A method for establishing a daytime electron density model for the Martian ionosphere

Abstract

This invention discloses a method for establishing a daytime electron density model for the Martian ionosphere. The method comprises the following steps: dividing the Martian ionosphere into the M1 and M2 layers, a transition layer, and a top layer; establishing electron density models for the M1 and M2 layers that vary with solar zenith angle and altitude; establishing electron density models for the transition layer that vary with solar zenith angle and altitude; establishing electron density models for the top layer that vary with altitude; and finally, combining these models to obtain a daytime electron density model for the Martian ionosphere. The method utilizes a layered modeling technique to establish a multilayer electron density calculation model that encompasses the electron density of the M1 layer and portions above the M2 layer. This new model is more complete and accurate than the local Chapman model that only considers the M2 layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of planetary space environment research, and in particular relates to a method for establishing a daytime electron density model of the Martian ionosphere. Background Art

[0002] Mars exploration has been a focus of deep space exploration in recent years. The Martian ionosphere, which influences the Martian orbit and signal transmission from the surface, is a crucial consideration in any Mars exploration mission. The Martian ionosphere exhibits a multi-layered electron density structure, with significant differences between daytime and nighttime, influenced by solar activity. The Martian ionosphere is primarily formed by the ionization of the neutral atmosphere by solar extreme ultraviolet radiation. The lower ionosphere is in photochemical equilibrium, while the upper ionosphere is in diffusional equilibrium. A vertical profile of daytime electron density exhibits a typical layered structure: the M2 layer (the main ionosphere) lies between 120 and 190 km above sea level, with a peak electron density at approximately 140 km. The M1 layer (the bottom layer) lies between 100 and 120 km above sea level, with a peak electron density at approximately 110 km. Above the M2 layer (the top layer), located above 190 km, the electron density decreases rapidly with increasing altitude.

[0003] Currently, research on the daytime electron density of the Martian ionosphere primarily focuses on theoretical research and regularity analysis of the M2 layer. It is believed that the M2 layer is affected by photochemical processes, and that the variation of electron density with altitude and solar zenith angle conforms to the Chapman theory, with electron density exhibiting a peak characteristic. The Chapman model used in existing technologies can well describe the vertical distribution of electron density in the M2 layer, including the main peak, and qualitatively provides the variation patterns between the solar zenith angle, peak electron density, and the altitude corresponding to the peak electron density. However, there is a lack of model descriptions for the electron density in the M1 layer and above the M2 layer. In other words, there is no model that can fully describe the daytime electron density of the Martian ionosphere. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for establishing a daytime electron density model of the Martian ionosphere, so as to solve the problem of the lack of a complete description model of the daytime electron density of the Martian ionosphere in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for establishing a daytime electron density model of the Martian ionosphere according to the present invention comprises the following steps:

[0007] (1) The Martian ionosphere is divided into the M1 & M2 layers, the transition layer, and the top layer;

[0008] (2) Establish an electron density model for the M1 & M2 layers that varies with the solar zenith angle and altitude

[0009] (3) Establish the electron density model N of the transition layer that changes with the solar zenith angle and altitude eMID (SZA,z);

[0010] (4) Establish the electron density model N of the top layer that changes with altitude eTOP (z);

[0011] (5) Combine the electron density models established in steps (2), (3), and (4) to obtain the daytime electron density model N of the Martian ionosphere eDAY (SZA,z).

[0012] Furthermore, the step (1) specifically includes:

[0013] According to the law of change of electron density with altitude, the Martian ionosphere is divided into M1&M2 layers, transition layer and top layer; among them, the Martian altitude z corresponding to the M1&M2 layers is: 80≤z<145km; the Martian altitude z corresponding to the transition layer is: 145≤z<190km; the Martian altitude z corresponding to the top layer is: z≥190km.

[0014] Furthermore, the step (2) specifically includes:

[0015] The electron density in the M1 and M2 layers is affected by photochemical processes, and has a significant double-peak distribution. The variations of the electron density peak and the altitude corresponding to the electron density peak with the solar zenith angle are consistent with the Chapman theory. The double Chapman model is used to describe the variation of the electron density in the M1 and M2 layers during the day with the solar zenith angle and altitude, as follows:

[0016]

[0017] Where, is the electron density of the M1 & M2 layers that varies with the solar zenith angle and altitude, SZA is the solar zenith angle, which is SZA∈(0,90°) during the day, z is the altitude of Mars, the subscript character variable α is M1 and M2 respectively, N mα is the peak electron density at a given SZA, N m0α is the peak electron density at the subsolar point, k α To determine the parameters of the photochemical process, z mα is the altitude corresponding to the peak electron density under a given SZA, z mα =z m0α +Hln[sec(SZA)],z m0αis the altitude corresponding to the peak electron density at the subsolar point, and H is the neutral atmospheric scale height;

[0018] In formula (1), the parameter to be determined is k α ,H,N m0α and z m0α ;Undetermined parameter k α Directly use the existing empirical values: for α = M1, the three cases of high solar activity, medium solar activity, and low solar activity correspond to The values ​​are 0.53, 0.551±0.024, and 0.55 respectively; for α=M2, the three cases of high, medium, and low solar activity years correspond to The values ​​are 0.49, 0.465±0.010, and 0.42 respectively; the altitude, solar zenith angle, and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (1), and the remaining model parameters H, and

[0019] Furthermore, the step (3) specifically includes:

[0020] The electron density in the transition layer is affected by both the photochemical process and the transport process. The photochemical process adopts the model established in step (2). The transport process is compensated by using a semi-parabolic calculation model in which the electron density changes with altitude, as follows:

[0021]

[0022] Where, N eMID is the electron density of the transition layer that varies with the solar zenith angle and altitude, az 2 +2a·bz+c is a semi-parabolic calculation model, z is the altitude of Mars, and a, b, and c are the unknown coefficients of the model. The altitude, solar zenith angle, and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (2) respectively, and the second-order polynomial fitting in the cftool toolbox in Matlab is used to obtain the model coefficients a, b, and c.

[0023] Furthermore, the step (4) specifically includes:

[0024] The electron density at the top layer is affected by the transport process and decreases exponentially with increasing altitude. The exponential calculation model is used as follows:

[0025] N eTOP (z) = NTOP exp(-k TOP z) (3)

[0026] Where, N eTOP is the top electron density that varies with altitude, z is the altitude of Mars, N TOP and k TOP The altitude and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (3) and fitted using the custom equation in the cftool toolbox in Matlab to obtain the model parameter N. TOP and k TOP .

[0027] Furthermore, the step (5) specifically includes:

[0028] According to the electron density models in step (2), step (3), and step (4), the calculation model N of the electron density of the Martian ionosphere during the day, which shows that the electron density varies with the solar zenith angle and altitude, is obtained. eDAY (SZA,z), that is:

[0029]

[0030] Discard N eDAY A value ≤0.

[0031] Beneficial effects of the present invention:

[0032] The method proposed in this paper uses layered modeling techniques to establish a multi-layer electron density calculation model that includes the electron density of the M1 layer and the portion above the M2 layer. This new model is more complete and accurate than the local Chapman model that only considers the M2 layer. For altitudes below 145 km, the model considers the influence of the M1 layer and better describes the peak distribution of electron density in the M1 layer. For altitudes between 145 and 190 km, the model better compensates for the effects of transport processes. For altitudes above 190 km, the model better describes the exponential decay of electron density caused by transport processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is a principle block diagram of the method of the present invention.

[0034] Figure 2 This is a daytime electron density map of the Martian ionosphere during a year of high solar activity in the embodiment. DETAILED DESCRIPTION

[0035] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and drawings. The contents mentioned in the embodiments are not intended to limit the present invention.

[0036] Reference Figure 1 As shown, a method for establishing a daytime electron density model of the Martian ionosphere of the present invention comprises the following steps:

[0037] (1) The Martian ionosphere is divided into the M1 & M2 layers, the transition layer, and the top layer; specifically:

[0038] Based on the statistical characteristics of MGS satellite detection data, the electron density of the Martian ionosphere during the day has a significant layered structure. Above 190 km, it is mainly affected by the transport process, while below 190 km, it is mainly affected by the photochemical process. According to the change pattern of electron density with altitude, the Martian ionosphere is divided into M1&M2 layers, transition layer and top layer. Among them, the Martian altitude z corresponding to the M1&M2 layers is: 80≤z<145km; the Martian altitude z corresponding to the transition layer is: 145≤z<190km; the Martian altitude z corresponding to the top layer is: z≥190km.

[0039] (2) Establish an electron density model for the M1 & M2 layers that varies with the solar zenith angle and altitude Specifically include:

[0040] The electron density in the M1 and M2 layers is affected by photochemical processes, and has a significant double-peak distribution. The variations of the electron density peak and the altitude corresponding to the electron density peak with the solar zenith angle are consistent with the Chapman theory. The double Chapman model is used to describe the variation of the electron density in the M1 and M2 layers during the day with the solar zenith angle and altitude, as follows:

[0041]

[0042] Where, is the electron density of the M1 & M2 layers that varies with the solar zenith angle and altitude, SZA is the solar zenith angle, which is SZA∈(0,90°) during the day, z is the altitude of Mars, the subscript character variable α is M1 and M2 respectively, N mα is the peak electron density at a given SZA, N m0α is the peak electron density at the subsolar point, k α To determine the parameters of the photochemical process, z mα is the altitude corresponding to the peak electron density under a given SZA, z mα =z m0α +Hln[sec(SZA)],z m0α is the altitude corresponding to the peak electron density at the subsolar point, and H is the neutral atmospheric scale height;

[0043] In formula (1), the parameter to be determined is k α ,H,N m0α and z m0α ;Undetermined parameter k α Directly use the existing empirical values: for α = M1, the three cases of high solar activity, medium solar activity, and low solar activity correspond to The values ​​are 0.53, 0.551±0.024, and 0.55 respectively; for α=M2, the three cases of high, medium, and low solar activity years correspond to The values ​​are 0.49, 0.465±0.010, and 0.42 respectively; the altitude, solar zenith angle, and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (1), and the remaining model parameters H, and

[0044] (3) Establish the electron density model N of the transition layer that changes with the solar zenith angle and altitude eMID (SZA,z); specifically includes:

[0045] The electron density in the transition layer is affected by both the photochemical process and the transport process. The photochemical process adopts the model established in step (2). The transport process is compensated by using a semi-parabolic calculation model in which the electron density changes with altitude, as follows:

[0046]

[0047] Where, N eMID is the electron density of the transition layer that varies with the solar zenith angle and altitude, az 2 +2a·bz+c is a semi-parabolic calculation model, z is the altitude of Mars, and a, b, and c are the unknown coefficients of the model. The altitude, solar zenith angle, and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (2) respectively, and the second-order polynomial fitting in the cftool toolbox in Matlab is used to obtain the model coefficients a, b, and c.

[0048] (4) Establish the electron density model N of the top layer that changes with altitude eTOP (z); specifically including:

[0049] The electron density at the top layer is affected by the transport process and decreases exponentially with increasing altitude. The exponential calculation model is used as follows:

[0050] N eTOP (z) = N TOP exp(-k TOP z) (3)

[0051] Where, N eTOP is the top electron density that varies with altitude, z is the altitude of Mars, N TOP and k TOP The altitude and electron density data detected by the Mars Global Surveyor (MGS) satellite are substituted into formula (3) and fitted using the custom equation in the cftool toolbox in Matlab to obtain the model parameter N. TOP and k TOP .

[0052] (5) Combine the electron density models established in steps (2), (3), and (4) to obtain the daytime electron density model N of the Martian ionosphere eDAY (SZA,z); specifically includes:

[0053] According to the electron density models in step (2), step (3), and step (4), the calculation model N of the electron density of the Martian ionosphere during the day, which shows that the electron density varies with the solar zenith angle and altitude, is obtained. eDAY (SZA,z), that is:

[0054]

[0055] Discard N eDAY A value ≤0.

[0056] Example

[0057] Taking the years of high solar activity (2012-2014) as an example, due to the high solar activity, the electron density of the Martian ionosphere mainly varies with altitude and solar zenith angle.

[0058] Based on statistical data from the Mars Global Surveyor (MGS) satellite, the daytime electron density of the Martian ionosphere exhibits a distinct stratified structure. Above 190 km, the electron density is primarily influenced by transport processes, while below 190 km, it is primarily influenced by photochemical processes. Based on the electron density variation, the Martian ionosphere is divided into the M1 & M2 layers, the transition layer, and the top layer. The M1 & M2 layers have a z value of 80 ≤ z < 145 km, where z is the altitude of Mars; the transition layer has a z value of 145 ≤ z < 190 km; and the top layer has a z value of 190 km or higher.

[0059] Using the M1&M2 layer electron density model The model parameters obtained by fitting are H = 9.1km, and That is, the M1&M2 layer electron density model for:

[0060]

[0061] Where,

[0062]

[0063] Using the transition layer electron density model N eMID The model coefficients of (SZA, z) were a = -19.96, b = -172.5 and c = -5.739 × 10 5 , that is, the transition layer electron density model N eMID (SZA,z) is:

[0064]

[0065] Using the top electron density model N eTOP (z) Fitting to obtain model parameters N TOP =7.89×10 8 cm -3 , k TOP = 0.055, that is, the top electron density model N eTOP (z) is:

[0066] N eTOP (z) = 7.89 × 10 8 exp(-0.055z) (7)

[0067] Substituting formulas (5), (6), and (7) into formula (8), we can obtain the calculation model N of the daytime electron density of the Martian ionosphere that changes with the solar zenith angle and altitude. eDAY (SZA,z), that is:

[0068]

[0069] Discard N eDAY A value ≤0.

[0070] The newly established Martian ionosphere daytime electron density model is a multi-layer calculation model that includes the electron density of the M1 layer (bottom layer) and the part above the M2 layer (top layer). Compared with the previous M2 layer local electron density model, the calculation results are more complete and accurate. The results of the Martian ionosphere daytime electron density model in the solar zenith angle of 71.8° in the year of high solar activity are as follows Figure 2 shown.

[0071] The invention has many specific application paths and is not limited to MGS satellites. The above is only a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the invention. These improvements should also be regarded as the scope of protection of the invention.

Claims

1. A method for establishing a daytime electron density model of the Martian ionosphere, characterized in that: Here are the steps: (1) The Martian ionosphere is divided into the M1 & M2 layers, the transition layer, and the top layer; (2) Establish an electron density model for the M1 & M2 layers that varies with solar zenith angle and altitude; (3) Establish an electron density model for the transition layer that varies with solar zenith angle and altitude; (4) Establish a model of the electron density of the top layer as it changes with altitude; (5) Combined to obtain the daytime electron density model of the Martian ionosphere; Step (2) specifically includes: The electron density in the M1 and M2 layers is affected by photochemical processes, and has a significant double-peak distribution. The variations of the electron density peak and the altitude corresponding to the electron density peak with the solar zenith angle are consistent with the Chapman theory. The double Chapman model is used to describe the variation of the electron density in the M1 and M2 layers during the day with the solar zenith angle and altitude, as follows: Where, is the electron density of the M1 & M2 layers that varies with the solar zenith angle and altitude, SZA is the solar zenith angle, which is SZA∈(0,90°) during the day, z is the altitude of Mars, the subscript character variable α is M1 and M2 respectively, N mα is the peak electron density at a given SZA, N m0α is the peak electron density at the subsolar point, k α To determine the parameters of the photochemical process, z mα is the altitude corresponding to the peak electron density under a given SZA, z mα =z m0α +Hln[sec(SZA)],z m0α is the altitude corresponding to the peak electron density at the subsolar point, and H is the neutral atmospheric scale height; In formula (1), the parameter to be determined is k α ,H,N m0α and z m0α ;Undetermined parameter k α Directly use the existing empirical values: for α = M1, the three cases of high solar activity, medium solar activity, and low solar activity correspond to The values ​​are 0.53, 0.551±0.024, and 0.55 respectively; for α=M2, the three cases of high, medium, and low solar activity years correspond to The values ​​are 0.49, 0.465±0.010, and 0.42 respectively; the altitude, solar zenith angle, and electron density data detected by the Mars Global Surveyor satellite are substituted into formula (1), and the remaining model parameters H, and Step (3) specifically includes: The electron density in the transition layer is affected by both the photochemical process and the transport process. The photochemical process adopts the model established in step (2). The transport process is compensated by using a semi-parabolic calculation model in which the electron density changes with altitude, as follows: Where, N eMID is the electron density of the transition layer that varies with the solar zenith angle and altitude, az 2 +2a·bz+c is a semi-parabolic calculation model, z is the altitude of Mars, a, b and c are the unknown coefficients of the model; the altitude, solar zenith angle and electron density data detected by the Mars Global Surveyor satellite are substituted into formula (2) respectively, and the second-order polynomial fitting in the cftool toolbox in Matlab is used to obtain the model coefficients a, b and c; Step (4) specifically includes: The electron density at the top layer is affected by the transport process and decreases exponentially with increasing altitude. The exponential calculation model is used as follows: N eTOP (z)=N TOP exp(-k TOP z) (3) Where, N eTOP is the top electron density that varies with altitude, z is the altitude of Mars, N TOP and k TOP is the model parameter; the altitude and electron density data detected by the Mars Global Surveyor satellite are substituted into formula (3), and the model parameter N is obtained by fitting the custom equation in the cftool toolbox in Matlab. TOP and k TOP .

2. The method for establishing a daytime electron density model of the Martian ionosphere according to claim 1, wherein: The step (1) specifically includes: According to the law of change of electron density with altitude, the Martian ionosphere is divided into M1&M2 layers, transition layer and top layer; among them, the Martian altitude z corresponding to the M1&M2 layers is: 80≤z<145km; the Martian altitude z corresponding to the transition layer is: 145≤z<190km; the Martian altitude z corresponding to the top layer is: z≥190km.

3. The method for establishing a daytime electron density model of the Martian ionosphere according to claim 1, wherein: The step (5) specifically includes: According to the electron density models in step (2), step (3), and step (4), the calculation model N of the electron density of the Martian ionosphere during the day, which shows that the electron density varies with the solar zenith angle and altitude, is obtained. eDAY (SZA,z), that is: Discard N eDAY A value ≤0.

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