A method for calculating satellite ground coverage time window considering geographical environment

Abstract

The present invention introduces a method for calculating the time window of satellite coverage of the earth taking into account the geographical environment, and the specific steps are: S1: calculating the position information of the remote sensing satellite; S2: determining the satellite-ground geometric relationship at the critical moment of the remote sensing satellite imaging window; S3: establishing the remote sensing satellite imaging time window prediction equation; S4: taking into account the time window calculation under the geographical environment. The method for calculating the time window of satellite coverage of the earth taking into account the geographical environment of the present invention considers the influence of the geographical environment such as rugged mountainous areas and gullies in some small area targets on the remote sensing satellite imaging window prediction, realizes the accurate calculation of the visible time window, provides more time windows for users to perform tasks, and further provides strong support and guarantee for special users to perform tasks.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing satellite imaging, and in particular to a method for calculating a satellite ground coverage time window taking into account the geographical environment. Background Art

[0002] A remote sensing satellite is an application satellite that uses the remote sensors on board to conduct optical or electronic detection of the earth's surface and lower atmosphere to obtain relevant information. It has the advantages of a large detection range, fast data acquisition, and no restrictions on airspace or national boundaries. It has produced huge benefits in the fields of land and resources exploration, disaster monitoring, ocean monitoring, and non-cooperative moving target positioning. The instantaneous coverage area of ​​a satellite sensor refers to the ground area that can be observed by satellite observation equipment such as sensors or antennas at a certain moment. The ground coverage area of ​​a satellite at any point in orbit is the area between the curved surface formed by the rays emitted from the sensor boundary at a certain angle and the earth. The area formed by the intersection of surfaces; when calculating the coverage characteristics of remote sensing sensors on the surface of celestial bodies, the existing calculation methods generally simplify the surface to be calculated into a standard ellipsoid, and then obtain the analytical results of the surface coverage characteristics based on its geometric relationship with the sensor; however, from a local perspective, the terrain of the celestial body surface is generally irregular. After simplifying it into a standard ellipsoid, the occlusion and edge effects caused by the irregular terrain cannot be reflected in the coverage calculation results; this has a serious loss of accuracy for the calculation of coverage results, especially for the coverage judgment of some key targets located in rugged mountainous areas, gullies, and deep valleys. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for calculating the satellite coverage time window taking into account the geographical environment, so as to achieve accurate calculation of the visible time window.

[0004] The technical solution adopted by the present invention is:

[0005] A method for calculating a satellite ground coverage time window taking into account the geographical environment, the specific steps are:

[0006] S1: Calculate remote sensing satellite position information

[0007] According to the six initial orbital elements of the remote sensing satellite at the initial time t0, the satellite position vector P can be obtained by formula (1):

[0008]

[0009] Where a is the semi-major axis of the orbit, e is the eccentricity, i is the inclination of the orbital plane, Ω is the right ascension of the ascending node, ω is the argument of perigee, E is the eccentric perigee angle, R(Ω), R(i), and R(ω) are the transformation matrices from the orbital coordinate system to the geocentric inertial coordinate system; expressed as

[0010]

[0011] The J2 perturbation of the Earth's oblateness is the main perturbation of remote sensing satellites. The magnitude of the J2 perturbation is 10 -3 , ignoring the short-term term of the J2 perturbation, taking into account the influence of the long-term J2 perturbation, the Kepler root numbers a, e, i do not change, and Ω, ω, and M will change over time:

[0012]

[0013] Where R e is the Earth's equatorial radius, is the average period of satellite motion, p = a(1-e 2 ) is the semi-diameter of the track, c = cosi;

[0014] S2: Determine the satellite-ground geometric relationship at the critical moment of the remote sensing satellite imaging window

[0015] Define a characteristic cone to describe the visible range of the satellite. The centerline of the cone points from the imaging center to the center of the earth. The semi-cone angle is the maximum visible angle of the satellite K. max ; Maximum viewing angle K max The maximum maneuvering angle L of the sensor max And the instantaneous field of view IFOV;

[0016]

[0017] When the ground target is located inside the characteristic cone, the angle between the ground target and the remote sensing satellite and its subsatellite point satisfies β≤K max ; The critical moments of the ground target entering and exiting the cone are denoted as t1 and t2, respectively, at which time β=K max ; Then the satellite imaging window is expressed as (t2-t1);

[0018] When the target enters or exits the characteristic cone, the remote sensing satellite position vector P and the ground target vector G must satisfy the following relationship:

[0019]

[0020] S3: Establishing the prediction equation of remote sensing satellite imaging time window

[0021] Write each variable in equation (4) as a function of time t and solve the equation;

[0022]

[0023] Substituting formula (5) into formula (2) yields:

[0024]

[0025] Substituting formula (6) into formula (1), the remote sensing satellite position vector P can be written as a function of E;

[0026]

[0027] Considering the earth as a standard ellipsoid, θ0 is the Greenwich hour angle at time t0, ω0 is the angular velocity of the earth's rotation, and the coordinates of G in the inertial coordinate system at time t are:

[0028]

[0029] In the formula, a E 、e E are the semi-major axis and eccentricity of the Earth reference ellipsoid, respectively;

[0030] Similarly, formula (4) can be expressed as:

[0031] (P(E)-G(E))·G(E)-|P(E)-G(E)|·|G(E)|cosK max =0 (9)

[0032] Formula (9) is the prediction equation. Solving this equation can obtain the perigee angle at the critical moment of the imaging window, and then the critical time window can be obtained.

[0033] S4: Time window calculation considering geographical environment

[0034] After the critical time window under the ellipsoid is calculated, the center point of the regional position and the discrete points of the regional boundary are taken as the union Calculate the visibility of remote sensing satellites that have entered the critical time window. If the union If any discrete point in the area is visible to the corresponding remote sensing satellite, then the corresponding remote sensing satellite is deemed to have effective coverage of the ground area. If all discrete points are not visible to the corresponding remote sensing satellite, it is considered that the ground target cannot be observed by the remote sensing satellite;

[0035] While judging whether the corresponding remote sensing satellite effectively covers the ground area, the digital elevation model DEM is used to express the terrain surface geographical environment. Considering the simulation operation time and accuracy results, the bilinear interpolation method is used to obtain the elevation value H of each sampling point in the line of sight projection direction to obtain a more refined DEM data model; the line of sight-based visual area analysis algorithm is used to calculate whether the terrain and landforms block the line of sight of the remote sensing satellite; specifically, first, the projection of the ground target point and the remote sensing satellite connection line on the DEM is uniformly sampled; then, the actual elevation value H of each sampling point is compared with its elevation value on the line of sight. If the actual elevation value of a certain sampling point is higher than the line of sight, it is considered that there is no line of sight, which means that the terrain blocks the line of sight of the remote sensing satellite, and the ground target point is not in the coverage area of ​​the remote sensing satellite in this time window.

[0036] Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages:

[0037] The present invention provides a method for calculating the time window of satellite coverage of the earth, which takes into account the geographical environment. It considers the influence of the geographical environment such as rugged mountainous areas and gullies in some small area targets on the prediction of remote sensing satellite imaging windows, realizes the accurate calculation of visible time windows, provides more time windows for users to perform tasks, and further provides strong support and guarantee for special users to perform tasks. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of this patent. DETAILED DESCRIPTION

[0039] The present invention will be further explained below in conjunction with the accompanying drawings and embodiments, which should not be used to limit the protection scope of the present invention. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention.

[0040] Combined with Figure 1 A method for calculating a satellite ground coverage time window taking into account the geographical environment is shown, and the specific steps are:

[0041] S1: Calculate remote sensing satellite position information

[0042] The satellite's spatial position simulation is the basis for calculating the satellite's earth coverage time window. Its accuracy directly affects the accuracy of the forecast time. The six parameters of the satellite orbit can be used to calculate the satellite's position and speed at any time, thereby determining the satellite's position in orbit in real time.

[0043] According to the six initial orbital elements of the remote sensing satellite at the initial time t0, the satellite position vector P can be obtained by formula (1):

[0044]

[0045] Where a is the semi-major axis of the orbit, e is the eccentricity, i is the inclination of the orbital plane, Ω is the right ascension of the ascending node, ω is the argument of perigee, E is the eccentric perigee angle, R(Ω), R(i), and R(ω) are the transformation matrices from the orbital coordinate system to the geocentric inertial coordinate system; expressed as

[0046]

[0047] The J2 perturbation of the Earth's oblateness is the main perturbation of remote sensing satellites. The magnitude of the J2 perturbation is 10 -3 , ignoring the short-term term of the J2 perturbation, taking into account the influence of the long-term J2 perturbation, the Kepler root numbers a, e, i do not change, and Ω, ω, and M will change over time:

[0048]

[0049] Where R e is the Earth's equatorial radius, is the average period of satellite motion, p = a(1-e 2 ) is the semi-diameter of the track, c = cosi;

[0050] S2: Determine the satellite-ground geometric relationship at the critical moment of the remote sensing satellite imaging window

[0051] Remote sensing satellites have the ability to maneuver sideways, forward and backward, etc., which means that their observation area is no longer a strip with the subsatellite point as the center line. The purpose of imaging time window prediction is to calculate when the target is within the maximum visible range of the satellite.

[0052] Define a characteristic cone to describe the visible range of the satellite. The centerline of the cone points from the imaging center to the center of the earth. The semi-cone angle is the maximum visible angle of the satellite K. max ; Maximum viewing angle K max The maximum maneuvering angle L of the sensor max And the instantaneous field of view IFOV;

[0053]

[0054] When the ground target is located inside the characteristic cone, the angle between the ground target and the remote sensing satellite and its subsatellite point satisfies β≤K max ; The critical moments of the ground target entering and exiting the cone are denoted as t1 and t2, respectively, at which time β=K max ; Then the satellite imaging window is expressed as (t2-t1);

[0055] When the target enters or exits the characteristic cone, the remote sensing satellite position vector P and the ground target vector G must satisfy the following relationship:

[0056]

[0057] S3: Establishing the prediction equation of remote sensing satellite imaging time window

[0058] Write each variable in equation (4) as a function of time t and solve the equation;

[0059]

[0060] Substituting formula (5) into formula (2) yields:

[0061]

[0062] Substituting formula (6) into formula (1), the remote sensing satellite position vector P can be written as a function of E;

[0063]

[0064] Considering the earth as a standard ellipsoid, θ0 is the Greenwich hour angle at time t0, ω0 is the angular velocity of the earth's rotation, and the coordinates of G in the inertial coordinate system at time t are:

[0065]

[0066] In the formula, a E 、e E are the semi-major axis and eccentricity of the Earth reference ellipsoid, respectively;

[0067] Similarly, formula (4) can be expressed as:

[0068] (P(E)-G(E))·G(E)-|P(E)-G(E)|·|G(E)|cosK max =0 (9)

[0069] Formula (9) is the prediction equation. Solving this equation can obtain the perigee angle at the critical moment of the imaging window, and then the critical time window can be obtained.

[0070] S4: Time window calculation considering geographical environment

[0071] After the critical time window under the ellipsoid is calculated, the center point of the regional position and the discrete points of the regional boundary are taken as the union Calculate the visibility of remote sensing satellites that have entered the critical time window. If the union If any discrete point in the area is visible to the corresponding remote sensing satellite, then the corresponding remote sensing satellite is deemed to have effective coverage of the ground area. If all discrete points are not visible to the corresponding remote sensing satellite, it is considered that the ground target cannot be observed by the remote sensing satellite;

[0072] While judging whether the corresponding remote sensing satellite effectively covers the ground area, the digital elevation model DEM is used to express the terrain surface geographical environment. Considering the simulation operation time and accuracy results, the bilinear interpolation method is used to obtain the elevation value H of each sampling point in the line of sight projection direction to obtain a more refined DEM data model; the line of sight-based visual area analysis algorithm is used to calculate whether the terrain and landforms block the line of sight of the remote sensing satellite; specifically, first, the projection of the ground target point and the remote sensing satellite connection line on the DEM is uniformly sampled; then, the actual elevation value H of each sampling point is compared with its elevation value on the line of sight. If the actual elevation value of a certain sampling point is higher than the line of sight, it is considered that there is no line of sight, which means that the terrain blocks the line of sight of the remote sensing satellite, and the ground target point is not in the coverage area of ​​the remote sensing satellite in this time window.

[0073] Parts of the present invention not described in detail are prior art.

[0074] The embodiments selected herein for the purpose of disclosing the invention are currently considered to be suitable, but it should be understood that the invention is intended to include all changes and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A method for calculating a satellite ground coverage time window taking into account the geographical environment, characterized in that: The specific steps are: S1: Calculate remote sensing satellite position information According to the six initial orbital elements of the remote sensing satellite at the initial time t0, the satellite position vector P can be obtained by formula (1): Where a is the semi-major axis of the orbit, e is the eccentricity, i is the inclination of the orbital plane, Ω is the right ascension of the ascending node, ω is the argument of perigee, and E is the eccentric perigee angle; S2: Determine the satellite-ground geometric relationship at the critical moment of the remote sensing satellite imaging window Define a characteristic cone to describe the visible range of the satellite. The centerline of the cone points from the imaging center to the center of the earth. The semi-cone angle is the maximum visible angle of the satellite K. max ; Maximum viewing angle K max The maximum maneuvering angle L of the sensor max And the instantaneous field of view IFOV; When the ground target is located inside the characteristic cone, the angle between the ground target and the remote sensing satellite and its subsatellite point satisfies β≤K max ; The critical moments of the ground target entering and exiting the cone are denoted as t1 and t2, respectively, at which time β=K max ; Then the satellite imaging window is expressed as (t2-t1); When the target enters or exits the characteristic cone, the remote sensing satellite position vector P and the ground target vector G must satisfy the following relationship: S3: Establishing the prediction equation of remote sensing satellite imaging time window (P(E)-G(E))·G(E)-|P(E)-G(E)|·|G(E)|cosK max =0 (9) Formula (9) is the prediction equation. Solving this equation can obtain the perigee angle at the critical moment of the imaging window, and then the critical time window can be obtained; S4: Time window calculation considering geographical environment After the critical time window is calculated, the center point of the regional location and the discrete points of the regional boundary are taken as the union. Calculate the visibility of remote sensing satellites that have entered the critical time window. If the union If any discrete point in the area is visible to the corresponding remote sensing satellite, then the corresponding remote sensing satellite is deemed to have effective coverage of the ground area. If all discrete points are not visible to the corresponding remote sensing satellite, it is considered that the ground target cannot be observed by the remote sensing satellite; While judging whether the corresponding remote sensing satellite effectively covers the ground area, the digital elevation model DEM is used to express the terrain surface geographical environment. Considering the simulation operation time and accuracy results, the bilinear interpolation method is used to obtain the elevation value H of each sampling point in the line of sight projection direction to obtain a more refined DEM data model; the line of sight-based visual area analysis algorithm is used to calculate whether the terrain and landforms block the line of sight of the remote sensing satellite; specifically, first, the projection of the ground target point and the remote sensing satellite connection line on the DEM is uniformly sampled; then, the actual elevation value H of each sampling point is compared with its elevation value on the line of sight. If the actual elevation value of a certain sampling point is higher than the line of sight, it is considered that there is no line of sight, which means that the terrain blocks the line of sight of the remote sensing satellite, and the ground target point is not in the coverage area of ​​the remote sensing satellite in this time window.

2. According to claim 1, it is characterized in that: In S1, R(Ω), R(i), and R(ω) are the transformation matrices from the orbital coordinate system to the geocentric inertial coordinate system; they are expressed as The J2 perturbation of the Earth's oblateness is the main perturbation of remote sensing satellites. The magnitude of the J2 perturbation is 10 -3 , ignoring the short-term term of the J2 perturbation, taking into account the influence of the long-term J2 perturbation, the Kepler root numbers a, e, i do not change, and Ω, ω, and M will change over time: Where R e is the Earth's equatorial radius, is the average period of satellite motion, p = a(1-e 2 ) is the semi-diameter of the track, c=cosi.

3. According to claim 2, it is characterized in that: The establishment process of the prediction equation (9) in S3 is specifically as follows: Write the variables in formula (4) as functions of time t and solve the equation; Substituting formula (5) into formula (2) yields: Substituting formula (6) into formula (1), the remote sensing satellite position vector P can be written as a function of E; Considering the earth as a standard ellipsoid, θ0 is the Greenwich hour angle at time t0, ω0 is the angular velocity of the earth's rotation, and the coordinates of G in the inertial coordinate system at time t are: In the formula, a E 、e E are the semi-major axis and eccentricity of the Earth reference ellipsoid, respectively; Similarly, formula (4) can be expressed as: (P(E)-G(E))·G(E)-|P(E)-G(E)|·|G(E)|cosKmax=0 (9).

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