METHOD AND SYSTEM FOR ALLOCATION OF EARTH OBSERVATIONS TO MULTIPLE SATELLITES

Description

Technical field

[0001] The present invention belongs to the field of Earth imaging by satellites, and relates more particularly to a method of allocating Earth observation requests to a plurality of satellites, as well as a system for implementing such an allocation method. State of the art

[0002] Today, numerous Earth observation satellites already orbit the Earth's surface and can be programmed to respond to Earth observation requests submitted by users. Generally, when a request to observe an area on the Earth's surface is received, it is allocated to the next satellite passing over that area, to which the observation request can be relayed before it reaches that area. If this satellite is unable to acquire images of that area (for example, because it is already acquiring other images to fulfill another observation request, or because weather conditions are unfavorable), then the observation request is allocated to the next available satellite capable of acquiring the necessary images, and so on.

[0003] The current trend is towards an increase in the number of observation satellites in Earth orbit, an increase in the number of observation requests to be processed, and a decrease in the desired time frame for retrieving images of the areas to be observed.

[0004] Conventional methods of allocating observations, such as those described for example in patent EP3375111, may prove to be of limited effectiveness when the number of satellites and the number of observation requests to be processed becomes too large.

[0005] Zhibo, E., Shi, R., Gan, L., Baoyin, H. and Li, J., 2021. Multi-satellite imaging scheduling using individual reconfiguration based integer coding genetic algorithm. Acta Astronautica, 178, pp.645-657, discloses a method according to the preamble of claim 1. Presentation of the invention

[0006] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above, by proposing a solution which makes it possible to allocate many observation requests to many satellites more efficiently.

[0007] To this end, and according to a first aspect, a method is proposed for allocating requests for observations of geographical areas to be carried out on a plurality of satellites, said method comprising the following steps: decomposition of each geographical area to be observed into one or more elementary areas to be acquired, each elementary area being adapted to be acquired by an observation instrument on one of the satellites during a flyover of said geographical area by said satellite, for each elementary area: determination of at least one acquisition opportunity for said elementary area corresponding to the flyover of this elementary area by at least one of the satellites, over a predetermined time window, provisional allocation of the elementary areas to the plurality of satellites, according to the acquisition opportunities and according to a preliminary model that approximates the attitude maneuvers and acquisitions of each satellite,For each satellite: a feasibility assessment over the time window for acquiring the provisionally allocated elementary areas of said satellite, based on an operational model that accurately models the attitude maneuvers and acquisitions of said satellite; and a final allocation to said satellite of each provisionally allocated elementary area, the acquisition of which is validated according to the operational model of said satellite over the time window.

[0008] Thus, the allocation process first allows the same geographical area to be observed to be broken down into several elementary areas that can be acquired by different satellites, so that several satellites can be used to respond to the same observation request.

[0009] For each elementary zone, acquisition opportunities are determined by the different satellites over a predetermined time window, for example, on the order of 24 or 48 hours. Each satellite that, during this time window, is in a position to acquire an elementary zone therefore represents, for that elementary zone, an acquisition opportunity comprising, for example, a start time (the earliest time at which acquisition can begin) and an end time (the latest time at which acquisition can end).

[0010] Furthermore, to plan the acquisition of elementary areas by the different satellites, the satellites' attitude maneuvers and acquisitions are modeled with two distinct levels of accuracy. A first model, called the preliminary model, models the satellite's attitude maneuvers and acquisitions approximately. A second model, called the operational model, models the satellite's attitude maneuvers and acquisitions precisely. It should be noted that the terms "approximate" and "precise" are relative terms here, simply meaning that the preliminary model models the satellite's behavior with less detail than the operational model, and vice versa.The preliminary model therefore allows for an approximate evaluation of the load of a satellite, with a lower computational complexity than the operational model, which however allows for a much more precise evaluation of the load of said satellite, taking into account more operational constraints, in particular the real time required to perform an attitude maneuver between two successive acquisitions, the real time required to carry out the acquisition of the elementary area considered, etc.

[0011] The allocation of the different elementary zones to the satellites then takes place in two main phases.

[0012] The elementary zones are initially all provisionally allocated to the various satellites, taking into account acquisition opportunities and the preliminary model for each satellite. However, the use of the preliminary model does not guarantee that all elementary zones provisionally allocated to a satellite will actually be acquired by that satellite, as operational constraints related to attitude maneuvers and acquisitions, in particular, are only approximated by the preliminary model. Nevertheless, the computational complexity required by the preliminary model is significantly lower than that of the operational model, which allows for the efficient global allocation of all elementary zones to all satellites. The provisional allocation is therefore performed globally for all satellites, for example, centrally.

[0013] After all the elementary zones have been provisionally allocated, they are then definitively allocated to the satellites during a phase that relies on the operational model to verify that the acquisitions of the provisionally allocated elementary zones to a satellite are indeed feasible for that satellite. In practice, the operational model determines the exact sequence of tasks to be performed by the satellite's resources (observation instruments, maneuvering means, etc.) to achieve the acquisition of predetermined elementary zones. This sequence of tasks is then converted into a sequence of timed commands for different subsystems (resources), which will be transmitted to the satellite and ultimately executed on board.For example, the operational model makes it possible to determine and take into account the exact date and attitude of the satellite at the time each acquisition must be performed, as well as the operational constraints related to, in particular, the attitude maneuvers required to move from an initial acquisition attitude for a first elementary zone to a second acquisition attitude for a second elementary zone, and so on. The final allocation is therefore carried out individually for each satellite (unlike the provisional allocation, which is global for all satellites), for example, in a decentralized manner at the level of each satellite operator. For each satellite, the associated operational model is then implemented to assess the feasibility, within the given time window, of acquiring the elementary zones provisionally allocated to that satellite.If the acquisition of a provisionally allocated area for a satellite is not validated by that satellite's operational model, the area can, for example, be provisionally re-allocated during a subsequent provisional allocation phase. In this case, during this subsequent provisional allocation phase, the previously unvalidated area is provisionally reallocated along with new areas to be acquired obtained by decomposing new observation requests.

[0014] Regarding allocation, the operational model is therefore only used for each satellite to validate finallyThe satellite can, in practice, acquire data from all the elementary areas provisionally allocated to it, whereas the preliminary model is used much more frequently, each time a provisional allocation of one elementary area, from among all the areas to be allocated, to each satellite is considered. Calls to the operational model are therefore much less frequent than calls to the preliminary model, so the computational complexity associated with using the operational model remains limited.

[0015] In particular modes of implementation, the allocation process may also optionally include one or more of the following characteristics, taken individually or in all technically possible combinations.

[0016] In specific implementation methods: The provisional allocation step is carried out by at least one provisional allocation server not having access to the operational models of all satellites, the at least one provisional allocation server carrying out a global allocation of elementary areas to the satellites, for at least one satellite: the feasibility assessment step and the final allocation step are carried out by a final allocation server, distinct from the at least one provisional allocation server, having access to the operational model of said at least satellite.

[0017] In certain implementation modes, at least one temporary allocation server has no access to any satellite operational model.

[0018] In particular implementation modes, multiple final allocation servers are implemented, with each final allocation server having access to the operational models of only a portion of the satellites.

[0019] In specific implementation modes, the elementary areas to be allocated are stored in a database. After the provisional allocation of each elementary area, if the acquisition of a provisionally allocated elementary area to a satellite is not validated according to the satellite's operational model within the specified time window, the said elementary area is maintained in the database as an unallocated elementary area. When the acquisition of a provisionally allocated elementary area is validated according to the satellite's operational model, it can be deleted from the database or maintained in the database as an allocated elementary area.

[0020] Thus, if it turns out that acquiring a provisionally allocated area for a satellite is not feasible for that satellite, then it is retained among the remaining areas to be allocated in the corresponding database. This area can then be allocated later to one of the satellites during a subsequent execution of the provisional and final allocation phases, for the same time window or a subsequent time window, and so on.

[0021] In specific implementation modes, the satellites belong to the same constellation and the ground footprint of the observation instrument is of the same shape and dimensions for each satellite in the constellation.

[0022] In particular modes of implementation, the satellites belong to at least two different constellations, the ground footprint of the observation instrument is of the same shape and dimensions for each satellite of the same constellation, the ground footprints of observation instruments being of different shapes and / or dimensions for satellites of different constellations.

[0023] In specific implementation modes, the elementary areas of the same observation to be carried out are allocated to satellites of the same constellation.

[0024] In specific implementation modes, the preliminary model models the behavior of a satellite as a function of predefined durations of attitude maneuver and / or acquisition.

[0025] In specific implementation modes, the preliminary model models the behavior of a satellite as a function of at least one of the following: a predefined duration of satellite attitude maneuver, independent of the attitude maneuver to be performed to carry out the acquisition, and / or a predefined duration of acquisition of the satellite observation instrument, independent of the acquisition to be carried out, a predefined duration of acquisition of the observation instrument per unit area, a predefined time margin which depends on a priority of the observation request associated with the elementary area.

[0026] In specific implementation methods: The preliminary model is used to estimate for each satellite a resource load plan for said satellite over the time window, and the provisional allocation of an elementary area to a satellite having an opportunity to acquire said elementary area involves determining, based on the preliminary model and based on the elementary areas already provisionally allocated to said satellite, whether said elementary area to be allocated can be provisionally allocated to said satellite taking into account the estimated load plan for said satellite over the time window.

[0027] In specific implementation methods, the provisional allocation includes, after determination of all acquisition opportunities for all elementary zones: an ordering of the elementary areas to be allocated according to at least one predetermined ordering parameter and, a successive processing of the elementary areas according to the ordering and, for each elementary area processed: a ranking of the acquisition opportunities according to at least one predetermined ranking parameter and an allocation of the elementary area to a satellite according to the order of ranking of the acquisition opportunities and the preliminary model.

[0028] In specific implementation modes, at least one parameter for scheduling the elementary zones is at least one of the following parameters: a priority of the observation request associated with said elementary zone, weather conditions forecast for the time window in the elementary zone, weather conditions required for the acquisition of the elementary zone, a useful area of ​​the elementary zone, an expiry date of an observation request associated with said elementary zone, a date of receipt of an observation request associated with said elementary zone, a frequency or number of acquisitions of the geographic area of ​​the observation request.

[0029] In specific implementation modes, at least one parameter for ranking acquisition opportunities is at least one of the following parameters: weather conditions forecast for the acquisition opportunity, a start date for the acquisition opportunity, a date for retrieving an image acquired during the acquisition opportunity, a satellite pointing parameter during the acquisition opportunity, a number of other acquisition opportunities towards other elementary areas.

[0030] In particular modes of implementation, the elementary areas definitively allocated to a satellite correspond to a set of elementary areas, among the elementary areas provisionally allocated to said satellite, for which it is possible to calculate, according to the operational model, a work plan executable by said satellite and enabling the acquisition of all the elementary areas of the set when said work plan is executed by said satellite.

[0031] The proposed allocation method optimizes the allocation of observation requests. For example, when a large number of satellites are involved, with several satellites potentially overflying the same geographic area within a short timeframe, the allocation method allows for a comprehensive response to a large number of observation requests. This can be achieved by assigning acquisitions of that geographic area to a different satellite than the first one to overfly it. Allocation thus becomes more efficient by taking into account the satellite constellation dimension, compared to a prior art solution where each satellite sequentially selects its acquisitions based on the order of its overflight.

[0032] Advantageously, the proposed allocation method does not directly apply the generally complex operational planning algorithms (operational model) to a large satellite constellation, which would lead to excessive computational complexity. The proposed allocation method thus allows for a limited and optimized execution of these operational planning algorithms.

[0033] Another advantage of the proposed allocation method is that it allows multiple satellite constellations to be addressed simultaneously for the same set of observation requests.

[0034] Another advantage of the allocation process is that it allows for a shorter processing time for each observation request and therefore the processing of a larger number of observation requests over a given period.

[0035] According to a second aspect, a computer program product is proposed comprising a set of program code instructions which, when executed by at least one processor, configure said at least one processor to implement an allocation process according to any of the implementation modes of this disclosure.

[0036] According to a third aspect, a system for allocating requests for observations of geographical areas to be carried out to a plurality of satellites is proposed, each satellite comprising an observation instrument, said allocation system comprising means configured to implement an allocation process according to any of the implementation methods of this disclosure.

[0037] In particular embodiments, the allocation system may also optionally include one or more of the following features, taken individually or in all technically possible combinations.

[0038] In specific embodiments, the allocation system includes: at least one temporary allocation server configured to provisionally allocate the elementary zones to be acquired, and at least one final allocation server, separate from the at least one temporary allocation server, configured to permanently allocate the elementary zones to be acquired.

[0039] In particular embodiments, the at least temporary allocation server does not have access to the operational models of all satellites.

[0040] A fourth aspect proposes a system for acquiring images of the Earth using a plurality of satellites, comprising: an allocation system according to any of the embodiments of this disclosure, means of transmitting work plans to satellites, the work plan of a satellite enabling the configuration of said satellite to carry out the acquisitions of the elementary areas definitively allocated to said satellite, means of receiving images, acquired by the satellites, representing the elementary areas. Presentation of figures

[0041] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to the figures which represent: Figure 1 : a diagram representing an example of the implementation of a query allocation process for observations, Figure 2: an example of a geographical area broken down into elementary zones of satellites from different constellations, Figure 3 : a schematic representation of a satellite in low Earth orbit acquiring elementary areas of different geographical observation requests, Figure 4 : a diagram representing an example of the implementation of a provisional allocation of elementary zones, Figure 5 : a representation of the unfolding of the different stages of the provisional allocation of the figure 4 , Figure 6 : a schematic representation of an example implementation of an observation request allocation system, Figure 7 : a schematic representation of another example of the implementation of an observation request allocation system.

[0042] In these figures, identical references from one figure to another designate identical or analogous elements. For clarity, the elements shown are not to scale unless otherwise indicated. Description of the method of realization

[0043] As indicated above, the present invention relates to a method 10 for allocating requests for observations of geographical areas to be made to a plurality of satellites 30. An observation request typically corresponds to the description of a geographical area for which a user wishes to obtain one or more images acquired by satellite.

[0044] In this case, several satellites 30 can be used to fulfill observation requests. These satellites 30 are placed in orbit around the Earth. Different orbits can be considered in the present invention, such as geosynchronous orbits, low Earth orbits (LEO), medium Earth orbits (MEO), etc. Preferably, all or some of the satellites 30 are placed in low Earth orbits, i.e., non-geostationary orbits. Preferably, all the satellites 30 that can be used to fulfill observation requests are in LEO. The satellites 30 may belong to the same constellation or to different constellations. A constellation is composed of satellites 30 with similar characteristics in terms of observation instrument (type of passive or active observation, wavelength band(s), etc.) and in terms of orbit (altitude, inclination, etc.).

[0045] Depending on the embodiment, the observation instruments of the 30 satellites can: be passive or active (e.g. synthetic aperture radar), perform acquisitions in different wavelengths (visible and / or infrared, etc.), present different fields of view (and therefore different ground footprints), use different acquisition modes, for example "push-broom", "push frame", "time-delay integration" or TDI, "step and stare" (see patent application FR 3107953 A1), etc.

[0046] The observation instruments of the 30 satellites in the same constellation have similar characteristics (same type of observation, same acquisition mode, same acquisition wavelength(s), same field of view, etc.). Furthermore, the orbits of the 30 satellites in the same constellation have similar characteristics (same altitude, same inclination, etc.).

[0047] The ground footprint of an observation instrument corresponds to the instantaneous intersection of the field of view of said observation instrument with the Earth's surface, considering a nadir pointing of said observation instrument. In the case of an elliptical orbit, the ground footprint corresponds, for example, to the instantaneous intersection of the field of view with the Earth's surface when the satellite is at the perigee of its orbit. In the following description, we consider, without limitation, the case where all satellites are in circular orbits. The ground footprint of the observation instrument of a satellite therefore depends primarily on the field of view of said instrument and the altitude of the satellite's orbit. Consequently, the ground footprint is essentially the same shape and dimensions for all satellites in the same constellation.Conversely, the characteristics of observation instruments and / or orbits vary from one constellation to another, so the ground footprints of observation instruments are of different shapes and / or dimensions for satellites from 30 different constellations.

[0048] There figure 1 schematically represents the main steps of a process 10 of allocating requests for observations of geographical areas to a plurality of satellites 30, which may belong to one or more different constellations.

[0049] As indicated above, an observation request typically corresponds to the description of a geographic area for which a user wishes to obtain one or more satellite images. An observation request may also include one or more metadata elements, provided by the user and / or added to the observation request upon receipt. For example, non-exhaustive examples of metadata that may be associated with an observation request include: an observation request priority, a type of observation to be carried out (passive / optical or active / radar), one or more wavelengths to be used for acquisition (e.g. visible or infrared wavelengths), weather conditions required for the acquisition of the geographic area, a spatial resolution required for the images, a date of receipt of the observation request, an expiry date of the observation request, a frequency or number of acquisitions of the geographic area, in the case of an observation request aimed at acquiring the same geographic area several times, etc.

[0050] As illustrated by the figure 1The allocation process 10 includes, for each observation request received, a step S10 of decomposing the geographic area to be observed into one or more elementary zones to be acquired. In practice, an elementary zone corresponds to a ground surface that can be acquired by a satellite 30 during a single overflight of the geographic area by said satellite 30. Depending on the shape and / or dimensions of the geographic area to be imaged, it may indeed prove impossible to acquire the entire geographic area by the same satellite in a single orbital period. It is also understood that this depends on the characteristics of the observation instrument of the satellite 30 in question and its orbit.

[0051] For example, in a "step and stare" acquisition mode, an elementary zone might correspond to a ground footprint of the observation instrument. In a "push-broom" acquisition mode, an elementary zone might correspond, for example, to a strip whose width matches the swath width of the observation instrument and whose length is equal to or less than a maximum length that can be acquired in a single pass by said observation instrument.

[0052] For example, for each constellation considered, it is possible to predetermine a global grid of the Earth in elementary zones, independently of the geographical areas that will subsequently be observed. The S10 decomposition step can then consist, for a constellation of 30 satellites, of identifying in the predetermined global grid the elementary zones that have a non-empty intersection with the geographical area to be imaged (i.e., the geographical area to be imaged lies entirely within the union of these elementary zones). Part a) of the figure 2 This schematically represents an example of the decomposition of a geographic area ZG by considering elementary zones ZE-C1 of a first constellation and elementary zones ZE-C2 of a second constellation, with the elementary zones ZE-C1 and ZE-C2 being distributed according to their respective global grids. As illustrated by part a) of the figure 2The decomposition depends on the shape and dimensions of the elementary zones ZE-C1, ZE-CE2. The decomposition results in a lower number of elementary zones with the first constellation than with the second constellation, however the useful imaged area (i.e. in this case the ratio between the area of ​​the geographic zone and the area of ​​the union of the elementary zones allowing to image said geographic zone) is lower with the first constellation than with the second constellation.

[0053] Following another example, it is possible to perform a decomposition according to a local mesh that depends on the geographic area to be imaged. Thus, in this case, the mesh is local and can be optimized for the geographic area to be imaged, for example by minimizing the number of elementary zones. Part b) of the figure 2schematically represents the decomposition of the geographical area ZG shown in part a), considering a local grid. As illustrated by part b) of the figure 2 The number of ZE-C1 elementary zones for the first constellation has been significantly reduced (and therefore the usable area greatly increased). It should be noted that, in part b) of the figure 2 , only translations were applied to the elementary zones with respect to part a) of the figure 2However, following other examples of local mesh usage, there is nothing to prevent varying the orientation of the elementary zones from one geographic area to another. For example, in the case of a "push-broom" acquisition mode, the elementary zones correspond to strips of fixed width but whose length can vary (up to a maximum length). In such a case, it can be advantageous to orient the elementary zones (strips) parallel to the direction in which the geographic area is longest.

[0054] In general, using a local mesh for decomposition allows, for a given constellation, minimizing the number of elementary zones per geographic area, and therefore maximizing the usable area. However, using a global mesh for decomposition facilitates the process (since the global mesh of elementary zones is known a priori) and also allows for the pooling of data acquisitions for observation requests in different geographic areas that have a non-zero overlap. Indeed, in such a case, the elementary zones corresponding to the overlap between these geographic areas can be acquired only once to fulfill these observation requests.

[0055] In preferred implementation modes, the elementary areas of a given observation are allocated to 30 satellites within the same constellation. In other words, in such implementation modes, the observation of a geographic area is carried out only with observation instruments having similar characteristics and being carried on satellites in orbits with similar characteristics. Such arrangements simplify the allocation of observation requests. The allocation of an observation request to one constellation rather than another can be imposed, for example, by the user or by other criteria. For instance, in the case of an observation request to be carried out with a synthetic aperture radar, constellations of 30 satellites carrying passive / optical observation instruments cannot be used.If two constellations can be considered to fulfill the same observation request, then it is possible, for example, to arbitrarily allocate this observation request to one of these constellations, and to allocate a subsequent observation request that can be processed by the same constellation to the other constellation, and so on. As another example, if two constellations can be considered to fulfill the same observation request, then it is possible to perform two decompositions of the geographic area into elementary zones, one decomposition for each constellation, and to select the constellation to use based on the two decompositions. For example, it is possible to select the constellation whose decomposition contains the fewest elementary zones, or the one whose decomposition has the largest usable area, etc.

[0056] In the following description, we consider, without limitation, the case where the acquisition of a geographical area is carried out by the same constellation. Furthermore, we consider, without limitation, that the constellation that must respond to an observation request is selected no later than the completion of the S10 decomposition step.

[0057] As illustrated by the figure 1The allocation process 10 further includes, for each elementary zone obtained at the end of the decomposition step S10, a step S11 for determining at least one acquisition opportunity for the elementary zone within a predetermined time window. The predetermined time window corresponds to a time horizon over which observation requests must be allocated. For example, time is decomposed into a plurality of successive time windows, for example every 24 hours or every 48 hours, and the time window considered during the acquisition opportunity determination step S11 corresponds to a time window that has not yet begun, for example, the next one. Within this time window, an acquisition opportunity corresponds to a satellite passing over the elementary zone.In other words, step S11, which determines acquisition opportunities for an elementary area, aims to identify all 30 satellites in the constellation that will be in a position to acquire that elementary area during the considered time window. At this stage, only geometric considerations are taken into account, and an acquisition opportunity simply indicates that the corresponding satellite 30 will pass sufficiently close to the elementary area during the time window to acquire it, regardless of the resource load of that satellite. For example, an acquisition opportunity includes a start time (the earliest time at which acquisition by that satellite 30 can begin) and an end time (the latest time at which acquisition by that satellite 30 can end).Furthermore, the interval between the start and end times must be sufficient to allow the observation instrument to acquire the data from the satellite in question. Depending on the characteristics of the satellite constellation, there may be one or more acquisition opportunities for a given area within the time window considered.

[0058] As illustrated by the figure 1The allocation process 10 then includes a provisional allocation step S12 of elementary zones to the plurality of satellites 30, based on acquisition opportunities. During the provisional allocation step S12, the behavior of a satellite 30 is modeled using a so-called preliminary model, which approximates the attitude maneuvers and acquisitions of each satellite, without taking into account all operational constraints. The same preliminary model can be implemented for all the satellites 30 in the same constellation, and examples of preliminary models are given below.

[0059] Following the provisional allocation step S12, all elementary areas were provisionally allocated to the various satellites 30. However, the use of the preliminary model does not guarantee that all elementary areas provisionally allocated to a satellite 30 will actually be acquired by that satellite 30, as the operational constraints related to attitude maneuvers and acquisitions are only approximated by the preliminary model. Nevertheless, the computational complexity required by the preliminary model is limited, thus allowing for the overall optimization of the allocation of elementary area acquisitions to the various satellites 30.

[0060] After provisionally allocating the elementary zones, the allocation process 10 includes, for each satellite 30 to which at least one elementary zone acquisition has been provisionally allocated, a feasibility assessment step S13 on the time window of the acquisitions of the elementary zones provisionally allocated to said satellite 30. This feasibility assessment takes into account all the operational constraints applicable to each satellite 30, by means of an operational model which accurately models the attitude maneuvers and acquisitions of said satellite 30.

[0061] It should be noted that, conventionally, it is known how to determine on the ground an exact sequence of tasks to be performed by the resources (observation instruments, maneuvering means, etc.) of a satellite 30 to acquire predetermined elementary areas. Such a sequence of tasks, also referred to below as a "work plan," is then transmitted to the satellite 30, which executes it. Existing tools used to generate such a sequence of tasks are already capable of adding tasks to a predetermined sequence (for example, to add an additional acquisition to be performed) and of returning an error message if it is not possible to add tasks to a predetermined sequence. Such tools (also known as operational planning algorithms) can therefore be used as operational models for satellites 30.In such a case, the operational model of a satellite 30 is therefore adapted to generate a work plan executable by that satellite 30. Such a work plan (also known as a mission plan) is, for example, converted into a sequence of timed commands that will be transmitted to the satellite 30 and executed by the on-board computer (OBC) of said satellite 30 in a timely manner. However, it should be noted that these tools are used here only once per satellite 30, after provisionally allocating all elementary areas, and not each time a new acquisition is considered for a given satellite. Furthermore, the use of the preliminary model during the provisional allocation step S12 reduces the probability of allocating elementary area acquisitions to a satellite 30 that are not feasible for it.

[0062] As illustrated by the figure 1, each elementary zone provisionally allocated to a satellite 30 and whose acquisition over the time window is validated by the operational model (reference S13a on the figure 1 ) is definitively allocated to said satellite 30, during an S14 step. Furthermore, if it turns out that the acquisition of an elementary area provisionally allocated to a satellite 30 is not validated by the operational model (reference S13b on the figure 1 ), then this elementary area can be retained for later allocation to one of the 30 satellites during a later execution of the S11 acquisition opportunity determination step and / or the S12 provisional allocation step, for the same time window or a subsequent time window.

[0063] For example, the elementary areas to be allocated are stored in a database 63 and, after the provisional allocation of each elementary area, when the acquisition of an elementary area provisionally allocated to a satellite 30 is not validated according to the operational model of said satellite 30 (reference S13b on the figure 1 ), said elementary area is maintained in database 63 as an elementary area to be allocated, while it can be deleted from said database 63 (or maintained in said database 63 as an allocated elementary area) after validation according to the operational model of said satellite (reference S13a on the figure 1 ).

[0064] There figure 3This schematically represents a satellite 30 in orbit, which successively acquires elementary zones belonging respectively to different geographical areas. For each geographical area, the elementary zones can therefore be acquired by 30 different satellites, and taking into account all the satellites and all the elementary zones during the provisional allocation allows for optimization of the processing of observation requests.

[0065] There figure 4 schematically represents a preferred example of implementation of the S12 provisional allocation step.

[0066] As illustrated by the figure 4After determining all acquisition opportunities for all elementary zones to be acquired during the considered time window, the provisional allocation step S12 first includes a scheduling step S120 for the elementary zones to be allocated based on at least one predetermined scheduling parameter. The scheduling step S120 aims to establish a scheduling order for all elementary zones, which will then be used to successively allocate the elementary zones to the satellites.

[0067] The scheduling of elementary zones can take into account one or more scheduling parameters. For example, scheduling can be performed by considering at least one of the following scheduling parameters: a priority of the observation request associated with said elementary zone, in order for example to prioritize (process first) elementary zones with high priority, weather conditions (for example in terms of percentage of clear sky, in terms of level of sunshine, etc.) forecast for the time window (for example on average over said time window, or the best or worst weather conditions forecast during said time window, etc.) in said elementary zone, in order for example to prioritize elementary zones with forecast favorable weather conditions over said time window compared to elementary zones with forecast unfavorable weather conditions, weather conditions required (by the user) for the acquisition of said elementary zone,for example, to prioritize elementary zones for which the weather conditions forecast for the time window are compatible with the weather conditions required by the user, compared to elementary zones for which this is not the case; a useful area of ​​the elementary zone (here: the intersection between the elementary zone and the geographical area to be observed), for example in km² or as a percentage of the elementary zone, for example, to prioritize elementary zones with a large useful area; an expiry date of an observation request associated with said elementary zone, for example, to prioritize elementary zones whose observation requests expire earliest; a date of receipt of an observation request associated with said elementary zone, for example, to prioritize elementary zones with the oldest observation requests.a frequency or number of acquisitions of the geographical area of ​​the observation request, in order, for example, to prioritize the elementary areas that should be acquired the greatest number of times, etc.

[0068] If several scheduling parameters are considered among the preceding parameters, they are preferably considered successively in the order given above (starting with priority, then weather conditions, then usable area, etc.). Thus, if the elementary zones are scheduled according to priority, usable area, and expiration date, then it is possible to: to first order the elementary zones according to their respective priorities, then to order the elementary zones having the same priority according to their respective usable areas, then to order the elementary zones having the same priority and the same usable area according to their respective expiry dates.

[0069] It is also possible to calculate a score for each elementary zone, based on several scheduling parameters from among those mentioned above. If necessary, weighting factors can be applied to the different scheduling parameters, for example, in descending order as described above. Thus, if the elementary zones are scheduled according to priority, usable area, and expiration date, then when calculating the score, it is possible to apply a higher weighting factor to priority, a lower weighting factor to usable area than to priority, and a lower weighting factor to expiration date than to usable area.

[0070] As illustrated by the figure 4The elementary zones are then processed successively according to the scheduling order, that is, from the elementary zone considered the most important according to the scheduling parameter(s), down to the elementary zone considered the least important. The processing of each elementary zone then includes: a step S121 of ranking the opportunities for acquisition of the treated elementary area according to at least one predetermined ranking parameter and, a step S122 of allocating the treated elementary area to a satellite 30 according to the ranking order of the acquisition opportunities and the preliminary model.

[0071] The S121 ranking step aims to establish a ranking order for all available acquisition opportunities for the processed elementary area. Subsequently, the S122 allocation step aims to determine the satellite 30 to which this elementary area will be provisionally allocated. In practice, during the S122 allocation step, ranking opportunities are processed according to the ranking order, that is, from the acquisition opportunity considered the best according to the ranking parameter(s) to the acquisition opportunity considered the least suitable. The processing of an acquisition opportunity during the S122 allocation step aims to verify whether the corresponding satellite 30 can, based on its preliminary model and the elementary areas previously provisionally allocated to this satellite 30, acquire the processed elementary area.Indeed, the preliminary model allows, for example, the estimation of a resource workload (observation instruments, maneuvering equipment, etc.) for satellite 30 over the given time window. Thus, by taking into account the estimated workload of satellite 30 for acquiring the previously provisionally allocated elementary areas, the preliminary model allows for an assessment of whether the increased workload resulting from the addition of the processed elementary area is acceptable. If satellite 30, corresponding to the processed acquisition opportunity, can acquire the processed elementary area, it is provisionally allocated to that satellite. Otherwise, the allocation step S122 processes the next acquisition opportunity according to the ranking order, and so on.

[0072] The ranking of acquisition opportunities can take into account one or more ranking parameters. For example, the ranking can be performed by considering at least one ranking parameter from the following: forecast weather conditions for the acquisition opportunity, in order, for example, to prioritize (process first) acquisition opportunities with the most favorable forecast weather conditions, or those compatible with the weather conditions required by the user for the observation request associated with the processed elementary area; a start date for the acquisition opportunity, in order, for example, to prioritize acquisition opportunities allowing the acquisition to be carried out as early as possible; a retrieval date for an image acquired during the acquisition opportunity (i.e., the date on which the image can be transmitted to a ground station by satellite 30), in order, for example, to prioritize acquisition opportunities allowing the corresponding image to be retrieved as quickly as possible; a pointing parameter for satellite 30 during the acquisition opportunity.for example, to prioritize acquisition opportunities allowing observation of the treated elementary area with a nadir pointing technique rather than with an oblique pointing technique.

[0073] As with the prior scheduling parameters, if several ranking parameters are considered among the preceding parameters, they are preferably considered sequentially in the order given above (starting with weather conditions, then start date, then recovery date, etc.). It is also possible, following other examples, to calculate a score for each acquisition opportunity based on several ranking parameters among the preceding parameters, for example, by applying decreasing weighting factors in the order given above.

[0074] Therefore, in the example illustrated by the figure 4The elementary zones are processed according to the scheduling order. For each elementary zone processed, acquisition opportunities are evaluated according to the ranking order, using the preliminary model of the relevant satellite 30. Thus, for a given elementary zone, the acquisition opportunity appearing first in the ranking order is evaluated first, and the preliminary model of satellite 30 is used to verify whether the increased workload resulting from realizing this acquisition opportunity is acceptable. If so, the processed elementary zone is provisionally allocated to that satellite 30. In the case of a processed elementary zone that needs to be acquired several times within the time window, this process is repeated until the processed elementary zone has been provisionally allocated enough times to perform the required number of acquisitions.When the provisional allocation of the elementary area being processed is complete, the next elementary area in the scheduling order can be processed. If this is not the case, the next acquisition opportunity in the ranking order is evaluated, and so on until an acquisition opportunity is identified that can be realized by the relevant satellite 30 according to the preliminary model of said satellite 30. If no acquisition opportunity is feasible by the relevant satellites 30 within the time window, then the elementary area in question is not allocated and can be maintained in database 63 as an unallocated elementary area. The elementary areas are processed successively in this manner until the last elementary area in the scheduling order is processed.

[0075] There figure 5 schematically represents an example of the implementation of the S12 provisional allocation step illustrated by the figure 4 . There figure 5 This schematically represents several ordered elementary zones from ZE-1 to ZE-N, with elementary zone ZE-1 being, according to this order, the first zone to be processed, followed by elementary zone ZE-2, then elementary zone ZE-3, and so on. For each elementary zone, acquisition opportunities are represented according to their start dates; however, in this example, these acquisition opportunities are ranked according to their weather conditions. On the figure 5The ranking order is explicitly indicated by specifying the rank of each acquisition opportunity. Furthermore, the corresponding satellite 30 for each acquisition opportunity is also indicated. More specifically, the reference "OA-ij(k)" designates acquisition opportunity #j for elementary area ZE-i, which is offered by satellite #k. Finally, the elementary areas provisionally allocated to each satellite 30 are indicated in the lower part of the figure 5 In this example: Elementary zone ZE-1 is allocated to satellite #2 associated with opportunity of rank #1, elementary zone ZE-2 is allocated to satellite #1 associated with opportunity of rank #1, elementary zone ZE-3 is allocated to satellite #3 associated with opportunity of rank #1, etc.

[0076] As can be seen, since the ranking opportunities were ranked according to the forecasted weather conditions, the elementary zones processed first in the scheduling order are not necessarily acquired first. In this example, elementary zone ZE-3 is acquired first, then elementary zone ZE-2, and then elementary zone ZE-1.

[0077] As stated above, the preliminary model is used to verify in a simplified manner whether an elementary area can be provisionally allocated to a given satellite 30, taking into account the elementary areas previously provisionally allocated to that satellite 30.

[0078] To perform this verification with limited computational complexity, the preliminary model approximates the behavior of satellite 30 (unlike the operational model, which is a precise model). In preferred implementation modes, the preliminary model is defined by a set of predefined durations associated with attitude maneuvers and / or data acquisitions.

[0079] For example, in the preliminary model, attitude maneuvers can be modeled using a predefined duration independent of the attitude maneuver to be performed. This could be, for example, an average duration of attitude maneuvers performed by satellite 30, or a maximum duration of attitude maneuvers by satellite 30. Thus, the actual amplitude, in roll and pitch, of the attitude maneuver that will be necessary to point the observation instrument towards the elementary area to be acquired is not taken into account.

[0080] Alternatively, or in addition, in the preliminary model, data acquisitions can be modeled using a predefined duration specific to the type of observation instrument. For example, the predefined acquisition duration can be independent of the elementary zone to be acquired, particularly when the shape and dimensions are substantially the same for all elementary zones (e.g., in the case of a "step and stare" acquisition mode). This could be, for example, an average acquisition duration performed by the observation instrument, or a maximum acquisition duration. Alternatively, or in addition, it is possible to specify several predefined acquisition durations, for example, associated with different possible surface areas for the elementary zones.As another example, when the area of ​​an elementary zone can vary (for example, in the case of a "push-broom" acquisition mode), it is possible to predict a predefined acquisition time per unit area. In such a case, the elementary zone can be expressed in units of area (for example, in the number of line images to scan an elementary zone corresponding to a strip, if the unit of area corresponds to a line image acquired in "push-broom" mode), and the acquisition time of the elementary zone in question, provided by the preliminary model, corresponds to the predefined time per unit of area multiplied by the number of units of area that make up the elementary zone.

[0081] Alternatively, or in addition, the preliminary model can include several predefined acquisition durations associated with different scheduling parameter values. For example, a first predefined acquisition duration can be used for a high-priority element and a second predefined acquisition duration for a low-priority element. The first acquisition duration is preferably longer than the second to better ensure the feasibility of acquiring high-priority elements, which then have a greater time buffer compared to the approximations in the preliminary model.More generally, it is therefore possible to predict predefined acquisition times that decrease with the scheduling order, with longer acquisition times for the elementary zones processed first in the scheduling order than for those processed last. Even more generally, the preliminary model can be configured to ensure that the provisional allocation of a high-priority (or high-score) elementary zone has a higher probability of being validated by the operational model than the provisional allocation of a low-priority (or low-score) elementary zone. As indicated above, using several predefined acquisition times (or several time margins) associated with different scheduling parameter values ​​is one way to make the preliminary model more or less conservative with respect to the operational model.

[0082] The preliminary model is for example implemented to estimate a load plan of satellite 30 which represents the estimated load of said satellite 30 over time on the time window considered.

[0083] We now describe a non-limiting example of using the preliminary model to assess whether an elementary area can be provisionally allocated to a satellite 30. The load plan of a given satellite 30 over the time window FT = [ t 1, t 2] is designated by plan ( t ) . The workload plan plan ( t ) is initially set to zero: plan t = 0 ∀ t ∈ FT

[0084] In addition, the elementary areas provisionally allocated to satellite 30 are added to an acquisition plan. acq, which is initially empty: a c q =

[0085] In order to check if an acquisition opportunity DTO 1 of an elementary zone ZE 1 can be achieved by this satellite 30, the duration τ acq ( DTO 1) necessary to perform the attitude maneuver and the corresponding acquisition is estimated using the preliminary model, for example according to the following expression: τ acq ¯ DTO 1 = τ acq ZE 1 + τ man expression in which: τ acq ( ZE 1) corresponds to the estimated acquisition time by the observation instrument, which may depend on the elementary area ZE 1 to be acquired; in the following description, we consider, in a non-limiting manner, the case where the predefined acquisition time is independent of the elementary zone τ acq ( ZE 1) = τ acq , τ man is the predefined duration for the maneuver, considered as independent of the attitude maneuver to be performed.

[0086] This is also referred to as T ( DTO1) The duration of the acquisition opportunity, for example, equal to the difference between the latest time the acquisition can end and the earliest time the acquisition can begin. Obviously, T ( DTO 1) is equal to or greater than τ acq ( DTO 1). In the following description, it is assumed, without limitation, that all acquisition opportunities have the same duration. T ( DTO 1) = T, However, nothing precludes considering acquisition opportunities of varying durations. This is also referred to as t* ( DTO 1) the moment in the middle of the acquisition opportunity DTO 1, so that the acquisition opportunity begins at a specific moment ( t *( DTO 1) - T / 2) and ends at a certain point ( t* (DTO 1) + T / 2) . Regarding the acquisition opportunity DTO1, the increase in load induced by the allocation of the elementary zone ZE 1 to satellite 30 is, for example, estimated at τ acq ( DTO 1) / T.

[0087] To verify if satellite 30 can acquire the elementary area ZE 1. During the acquisition opportunity DTO 1. We calculate the average available time AvTime ( DTO 1) of satellite 30 on the acquisition opportunity, for example according to the following expression: AvTime DTO 1 = T − ∫ t * DTO 1 − T / 2 t * DTO 1 + T / 2 plan t dt

[0088] In general, the elementary zone ZE 1 can be considered feasible by satellite 30 if, for example AvTime ( DTO 1) > τ acq ( DTO 1). If so, the elementary zone ZE 1 can be provisionally allocated to said satellite 30. Given that at this stage, the workload plan plan ( t ) is empty, the expression AvTime ( DTO 1) > τ acq ( DTO 1) is verified. The elementary zone ZE 1 is provisionally allocated to satellite 30 and acq = [ acq ; ZE 1]. The workload plan for satellite 30 is further increased to take into account the addition of the elementary area ZE 1: plan t = plan t + τ acq ¯ DTO 1 T ∀ t ∈ t * DTO 1 − T / 2 ; t * DTO 1 + T / 2

[0089] Next, to assess whether an acquisition opportunity DTO 2 of an elementary zone ZE 2 can be achieved by this satellite 30, it is possible to calculate the duration τ acq ( DTO 2 ) according to the same principle and to calculate the average available time AvTime ( DTO 2) according to the following expression: AvTime DTO 2 = T − ∫ t * DTO 2 − T / 2 t * DTO 2 + T / 2 plan t dt

[0090] If AvTime ( DTO 2) > τ acq ( DTO 2), then the elementary zone ZE 2 is provisionally allocated to satellite 30 and: acq = acq ; ZE 2 plan t = plan t + τ acq ¯ DTO 2 T ∀ t ∈ t * DTO 2 − T / 2 ; t * DTO 2 + T / 2

[0091] Otherwise, the elementary zone ZE2 is not provisionally allocated to satellite 30.

[0092] The same steps are repeated each time it is considered to provisionally allocate an elementary area to this satellite 30. In addition, the same steps are executed in parallel for the other satellites 30, each satellite 30 having its own workload plan plan ( t ) and its own acquisition plan acquired. During the S13 feasibility assessment stage using the operational model, the elementary areas are addressed according to the order given by the acquisition plan. acq, in which the provisionally allocated elementary zones are progressively inserted according to the scheduling order.

[0093] The allocation process 10 is implemented by an allocation system 60. The allocation system 60 includes, for example, one or more processors and storage means (magnetic hard drive, electronic memory, optical disc, etc.) in which a computer program product is stored, in the form of a set of program code instructions to be executed to implement the various steps of the allocation process 10. Alternatively or in addition, the allocation system 60 includes one or more programmable logic circuits (FPGA, PLD, etc.), and / or one or more specialized integrated circuits (ASIC, etc.), and / or a set of discrete electronic components, etc., adapted to perform all or part of the said steps of the allocation process 10. Thus, the allocation system 60 includes means configured in software (specific computer program product) and / or hardware (FPGA, PLD, ASIC, discrete electronic components, etc.).) to perform all or part of the steps in process 10 for allocating observation requests.

[0094] There figure 6 This schematically represents an example of an implementation of an allocation system 60. In this non-limiting example, the provisional allocation phase (steps S10 to S12 of the allocation process 10) and the final allocation phase (steps S13 to S14 of the allocation process 10) are implemented using separate hardware. Specifically, the allocation system 60 in this example comprises: at least one temporary allocation server 61 configured to provisionally allocate the elementary areas to be acquired, and at least one final allocation server 62, separate from the at least one temporary allocation server, configured to permanently allocate the elementary areas to be acquired.

[0095] In the non-limiting example illustrated by the figure 6The allocation system 60 comprises a single temporary allocation server 61 and a single final allocation server 62. However, following other examples, it is possible to have several temporary allocation servers 61 and / or several final allocation servers 62. In fact, it is advantageous to have several final allocation servers 62, for example, one final allocation server 62 per satellite 30, to more easily guarantee the execution of the final allocation during critical time.

[0096] This embodiment is particularly advantageous when different entities perform the provisional allocation of elementary zones and the final allocation. For example, the entity performing the provisional allocation (steps S10 to S12 of allocation process 10) may be a global planning entity that does not have access to the operational models of the satellites 30 (and does not operate any of said satellites 30) but only to their preliminary models. For example, the entity performing the final allocation (steps S13 to S14 of allocation process 10) may be an operator of a satellite constellation 30, which may be the only one to possess the operational model(s) of this satellite constellation 30. In this case, the operator's final allocation server 62 receives as input acquisition plans comprising elementary zones provisionally allocated to the satellites 30 of the constellation it operates.Next, the work plans to be executed to carry out the acquisitions of the validated elementary areas according to the operational model are transmitted to the various satellites of the constellation. Information relating to the elementary areas that have been definitively allocated and to the elementary areas whose acquisitions have not been validated by the operational model is, for example, sent to the provisional allocation server, for example, to update the database in which the elementary areas to be allocated are stored.

[0097] In some cases, and as illustrated by the figure 7, a single provisional allocation server 61 can communicate with several final allocation servers 62, which belong, for example, to operators of different satellite constellations 30. It should be noted that the entity that carries out the provisional allocation may also, in some cases, operate a satellite constellation 30, so that the same entity may hold a provisional allocation server 61 and a final allocation server 62 associated with this satellite constellation 30. In such a case, the provisional allocation server 61 and the final allocation server 62 of this satellite constellation 30 may be integrated into the same server, which is connected to remote final allocation servers 62 belonging to operators of other satellite constellations 30 not operated by the entity that carried out the provisional allocation of the elementary areas.

[0098] More generally, the processing of observation requests and the provisional allocation of elementary zones are preferably centralized, as this allows for more efficient provisional allocation by providing a comprehensive overview of all the elementary zones to be acquired and all 30 satellites available for this purpose. However, the 30 satellites may not all be operated by a single operator and may be operated, in whole or in part, by an entity separate from the overall planning entity that handles the processing of observation requests and the provisional allocation of elementary zones.Thus, the global planning entity performs a filtering of the set of elementary areas to be acquired in that a satellite constellation operator typically receives only a subset of elementary areas corresponding to the elementary areas provisionally allocated to the satellites operated by that operator.

[0099] For example, the provisional allocation server 61 centrally performs the provisional allocation of elementary zones to a plurality of satellites 30, which may belong to different operators. This provisional allocation is based solely on the preliminary model of each satellite 30. Therefore, the provisional allocation server 61 does not need access to the operational model of each satellite 30; in other words, it does not need to know the operational model of each satellite 30. For each satellite 30, the provisional allocation server 61 sends the list of provisionally allocated elementary zones to the final allocation server 62, which is typically separate from the provisional allocation server 61, associated with that satellite 30, and which has access to the operational model of said satellite 30.The final allocation server 62 associated with a satellite 30 can definitively allocate to that satellite 30 each elementary zone provisionally allocated to said satellite 30 whose acquisition is validated by the operational model of that satellite 30, for example by calculating a work plan for that satellite 30. Such a final allocation is typically carried out, in a decentralized / distributed manner, by each final allocation server 62 associated with a different satellite 30 to which the provisional allocation server 61 has provisionally allocated elementary zones to be acquired.When a final allocation server 62 determines that the acquisition of an elementary zone, provisionally allocated to a satellite 30 to which said final allocation server 62 is assigned, is not validated according to the operational model of said satellite 30, said final allocation server 62 may, for example, inform the provisional allocation server 61 that this elementary zone could not be definitively allocated. Such an architecture (centralized provisional allocation by the provisional allocation server 61 and decentralized final allocation by each final allocation server 62 responsible for a satellite 30 to which the provisional allocation server 61 has provisionally allocated at least one elementary zone to be acquired) is advantageous in that it allows for the management of a large number of satellites 30 and also makes it easy to increase the number of satellites 30 considered.For example, if a new constellation of 30 satellites can be used for acquisitions, it is sufficient to add the preliminary models of these 30 satellites to the temporary allocation server 61 and interface this server with the final allocation server(s) 62 responsible for this new constellation of 30 satellites, which have their operational models. In this architecture, the preliminary models are implemented centrally, and the operational models are implemented in a decentralized manner, independently of the preliminary models.

[0100] The allocation system 60 can therefore be implemented in an Earth image acquisition system (not shown in the figures) using a plurality of satellites 30. In addition to the allocation system 60 implementing the allocation method 10, such an image acquisition system also includes means for transmitting work plans to the satellites 30. The work plan of a satellite allows the configuration of said satellite to perform acquisitions of the elementary areas definitively allocated to said satellite, and means for receiving images, acquired by the satellites 30, representing the elementary areas. The transmission / reception means are conventional means, including ground stations adapted to exchange data with satellites via radio frequency and / or optical links. As indicated previously, the work plans are preferably established using the operational models of the satellites 30.

[0101] More generally, it should be noted that the implementation and realization methods considered above have been described as non-limiting examples, and that other variants are therefore conceivable.

[0102] In particular, the invention has been described primarily considering the case where the acquisition of a geographic area is carried out by a single constellation. However, following other examples, nothing precludes the acquisition of the same geographic area by different constellations of satellites. For example, it is possible to decompose the geographic area into intermediate zones, each intermediate zone then being decomposed into one or more elementary zones depending on the constellation in question. For example, it is possible to first establish a global grid of the Earth in intermediate zones. The intermediate zones can then be allocated to different constellations, and each intermediate zone is then decomposed into elementary zones corresponding to the characteristics of the constellation to which it is allocated.

[0103] Furthermore, the invention has been described primarily considering the case where the constellation to respond to an observation request is selected no later than the end of the S10 decomposition step. However, it is also possible, according to other examples of implementations of the invention, to perform this selection during the provisional allocation, or even to forgo any selection altogether by allowing several satellite constellations to respond to an observation request.

[0104] For example, considering the above decomposition into intermediate zones, it is also possible to consider several constellations for the acquisition of the same geographic area during provisional allocation. Because multiple constellations are considered, this generates more elementary zones and acquisition opportunities. For example, as soon as an elementary zone within an intermediate zone is provisionally allocated to a constellation of 30 satellites, then that intermediate zone can be allocated entirely to that constellation of 30 satellites. The elementary zones corresponding to the decomposition of that same intermediate zone for other constellations can then be eliminated.

[0105] Similarly, if the decomposition of a geographic area results in a single elementary zone for each satellite constellation (a geographic area smaller than the elementary zones of the individual satellite constellations), then it is possible to consider several constellations for acquiring this geographic area during the provisional allocation. Once an elementary zone enabling the acquisition of this geographic area is provisionally allocated to a satellite constellation, the elementary zones associated with the other satellite constellations can be removed.

[0106] As another example, the geographic area can be decomposed into elementary zones for several satellite constellations, resulting in multiple sets of elementary zones associated with each constellation. All these sets of elementary zones can be considered during provisional allocation. The different elementary zones (from all sets) can be ordered by calculating a score for each elementary zone that takes into account its usable area, and the elementary zones are processed sequentially according to the order of allocation. When an elementary zone of the geographic area is provisionally allocated, the scores of the remaining elementary zones to be provisionally allocated are updated, reflecting their remaining usable areas.The remaining usable area of ​​an elementary zone corresponds to the intersection between that elementary zone and the residual geographic zone. The residual geographic zone corresponds to the area obtained by subtracting from the geographic zone the intersection with each elementary zone already provisionally allocated for that geographic zone. Thus, the usable area of ​​an elementary zone remaining to be provisionally allocated will be reduced (and its score modified) if it has a non-zero intersection with the intersection between the geographic zone and the elementary zone that has just been provisionally allocated. The order of the remaining elementary zones to be provisionally allocated is then also updated according to their new scores, and the provisional allocation continues for that geographic zone.When all the remaining elementary areas to be provisionally allocated for this geographical area have a zero remaining usable area (i.e., when the entire geographical area has been provisionally allocated), then they can be deleted.

Claims

1. A method (10) for allocating requests for observations of geographic areas (ZG) to be carried out to a plurality of satellites (30), said method including steps of: - (S10) decomposition of each geographic area to be observed into one or more elementary areas to be acquired, each elementary area being adapted to be acquired by an observation instrument of one of the satellites during an overflight of said geographic area by said satellite, - for each elementary area: (S11) determination of at least one acquisition opportunity of said elementary area corresponding to the overflight of this elementary area by at least one of the satellites, over a predetermined time window, - (S12) provisional allocation of the elementary areas to the plurality of satellites, depending on the acquisition opportunities and depending on a preliminary model which approximately models the attitude manoeuvres and acquisitions of each satellite, characterised in that said method comprises a step of: - for each satellite: (S13) evaluation of feasibility over the time window of the acquisitions of the elementary areas provisionally allocated to said satellite depending on an operational model which accurately models the attitude manoeuvres and the acquisitions of said satellite, and definitive allocation to said satellite of each elementary area which is provisionally allocated to said satellite and whose acquisition is validated according to the operational model of said satellite over the time window.

2. The method (10) according to claim 1, wherein: - the provisional allocation step (S12) is carried out by at least one provisional allocation server (61) not having access to the operational models of all satellites (30), the at least one provisional allocation server (61) carrying out a global allocation of the elementary areas to the satellites (30), - for at least one satellite (30): the feasibility assessment step (S13) and the definitive allocation step (S14) are carried out by a definitive allocation server (62), distinct from the at least one provisional allocation server (61), having access to the operational model of said at least one satellite.

3. The method (10) according to claim 2, wherein the at least one provisional allocation server (61) does not have access to any satellite operational model.

4. The method (10) according to claim 2 or 3, wherein several definitive allocation servers (62) are implemented, each definitive allocation server (62) having access to the operational models of only a portion of the satellites.

5. The method (10) according to any one of claims 1 to 4, wherein the elementary areas to be allocated are stored in a database and, after the provisional allocation of each elementary area, when the acquisition of an elementary area which is provisionally allocated to a satellite is not validated according to the operational model of said satellite, over the time window, said elementary area is maintained in the database as an unallocated elementary area.

6. The method (10) according to claim 5, wherein an elementary area maintained in the database as an unallocated elementary area is again provisionally allocated to a satellite having an acquisition opportunity over a subsequent time window.

7. The method (10) according to any one of claims 1 to 6, wherein the satellites belong to the same constellation and a footprint of the observation instrument is of the same shape and the same dimensions for each satellite of the constellation.

8. The method (10) according to any one of claims 1 to 6, wherein the satellites belong to at least two different constellations, a footprint of the observation instrument is of the same shape and the same dimensions for each satellite of the same constellation, the footprints of observation instruments being of different shapes and / or dimensions for satellites of different constellations.

9. The method (10) according to claim 8, wherein the elementary areas of the same observation to be carried out are allocated to satellites of the same constellation.

10. The method (10) according to any one of claims 1 to 9, wherein the preliminary model models the attitude manoeuvres of a satellite depending on a predefined duration of attitude manoeuvre of the satellite, independent of the attitude manoeuvre to be carried out in order to perform the acquisition.

11. The method (10) according to any one of claims 1 to 10, wherein the preliminary model models the acquisitions of a satellite depending on at least one of: - a predefined acquisition duration of the satellite observation instrument, independent of the acquisition to be carried out, - a predefined acquisition duration of the observation instrument per unit area, - a predefined time margin which depends on a priority of the request for the observation associated with the elementary area.

12. The method (10) according to any one of claims 1 to 11, wherein the preliminary model is used to estimate for each satellite a resource load plan of said satellite over the time window and wherein the provisional allocation of an elementary area to a satellite having an opportunity to acquire said elementary area includes determining, depending on the preliminary model and depending on the elementary areas which are already provisionally allocated to said satellite, whether said elementary area to be allocated can be provisionally allocated to said satellite taking into account the estimated load plan of said satellite over the time window.

13. The method (10) according to any one of claims 1 to 12, wherein the provisional allocation includes, after determining all acquisition opportunities for all elementary areas: - a scheduling of the elementary areas to be allocated depending on at least one predetermined ordering parameter and, - a successive processing of the elementary areas according to the scheduling order and, for each elementary area processed: a classification of the acquisition opportunities depending on at least one predetermined classification parameter and an assignment of the elementary area to a satellite depending on the order of classification of the acquisition opportunities and the preliminary model.

14. The method (10) according to claim 13, wherein the at least one parameter for scheduling the elementary areas is at least one of the following parameters: - a priority of the request for the observation associated with said elementary area, - meteorological conditions expected for the time window in the elementary area, - meteorological conditions required for the acquisition of the elementary area, - a useful surface area of the elementary area, - an expiry date of a request for the observation associated with said elementary area, - a date of receipt of a request for the observation associated with said elementary area, - a frequency or a number of acquisitions of the geographical area of the observation request.

15. The method (10) according to any one of claims 13 to 14, wherein the at least one parameter for classifying the acquisition opportunities is at least one of the following parameters: - weather conditions expected for the acquisition opportunity, - a start date of the acquisition opportunity, - a date of recovery of an image acquired during the acquisition opportunity, - a satellite pointing parameter during the acquisition opportunity, - a number of other acquisition opportunities towards other elementary areas.

16. The method (10) according to any one of claims 1 to 15, wherein the elementary areas which are definitively allocated to a satellite correspond to a set of elementary areas, among the elementary areas which are provisionally allocated to said satellite, for which it is possible to calculate, depending on the operational model, a work plan executable by said satellite and allowing carrying out the acquisition of all elementary areas of the set when said work plan is executed by said satellite.

17. A computer program product including a set of program code instructions which, when executed by at least one processor, configure said at least one processor to implement an allocation method (10) according to any one of claims 1 to 16.

18. A system (60) for allocating requests for observations of geographic areas (ZG) to be carried out to a plurality of satellites (30), each satellite including an observation instrument, said allocation system including means configured to implement an allocation method (10) according to any one of claims 1 to 16.

19. The allocation system (60) according to claim 18, including: - at least one provisional allocation server configured to provisionally allocate the elementary areas to be acquired, and - at least one definitive allocation server, distinct from the at least one provisional allocation server, configured to definitively allocate the elementary areas to be acquired.

20. The allocation system (60) according to claim 19, wherein the at least one provisional allocation server does not have access to the operational models of all satellites (30).

21. A system for acquiring Earth images by a plurality of satellites (30), including: - an allocation system (60) according to any one of claims 18 to 20, - means for transmitting work plans to the satellites, the work plan of a satellite allowing configuring said satellite to carry out the acquisitions of the elementary areas which are definitively allocated to said satellite, - means for receiving images, acquired by the satellites, representing the elementary areas.