JPH0812237B2 - Cyclic orbit positioning system - Google Patents

Description

The present invention relates to a synchronous orbit type positioning method for detecting the position of a radio wave source using an artificial satellite having a synchronous orbit.

[Conventional technology]

Conventionally, the following is known as a search and rescue (search and rescue) system for searching the position of a specific radio wave source such as a beacon installed in a rescue buoy.
That is, as shown in FIG. 6, a receiver is mounted on a low-altitude satellite 21 of 500 to 2000 km to receive a radio wave 23 such as a rescue beacon wave emitted from a radio source 22 such as a rescue buoy and receive the received signal. There is a method of identifying the radio wave source 22 from the Doppler shift data of the signal. Further, as shown in FIG. 7 (A), two orthogonal array antennas 25, 26 are provided to the geostationary satellite 24 in the geostationary orbit.
Equipped with a receiver equipped with, as shown in FIG. 7 (B),
A method has been proposed in which the fan beams 27 and 28 of the array antennas 25 and 26 are electrically scanned to identify the radio wave source 29 on the earth.

[Problems to be solved by the invention]

However, with the former method, it is not possible to constantly monitor a specific area, and it takes a long time (1 to 2 hours) for a low altitude satellite to orbit the earth after the observation at a certain point until the next observation of the same area. When it is continuously used as such, there is a problem that it takes too much time and does not function as a search / rescue system. On the other hand, since the latter method is installed on a geostationary orbit, it is possible to constantly monitor a predetermined area, but the two orthogonal array antennas become huge, which makes it difficult to implement on a satellite.

The present invention has been made to solve the above-mentioned problems of the positioning method known as a conventional search / rescue system, etc., and provides a positioning method that can be constantly monitored and is easily mounted on a satellite. That is the purpose.

[Means and Actions for Solving Problems]

In order to solve the above problems, the present invention provides a radio wave that emits a radio wave having coherency to an artificial satellite having a synchronous orbit whose orbit viewed from the earth is reciprocating by changing the orbit inclination angle and / or the eccentricity. The receiver is equipped with a passive synthetic aperture function that performs autocorrelation processing on each received signal at different times from the source, and a receiver that has the function of observing the radio source by scanning a fan beam. The position of the radio wave source is detected by measuring the reciprocal movement direction of the above by the passive synthetic aperture method, and the direction orthogonal thereto by the fan beam scanning method.

In the synchronous orbital positioning system configured in this way,
Since satellites that have synchronous orbits are used, it is possible to perform constant observation of a prescribed area, and only one array antenna for fan beam scanning is required.
It is possible to facilitate mounting on an artificial satellite.

〔Example〕

Examples will be described below. The receiving device having the passive synthetic aperture function and the fan-beam scanning function used in the present invention is mounted on an artificial satellite having a synchronous orbit. In the synchronous orbit, the period of the artificial satellite is the rotation period of the earth. It is obtained by changing one or both of the orbital inclination angle and the eccentricity of the satellite orbital elements in coincident orbits.

In the present invention, an artificial satellite is used in which one or both of the orbital inclination angle i and the eccentricity e are changed, and which is placed on a synchronous orbit whose trajectory seen from the earth is reciprocating. As shown in FIG. 1, by changing the orbit inclination angle i, the orbit inclination angle i ≠ 0 and the eccentricity e = 0, the artificial satellite 1 on the synchronous orbit is the earth axis O of the earth 2 and the artificial satellite 1. When the distance between the R _G, 2 · R _G · in the north-south direction when viewed from the surface
Reciprocates relative to the ground surface in the range of i. In FIG. 1, 3 is the equatorial plane, N is the north pole, and S is the south pole.

Further, as shown in FIGS. 2A and 2B, the eccentricity e ≠
The artificial satellite 1 in a synchronous orbit with a perspective orbital angle i = 0 of 0 makes a reciprocating motion relative to the surface of the earth in the east-west direction in the range of 4R _G · e when viewed from the surface of the earth. In the figure, E
Indicates east, W indicates west, P indicates orbit inclination angle i = 0, eccentricity e =
The stationary position of the artificial satellite 1 when 0 is shown.

Moreover, when both the orbit inclination angle i and the eccentricity e are changed (i ≠ 0, e ≠ 0), a locus such as a circle or a figure 8 is shown.
Artificial satellites in a synchronous orbit that exhibits a reciprocating trajectory in the east-west or north-south direction such as a letter shape can also be used in the present invention.

In this way, when the artificial satellite 1 is placed on the synchronous orbit in which the orbit inclination angle i and / or the eccentricity e is appropriately changed according to the purpose, the equipment mounted on the artificial satellite 1 is set to the ground surface of the specific area. A reciprocating motion can be relatively performed in the north-south direction or the east-west direction.

FIG. 3 (A) illustrates an embodiment of the present invention using the artificial satellite having the synchronous orbit shown in FIG. 1 in which the orbit inclination angle i ≠ 0, the eccentricity e = 0, and the cycle≈24 hours. It is a figure. In the figure, 11 is an artificial satellite in orbit with a changed orbit inclination angle, and the satellite 11 is equipped with a receiving device including an array antenna 12 and a receiver arranged in the east-west direction,
As shown in FIG. 3B, the fan beam 13 of the array antenna 12 is scanned in the east-west direction, so that the position of the radio wave source 14 in the east-west direction can be detected with high accuracy.

On the other hand, by utilizing the fact that the receiving device mounted on the artificial satellite 11 reciprocates in the north-south direction when viewed from the earth, the fan beam spreading in the north-south direction is processed by data processing by the passive synthetic aperture method described in detail later. Equivalently narrow the radio source
The 14 north-south positions are detected with high accuracy.

As shown in FIG. 4, the receiving device mounted on the artificial satellite includes one array antenna 12 and a receiving beam direction controller 15 that electronically or mechanically scans the fan beam of the antenna 12. It is composed of a receiver 16 and a data processing device 17 that performs processing such as autocorrelation processing on the received signal.

The synthetic aperture method used in the present invention is a passive synthetic aperture method that realizes a function equivalent to that of a conventional synthetic aperture radar only with a reception function. As shown in FIG. 5 (A), a synthetic aperture radar equipped with a general transmitter / receiver obtains a high-resolution image by subjecting a received signal to cross-correlation processing using a transmitted wave as a reference signal. However, in the passive synthetic aperture method, instead of the cross-correlation processing using the transmitted wave as the reference signal, data processing different from the cross-correlation processing called the auto-correlation processing of the received signals different in time is performed, High resolution is obtained.

Conventionally, for the observation data observed by artificial satellites,
No autocorrelation processing is performed. This is because observation by artificial satellites is performed for the purpose of earth observation, etc., and the observation target is mainly natural products and natural phenomena such as the ocean and land, so the received signals obtained from them are of coherency. It is not a random noise signal, so even if you try to autocorrelate the received signals at different times, it was considered to be noiseless as a result because the signals themselves were originally uncorrelated, so it was meaningless. Is.

The present inventor has reviewed this point and is limited to signals having an artificial radio wave source, for example, a signal radio wave from a beacon of a rescue buoy or a microwave from a natural object in a narrow area, which has a temporal coherency. Then, since there is a strong autocorrelation with respect to the temporal change of those signals, we focus on the fact that the autocorrelation processing is effective, and the passive synthetic aperture method that performs this autocorrelation processing is adopted. It is used in a receiver mounted on an artificial satellite that reciprocates in the north-south direction, and detects the position of the radio wave source in the north-south direction with high accuracy as described above.

The autocorrelation process itself performed by the passive synthetic aperture method used in the present invention is not a process by a new means, but a conventional means well known in the field of signal processing and mathematics. That is, the autocorrelation function has a τ time of 2 when X (t) is a random variable with respect to time.
It is well known that it is a statistical function defined by the average value C (t, τ) of the products of two fluctuations and is expressed by the following equation.

C (t, τ) = E [X (t) · X (t + τ)] Therefore, for a general observed (received) signal in which the originally desired coherency signal component and other noise components are mixed, When an autocorrelation process to find an autocorrelation function like this is performed, only the coherency signal component to be found is emphasized by overlapping (integration effect) when averaged by its correlation, and there is no correlation for the noise component. They will be canceled and reduced.

This will be described with reference to FIG. 5B. Autocorrelation processing is performed on the received signal at the time point t _{0 and} the received signal at the time point (t ₀ + t), that is, for the received signals that are different in time. And, when the received wave is a radio wave from a demodulated radio wave source such as a beacon, there is coherency (coherence), so that the beam width obtained is narrowed by superimposing on the time axis and then spatially. That is, it is compressed. This compression processing, which is usually used as a synonym for synthetic aperture processing, cross-correlation processing, or auto-correlation processing, is data sampling processing (decimation) in image processing, etc.
The meaning of the compression process is different from that of the compression process, which means the process of narrowing the virtual beam width according to the wording.Therefore, this compression process identifies the position of the radio wave source in the north-south movement method with high accuracy. can do.

As the means for performing the above-mentioned autocorrelation processing, a well-known configuration can be used, and the basic configuration is that the signal X (t) at every moment and the signal X (t) are obtained once through a delay circuit. Signal X (t
-Τ) is put in a multiplication circuit and the average value of the outputs is taken out.

In the above embodiment, the receiving device including the data processing device is mounted on the artificial satellite in the synchronous orbit, but the receiving data may be transmitted to the ground and the data processing may be performed on the ground. it can.

In the above embodiment, the artificial satellite on the synchronous orbit with a changed orbit inclination angle is used.However, when the artificial satellite on the synchronous orbit with a changed eccentricity is used, the array antenna is arranged in the north-south direction. The position of the radio wave source is detected with high accuracy in the same manner as in the above embodiment by arranging and measuring the position in the north-south direction by the fan beam scanning method and measuring the position in the east-west direction by the passive synthetic aperture method. You can

Furthermore, when an orbital tilt angle and eccentricity are both changed and a satellite on a synchronous orbit whose trajectory shows a reciprocating motion is used, the passive synthetic aperture method and the fan beam scanning method are used to detect the radio wave source. It is possible to detect the position with high accuracy.

〔The invention's effect〕

As described in the above embodiments, according to the present invention, the position in one direction is measured by the passive synthetic aperture method, and the position in the direction orthogonal thereto is measured by the fan beam scanning method. It is possible to detect the position of the power source that radiates a radio wave having coherency with accuracy.

Also, because we are using artificial satellites with synchronous orbits,
Since a specific area can be constantly monitored and only one array antenna is required, there are advantages such as easy installation of the device according to this method on an artificial satellite.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a synchronous orbit in which the orbit inclination angle is changed,
FIG. 2 (A) is an explanatory diagram of a synchronous orbit with changed eccentricity, and FIG. 2 (B) is a view of the artificial satellite on the synchronous orbit shown in FIG. FIG. 3 (A) is an explanatory view showing a relative locus, FIG. 3 (A) is an explanatory view of an embodiment of the present invention, and FIG. 3 (B) is a view showing a scanning mode of a fan beam of the array antenna. FIG. 5 is a block diagram showing an example of a receiver, FIG. 5 (A) is a block diagram showing a data processing method in a general synthetic aperture radar, and FIG. 5 (B) is data in a passive synthetic aperture method. FIG. 6 is a block diagram showing a processing method, FIG. 6 is an explanatory diagram showing a conventional positioning method using a low altitude satellite, and FIGS. 7 (A) and 7 (B) are
It is explanatory drawing which shows the conventional positioning method using a geostationary satellite. In the figure, 1 is an artificial satellite, 2 is the earth, 3 is the equatorial plane, 11
Is an artificial satellite, 12 is an array antenna, 13 is a fan beam,
14 is a radio wave source, 15 is a receiving beam direction controller, 16 is a receiver,
Reference numeral 17 represents a data processing device.

Claims (1)

[Claims] 1. An artificial satellite having a synchronous orbit whose trajectory seen from the earth is reciprocating by changing the orbit inclination angle and / or the eccentricity, has different times from a radio wave source emitting a coherent radio wave. The receiver is equipped with a passive synthetic aperture function that observes the radio wave source by subjecting the received signal to autocorrelation processing, and a receiver that has the function of observing the radio wave source by scanning the fan beam. The position of the reciprocating direction of the passive synthetic aperture method,
A synchronous orbit positioning system characterized by detecting the position of the radio wave source by measuring the position in the direction orthogonal to it by the fan-beam scanning method.