Apparatus, method and program for recording satellite radio frequency activity

Abstract

The present invention relates to a method and a device for recording the radio frequency activity of an artificial satellite orbiting the Earth and emitting electromagnetic signals, the device comprising an antenna for receiving the acquired signals, a receiving chain, a computer capable of calculating the power spectral density (PSD) of at least one frequency subband on the basis of the signals, a set of defined orbital positions (PSDs) spaced apart in succession from one another, i ) a control device for directing the antenna line of sight to at least one sequence of

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for recording the radio frequency activity of an artificial satellite orbiting the Earth, and a computer program for their implementation.

[0002] General Technology Area The field of the invention relates to active orbital satellites of any kind. [Background technology]

[0003] Services for determining the orbits of geostationary satellites are known, using declarations provided by operators regarding the use of the radio frequency spectrum made by these satellites: this is called the "orbit tracking" system.

[0004] Known orbital tracking services use correlation techniques of signals transmitted by satellites and acquired by stations distant from each other, typically hundreds of kilometers apart. This technique requires the transfer of large amounts of data to a computing center. A systematic survey of orbits, such as the Clark Belt (geostationary orbit), by this technique would require unacceptable measurement times and high communication costs, since it is limited by the bandwidth of long-distance communication to the computing center.

[0005] Also, sporadically emitting satellites may not be detected by this method because they revisit their orbital positions too slowly (more than a day). Furthermore, if orbital tracking by a remote station fails, it is not clear what the cause is (plan / frequency change by the satellite, satellite communication outage, or other cause). Summary of the Invention [Problem to be solved by the invention]

[0006] One of the objects of the present invention is to obtain an apparatus, a method and a computer program for recording radio frequency activity from artificial satellites orbiting the Earth, which allows automatic detection and identification of radio frequency emissions emanating from the satellites, without prior third-party information, i.e. without taking into account declarations provided by the operators, and with short revisit times. [Means for solving the problem]

[0007] To this end, a first subject of the invention is a method for recording the radio frequency activity of at least one artificial satellite orbiting the Earth and emitting radio frequency signals, the method comprising the steps of: an antenna controller pointing at least one antenna and moving a line of sight axis of the antenna towards at least one sequence of distinct successive defined pointing positions, the antenna being in the form of a reflector the outer periphery of which defines a maximum aperture diameter of 6 meters or less; For each specified pointing position, collecting radio frequency signals by an antenna and converting the radio frequency signals into digital signals by a radio frequency chain; calculating, by a computer, at least one record of raw power spectral density over at least one received frequency subband from the digital signal; and a computer reprocessing the raw power spectral density record into a refined power spectral density record by applying a deconvolution process of the antenna radiation pattern of the receive frequency subbands.

[0008] Thus, the invention, by combining small antennas with deconvolution, allows to detect more satellites, because the main lobe of the above-mentioned small diameter antennas is wider and can cover more satellites at each antenna pointing position, and the revisit time (the time that elapses to perform all the planned scanning sequences) can be reduced, thus increasing the possibility of detecting non-persistent emissions from the satellites. This allows to increase the measurement pitch from one pointing position to the next in the sequence, thus increasing the speed of obtaining the refined power spectral density, while reducing the infrastructure costs.

[0009] Thus, the invention makes it possible to detect all satellites with radio frequency activity, whether listed or not. This system is called "spectrum mapping". It is therefore envisaged to inspect the stations, in which the device according to the invention is installed, using only one at a time. The invention lists any use not declared by the operator, any change in frequency plan, any change in orbital position, any acquisition of new stations or any faults on the satellites in orbit around the Earth. The invention makes it possible to detect as many events as possible with a short revisit time. The invention makes it possible to establish an accurate mapping with a quick revisit (a few hours at most), while using one or more antennas of limited size and low cost. The spectrum mapping can therefore be updated frequently, several times a day, every day, so as to be able to reliably identify any changes in use made by the operator. The invention makes it possible to create a mapping in the form of a power spectral density map as a function of pointing position and frequency, which allows the visualization and interpretation of the origin of the received radio frequency spectrum and its changes over time. In this way, celestial objects and changes in use (failures, acquisition of stations, changes in frequency plan) on the satellites can be detected. The invention can map the frequency spectrum usage as a function of orbital position (longitude or anomaly if the orbit is scanned) for all or part of the orbit under consideration, over one or more receive frequency subbands. The invention can be used to detect satellites in all types of orbits, thus including non-geostationary orbits.

[0010] The present invention allows for orbital tracking of detected satellites, thereby bypassing the operator's frequency usage declarations and allowing these objects to be tracked whether declared or not.

[0011] According to one embodiment of the present invention, the maximum aperture of the antenna is less than or equal to 4 meters.

[0012] According to one embodiment of the present invention, the maximum aperture of the antenna is less than or equal to 2.50 meters.

[0013] According to one embodiment of the present invention, the maximum aperture of the antenna is less than or equal to 2.10 meters.

[0014] According to one embodiment of the present invention, the step of reprocessing the raw power spectral density records comprises: deconvolving the radiation pattern of the antenna at frequencies within the receive frequency subband; calculating the deconvolution impulse response from the antenna radiation pattern pre-measured at the same frequency and pre-recorded in the memory of the computer.

[0015] According to one embodiment of the present invention, the deconvolution is performed on a linear combination of several successive raw power spectral densities for successive defined steering positions.

[0016] According to one embodiment of the invention, the method comprises the step of pointing the line of sight axis of the antenna according to a defined scanning trajectory passing through defined pointing positions at successive instants.

[0017] According to one embodiment of the present invention, the prescribed scan trajectory tracks each prescribed pointing position for a non-zero period of time.

[0018] According to one embodiment of the present invention, the prescribed scanning trajectory connects successive prescribed pointing positions at a constant velocity.

[0019] According to one embodiment of the present invention, the antenna controller discontinues movement of the line of sight axis when a prescribed pointing position is below a prescribed minimum elevation.

[0020] According to one embodiment of the present invention, successive prescribed pointing positions have the same orbital period.

[0021] According to one embodiment of the invention, the defined pointing positions of at least one of the sequences of defined pointing positions move on a predetermined trajectory.

[0022] According to one embodiment of the present invention, the predetermined orbit is the Clarke belt of geostationary satellites.

[0023] According to one embodiment of the present invention, the line of sight axes of successive prescribed pointing positions are spaced apart by an angle less than the width of the main radiation lobe of the antenna during the time interval in which the antenna moves from one prescribed pointing position to the next in the sequence.

[0024] According to one embodiment of the present invention, a computer reads the raw power spectral density at each defined pointing position from the digital signal.

[0025] According to one embodiment of the present invention, the recording of the raw power spectral density is performed by acquisition of a radio frequency signal collected by the antenna and digitized by the radio frequency chain according to discrete windows of predefined minimum duration.

[0026] According to one embodiment of the present invention, to measure the raw power spectral density record at each defined pointing position, a computer calculates the Fourier transform for each duration window of the digital signal, then squares the module and divides the whole by the duration of the window.

[0027] According to one embodiment of the present invention, the average scanning speed of the antenna relative to the tracking speed of the pointing position in the sequence is less than θ / D, where θ is the width of the main radiation lobe of the antenna.

[0028] According to one embodiment of the present invention, the method includes computing and recording, by the computer, a mapping consisting of a recording of refined power spectral density as a function of frequency and a defined pointing position.

[0029] According to one embodiment of the invention, an image is extracted from the mapping by a computer, in which refined power spectral density levels read consecutively at defined pointing positions in at least one receive frequency subband are arranged side by side, with orbit pointing position and frequency forming the horizontal and vertical axes of the image, as appropriate.

[0030] According to an embodiment of the present invention, each refined power spectral density level is represented by a pixel value, in particular a colour or luminance level or grey level.

[0031] According to one embodiment of the present invention, the computer searches for peaks in some or all of the raw or refined power spectral density vertical level curves to determine the most likely location of at least one emitter satellite in the reading spectrum.

[0032] According to one embodiment of the present invention, a computer compares the likely positions of the satellites and their associated power spectral density records with the operator's declarations.

[0033] According to one embodiment of the present invention, the computer transmits the likely positions of the associated satellites, and possibly all or part of their power spectral density records, to the orbital tracking system.

[0034] A second subject of the invention is a device for recording the radio frequency activity of at least one satellite emitting radio frequency signals, said device comprising: at least one receiving antenna directed along a line of sight axis and capable of collecting radio frequency signals, said antenna being in the form of a reflector the outer periphery of which defines a maximum aperture of not more than six meters; an antenna control unit for directing a line of sight axis of the antenna into at least one sequence of consecutive defined pointing positions which are distinct from one another; a radio frequency receiving and digital conversion chain for obtaining a radio frequency signal as a digital signal on at least one receiving frequency sub-band; a computer operable to calculate from the digital signal at least one record of power spectral density over a receive frequency subband and to reprocess the raw power spectral density record into a refined power spectral density record by applying a deconvolution process of the antenna radiation pattern in the receive frequency subband.

[0035] According to one embodiment of the invention, the driver is capable of directing the line of sight axis of the antenna according to a defined scanning trajectory passing through defined pointing positions at successive instants.

[0036] According to one embodiment of the present invention, the antenna is selected to be just large enough to be able to detect signals from satellites radiating at the equivalent isotropic radiated power threshold to be detected.

[0037] According to one embodiment of the present invention, the recording device for radio frequency activity includes a recording device capable of recording a mapping constituted by a recording of power spectral density as a function of frequency and a defined pointing position.

[0038] According to one embodiment of the present invention, the recording device is capable of recording a mapping history, i.e. multiple power spectral density recordings made on different days for the same defined pointing position.

[0039] According to one embodiment of the present invention, the computer and recorder are capable of constructing at least one difference image between mapping histories corresponding to different acquisition dates for the same sequence of defined pointing positions.

[0040] According to one embodiment of the present invention, the recording of the spectral density is performed by acquisition of radio frequency signals collected by the antenna and digitized by the radio frequency chain according to discrete windows of predefined minimum duration D.

[0041] According to one embodiment of the present invention, to measure the power spectral density of the signal at each defined pointing position, the calculator is configured to calculate the Fourier transform for each duration window of the digital signal, then square the modulus and divide the whole by the duration of the window.

[0042] A third subject of the invention is a computer program for implementing the method of recording the radio frequency activity of at least one satellite as described above, comprising code instructions for carrying out the steps of pointing, collecting, converting, calculating and reprocessing, when the computer program is executed on one or more computers. [Brief description of the drawings]

[0043] The invention will be better understood on reading the following description, given by way of non-limiting example only, with reference to the following figures in relation to the attached drawings, in which: [Figure 1] 1 is a schematic perspective view of an apparatus for recording radio frequency activity of an artificial satellite orbiting the Earth, according to one embodiment of the present invention; [Diagram 2] 1 is a modular schematic diagram of an apparatus for recording radio frequency activity of an artificial satellite orbiting the Earth, according to one embodiment of the present invention; [Diagram 3] 1 is a flow chart of a method for recording radio frequency activity of a satellite orbiting the Earth, according to one embodiment of the present invention. [Figure 4] FIG. 2 illustrates a first example of a power spectral density map image acquired during a first orbital scan by an apparatus, method, and computer program for recording radio frequency activity of a satellite according to an embodiment of the present invention; [Diagram 5] FIG. 10 illustrates a second example of a power spectral density map image acquired during a second orbital scan subsequent to the first orbital scan by an apparatus, method, and computer program for recording satellite radio frequency activity in accordance with an embodiment of the present invention; [Figure 6]FIG. 6 illustrates a power spectral density difference map image obtained from the first example map image of FIG. 4 and the second example map image of FIG. 5 by an apparatus, method, and computer program for recording satellite radio frequency activity according to an embodiment of the present invention. [Figure 7] FIG. 1 is a diagram illustrating frequency sections of a Diracs set representing a satellite ideally viewed as a point, scanned and acquired by an apparatus, method, and computer program for recording radio frequency activity of a satellite according to an embodiment of the present invention. [Figure 8] 2 is a diagram illustrating an example of an antenna radiation pattern of an apparatus, method, and computer program for recording radio frequency activity of a satellite, according to an embodiment of the present invention. [Figure 9] 2 is a diagram illustrating an example of power spectral density received by an antenna of an apparatus, method, and computer program for recording radio frequency activity of a satellite, according to an embodiment of the present invention. [Figure 10] FIG. 2 illustrates an example of a power spectral density map image obtained after deconvolution by an apparatus, method and computer program for recording radio frequency activity of a satellite according to an embodiment of the present invention. [Figure 11] FIG. 11 illustrates an example of a power spectral density map image obtained after deconvolution and peak detection according to FIG. 10 by an apparatus, method and computer program for recording radio frequency activity of a satellite according to an embodiment of the present invention. [Figure 12] FIG. 2 is a schematic representation of a geocentric reference frame in which parameters of a satellite can be defined; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] In FIG. 1, a recording device 1 according to the invention is located at one or more terrestrial orbital positions P around the Earth T. sThe recording device 1 can be used to detect the radio frequency activity of one or more satellites SAT1, SAT2, SAT3, SAT4 (or generally space objects or celestial bodies) located at . The recording device 1 is installed at a given geographical position Y on the surface ST of the Earth T. The satellites SAT1, SAT2, SAT3, SAT4 or space objects can emit electromagnetic signals towards the surface ST and towards the recording device 1. In Fig. 1, the orbits ORB of the satellites SAT1, SAT2, SAT3, SAT4 can be any orbit, for example a low Earth orbit LEO with an orbital period of less than 128 minutes, a geostationary orbit that appears fixed from the Earth T and therefore has an orbital period equal to one sidereal day, or a medium orbit MEO, i.e. an orbit intermediate between the two. The recording device 1 performs the following steps of the method for recording the radio frequency activity of one or more satellites according to the invention:

[0045] One or several stations may be provided, located on the surface ST of the Earth T, the station or each station comprising a recording device 1 according to the invention. The work of each station is for example planned centrally in the case of several stations, whereby the work of the stations is complementary.

[0046] In a non-limiting embodiment, all sub-bands W of all orbital positions and target frequencies of interest are x A number of antennas 2 and devices 1 according to the invention can be distributed at different points on the Earth T so as to cover

[0047] Main parts of the recording device The recording device 1 according to the invention comprises the elements described in more detail below: Antenna 2, Radio frequency receiving and digital conversion chain 20; ·Calculator 3, a device 4 for directing the antenna 2, · Device for recording mapping 5.

[0048] Steps for tracking method In a preferred embodiment, the steps of the recording method according to the invention follow the following description. These steps describe various operations that contribute to the invention. These steps are actually performed non-sequentially, i.e. several steps are performed simultaneously. One or more of these steps can be omitted or implemented according to alternatives, see FIG. 3.

[0049] -Step E0: Configuration of device 1 The user of the recording system must plan the scans and signal acquisitions to be performed. To do this, he configures the device 1 for recording the mapping. The user first configures certain characteristics of the station, which serve to carry out the following steps: In step E1 of orienting the antenna, the geographical position O of antenna 2 (longitude and latitude), - minimum pointing elevation angle El0 of antenna 2, ·Maximum pointing speed, Main lobe width θ, one or more tracks, or more generally a sequence of successive track positions, to be scanned in each recording, · The normal or individual scanning modes to be implemented are configured.

[0050] In a step E2 of acquiring a signal, The radio frequency chain 20, in particular the drive of the instrument gain, Subband W read from the spectrum x , the frequency plan of the converter is configured.

[0051] In step E3 of recording the power spectral density, - expected frequency resolution, · Averaging to be implemented is configured.

[0052] In step E4 of constructing the mapping, A data structure is constructed to be recorded that covers all orbital positions to be examined.

[0053] In visualization step E5, User-modifiable visualization parameters are configured.

[0054] In the optional step E6, to reprocess the mapping, The radiation pattern of antenna 2 when performing the deconvolution operation is constructed. The radiation pattern may be measured in advance.

[0055] In optional step E7, which starts the trajectory tracing, The format and destination of the data to be provided to the tracking system is configured.

[0056] - Step E1: Positioning / pointing The recording device 1 is located at its track position P s The antenna 2 includes a control unit 4, called ACU, for pointing the satellite to an elevation angle higher than the minimum elevation angle El0 defined in the configuration step E0. The ACU 4, which includes a computer, controls the motors of the positioning device of the antenna 2 so that its line of sight 21 points to a pointing position, for example as described below. The ACU 4 of a state-of-the-art station in communication with the satellite SAT in this pointing position determines the position S(P s , t) as a function of time t, and then the angle β[OS(P s ,t)], which for simplicity is s ,t), where O is the geographical position of the station. By convention, the angle of the line of sight 21 is determined by the azimuth and elevation angles of the straight line OS(t) relative to the horizontal plane and to the geographical north. The ACU 4 must also first convert the geographical position O of the station into a position in a geocentric reference frame given the orbital parameters of the satellite. For this purpose, it is therefore necessary to take into account the rotation of the Earth on its axis and its rotation around the Sun.

[0057] Within the framework of classical mechanics and gravity due to a single orbiting star, the orbits obey Kepler's laws. In a geocentric reference system, located at the center of the Earth and with its axis pointing to the star, as shown in Figure 12, each orbital ORB is an ellipse inscribed in an orbital plane, one of whose foci is the center of the Earth. The orbital position of a satellite is completely determined by six parameters. In the most common standardized description, such as TLE (two line elements), the orbital plane is defined by two parameters: the inclination i relative to the reference plane PREF and the ascending node. The orientation of the ellipse in the orbital plane is defined by the angle of its perigee (the point where the orbital ORB is closest to the Earth), where the eccentricity indicates the flattening of the ellipse and therefore the ratio between the major and minor axes. The size of the semimajor axis a of the ellipse and the orbital period P r are related by Kepler's third law :P r 2 / a 3 =4π 2 / GM (where M is the mass of the Earth and G is the gravitational constant). Thus, the fifth parameter can be either the orbital period or the semimajor axis. By convention, in the following, the orbit ORB is defined as the orbital period P r The TLE actually gives the mean motion, not the orbital period, which corresponds to and is equivalent to the number of (fractional) rotations per day.

[0058] These first five parameters allow us to unambiguously determine the ellipse in space, or the path that the satellite follows, called the orbit. The last parameter that describes the orbital position is the anomaly, which allows us to know the angular position of the satellite on the ellipse at any time. The anomaly can be defined in several ways, such as the true anomaly ν, the eccentricity anomaly, or the mean anomaly, but the choice is not important to the present invention.

[0059] A satellite's orbital position drifts slowly due to the effects of Earth's gravity, lunar and solar tides, general relativity, and solar wind variations. These effects can become noticeable over a period of days. In most cases, satellites are assigned to an orbital position and steered to stay there. Some satellites are designed to change their orbital position (space surveillance, on-orbit servicing). The present invention allows all these movements to be identified.

[0060] In the present invention, the plan programmed in step E0 is to move the line of sight 21 of the antenna 2 through a sequence of successive defined pointing positions P i These positions are, for example, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10 in FIG. 1, where i varies, for example, from 1 to 10. There may be a defined pitch between successive pointing positions. The defined pointing positions may be, for example, defined orbital positions P1, P2, P3, P4, P5, P6, P7, P8, P9, P10. The index i may successively take values ​​ranging from 1 to N, where N is any integer number of pointing positions. During the scan, the positions P i is in fact the moment t that constitutes an increasing sequence of dates. i These prescribed pointing positions P i are spatial locations of interest where the satellites SAT1, SAT2, SAT3, SAT4 may be located, from which the radio signals emitted are collected and their power spectral density is measured. The antenna control unit which drives the antenna 2 according to the invention determines the orbital position P s The ACU performs the same line of sight axis 21 calculation operation as an ACU tracking a satellite, but repeats this operation by obtaining the next pointing position in the sequence each time while the ACU in tracking mode maintains the same orbital position.

[0061] The line of sight axis 21 necessarily needs to evolve continuously, and the ACU must determine the time from moment t to create a continuous scanning curve B(t). i and i+1Two scanning modes are possible. The first mode, called the discrete scanning mode, tracks a fixed pointing position and then connects to the next pointing position as quickly as possible, given the maximum speed at which the positioner can move. In this case, the pointing position is t i In P i Stop at the top, stay there for a certain amount of time, then jump to the top as quickly as possible. i+1 The second mode, called the normal scanning mode, gradually changes the characteristics from one pointing position to the next. In this case, each pointing parameter is i and i+1 Between the directional position P i From the parameter value of P i+1 By construction, in the two scanning modes, at each instant t i For B(ti)=β[OS(P i ,t i )]=b(P i ,t i )

[0062] The ACU 4 must check at each instant that the elevation of the line of sight axis 21 remains greater than the minimum value El0 defined in the configuration step E0. For each pointing position, the ACU must determine whether the minimum elevation is respected. If during the scan, a pointing position causes the elevation of the line of sight axis 21 to be lower than the minimum elevation El0, the ACU ignores the pointing position and moves directly to the next pointing position. In each sequence, the scanning curve B(t) crosses a circular arc section, the development angle of which is denoted by α. Thus, as long as a part of this arc is at an elevation lower than the minimum elevation, this arc will be smaller than the arc planned for the scan in step E0. Once the ACU has completed the entire scan of each sequence, it can start again from the beginning. The time that has elapsed until all the planned scanning sequences have been completed is called the revisit time R.

[0063] In the most general embodiment, a defined pointing position P ican be arranged in any order, but to optimize the revisit time R, the curve B(t) should be arranged so that it shows the shortest possible deployment angle α, i.e., B(t) is aligned with the pointing position P i It is advantageous to define the sequence so that it is the shortest path connecting the points. If the sequences have pointing positions with different orbital periods, the optimal solution will be significantly different for each sequence, since the orbital positions will have evolved independently. Also, in a preferred embodiment, the pointing positions of a sequence are all chosen to point to the same orbital period, which ensures that the relative distances change very little from scan to scan, and allows a suboptimal sequence to be defined in one go.

[0064] In a particular embodiment, a quasi-circular orbit is scanned, i.e. an orbit with an eccentricity of approximately zero associated with the majority of satellites. The best known circular orbit is the geostationary orbit. In this case, the orbital position is in the equatorial plane and fixed with respect to a stationary observer on the Earth's surface. The maximum possible arc section α is the measurement from the eastern to western extremities of the geostationary arc at the minimum elevation angle El0. If the sequence only scans the geostationary arc, the revisit time R defined above is the elapsed time between two successive measurements of the same pointing or orbital position. If a LEO orbit is scanned, this revisit time does not have to be an integer multiple of the revolution period of the orbit considered, thus separating measurements that can be performed on different anomalies.

[0065] Figure 4 onwards has been carried out taking into account the scanning of a geostationary arc. In this case the scanned pointing position elements are the longitudes that correspond specifically to anomalies on the geostationary arc. In the case of a more general scanning of any orbit the longitudes must be replaced by the anomalies, but this does not change the scope of the figures.

[0066] Another special case is scanning the position of a constellation of satellites. In general, a constellation consists of a small number of orbital periods (1 for GPS, Galileo, O3B, OneWeb, Iridium Next, 3 for the KuiPer project and Starlink Phase 2, 4 for Starlink Phase 1). Each of these periods P r(corresponding to altitude), the constellation arranges a number of satellites in a circular orbit and in a series of orbital planes, all equally spaced with the same inclination angle; that is, their ascending nodes are multiples of 360 / p°, with p different orbital planes. Here, the planned scan may consist of changing both the anomaly and the ascending node. For example, in the case of a strongly inclined constellation, the planned scan may be required to scan the orbital positions corresponding to the positions of each orbit closest to the polar axis, while traversing successive planes, i.e. by gradually changing the ascending node in an increasing or decreasing direction. The resulting scan forms a circle around the polar axis, with small angular displacements to traverse the considered altitude of the constellation. If the antenna position is close enough to the pole, the line of sight axis 21 of this scan always has a significant elevation angle, and the sequence can be maintained indefinitely.

[0067] Step E2: Signal collection, acquisition and recording In Fig. 2, a recording device 1 according to the invention comprises one (or several) receiving antennas 2 oriented along a line of sight axis 21. The antennas 2 oriented above El0 collect a radio frequency signal X(t) that is a function of time.

[0068] The device 1 comprises a radio frequency reception and digital conversion chain 20 of a radio frequency signal X(t), which obtains the radio frequency signal X(t) in the form of digital samples X(n).

[0069] An example of a receive chain 20 downstream of an antenna 2 in a station is described below with reference to figure 2. The station incorporates a radio frequency chain 20 between the antenna 2 and a computer 3. In step E2, the radio frequency signal X(t) output by the antenna 2 is digitized at the end of the radio frequency receive chain 20. Conventionally, this receive chain 20 consists of a microwave filter to select the useful band, a low noise amplifier (LNA) to lower the frequency and enhance the signal to sufficient power, followed by a downconverter which brings the band of interest into an intermediate band where the signal is finally sampled at the sampling frequency f eThe signal is then sampled and digitized by an analog-to-digital converter (ADC) operating at n / f e Instead of this single channel diagram shown in FIG. 2, the pre-amplified signal can be split into multiple channels of index x, each of which has an acquisition chain of subbands W x Then, for each channel there is a frequency converter and a digitizer, which allows the instantaneous bandwidth to be processed to be increased. Otherwise, there is only one digitizer, and at its input each subband W x , but this cheaper architecture comes at the expense of increasing the time required to perform the acquisition.

[0070] The digitized signal X(n) is then recorded. The recording of the raw signal can be kept for as long as required, depending on the memory capacity 51.

[0071] In practice, the antenna 2 can generally be in the form of a parabolic reflector 22 whose outer edge 23 delimits an aperture diameter 24. Of course, the antenna can also be in the form of a reflector of a shape other than parabolic. The antenna 2 is not a perfect antenna with an infinitely thin beam. It also collects not only the signal obtained from the line of sight axis 21, but also a number of contributions from different directions weighted according to the radiation pattern at the frequency of interest. The radiation pattern at frequency f, as shown for example in FIG. 8, exhibits a main lobe of width θ, concentrating the maximum power contribution around the antenna axis aligned with the line of sight axis 21. The side lobes collect weaker signals coming from directions further away from the line of sight axis 21. For a satellite S radiating an EIRP (equivalent isotropically radiated power) Pe from a direction of angle γ, determined by the azimuth and elevation angles, the power received by an antenna directed to the line of sight β (also determined by the azimuth and elevation angles) is given by P r = Pl.Pe.D(γ-β,f), where Pl is the free space loss (λ / 4πd) 2where λ is the wavelength and d is the distance from the satellite, where the subtraction of angles is to be understood in the sense of the synthesis of rotations, and -β represents the rotation opposite to that which allows pointing the line of sight axis β.

[0072] The pattern D(γ,f) is a function of frequency and of the depointing angle γ (angular deviation with respect to the line of sight axis 21, as shown by way of example in FIG. 8) that provides the power gain of the antenna. It is maximum for zero depointing. In principle, antennas, for example of parabolic shape, are rotationally symmetric. The main lobe is therefore also rotationally symmetric and its width θ does not depend on the depointing orientation. A width θ of the main lobe at 3 dB or a width θ of the main lobe at y dB where y is other than 3 is specified. Since the width of the lobe is twice the allowable depointing, y dB of gain is lost. For y = 3 dB, this corresponds to a loss of half the maximum gain of the line of sight axis 21.

[0073] In one embodiment, the successive defined pointing positions are isolated positions of interest. In another preferred embodiment, the objective of the scan is to collect in the process signals obtained from all intermediate positions between two successive pointing positions defined in the sequence, to detect possible active satellites present there. To fulfill this, these positions must be collected in the main lobe of the previous or next pointing position, as appropriate. More specifically, each intermediate position must be located within a cone of lobe width θ around the previous or next pointing position, which guarantees a certain quality of collection of signals that may originate from it. As a result, in this preferred embodiment of the invention, two successive pointing positions for which the spectral density is measured must correspond to tracking orbits that are offset by a value of the line of sight axis 21 that is smaller than the width θ of the main lobe, which occurs in the time interval of switching from one to the other. This condition is reflected by the following inequality: |b(P i+1 ,t i )-b(P i, t i )|<θ ydB et / ou|b(Pi+1 ,t i+1 )-b(P i ,t i+1 )|<θ ydB Here, when y is selected equal to 1 or 2 dB, the antenna lobe considered is narrow and the signals collected at each intermediate pointing position are hardly distorted, whereas when y is equal to 3 or 4 dB, the antenna lobe is wide but the signals collected at the intermediate pointing positions are highly distorted.

[0074] - Step E3: Recording of power spectral density During a step E3, the recording device 1 records, from the samples X(n) of the digitized signal acquired in a window around a date t (hereinafter the terms date t and instant are synonymous), a frequency sub-band W x The raw power spectral density DSb(P s ,t,f) on date t=t i A series of consecutive prescribed pointing positions P i (t i ) for each directional position across the directional line. The number of calculators 3 and their central processing units (CPUs) is adjusted according to the computing power. The calculator 3 can be implemented by one (or more) processors, and / or one (or more) microprocessors, and / or one (or more) central processing units, and / or one (or more) computers, and / or the like.

[0075] The device, which is made up of a downconverter, a sampler of the radio frequency chain 20, and a computer 3, calculates each subband W x The advantage of the architecture of Fig. 2 compared to a spectrum analyzer is that it allows the acquisition and exhaustive recording of the power spectral density and is faster to execute. In fact, it avoids the dead time between the windows used to calculate the power spectral density. Thus, the same processing operations in a spectrum analyzer would result in a longer revisit time R.

[0076] Radio frequency activity is evident in the spectral content of the collected signal, which is higher than the background noise level. The recording of radio frequency activity is therefore performed by measuring the power spectral density of the signal at each defined pointing position. To do so, it is necessary to select a window F of the signal's duration, calculate its Fourier transform, then square its module and divide the whole by the duration of the window. This gives a raw estimate of the power spectral density with a frequency resolution of 1 / F and a large noise-related level fluctuation. To limit this effect, two possible methods can be used to average the power spectral density: the first is to average q adjacent frequencies, the second is to average q consecutive measurements to process a signal period D=qF. In analog spectrum analyzers, this is called video filtering or averaging, respectively. In both cases, the effective resolution is reduced by a factor q compared to what the raw Fourier transform allows over the same signal acquisition period D. Thus, a frequency resolution df with averaging of depth q requires an acquisition period also called exposure time D=q / df.

[0077] According to one embodiment of the present invention, the computer 3 calculates the digitized signal X(n) at each position P i D i We start by dividing the image into windows of,M,. i samples, and therefore period D i =M i / f e Typically, when the scan is discrete, the window D i is the moment i and before the ACU tracks the next pointing position, i.e., t i+1 If the scan is regular, it will stop before window D i is the moment i Therefore, the spectral density calculated in step i is centered on the pointing position P i Therefore, each raw spectral density measurement before reprocessing corresponds to a set of radio frequency signals X(t) centered on subband Wx The frequency f and the continuous directional position P i In the description of step E2, it was seen that antenna 2 collects signals coming from a cone of width θ around the line of sight axis. This therefore means that θ constitutes the spatial resolution of the spectral density measurement.

[0078] Moment i and i+1 Between, the average pointing speed is defined as the change in angle of line of sight divided by the time interval. This is decomposed into relative scanning and tracking speeds according to the following formula: [b(P i+1 ,t i+1 )-b(P i ,t i )] / (t i+1 -t i )=V p (t i+1 )=[b(P i+1 ,t i+1 )]-b(P i ,t i+1 )] / (t i+1 -t i )+[b(P i ,t i+1 )-b(P i ,t i )] / (t i+1 -t i )=V s (t i+1 )+V t (t i+1 ).

[0079] To select a minimum acquisition period D to guarantee the quality of the measured spectral density, i.e. its frequency resolution and noise variation, the pointing positions must track each other at moments spaced at least by the exposure time: t i+1 -t i >D i As a result, in preferred embodiments where the line of sight of successive pointing positions is less than the lobe width θ, the average pointing velocity V p and the tracking speed of the current pointing position V t The relative scanning velocity V is the difference between s must be kept below θ / D.

[0080] The maximum scan speed is determined by the exposure time and the side lobe width. If the pointing position is simply tracked, this scan speed is nominally zero. The decomposition of the pointing speed into the tracking speed and the scanning speed applies to the apparent speed, which is an average, regardless of the scanning mode. This is valid whether running in discrete or normal mode. In the specific case of scanning the Clark Belt, since the orbital position is fixed from the geographical position O of the station, the tracking speed is zero and the pointing speed is equal to the scanning speed and must therefore be kept less than θ / D.

[0081] The tracking speed is dictated by the celestial mechanics of the selected orbital position. It depends heavily on the orbital period of the orbital position within the scan. On the other hand, the scanning speed is limited by θ / D. Once the expected quality of the power spectral density measurement, and hence the exposure time D, is chosen, the scanning speed is proportional to the lobe width θ. Thus, by maximizing the lobe width, we maximize the scanning speed, and therefore the pointing speed, and thus minimize the revisit time R, regardless of the sequence of pointing positions planned in step E0.

[0082] Based on this finding, the present invention proposes that in a preferred embodiment, the maximum aperture diameter 24 of the antenna 2 is equal to or less than 6 meters. For example, the maximum aperture diameter may be equal to or greater than 1 meter and equal to or less than 6 meters.

[0083] The antenna 2 has a maximum aperture 24, which is less than or equal to 4 meters, and is adapted to receive at least the reception frequency sub-band W x For example, the maximum aperture of the antenna 2 may be greater than or equal to 1 meter and less than or equal to 4 meters, and the antenna may be provided for at least the receiving frequency subband W x =Ku or other.

[0084] The antenna 2 has a maximum aperture 24, which is less than 6 meters, and is adapted to receive at least the reception frequency sub-band W xFor example, the maximum aperture of the antenna 2 may be greater than or equal to 1.5 meters and less than or equal to 6 meters, and the antenna may be provided for at least the receiving frequency subband W x =C or other.

[0085] Thus, the present invention provides an antenna size large enough to reliably identify signals at the minimum density threshold of the EIRP (equivalent isotropically radiated power) of the object being sought. The antenna 2 is selected to be large enough to be able to detect signals from satellites radiating at the equivalent isotropically radiated power threshold being read.

[0086] For example, the antenna 2 may have a maximum aperture diameter 24 that is equal to or smaller than 2.50 meters (2 meters 50 centimeters) and may receive a reception frequency sub-band W x For example, the maximum aperture 24 may be greater than or equal to 1.50 meters (1 meter 50 centimeters) and less than or equal to 2.50 meters, and the reception frequency subband W x = Ku and / or C or others may be provided.

[0087] For example, the antenna 2 may have a maximum aperture diameter 24 of 2.10 meters (2 meters 10 centimeters) or less and may receive a reception frequency sub-band W x = Ku and / or C or other. For example, the maximum aperture 24 may be greater than or equal to 1.90 meters (1 meter 90 centimeters) and less than or equal to 2.10 meters, and the receiving frequency sub-band W x = Ku and / or C or other. This allows the reception frequency subband W x = Ku and / or C or in other cases, it becomes possible to employ an antenna 2 with a diameter of, for example, around 2 meters. These choices allow the shortest possible revisit times R.

[0088] The above-mentioned maximum aperture 24 of the antenna 2 is particularly advantageous in combination with the recording of the refined power spectral density DSa calculated in step E6 described below, since this combination allows the detection of more satellites with shorter revisit times and lower costs.

[0089] -Step E4: Building the mapping Mapping C is the directional position P i and one or more directional positions P i For each of them, the power spectral density DSP could be recorded as a function of frequency f for measurements made on date t. This means that in each recording sequence, for i ranging from 1 to N, consecutively defined steering positions P i The frequency f corresponds to one of the reception frequency subbands W x , where C is the frequency of one of the subbands. Although the recording can be transmitted directly for visualization or for use in another system, in a preferred embodiment the mapping C is recorded.

[0090] To do this, according to one embodiment, the recording device 1 detects whether the antenna 2 is in a pointing position P i The read power spectral density DSP(P s , f,t) to date t. The recording device 5 may include one or more permanent memories 51 etc. for recording the mapping C, and / or one or more display screens 52 for displaying an image I of the mapping C, and / or one or more physical outputs 53 for providing the mapping C or an image I thereof, and / or one or more modules 54 for processing the mapping C.

[0091] In one embodiment, the read power spectral density DSP(P s ,f,t) is the raw power spectral density DSb(P s, t, f). In an alternative embodiment described below in step E6, the read power spectral density DSP(P s ,t,f) is the raw power spectral density DSb(P s , t, f) are calculated by computer 3 through reprocessing.

[0092] Each directional position P of mapping C i Depending on the need and available memory capacity 51, the last spectral density record DSP can be kept or the depth history can be kept. i The organization of the storage in the memory 51 of the predetermined orbital positions P i In the case of a system with multiple antennas 2, the mappings established by each antenna are grouped together and, in step E0, each antenna is assigned to a different orbit or part of an orbit, or more generally to a separate defined pointing position P i Considering the main lobe of the antenna, the pointing position P i The DSP of actually incorporates the spectral components collected within a cone of lobe width θ around the line of sight axis 21 at date t. Thus, the signal is generated at a prescribed pointing position P i The signals are collected from a position in the area near the specified pointing position P i A satellite with an orbital period equal to θ will remain in the vicinity, but with a slightly different orbital period P s For example, in the specific case of scanning a circular orbit, the mapping C incorporates satellites in the same plane that have close quasi-circular orbits but the same orbital period, and these satellites are aligned to a prescribed pointing position P that is perfectly circular. i It can be seen that the orbital period of the orbital sphere oscillates in time around the orbital period θ. Satellites in the same plane with slightly lower or higher orbital periods, while in perfectly circular orbits, appear to have linearly increasing or decreasing anomalies.

[0093] -Step E5: Visualization, HMI Thus, the mapping C can be graphically represented in an easy-to-interpret image for slowly changing objects with little change in relative position. The image I constructed to represent the mapping C is thus formed as a function of the power spectral density DSP of the last recording, or a previous recording specified by the user, and is expressed as a two-dimensional variable (frequency and pointing position P i The directional position P of a given mapping is determined according to the variation parameters i This corresponds to:

[0094] In one embodiment described below with reference to Figs. 4 and 5, an image I of a mapping C is shown with a horizontal axis showing successively defined pointing positions P i Thus, the directional positions are arranged in the chronological order of each recording, and the vertical axis represents frequency f. i , it is also possible to place the frequency on the horizontal axis and invert the axis. In the particular case where the scanning of the orbit is planned by changing only one anomaly, successive pointing positions P i corresponds to increasing or decreasing anomalies on this orbit.

[0095] In another embodiment, the pointing position P i The variation parameters of are synthetically reconstructed from a mapping C that contains records of the power spectral density DSP of a number of orbits with the same orbital period. For example, in the case of the constellation shown above, the pointing position P i Since there is an anomaly in the ascending node, the prescribed sequence P i Even if the are acquired in a different order, the pointing position P i It is possible to reconstruct an image I whose variation parameter is the ascending node.

[0096] The pixel values ​​of each ordinate and each abscissa of the image I represent the level A of the read power spectral density DSP measured at frequency f during the scan B(t). The spectral density DSP is thus arranged vertically in the image I, with the spectrum arranged per abscissa of the image I. The level A of each read power spectral density DSP is typically represented by a color according to a decrease in wavelength from blue to red, or by a brightness level or gray level that varies clearly according to the level A, for example in a monotonic, increasing or decreasing manner. For example, the level A is represented in dBm in Figs. 4 and 5.

[0097] Instead of an image where the pixel values ​​represent a DSP function, i It is also possible to perform a projection of the surface of a curve of level A, which is a function of . In this case, level A is represented along a third lateral axis perpendicular to the horizontal and vertical axes, providing a three-dimensional surface, which is then projected into two dimensions. An isometric projection of the surface can be performed on a grid, according to a series of section lines arranged at an offset. It is also possible to compose an image by visualizing the cutting planes moving forward or backward, but it is not possible to represent everything in one image. Other image composition techniques exist in the state of the art and are applicable.

[0098] The presence of an active satellite becomes evident as the value of level A is well above the background sky noise level. The formation of image I therefore constitutes a preferred embodiment for representing the mapping, since it allows easy visualization of the use of the radio frequency spectrum by artificial celestial objects. Typically, as the construction of an image is a very quick process, it is not necessary to record the results, but in a preferred embodiment a history of the last displayed images I is recorded.

[0099] - Step E6: Optional processing operations for the mapping The use and processing of the mappings for the purposes of identifying satellites can be performed by a human operator, but can also be largely automated. These optional processing operations of the raw mappings DSb can be performed by one or more mapping processing modules 54 of Figure 2, or by the same computer 3. These processing operations can include comparison of the positions and frequency plans with the operator's declarations, and difference processing between successive mappings to identify changes (see below).

[0100] Transmission to a tracking system can be provided to refine the exact orbital position of each spectral portion and thus separate coexisting objects, i.e. objects whose orbital positions are close enough to be captured in the main lobe of a single spectral measurement.

[0101] Sequential Mapping and Differential Processing In one embodiment, referred to as the continuous mapping embodiment and described below with reference to FIGS. 1-6, the antenna 2, computer 3, drive unit 4 and recorder 5 record a mapping history C1, C2 (or more) and then calculate a defined pointing position P i (t i ) several images I1, I2 can be deduced for two scans of the same sequence. The image I2 extracted from the mapping C2 is made with a successive acquisition time interval of, for example, hours or days, as shown in figures 4 and 5, compared to the acquisition time interval of the image I1 extracted from the mapping C1. In principle, successive acquisitions are spaced by a revisit time R by default, when all the scan sequences are visible above a minimum elevation from the geographical position O of the station. Accumulating the acquisitions obtained from successive cycles at the same position allows averaging out the effects of noise beyond the averaging depth.

[0102] According to an improvement of this embodiment, referred to as the differential mapping improvement embodiment, which will be described below with reference to FIG. 6, the antenna 2, the computer 3 and the actuator 4 are all aligned to the same defined pointing position P iAt least one difference mapping CD between two different historical records C1, C2 of mappings in the 3D space can be calculated. A difference image ID shown in FIG. 6 and equal to the image I2 of FIG. 5 is obtained from the image I1 of FIG. 4 at the same abscissa and ordinate, i.e. at the same frequency and pointing position P i The power level A at each pixel is subtracted by subtracting the pixel values ​​from each other. This difference processing of successive mappings C1, C2 allows to reliably detect spectrum use change events (acquisition or decommissioning of stations, changes in frequency plan, changes in location, etc.) for a period longer than the revisit time R. For example, image I1 in FIG. 4 was created on April 1, 2021, and image I2 in FIG. 5 was created on April 5, 2021. The difference image ID in FIG. 6 shows the appearance and disappearance ID1, ID2, ID3 of lines of power spectral density DSP (which allows the frequency f to be determined) of a satellite at position P6 and the appearance and disappearance ID4 of a spectral line (which allows the frequency f to be determined) of a satellite at position P8.

[0103] Peak identification and approximation by operator declaration In one embodiment, the calculator 3 and the recorder 5 are configured to identify the spatial lines of the power spectral density DSP by a peak detection, i.e. local maximum detection algorithm. The peaks at level A can be used to summarise the content of the vertical curve of level A of the power spectral density shown in FIG.

[0104] The peak at a frequency f is the best estimate of the location of the satellite emitting a signal at that frequency f. We can approximate these results using operator-provided declarations to name discovered satellites and indicate undeclared satellites.

[0105] Deconvolution In one embodiment, referred to as the spectral density recombination embodiment, the computer 3 and the recording device 5 apply a deconvolution process aimed at reducing the effects induced by the radiation pattern of the antenna 2 to obtain the raw power spectral density DSb(P i ,t iThe mapping can be reprocessed by converting the raw power spectral density DSb(P i ,t i , f) to obtain the refined power spectral density DSA or DSa(P i ,t i ,f) at the moment t i +k's pointing position P i The raw power spectral density DSb(P i+k ,t i+k ,f), where k ranges from -m to -m.

[0106] In step E2, it was found that an antenna oriented along the axis 21 of the line of sight β collects signals from satellites S emitting from a direction of angle γ according to a received power proportional to Pe.D(γ-β,f), where Pe is the EIRP of the satellites and D is the pattern of the antenna 2 of the station. According to this formula, the antenna pattern has the effect of spreading the satellite contribution over the entire width of the main lobe θ and forming an artifactual response at the position of the side lobes. For a group of satellites S whose EIRP is Pj (j varies from 1 to P), j When approaching each satellite S j The power received is the sum of the contributions of DSb(β,f) = ΣPj.D(γ j -β,f). In the mathematical sense of distribution, the spectrum of a signal obtained from the sky at frequency f is expressed as a function of the line of sight γ j and its amplitude is EIRP P j The distribution P=ΣPj.δ(γ-γ j) (where δ is the Kronecker symbol for Dirac at position 0, shown in Figure 7) is the perfect mapping we are trying to measure, the mapping we would get with an antenna with an infinitely thin main lobe and infinitely low side lobes. Figure 7 shows an example of such a distribution P(β,f), constructed from a Dirac representing the satellite observed by antenna 2 scanning a geostationary arc, with the horizontal axis at angular position β=γ j (expressed in equivalent degrees), and the vertical axis is the power in dBm. The power received by antenna 2 at frequency f is proportional to the integral:

number

[0107] The convolution of the above equation is the satellite's line of sight angle and the pointing position P iThe convolution, which is two-dimensional in nature, like the line of sight angle, can be compared to a one-dimensional convolution performed along the scanning curve B(t), if all satellites acquired during the scan can be considered to be on the scanning curve B(t). This is because the subbands W considered x This is considered to be the case in the case of a single orbit scan by varying the only anomaly, when the satellites collecting the signals are necessarily in this same orbit to comply with the ITU international regulations preventing interference. In this case, the impulse response of another one-dimensional convolution, called deconvolution, is determined, which in a sense makes it possible to neutralize the effect of the convolution by the antenna pattern. That is, the combination of the two convolutions approximates the convolution by Dirac, providing a finer main lobe and significantly reduced side lobes.

[0108] When the scanned orbit is a geostationary arc (Clark belt), the pointing position P i Since the line of sight angle γ of the antenna 2 is fixed, there is a one-to-one relationship between the two. The instant t when antenna 2 collects on line of sight axis β is not important. The impulse D(γ-β) as a function of the variable γ moves (translates) as the antenna line of sight angle β changes, but is barely distorted. The deconvolution therefore gives good results, as shown in Figure 10. If the scanned orbit is outside the Clarke belt, it moves in the sky as a function of the Earth's rotation and the pointing position P i is the orbital period P r Therefore, before proceeding with the deconvolution, we first calculate the line of sight angle β(P s , t) are calculated by dividing the DSb measurement values ​​by the corresponding pointing position P i is the gaze angle on a single reference date t0, that is, β(P s ,t0) by the time series t0 (t0,t1,t2). However, this correction introduces some distortions to the record, which is the complete result of an instantaneous one-dimensional convolution between the distribution of satellites along the scanning curve B(t) and the antenna pattern. The deconvolution is performed because high orbits are scanned and therefore the period P r The lower it is, the more efficient it will be.

[0109] In one embodiment, which will be described below with reference to FIGS. 3 and 7 to 10 and which is referred to as the inverse spatial convolution embodiment, which is a submode of the recombination of the spectral densities, the calculator 3 calculates during step E6 the subbands W x The refined power spectral density DSa(β,f) can be calculated by deconvolution of the raw power spectral density DSb(β,f) of the signal received by antenna 2 at frequency f in β, the deconvolution being performed according to the line of sight angle β variable. The impulse response of the deconvolution is calculated during step E0 of the method from the radiation pattern D(β,f) of antenna 2 previously measured at the same frequency f and recorded in tabular form in the memory 51 of the calculator 3.

[0110] In practice, the improvement in the response due to this deconvolution operation is remarkable, the side lobe artifacts disappear and the width of the main lobe is reduced by almost half. In Fig. 10, it can be seen that the artifacts that in Fig. 4 and Fig. 5 spread the orbital position response by more than 4° are clearly reduced to less than 1°. Thus, by correcting the imperfections introduced by the antenna radiation pattern, the spatial discrimination is improved. This significantly reduces the rate of false alarms and the rate of object non-detection. If the search for peaks is applied to the refined power spectral density DSa instead of the raw power spectral density DSb, its contribution can be significantly improved. The result is shown in Fig. 11, where the detected positions are on the horizontal axis and the satellites emitting signals at the frequencies indicated on the vertical axis are shown as dots. A slight deviation in the longitude of the geo arcs makes it possible to identify satellites that are indeed different but at the same position, which were not detected in Fig. 4 or Fig. 5.

[0111] - Step E7 (optional): Tracking The mapping C can be reprocessed by tracking, which allows for improved spatial resolution. By calculating the correlation of signals received by antennas spaced apart from each other, orbital tracking systems allow for very accurate resolution of the orbit, which approximates full Dirac resolution, with an accuracy of the order of 150 meters possible in geostationary orbit.

[0112] Once the spectral lines have been identified in the mapping C by the device 1 according to the invention, the individual characteristics of these spectral lines can be transmitted to the known orbital tracking system, which can carry out a new remote acquisition, so that all the celestial objects can be separated by a processing operation based on correlation. These objects can then be tracked individually using techniques that require more computing power or acquisition time, in particular by correlation of the remote acquisitions used in the known orbital tracking system. Thus, the pointing position P i The spatial separation of the objects detected at can be performed by a trajectory tracking system. The technique for determining the trajectory by a trajectory tracking system is to determine the trajectory from a given pointing position P i The object detected at this directional position P i The orbital tracking system can be used to separate the remote acquisitions made only with tracked orbital positions, thereby minimizing the duration of the orbit determination process. Known orbital tracking systems only perform correlation of remote acquisitions made only with tracked orbital positions.

[0113] The orbital tracking system and the radio frequency activity recording device of the invention can use the same antenna 2 or share the same antenna farm. In fact, the constraint of a sufficient signal-to-noise ratio to detect the signals obtained from the satellites is the same for these two systems. The mapping established by the system recording the radio frequency activity provides a spatial resolution which, once refined by one or more methods of step E6, makes it possible to place the radiation in a cone of a width less than the main lobe width of the antenna. Thus, tracking is real-time and the orbital tracking system, unlike the radio frequency activity recording system, can determine this pointing position P from a remote site without the need to perform scanning. i Therefore, acquisition by the tracking system is time-optimized. Finally, mapping advantageously replaces the use of operator declarations.

[0114] The combination of the two systems, according to one embodiment of the present invention, argues for the choice of a small antenna 2. Thanks to reprocessing by the orbital tracking system, the device is cheaper, faster and ultimately more accurate than a single antenna.

[0115] Of course, the above embodiments, features, possibilities and examples can be combined with each other or selected independently of each other.

[0116] Thus, the invention allows the monitoring of space by observing the use of the radio frequency spectrum and makes it possible to map the spectrum situation in space. The method and the recording device 1 according to the invention allow the detection of any active radiating object orbiting the Earth without using external information from the operator. The invention makes it possible to track the activity of satellites, whether they are LEO, MEO or geostationary satellites. The invention makes it possible to determine the life cycle of a space object, that is to say the evolution of the use of the frequency spectrum. As for the performance of the device, it is possible to improve the spatial resolution (obtained by a sensor consisting of a single measuring antenna 2) if necessary by applying complementary processing operations, in particular those using deconvolution. The orbital positions emitting signals can be tracked by a system using the same antenna 2 at a remote location. The mapping system described in the invention can substitute the use of the operator's declarations and can perform both services autonomously, without degrading the performance of known orbital tracking systems.

Claims

1. 1. A method for recording radio frequency activity of at least one artificial satellite orbiting the Earth and emitting radio frequency signals, the method comprising: An antenna control device (4) directs at least one antenna (2) to different consecutive prescribed directing positions (P ｉ ), said antenna (2) being in the form of a reflector the outer edge (23) of which defines a maximum aperture of less than or equal to 6 meters; The specified pointing position (P ｉ ) for each collecting (E2) a radio frequency signal (X(t)) by said antenna (2) and converting (E2) said radio frequency signal (X(t)) into a digital signal (X(n)) by a radio frequency chain (20); A computer (3) calculates at least one received frequency subband (W(n)) from said digital signal (X(n)). ｘ ) calculating at least one record of the raw power spectral density (PSD) on the The computer (3) selects the reception frequency subband (W ｘ and (E6) reprocessing the raw power spectral density (DSb) record into a refined power spectral density (DSa) record by applying a deconvolution process of the radiation pattern (D(β,f)) of said antenna (2) in method.

2. 2. The method of claim 1, wherein the maximum aperture of the antenna (2) is less than or equal to 4 meters.

3. 3. The method according to claim 1 or 2, wherein the maximum aperture of the antenna (2) is less than or equal to 2.50 meters.

4. 4. The method according to claim 1, wherein the maximum aperture of the antenna (2) is less than or equal to 2.10 meters.

5. The step (E6) of reprocessing said raw power spectral density (DSb) records comprises the steps of: The reception frequency subband (W ｘ deconvolving the radiation pattern (D(β,f)) of the antenna (2) at a frequency (f) within and calculating the impulse response of the deconvolution from the radiation pattern (D(β,f)) of the antenna (2) pre-measured (E0) at the same frequency (f) and pre-recorded (51) in a memory (51) of the calculator (3).

6. The deconvolution is performed by convolving consecutively the defined pointing positions (P ｉ ) for several consecutive raw power spectral densities (DSb(P ｉ , t ｉ 6. The method according to claim 1 , wherein the method is performed on a linear combination of:

7. The successive predetermined directional positions (P ｉ , P ｉ＋１ The line of sight axis (21) of the antenna (2) is aligned in the predetermined pointing position (P ｉ ) to the next specified pointing position (P ｉ＋１ 7. The method according to claim 1, wherein the time intervals from the first to the second moving from the first to the second moving from the first to the second moving from the first to the second moving from the first to the second moving from the first to the second moving from the first to the second moving from the first to the second moving

8. 8. The method according to any one of claims 1 to 7, wherein the recording of the raw power spectral density (DSP) is performed by acquisition of the radio frequency signals (X(t)) collected by the antenna (2) and digitized by the radio frequency chain (20) according to discrete windows of predefined minimum duration (D).

9. Each prescribed pointing position (P ｉ To measure the raw power spectral density (PSD) record in the digital signal (X(n)), the computer (3) measures the power spectral density (PSD) of each period (F) window (D ｉ ), then square the module and apply the whole to the window (D ｉ 12. The method of claim 11, wherein the period is divided by a period of 1.

10. The pointing position (P ｉ 10. The method according to claim 8 or 9, wherein the average scanning speed of the antenna (2) relative to the tracking speed of the target object (1) is less than θ / D, where θ is the width of the main radiation lobe of the antenna (2).

11. The calculation by the computer (3), and the frequency and the specified pointing position (P ｉ 11. The method according to claim 1 , further comprising: a mapping (C) constituted by a recording of the refined power spectral density (DSP, DSa) as a function of the power spectral density (PS) of the input signal; and a recording of said mapping (C).

12. The computer (3) extracts an image from the mapping (C), the image including at least one reception frequency subband (W ｘ ) at the specified directional position (P ｉ The refined power spectral density (DSP) levels (A) read consecutively at the trajectory are arranged in a line, and the pointing position (P ｉ 12. A method according to any one of claims 1 to 11, wherein the frequency and the amplitude of the signal constitute the horizontal and vertical axes of the image, as appropriate.

13. 13. The method according to claim 12, wherein the level (A) of each refined power spectral density (PSD) is represented by a pixel value, in particular a color or luminance level or a grey level.

14. A device (1) for recording the radio frequency activity of at least one artificial satellite emitting a radio frequency signal, the device comprising: at least one receiving antenna (2) directed along a line of sight axis (21) and capable of collecting radio frequency signals (X(t)), said antenna (2) being in the form of a reflector, the outer edge (23) of which defines a maximum aperture of less than or equal to 6 meters; The line of sight axis (21) of the antenna (2) is aligned in a series of predetermined pointing positions (P ｉ an antenna (2) control unit (4) for directing at least one sequence of The radio frequency signal (X(t)) is divided into at least one reception frequency subband (W ｘ a radio frequency receiving and digital conversion chain (20) for obtaining a digital signal (X(n)) on A computer (3) for calculating from the digital signal (X(n)) the received frequency sub-bands (W ｘ ) and calculating at least one record of the power spectral density (DSP) on said reception frequency subbands (W ｘ (E6) the raw power spectral density (DSb) record is reprocessed into a refined power spectral density (DSa) record by applying a deconvolution process of the radiation pattern (D(β,f)) of the antenna (2) in Device.

15. A computer program for implementing the method for recording the radio frequency activity of at least one satellite according to any one of claims 1 to 13, comprising code instructions for carrying out the steps of pointing, collecting, converting, calculating and reprocessing when the computer program is executed on one or more computers (3).

Images