A method and device for compensating for additional attenuation of onboard calibration equipment

Abstract

The present invention provides an additional attenuation compensation method and device for on-board calibration equipment, the method comprising: determining the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated based on the cross-calibration method of the radiation transmission model; calibrating the sensor to be calibrated according to the calibration coefficient to obtain the first apparent reflectivity of the sensor to be calibrated after calibration; calculating the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient according to the DN value, calibration coefficient, first apparent reflectivity and theoretical apparent reflectivity obtained by the sensor to be calibrated after calibration; judging whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient; if so, determining the correction coefficient according to the relative error of the on-board calibration coefficient. The additional attenuation compensation method for on-board calibration equipment provided by the present solution compensates for the additional attenuation and improves the accuracy of on-orbit calibration.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing sensors, and in particular to an additional attenuation compensation method and device for on-board calibration equipment. Background Art

[0002] The accuracy of quantitative inversion based on satellite remote sensing data depends on high-precision radiometric calibration data. The sensor has been launched into space with the satellite and operates in an environment of vacuum, weightlessness, and drastic changes in light and temperature. The response of each channel will change greatly, and the calibration coefficient will be different from that before launch. Therefore, it is necessary to carry out on-orbit calibration to obtain accurate calibration coefficients for each channel.

[0003] As on-orbit calibration equipment on board, the performance of diffuse reflectors and monitors will decay over time and cannot maintain long-term stability. Although the monitor monitors the attenuation of the diffuse reflector during on-orbit calibration, as the cumulative exposure time on-orbit increases, the monitor also decays, resulting in a certain amount of additional attenuation that cannot be compensated, which in turn affects the accuracy of on-orbit calibration. At the same time, since frequent on-board calibration will also affect devices such as diffuse reflectors, and the detection work of the detector will be terminated during this period, it is impossible to achieve high-frequency and long-time series on-board calibration, which will also make it impossible to estimate the attenuation law of the calibration system, thereby affecting the on-orbit calibration accuracy and greatly limiting the application of remote sensing observation data. Summary of the invention

[0004] The present invention provides an additional attenuation compensation method and device for on-board calibration equipment. The method compensates for the additional attenuation and improves the accuracy of on-orbit calibration.

[0005] In a first aspect, an embodiment of the present invention provides an additional attenuation compensation method for an onboard calibration device, comprising:

[0006] Based on the cross-calibration method of radiation transfer model, the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated are determined;

[0007] Calibrate the sensor to be calibrated according to the calibration coefficient, and obtain a first apparent reflectivity of the sensor to be calibrated after the calibration;

[0008] According to the DN value obtained by the sensor to be calibrated after the calibration, the calibration coefficient, the first apparent reflectivity and the theoretical apparent reflectivity, a relative error of the cross-radiation calibration coefficient and a relative error of the on-board calibration coefficient are calculated;

[0009] Determining whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient;

[0010] If yes, then the correction coefficient is determined according to the relative error of the on-board calibration coefficient.

[0011] Optionally, the cross-calibration method based on the radiation transfer model to determine the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated includes:

[0012] Based on the cross-calibration method of radiation transfer model, a cross-radiation transfer model is constructed;

[0013] According to the cross-radiation transmission model, the theoretical apparent reflectivity is obtained;

[0014] The calibration coefficient is obtained by performing a linear fit on the theoretical apparent reflectivity and the DN value obtained by the sensor to be calibrated.

[0015] Optionally, the calculating of a relative error of a cross-radiation calibration coefficient and a relative error of an on-board calibration coefficient according to the DN value obtained by the sensor to be calibrated after the calibration, the calibration coefficient, the first apparent reflectivity and the theoretical apparent reflectivity comprises:

[0016] Acquiring a DN value of the sensor to be calibrated after the calibration; wherein the DN value is the same as the remote sensing image corresponding to the first apparent reflectance;

[0017] Determining a second apparent reflectivity according to the DN value and the calibration coefficient;

[0018] Calculating a relative error of a cross-radiance calibration coefficient according to the second apparent reflectivity and the theoretical apparent reflectivity;

[0019] The relative error of the on-board calibration coefficient is calculated based on the first apparent reflectivity and the theoretical apparent reflectivity.

[0020] Optionally, the second apparent reflectivity is determined by the following formula:

[0021] ″

[0022] R″ cn =A n DB cn +B n

[0023] Among them, n is used to represent the nth channel; for the nth channel, R″ cn Used to characterize the second apparent reflectivity; A n and B n Both are used to characterize the calibration coefficient; DN cn Used to characterize the DN value;

[0024] The relative error of the cross-radiation calibration coefficient is determined by the following formula:

[0025]

[0026] The relative error of the on-board calibration coefficient is determined by the following formula:

[0027]

[0028] Wherein, n is used to characterize the nth channel; for the nth channel, Dif2 is used to characterize the relative error of the cross-radiation calibration coefficient; R′ cn Used to characterize the second apparent reflectivity; Dif1 is used to characterize the relative error of the on-board calibration coefficient; R′ cn Used to characterize the first apparent reflectivity; is used to characterize the theoretical apparent reflectance; k is used to characterize the number of pixels in the remote sensing image.

[0029] Optionally, judging whether the sensor to be calibrated needs to perform additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient includes:

[0030] Performing a difference operation and an absolute value operation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in sequence to obtain a difference;

[0031] Determine whether the relative error of the on-board calibration coefficient shows a monotonically increasing trend during the on-orbit time of the sensor to be calibrated; and determine whether the difference shows an increasing trend during the on-orbit time;

[0032] If the judgment results are all yes, it is determined that the sensor to be calibrated needs additional attenuation compensation.

[0033] Optionally, obtaining the difference includes:

[0034] Dividing the on-orbit time of the sensor to be calibrated into a number of time periods;

[0035] For each time period, the following steps are performed: obtaining the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient of the preset on-orbit time in the time period, and performing difference operation and absolute value operation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in turn to obtain the difference; wherein, the preset on-orbit times in adjacent time periods are not adjacent.

[0036] Optionally, determining the correction coefficient according to the relative error of the on-board calibration coefficient includes:

[0037] Dividing the on-orbit time of the sensor to be calibrated into a number of time periods;

[0038] Obtain the relative error of the on-board calibration coefficient of the preset on-orbit time in each time period;

[0039] Perform linear fitting on each preset on-orbit time and the corresponding relative error of the on-board calibration coefficient to obtain a fitting relationship; wherein the preset on-orbit times in adjacent time periods are not adjacent;

[0040] Obtaining the target on-orbit time of the sensor to be calibrated;

[0041] A correction coefficient of the sensor to be calibrated during the target on-orbit time is determined according to the target on-orbit time and the fitting relationship.

[0042] In a second aspect, an embodiment of the present invention further provides an additional attenuation compensation device for an onboard calibration device, comprising:

[0043] A cross calibration module is used to determine the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated based on the cross calibration method of the radiation transfer model;

[0044] An acquisition module, used for calibrating the sensor to be calibrated according to the calibration coefficient, and acquiring a first apparent reflectivity of the sensor to be calibrated after calibration;

[0045] An error calculation module, used for calculating the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient according to the DN value obtained by the sensor to be calibrated after the calibration, the calibration coefficient, the first apparent reflectivity and the theoretical apparent reflectivity;

[0046] The judgment processing module is used to judge whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient; and when the judgment result is yes, determine the correction coefficient according to the relative error of the on-board calibration coefficient.

[0047] In a third aspect, an embodiment of the present invention further provides a computing device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the additional attenuation compensation method for the on-board calibration device described in any one of the above items is implemented.

[0048] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed in a computer, the computer is caused to execute any of the above-mentioned additional attenuation compensation methods for the onboard calibration device.

[0049] The embodiment of the present invention provides a method and device for compensating for additional attenuation of an on-board calibration device. The method combines the accuracy verification of the relative error of the on-board cross-radiation calibration coefficient, analyzes the relative error of the on-board calibration coefficient of the sensor to be calibrated, determines the correction coefficient for the sensor to be calibrated that needs additional attenuation compensation, and performs compensation. In this way, the method provided by the present invention compensates for the additional attenuation caused by the attenuation of the monitor caused by the increase in the on-orbit cumulative exposure time, thereby improving the accuracy of on-orbit calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1 It is a flow chart of an additional attenuation compensation method for an on-board calibration device provided by an embodiment of the present invention;

[0052] Figure 2 The relative error of the cross-radiation calibration coefficient of CAPI in the 0.67 μm channel and the relative error of the calibration coefficient on the satellite vary with the number of days after launch, provided by an embodiment of the present invention;

[0053] Figure 3 The relative error of the cross-radiation calibration coefficient of CAPI in the 0.87 μm channel and the relative error of the calibration coefficient on the satellite vary with the number of days after launch, provided by an embodiment of the present invention;

[0054] Figure 4 The relative error of the cross-radiation calibration coefficient of CAPI in the 1.64 μm channel and the relative error of the calibration coefficient on the satellite vary with the number of days after launch, provided by an embodiment of the present invention;

[0055] Figure 5 is a curve showing the variation of the difference of CAPI before correction in 0.67 μm, 0.87 μm and 1.64 μm channels with the number of days after launch provided by an embodiment of the present invention;

[0056] Figure 6 is a curve showing the variation of the difference of the corrected CAPI at 0.67 μm, 0.87 μm and 1.64 μm channels with the number of days after launch provided by an embodiment of the present invention;

[0057] Figure 7 is a hardware architecture diagram of a computing device provided by an embodiment of the present invention;

[0058] Figure 8It is a structural diagram of an additional attenuation compensation device of an on-board calibration device provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0060] like Figure 1 As shown, an embodiment of the present invention provides an additional attenuation compensation method for an on-board calibration device, the method comprising:

[0061] Step 100, determining the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated based on the radiation transfer model cross calibration method;

[0062] Step 102, calibrating the sensor to be calibrated according to the calibration coefficient, and obtaining the first apparent reflectivity of the sensor to be calibrated after the calibration;

[0063] Step 104, calculating the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient according to the DN value, calibration coefficient, first apparent reflectivity and theoretical apparent reflectivity obtained by the sensor to be calibrated after calibration;

[0064] Step 106, judging whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient; if the judgment result is yes, executing step 108;

[0065] Step 108, determining the correction coefficient according to the relative error of the on-board calibration coefficient.

[0066] In an embodiment of the present invention, by combining the accuracy verification of the relative error of the on-board cross-radiation calibration coefficient, and analyzing the relative error of the on-board calibration coefficient of the sensor to be calibrated, the correction coefficient is determined and compensated for the sensor to be calibrated that needs additional attenuation compensation. In this way, the method provided by the present invention compensates for the additional attenuation caused by the attenuation of the monitor caused by the increase in the cumulative exposure time on orbit, improves the accuracy of on-orbit calibration, solves the problem that the on-board equipment cannot guarantee long-term sustainable high-precision on-orbit calibration due to the drastically changing space environment and the uncertain attenuation of the on-board calibration equipment, and is of great significance to improving the application accuracy of remote sensing data.

[0067] Described below Figure 1 How the various steps are performed.

[0068] First, for step 100, based on the radiation transfer model cross calibration method, the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated are determined, including:

[0069] Based on the cross-calibration method of radiation transfer model, a cross-radiation transfer model is constructed;

[0070] According to the cross-radiation transmission model, the theoretical apparent reflectivity is obtained;

[0071] The calibration coefficient is obtained by linearly fitting the theoretical apparent reflectance and the DN value obtained by the sensor to be calibrated.

[0072] It should be noted that for the cross-calibration method based on the radiation transfer model, the reference satellite sensor of the sensor to be calibrated has a complete on-board calibration system and has a similar channel to the sensor to be calibrated. The cross-data of the reference satellite sensor and the sensor to be calibrated should try to select a site with uniform surface reflectivity, flat surface, and stable atmospheric conditions throughout the year, preferably a calibration site. The key to the cross-calibration method based on the radiation transfer model is to construct a cross-radiation transmission model from the reference satellite sensor to the sensor to be calibrated. The model is composed of an observation zenith angle correction model and a spectral response correction model. The process of constructing the cross-radiation transmission model is the process of solving the spectral matching factor. To solve the spectral matching factor, the simulated data of 6SV (atmospheric radiation transfer model) is used. This model is used to convert the measured apparent reflectance of the reference sensor into the theoretical apparent reflectance of the sensor to be calibrated;

[0073] Perform a linear fit on the theoretical apparent reflectance of the sensor to be calibrated and the DN value obtained by the sensor to be calibrated, and the following formula is obtained:

[0074]

[0075] Among them, n is used to represent the nth channel; for the nth channel, Used to characterize theoretical apparent reflectance; DN cn Used to characterize DN value; A n and B n Both are used to characterize the calibration coefficient.

[0076] Specifically, for example, the TANSAT-Cloud and Aerosol Polarimetric Imager (CAPI) onboard calibration equipment is selected as the sensor to be calibrated, and MODIS Aqua is used as the reference satellite sensor for the on-orbit radiation transfer model cross-calibration method. The MODIS sensor has a complete on-board calibration system, and the on-orbit calibration accuracy is better than 5%. It is often used as the standard for cross-radiation calibration in the industry. Therefore, Aqua-MODIS is selected as the reference satellite sensor for CAPI. The 14 (678nm), 16 (870nm), and 6 (1640nm) channels of MODIS 1000m spatial resolution correspond to the 0.67μm, 0.87μm, and 1.64μm channels of CAPI 1000m spatial resolution, respectively. Australia's Frome Dry Lake is a calibration site with high surface reflectivity, altitude close to sea level, flat surface, and stable atmospheric conditions throughout the year. Therefore, the cross data used for calibration is selected at the center of the dry lake bed of the site (139°12'E-141°30'E, 30°35'S-31°30'S). From 2017 to mid-2019, four days of CAPI and MODIS data at Frome Dry Lake were selected for cross-radiation calibration. The MODIS measured apparent reflectance was converted into the theoretical apparent reflectance of CAPI through the cross-radiation transfer model.

[0077] Theoretical apparent reflectance of CAPI and the measured digital count value DN of CAPI cn Perform linear fitting to obtain formula (1) and the calibration coefficient of CAPI.

[0078] With respect to step 102 , the sensor to be calibrated is calibrated according to the calibration coefficient, and a first apparent reflectivity of the sensor to be calibrated after the calibration is obtained.

[0079] In step 104, the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient are calculated based on the DN value, calibration coefficient, first apparent reflectivity and theoretical apparent reflectivity obtained by the sensor to be calibrated after calibration, including:

[0080] Obtaining a DN value of the sensor to be calibrated after calibration; wherein the DN value is the same as the remote sensing image corresponding to the first apparent reflectance;

[0081] Determine the second apparent reflectivity according to the DN value and the calibration coefficient;

[0082] According to the second apparent reflectivity and the theoretical apparent reflectivity, the relative error of the cross-radiance calibration coefficient is calculated;

[0083] According to the first apparent reflectivity and the theoretical apparent reflectivity, the relative error of the on-board calibration coefficient is calculated.

[0084] It should be noted that steps 104 to 108 are performed for each channel, so that the correction coefficient of the sensor to be calibrated when performing additional attenuation compensation in each channel can be determined.

[0085] In a preferred embodiment, in step 104, the second apparent reflectivity is determined by the following formula:

[0086] R′ cn =A n DN cn +B n (2)

[0087] Among them, n is used to represent the nth channel; for the nth channel, R′ cn Used to characterize the second apparent reflectance; A n and B n Both are used to characterize the calibration coefficient; DN cn Used to characterize DN value;

[0088] The relative error of the cross-radiation calibration coefficient is determined by the following formula:

[0089]

[0090] The relative error of the on-board calibration coefficient is determined by the following formula:

[0091]

[0092] Among them, n is used to represent the nth channel; for the nth channel, Dif2 is used to represent the relative error of the cross-radiation calibration coefficient; R′ cn Used to characterize the second apparent reflectivity; Dif1 is used to characterize the relative error of the on-board calibration coefficient; R′ cn Used to characterize the first apparent reflectance; Used to characterize the theoretical apparent reflectance; k is used to characterize the number of pixels in the remote sensing image.

[0093] In step 106, judging whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient includes:

[0094] Divide the on-orbit time of the sensor to be calibrated into several time periods;

[0095] For each time period, the following steps are performed: obtaining the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient of the preset on-orbit time in the time period, and performing difference calculation and absolute value calculation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in sequence to obtain the difference; wherein the preset on-orbit times in adjacent time periods are not adjacent;

[0096] Determine whether the relative error of the on-board calibration coefficient shows a monotonically increasing trend during the on-orbit time of the sensor to be calibrated; and determine whether the difference shows an increasing trend during the on-orbit time;

[0097] If the judgment results are all yes, it is determined that the sensor to be calibrated needs additional attenuation compensation.

[0098] It should be noted that if the judgment results are all yes, it means that the calibrated sensor still needs additional attenuation compensation. In addition, it should be noted that the increasing trend means that the difference value shows an overall increasing trend with the on-orbit time, and it is not a strictly monotonically increasing trend. For example, the distribution of the difference value during the on-orbit time is 2.1% (200th day), 2.2% (300th day), 2% (400th day), 3.1% (780th day), 2.8% (880th day), 2.7% (980th day), 3.25% (1080th day), which is in line with the increasing trend. The difference is |Dif2-Dif1|.

[0099] Since the reference satellite sensor also has its own uncertainty (for example, the on-orbit calibration accuracy of the MODIS sensor is better than 5%), the calculated relative error cannot represent the absolute calibration accuracy of the sensor to be calibrated. In the present invention, it is determined that the relative error of the on-board calibration coefficient shows a monotonically increasing trend during the on-orbit time of the sensor to be calibrated, and the difference also shows an increasing trend as the on-orbit time increases, which means that the calibration coefficient of the on-orbit calibration system is increasingly deviating from the normal value, proving that the on-orbit calibration system of the sensor to be calibrated has attenuated. Although the monitor has compensated for the attenuation of the diffuse reflection plate, there is still an additional attenuation part that has not been compensated, and the deviation has an increasing trend as the number of days on orbit after launch increases, which means that the on-board calibration can no longer provide a sufficiently reliable on-orbit calibration coefficient to perform radiation correction on the sensor data to be calibrated, and it is necessary to correct the uncompensated attenuation of the sensor to be calibrated. Therefore, the on-orbit radiation recalibration of the sensor to be calibrated is of great significance.

[0100] In step 108, the correction coefficient is determined according to the relative error of the on-board calibration coefficient, including:

[0101] Divide the on-orbit time of the sensor to be calibrated into several time periods;

[0102] Obtain the relative error of the on-board calibration coefficient of the preset on-orbit time in each time period;

[0103] Perform linear fitting on each preset on-orbit time and the corresponding relative error of the on-board calibration coefficient to obtain a fitting relationship; wherein the preset on-orbit times in adjacent time periods are not adjacent;

[0104] Obtain the target on-orbit time of the sensor to be calibrated;

[0105] According to the target on-orbit time and the fitting relationship, the correction coefficient of the sensor to be calibrated during the target on-orbit time is determined.

[0106] In the present invention, in order to further reduce the amount of calculation, the on-orbit time is divided into several time periods, and a preset on-orbit time is determined in each time period. By determining the difference between each preset on-orbit time or the relative error of the on-board calibration coefficient, the change trend of the difference in the entire on-orbit time and the change trend of the relative error of the on-board calibration coefficient can be correspondingly determined.

[0107] More specifically, when it is determined that the sensor to be calibrated needs additional attenuation compensation, a linear fit is performed on each channel in each time period to obtain the corresponding fitting relationship:

[0108] K n =Slope*Day+Intercept (5)

[0109]

[0110] Among them, n is used to represent the nth channel; for the nth channel, K n It is used to characterize the relative error of the calibration coefficients on the satellite; Slope and Intercept are used to characterize the coefficients in the fitting relationship; Day is used to characterize the on-orbit time; R′ cn,L Used to characterize the corrected data; 1 / (1-K n ) or 1 / (1+K n ) is used to characterize the correction factor; R cn,L It is used to characterize the data before correction; D0 is used to characterize the average error of the calibration coefficient on the satellite. R′ cn Used to characterize the first apparent reflectance; is used to characterize the theoretical apparent reflectivity; k is used to characterize the number of pixels in the remote sensing image. In this way, the present invention can determine the corresponding correction coefficient according to the corresponding fitting relationship for any target on-orbit time, thereby realizing compensation for the additional attenuation and effectively improving the accuracy of on-orbit calibration.

[0111] Continuing with the previous example, after calibrating the sensor to be calibrated according to the calibration coefficient, the days after CAPI was launched are divided into seven time periods. One day is selected from each time period to compare the relative errors of CAPI and MODIS cross images in the Australian region. After geometric registration of MODIS and CAPI images, the relative errors of the cross-radiation calibration coefficients and the on-board calibration coefficients corresponding to each channel after CAPI was launched on orbit are calculated based on formulas (2) to (4), where the reflectivity data in the CAPI L1B product data is the first apparent reflectivity. Then, the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient are subtracted, and the absolute value of the result is taken to obtain the difference. For the convenience of analysis, the relative error result data is made into a line graph, as shown in Figures 2 to 5 As shown. Figures 2 to 5 It can be seen that the relative errors of the cross-radiation calibration coefficients of each channel of CAPI in different time periods are relatively stable, which proves the rationality of the cross-radiation calibration time interval, that is, the rationality of dividing the on-orbit time into time periods and selecting the preset on-orbit time within the time period, which can improve the calculation efficiency while ensuring that the data change characteristics do not change. Figure 2 It can be seen that the relative error of the cross-radiation calibration coefficient of the 0.67μm channel is between 4% and 4.5%. Figure 3 It can be seen that the relative error of the cross-radiation calibration coefficient of the 0.87μm channel is between 4.3% and 4.7%. Figure 4 It can be seen that the relative error of the cross-radiation calibration coefficient of the 1.64μm channel is slightly larger, between 5% and 5.9%. Based on the absolute radiation calibration accuracy of MODIS itself, which is better than 5%, the maximum uncertainty of CAPI's cross-radiation calibration is 11%. The above results are within the allowable range of the relative error of the cross-radiation calibration coefficient, which proves the rationality and timeliness of the cross-radiation calibration coefficient.

[0112] It should be noted that Figures 2 to 4 (including Figure 2 ) shows the 7 days of preset on-orbit time selected from 0 to 1100 days of on-orbit time, which are not adjacent and are evenly distributed in the time period.

[0113] like Figure 5 As shown in the figure, the relative error of the on-board calibration coefficient increases with the increase of the number of days on orbit after launch, and the corresponding difference also shows an increasing trend, indicating that the calibration coefficient of the on-orbit calibration system is increasingly deviating from the normal value, proving that the on-orbit calibration system on CAPI has indeed experienced attenuation. Although the monitor has compensated for the attenuation of the diffuse reflector, Figure 5It can be seen that there is still an additional attenuation part that has not been compensated, and the deviation tends to increase with the increase of the number of days on orbit after launch. It can be said that the on-board calibration can no longer provide sufficiently reliable on-orbit calibration coefficients to perform radiation correction on CAPI data. Therefore, it is necessary to correct the uncompensated attenuation of CAPI: First, a linear fit is performed on the relative error of the on-board calibration coefficient as the number of days on orbit after launch, and the fitting relationship formula (7) is obtained:

[0114] K 0.67μm =0.0021*Day+4.7

[0115] K 0.87μm =0.00082*Day+5.4

[0116] K 1.64μm =0.00077*Day+7.6 (7)

[0117] The correction coefficient of the diffuse reflection plate of each channel is determined according to formula (7), and the correction coefficient is substituted into the above formula (6) to obtain the corrected data of L1B of each channel, thus completing the additional attenuation compensation.

[0118] Furthermore, the corrected data of L1B of each channel is used as the first apparent reflectivity, and the corrected relative error of the on-board calibration coefficient is obtained based on the above formula (4). Then, the corrected relative error of the on-board calibration coefficient and the relative error of the cross-radiation calibration coefficient are subjected to difference calculation and absolute value calculation in sequence, and the following is obtained: Figure 6 The change curve of the corrected difference is shown by Figure 6 It can be seen that the corrected difference change curve is Figure 5 The difference change curve before correction is shown. Figure 6 The difference in the value of changes with the number of days in orbit after launch is obviously gentle, which indicates that the additional attenuation of the diffuse reflection plate has been corrected to a certain extent.

[0119] It should be noted that Figures 2 to 4 In , the relative error of the original on-orbit radiation calibration coefficient is the relative error of the on-board calibration coefficient; Figure 5 The ordinate in is used to represent the difference of CAPI before correction, where the relative error of the original calibration coefficient is the relative error of the on-board calibration coefficient; Figure 6 The vertical axis is used to represent the difference in CAPI after correction.

[0120] like Figure 7 , Figure 8 As shown, an embodiment of the present invention provides an additional attenuation compensation device for a satellite calibration device. The device embodiment can be implemented by software, or by hardware or a combination of software and hardware. From the hardware level, Figure 7As shown, it is a hardware architecture diagram of a computing device where an additional attenuation compensation device of an on-board calibration device provided by an embodiment of the present invention is located, except Figure 7 In addition to the processor, memory, network interface, and non-volatile memory shown in the figure, the computing device in which the device is located in the embodiment may also generally include other hardware, such as a forwarding chip responsible for processing messages, etc. Taking software implementation as an example, Figure 8 As shown, as a device in a logical sense, the CPU of the computing device in which it is located reads the corresponding computer program in the non-volatile memory into the memory and runs it. This embodiment provides an additional attenuation compensation device for an on-board calibration device, including: a cross calibration module 800, an acquisition module 802, an error calculation module 804 and a judgment processing module 806;

[0121] A cross calibration module 800 is used to determine the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated based on a cross calibration method of a radiation transfer model;

[0122] An acquisition module 802 is used to calibrate the sensor to be calibrated according to the calibration coefficient, and acquire the first apparent reflectivity of the sensor to be calibrated after calibration;

[0123] The error calculation module 804 is used to calculate the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient according to the DN value, calibration coefficient, first apparent reflectivity and theoretical apparent reflectivity obtained by the sensor to be calibrated after calibration;

[0124] The judgment processing module 806 is used to judge whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient; and when the judgment result is yes, determine the correction coefficient according to the relative error of the on-board calibration coefficient.

[0125] In some specific implementations, the cross calibration module 800 may be used to execute the above step 100 , the acquisition module 802 may be used to execute the above step 102 , the error calculation module 804 may be used to execute the above step 104 , and the judgment processing module 806 may be used to execute the above steps 106 and 108 .

[0126] In some specific implementations, the cross calibration module 800 is further configured to perform the following operations:

[0127] Based on the cross-calibration method of radiation transfer model, a cross-radiation transfer model is constructed;

[0128] According to the cross-radiation transmission model, the theoretical apparent reflectivity is obtained;

[0129] The calibration coefficient is obtained by linearly fitting the theoretical apparent reflectance and the DN value obtained by the sensor to be calibrated.

[0130] In some specific implementations, the error calculation module 804 is further configured to perform the following operations:

[0131] Obtaining a DN value of the sensor to be calibrated after calibration; wherein the DN value is the same as the remote sensing image corresponding to the first apparent reflectance;

[0132] Determine the second apparent reflectivity according to the DN value and the calibration coefficient;

[0133] The second apparent reflectance is determined by the following formula:

[0134] R′ cn =A n DN cn +B n (2)

[0135] Among them, n is used to represent the nth channel; for the nth channel, R′ cn Used to characterize the second apparent reflectance; A n and B n Both are used to characterize the calibration coefficient; DN cn Used to characterize DN value;

[0136] According to the second apparent reflectivity and the theoretical apparent reflectivity, the relative error of the cross-radiance calibration coefficient is calculated;

[0137] The relative error of the cross-radiation calibration coefficient is determined by the following formula:

[0138]

[0139] According to the first apparent reflectivity and the theoretical apparent reflectivity, the relative error of the on-board calibration coefficient is calculated.

[0140] The relative error of the on-board calibration coefficient is determined by the following formula:

[0141]

[0142] Among them, n is used to represent the nth channel; for the nth channel, Dif2 is used to represent the relative error of the cross-radiation calibration coefficient; R′ cn Used to characterize the second apparent reflectivity; Dif1 is used to characterize the relative error of the on-board calibration coefficient; R′ cn Used to characterize the first apparent reflectance; Used to characterize the theoretical apparent reflectance; k is used to characterize the number of pixels in the remote sensing image.

[0143] In some specific implementations, the determination processing module 806 is further configured to perform the following operations:

[0144] Divide the on-orbit time of the sensor to be calibrated into several time periods;

[0145] For each time period, the following steps are performed: obtaining the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient of the preset on-orbit time in the time period, and performing difference calculation and absolute value calculation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in sequence to obtain the difference; wherein the preset on-orbit times in adjacent time periods are not adjacent;

[0146] Perform difference calculation and absolute value calculation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in turn to obtain the difference;

[0147] Determine whether the relative error of the on-board calibration coefficient shows a monotonically increasing trend during the on-orbit time of the sensor to be calibrated; and determine whether the difference shows an increasing trend during the on-orbit time;

[0148] If the judgment results are all yes, it is determined that the sensor to be calibrated needs additional attenuation compensation.

[0149] In some specific implementations, the determination processing module 806 is further configured to perform the following operations:

[0150] Obtain the relative error of the on-board calibration coefficient of the preset on-orbit time in each time period;

[0151] Perform linear fitting on each preset on-orbit time and the corresponding relative error of the on-board calibration coefficient to obtain a fitting relationship; wherein the preset on-orbit times in adjacent time periods are not adjacent;

[0152] Obtain the target on-orbit time of the sensor to be calibrated;

[0153] According to the target on-orbit time and the fitting relationship, the correction coefficient of the sensor to be calibrated during the target on-orbit time is determined.

[0154] It is to be understood that the structure illustrated in the embodiment of the present invention does not constitute a specific limitation on the additional attenuation compensation device of an onboard calibration device. In other embodiments of the present invention, an additional attenuation compensation device of an onboard calibration device may include more or fewer components than shown in the figure, or combine some components, or split some components, or arrange the components differently. The components shown in the figure may be implemented in hardware, software, or a combination of software and hardware.

[0155] The information interaction, execution process and other contents between the modules in the above-mentioned device are based on the same concept as the embodiment of the method of the present invention. For the specific contents, please refer to the description in the embodiment of the method of the present invention, and no further description is given here.

[0156] An embodiment of the present invention further provides a computing device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, an additional attenuation compensation method for an on-board calibration device in any embodiment of the present invention is implemented.

[0157] An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the processor executes an additional attenuation compensation method for an onboard calibration device in any embodiment of the present invention.

[0158] Specifically, a system or device equipped with a storage medium can be provided, on which software program code that implements the functions of any of the above-mentioned embodiments is stored, and a computer (or CPU or MPU) of the system or device can read and execute the program code stored in the storage medium.

[0159] In this case, the program code itself read from the storage medium can realize the function of any one of the above-mentioned embodiments, and thus the program code and the storage medium storing the program code constitute a part of the present invention.

[0160] The storage medium embodiments for providing the program code include a floppy disk, a hard disk, a magneto-optical disk, an optical disk (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), a magnetic tape, a non-volatile memory card, and a ROM. Alternatively, the program code can be downloaded from a server computer by a communication network.

[0161] In addition, it should be clear that the functions of any of the above embodiments can be implemented not only by executing the program code read by the computer, but also by enabling an operating system operating on the computer to complete part or all of the actual operations based on instructions from the program code.

[0162] In addition, it can be understood that the program code read from the storage medium is written to a memory provided in an expansion board inserted into the computer or to a memory provided in an expansion module connected to the computer, and then based on the instructions of the program code, a CPU installed on the expansion board or expansion module is enabled to perform part or all of the actual operations, thereby realizing the functions of any of the above-mentioned embodiments.

[0163] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical factors in the process, method, article or device including the elements.

[0164] A person of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by hardware related to program instructions, and the aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it executes the steps of the above method embodiments; and the aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk, etc., various media that can store program codes.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for compensating for additional attenuation of an onboard calibration device, characterized in that: include: Based on the cross-calibration method of radiation transfer model, the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated are determined; Calibrate the sensor to be calibrated according to the calibration coefficient, and obtain a first apparent reflectivity of the sensor to be calibrated after the calibration; Acquiring a DN value of the sensor to be calibrated after the calibration; wherein the DN value is the same as the remote sensing image corresponding to the first apparent reflectance; According to the DN value and the calibration coefficient, a second apparent reflectivity is determined; the second apparent reflectivity is determined by the following formula: in, n To characterize the n channel; for the n channels, Used to characterize the second apparent reflectivity; A n and B n are used to characterize the calibration coefficient; DN cn Used to characterize the DN value; According to the second apparent reflectivity and the theoretical apparent reflectivity, a relative error of a cross-radiation calibration coefficient is calculated; the relative error of the cross-radiation calibration coefficient is determined by the following formula: The relative error of the on-board calibration coefficient is calculated based on the first apparent reflectivity and the theoretical apparent reflectivity; the relative error of the on-board calibration coefficient is determined by the following formula: in, n To characterize the n channel; for the n channels, Dif2 is used to characterize the relative error of the cross-radiation calibration coefficient; Used to characterize the second apparent reflectivity; Dif1 is used to characterize the relative error of the on-board calibration coefficient; Used to characterize the first apparent reflectivity; Used to characterize the theoretical apparent reflectance; k Used to represent the number of pixels in the remote sensing image; Dividing the on-orbit time of the sensor to be calibrated into a number of time periods; For each time period, the following steps are performed: obtaining the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient of the preset on-orbit time in the time period, and performing difference calculation and absolute value calculation on the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient in sequence to obtain the difference; wherein the preset on-orbit times in adjacent time periods are not adjacent; Determine whether the relative error of the on-board calibration coefficient shows a monotonically increasing trend during the on-orbit time of the sensor to be calibrated; and determine whether the difference shows an increasing trend during the on-orbit time; If the judgment results are all yes, it is determined that the sensor to be calibrated needs additional attenuation compensation, and the correction coefficient is determined according to the relative error of the on-board calibration coefficient.

2. The method according to claim 1, characterized in that The cross-calibration method based on the radiation transfer model determines the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated, including: Based on the cross-calibration method of radiation transfer model, a cross-radiation transfer model is constructed; According to the cross-radiation transmission model, the theoretical apparent reflectivity is obtained; The calibration coefficient is obtained by performing a linear fit on the theoretical apparent reflectivity and the DN value obtained by the sensor to be calibrated.

3. The method according to claim 1 or 2, characterized in that: Determining the correction coefficient according to the relative error of the on-board calibration coefficient includes: Dividing the on-orbit time of the sensor to be calibrated into a number of time periods; Obtain the relative error of the on-board calibration coefficient of the preset on-orbit time in each time period; Perform linear fitting on each preset on-orbit time and the corresponding relative error of the on-board calibration coefficient to obtain a fitting relationship; wherein the preset on-orbit times in adjacent time periods are not adjacent; Obtaining the target on-orbit time of the sensor to be calibrated; A correction coefficient of the sensor to be calibrated during the target on-orbit time is determined according to the target on-orbit time and the fitting relationship.

4. An additional attenuation compensation device for on-board calibration equipment, used to implement the method according to any one of claims 1 to 3, characterized in that: include: A cross calibration module is used to determine the theoretical apparent reflectivity and calibration coefficient of the sensor to be calibrated based on the cross calibration method of the radiation transfer model; An acquisition module, used to calibrate the sensor to be calibrated according to the calibration coefficient, and acquire a first apparent reflectivity of the sensor to be calibrated after calibration; An error calculation module, used for calculating the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient according to the DN value obtained by the sensor to be calibrated after the calibration, the calibration coefficient, the first apparent reflectivity and the theoretical apparent reflectivity; The judgment processing module is used to judge whether the sensor to be calibrated needs additional attenuation compensation according to the relative error of the cross-radiation calibration coefficient and the relative error of the on-board calibration coefficient; and when the judgment result is yes, determine the correction coefficient according to the relative error of the on-board calibration coefficient.

5. A computing device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method according to any one of claims 1 to 3 is implemented.

6. A computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to execute the method according to any one of claims 1 to 3.

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