A method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation

Abstract

The present invention discloses a method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation. First, the factors affecting the determination of water vapor correction accuracy are derived from a water vapor correction model: sea conditions, brightness temperature measurement values ​​of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy. Then, the brightness temperature measurement values ​​are numerically simulated by a brightness temperature determination theoretical model, and the range of brightness temperature measurement values ​​is traversed to calculate and give an error propagation coefficient. Finally, the water vapor correction accuracy under different sea conditions is calculated. Compared with the water vapor correction accuracy analysis method obtained by using test data in the prior art method, the present method considers the problem more comprehensively and finely, obtains the water vapor correction accuracy under different sea conditions, and provides a solution for realizing the refined determination of satellite height measurement accuracy under different sea conditions.

Description

Technical Field

[0001] The invention relates to the field of ocean altimetry satellite mission analysis and data product processing, and in particular to a method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation. Background Art

[0002] Satellite altimetry technology uses a satellite-borne radar altimeter to measure the distance from the satellite to the ocean surface, and subtracts it from the satellite orbit altitude to obtain sea surface height data. It has become an effective measurement method for obtaining sea surface height information over a large area. The electromagnetic waves emitted by the satellite-borne radar altimeter during measurement are affected by the atmosphere, resulting in ranging deviations. The influence of water vapor content has a large degree of randomness and uncertainty. The measurement data of the microwave radiometer is usually used to obtain the correction amount of water vapor content for the altimeter ranging.

[0003] The correction amount of the altimeter ranging by the water vapor content in the atmosphere is usually called the water vapor correction. The satellite-borne microwave radiometer measures the brightness temperature values ​​of different microwave frequencies, and applies the atmospheric and ocean physics theory to invert the water vapor correction amount in the altimeter ranging path from the brightness temperature data. With the improvement of the altimeter ranging accuracy, how to improve the satellite height measurement accuracy under different sea conditions, especially high sea conditions, is a current research hotspot. Therefore, it is very necessary to study the error propagation relationship between the microwave radiometer brightness temperature data and the water vapor correction amount under different sea conditions, as well as the influencing factors of the water vapor correction accuracy. However, the accuracy analysis method of water vapor correction in the existing literature has the following shortcomings:

[0004] (1) Existing literature mainly focuses on the data inversion method of microwave radiometers, and less research is done on the accuracy matching between measured data and correction values, which makes it difficult to determine the measurement accuracy indicators of satellite-borne microwave radiometers in engineering practice.

[0005] (2) Existing literature uses experimental data to give the error propagation relationship between microwave radiometer brightness temperature data and water vapor correction, without considering the accuracy of water vapor correction under different sea conditions. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, to provide a method for analyzing the accuracy of water vapor correction under different sea conditions based on microwave radiation, and to provide a solution for realizing the refined determination of the satellite height measurement accuracy under different sea conditions.

[0007] The technical solution of the present invention is: a method for analyzing the accuracy of water vapor correction under different sea conditions based on microwave radiation, the steps are as follows:

[0008] (1) According to the error propagation theory, the water vapor correction model is analyzed to find out the factors affecting the accuracy of water vapor correction, including sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy;

[0009] (2) Based on the theoretical model determined by the brightness temperature measurement values, the brightness temperature measurement values ​​are simulated and numerically traversed to obtain the range of brightness temperature measurement values ​​at different frequencies;

[0010] (3) Traversing the range of brightness temperature measurements at different frequencies obtained in step (2), applying the influencing factors of water vapor correction accuracy obtained in step (1), and calculating the error propagation coefficient under different sea conditions;

[0011] (4) using probability statistics theory, according to the error propagation coefficients under different sea conditions obtained in step (3), calculating the statistical mean of the error propagation coefficients under different sea conditions;

[0012] (5) Apply the statistical mean of the error propagation coefficient under different sea conditions in step (4) to the water vapor correction error analysis result in step (1) to obtain the water vapor correction accuracy under different sea conditions.

[0013] The specific process of step (1) is as follows:

[0014] (1.1) Obtaining the water vapor correction model

[0015] The water vapor correction model used is the water vapor correction model of the microwave radiometer carried by the T / P series satellites jointly developed by the United States and France. The frequencies of its microwave radiometers are 18.7 GHz, 21 GHz and 37 GHz.

[0016] (1.2) The error propagation coefficient is analyzed and the water vapor correction accuracy factors are obtained as follows: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

[0017] The specific process of step (1.2) is as follows: the water vapor correction model of step (1.1) is used to obtain the water vapor correction amount h Vap ; From the water vapor correction model in step (1.1), we know that a set of brightness temperature measurements T 18 、T 21 、T 37 After confirmation, B0, B 18 , B 21 and B 37 These four coefficients and the water vapor correction can be determined; according to the error propagation theory, the error propagation equation between the water vapor correction and the brightness temperature is:

[0018] C Vap,f =-B f / 280-T f ,f=18、21、37

[0019] Among them C Vap,f is the error propagation coefficient, where Bf With a set of brightness temperature measurements T 18 、T 21 、T 37 Related, written as B f (T 18 ,T 21 ,T 37 ), so C Vap,f Can also be written as C Vap,f (T 18 ,T 21 ,T 37 );

[0020] It can be concluded that the accuracy of water vapor correction at different wind speeds requires the error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) and brightness temperature measurement accuracy σ(T f ), where the error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) is not only related to the brightness temperature measurement value of this frequency, but also to the brightness temperature values ​​of other frequencies; therefore, the factors affecting the accuracy of water vapor correction include: wind speed, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy;

[0021] The classification of different sea conditions is based on the wind speed. According to the wind speed value, the water vapor correction accuracy under different wind speeds can be converted into the water vapor correction accuracy under different sea conditions. Therefore, the water vapor correction accuracy factors include: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

[0022] The water vapor correction amount h Vap :

[0023] h Vap =B0+B 18 ln(280-T 18 )+B 21 ln(280-T 23 )+B 37 ln(280-T 37 )

[0024] where h Vap is the water vapor correction amount, B0, B 18 , B 21 and B 37 is the coefficient.

[0025] The specific process of step (2) is as follows:

[0026] In order to calculate the accuracy of water vapor correction under different sea conditions, the error propagation coefficient C needs to be known. Vap,f (T 18 ,T 23 ,T 37 ) and σ(T f ); where σ(T f ) is determined by the accuracy of the microwave radiometer instrument, and the error propagation coefficient C Vap,f (T 18 ,T 23 ,T 37 ) requires the brightness temperature measurement value to be known, so the brightness temperature measurement value is determined by the following method:

[0027] The theoretical model for determining brightness temperature measurements is:

[0028] T=T U +τ[e S t S +r S (T D +τT B )]

[0029] Where T U 、T D is the uplink and downlink brightness temperature, T B is the cosmic background brightness temperature T B =2.7K,t S is the sea surface thermodynamic temperature, τ is the atmospheric transmittance, e S and r S are the emissivity and reflectivity of the sea surface, respectively;

[0030] Atmospheric transmittance τ and uplink brightness temperature T U 、T D and atmospheric water vapor content Q WV and liquid water content Q L The relationship is:

[0031] lnτ=a 0,τ Q WV +a 1,τ Q L +a 2,τ

[0032]

[0033] T U =mT D +n

[0034] Where τ is the atmospheric transmittance, Q WV is the atmospheric water vapor content, Q L is the liquid water content, T U is the uplink brightness temperature, T Dis the downlink brightness temperature, a 0,τ 、a 1,τ 、a 2,τ 、a 0,TD 、a 1,TD 、a 2,TD 、a 3,TD 、a 4,TD , m, n are coefficients;

[0035] Sea surface reflectivity r S With emissivity e S The following relationship exists:

[0036] r S =Ω(1-e S )

[0037] Where: r S is the sea surface reflectivity, e S is the emissivity, Ω is the correction coefficient of the change in sea surface emissivity caused by the rough surface, and we have:

[0038]

[0039] Where τ is the atmospheric transmittance, f is the frequency, and U WS is the wind speed; a 0,Ω 、a 1,Ω 、a 2,Ω 、a 3,Ω 、a 4,Ω 、a 5,Ω 、a 6,Ω 、a 7,Ω 、a 8,Ω is the coefficient;

[0040] Sea surface emissivity S for:

[0041] e S =(1-e F )(e C +e WS )+e F +e WD

[0042] where e C is the calm sea surface emissivity, e WS is the sea surface emissivity caused by wind speed, e WD is the sea surface emissivity caused by wind direction, e F is the foam coverage, with:

[0043]

[0044] Among them U WS is the wind speed; the calm sea surface emissivity e C for:

[0045]

[0046] Where S S is the sea surface salinity, Ω is the correction factor for the change in sea surface emissivity caused by the rough surface, t S is the sea surface thermodynamic temperature; a 0,rC 、a 1,rC 、a 2,rC 、a 3,rC 、a 4,rC 、a 5,rC 、a 6,rC 、a 7,rC 、a 8,rC 、a 9,rC is the coefficient;

[0047] Sea surface emissivity caused by wind speed WS for:

[0048]

[0049] Among them U WS is the wind speed, a 0,eWS 、a 1,eWS 、a 2,eWS is the coefficient;

[0050] Sea surface emissivity e related to wind direction WD for:

[0051]

[0052] Among them, U WS is the wind speed, θ WD is the wind direction, a 0,eWD 、a 1,eWD 、a 2,eWD 、a 3,eWD 、a 4,eWD 、a 5,eWD 、a 6,eWD 、a 7,eWD is the coefficient;

[0053] The above results show that the physical quantities related to the brightness temperature measurement are: atmospheric water vapor content Q WV , atmospheric liquid water content Q L , sea surface wind speed U WS 、wind directionθ WD , sea surface temperature t S and salinity S S ; Traverse the numerical values ​​of the six physical quantities in the atmosphere, and then use the theoretical model of the brightness temperature value mentioned above to obtain the numerical simulation and full range traversal of the brightness temperature measurement values ​​at three frequencies of 18.7 GHz, 21 GHz and 37 GHz.

[0054] The specific process of step (3) is as follows:

[0055] The calculation formula of the error propagation coefficient obtained from step (1) is:

[0056] C Vap,f (T 18 ,T 21 ,T 37 )=-B f / 280-T f ,f=18、21、37

[0057] Among them C Vap,f (T 18 ,T 21 ,T 37 ) is the error propagation coefficient, T 18 ,T 21 ,T 37 is the brightness temperature value of the three frequencies, calculated by step (2), and B is obtained by using the water vapor correction model in step (1) f (T 18 ,T 21 ,T 37 ); The classification of different sea conditions is based on the wind speed. The wind speed is calculated using the expression for calculating wind speed from brightness temperature in step (1). Then, the error propagation coefficient under different sea conditions is obtained from the corresponding relationship between wind speed and sea conditions.

[0058] The specific process of step (4) is as follows:

[0059] According to probability statistics theory, the statistical mean of the error propagation coefficient under different sea conditions is:

[0060]

[0061]

[0062]

[0063] Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and water vapor correction values ​​at different sea conditions, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,23 (T 18 ,T21 ,T 37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3); p(T 18 ,T 21 ,T 37 ) is the joint probability density of brightness temperature at three frequencies; it can be considered that the value probabilities of brightness temperature at different frequencies are independent of each other, and the joint probability density is expressed as:

[0064] p(T 18 ,T 21 ,T 37 )=p(T 18 )p(T 21 )p(T 37 )

[0065] Where p(T 18 ,T 21 ,T 37 ) is the joint probability density, p(T 18 )、p(T 21 )、p(T 37 ) are the probabilities of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz and 37 GHz;

[0066] It can be concluded that the statistical mean of the error propagation coefficient between the brightness temperature measurement and the water vapor correction under different sea conditions is:

[0067]

[0068]

[0069]

[0070] Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and the water vapor correction, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,21 (T 18 ,T 21 ,T37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3); p(T 18 )、p(T 23 )、p(T 37 ) are the probability densities of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz and 37 GHz.

[0071] The specific process of step (5) is as follows:

[0072] Applying the mean value of the error propagation coefficient in step (4) to step (1), the water vapor correction accuracy under different sea conditions is obtained as follows:

[0073]

[0074] Where σ(h Vap ,U WS ) is the water vapor correction accuracy, C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at 18.7 GHz, 21 GHz, and 37 GHz and the water vapor correction under different sea conditions; σ(T 18 ),σ(T 23 ),σ(T 37 ) are the brightness temperature measurement accuracies of 18.7 GHz, 21 GHz, and 37 GHz respectively.

[0075] The advantages of the present invention compared with the prior art are:

[0076] 1. The existing technical methods do not analyze the factors of error propagation relationship between the brightness temperature measurement value and the water vapor correction value of the microwave radiometer. The method in this paper derives through theory that the error propagation coefficient is not only related to the brightness temperature value of the frequency, but also closely related to the brightness temperature values ​​of other frequencies and sea conditions. This conclusion provides theoretical support for determining the accuracy of water vapor correction under different sea conditions.

[0077] 2. The existing technical methods have not found a matching relationship between the brightness temperature measurement accuracy of the microwave radiometer and the water vapor correction accuracy under different sea conditions. The method in this paper establishes the error propagation relationship between the brightness temperature value of the microwave radiometer and the water vapor correction value under different sea conditions through numerical simulation. It has practical engineering significance in the refinement of the satellite height measurement accuracy under different sea conditions.

[0078] 3. Most existing technical methods use on-orbit or ground test data to derive the error propagation relationship between brightness temperature measurement values ​​and water vapor correction values. Due to the limited detection range of existing instruments and the low probability of high sea conditions, it is difficult to derive the error propagation relationship under high sea conditions. The method in this paper uses a numerical simulation method to traverse and calculate the error propagation relationship under different sea conditions, providing a solution for achieving the refined determination of satellite height measurement accuracy under different sea conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 Flow chart of the method of the present invention.

[0080] Figure 2 This is the probability density distribution diagram of brightness temperature at 18.7 GHz.

[0081] Figure 3 This is the probability density distribution diagram of brightness temperature at 21GHz.

[0082] Figure 4 This is the probability density distribution diagram of brightness temperature at 37GHz.

[0083] Figure 5 is the relationship between the 18 GHz brightness temperature and the 18 GHz brightness temperature error propagation coefficient.

[0084] Figure 6 This is the relationship between the brightness temperature at 21 GHz and the brightness temperature error propagation coefficient at 18 GHz.

[0085] Figure 7 This is the relationship between the brightness temperature at 37 GHz and the brightness temperature error propagation coefficient at 18 GHz.

[0086] Figure 8 This is the relationship between the brightness temperature at 18 GHz and the brightness temperature error propagation coefficient at 21 GHz.

[0087] Fig. 9 is the relationship between the 21 GHz brightness temperature and the 21 GHz brightness temperature error propagation coefficient.

[0088] Fig.10 This is the relationship between the brightness temperature at 37 GHz and the brightness temperature error propagation coefficient at 21 GHz.

[0089] Fig.11 This is the relationship between the brightness temperature at 18 GHz and the brightness temperature error propagation coefficient at 37 GHz.

[0090] Fig.12 This is the relationship between the brightness temperature at 21 GHz and the brightness temperature error propagation coefficient at 37 GHz.

[0091] Fig.13 is the relationship between the 37 GHz brightness temperature and the 37 GHz brightness temperature error propagation coefficient. DETAILED DESCRIPTION

[0092] like Figure 1 As shown, the steps of the method of the present invention are as follows:

[0093] (1) Analysis of water vapor correction accuracy factors.

[0094] According to the error propagation theory, the water vapor correction model is analyzed and the accuracy factors of water vapor correction are found to be: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies and brightness temperature measurement accuracy.

[0095] (2) Numerical simulation of brightness temperature measurements.

[0096] According to the theoretical model determined by the brightness temperature measurements, the brightness temperature measurements were simulated and numerically traversed to obtain the range of brightness temperature measurements at different frequencies.

[0097] (3) Numerical simulation of error propagation coefficient.

[0098] Traverse the values ​​within the brightness temperature range obtained in step (2), apply the water vapor correction model in step (1) and the conclusion of the error propagation coefficient factor analysis, and calculate the error propagation coefficient under different sea conditions.

[0099] (4) Statistical mean of the error propagation coefficient under different sea conditions.

[0100] Using probability statistics theory, the error propagation coefficient obtained in step (3) is used to calculate the statistical mean of the error propagation coefficient under different sea conditions.

[0101] (5) Determination of water vapor correction accuracy under different sea conditions.

[0102] The mean value of the error propagation coefficient in step (4) is applied to the water vapor correction error analysis result in step (1) to obtain the water vapor correction accuracy under different sea conditions.

[0103] The specific process is as follows:

[0104] (1) Analysis of water vapor correction accuracy factors

[0105] (1.1) Water vapor correction model

[0106] The water vapor correction model used in this paper is the water vapor correction model of the microwave radiometer carried by the T / P series satellites (TOPEX / Poseidon, Jason-1, Jason-2, and Jason-3 series satellites) jointly developed by the United States and France. The frequencies of its microwave radiometers are 18.7 GHz, 21 GHz, and 37 GHz.

[0107] The model for T / P series satellites to use microwave radiation data for water vapor correction can be found in the literature TOPEX Poseidon microwave radiometer wet troposphere range correction algorithm and pre launch error budget. It is divided into the following three steps:

[0108] Step ①, make a preliminary estimate of the water vapor correction amount (unit: cm):

[0109]

[0110] in is the preliminary estimate of the water vapor correction, T 18 、T 21 and T 37 They are the brightness temperature data measured by the microwave radiometer at 18.7 GHz, 21 GHz and 37 GHz, and They are the coefficients corresponding to different wind speeds, as shown in Table 1. The coefficients corresponding to the correction amount of 0-60cm in the table are used. WS The calculation formula is:

[0111] U WS =-75.0+1.795T 18 -0.561T 21 -0.433T 37 (2)

[0112] Step 2: According to The calculated value is shown in Table 1, and the parameters of the corresponding interval nearby are selected for fine correction. and The calculation of is:

[0113]

[0114]

[0115] in: and is the fine correction value, They are the coefficients corresponding to different wind speeds, as shown in Table 1. 18 、T 21 and T 37 These are the brightness temperature data measured by the microwave radiometer at 18.7 GHz, 21 GHz and 37 GHz.

[0116] For example, The calculated value of is 12.3, and The calculation requires parameters in the range 0-10 and 10-20. If If the calculated value is less than 5 or greater than 35, just use the boundary interval (0-10 or >30) to calculate directly.

[0117] Step ③, by and Calculate h Vap ,have:

[0118]

[0119] where h Vap is the water vapor correction amount, is a preliminary estimate of the water vapor correction, and is the fine correction value, for and The common boundary value of two intervals.

[0120] (1.2) Factor analysis of error propagation coefficient

[0121] From the water vapor correction model in step (1.1), if Then there is It indicates that steps ② and ③ in the water vapor calibration process are the same as those in step ①. coefficient and Further accurate correction, thus, the water vapor correction amount h Vap It can be written as follows:

[0122] h Vap =B0+B 18 ln(280-T 18 )+B 21 ln(280-T 23 )+B 37 ln(280-T 37 ) (6)

[0123] Among them, B0, B 18 , B 21 and B 37 is the corrected coefficient. From the water vapor correction model in step (1.1), we know that a set of brightness temperature measurements T 18 、T 21 、T 37 After being determined, these four coefficients and the water vapor correction can be determined. According to the error propagation theory, the error propagation equation of the water vapor correction and the brightness temperature is:

[0124]

[0125] Among them C Vap,f is the error propagation coefficient, where B f With a set of brightness temperature measurements T 18 、T 21 、T 37 Related, can be written as B f (T 18 ,T 21 ,T 37 ), so C Vap,f Can also be written as C Vap,f (T 18 ,T 21 ,T 37 ).

[0126] It can be concluded that the accuracy of water vapor correction at different wind speeds requires the error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) and brightness temperature measurement accuracy σ(T f ). The error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) is not only related to the brightness temperature measurement value of this frequency, but also to the brightness temperature values ​​of other frequencies. Therefore, the factors affecting the accuracy of water vapor correction include: wind speed, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

[0127] The sea state classification table is shown in Table 2. It can be seen from Table 2 that the classification of different sea conditions is based on the size of the wind speed. According to the value of the wind speed, the water vapor correction accuracy under different wind speeds can be converted into the water vapor correction accuracy under different sea conditions. Therefore, the water vapor correction accuracy factors include: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

[0128] (2) Numerical simulation of brightness temperature measurements

[0129] In order to calculate the accuracy of water vapor correction under different sea conditions, the error propagation coefficient C needs to be known. Vap,f (T 18 ,T 23 ,T 37 ) and σ(T f ). Among them, σ(T f ) is determined by the accuracy of the microwave radiometer instrument, and the error propagation coefficient C Vap,f (T 18 ,T 23 ,T 37 ) requires the known brightness temperature measurement value, and the brightness temperature measurement value is determined by the following method.

[0130] The theoretical model for determining brightness temperature measurements is:

[0131] T=T U +τ[e S t S +r S (T D +τT B )] (8)

[0132] Where T U 、T D is the uplink and downlink brightness temperature, T B is the cosmic background brightness temperature T B =2.7K,t S is the sea surface thermodynamic temperature, τ is the atmospheric transmittance, e S and r S are the emissivity and reflectivity of the sea surface, respectively.

[0133] Atmospheric transmittance τ and uplink brightness temperature T U 、T D and atmospheric water vapor content Q WV (Unit: mm) and liquid water content Q L (Unit: mm) is:

[0134] lnτ=a 0,τ Q WV +a 1,τ Q L +a 2,τ (9)

[0135]

[0136] T U =mT D +n (11)

[0137] Where τ is the atmospheric transmittance, Q WV is the atmospheric water vapor content, Q L is the liquid water content, T U is the uplink brightness temperature, T D is the downlink brightness temperature, a 0,τ 、a 1,τ 、a 2,τ 、a 0,TD 、a 1,TD 、a 2,TD 、a 3,TD 、a 4,TD , m, n are coefficients.

[0138] Sea surface reflectivity r S With emissivity e S The following relationship exists:

[0139] r S =Ω(1-e S ) (12)

[0140] Where: r S is the sea surface reflectivity, e S is the emissivity, Ω is the correction coefficient of the change in sea surface emissivity caused by the rough surface, and we have:

[0141]

[0142] Where τ is the atmospheric transmittance, f is the frequency, and U WS is the wind speed. 0,Ω 、a 1,Ω 、a 2,Ω 、a 3,Ω 、a 4,Ω 、a 5,Ω 、a 6,Ω 、a 7,Ω 、a 8,Ω is the coefficient.

[0143] Sea surface emissivity S for:

[0144] e S =(1-e F )(e C +e WS )+e F +e WD (14)

[0145] where e C is the calm sea surface emissivity, e WS is the sea surface emissivity caused by wind speed, e WD is the sea surface emissivity caused by wind direction, e F is the foam coverage, with:

[0146]

[0147] Among them U WS is the wind speed. Calm sea surface emissivity e C for:

[0148]

[0149] Where S S is the sea surface salinity, Ω is the correction factor for the change in sea surface emissivity caused by the rough surface, t S is the sea surface thermodynamic temperature. 0,rC 、a 1,rC 、a 2,rC 、a 3,rC 、a 4,rC 、a5,rC 、a 6,rC 、a 7,rC 、a 8,rC 、a 9,rC is the coefficient.

[0150] Sea surface emissivity caused by wind speed WS for:

[0151]

[0152] Among them U WS is the wind speed, a 0,eWS 、a 1,eWS 、a 2,eWS is the coefficient.

[0153] Sea surface emissivity e related to wind direction WD for:

[0154]

[0155] Among them, U WS is the wind speed, θ WD is the wind direction, a 0,eWD 、a 1,eWD 、a 2,eWD 、a 3,eWD 、a 4,eWD 、a 5,eWD 、a 6,eWD 、a 7,eWD is the coefficient.

[0156] The above equations (8) to (18) are theoretical simulation methods for brightness temperature values, where the coefficients are different at 18.7 GHz, 21 Hz and 37 GHz. For details, see the document “Inversion of Ocean Geophysical Parameters Using AMSR-E Data from Spaceborne Microwave Radiometer”.

[0157] As can be seen from the above, the physical quantities related to the brightness temperature measurement are: atmospheric water vapor content Q WV , atmospheric liquid water content Q L , sea surface wind speed U WS 、wind directionθ WD , sea surface temperature t S and salinity S S By traversing the range of values ​​of these six physical quantities in the atmosphere and using the theoretical model of brightness temperature mentioned above, we can obtain numerical simulation and full range traversal of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz, and 37 GHz.

[0158] (3) Numerical simulation of error propagation coefficient

[0159] The calculation formula of the error propagation coefficient obtained from step (1) is:

[0160] C Vap,f (T 18 ,T 21 ,T 37 )=-B f / 280-T f ,f=18、21、37

[0161] Among them C Vap,f (T 18 ,T 21 ,T 37 ) is the error propagation coefficient, T 18 ,T 21 ,T 37 is the brightness temperature value of the three frequencies, calculated by step (2), and B is obtained by using the water vapor correction model in step (1) f (T 18 ,T 21 ,T 37 The classification of sea conditions is shown in Table 2. It can be seen from Table 2 that the classification of different sea conditions is based on the size of the wind speed. The wind speed can be calculated by using the expression for calculating the wind speed from the brightness temperature in step (1). Then, the error propagation coefficient under different sea conditions can be obtained from the corresponding relationship between the wind speed and the sea condition.

[0162] (4) Statistical mean of error propagation coefficient under different sea conditions

[0163] According to probability statistics theory, the statistical mean of the error propagation coefficient under different sea conditions is:

[0164]

[0165]

[0166]

[0167] Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and water vapor correction values ​​at different sea conditions, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,23 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,37 (T 18,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3). p(T 18 ,T 21 ,T 37 ) is the joint probability density of brightness temperature at three frequencies. It can be considered that the value probabilities of brightness temperature at different frequencies are independent of each other, and the joint probability density can be expressed as:

[0168] p(T 18 ,T 21 ,T 37 )=p(T 18 )p(T 21 )p(T 37 )

[0169] Where p(T 18 ,T 21 ,T 37 ) is the joint probability density, p(T 18 )、p(T 21 )、p(T 37 ) are the probabilities of brightness temperature measurement at three frequencies: 18.7 GHz, 21 GHz and 37 GHz. The statistical results of brightness temperature measurement data at 18 GHz, 21 GHz and 37 GHz are obtained by using the literature “Data Quality Evaluation and Parameter Inversion of FY-3B Microwave Imager”. Figure 2-Figure 4 .

[0170] It can be concluded that the statistical mean of the error propagation coefficient between the brightness temperature measurement and the water vapor correction under different sea conditions is:

[0171]

[0172]

[0173]

[0174] Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and the water vapor correction, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,21 (T 18 ,T 21 ,T37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3). p(T 18 )、p(T 23 )、p(T 37 ) are the probability densities of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz and 37 GHz.

[0175] (5) Water vapor correction accuracy in different sea conditions

[0176] Applying the mean value of the error propagation coefficient in step (4) to step (1), the water vapor correction accuracy under different sea conditions is obtained as follows:

[0177]

[0178] Where σ(h Vap ,U WS ) is the water vapor correction accuracy, C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at 18.7 GHz, 21 GHz, and 37 GHz and the water vapor correction under different sea conditions. σ(T 18 ),σ(T 23 ),σ(T 37 ) are the brightness temperature measurement accuracies of 18.7 GHz, 21 GHz, and 37 GHz respectively.

[0179] Application Examples

[0180] The theoretical model of the brightness temperature measurement value in step (2) is used to traverse the six physical quantities involved. The range of water vapor content in the atmosphere is 3-70 mm, the range of liquid water content is 0-0.3 mm, the range of sea surface wind speed is 0-30 m / s, the range of sea surface wind direction is 0-360°, the range of sea surface temperature is 273-302 K, and the range of sea surface salinity is 29-37‰. It can be concluded that the brightness temperature amplitude ranges of 18.7 GHz, 21 GHz, and 37 GHz are 183-240 K, 194-265 K, and 210-274 K, respectively.

[0181] Traversing the values ​​within the brightness temperature range of the three frequencies obtained above, using the water vapor correction model in step (1) and the error propagation coefficient simulation method in step (3), calculate C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,21 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ), that is, the relationship between the brightness temperature measurement value and the brightness temperature error propagation coefficient under different sea conditions, such as Figure 5-Figure 13 shown.

[0182] Apply step (4) to obtain the statistical mean C of the error propagation coefficient under different sea conditions: Vap,18 , C Vap,21 , C Vap,37 , see Table 3.

[0183] The water vapor correction accuracy under different sea conditions is calculated using the method in step (5), where C Vap,18 , C Vap,21 , C Vap,37 According to the results in Table 3, the brightness temperature measurement accuracy σ(T 18 )=σ(T 21 )=σ(T 37 )=0.4K, and the calculated water vapor correction accuracy under different sea conditions is shown in Table 4. As can be seen from Table 4, the water vapor correction accuracy is about 1.2cm, which is basically consistent with the statistical results of the measured data in the literature "TOPEX Poseidon microwave radiometer wet troposphere range correction algorithm and pre launch error budget".

[0184] Table 1 Water vapor correction model parameters

[0185]

[0186] Table 2 Correspondence between sea conditions and wind speed

[0187] Sea state level Wind speed m / s 0 0-2 1 2-3 2 3-5 3 5-8 4 8-11 5 11-14 6 14-17 7 17-20 8 20-24 9 24-36

[0188] Table 3 Error propagation coefficient under different sea conditions (K / cm)

[0189] Sea conditions <![CDATA[C Vap,18 ]]> <![CDATA[C Vap,21 ]]> <![CDATA[C Vap,37 ]]> 0 0.45 3.13 1.19 1 0.45 3.14 1.11 2 0.45 3.04 1.12 3 0.46 2.97 1.12 4 0.47 2.81 1.06 5 0.48 2.76 1.06 6 0.51 2.70 1.03 7 0.52 2.56 1.00 8 0.55 2.51 0.98 9 0.56 2.37 0.94

[0190] Table 4 Water vapor correction accuracy under different sea conditions (cm)

[0191] Sea conditions <![CDATA[C Vap,18 cm / K]]> <![CDATA[C Vap,21 cm / K]]> <![CDATA[C Vap,37 cm / K]]> <![CDATA[σ(h Vap )cm]]> 0 0.45 3.13 1.19 1.35 1 0.45 3.14 1.11 1.35 2 0.45 3.04 1.12 1.31 3 0.46 2.97 1.12 1.28 4 0.47 2.81 1.06 1.22 5 0.48 2.76 1.06 1.20 6 0.51 2.70 1.03 1.18 7 0.52 2.56 1.00 1.12 8 0.55 2.51 0.98 1.10 9 0.56 2.37 0.94 1.04

[0192] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for analyzing the accuracy of water vapor correction under different sea conditions based on microwave radiation, characterized in that Here are the steps: (1) According to the error propagation theory, the water vapor correction model is analyzed to find out the factors affecting the accuracy of water vapor correction, including sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy; (2) Based on the theoretical model determined by the brightness temperature measurement values, the brightness temperature measurement values ​​are simulated and numerically traversed to obtain the range of brightness temperature measurement values ​​at different frequencies; (3) Traversing the range of brightness temperature measurements at different frequencies obtained in step (2), applying the influencing factors of water vapor correction accuracy obtained in step (1), and calculating the error propagation coefficient under different sea conditions; (4) using probability statistics theory, according to the error propagation coefficients under different sea conditions obtained in step (3), calculating the statistical mean of the error propagation coefficients under different sea conditions; (5) Apply the statistical mean of the error propagation coefficient under different sea conditions in step (4) to the water vapor correction error analysis result in step (1) to obtain the water vapor correction accuracy under different sea conditions.

2. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 1, characterized in that: The specific process of step (1) is as follows: (1.1) Obtaining the water vapor correction model The water vapor correction model used is the water vapor correction model of the microwave radiometer carried by the T / P series satellites jointly developed by the United States and France. The frequencies of its microwave radiometers are 18.7 GHz, 21 GHz and 37 GHz. (1.2) The error propagation coefficient is analyzed and the water vapor correction accuracy factors are obtained as follows: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

3. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 2, characterized in that: The specific process of step (1.2) is as follows: the water vapor correction model of step (1.1) is used to obtain the water vapor correction amount h Vap ; From the water vapor correction model in step (1.1), we know that a set of brightness temperature measurements T 18 、T 21 、T 37 After confirmation, B0, B 18 , B 21 and B 37 These four coefficients and the water vapor correction can be determined; according to the error propagation theory, the error propagation equation between the water vapor correction and the brightness temperature is: Among them C Vap,f is the error propagation coefficient, where B f With a set of brightness temperature measurements T 18 , T 21 , T 37 Related, written as B f (T 18 ,T 21 ,T 37 ), so C Vap,f Can also be written as C Vap,f (T 18 ,T 21 ,T 37 ); It can be concluded that the accuracy of water vapor correction at different wind speeds requires the error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) and brightness temperature measurement accuracy σ(T f ), where the error propagation coefficient C Vap,f (T 18 ,T 21 ,T 37 ) is not only related to the brightness temperature measurement value of this frequency, but also to the brightness temperature values ​​of other frequencies; therefore, the factors affecting the accuracy of water vapor correction include: wind speed, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy; The classification of different sea conditions is based on the wind speed. According to the wind speed value, the water vapor correction accuracy under different wind speeds can be converted into the water vapor correction accuracy under different sea conditions. Therefore, the water vapor correction accuracy factors include: sea conditions, brightness temperature measurement value of this frequency, brightness temperature values ​​of other frequencies, and brightness temperature measurement accuracy.

4. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 3 is characterized by: The water vapor correction amount h Vap : h Vap =B0+B 18 ln(280-T 18 )+B 21 ln(280-T 23 )+B 37 ln(280-T 37 ) where h Vap is the water vapor correction amount, B0, B 18 , B 21 and B 37 is the coefficient.

5. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 4, characterized in that: The specific process of step (2) is as follows: In order to calculate the accuracy of water vapor correction under different sea conditions, the error propagation coefficient C needs to be known. Vap,f (T 18 ,T 23 ,T 37 ) and σ(T f ); where σ(T f ) is determined by the accuracy of the microwave radiometer instrument, and the error propagation coefficient C Vap,f (T 18 ,T 23 ,T 37 ) requires the brightness temperature measurement value to be known, so the brightness temperature measurement value is determined by the following method: The theoretical model for determining brightness temperature measurements is: T=T U +τ[e S t S +r S (T D +τT B )] Where T U 、T D is the uplink and downlink brightness temperature, T B is the cosmic background brightness temperature T B =2.7K,t S is the sea surface thermodynamic temperature, τ is the atmospheric transmittance, e S and r S are the emissivity and reflectivity of the sea surface, respectively; Atmospheric transmittance τ and uplink and downlink brightness temperature T U , T D and atmospheric water vapor content Q WV and liquid water content Q L The relationship is: lnτ=a 0,τ Q WV +a 1,τ Q L +a 2,τ T U =mT D +n Where τ is the atmospheric transmittance, Q WV is the atmospheric water vapor content, Q L is the liquid water content, T U is the uplink brightness temperature, T D is the downlink brightness temperature, a 0,τ 、a 1,τ 、a 2,τ 、a 0,TD 、a 1,TD 、a 2,TD 、a 3,TD 、a 4,TD , m, n are coefficients; Sea surface reflectivity r S With emissivity e S The following relationship exists: r S =Ω(1-e S ) Where: r S is the sea surface reflectivity, e S is the emissivity, Ω is the correction coefficient of the change in sea surface emissivity caused by the rough surface, and we have: Where τ is the atmospheric transmittance, f is the frequency, and U WS is the wind speed; a 0,Ω 、a 1,Ω 、a 2,Ω 、a 3,Ω 、a 4,Ω 、a 5,Ω 、a 6,Ω 、a 7,Ω 、a 8,Ω is the coefficient; Sea surface emissivity S for: And S =(1-e F )(And C +e WS )+e F +e WD where e C is the calm sea surface emissivity, e WS is the sea surface emissivity caused by wind speed, e WD is the sea surface emissivity caused by wind direction, e F is the foam coverage, with: Among them U WS is the wind speed; the calm sea surface emissivity e C for: Where S S is the sea surface salinity, Ω is the correction factor for the change in sea surface emissivity caused by the rough surface, t S is the sea surface thermodynamic temperature; a 0,rC 、a 1,r C.a 2 ,r C.a 3 ,rC 、a 4,r C.a 5 ,r C.a 6,r C.a 7 ,r C.a 8 ,r C.a 9,r C is the coefficient; Sea surface emissivity caused by wind speed WS for: Among them U WS is the wind speed, a 0,eWS 、a 1,eWS 、a 2,eWS is the coefficient; Sea surface emissivity e related to wind direction WD for: Among them, U WS is the wind speed, θ WD is the wind direction, a 0,eWD 、a 1,eWD 、a 2,eWD 、a 3,eWD 、a 4,eWD 、a 5,eWD 、a 6,eWD 、a 7,eWD is the coefficient; The above results show that the physical quantities related to the brightness temperature measurement are: atmospheric water vapor content Q WV , atmospheric liquid water content Q L , sea surface wind speed U WS 、wind directionθ WD , sea surface temperature t S and salinity S S ; Traverse the numerical values ​​of the six physical quantities in the atmosphere, and then use the theoretical model of the brightness temperature value mentioned above to obtain the numerical simulation and full range traversal of the brightness temperature measurement values ​​at three frequencies of 18.7 GHz, 21 GHz and 37 GHz.

6. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 5, characterized in that: The specific process of step (3) is as follows: The calculation formula of the error propagation coefficient obtained from step (1) is: C Vap,f (T 18 ,T 21 ,T 37 )=-B f / 280-T f ,f=18、21、37 Among them C Vap,f (T 18 ,T 21 ,T 37 ) is the error propagation coefficient, T 18 ,T 21 ,T 37 is the brightness temperature value of the three frequencies, calculated by step (2), and B is obtained by using the water vapor correction model in step (1) f (T 18 ,T 21 ,T 37 ); The classification of different sea conditions is based on the size of the wind speed. The wind speed is calculated using the expression for calculating the wind speed from the brightness temperature in step (1). Then, the error propagation coefficient under different sea conditions is obtained from the corresponding relationship between the wind speed and the sea condition.

7. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 6, characterized in that: The specific process of step (4) is as follows: According to probability statistics theory, the statistical mean of the error propagation coefficient under different sea conditions is: Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and water vapor correction values ​​at different sea conditions, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,23 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3); p(T 18 ,T 21 ,T 37 ) is the joint probability density of brightness temperature at three frequencies; it can be considered that the value probabilities of brightness temperature at different frequencies are independent of each other, and the joint probability density is expressed as: p(T 18 ,T 21 ,T 37 )=p(T 18 )p(T 21 )p(T 37 ) Where p(T 18 ,T 21 ,T 37 ) is the joint probability density, p(T 18 )、p(T 21 )、p(T 37 ) are the probabilities of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz and 37 GHz; It can be concluded that the statistical mean of the error propagation coefficient between the brightness temperature measurement and the water vapor correction under different sea conditions is: Among them C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at different frequencies and the water vapor correction, C Vap,18 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,21 (T 18 ,T 21 ,T 37 ,U WS ), C Vap,37 (T 18 ,T 21 ,T 37 ,U WS ) is the error propagation coefficient of brightness temperature values ​​of different frequencies in different sea conditions obtained in step (3); p(T 18 )、p(T 23 )、p(T 37 ) are the probability densities of brightness temperature measurements at three frequencies: 18.7 GHz, 21 GHz and 37 GHz.

8. The method for analyzing water vapor correction accuracy under different sea conditions based on microwave radiation according to claim 7, characterized in that: The specific process of step (5) is as follows: Applying the mean value of the error propagation coefficient in step (4) to step (1), the water vapor correction accuracy under different sea conditions is obtained as follows: Where σ(h Vap ,U WS ) is the water vapor correction accuracy, C Vap,18 (U WS ), C Vap,21 (U WS ), C Vap,37 (U WS ) is the statistical mean of the error propagation coefficient between the brightness temperature measurements at 18.7 GHz, 21 GHz, and 37 GHz and the water vapor correction under different sea conditions; σ(T 18 ),σ(T 23 ),σ(T 37 ) are the brightness temperature measurement accuracies of 18.7 GHz, 21 GHz, and 37 GHz respectively.

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