CN112985607B - Method for correcting heat radiation directivity of geostationary satellite earth surface uplink long-wave radiation product - Google Patents
Method for correcting heat radiation directivity of geostationary satellite earth surface uplink long-wave radiation product Download PDFInfo
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Abstract
The invention discloses a method for correcting the heat radiation directivity of a geostationary satellite earth surface uplink long-wave radiation product, wherein the geostationary satellite can carry out high-frequency shooting on the earth surface from a fixed angle, a new generation of geostationary satellite can realize earth observation every fifteen minutes, and the earth surface uplink long-wave radiation precision estimated based on a single-angle satellite signal is limited by the earth surface heat radiation directivity. The existing satellite scale heat radiation directivity correction methods all need multi-angle instantaneous synchronous observation, while the multiple observation of a stationary satellite in one day is not synchronous, and the existing correction methods cannot be applied due to the interference of the phenomena of surface temperature rise and temperature reduction. The input data of the invention is only the atmospheric layer top radiation brightness value of the geostationary satellite at multiple times, so that the separation of the heat radiation directivity error and the hemispherical integral true value in the earth surface uplink long wave radiation can be realized, and the accuracy and the simplicity are both realized.
Description
Technical Field
The invention relates to a practical method for correcting the thermal radiation directivity of a geostationary satellite earth surface uplink long-wave radiation product, which can be used for correcting the angle of the geostationary satellite earth surface uplink long-wave radiation product and belongs to the technical field of spatial information.
Background
The remote sensing product of surface ascending long wave radiation is widely applied to the fields of hydrology, ecology, meteorology, environment and the like, is a direct index for representing the changes in temperature of the earth and is one fourth of the surface radiation balance. Geostationary satellites, represented by GOES-16, MSG, Hiwari-8, FengYun-4, are all provided with thermal infrared channels to observe long-wave radiation up the earth's surface. Because the geostationary satellite can only observe the earth from a fixed angle, the existing algorithm for estimating the earth surface uplink long wave radiation by utilizing the geostationary satellite atmospheric layer top brightness temperature assumes that the earth surface heat radiation is isotropic, namely, the earth surface uplink long wave radiation inverted from an observation signal in a certain direction is considered to be equal to the uplink long wave radiation of the hemispherical integral actually measured on the ground.
However, ground, aviation, and satellite scale studies have shown that earth surface thermal radiation is non-isotropic, and this phenomenon is referred to as thermal radiation directionality. For the different-temperature pixel with a complex three-dimensional structure, the directional brightness and temperature difference observed in different directions can be up to 10K due to the thermal radiation directivity, and the precision of the long-wave radiation product on the earth surface is severely limited. Even on the ground surface such as uniform desert, water surface, etc., there is a remarkable directional phenomenon of heat radiation. The phenomenon of the radiation directivity is more prominent in summer than in winter, daytime than at night and sparsely-and densely-populated vegetation, and research shows that the avoidance of the radiation directivity is the largest, which can cause 10% of estimation errors of long-wave radiation products on the earth surface.
Therefore, for different earth surface types (vegetation, cities, soil, water, ice and snow and the like), researchers at home and abroad propose a plurality of physical models to describe the directional phenomenon of thermal radiation, establish the relationship between the directional brightness temperature and the parameters such as earth surface structure, attributes, spectrum, temperature difference and the like, and try to correct the angle effect of long-wave radiation products on the earth surface. However, these physical models cannot be put into practical use because of too many driving parameters, so in recent years, a semi-empirical semi-physical simulation model of a thermal infrared band is proposed, the solution of the nuclear coefficient and the calculation of the brightness temperature/temperature in any direction are realized directly by inputting the brightness temperature/temperature in a plurality of directions, and after the brightness temperature in all directions of the hemisphere is calculated, the accurate estimation of the long-wave radiation on the earth surface can be realized through hemisphere integration. The current thermal infrared semi-empirical semi-physical simulation models mainly comprise 8 models: three-parameter Ross-Li model, RL model, LSF-Li model and Vinnikov model, and four-parameter LSF-RL model, LSF-Chen model, Vinnikov-RL model and Vinnikov-Chen model. The accuracy of the four-parameter model is obviously superior to that of the three-parameter model, but the models are static models, namely quasi-synchronous thermal infrared observation data of 3-4 angles are required to be input so as to ensure the stability of the surface temperature state.
For a certain pixel, the observation angle of a stationary satellite is unchanged, and the sun angle changes within one day, so that a multi-angle data set can be formed, however, the multi-angle data set is not quasi-synchronous, because the earth surface temperature state changes along with the change of the illumination condition and is simultaneously influenced by thermal inertia, which is generally expressed as the trend of temperature increase in the morning and temperature decrease in the afternoon. Due to the lack of the semi-empirical semi-physical model of the dynamic thermal radiation directivity, no practical method is available at home and abroad at present to effectively correct the thermal radiation directivity by utilizing the dynamic multi-angle information of the geostationary satellite.
Disclosure of Invention
In order to solve the defects of the technology, the invention provides a method for correcting the thermal radiation directivity of a long-wave radiation product on the earth surface of a geostationary satellite.
In order to solve the technical problems, the invention adopts the technical scheme that: a method for correcting the thermal radiation directivity of a long-wave radiation product on the earth surface of a stationary satellite comprises the following steps:
calculating an initial value SULRe (t) of the earth surface uplink long wave radiation of the geostationary satellite under a clear sky condition by using a classical multiband atmospheric layer top radiance direct estimation method;
step two, fitting the initial values of the earth surface uplink long wave radiation estimated in the step one by using a daily variation model to obtain initial coefficient values of four daily variation models, and limiting the daily variation parameter range of the earth surface uplink long wave radiation truth value SURRM (t) on the basis of the initial coefficient values;
step three, modeling a heat radiation directivity correction term TRD (t) related to a time-related angle;
step four, solving six unknowns by combining the results of the first three steps, wherein the six unknowns comprise four unknowns of a daily variation model and two unknowns of heat radiation directional modeling;
step five, calculating an earth surface uplink long wave radiation truth value by using the four daily change parameters solved in the step four;
and step six, verifying the result of the step five by utilizing ground measured data, wherein the selected evaluation indexes comprise root mean square error RMSE and average deviation MBE.
Further, the specific process of the step one is as follows:
firstly, simulating multi-channel atmospheric layer top radiance (LTOA,1, LTOA,2 … L TOA, n) and ground surface ascending long-wave radiation truth values under the conditions of different ground surface temperatures, ground surface emissivity and atmospheric profiles based on an MODTRAN atmospheric radiation transmission model, and then obtaining a regression coefficient of each channel by using a multiple linear regression method, wherein the regression coefficient is shown in a formula (1):
SULRe(t)＝(a0,a1,a2…an)T·(1,LTOA,1(t),LTOA,2(t)…LTOA,n(t)) (1)
in the above formula, LTOA,1 is the top radiance of the atmosphere layer in the first atmospheric window band, LTOA,2 is the top radiance of the atmosphere layer in the second atmospheric window band, and three characteristic bands of 8.5 microns, 11 microns and 12 microns are generally selected, a1,a2…anFitting coefficients of a first wave band … and an Nth wave band a0Is a constant term.
Further, the specific process of the second step is as follows:
the daily variation model consists of a day section model and a night section model, but because the earth surface heat radiation directivity at night is weak, the earth surface heat radiation directivity phenomenon at the day section is only corrected, and the SULR daily variation at day is fitted by a cosine function shown in a formula (2-3):
SULRe(t)＝SULR0+SULRa·cos(π(t-tm)/ω) (2)
SULRm(t)＝SULR0’+SULRa’·cos(π(t-tm’)/ω’) (3)
the formula (2) is used for fitting the daily change of the initial value SULRe, the formula 3 is used for fitting the corrected daily change of the surface uplink long-wave radiation SULRm, and the results all have 4 coefficients, namely initial surface uplink long-wave radiation SULR0 and SULR0 'near the sunrise time, change amplitudes SULRa and SULRa', maximum surface uplink long-wave radiation occurrence times tm and tm ', and cosine half-cycle widths ω and ω'; obtaining SULR0, SULRa, tm and ω based on the estimation result in the step one, and obtaining initial values and value ranges of SULR0, SULRa, tm and ω based on the initial values and value ranges: SULR0-100< SULR 0' < SULR0+ 100; SULRa-100< SULRa' < SULRa + 100; tm-2< tm' < tm + 2; omega-2 < omega' < omega + 2.
Further, the specific process of step three is as follows:
instantaneous angle-dependent earth surface thermal radiation directivity modeling mainly considers the influence of three factors: the size of the surface temperature difference affects the hot spot amplitude, and the surface structure affects the hot spot width; the surface structure is considered to be unchanged within one day; the angular distance between the observation direction and the sun direction is analyzed and calculated by a formula (5); the surface temperature difference is a time-dependent quantity, which is related to the incident intensity of sunlight and is influenced by the surface thermal inertia, and is calculated by the formula (4):
TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (4)
in the formula (4), cos θs(t) is used to characterize the solar illumination conditions at different times of the day, sulrm (t) represents the effect of thermal inertia on the surface temperature difference change, a is a scaling factor to constrain the maximum value of trd (t), and B is a scene structure related quantity used to characterize the hotspot width; theta in the formula (5)sIs the solar zenith angle; thetavObserving a zenith angle;
and
representing the solar azimuth and the observation azimuth, respectively.
Further, the specific process of step four is as follows:
simultaneous equations (1-5) can yield the following equations:
SULRe(t)-SULRm(t)＝TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (6)
after the shift, the following formula is obtained:
SULRe(t)＝SULRm(t)·(1+cosθs(t)·A·e-f(t)/(π·B)) (7)
substituting equation (3) into equation (7) yields the following result:
SULRe(t)＝(SULR0’+SULRa’·cos(π(t-tm’)/ω’)·(1+cosθs(t)·A·e-f(t)/(π·B)) (8)
the formula contains six unknowns, namely initial earth surface uplink long-wave radiation SULR0 'near sunrise time, change amplitude SULRa', maximum SULR occurrence time tm ', cosine half-cycle width omega', scaling factor A and hot spot width B; when the effective observation of the stationary satellite in one day is not less than six, the equation can be directly solved; the nonlinear solution needs to assign initial values and value ranges to the unknowns, the ranges of the first four parameters are determined in the step two, and the initial values of A and B are as follows: a is 0.05, B is 0.25, and the value ranges of A and B are as follows: 0< a <0.1, 0< B < 0.5.
Further, the specific process of step five is as follows:
four daily change parameters of SULRm, namely initial surface upward long-wave radiation SULR0 ', change amplitude SULRa', maximum SULR occurrence time tm 'and cosine half-cycle width ω', are obtained in the fourth step, and then the true value of SULRm (t), namely the surface upward long-wave radiation result after the thermal radiation directivity correction, is calculated by using the formula (3).
Further, the specific process of the step six is as follows:
the parameters measured by the ground radiation meter are the semi-sphere integral surface ascending long-wave radiation value (SULRt), which is completely consistent with SULRm in formula (3) in physical sense, the SULRm result obtained in the fifth step for correcting the thermal radiation directivity can be verified by using the observed value SULRt of the ground radiation meter, 2 selected evaluation indexes are shown in formula (9-10):
in the above formula, tiRepresenting the satellite observation time, t1And tNRespectively start-stop and end times.
The invention provides a heat radiation directivity correction term related to a time-related angle, effectively utilizes multi-angle information formed by multiple observations of a geostationary satellite in one day, realizes dynamic correction of heat radiation directivity, obviously improves estimation precision of earth surface uplink long wave radiation of the geostationary satellite, and solves the problem of avoiding heat radiation directivity in estimation of earth surface uplink long wave radiation of the geostationary satellite all the time. The input data of the invention is only the atmospheric layer top radiation brightness value of the geostationary satellite at multiple times, so that the separation of the heat radiation directivity error and the hemispherical integral true value in the earth surface uplink long wave radiation can be realized, and the accuracy and the simplicity are both realized.
Drawings
FIG. 1 is an overall flow chart of the method of the present invention.
FIG. 2 is a graph of the results of tests based on GOES-16ABI data.
Fig. 3 is a scatter plot of SULRe and SULRm with SULRt as a standard.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
A method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite, as shown in fig. 1, comprises the steps of:
calculating an initial value SULRe (t) of the earth surface uplink long wave radiation of the geostationary satellite under a clear sky condition by using a classical multiband atmospheric layer top radiance direct estimation method;
step two, fitting the initial values of the earth surface uplink long wave radiation estimated in the step one by using a daily variation model to obtain initial coefficient values of four daily variation models, and limiting the daily variation parameter range of the earth surface uplink long wave radiation truth value SURRM (t) on the basis of the initial coefficient values;
step three, modeling a heat radiation directivity correction term TRD (t) related to a time-related angle;
step four, solving six unknowns by combining the results of the first three steps, wherein the six unknowns comprise four unknowns of a daily variation model and two unknowns of heat radiation directional modeling;
step five, calculating an earth surface uplink long wave radiation truth value by using the four daily change parameters solved in the step four;
and step six, verifying the result of the step five by utilizing ground measured data, wherein the selected evaluation indexes comprise root mean square error RMSE and average deviation MBE.
The specific process of the step one is as follows:
firstly, simulating multichannel atmospheric layer top radiance (LTOA,1, LTOA,2 … L TOA, n) and ground surface uplink long wave radiation truth values under the conditions of different ground surface temperatures, ground surface emissivity and atmospheric profiles based on an MODTRAN atmospheric radiation transmission model, and then obtaining a regression coefficient of each channel by using a multivariate linear regression method, wherein the radiance of the atmospheric layer top observed in the atmospheric window channel comprises effective information of ground surface uplink long wave radiation, and the results can be used for regressing the results of the ground surface uplink long wave radiation, and are shown in a formula (1):
SULRe(t)＝(a0,a1,a2…an)T·(1,LTOA,1(t),LTOA,2(t)…LTOA,n(t)) (1)
in the above formula, LTOA,1 is the top radiance of the atmosphere layer in the first atmospheric window band, LTOA,2 is the top radiance of the atmosphere layer in the second atmospheric window band, and three characteristic bands of 8.5 microns, 11 microns and 12 microns are generally selected, a1,a2…anFitting coefficients of a first wave band … and an Nth wave band a0Is a constant term;
the method has become the mainstream algorithm for producing global earth surface uplink long wave radiation products at present due to the indirection and the accuracy, multiple observations of the geostationary satellite in one day can be directly estimated by using the formula for multiple times to obtain a dynamic SULRe result, the result is based on the radiation brightness in a single direction to estimate the earth surface uplink long wave radiation, the radiation is influenced by the directivity of the earth surface heat radiation, and the deviation exists between the actual value of the earth surface actual measurement uplink long wave radiation and can be used as an initial value of estimation.
The specific process of the second step is as follows:
the earth surface temperature and the daily change of the upward long-wave radiation of the earth surface can be accurately depicted by adopting a daily change model, the daily change model consists of a day section model and a night section model, but the directivity of the thermal radiation of the earth surface at night is weak, so that the directivity phenomenon of the thermal radiation of the earth surface at the day section is only corrected, and the daily change of the SULR at the day is fitted by a cosine function shown in a formula (2-3):
SULRe(t)＝SULR0+SULRa·cos(π(t-tm)/ω) (2)
SULRm(t)＝SULR0’+SULRa’·cos(π(t-tm’)/ω’) (3)
the formula (2) is used for fitting the daily change of the initial value SULRe, the formula 3 is used for fitting the corrected daily change of the surface uplink long-wave radiation SULRm, and the results all have 4 coefficients, namely initial surface uplink long-wave radiation SULR0 and SULR0 'near the sunrise time, change amplitudes SULRa and SULRa', maximum surface uplink long-wave radiation occurrence times tm and tm ', and cosine half-cycle widths ω and ω'; obtaining SULR0, SULRa, tm and ω based on the estimation result in the step one, and obtaining initial values and value ranges of SULR0, SULRa, tm and ω based on the initial values and value ranges: SULR0-100< SULR 0' < SULR0+ 100; SULRa-100< SULRa' < SULRa + 100; tm-2< tm' < tm + 2; omega-2 < omega' < omega + 2.
The concrete process of the third step is as follows:
instantaneous angle-dependent earth surface thermal radiation directivity modeling mainly considers the influence of three factors: the size of the surface temperature difference affects the hot spot amplitude, and the surface structure affects the hot spot width;
for a multi-angle data set constructed by observing a stationary satellite for multiple times a day, a dynamic modeling method is required to depict the heat radiation directivity so as to consider the time correlation of the magnitude of the surface temperature difference and the angle correlation of the angle distance between the observation direction and the sun direction;
the surface structure may be considered to be constant throughout the day; the angular distance between the observation direction and the sun direction can be analyzed and calculated by a formula (5); the surface temperature difference is a time-dependent quantity, which is related to the incident intensity of sunlight and is influenced by the surface thermal inertia, so the invention provides a new method for calculating a thermal radiation directivity correction term trd (t) related to a time-dependent angle, which can be calculated by the formula (4):
TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (4)
in the formula (4), cos θs(t) is used to characterize the solar illumination conditions at different times of the day, sulrm (t) represents the effect of thermal inertia on the surface temperature difference change, a is a scaling factor to constrain the maximum value of trd (t), and B is a scene structure related quantity used to characterize the hotspot width; theta in the formula (5)sIs the solar zenith angle; thetavObserving a zenith angle;
and
representing the solar azimuth and the observation azimuth, respectively.
The concrete process of the step four is as follows:
simultaneous equations (1-5) can yield the following equations:
SULRe(t)-SULRm(t)＝TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (6)
after the shift, the following formula is obtained:
SULRe(t)＝SULRm(t)·(1+cosθs(t)·A·e-f(t)/(π·B)) (7)
substituting equation (3) into equation (7) yields the following result:
SULRe(t)＝(SULR0’+SULRa’·cos(π(t-tm’)/ω’)·(1+cosθs(t)·A·e-f(t)/(π·B)) (8)
the formula contains six unknowns, namely initial earth surface uplink long-wave radiation SULR0 'near sunrise time, change amplitude SULRa', maximum SULR occurrence time tm ', cosine half-cycle width omega', scaling factor A and hot spot width B; when the effective observation of the stationary satellite in one day is not less than six, the equation can be directly solved; the nonlinear solution needs to assign initial values and value ranges to the unknowns, the ranges of the first four parameters are determined in the step two, and the initial values of A and B are as follows: a is 0.05, B is 0.25, and the value ranges of A and B are as follows: 0< a <0.1, 0< B < 0.5.
The concrete process of the step five is as follows:
four daily change parameters of SULRm, namely initial surface upward long-wave radiation SULR0 ', change amplitude SULRa', maximum SULR occurrence time tm 'and cosine half-cycle width ω', are obtained in the fourth step, and then the true value of SULRm (t), namely the surface upward long-wave radiation result after the thermal radiation directivity correction, is calculated by using the formula (3).
The concrete process of the step six is as follows:
the parameters measured by the ground radiation meter are the semi-sphere integral surface ascending long-wave radiation value (SULRt), which is completely consistent with SULRm in formula (3) in physical sense, the SULRm result obtained in the fifth step for correcting the thermal radiation directivity can be verified by using the observed value SULRt of the ground radiation meter, 2 selected evaluation indexes are shown in formula (9-10):
in the above formula, tiRepresenting the satellite observation time, t1And tNRespectively start-stop and end times.
The invention will be further elucidated with reference to specific examples.
Examples 1,
GOES-16 is the first satellite of the new generation of geos-R family geostationary satellites in the united states, and was launched in 2016 and data was released 2017. The loaded main load ABI can realize the earth observation once every 15 minutes, the central wavelengths of 11 th, 14 th and 15 th wave bands are 8.5, 11.2 and 12.3 mu m, and the initial value SULRe of the long-wave radiation on the earth surface can be directly estimated by utilizing the top radiation brightness of the atmospheric layer of the three characteristic channels. The method provided by the invention can be used for further estimating and obtaining a result SULRm after the heat radiation directivity is corrected, and the accuracy of SULRm can be directly verified by using measured data SULRt of the American flux site, so as to test the efficacy of the method, and the specific implementation mode is shown in figure 1.
Fig. 2 shows the result of directly estimating SULRe by using the ABI atmospheric layer top radiation brightness, which includes the initial estimation result (SULRe) of long-wave radiation on the earth surface, the correction result (SULRm) considering the radiation directivity, and the ground site actual measurement result (SULRt). As indicated by the circles in fig. 2, and the SULR results after the heat radiation directivity correction, as indicated by the green boxes in fig. 2, the site measured SULR data is once every 30 minutes, as indicated by the star in fig. 2, so the estimated SULRe and SULRm are also sampled to the time frequency, from 9 am to 16 pm, including 15 observations per day. Fig. 2(a) - (d) show the results of the site at 30 days 08/month 2019, 26 days 08/month 2019, 13 days 08/month 2019 and 12 days 08/month 2019, respectively, the RMSE of SULRe is 22.9, 28.5, 23.2 and 18.7W/m2, the RMSE of SULRm is reduced to 12.7, 4.8, 7.7 and 9.6W/m2, respectively, and the overestimation phenomenon of SULRe is remarkably suppressed.
Fig. 3 shows a scatter diagram of the estimation results of all 4 days (60 points in total, 30 days on 08 month 2019, 26 days on 08 month 2019, 13 days on 08 month 2019 and 12 days on 08 month 2019), and it can be seen that overall, RMSE of SULRe is 23.6W/m2, RMSE of SULRm is 9.2W/m2, and RMSE is greatly reduced by 14.4W/m2, which proves the effectiveness and advancement of the present invention.
The invention firstly provides a heat radiation directivity correction term related to a time-related angle, and a six-parameter heat radiation directivity correction algorithm of geostationary satellite earth surface uplink long-wave radiation is constructed on the basis of the heat radiation directivity correction term. Site actual measurement verification based on the GOES-16 geostationary satellite and the America Flux shows that the method effectively inhibits the error caused by the radiation directivity of the ground surface uplink long wave radiation, and obviously improves the precision of the ground surface uplink long wave radiation. The method has important application value in the technical field of spatial information, particularly in the field of surface energy balance remote sensing.
The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make variations, modifications, additions or substitutions within the technical scope of the present invention.
Claims (7)
1. A method for correcting the thermal radiation directivity of a long-wave radiation product on the earth surface of a stationary satellite is characterized in that: the method comprises the following steps:
calculating an initial value SULRe (t) of the earth surface uplink long wave radiation of the geostationary satellite under a clear sky condition by using a classical multiband atmospheric layer top radiance direct estimation method;
step two, fitting the initial values of the earth surface uplink long wave radiation estimated in the step one by using a daily variation model to obtain initial coefficient values of four daily variation models, and limiting the daily variation parameter range of the earth surface uplink long wave radiation truth value SURRM (t) on the basis of the initial coefficient values;
step three, modeling a heat radiation directivity correction term TRD (t) related to a time-related angle;
step four, solving six unknowns by combining the results of the first three steps, wherein the six unknowns comprise four unknowns of a daily variation model and two unknowns of heat radiation directional modeling;
step five, calculating an earth surface uplink long wave radiation truth value by using the four daily change parameters solved in the step four;
and step six, verifying the result of the step five by utilizing ground measured data, wherein the selected evaluation indexes comprise root mean square error RMSE and average deviation MBE.
2. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the specific process of the step one is as follows:
firstly, simulating multi-channel atmospheric layer top radiance (LTOA,1, LTOA,2 … LTOA, n) and ground surface ascending long-wave radiance truth values under the conditions of different ground surface temperatures, ground surface emissivity and atmospheric profiles based on an MODTRAN atmospheric radiation transmission model, and then obtaining a regression coefficient of each channel by using a multiple linear regression method, wherein the regression coefficient is shown in a formula (1):
SULRe(t)＝(a0,a1,a2…an)T·(1,LTOA,1(t),LTOA,2(t)…LTOA,n(t)) (1)
in the above formula, LTOA,1 is the top radiance of the atmosphere layer in the first atmospheric window band, LTOA,2 is the top radiance of the atmosphere layer in the second atmospheric window band, and three characteristic bands of 8.5 microns, 11 microns and 12 microns are generally selected, a1,a2…anFitting coefficients of a first wave band … and an Nth wave band a0Is a constant term.
3. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the specific process of the second step is as follows:
the daily variation model consists of a day section model and a night section model, but because the earth surface heat radiation directivity at night is weak, the earth surface heat radiation directivity phenomenon at the day section is only corrected, and the SULR daily variation at day is fitted by a cosine function shown in a formula (2-3):
SULRe(t)＝SULR0+SULRa·cos(π(t-tm)/ω) (2)
SULRm(t)＝SULR0’+SULRa’·cos(π(t-tm’)/ω’) (3)
the formula (2) is used for fitting the daily change of the initial value SULRe, the formula 3 is used for fitting the corrected daily change of the surface uplink long-wave radiation SULRm, and the results all have 4 coefficients, namely initial surface uplink long-wave radiation SULR0 and SULR0 'near the sunrise time, change amplitudes SULRa and SULRa', maximum surface uplink long-wave radiation occurrence times tm and tm ', and cosine half-cycle widths ω and ω'; obtaining SULR0, SULRa, tm and ω based on the estimation result in the step one, and obtaining initial values and value ranges of SULR0, SULRa, tm and ω based on the initial values and value ranges: SULR0-100< SULR 0' < SULR0+ 100; SULRa-100< SULRa' < SULRa + 100; tm-2< tm' < tm + 2; omega-2 < omega' < omega + 2.
4. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the specific process of the third step is as follows:
instantaneous angle-dependent earth surface thermal radiation directivity modeling mainly considers the influence of three factors: the size of the surface temperature difference affects the hot spot amplitude, and the surface structure affects the hot spot width; the surface structure is considered to be unchanged within one day; the angular distance between the observation direction and the sun direction is analyzed and calculated by a formula (5); the surface temperature difference is a time-dependent quantity, which is related to the incident intensity of sunlight and is influenced by the surface thermal inertia, and is calculated by the formula (4):
TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (4)
in the formula (4), cos θs(t) is used to characterize the solar illumination conditions at different times of the day, sulrm (t) represents the effect of thermal inertia on the surface temperature difference change, a is a scaling factor to constrain the maximum value of trd (t), and B is a scene structure related quantity used to characterize the hotspot width; theta in the formula (5)sIs the solar zenith angle; thetavObserving a zenith angle;
and
representing the solar azimuth and the observation azimuth, respectively.
5. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the specific process of the step four is as follows:
simultaneous equations (1-5) can yield the following equations:
SULRe(t)-SULRm(t)＝TRD(t)＝SULRm(t)·cosθs(t)·A·e-f(t)/(π·B) (6)
after the shift, the following formula is obtained:
SULRe(t)＝SULRm(t)·(1+cosθs(t)·A·e-f(t)/(π·B)) (7)
substituting equation (3) into equation (7) yields the following result:
SULRe(t)＝(SULR0’+SULRa’·cos(π(t-tm’)/ω’)·(1+cosθs(t)·A·e-f(t)/(π·B)) (8)
the formula contains six unknowns, namely initial earth surface uplink long-wave radiation SULR0 'near sunrise time, change amplitude SULRa', maximum SULR occurrence time tm ', cosine half-cycle width omega', scaling factor A and hot spot width B; when the effective observation of the stationary satellite in one day is not less than six, the equation can be directly solved; the nonlinear solution needs to assign initial values and value ranges to the unknowns, the ranges of the first four parameters are determined in the step two, and the initial values of A and B are as follows: a is 0.05, B is 0.25, and the value ranges of A and B are as follows: 0< a <0.1, 0< B < 0.5.
6. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the concrete process of the step five is as follows:
four daily change parameters of SULRm, namely initial surface upward long-wave radiation SULR0 ', change amplitude SULRa', maximum SULR occurrence time tm 'and cosine half-cycle width ω', are obtained in the fourth step, and then the true value of SULRm (t), namely the surface upward long-wave radiation result after the thermal radiation directivity correction, is calculated by using the formula (3).
7. The method for correcting the directionality of thermal radiation of a long-wave radiation product traveling on the earth's surface of a geostationary satellite according to claim 1, characterized in that: the concrete process of the step six is as follows:
the parameters measured by the ground radiation meter are the semi-sphere integral surface ascending long-wave radiation value (SULRt), which is completely consistent with SULRm in formula (3) in physical sense, the SULRm result obtained in the fifth step for correcting the thermal radiation directivity can be verified by using the observed value SULRt of the ground radiation meter, 2 selected evaluation indexes are shown in formula (9-10):
in the above formula, tiRepresenting the satellite observation time, t1And tNRespectively start-stop and end times.
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