CN114216559A - Partial aperture factor measuring method and device of on-satellite calibration mechanism - Google Patents
Partial aperture factor measuring method and device of on-satellite calibration mechanism Download PDFInfo
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Abstract
The invention provides a method and a device for measuring partial aperture factors of an on-satellite scaling mechanism, which can accurately measure partial aperture factors of the scaling mechanism without an external instrument cutting into a scaling or imaging light path of a remote sensor. The method comprises the following steps: the method comprises the steps of establishing a linear relation between response count values of a specific radiometer and a remote sensor for observing the same radiation source under different energy level states, establishing a BRDF relative proportion relation between a specific radiometer observation direction and a remote sensor observation direction under the same illumination condition according to BRDF measurement data of a diffuse reflection plate laboratory, calculating a full aperture response count value of the remote sensor during the same radiation input through the count value of the specific radiometer observation diffuse reflection plate in a calibrator under the same illumination angle, and calculating an aperture factor by combining the actual measurement value of a calibration light path of the remote sensor.
Description
Technical Field
The invention relates to a radiation calibration technology of a satellite-borne remote sensor, in particular to a partial aperture factor measuring method of a satellite-borne calibration mechanism and a device applying the method.
Background
With the social development, people have high requirements on geological survey, weather forecast and the like, so that the high-precision quantitative remote sensing of satellites is urgently needed. The radiometric calibration of the satellite-borne remote sensor can ensure the quantification level of remote sensing data, so that the use performance of the remote sensor is improved.
Radiometric calibration is generally defined as determining the radiation properties of an instrument in the spatial, time, and spectral domains during a series of measurements, the output of which is a value related to the actual radiation energy measurement.
Radiometric calibration can be divided into pre-emission calibration and on-track calibration. Due to vibration, acceleration shock and difference between the on-orbit environment and the ground environment when the remote sensor is launched, system parameters measured before launching are not applicable any more as the on-orbit time becomes longer, so that calibration on an orbit star is needed to regularly correct a laboratory calibration coefficient.
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 simplification of the design is very important. For example, the calibration mechanism is configured for a large-aperture remote sensor or the whole structure of the remote sensor is limited and cannot realize full-aperture calibration, and a partial-aperture full-light-path on-satellite calibration method based on a diffuse reflection plate can be adopted to obtain a full-aperture calibration coefficient of the remote sensor through partial-aperture calibration measurement. The size of the calibration mechanism is reduced by sacrificing the complexity of the satellite calibration mechanism and a physical model thereof, so that the satellite calibration can be realized under the condition that the available space of a large-caliber remote sensor or the remote sensor is insufficient and limited.
Advanced Baseline Imager (ABI) carried by GOES-16 in the United states and Advanced Geostationary Radiometer (AGRI) in China adopt a partial aperture full optical path on-board calibration scheme. The measurement of partial aperture factor is the key to determine whether the scaling scheme is feasible, and the measurement uncertainty is also the maximum uncertainty source influencing the final on-satellite scaling.
Disclosure of Invention
Technical problem to be solved by the invention
The ground imaging observed by the remote sensor is in a full aperture mode, and the diffuse reflection plate observed by the remote sensor is calibrated in a partial aperture mode, so that the guiding idea of measuring partial apertures is to compare the two modes for observing the same radiance source, and calculate partial aperture factors.
Thus, ideally, the radiation inputs are provided by the same radiation source for the remote sensor calibration and imaging paths, respectively, and in the case of good remote sensor response linearity, the fractional aperture factor can be expressed as a ratio of the calibration path response count value to the imaging path response count value.
At present, partial aperture factor measurement is mainly to cut a hyperspectral meter into a remote sensor calibration light path and an imaging light path respectively and simultaneously measure with a remote sensor to obtain response values of the two light paths, the radiation response of the two light paths is corrected to be the same radiation input by taking the spectrum radiance measured by the hyperspectral meter as a reference, and the ratio of the count values of the two light paths in the state is the partial aperture factor for partial aperture calibration. The final measurement of part of the aperture factors should be carried out after the remote sensor is assembled, and belongs to parameters which can be obtained only by system-level measurement.
However, in the measurement process, it is difficult for the hyperspectral meter to ensure that the direction of the measurement radiation source is consistent with that of the remote sensor no matter the hyperspectral meter is cut into the calibration or imaging light path, and the remote sensor after the hyperspectral meter is assembled has the risk of failure of the calibration system caused by touching the optical surface of the scatterer in the process of cutting the probe of the hyperspectral meter into the calibration light path, so that the measurement efficiency is low, the repeated stability of the measurement result is poor, and the difference between the measurement result and the real application state of the remote sensor is large.
The invention provides a method for measuring partial aperture factors of a satellite calibration mechanism aiming at the problems in the prior art, which can accurately measure partial aperture factors of the calibration mechanism without cutting into a hyperspectral meter in a calibration or imaging light path of a remote sensor, can improve the measurement efficiency of the partial aperture factors and the stability of measurement results, is closer to the real application state of the remote sensor, and finally makes a contribution to improving the calibration precision of satellite calibration. In particular, the specific radiometer, which is usually used for monitoring the reflectivity of the diffuse reflection plate in the satellite calibration mechanism, is also used for partial aperture factor measurement, so that the stability can be improved, and the structure and the measurement steps can be simplified.
Means for solving the problems
The invention provides a method for measuring partial aperture factors of an on-board calibration mechanism, wherein the on-board calibration mechanism is used for performing on-orbit radiometric calibration on a satellite-borne remote sensor and comprises a diffuse reflection plate and a specific radiometer for monitoring the reflectivity of the diffuse reflection plate, and the method comprises the following steps: the first step, establishing a linear relation between the specific radiometer and the remote sensor for observing response count values of the same radiation source under different energy level states; secondly, establishing a BRDF relative proportion relation between a diffuse reflection plate observation direction of the specific radiometer and a diffuse reflection plate observation direction of the remote sensor under the same illumination condition according to pre-obtained BRDF basic data of the diffuse reflection plate; and a third step of obtaining a response count value of the diffuse reflection plate observed by the calibration optical 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 a partial aperture factor of the satellite-borne calibration mechanism by combining the obtained response count value of the calibration optical path of the remote sensor.
In the partial aperture factor measuring method of the present invention, in the first step, the radiation source for simulating the brightness of reflected radiation of the satellite diffuse reflector is observed by the remote sensor, the specific radiometer is switched in/out of a radiation measuring optical 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 relationship is established in accordance with a linear regression equation based on the measured response count values.
In the partial aperture factor measuring method according to the present invention, in the second step, a relationship between a diffuse reflection plate observation direction of the specific radiometer and a diffuse reflection plate observation direction of the remote sensor in a state where the on-satellite scaling mechanism is actually in-orbit scaled is obtained, and based on the obtained relationship, corresponding data is extracted from the BRDF basis data to calculate the relative BRDF ratio relationship.
In the partial aperture factor measuring method of the present invention, in the third step, the on-satellite calibration mechanism is configured by assembling the specific radiometer and the diffuse reflection plate, and is further assembled integrally with the remote sensor and the diffuse reflection plate is illuminated by a solar simulator, and a calibration optical path of the remote sensor and a response count value of the diffuse reflection plate at the same angle of incidence as observed by the specific radiometer are obtained.
And, using the relative proportion relationship of the BRDF obtained in the second step, equating a response count value of the diffuse reflection plate illuminated by the solar simulator observed by the radiometer to a diffuse reflection plate observation direction of the remote sensor, and using the linear relationship obtained in the first step, obtaining a full aperture response count value of the remote sensor at the time of the same radiation input, and calculating the partial aperture factor based on the obtained full aperture response count value of the remote sensor at the time of the same radiation input and the obtained response count value of the diffuse reflection plate illuminated by the solar simulator observed by the calibration optical path of the remote sensor.
The invention also provides a device for measuring partial aperture factors of an on-board calibration mechanism, wherein the on-board calibration mechanism is used for performing on-orbit radiometric calibration on a satellite-borne remote sensor 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 between the specific radiometer and the remote sensor for observing response count values of the same radiation source under different energy level states; the second module is used for establishing the relative proportion relation of BRDF (bidirectional reflectance distribution function) 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 pre-acquired BRDF basic data of the diffuse reflection plate; and the third module is used for acquiring the response count value of the diffuse reflection plate observed by the calibration light path of the specific 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 acquired response count value of the specific radiometer, and calculating the partial aperture factor of the satellite-borne calibration mechanism by combining the acquired response count value of the calibration light path of the remote sensor.
Effects of the invention
By adopting the method and the device for measuring the partial aperture factors of the on-satellite calibration mechanism, the partial aperture factors of the calibration mechanism can be accurately measured without cutting into a hyperspectral meter in a calibration or imaging light path of a remote sensor, the measurement efficiency of the partial aperture factors and the stability of measurement results can be improved, the method is closer to the real application state of the remote sensor, a solution is finally provided for realizing high-frequency on-satellite radiometric calibration of medium and large remote sensors, and meanwhile, the contribution is made to improving the calibration precision of on-satellite calibration. In particular, a specific radiometer which is usually used for monitoring the reflectivity of the diffuse reflection plate in the satellite calibration mechanism is also used as a reference radiometer to realize partial aperture factor measurement, so that the stability can be improved, and the structure and the measurement steps can be simplified.
Drawings
Fig. 1 is a schematic diagram showing the principle of a satellite-based calibration method based on a diffusely reflecting plate.
Fig. 2 is a conceptual diagram illustrating a scaler of the present invention 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 invention.
Fig. 4 is a schematic optical path diagram showing the linear relationship between the response count values of the radiometer and the remote sensors in step 301, which is a plan view along the y-axis.
Fig. 5 is a 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 a partial aperture factor measuring method of the on-satellite scaling mechanism of the present invention is applied.
Detailed Description
The following describes a specific embodiment of the present invention with reference to the drawings.
In the following embodiments, when reference is made to a number of an element or the like (including a number, a numerical value, an amount, a range, and the like), the element or the like is not limited to a specific number except for a case where the element or the like is specifically and clearly described and a case where the element or the like is obviously limited to the specific number in principle, and may be a specific number or more or less. In the present application, the expression "constituted using … …" or "constituted by … …" merely indicates a main constituent element, and does not exclude other elements from being included.
In the following embodiments, the constituent elements (including step elements and the like) are not necessarily essential unless explicitly stated otherwise or clearly understood to be essential in principle, and may include elements not explicitly stated in the description.
The embodiment described in this specification is only an example of a complete description, and does not limit the scope of the present invention, and all other embodiments that can be obtained by those skilled in the art without inventive efforts based on the embodiment of the present invention belong to the scope of the present invention.
[ embodiment ]
With the development of years, the highest calibration precision can be realized by using a calibration mode of 'sunlight + diffuse reflection plate' at present. This is because the sun is considered as a stable light source throughout the year, but the remote sensor may be damaged by direct observation of the sun by 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 Bidirectional Reflection Distribution Function (BRDF) of the diffuse reflection plate can reach a high level.
Fig. 1 is a schematic diagram showing the principle of a satellite-based calibration method based on a diffusely reflecting plate.
As shown in fig. 1, in the calibration method, a relatively stable sun S throughout the year is used as a light source, sunlight reflected by a diffuse reflection plate 101 is used as a standard radiance source, a remote sensor (a detector 102) observes the diffuse reflection plate 101 with known radiance, a relationship between a physical quantity and a count value is established, and a radiometric calibration coefficient is determined.
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, as shown in fig. 1, a solar diffuse reflector reflectivity calibrator (hereinafter abbreviated as "radiometer") 102 is also provided to monitor the stability of the diffuse reflector 101.
Fig. 2 is a conceptual diagram illustrating a scaler of the present invention to which the on-satellite scaling scheme shown in fig. 1 is applied.
In fig. 2, a scaler (i.e., an on-satellite scaling mechanism) 200 is constituted by a scaling box 201, a diffuse reflection plate 202, a specific radiometer 203, and a partial aperture stop 204, and a dashed square in the drawing indicates a remote sensor optical system 205, and the scaler 200 is configured to be able to externally attach the scaling box 201 to a 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 substantially in a rectangular shape (similar to a triangular shape) with one corner cut off, the faces constituting the calibration box 201 mainly include two faces perpendicular to each other in the cross-sectional view of fig. 2, namely a light incident face 2011 and a light emitting face 2012, and an inclined face 2013, and the inner surfaces of the faces are coated with a matting coating. The light incident surface 2011 and the light emitting surface 2012 are respectively provided with an incident opening and an exit opening. A partial aperture stop 204 is provided at the exit opening to allow the optical path to enter the remote sensor entrance pupil at a specified aperture. The diffuse reflection plate 202 is made of a polytetrafluoroethylene material, a quartz material, or the like, is disposed on the inclined surface 2013 by a mounting fixture 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 diffuse reflection occurs on the diffuse reflection plate 202, a part of the reflected light enters the remote sensor optical system 205 through a part of the aperture stop 204.
The light incident surface 2011 is provided with an opening for a radiometer in addition to an incident opening. As shown in fig. 2, a specific radiometer 203 using a two-port symmetric monitoring method is provided near a portion where a light incident surface 2011 and a light emitting surface 2012 intersect in the calibration box 201. The bolometer 203 has a sun observation port 2031 and a diffuse reflection plate observation port 2032, the sun observation port 2031 faces the sunlight side, the same sunlight as the incident light on the diffuse reflection plate 202 can be observed from the specific radiometer opening of the calibration tank 201, and the diffuse reflection plate observation port 2032 faces the diffuse reflection plate side. Therefore, the sun is observed through the sun observation port 2031 to realize the monitoring of the detector response of the specific radiometer, the diffuse reflection plate is observed through the diffuse reflection plate observation port 2032 to realize the monitoring of the product of the detector response of the specific radiometer and the diffuse reflection plate reflectivity, and the monitoring of the diffuse reflection plate reflectivity can be realized through the ratio of the two types of monitoring.
Therefore, the BRDF of the diffuse reflection plate is accurately measured before launching, and the reflectivity of the diffuse reflection plate is monitored before launching and in track from the moment of measuring the BRDF so as to correct the BRDF in real time, so that the high calibration precision can be further ensured.
However, the structure of the scale 200 described herein is merely an example and does not limit the scope of the present invention, and for example, the shape of the scale box and the material of the diffuse reflection plate are not limited to the above description.
As mentioned above, currently, when measuring a portion of the aperture factor of a calibrator, the main method used requires that a hyperspectral meter be cut into the calibration and imaging paths. However, it is difficult to ensure that the direction of the hyperspectral meter measuring radiation source is consistent with that of the remote sensor no matter the hyperspectral meter is cut into a calibration or imaging light path, and the measurement of partial aperture factors can be performed after the remote sensor is assembled, so that the risk that the hyperspectral meter is cut into the light path can cause the probe to touch the optical surface of the scatterer, so that the calibration system fails.
Therefore, the invention provides a novel method for measuring the aperture factor of the part of the satellite calibration mechanism.
FIG. 3 is a flow chart of a partial aperture factor measurement method of the on-board calibration mechanism of the present invention, comprising: establishing a linear relation between a specific radiometer and response count values of a remote sensor under different energy level states of the same radiation source, observing by the specific radiometer, establishing a BRDF relative proportion relation between the observation direction of the specific radiometer and the observation direction of the remote sensor under the same illumination condition according to BRDF measurement data of a diffuse reflection plate laboratory, calculating a full aperture response count value of the remote sensor during the same radiation input by the count value of the specific radiometer observation diffuse reflection plate in a calibrator under the same illumination angle, and calculating an aperture factor by combining the actual measurement value of a calibration light path of the remote sensor.
That is, the 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 specific radiometer, thereby being capable of measuring the aperture factor compared with the actual measured response count value of the remote sensor.
Therefore, by adopting the method of the invention, the partial aperture factor measurement of partial aperture full optical path calibration can be indirectly realized under the condition that an external instrument is not introduced to cut into the optical path for auxiliary measurement, and the measurement difficulty and the measurement risk are reduced. The invention uses the specific radiometer which is originally assembled on the satellite calibration mechanism and is usually used for monitoring the reflectivity of the diffuse reflection plate as the reference radiometer to realize partial aperture factor measurement, and particularly in the step 303, an external instrument is not required to be cut into a calibration optical path of the remote sensor under the condition that the calibrator and the remote sensor are integrally assembled, so that the stability can be improved, and the structure and the measurement steps can be simplified.
The following takes the scaler (i.e. the on-satellite scaling mechanism) 200 shown in fig. 2 as an example, and specifically describes an embodiment of a partial aperture factor measuring method of the scaler.
(1) Step 301
In step 301, a linear relationship is established between the radiometer and the remote sensor for observing the response count values of the same radiation source at different energy levels.
Fig. 4 is a schematic optical path diagram showing the linear relationship between the response count values of the radiometer and the remote sensors in step 301, which is a plan view along the y-axis.
As shown in fig. 4, a remote sensor 401, a specific radiometer 402, and a large-aperture integrating sphere radiation source 403 are disposed in the optical path. It should be noted that since the objective of the present invention is to measure the partial aperture factor of the scaler 200 of fig. 2, the remote sensor 401 is the portion shown in 205 of fig. 2, and the specific radiometer 402 is the specific radiometer 203 of fig. 2. However, at step 301, although the remote sensor is assembled, the radiometer is not yet assembled into the calibrator, and therefore, for convenience of explanation, different reference numerals are used herein.
The large aperture integrating sphere radiation source 403 is used to simulate the brightness of the reflected radiation from an on-board diffuse reflector. In the present embodiment, the inside is a cavity, and a diffuse reflection layer is formed on the inner surface by integrally molding, for example, a polytetrafluoroethylene material having a high reflectance, and the halogen lamp 404 is used as a light source. The light emitted from the halogen lamp 404 is reflected multiple times in the integrating sphere to obtain a uniform, wide-spectrum, relatively flat lambertian surface light source (for convenience of illustration, only parallel emergent light is shown in the figure) at the exit. In addition, the radiation source can have high stability, high uniformity and multiple energy levels by matching with a high-precision voltage-stabilized direct-current power supply (not shown).
As shown in fig. 4, the remote sensor 401 is aimed at (the exit port of) the large aperture integrating sphere radiation source 403. Meanwhile, the radiation meter 402 is disposed on a moving mechanism such as a translation stage or an elevating stage (not shown) that can translate or elevate in the direction indicated by the arrow (perpendicular to the light-emitting direction of the radiation source), so that the radiation meter 402 can be switched in and out of the radiation measurement optical path flexibly in a short time. The radiometer 402 is disposed in such a direction that the diffuse reflection plate observation port can be aligned with the large-aperture integrating sphere radiation source 403 when the radiometer 402 is cut into the radiation measurement optical path by the translation stage or the elevating stage.
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-aperture integrating sphere radiation source 403, the response values of the remote sensor 401 and the specific radiometer 402 at multiple energy levels are obtained at the same time, and the pure response value relationship between the two at different energy levels is established according to the linear regression equation, as shown in formula (1).
C′imf(Bj)＝aCSDRDM,t(Bj)+b (1)
The meaning of each parameter in the formula (3) is described below since it is used in the formula (3).
Here, the different energy levels of the large-aperture integrating sphere radiation source 403 are not particularly limited in this embodiment, and may be any energy levels and the number of energy levels that can be conceived and implemented by those skilled in the art.
(2) Step 302
In step 302, a relative proportion relation of the BRDF between the observation direction of the radiometer and the observation direction of the remote sensor under the same illumination condition is established according to BRDF measurement data of a diffuse reflection plate laboratory.
The on-satellite calibration technology based on the diffuse reflection plate utilizes the diffuse reflection plate to reflect sunlight to form an approximately lambertian uniform surface light source, and BRDF of the diffuse reflection plate is needed to be used for calculating radiance. Therefore, the accuracy of the BRDF used on the diffusely reflecting plate star is a key factor in ensuring the calibration accuracy.
Here, BRDF (bidirectional reflectance distribution function) is used to describe the scattering properties of a surface over a range of incident illumination angles and reflection angles. Which is defined as when a beam of light is directed onto a surface along the line theta as shown in figure 5r,
Spectral radiance and sum of directions theta internally reflected at unit solid anglei,
The ratio of the increment of reflected radiance per unit solid angle to the increment of incident irradiance. Because solar irradiation is considered to be stable throughout the year, a diffuse reflector-based BFDF enables accurate calculation of the radiance observed by the remote sensor.
The diffuse reflection plate BRDF of the sun illumination angle change range in the satellite calibration machine all year around can be measured in a laboratory before the satellite calibration and emission based on the diffuse reflection plate, and the measured data is called 'BRDF basic data' in the embodiment.
The radiometer 402 and the remote sensor 401 used in step 301 are configured in the state shown in fig. 2 when actually used on a satellite. In step 302, first, a fixed geometric relationship (for example, an angular relationship) between the direction of the diffuse reflector observed by the radiometer and the direction of the diffuse reflector observed by the remote sensor is obtained in a state of actual on-track calibration, that is, in a state in which the radiometer 402 is mounted as the calibrator 200 and the calibrator 200 is disposed at the entrance pupil of the remote sensor. Based on the relation, corresponding data are extracted from the BRDF basic data to calculate the BRF (Bidirectional Reflectance Factor) relative proportion relation between the BRDF and the two exit directions under the same incident angle.
Here, as for the fixed geometrical relationship between the direction of the diffuse reflection plate observed by the radiometer and the direction of the diffuse reflection plate observed by the remote sensor, for example, the radiometer 402 may be actually assembled to the scaler 200 shown in fig. 2 and actually disposed on the remote sensor 401 to obtain the relationship, but even if not actually assembled, the relationship between the two may be previously designed, for example, the relative BRDF ratio may be obtained from the relationship, and the assembly may be performed in accordance with the previously designed relationship at the time of actual assembly.
The calculated relative ratio relation BRF of the BRDF in the two emergent directions is shown as a formula (2), and the BRF is used as a correction coefficient for calculating the reflectivity difference of the diffuse reflection plate between the observation direction of the radiometer and the observation direction of the remote sensor.
In the formula, BRF (theta)SD,φSD,Bj) Relative BRDF ratio BRF, f representing the relative BRDF ratio between the remote sensor observation direction and the specific radiometer observation directionSD,lab(θSD,φSD；θv,φv；Bj) And fSD,lab(θSD,φSD；φr,φr；Bj) The BRDF values are respectively the observation direction of the remote sensor and the observation direction of the specific radiometer under the same illumination condition.
(2) Step 303
In step 303, under the same illumination angle, the full aperture response count value of the remote sensor during the same radiation input is calculated according to the count value of the diffuse reflection plate observed by the radiometer in the calibrator, and the aperture factor is calculated according to the actual measurement value of the calibration optical 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 diffuser direction) at the same incident angle with respect to the diffuse reflection plate, one (the count value of the specific radiometer) is estimated based on the other (the full aperture response count value of the remote sensor).
Fig. 6 shows a schematic diagram of the measurement in step 303.
As shown in fig. 6, a remote sensor 401 is integrated with a system of scalers 200 assembled from a radiometer 402, and placed on the working surface of a solar simulator 601 of small divergence angle. The attitude of the remote sensor is adjusted on the working surface of the solar simulator 601 so that the angle of the diffuse reflection plate 202 of the calibrator 200 illuminated by the solar simulator 601 reaches a predetermined value. The preset value is a certain angle (optional) in the designated time marker, and the preset value can be selected as 0 degree hour angle and 0 degree declination angle for illumination for convenient adjustment. The purpose is to ensure a known BRDF from the radiometer and the remote sensor viewing direction.
On the basis, the remote sensor 401 measures the diffuse reflection plate 202 illuminated by the solar simulator 601 simultaneously with the specific radiometer 203 by adjusting the angle of the scanning mirror 602 thereof by using the calibration optical path, and records the diffuse reflection plate response signals under the same incident angle measured by the two instruments of the remote sensor 401 and the specific radiometer 203.
Based on the measurement response value of the specific radiometer 203, the relative reflectance is corrected according to the relative ratio relationship between the BRDFs in the two emission directions shown in the formula (2) obtained in step 302, and the actual observation direction of the specific radiometer 203 is equalized to the observation direction of the remote sensor 401. Then, according to the linear relationship of the response count value shown in the formula (1) obtained in step 301, a full aperture response estimation count value of the remote sensor 401 and the same radiation source observed in the same direction than the radiometer 203 is obtained. Finally, according to the aperture factor definition, the actual measurement response value of the calibration light path of the remote sensor 401 is compared with the full aperture response value of the imaging light path simulated by the radiometer, and the value of the partial aperture factor is obtained, as shown in formula (3).
In the formula, k (B)j) Is measuredA partial pore size factor; c'ca,p(Bj) Is the response count value of the diffuse reflection plate 202 actually measured by the calibration optical path of the remote sensor 401; c'im,f(Bj) The method is characterized in that a remote sensor full-aperture response counting value is obtained by equivalent conversion according to a formula (1) and a formula (2) according to the emergent radiance level in the direction of observing the diffuse reflection plate by a radiometer when the same radiation is input; cSDRDM(Bj) A response count value for observing the diffuse reflection plate 202 with the radiometer 203; a. b is the conversion relation coefficient of response count value of the same radiation source observed by a specific radiometer and a remote sensor, a subscript j represents the serial number of a wave band, BjUsed to refer to the j-th band.
Although the expressions (1) and (2) obtained in steps 301 and 302 are used in step 303, the processing results of steps 301 and 302 are not used, and therefore the order of steps 301 and 302 is not fixed, and step 301 may be executed after step 302.
As described above, by adopting the partial aperture factor measuring method of the on-satellite calibration mechanism, the partial aperture factor measurement of partial aperture full optical path calibration is indirectly realized under the condition that an external instrument is not introduced to cut into an optical path for auxiliary measurement, and the measurement difficulty and the measurement risk are reduced.
In addition, the method utilizes the existing BRDF basic data and the response linear change rule of the specific radiometer and the remote sensor to realize that the full aperture response value of the remote sensor with the same radiation input is simulated by measuring the response counting value through the specific 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 uncertainty of measurement is smaller. Therefore, a solution can be finally provided for realizing the high-frequency sub-on-satellite radiometric calibration of the medium-large remote sensor, and meanwhile, contribution is made to improving the calibration precision of on-satellite calibration.
Moreover, the invention uses the specific radiometer which is originally assembled on the satellite calibration mechanism and is usually used for monitoring the reflectivity of the diffuse reflection plate as the reference radiometer to realize partial aperture factor measurement, and particularly in the step 303, under the condition that the calibrator and the remote sensor are integrally assembled, an external instrument is not required to be cut into a calibration light path of the remote sensor, so that the stability can be improved, and the structure and the measurement steps can be simplified.
Fig. 7 is a schematic block diagram of an apparatus 700 to which a partial aperture factor measurement method of the on-satellite scaling mechanism of the present invention is applied.
As shown in fig. 7, the apparatus 700 includes a first module 701, a second module 702, and a third module 703, and 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 executed in the first module 701 corresponds to step 301, namely, 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 remote sensor for observing the response count values at different energy levels of the same radiation source.
The processing performed in the second module 702 corresponds to step 302, i.e., establishing a relative proportional relationship of BRDF between the direction of observation of the specific radiometer and the direction of observation of the remote sensor under the same lighting conditions, based on pre-obtained diffuse reflectance laboratory BRDF measurement data and the relationship between the direction of observation of the diffuse reflectance by the specific radiometer and the direction of observation of the diffuse reflectance by the remote sensor.
The processing performed in the third module 703 corresponds to step 303, that is, obtaining the count value of the diffuse reflection plate observed through the calibration optical path of the specific radiometer and the remote sensor in the calibrator 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 measurement value of the calibration optical path of the remote sensor.
Thus, the same effect as the above-described partial aperture factor measuring method can be obtained by using the apparatus 700 of the present invention.
Furthermore, it should be understood that the modules in the apparatus 700 can be implemented by a computer executing a specified program, or can be implemented by hardware through an integrated circuit design, and the present invention is not limited in this respect.
TABLE 1
Table 1 above gives the confirmatory experimental data for a partial aperture factor measurement method of the present invention, which is a measurement result of aperture factors of three bands (450nm, 550nm, 750nm) of a certain remote sensor. According to the data in the table, the repeatability of the measurement of the two-time repeated starting-up of the testing equipment is better than 0.26% for each wave band, which fully proves that the partial aperture factor measuring method has the technical effects of 'improving the reliability and reducing the uncertainty of the measurement'.
Industrial applicability
The method is suitable for measuring partial aperture factors of the on-satellite calibration mechanism of the satellite-borne remote sensor.
Claims (10)
1. A partial aperture factor measuring method of an on-board calibration mechanism used for on-orbit radiometric calibration of a satellite-borne remote sensor comprises a diffuse reflection plate and a specific radiometer used for monitoring the reflectivity of the diffuse reflection plate,
the partial aperture factor measuring method is characterized by comprising:
the first step, establishing a linear relation between the specific radiometer and the remote sensor for observing response count values of the same radiation source under different energy level states;
secondly, establishing a BRDF relative proportion relation between a diffuse reflection plate observation direction of the specific radiometer and a diffuse reflection plate observation direction of the remote sensor under the same illumination condition according to pre-obtained BRDF basic data of the diffuse reflection plate; and
and a third step of obtaining a response count value of the diffuse reflection plate observed by the calibration light path 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 a partial aperture factor of the satellite-borne calibration mechanism by combining the obtained response count value of the calibration light path of the remote sensor.
2. The partial aperture factor measurement method of claim 1, wherein:
in the first step, the radiation source for simulating the brightness of the reflected radiation of the satellite diffuse reflection plate is observed by the remote sensor, and the specific radiometer is switched in/out of a radiation measuring optical path of the remote sensor by a moving mechanism,
measuring respective response count values of the remote sensor and the specific radiometer while changing an energy level of the radiation source, and establishing the linear relationship according to a linear regression equation based on the measured respective response count values.
3. The partial aperture factor measurement method of claim 1 or 2, wherein:
the radiation source is a large-caliber integrating sphere radiation source with an exit port forming a Lambert 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 formed to form a diffuse reflection layer on the inner surface.
5. The partial aperture factor measurement method of claim 1, wherein:
in the second step, a known geometric relationship between a diffuse reflection plate observation direction of the specific radiometer and a diffuse reflection plate observation direction of the remote sensor in a state where the on-satellite calibration mechanism is actually in-orbit calibrated is obtained, and based on the obtained relationship, corresponding data is extracted from the BRDF basic data to calculate the relative ratio relationship of the BRDF.
6. The partial aperture factor measurement method of claim 5, wherein:
the BRDF basic data is obtained by measuring the BRDF of the diffuse reflection plate in the sun illumination angle change range on the whole satellite calibration machine in a laboratory.
7. The partial aperture factor measurement method of claim 1, wherein:
in the third step, the specific radiometer and the diffuse reflection plate are assembled to form the on-satellite calibration mechanism, and then the on-satellite calibration mechanism is integrally assembled with the remote sensor and illuminates the diffuse reflection plate through 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 same observation angle of incidence of the specific radiometer are obtained.
8. The partial aperture factor measurement method of claim 7, wherein:
using the relative proportion relation of the BRDF obtained in the second step, enabling the specific radiometer to observe the response count value of the diffuse reflection plate illuminated by the solar simulator to be equivalent to the diffuse reflection plate observation direction of the remote sensor, and using the linear relation obtained in the first step to obtain the full aperture response count value of the remote sensor during the simultaneous radiation input,
and calculating the partial aperture factor based on the calculated full aperture response count value of the remote sensor during simultaneous 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.
9. The partial aperture factor measurement method of claim 1, wherein:
the on-satellite calibration mechanism arranges the specific radiometer and the diffuse reflection plate in a calibration box, and the surface of the calibration box at the light emergent side is provided with a partial aperture diaphragm, so that the light reflected by the diffuse reflection plate enters the entrance pupil of the remote sensor through a specified aperture.
10. A partial aperture factor measuring device of a satellite-borne calibration mechanism, which is used for on-orbit radiometric calibration of a satellite-borne remote sensor, comprises a diffuse reflection plate and a specific radiometer for monitoring the reflectivity of the diffuse reflection plate,
the partial aperture factor measuring apparatus is characterized by comprising:
the first module is used for establishing a linear relation between the specific radiometer and the remote sensor for observing response count values of the same radiation source under different energy level states;
the second module is used for establishing the relative proportion relation of BRDF (bidirectional reflectance distribution function) 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 pre-acquired BRDF basic data of the diffuse reflection plate; and
and the third module is used for acquiring the response count value of the diffuse reflection plate observed by the calibration light path of the specific 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 acquired response count value of the specific radiometer, and calculating the partial aperture factor of the satellite-borne calibration mechanism by combining the acquired response count value of the calibration light path of the remote sensor.
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