A correction algorithm for buoy shortwave radiation measurement

Abstract

The present invention belongs to the technical field of ocean surface shortwave radiation measurement and correction, and particularly relates to a correction algorithm for buoy shortwave radiation measurement. First, based on the longitude and latitude, date and time information of the buoy, the time difference, hour angle, declination angle, azimuth, zenith angle and incident angle of the sun are calculated; then, combined with the attitude information of the radiometer, the field of view difference caused by the tilt of the radiometer is calculated; then, according to the radiation parameter conversion relationship between the non-horizontal and horizontal attitudes of the radiometer, the measured value of the radiometer in the non-horizontal attitude is corrected to obtain the shortwave total radiation value on the corresponding horizontal plane. The present invention converts the measured value of the non-horizontal plane into the corresponding horizontal plane radiation value by establishing a radiation conversion model, thereby realizing the accurate correction of the measured value of the radiometer in different attitudes. The algorithm is suitable for stable or shaking platforms, can significantly improve the measurement accuracy of the buoy shortwave radiation, and has broad application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of ocean surface shortwave radiation measurement correction, and in particular relates to a correction algorithm for buoy shortwave radiation measurement. Background Art

[0002] As global climate change intensifies, the role of ocean heat balance observation in climate research becomes increasingly prominent. In the ocean heat balance, shortwave radiation is particularly critical, as it is the most important source of ocean heat. As the instrument-carrying platform closest to the sea surface, the buoy system is an important carrier for ocean boundary layer observations and is widely used in long-term monitoring of meteorological elements such as ocean surface radiation, temperature, air pressure and wind speed. In the real ocean, the buoy system is affected by sea waves and shakes, causing the instruments on the buoy to tilt.

[0003] Radiometers are mainly used to measure radiation. Commonly used radiometers are usually used in fixed and horizontal installation environments and cannot effectively adapt to dynamic carrying platforms such as buoys. Therefore, when these radiometers are used directly on buoys, measurement deviations often occur, especially when the buoy shakes to a large extent, the measurement results deviate significantly from the true value. How to effectively correct these deviations has become a key technical problem to improve the quality of ocean observation data and promote marine scientific research. At present, researchers mainly use statistical averaging methods to offset the deviations caused by the tilt of the radiometer. The sampling rate of the radiometer is usually set to once per minute, and the average value of 30 minutes is used to characterize the radiation value. However, the buoy is affected by boundary layer dynamic factors such as waves, wind, and currents, and its shaking is not symmetrical. Therefore, it is difficult for existing technical means to accurately invert the shortwave radiation on the ocean surface after measurement. Summary of the invention

[0004] In view of the various deficiencies in the prior art, the inventors have designed a correction algorithm for buoy shortwave radiation measurement in long-term practice, aiming to improve the accuracy of ocean surface shortwave radiation measurement data and effectively correct the incident shortwave radiation measurement error caused by buoy shaking.

[0005] The correction algorithm of the present invention includes the following steps.

[0006] Step 1: Calculate the solar time difference, solar hour angle and solar declination angle based on the measured local geographic longitude information of the buoy, the solar annual day and Beijing time.

[0007] Step 2: Calculate the solar altitude angle, solar zenith angle and solar azimuth angle based on the solar declination angle and solar hour angle calculated in step 1 and the local geographic latitude information of the buoy measured.

[0008] Step 3: Based on the roll angle (roll) and pitch angle (pitch) of the radiometer measured by the inclinometer, calculate the angle between the zenith direction of the radiometer after tilting and the zenith direction when the radiometer is horizontal.

[0009] Step 4: Calculate the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted, based on the roll angle and pitch angle of the radiometer measured by the inclinometer and the azimuth of the sun calculated in step 2.

[0010] Step 5. Calculate the solar incident angle based on the azimuth angle and zenith angle of the sun calculated in step 2, the angle between the zenith direction after the radiometer is tilted calculated in step 3 and the zenith direction when the radiometer is horizontal, and the angle between the projection of the zenith direction on the horizontal plane after the radiometer is tilted calculated in step 4 and the due north direction.

[0011] Step six, calculate the observation field of view difference score caused by the tilt of the radiometer based on the angle between the zenith direction after the radiometer is tilted calculated in step three and the zenith direction when the radiometer is horizontal, and the zenith angle and azimuth of the sun calculated in step two.

[0012] Step 7: The incident shortwave total radiation E measured by the radiometer in a horizontal position H It can be expressed as direct short-wave radiation and diffuse short-wave radiation, that is, E H =E dir +E diff .

[0013] Among them, E dir is the direct short-wave radiation received by the horizontal plane, E diff The horizontal plane receives diffuse shortwave radiation.

[0014] Step 8: The incident shortwave total radiation E measured by the radiometer in a non-horizontal posture T It can be expressed as direct short-wave radiation, diffuse short-wave radiation and short-wave radiation reflected by the underlying surface, that is, E T =E′ dir +E′ diff +E′ ref .

[0015] Among them, E′ dir is the shortwave radiation received directly by the non-horizontal surface, E′ diff For the diffuse shortwave radiation received by the non-horizontal surface, E′ ref A non-horizontal surface receives shortwave radiation reflected by the underlying surface.

[0016] Step 9: Assuming that the radiation is isotropic, E′ in step 8 dir , E′diff , E′ ref Can be combined with E in step 7 dir 、E diff The conversion relationship can be established using the following formula.

[0017]

[0018]

[0019] Among them, θ is the zenith angle of the sun, ξ is the incidence angle of the sun, γ is the difference fraction of the observation field of view caused by the tilt of the radiometer, ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, and β is the albedo of the underlying surface.

[0020] Step 10: The radiometer measures the incident shortwave total radiation E in a non-horizontal position. T :E T =E′ dir +E′ diff +E′ ref .

[0021] According to E' in step nine dir , E′ diff , E′ ref With E dir The conversion relationship is: the total short-wave radiation E incident on the radiometer in a non-horizontal posture T It is expressed by the following formula.

[0022]

[0023] Transform the above formula into

[0024] Among them, E T is the total incident shortwave radiation measured by the radiometer in a non-horizontal attitude, E H It is the total shortwave radiation incident on the horizontal plane calculated based on the measurement results of the radiometer in a non-horizontal posture. ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, θ is the zenith angle of the sun, ξ is the incident angle of the sun, β is the albedo of the underlying surface, and γ is the difference fraction of the observation field of view caused by the tilt of the radiometer.

[0025] Furthermore, calculating the solar time difference, the solar hour angle and the solar declination angle in step one specifically includes the following sub-steps.

[0026] Sub-step 1.1, calculate the solar time difference E according to the following formula.

[0027] E=9.87sin2B-7.53cosB-1.5sinB;

[0028] in: Where N is the number of days per year.

[0029] Sub-step 1.2, calculate the solar hour angle ω according to the following formula.

[0030]

[0031] Among them, T b is Beijing time, Φ long is the local geographical longitude.

[0032] Sub-step 1.3, calculate the solar declination angle δ according to the following formula.

[0033]

[0034] Where N is the accumulated days per year.

[0035] Furthermore, the calculation of the solar altitude angle, solar zenith angle and solar azimuth angle in step 2 specifically includes the following sub-steps:

[0036] Sub-step 2.1, calculate the solar altitude angle h according to the following formula.

[0037] h=arcsin(sinΦ lat sinδ+cosΦ lat cosδcosω);

[0038] Among them, Φ lat is the local geographical latitude, δ is the solar declination angle, and ω is the solar hour angle.

[0039] Sub-step 2.2, calculate the solar zenith angle θ according to the following formula.

[0040] θ = 90-h;

[0041] Here, h is the altitude angle of the sun.

[0042] Sub-step 2.3, calculate the azimuth angle Φs of the sun according to the following formula.

[0043]

[0044] Among them, Φ lat is the local geographical latitude, δ is the solar declination angle, h is the solar altitude angle, and ω is the solar hour angle.

[0045] Furthermore, in step three, the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal is calculated, and the specific method is as follows.

[0046] There is an angle α between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal. The angle α is calculated according to the following formula.

[0047] α=arccos(cosρcosσ);

[0048] Among them, ρ is the tilt angle of the radiometer in the roll direction, which is higher in the west and lower in the east (ρ>0), and higher in the east and lower in the west (ρ<0); σ is the tilt angle of the radiometer in the pitch direction, which is higher in the south and lower in the north (σ>0), and higher in the north and lower in the south (σ<0).

[0049] Furthermore, in step 4, the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted is calculated, and the specific method is as follows.

[0050] The angle Φ between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted is calculated according to the following formula: B .

[0051]

[0052] Among them, Φs is the azimuth of the sun, ρ is the tilt angle of the radiometer in the roll direction, and σ is the tilt angle of the radiometer in the pitch direction.

[0053] Furthermore, in step five, the incident angle of the sun is calculated, and the specific method is as follows.

[0054] The incident angle ξ of the sun is calculated according to the following formula.

[0055] cosξ=cosθcosα+sinθsinαcos(φ S -φ B );

[0056] Among them, θ is the zenith angle of the sun, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φs is the azimuth angle of the sun, and Φ B It is the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted.

[0057] Furthermore, in step six, the observation field of view difference score caused by the tilt of the radiometer is calculated, which specifically includes the following sub-steps.

[0058] Sub-step 6.1, calculate the solid angle change ΔΩ caused by the tilt of the radiometer according to the following formula.

[0059]

[0060] Among them, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φ is the azimuth angle of the sun, and θ is the zenith angle of the sun.

[0061] Use trigonometric functions to approximate the above formula at a small angle and simplify it to the formula

[0062]

[0063] Sub-step 6.2, calculate the observation field difference fraction γ caused by the radiometer tilting at an angle α in the zenith direction according to the following formula.

[0064] γ=ΔΩ / (2π)≈α / π;

[0065] Among them, ΔΩ is the change in solid angle caused by the tilt of the radiometer, and α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal.

[0066] The beneficial effects of the present invention are:

[0067] By integrating the latitude and longitude, date, time, attitude information of the buoy, and the incident shortwave radiation measurement values ​​under the corresponding attitude, a model for converting non-horizontal surface irradiance to horizontal surface irradiance was constructed. This model can convert the actual measured non-horizontal surface incident shortwave radiation measurement values ​​into the corresponding horizontal surface incident shortwave radiation values, significantly improving the measurement accuracy of the radiometer in measuring incident shortwave radiation under non-horizontal attitudes, and to a certain extent broadening the scope of application of the radiometer, that is, on the premise of ensuring the accuracy of the measurement data, it can be carried not only on a stable platform but also on a shaking platform, and has a wide range of application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a schematic diagram of the relationship between the sun and the radiometer plane.

[0069] Figure 2 This is a graph showing the variation of incident shortwave with time on a clear day.

[0070] Figure 3 This is a graph showing the variation of incident shortwave with time on a cloudy day.

[0071] Figure 4 This is a graph showing the variation of incident shortwave with time during cloudy weather.

[0072] Figure 5 It is a difference graph of incident shortwave on a clear day.

[0073] Figure 6 It is a difference map of incident shortwave in cloudy weather.

[0074] Figure 7 It is a difference diagram of incident shortwave on a cloudy day.

[0075] Figure 8 This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 10, 2021.

[0076] Fig. 9This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 11, 2021.

[0077] Fig.10 This is a comparison chart of the difference in incident shortwave before and after correction of the observed data on August 14, 2021.

[0078] Fig.11 This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 15, 2021.

[0079] Fig.12 This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 16, 2021.

[0080] Fig.13 This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 19, 2021.

[0081] Fig.14 This is a comparison chart of the difference in incident shortwave before and after correction of the observation data on August 25, 2021. DETAILED DESCRIPTION

[0082] The present invention will be further described in detail below in conjunction with the accompanying drawings and implementation examples. These implementation examples are described in sufficient detail so that those skilled in the art can understand and practice the present invention. Without departing from the spirit and scope of the present invention, logical, achievable and other changes may be made to the implementation. Therefore, the following detailed description should not be construed as limiting, and the scope of the present invention is limited only by the claims.

[0083] In view of the deviation problem existing in the current measurement of incident shortwave radiation on a buoy, the present invention proposes a correction algorithm for the measurement of shortwave radiation of a buoy, which specifically includes the following steps.

[0084] Step 1: Calculate the solar time difference, solar hour angle and solar declination angle based on the measured local geographic longitude information of the buoy, the solar annual cumulative day and Beijing time. Specifically, the following sub-steps are included.

[0085] Sub-step 1.1, calculate the solar time difference E according to the following formula.

[0086] E=9.87sin2B-7.53cosB-1.5sinB;

[0087] in Where N is the yearly cumulative day. Yearly cumulative day is a method of calculating dates continuously only in one year, and is the number of days starting from January 1st of the current year. For example, January 1st of each year is the 1st day, February 1st is the 32nd day, and so on. December 31st of a common year is the 365th day, and December 31st of a leap year is the 366th day. It can be used to easily calculate the time interval between two times in a year.

[0088] Sub-step 1.2, calculate the solar hour angle ω according to the following formula.

[0089]

[0090] Among them, T b is Beijing time, Φ long is the local geographical longitude.

[0091] Sub-step 1.3, calculate the solar declination angle δ according to the following formula.

[0092]

[0093] Where N is the accumulated days per year.

[0094] Step 2: Calculate the solar altitude angle, solar zenith angle and solar azimuth angle according to the solar declination angle and solar hour angle calculated in step 1 and the local geographic latitude information of the buoy measured. Specifically, the following sub-steps are included.

[0095] Sub-step 2.1, calculate the solar altitude angle h according to the following formula.

[0096] h=arcsin(sinΦ lat sinδ+cosΦ lat cosδcosω);

[0097] Among them, Φ lat is the local geographical latitude, δ is the solar declination angle, and ω is the solar hour angle.

[0098] Sub-step 2.2, calculate the solar zenith angle θ according to the following formula.

[0099] θ = 90-h;

[0100] Here, h is the altitude angle of the sun.

[0101] Sub-step 2.3, calculate the azimuth angle Φs of the sun according to the following formula.

[0102]

[0103] Among them, Φ lat is the local geographical latitude, δ is the solar declination angle, h is the solar altitude angle, and ω is the solar hour angle.

[0104] Step three, based on the roll angle (roll) and pitch angle (pitch) of the radiometer measured by the inclinometer, calculate the angle between the zenith direction of the radiometer after tilting and the zenith direction when the radiometer is horizontal, which specifically includes the following sub-steps.

[0105] Sub-step 3.1, Figure 1 The relationship between the sun and the radiometer plane is shown. There is an angle α between the zenith direction of the radiometer after tilting and the zenith direction when the radiometer is horizontal. The angle α is calculated according to the following formula.

[0106] α=arccos(cosρcosσ);

[0107] Among them, ρ is the tilt angle of the radiometer in the roll direction, which is higher in the west and lower in the east (ρ>0), and higher in the east and lower in the west (ρ<0); σ is the tilt angle of the radiometer in the pitch direction, which is higher in the south and lower in the north (σ>0), and higher in the north and lower in the south (σ<0).

[0108] Step 4, based on the roll angle (roll) and pitch angle (pitch) of the radiometer measured by the inclinometer and the azimuth angle of the sun calculated in step 2, calculate the angle between the projection of the zenith direction on the horizontal plane after the radiometer is tilted and the north direction, which specifically includes the following sub-steps.

[0109] Sub-step 4.1, calculate the angle Φ between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted according to the following formula: B .

[0110]

[0111] Where Φs is the azimuth of the sun, ρ is the tilt angle of the radiometer in the roll direction (same as above), and σ is the tilt angle of the radiometer in the pitch direction (same as above).

[0112] Step 5, according to the azimuth angle of the sun and the zenith angle of the sun calculated in step 2, the angle between the zenith direction after the radiometer is tilted calculated in step 3 and the zenith direction when the radiometer is horizontal, and the angle between the projection of the zenith direction on the horizontal plane after the radiometer is tilted calculated in step 4 and the due north direction, calculate the incident angle of the sun, specifically including the following sub-steps.

[0113] Sub-step 5.1, calculate the solar incident angle ξ according to the following formula.

[0114] cosξ=cosθcosα+sinθsinαcos(φ S -φ B );

[0115] Among them, θ is the zenith angle of the sun, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φs is the azimuth angle of the sun, and Φ B It is the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted.

[0116] According to the formula, when the radiometer is in a horizontal state, the solar incident angle ξ is equal to the solar zenith angle θ.

[0117] Step six, based on the angle between the zenith direction after the radiometer is tilted calculated in step three and the zenith direction when the radiometer is horizontal, and the zenith angle and azimuth of the sun calculated in step two, calculate the observation field of view difference score caused by the tilt of the radiometer, which specifically includes the following sub-steps.

[0118] Sub-step 6.1, calculate the change in solid angle caused by the tilt of the radiometer. The solid angle observed by the radiometer is a 2π stereo degree. When the radiometer is horizontal, the observation field is the entire sky. When the radiometer is tilted at an angle α in the zenith direction, the observation field of the radiometer changes, and part of the sky view is lost. At the same time, part of the observation of the underlying surface is increased. The corresponding solid angle ΔΩ is calculated according to the following formula.

[0119]

[0120] Among them, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φ is the azimuth angle of the sun, and θ is the zenith angle of the sun.

[0121] Use trigonometric functions to approximate the above formula at small angles and simplify it to the following formula.

[0122]

[0123] Sub-step 6.2, calculate the observation field difference fraction γ caused by the radiometer tilting at an angle α in the zenith direction according to the following formula.

[0124] γ=ΔΩ / (2π)≈α / π;

[0125] Among them, ΔΩ is the change in solid angle caused by the tilt of the radiometer, and α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal.

[0126] Step 7: The incident shortwave total radiation E measured by the radiometer in a horizontal position H It can be expressed as direct shortwave radiation and diffuse shortwave radiation, and the formula is as follows.

[0127] E H =E dir +E diff ;

[0128] Among them, E dir is the direct short-wave radiation received by the horizontal plane, E diff The diffuse short-wave radiation received by the horizontal plane;

[0129] Step 8: The incident shortwave total radiation E measured by the radiometer in a non-horizontal posture T It can be expressed as direct short-wave radiation, diffuse short-wave radiation and short-wave radiation reflected by the underlying surface, and the formula is as follows.

[0130] E T =E′ dir +E′ diff +E′ ref ;

[0131] Among them, E′ dir is the shortwave radiation received directly by the non-horizontal surface, E′ diff For the diffuse shortwave radiation received by the non-horizontal surface, E′ ref A non-horizontal surface receives shortwave radiation reflected by the underlying surface.

[0132] Step 9: Assuming that the radiation is isotropic, E′ in step 8 dir , E′ diff , E′ ref Can be combined with E in step 7 dir 、E diff Establishing a transformation relationship can be expressed as.

[0133]

[0134] Among them, θ is the zenith angle of the sun, ξ is the incidence angle of the sun, γ is the difference fraction of the observation field of view caused by the tilt of the radiometer, ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, and β is the albedo of the underlying surface.

[0135] Step 10: The radiometer measures the incident shortwave total radiation E in a non-horizontal position. T .

[0136] E T =E′ dir +E′ diff +E′ ref ;

[0137] According to E' in step nine dir , E′ diff , E′ ref With E dir The conversion relationship is: the total short-wave radiation E incident on the radiometer in a non-horizontal posture T Expressed as.

[0138]

[0139] Transform the above formula into

[0140] Among them, E T is the total incident shortwave radiation measured by the radiometer in a non-horizontal attitude, E H It is the total shortwave radiation incident on the horizontal plane calculated based on the measurement results of the radiometer in a non-horizontal posture. ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, θ is the zenith angle of the sun, ξ is the incident angle of the sun, β is the albedo of the underlying surface, and γ is the difference fraction of the observation field of view caused by the tilt of the radiometer.

[0141] The correction algorithm proposed in the present invention obtains the latitude and longitude, date, time, radiometer attitude information of the buoy and the incident shortwave radiation measurement value under the corresponding attitude, and calculates based on the above data to convert the radiation measurement value into the incident shortwave radiation value of the horizontal plane at the same position and time. The algorithm corrects the deviation caused by tilt from a mechanism point of view, and can more accurately reflect the true value compared with the existing time statistical averaging method, significantly improving the measurement accuracy of shortwave radiation on the ocean surface.

[0142] In order to verify the effect of the incident shortwave radiation measurement correction algorithm proposed in the present invention, the inventor conducted experiments on an open rooftop from August 7, 2021 to September 2, 2021, using three CNR4 net radiometers. One was kept absolutely horizontal (roll and pitch were both 0°, and heading was 180°), and the measured value was used as the true value of the horizontal shortwave radiation. Under the condition of controlling a single variable, the other two radiometers had their pitch set to 0°, their heading set to 180°, and their roll directions tilted by 5° and 10° respectively (the zenith direction tilted to the west, higher in the east and lower in the west).

[0143] The three radiometers kept their positions unchanged during the experiment, and a total of 27 days of shortwave radiation data were obtained under different positions of the radiometers. The experiment was conducted on land instead of on a buoy because the land environment can obtain the real horizontal shortwave radiation value, which helps to more reliably verify the effect of the correction algorithm. In addition, for the study of incident shortwave total radiation, the experimental results are not affected by the type of underlying surface (land or sea) of the radiometer.

[0144] By analyzing the experimental data on the 27th, it was found that the radiometer had different effects on incident shortwaves under different weather conditions under the same tilt state, see Figure 2 to Figure 4 , so the weather was classified according to the incident shortwave data, and the weather was mainly divided into the following three categories: sunny, cloudy, and overcast. It was further found that the tilt of the radiometer had the greatest impact on the incident shortwave on sunny days (see Figure 5), the measurement deviations caused by inclinations of 10° and 5° account for 29.83% and 10.47% of the horizontal shortwave radiation measurement values ​​respectively; the impact of incident shortwave on cloudy days is minimal (see Figure 6 ), the measurement deviations caused by tilts of 10° and 5° accounted for 3.0% and 1.9% of the horizontal shortwave radiation measurement values ​​respectively; however, under cloudy conditions, the effect of the radiometer tilt on the incident shortwave is unstable (see Figure 7 ), when there is no cloud blocking the zenith direction of the radiometer, it is equivalent to a sunny day, and the difference between the tilt and the horizontal measurement value is relatively large. When there is cloud blocking, it is equivalent to a cloudy day, and the difference between the tilt and the horizontal measurement value is relatively small.

[0145] Through the experimental measurement results, it can be found that even if the buoy is only tilted by 10°, the measured value of the radiometer has deviated from the true value by nearly 30%, and it is very common for the buoy to tilt by 10°, so the buoy shortwave radiation measurement value must be corrected to ensure the quality of the ocean surface shortwave radiation data. Since the tilt of the radiometer causes the greatest deviation in the incident shortwave radiation under sunny conditions, the inventor first uses the correction algorithm of the present invention to correct the deviation of the incident shortwave under sunny conditions, and verifies the effect of the incident shortwave radiation measurement correction algorithm proposed by the present invention through experimental data.

[0146] According to the above correction algorithm, combined with the latitude and longitude of the experimental site, date, time, radiometer tilt attitude information and the incident shortwave radiation measurement value at the corresponding attitude, the inventor calculated the correction value of the radiometer at each moment when it was tilted 5° and 10°. Subsequently, the corrected radiation value was compared with the true horizontal measurement value, and the results of all sunny days in the experimental data (a total of 7 days) were analyzed. The evaluation indicators of the correction results include the mean absolute error (MAE) and root mean square error (RMSE) before and after correction.

[0147] Mean absolute error (MAE) before and after correction:

[0148] Where n represents the total number of data, E′ t Indicates the tilt measurement value of the radiometer before (after) correction, E t Indicates the radiometer level measurement value before and after correction. The comparison data of mean absolute error (MAE) before and after correction are shown in Table 1 and Table 2.

[0149] Table 1: Comparison of mean absolute error (MAE) before and after 5° tilt correction

[0150]

[0151] Table 2: Comparison of mean absolute error (MAE) before and after 10° tilt correction

[0152]

[0153] Root mean square error (RMSE) before and after correction:

[0154] Where n represents the total number of data, E′t represents the tilt measurement value of the radiometer before (after) correction, and Et represents the horizontal measurement value of the radiometer before (after) correction. The root mean square error (RMSE) comparison data before and after correction are shown in Tables 3 and 4.

[0155] Table 3: Comparison of root mean square error (RMSE) before and after 5° tilt correction

[0156]

[0157] Table 4: Comparison of root mean square error (RMSE) before and after 10° tilt correction

[0158]

[0159] Figure 8 to Figure 14 A comparison chart of the difference in incident shortwave radiation before and after correction is shown. In the figure, the horizontal axis represents time, and the vertical axis represents the difference in incident shortwave radiation. The solid blue line represents the difference between the original radiometer tilted 5° west and the horizontal measurement value, the dotted blue line represents the difference between the value corrected by the radiometer tilted 5° west and the horizontal measurement value, the solid red line represents the difference between the original radiometer tilted 10° west and the horizontal measurement value, and the dotted red line represents the difference between the value corrected by the radiometer tilted 10° west and the horizontal measurement value.

[0160] The above data combined with the diagrams show that the correction algorithm effectively corrects the measurement deviation of the radiometer at different tilt angles. When the radiometer is tilted 5°, the mean absolute error (MAE) correction ratios of the algorithm under all sunny conditions are 81.36%, 80.88%, 85.40%, 85.61%, 86.27%, 76.77% and 75.12%, respectively, and the average correction ratio reaches 81.63%.

[0161] In comparison, the algorithm also corrected the measurement deviation of the radiometer when it was tilted 10°, but the effect was slightly worse than that of the 5° case. The MAE correction ratios under all sunny conditions were: 68.04%, 60.60%, 61.88%, 59.11%, 52.50%, 53.18% and 55.25%, and the average correction ratio was 58.65%.

[0162] In addition, from the data results of the root mean square error (RMSE), for the case of a 5° tilt of the radiometer, the RMSE correction ratios of the algorithm under all sunny conditions are: 80.93%, 77.17%, 81.58%, 81.28%, 86.54%, 72.56% and 69.75%, and the average correction ratio is 78.54%. In comparison, the algorithm's measurement deviation correction effect is slightly worse at a tilt of 10°, and the RMSE correction ratios under all sunny conditions are: 65.41%, 57.52%, 54.93%, 54.75%, 58.10%, 50.21% and 50.20%, and the average correction ratio is 55.87%.

[0163] In general, the correction algorithm can effectively reduce the MAE and RMSE deviations under the tilt conditions of 5° and 10°, and the effect is especially ideal under the tilt of 5°.

[0164] However, the prior art uses a time statistical average method to forcibly offset errors. The sampling rate of the radiometer is usually set to once per minute, and 30 minutes of time average data is used to characterize the true shortwave radiation value. The solution proposed by the present invention is to perform tilt correction on the shortwave radiation data based on the mechanism of error generation. Although this method cannot completely eliminate all errors, it significantly improves the measurement accuracy of the incident shortwave radiation of the radiometer in a non-horizontal state compared with the prior art.

[0165] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A correction algorithm for buoy shortwave radiation measurement, characterized in that: The following steps are involved: Step 1: Calculate the solar time difference, solar hour angle and solar declination angle based on the measured local geographic longitude information of the buoy, the annual accumulated day and time of the sun; Step 2, calculating the solar altitude angle, solar zenith angle and solar azimuth angle according to the solar declination angle and solar hour angle calculated in step 1 and the local geographic latitude information of the buoy measured; Step 3: Calculate the angle between the zenith direction of the radiometer after tilting and the zenith direction when the radiometer is horizontal according to the roll angle and pitch angle of the radiometer measured by the inclinometer; Step 4, calculating the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted, based on the roll angle and pitch angle of the radiometer measured by the inclinometer and the azimuth of the sun calculated in step 2; Step 5, according to the azimuth angle of the sun and the zenith angle of the sun calculated in step 2, the angle between the zenith direction after the radiometer is tilted calculated in step 3 and the zenith direction when the radiometer is horizontal, and the angle between the projection of the zenith direction on the horizontal plane after the radiometer is tilted calculated in step 4 and the true north direction, calculate the incident angle of the sun; Step 6, calculating the observation field difference score caused by the tilt of the radiometer according to the angle between the zenith direction after the radiometer is tilted calculated in step 3 and the zenith direction when the radiometer is horizontal and the zenith angle and azimuth of the sun calculated in step 2; Step 7: The incident shortwave total radiation E measured by the radiometer in a horizontal position H It can be expressed as direct shortwave radiation and diffuse shortwave radiation, the formula is as follows: AND H =And dir +E diff ; Among them, E dir is the direct short-wave radiation received by the horizontal plane, E diff The diffuse short-wave radiation received by the horizontal plane; Step 8: The incident shortwave total radiation E measured by the radiometer in a non-horizontal posture T It can be expressed as direct shortwave radiation, diffuse shortwave radiation and shortwave radiation reflected by the underlying surface. The formula is as follows: AND T =It's dir +E′ diff +E′ ref ; Among them, E′ dir is the shortwave radiation received directly by the non-horizontal surface, E′ diff For the diffuse shortwave radiation received by the non-horizontal surface, E′ ref For non-horizontal surfaces, shortwave radiation is received that is reflected by the underlying surface; Step 9: Assuming that the radiation is isotropic, E′ in step 8 dir , E′ diff , E′ ref Can be combined with E in step 7 dir 、E diff Establishing a conversion relationship can be expressed as: Among them, θ is the zenith angle of the sun, ξ is the incident angle of the sun, γ is the difference fraction of the observation field of view caused by the tilt of the radiometer, ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, and β is the albedo of the underlying surface; Step 10: The radiometer measures the incident shortwave total radiation E in a non-horizontal position. T : AND T =It's dir +E′ diff +E′ ref ; According to E' in step nine dir , E′ diff , E′ ref With E dir The conversion relationship is that the total short-wave radiation E incident on the radiometer in a non-horizontal posture T It is expressed as: Transform the above formula into: Among them, E T is the total incident shortwave radiation measured by the radiometer in a non-horizontal attitude, E H It is the total shortwave radiation incident on the horizontal plane calculated based on the measurement results of the radiometer in a non-horizontal posture. ε is the proportion of direct radiation to the total shortwave radiation in the horizontal posture of the radiometer, θ is the zenith angle of the sun, ξ is the incident angle of the sun, β is the albedo of the underlying surface, and γ is the difference fraction of the observation field of view caused by the tilt of the radiometer.

2. The algorithm according to claim 1, characterized in that The calculation of the solar time difference, solar hour angle and solar declination angle in step 1 specifically includes the following sub-steps: Sub-step 1.1, calculate the solar time difference E according to the following formula: E=9.87sin2B-7.53cosB-1.5sinB; in: Where N is the accumulated days per year; Sub-step 1.2, calculate the solar hour angle ω according to the following formula: Among them, T b is Beijing time, Φ long is the local geographical longitude; Sub-step 1.3, calculate the solar declination angle δ according to the following formula: Where N is the number of days per year.

3. The algorithm according to claim 1, characterized in that Step 2 calculates the solar altitude angle, solar zenith angle and solar azimuth angle, which specifically includes the following sub-steps: Sub-step 2.1, calculate the solar altitude angle h according to the following formula: h=arcsin(sinΦ lat sinδ+cosΦ lat cosδcosω); Among them, Φ lat is the local geographic latitude, δ is the solar declination angle, and ω is the solar hour angle; Sub-step 2.2, calculate the sun's zenith angle θ according to the following formula: θ = 90-h; Where h is the altitude angle of the sun; Sub-step 2.3, calculate the solar azimuth angle Φs according to the following formula: Among them, Φ lat is the local geographical latitude, δ is the solar declination angle, h is the solar altitude angle, and ω is the solar hour angle.

4. The algorithm according to claim 1, characterized in that In step 3, the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal is calculated as follows: There is an angle α between the zenith direction of the radiometer after tilting and the zenith direction when the radiometer is horizontal. The angle α is calculated according to the following formula: α=arccos(cosρcosσ); Among them, ρ is the tilt angle of the radiometer in the roll direction, ρ>0 when it is higher in the west and lower in the east, and ρ<0 when it is higher in the east and lower in the west; σ is the tilt angle of the radiometer in the pitch direction, σ>0 when it is higher in the south and lower in the north, and σ<0 when it is higher in the north and lower in the south.

5. The algorithm according to claim 1, characterized in that In step 4, the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted is calculated as follows: The angle Φ between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted is calculated according to the following formula: B : Among them, Φs is the azimuth of the sun, ρ is the tilt angle of the radiometer in the roll direction, and σ is the tilt angle of the radiometer in the pitch direction.

6. The algorithm according to claim 1, characterized in that In step 5, the angle of incidence of the sun is calculated as follows: The incident angle ξ of the sun is calculated according to the following formula: cosξ=cosθcosα+sinθsinαcos(φ S -f B ); Among them, θ is the zenith angle of the sun, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φs is the azimuth angle of the sun, and Φ B It is the angle between the projection of the zenith direction on the horizontal plane and the true north direction after the radiometer is tilted.

7. The algorithm according to claim 6, characterized in that When the radiometer is in a horizontal position, the solar incident angle ξ is equal to the solar zenith angle θ.

8. The algorithm according to claim 1, characterized in that Step 6 calculates the difference score of the observation field caused by the tilt of the radiometer, which specifically includes the following sub-steps: Sub-step 6.1, calculate the solid angle change ΔΩ caused by the tilt of the radiometer according to the following formula: Among them, α is the angle between the zenith direction after the radiometer is tilted and the zenith direction when the radiometer is horizontal, Φ is the azimuth angle of the sun, and θ is the zenith angle of the sun; Use trigonometric functions to approximate the above formula at a small angle and simplify it to the following formula: Sub-step 6.2, calculate the difference fraction γ of the observation field of view caused by the tilt angle α of the radiometer zenith direction according to the following formula: γ=ΔΩ / (2π)≈α / π; Among them, ΔΩ is the change in solid angle caused by the tilt of the radiometer, and α is the angle between the zenith direction after the tilt of the radiometer and the zenith direction when the radiometer is horizontal.

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