values of a self-scaling light path of the remote sensor.
Description
Technical Field
The application relates to a space-borne remote sensor radiometric calibration technology, in particular to a partial aperture factor measurement method of a space-borne calibration mechanism and a device applying the method.
Background
With the social development, the requirements of people on geological survey, weather forecast and the like become high, so that the high-precision quantitative remote sensing of satellites is urgently needed. And the remote sensing data quantification level can be ensured by carrying out radiometric calibration on the satellite-borne remote sensor, so that the service performance of the remote sensor is improved.
Radiometric calibration is generally defined as determining the radiation performance of an instrument in the spatial, temporal, spectral domain during a series of measurements, the output of which is a value related to the actual radiant energy measurement.
Radiometric calibration can be classified into pre-transmit calibration and on-orbit calibration. Because of vibration, acceleration shock and differences between the on-orbit and ground environments when remote sensors are transmitting, the system parameters measured before transmitting will no longer apply as the on-orbit time becomes longer, and thus on-orbit on-satellite calibration is required to periodically correct laboratory calibration coefficients.
However, the on-board calibration mechanism is affected by many factors such as power consumption, volume, weight, etc., and cannot adopt an excessively complex or heavy structure, and the design simplification is very important. For example, when the calibration mechanism is configured for a large-caliber remote sensor or the overall structure of the remote sensor is limited and cannot realize full-aperture calibration, the remote sensor Quan Kongjing calibration coefficient can be obtained through partial aperture calibration measurement by adopting a partial aperture full-optical path on-board calibration method based on a diffuse reflection plate. The space of the calibration mechanism is reduced by sacrificing the complexity of the on-board calibration mechanism and the physical model thereof, so that on-board calibration can be realized under the condition that the available space of the large-caliber remote sensor or the remote sensor is insufficient and limited.
Advanced baseline imagers (Advanced Baseline Imager, ABI) carried by GOES-16 in the United states and wind cloud No. four multichannel scanning imaging radiometers (Advanced Geostationary Radiation Imager, AGRI) in China all adopt a partial aperture full optical path on-satellite calibration scheme. Wherein the measurement of the partial aperture factor is the key to determine whether the scaling scheme is viable or not, and its measurement uncertainty is also the source of the greatest uncertainty affecting the final on-star scaling.
Disclosure of Invention
Technical problem to be solved by the application
The ground imaging of the remote sensor observation is in a full aperture mode, and the diffuse reflection plate of the remote sensor observation is calibrated into a partial aperture mode, so that the guiding thought of measuring the partial aperture is to observe the same radiance source in two modes for comparison, and thus the partial aperture factor is calculated.
Thus, ideally, the same radiation source provides radiation input to the remote sensor calibration optical path and the imaging optical path respectively, and in the case of better remote sensor response linearity, the partial aperture factor can be expressed as the ratio of the calibration optical path response count value to the response count value of the imaging optical path.
At present, the partial aperture factor measurement mainly comprises the steps of simultaneously measuring and obtaining response values of a calibration light path and an imaging light path of a hyperspectral instrument cut into a remote sensor and the remote sensor respectively, correcting the radiation response of the two light paths into the same radiation input by taking the spectral radiance measured by the hyperspectral instrument as a reference, and the ratio of the count values of the two light paths in the state is the partial aperture factor of partial aperture calibration. The final measurement of the partial aperture factor should be performed after the remote sensor is assembled, which belongs to the parameters that can not be obtained by the system level measurement.
However, in the measurement process, the hyperspectral probe is difficult to cut into a calibration or imaging light path to ensure that the direction of a measured radiation source is consistent with that of the remote sensor, and the remote sensor after assembly is in the process of cutting the hyperspectral probe into the calibration light path, the risk of failure of the calibration system caused by touching the optical surface of the scatterer is also caused, the measurement efficiency is low, the repeated stability of the measurement result is poor, and the difference between the actual application state of the remote sensor and the actual application state of the remote sensor is large.
Aiming at the problems in the prior art, the application provides a partial aperture factor measuring method of an on-board calibration mechanism, which can accurately measure partial aperture factors of the calibration mechanism without cutting into a hyperspectral instrument in a calibration or imaging light path of a remote sensor, can improve the measuring efficiency of the partial aperture factors and the stability of a measuring result, is closer to the actual application state of the remote sensor, and finally contributes to improving the calibration precision of on-board calibration. In particular, the specific radiometer which is commonly used for monitoring the reflectivity of the diffuse reflection plate in the on-board calibration mechanism is used for measuring part of aperture factors, so that the stability can be improved, the structure can be simplified, and the measuring steps can be simplified.
Technical means for solving the problems
The application provides a partial aperture factor measuring method of an on-board calibration mechanism, which is used for carrying out on-orbit radiometric calibration on a remote sensor on board, and comprises a diffuse reflection plate and a specific radiometer for monitoring the reflectivity of the diffuse reflection plate, wherein the method comprises 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 BRDF basic data of the diffuse reflection plate obtained in advance, establishing the 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 lighting condition; and a third step of obtaining response count values of the diffuse reflection plate observed by the calibration light paths of the specific radiometer and the remote sensor under the same illumination angle, calculating a 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 paths of the remote sensor.
In the partial aperture factor measurement method of the present application, in the first step, the radiation source for simulating the reflection radiance of a satellite diffuse reflection plate is observed by the remote sensor, the specific radiometer is cut into/out of a radiation measurement light path of the remote sensor by a moving mechanism, the respective response count values of the remote sensor and the specific radiometer are measured while changing the energy level of the radiation source, and the linear relation is established according to a linear regression equation based on the measured response count values.
In the partial aperture factor measurement method of the present application, in the second step, a relationship between the diffuse reflection plate observation direction of the radiometer and the diffuse reflection plate observation direction of the remote sensor in the on-orbit calibration state of the on-satellite calibration mechanism is obtained, and based on the obtained relationship, the BRDF relative proportional relationship is calculated by extracting corresponding data from the BRDF basic data.
In the third step, the on-board calibration mechanism is formed by assembling 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 incident angle are obtained.
And using the BRDF relative proportion obtained in the second step, equating 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, obtaining a full aperture response count value of the remote sensor at the same radiation input time by using the linear relation obtained in the first step, and calculating the partial aperture factor based on the obtained full aperture response count value of the remote sensor at the same radiation input time 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.
The application also provides a partial aperture factor measuring device of an on-board calibration mechanism, wherein the on-board calibration mechanism is used for carrying out on-orbit radiometric calibration on a remote sensor on board, and comprises a diffuse reflection plate and a specific radiometer for monitoring the reflectivity of the diffuse reflection plate, and the device comprises: 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 lighting condition according to the BRDF basic data of the diffuse reflection plate, which is obtained in advance; 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.
Effects of the application
The partial aperture factor measuring method and the device of the on-board calibration mechanism can accurately measure the partial aperture factor of the calibration mechanism without cutting into a hyperspectral instrument in the calibration or imaging light path of the remote sensor, can improve the measuring efficiency of the partial aperture factor and the stability of a measuring result, are more similar to the real application state of the remote sensor, and finally provide a solution for realizing the high-frequency on-board radiometric calibration of the medium-to-large remote sensor, and simultaneously contribute to improving the calibration precision of the on-board calibration. In particular, the ratio radiometer commonly used for monitoring the reflectivity of the diffuse reflection plate in the on-board calibration mechanism is used as a reference radiometer to realize partial aperture factor measurement, so that the stability can be improved, the structure can be simplified, and the measurement steps can be simplified.
Drawings
Fig. 1 is a schematic diagram showing the principle of the on-board calibration method based on the diffuse reflection plate.
Fig. 2 is a conceptual diagram illustrating a scaler of the present application to which the on-satellite scaling scheme shown in fig. 1 is applied.
FIG. 3 is a flow chart of a partial aperture factor measurement method of the on-board calibration mechanism of the present application.
Fig. 4 is a schematic light path diagram showing the use of the linear relationship of the response count values of the radiometer and the remote sensor in step 301, which is a top view along the y-axis.
Fig. 5 is a schematic diagram showing BRDF definitions.
Fig. 6 is a measurement schematic diagram of step 303.
Fig. 7 is a schematic block diagram of an apparatus to which the partial aperture factor measurement method of the on-board calibration mechanism of the present application is applied.
Detailed Description
The following describes specific embodiments of the present application with reference to the drawings.
In the following embodiments, when reference is made to a number or the like (including a number, a value, an amount, a range, and the like) of an element, the number is not limited to the specific number except for a case where the number is specifically described and a case where the number is obviously limited to the specific number in principle, and the number may be more or less than the specific number. In the present application, the expression "constituted by … …" or "constituted by … …" merely indicates the main constituent elements, and does not exclude other elements.
In the following embodiments, the constituent elements (including the step elements) are not necessarily essential except those specifically described and those obviously understood to be essential in principle, and may include elements not explicitly mentioned in the specification.
The embodiments described in the present specification are only examples of a complete description and do not limit the scope of the present application, and all other embodiments that can be obtained by a person skilled in the art without any inventive effort based on the embodiments of the present application are within the scope of the present application.
Embodiment(s)
With the development of years, the on-board calibration can realize the highest calibration precision in a calibration mode of sunlight and diffuse reflection plate at present. This is because the sun is considered as a stable light source throughout the year, but direct observation of the sun by a remote sensor damages the remote sensor, and the diffuse reflection plate can accurately calculate the radiance observed by the remote sensor by using the "sun+diffuse reflection plate" because the measurement accuracy of the bi-directional reflection distribution function (Bidirectional Reflectance Distribution Function, BRDF) can already reach a high level.
Fig. 1 is a schematic diagram showing the principle of the on-board calibration method based on the diffuse reflection plate.
As shown in fig. 1, in this calibration method, sun S, which is relatively stable throughout the year, is used as a light source, sunlight reflected by diffuse reflection plate 101 is used as a standard radiance source, and a remote sensor (detector 102) observes that diffuse reflection plate 101 with known radiance establishes a relationship between a physical quantity and a count value, and determines a radiance calibration factor.
In addition, the diffuse reflection plate 101 is affected by ultraviolet radiation, space particles and the like in a space environment, and the reflection characteristics of the diffuse reflection plate are degraded, so that the diffuse reflection plate BRDF measured in a laboratory cannot be suitable for calculating the radiance of the diffuse reflection plate after the diffuse reflection plate BRDF runs for a period of time. Therefore, a solar diffuse reflection plate reflectance calibrator (hereinafter referred to simply as a specific radiometer, SDRDM) 102 for monitoring the stability of the diffuse reflection plate 101 is also provided as shown in fig. 1.
Fig. 2 is a conceptual diagram illustrating a scaler of the present application to which the on-satellite scaling scheme shown in fig. 1 is applied.
In fig. 2, corresponding to fig. 1, a scaler (i.e., an on-board scaling mechanism) 200 is composed of a scaling tank 201, a diffuse reflection plate 202, a radiometer 203, and a partial aperture stop 204, in which a dashed box represents a remote sensor optical system 205, and the scaler 200 is configured to enable the scaling tank 201 to be externally hung to a remote sensor. The specific structure of the remote sensor optical system 205 is not directly relevant to the present application and is not described herein.
The cross section of the calibration box 201 is substantially rectangular (triangular-like) with one corner cut away, and the surfaces constituting the calibration box 201 mainly include two mutually perpendicular surfaces, namely, a light incident surface 2011 and a light emergent surface 2012 in the cross section of fig. 2, and inclined surfaces 2013, the inner surfaces of which are coated with a matting coating. The light incident surface 2011 and the light emergent surface 2012 are respectively provided with an incident opening and an emergent opening. A portion of the aperture stop 204 is positioned at the exit opening to allow the light path to enter the remote sensor entrance pupil at a specified aperture. The diffuse reflection plate 202 is made of polytetrafluoroethylene material, quartz material, or the like, and is disposed on the inclined surface 2013 by a mounting fitting inside the calibration box 201, and is mounted at a predetermined angle with respect to the incident light. Then, parallel incident light from the sun enters the scaler 200 through the entrance opening, and after being diffusely reflected by the diffusely reflecting plate 202, a part of the reflected light enters the remote sensor optical system 205 through the partial aperture stop 204.
The light incident surface 2011 is provided with an opening for a specific radiometer in addition to the incident opening. As shown in fig. 2, a specific radiometer 203 using a dual-port symmetry monitoring method is provided near a portion where a light incident surface 2011 and a light emergent surface 2012 in a calibration box 201 intersect. The radiometer 203 has a solar observation port 2031 and a diffuse reflection plate observation port 2032, and the solar observation port 2031 faces the sunlight side, and can observe the same sunlight as the incident light on the diffuse reflection plate 202 from the radiometer opening of the calibration box 201, and the diffuse reflection plate observation port 2032 faces the diffuse reflection plate side. Then, the monitoring of the detector response of the specific radiometer is realized by observing the sun through the sun observation port 2031, the monitoring of the product of the detector response of the specific radiometer and the diffuse reflection plate reflectivity is realized by observing the diffuse reflection plate through the diffuse reflection plate observation port 2032, and the monitoring of the diffuse reflection plate reflectivity can be realized by the ratio of the two monitoring.
Therefore, by accurately measuring the BRDF of the diffuse reflection plate before transmitting and monitoring the reflectivity of the diffuse reflection plate before transmitting and during on-track to correct the BRDF in real time from the moment of measuring the BRDF, the sufficiently high calibration accuracy can be further ensured.
However, the structure of the scaler 200 described herein is merely an example, and the scope of the present application is not limited thereto, and the shape of the scaler case and the material of the diffuse reflection plate are not limited thereto.
As previously mentioned, currently, the method mainly employed in measuring part of the aperture factor of the sealer requires cutting the hyperspectral meter into the scaling and imaging light path. However, it is difficult to ensure that the direction of the radiation source measured by the hyperspectral spectrometer is consistent with that of the remote sensor no matter the hyperspectral spectrometer is cut into the calibration or imaging light path, and the measurement of part of aperture factors is required to be carried out after the remote sensor is assembled, and the risk that the calibration system is disabled due to the fact that a probe touches the optical surface of a scatterer when the hyperspectral spectrometer is cut into the light path is possibly caused.
Therefore, the application provides a novel method for measuring the partial aperture factor of the on-board calibration mechanism.
FIG. 3 is a flow chart of a partial aperture factor measurement method of the on-board calibration mechanism of the present application, comprising: the method comprises the steps of (301) establishing a linear relation of response count values of a specific radiometer and a remote sensor under different energy level states of the same radiation source, (302) establishing a relative proportion relation of BRDF (binary-coded decimal) of the specific radiometer observation direction and the remote sensor observation direction under the same illumination condition according to BRDF measurement data of a diffuse reflection plate laboratory, (303) calculating a full-aperture response count value of the remote sensor under the same illumination angle by comparing count values of the specific radiometer observation diffuse reflection plate in a scaler, and calculating an aperture factor by combining actual measurement count values of a scaling optical path of the remote sensor.
That is, the present application simulates the full aperture response value of the remote sensor full aperture and the radiation input based on the specific radiometer measurement response count value, thereby being able to measure the aperture factor compared with the remote sensor actual measurement response count value.
Therefore, by adopting the method of the application, the measurement of the partial aperture factor of the partial aperture full-optical path calibration can be indirectly realized under the condition of not introducing an external instrument to cut into the optical path for auxiliary measurement, thereby reducing the measurement difficulty and the measurement risk. The present application uses the specific radiometer originally equipped in the on-board calibration mechanism and commonly used for monitoring the reflectivity of the diffuse reflection plate as the reference radiometer to realize the measurement of the partial aperture factor, especially in the step 303, when the calibration device and the remote sensor are assembled integrally, an external instrument is not needed to be cut into the calibration light path of the remote sensor, so that the stability can be improved, the structure can be simplified, and the measurement step can be simplified.
An embodiment of a partial aperture factor measurement method of the scaler (i.e., an on-board scaling mechanism) 200 shown in fig. 2 will be specifically described below.
(1) Step 301
In step 301, a linear relationship is established with response count values for different energy level states of the same radiation source than observed by the radiometer and the remote sensor.
Fig. 4 is a schematic light path diagram showing the use of the linear relationship of the response count values of the radiometer and the remote sensor in step 301, which is a top view along the y-axis.
As shown in fig. 4, a remote sensor 401, a specific radiometer 402, and a large-caliber integrating sphere radiation source 403 are arranged in the optical path. It should be noted that, since the purpose of the present application is to measure a partial aperture factor of the scaler 200 of fig. 2, the remote sensor 401 is a portion shown as 205 in fig. 2, and the specific radiometer 402 is the specific radiometer 203 in fig. 2. However, at the stage of step 301, the remote sensor is assembled but the radiometer is not yet assembled into the scaler, and therefore different reference numerals are used herein for ease of illustration.
The large-caliber integrating sphere radiation source 403 is used for simulating the reflection radiance of the on-board diffuse reflection plate. In the present embodiment, a cavity is formed inside, and for example, a high-reflectivity polytetrafluoroethylene material is integrally molded to form a diffuse reflection layer on the inner surface, and a halogen lamp 404 is used as a light source. The light emitted by the halogen lamp 404 is reflected multiple times within the integrating sphere to obtain a uniform lambertian surface light source with a wide spectral range and a relatively flat spectrum at the exit (only parallel exit light is shown for ease of illustration). The radiation source can have high stability and high uniformity and multiple energy levels by being matched with a high-precision voltage-stabilizing direct current power supply (not shown).
As shown in fig. 4, remote sensor 401 is aligned with (the exit port of) large-caliber integrating sphere radiation source 403. Meanwhile, the radiometer 402 is disposed on a translation stage or a lifting stage (not shown) or other moving mechanism capable of translating or lifting in the direction indicated by the arrow (perpendicular to the direction of light emission from the radiation source), so that the radiometer 402 can flexibly cut into and out of the radiation measurement optical path in a short time. The specific radiation meter 402 is arranged in such a direction that, when the specific radiation meter 402 is cut into the radiation measurement optical path by the translation stage or the lift stage, the diffuse reflection plate observation port can be aligned with the large-caliber integrating sphere radiation source 403.
In step 301, the light path shown in fig. 4 is adopted, the radiation energy level is adjusted by adjusting the power supply of the large-caliber integrating sphere radiation source 403, the response values of the remote sensor 401 and the specific radiometer 402 under a plurality of energy levels are obtained, and the pure response value relationship under different energy levels of the two is established according to a linear regression equation, as shown in formula (1).
C′ imf (B j )＝aC SDRDM,t (B j )+b (1)
The meaning of each parameter in the formula (3) will be described later.
Here, the energy levels of the large-caliber integrating sphere radiation source 403 are not particularly limited, and may be any energy levels and the number of energy levels that can be realized and practiced by those skilled in the art.
(2) Step 302
In step 302, a BRDF relative proportional relationship is established between the radiometer observation direction and the remote sensor observation direction under the same illumination condition according to the BRDF measurement data of the diffuse reflection plate laboratory.
The on-board calibration technology based on the diffuse reflection plate utilizes the diffuse reflection plate to reflect sunlight to form a uniform surface light source similar to lambertian, and BRDF of the diffuse reflection plate is needed to be used for calculating the radiance. Therefore, the accuracy of the BRDF used on the diffuse reflector star is a key factor in ensuring calibration accuracy.
Here, BRDF (bidirectional reflectance distribution function) is used to describe the scattering characteristics of a surface over a range of incident illumination angles and reflection angles. Which is defined as when a beam of light is irradiated onto a surface, as shown in FIG. 5, along θ r ,Spectral radiance and edge θ of internal reflection per direction unit solid angle i ,/>The ratio of the increase in reflected radiance per unit solid angle to the increase in incident irradiance. Since the solar radiation is considered to be stable throughout the year, the BFDF based on the diffuse reflecting plate can accurately calculate the radiance observed by the remote sensor.
The diffuse reflection plate BRDF of the solar illumination angle change range in the whole-year on-satellite calibration time is measured in a laboratory before on-satellite calibration emission based on the diffuse reflection plate, and the measured data are called as BRDF basic data in the embodiment.
The radiometer 402 and remote sensor 401 used in step 301 are configured in the state shown in fig. 2 when in actual use on the satellite. In step 302, first, a fixed geometrical relationship (e.g., an angular relationship) of the direction of the diffuse reflection plate observed by the specific radiometer and the direction of the diffuse reflection plate observed by the remote sensor in the actual on-orbit calibration state, that is, in a state where the specific radiometer 402 is assembled into the calibrator 200 and the calibrator 200 is disposed at the entrance pupil of the remote sensor, is obtained. Based on this relationship, the BRDF relative proportion relationship BRF (bidirectional reflectance factor (Bidirectional Reflectance Factor)) of the two outgoing directions at the same incident angle is calculated by extracting the corresponding data from the BRDF basic data.
Here, regarding the fixed geometric relationship between the diffuse reflection plate direction observed by the radiometer and the diffuse reflection plate direction observed by the remote sensor, for example, the relationship may be obtained by actually assembling the radiometer 402 into the scaler 200 shown in fig. 2 and actually disposing it on the remote sensor 401, but even if it is not actually assembled, for example, the relationship between the two may be designed in advance, the BRDF relative ratio may be obtained from the relationship, and the assembly may be performed in accordance with the relationship designed in advance at the time of the actual assembly.
The calculated BRDF relative proportion relation BRF between the two emitting directions is shown as a formula (2), and is used as a correction coefficient for calculating the difference of reflectivity of the diffuse reflection plate between the observation direction of the radiometer and the observation direction of the remote sensor.
In the formula, BRF (θ) SD ,φ SD ,B j ) BRDF relative proportional relation BRF, f representing remote sensor observation direction and specific radiometer observation direction 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 ) BRDF values for the remote sensor observation direction and the specific radiometer observation direction under the same illumination conditions are respectively.
(2) Step 303
In step 303, the full aperture response count value of the remote sensor during the same radiation input is calculated through the count value of the specific radiometer observation diffuse reflection plate in the scaler under the same illumination angle, and the aperture factor is calculated by combining the actual measurement count value of the scaling light path of the remote sensor. That is, the estimation here means that, between two emission directions (the remote sensor observation direction and the specific radiometer observation diffusion plate direction) at the same incidence angle with respect to the diffusion plate, the other (the total aperture response count value of the remote sensor) is estimated based on one (the count value of the specific radiometer).
Fig. 6 shows a measurement schematic of step 303.
As shown in fig. 6, remote sensor 401 is integrated with scaler 200 system assembled from radiometer 402 and placed on the working surface of solar simulator 601 with a small divergence angle. The remote sensor posture is adjusted on the working surface of the solar simulator 601, so that the angle of the diffuse reflection plate 202 of the scaler 200 illuminated by the solar simulator 601 reaches a predetermined value. The predetermined value is a certain angle (can be arbitrary) in the designated marking time, and the predetermined value can be selected as 0-degree declination angle illumination for convenient adjustment. The purpose is to ensure that there is a known BRDF versus radiometer and remote sensor viewing direction.
Based on this, the remote sensor 401 measures the diffuse reflection plate 202 illuminated by the solar simulator 601 by adjusting the angle of the scanning mirror 602 by using the calibration light path and the specific radiometer 203 at the same time, and records the diffuse reflection plate response signals of the remote sensor 401 and the specific radiometer 203 under the same incident angle.
Based on the measurement response value of the specific radiometer 203, the relative reflectance correction is performed according to the BRDF relative proportional relationship between the two emission directions shown in the formula (2) obtained in step 302, and the actual observation direction of the specific radiometer 203 is equivalent to the observation direction of the remote sensor 401. Then, the linear relation of the response count value shown in equation (1) obtained in step 301 is used to obtain the estimated count value of the full aperture response of the remote sensor 401 and the specific radiometer 203, which are observed in the same direction from the same radiation source. Finally, according to the definition of the aperture factor, comparing the actual measurement response value of the calibration optical path of the remote sensor 401 with the full aperture response value of the imaging optical path simulated by the radiometer to obtain the value of the partial aperture factor, as shown in the formula (3).
Wherein k (B) j ) Is the measured partial pore size factor; c'. ca,p (B j ) Is the response count value of the diffuse reflection plate 202 actually measured by the remote sensor 401 calibration light path; c'. im,f (B j ) The total aperture response count value of the remote sensor during the same radiation input is obtained by equivalent conversion according to the emergent radiance level of the direction of the diffuse reflection plate observed by the specific radiometer and the formula (1) and the formula (2); c (C) SDRDM (B j ) A response count value of the diffuse reflection plate 202 is observed for the specific radiometer 203; a. b is a conversion relation coefficient of response count values of the same radiation source observed by the radiometer and the remote sensor, and the subscript j represents a band sequence number and B j For referring to the j-th band.
In step 303, the formulas (1) and (2) obtained in steps 301 and 302 are used, but the processing results of steps 301 and 302 are not used, and thus the order of steps 301 and 302 is not fixed, and step 302 may be executed first and then step 301 may be executed.
As described above, by adopting the partial aperture factor measurement method of the on-board calibration mechanism, the partial aperture factor measurement of the partial aperture full-optical-path calibration is indirectly realized under the condition of not introducing external instruments to cut into the optical path for auxiliary measurement, and the measurement difficulty and the measurement risk are reduced.
The method utilizes the existing BRDF basic data and the response linear change rule of the ratio radiometer and the remote sensor, and realizes the simulation of the full aperture response value of the full aperture same radiation input of the remote sensor through the measurement response count value of the ratio radiometer.
In addition, compared with the traditional measuring method, the measuring process of the method is closer to the real use state, the measuring process is simplified, the reliability is improved, and the measuring uncertainty is smaller. Therefore, a solution can be provided for realizing high-frequency on-board radiometric calibration of medium-and-large-sized remote sensors, and contribution is made to improving the calibration precision of on-board calibration.
In addition, the application uses the specific radiometer which is originally assembled by the on-board calibration mechanism and is used for monitoring the reflectivity of the diffuse reflection plate as the reference radiometer to realize the measurement of the partial aperture factor, and particularly in the step 303, when the calibration device and the remote sensor are assembled integrally, an external instrument is not needed to be cut into a calibration light path of the remote sensor, so that the stability can be improved, the structure can be simplified, and the measurement step can be simplified.
Fig. 7 is a schematic block diagram of an apparatus 700 for applying a partial aperture factor measurement method of the on-board calibration mechanism of the present application.
As shown in fig. 7, the apparatus 700 includes a first module 701, a second module 702, and a third module 703, and processing results of the first module 701 and the second module 702 are output to the third module 703 for use thereof.
Specifically, the process performed in the first module 701 corresponds to step 301, i.e., obtaining the response values of the remote sensor 401 and the specific radiometer 402 at a plurality of energy levels of the optical path shown in fig. 4, and establishing a linear relationship between the specific radiometer and the response count values of the remote sensor under different energy level states of the same radiation source.
The processing performed in the second module 702 corresponds to step 302 of establishing a BRDF relative proportional relationship under the same illumination condition between the specific radiometer observation direction and the remote sensor observation direction based on the pre-acquired diffuse reflectance plate laboratory BRDF measurement data and the relationship between the specific radiometer observation diffuse reflectance plate direction and the remote sensor observation diffuse reflectance plate direction.
The processing performed in the third module 703 corresponds to step 303, namely, obtaining the count value of the diffuse reflection plate observed through the specific radiometer and the remote sensor self-calibration light path in the scaler under the same illumination angle, calculating the full aperture response count value of the remote sensor during the same radiation input based on the count value of the specific radiometer, and calculating the aperture factor by combining the measured count value of the remote sensor self-calibration light path.
Thus, the apparatus 700 of the present application can provide the same effects as those of the partial aperture factor measurement method described above.
Furthermore, it should be understood that the modules in the apparatus 700 may be implemented by a computer executing a prescribed program, or may be implemented by hardware through an integrated circuit design, which is not limited in any way by the present application.
TABLE 1
Table 1 above presents experimental data for the validation of the partial aperture factor measurement method of the present application, which is the result of a three-band (450 nm, 550nm, 750 nm) aperture factor measurement for a particular remote sensor. According to the data in the table, the repeatability of the measurement of the repeated startup of the test equipment for each wave band is better than 0.26%, which fully proves that the partial aperture factor measurement method has the technical effects of improving the reliability and having smaller measurement uncertainty.
Industrial applicability
The method is suitable for measuring the partial aperture factors of the on-board calibration mechanism of the on-board 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.
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