Method of observing a planet using observation satellites orbiting the planet

The present invention relates to the field of the observation of a planet using observation satellites in orbit around the planet.

An observation satellite orbiting a planet may be in a stationary orbit, in which case the observation satellite is stationary relative to the surface of that planet, or in scrolling orbit, in which case the observation satellite is in movement relative to the surface of this planet.

An observation satellite in stationary orbit makes it possible to continuously observe a fixed area of ​​the planet. This fixed zone is limited to a disc, or more precisely a spherical cap of the surface of the planet.

A scrolling orbit satellite revolves around the planet by observing an observation area (generally called the "swath") that moves on the planet along a trajectory corresponding to a projected from the orbit of the scrolling orbiting satellite. on the surface of the planet. Each zone observed by the observation satellite in scrolling orbit is observed at a frequency called the revisit frequency.

One of the aims of the invention is to provide an observation method which makes it possible to collect reliable and complete data in terms of space and time.

To this end, the invention provides a method of observing a planet implemented by computer, the method comprising:

a step of calculating first predicted observation data for a first area of ​​interest and a first time period during which the first area of ​​interest has not been observed by a first observation satellite in scrolling orbit, in function of second observation data acquired by the second observation satellite in stationary orbit, for the first area of ​​interest and during said first time period, and / or of first observation data acquired by the first observation satellite , for first observation zones situated close to the first zone of interest and during said first time period, and of reference observation data previously recorded in a database; and or

a step of calculating second predicted observation data, for a second area of ​​interest and a second time period during which the area of ​​interest has not been observed by the second observation satellite in stationary orbit, in function of first observation data acquired by the first observation satellite in scrolling orbit for the second area of ​​interest and during said second time period, and of reference observation data previously recorded in the database.

The constitution of a database containing pre-recorded reference observation data makes it possible to predict, for example by machine learning, what types of first observation data and / or second observation data could have been observed, then that these data are missing.

It is thus possible, when one has first observation data but no second observation data, to predict second observation data which could have been observed by the second observation satellite and / or, when second observation data is available but no first observation data, to predict first observation data which could have been observed by the first observation satellite, in particular when the reference observation data contain joint observations, each joint observations comprising first observation data and second observation data acquired for the same joint observation area and the same joint observation time period.

The constitution of such a database also makes it possible to determine, for example by machine learning, the first observation data which could have been observed by a satellite in scrolling orbit in an area of ​​interest which was not observed. by this moving orbiting satellite for a given time period, as a function of first observation data acquired by the moving orbiting satellite during the given time period in observation areas located near the area of ​​interest, and reference observation data previously recorded in the database, in particular as a function of first reference observation data or as a function of joint reference observations.

It is thus possible to reconstitute observation data for an extended area from first observation data relating to first observation areas not completely covering the extended area.

In particular embodiments, the observation method can comprise one or more of the following optional characteristics:

- updating the database with data from observations made by the first observation satellite and / or the second observation satellite;

- updating the database with joint observations made by the first observation satellite and the second observation satellite;

- the baseline observation data contains joint baseline observations, each joint observation including first data

observation and second observation data acquired for the same joint observation zone and in the same joint observation temporal period;

- each calculation step is carried out by a predictive algorithm updated by machine learning as a function of the reference observation data previously recorded in the database for at least one area of ​​interest observed jointly by the first observation satellite and the second observation satellite;

- the second observation data make it possible to detect meteorological phenomena in the planet's atmosphere, variations in the composition of the atmosphere, variations on the surface or inside the planet, and variations in electric fields , electromagnetic, gravitic and quantum whatever the wavelengths;

- the first observation data make it possible to detect meteorological phenomena on the surface of the planet, variations in the composition of the atmosphere, variations on the surface or inside the planet and variations in electric and electromagnetic fields , gravitic and quantum whatever the wavelengths;

an observation satellite comprises at least one onboard image sensor.

each image sensor operates in any wavelength range, for example one or more among visible wavelengths, infrared wavelengths and microwaves;

an observation satellite has at least one radar sensor (56) on board, for example a synthetic aperture radar sensor; and

- the planet is Earth.

The invention also relates to a system for observing a planet configured for implementing the observation method as defined above, the observation system comprising a first observation satellite in scrolling orbit and a second observation satellite in stationary orbit, a database in which are stored the data of reference observations, and a computer on which is installed a prediction algorithm configured to implement each calculation step during its execution by the 'computer.

The invention also relates to a computer program product comprising code instructions for implementing an observation method as defined above.

The invention and its advantages will be better understood on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

- Figure 1 is a schematic view of observation satellites of a satellite observation system of a planet;

- Figure 2 is a schematic view of the satellite observation system;

- Figures 3 to 6 are schematic views illustrating areas of interest located between observation areas.

In Figure 1, a satellite observation system 2 configured for the observation of a planet 4 has a first observation satellite 6 in scrolling orbit around the planet 4 and a second observation satellite 8 in stationary orbit around planet 4.

Planet 4 has an axis of rotation A and turns on itself around this axis of rotation A. The axis of rotation A passes through two points of planet 4, which are two diametrically opposed points of planet 4. La planet 4 is for example the Earth.

The first observation satellite 6 is in motion relative to the surface of the planet 4 and observes at a given moment a first observation zone 10, this first observation zone 10 (the swath) moving on the surface of the planet 4 along a trajectory 11 which is a projection of the orbit of the first observation satellite on the surface of the planet.

Each first observation zone 10 observed by the first observation satellite 6 is observed with a frequency called the revisit frequency. Due to the rotation of the planet 4, the first observation satellite 6 does not pass again over the same observation zones at each revolution of the first observation satellite around the planet.

In the example illustrated, the first observation satellite 6 moves in a substantially polar low orbit, ie located in a plane containing the axis of rotation A or making a small angle with the axis of rotation A. The frequency of revisit is then a multiple of the frequency of rotation of the first observation satellite 6 around planet 4.

As a variant, the first observation satellite 6 moves in a low non-polar orbit, for example of equatorial or other type.

The second observation satellite 8 is stationary relative to the surface of the planet 4, and continuously observes the second fixed observation zone 12 of the planet 4. The second observation satellite 8 rotates around the planet 4 at the same speed as the rotation of planet 4 around its axis of rotation A.

The orbit of the second observation satellite 8 is located for example in an equatorial plane.

As illustrated in Figure 2, the first observation satellite 6 acquires first observation data 16 and the second observation satellite 8 acquires second observation data 18.

The first observation data 16 and the second observation data 18 are for example of different types. As a variant, they can be of the same type.

The first observation data 16 make it possible for example to detect a first type of phenomenon and the second observation data 18 make it possible to detect a second type of phenomenon distinct or identical to the first type of phenomenon.

When the first type of phenomenon and the second type of phenomenon are distinct, the phenomena of the first type and of the second type are preferably linked.

By “phenomena of related types” is meant that the occurrence of a phenomenon of the first type in an area may be accompanied by the occurrence of a phenomenon of the second type in this same area.

The satellite observation system 2 includes a computer 30 configured to execute a computer-implemented prediction algorithm 32.

The computer 30 comprises for example a processor 34 and a memory 36 in which the prediction algorithm 32 is stored, the prediction algorithm 32 having code instructions that can be executed by the processor 34 and configured to carry out an observation method. when the algorithm is executed by processor 34.

The satellite observation system 2 comprises a database 38 in which are recorded reference observation data.

The reference observation data comprises, for example, first reference observation data and / or second reference observation data.

The first reference observation data and / the second reference observation data contained in the database 38 have been acquired by the first observation satellite 6, the second observation satellite 8, and / or one or more several other observation satellites of the satellite observation system 2, each of these other satellites being configured to collect first observation data and / or second observation data.

In other words, the database 38 is supplied with observation data by the first observation satellite 6, the second observation satellite 8 and / or by other satellites configured to acquire the same types of data from. observation.

Advantageously, the reference observation data comprise joint reference observations 40, each joint reference observation 40 comprising first reference observation data 42 and second reference observation 44 acquired jointly, ie in the same period. time of joint observation and for the same joint observation area.

The temporal period of joint observation is a duration which depends on the speed of variation of the observed phenomena. This period can be very short - 1 second - for fast natural phenomena (for example for gusts of winds) to a few minutes (clouds), a few hours or even days in the case of slower phenomena (for example erosion), to years (for example variation of the magnetic field of the planet).

The first reference observation data 42 and the second reference observation data 44 of each joint reference observation 40 were acquired jointly by the first observation satellite 6 and the second observation satellite 8, or by d other observation satellites of the satellite observation system 2, each of these other satellites being configured to collect first observation data and / or second observation data.

In other words, the database 38 is fed with joint observations by the first observation satellite 6 and the second observation satellite 8 and / or by other satellites configured to acquire the same types of data from. observation.

The prediction algorithm 32 is configured to implement an observation method from first observation data 16 acquired by the first observation satellite 6 and / or from second observation data 18 acquired by the second satellite observation 8.

The observation process includes:

a step of calculating first predicted observation data 46 for a first area of ​​interest and a first time period during which the first area of ​​interest has not been observed by a first observation satellite 6, as a function of , on the one hand, second observation data 18 acquired by the second observation satellite 8, for the first area of ​​interest and during said first time period, and / or first observation data 16 acquired by the first observation satellite 6, for first observation zones located near the first zone of interest and during said first time period, and, on the other hand, reference observation data previously recorded in the database 38, for example based on joint observations 40; and or

a step of calculating second predicted observation data 48, for a second area of ​​interest and a second time period during which the area of ​​interest has not been observed by the second observation satellite, as a function of first observation data 16 acquired by the first observation satellite 6 for the second area of ​​interest and during said second time period, and reference observation data previously recorded in the database 38, for example based on Joint Benchmark Observations 40.

The calculation of the first predicted observation data 46 and / or of the second predicted observation data 48 is for example based on a machine learning carried out by the predictive algorithm 32 from the reference observation data in the database. data 38, for example according to the joint reference observations 40 previously recorded in the database 38.

The multitude of reference observations pre-recorded in the database 38 makes it possible to predict which first observation data and / or which second observation data could have been observed in an area of ​​interest and in a given time period while the 'we do not have, or at least not completely, these first observation data and / or these second observation data for the area of ​​interest.

In particular, prerecorded joint reference observations 40 make it possible, by machine learning, to know what type of first observation data should be observed in the presence of second observation data 18 acquired by the second observation satellite 8 in the period considered, to know what type of second observation data should be observed in the presence of first observation data 16 acquired by the first observation satellite 6 in the time period considered, and / or to predict which first observation data observation should be observed by the first observation satellite 6 in an area of ​​interest based on first observation data acquired by the first observation satellite 6 in observation areas located nearby.

The observation method comprises for example the calculation of first observation data 46 predicted for a first area of ​​interest 50 and a first time period during which the first area of ​​interest 50 has not been observed by the first satellite. observation 6, no first observation data 16 acquired by the first observation satellite 6 therefore not being available for the time period considered.

Thus, despite the absence of first observation data 16 acquired by the first observation satellite 6 for the first area of ​​interest 50 in the first time period considered, the prediction algorithm 32 provides first observation data 46 predicted.

The prediction algorithm 32 associated with the database 38 containing joint reference observations 40 thus makes it possible to predict what could have been observed by the first observation satellite 6 in the first area of ​​interest 50 and in the first period of time considered during which the first observation satellite 6 did not observe this first zone of interest 50.

As illustrated in FIG. 3, the first observation satellite 6 successively observes a series of first observation zones 10 distributed over the surface of the planet along the trajectory of the first observation satellite 6.

The second observation satellite 8 continuously observes the second observation zone 12 fixed on the surface of the planet 4 observed.

Due to the rotation of the planet 4 around its axis of rotation A and the moving orbit of the first observation satellite 6, the trajectory of the first observation satellite 6 periodically passes above the second zone of observation 12, so that the first observation zones 10 are located in the second observation zone 12.

The first observation satellite 6 observes for example two successive observation bands 52 separated by an unobserved band 54 which is not observed by the first observation satellite 6 during the time period separating the observations of the two bands of. observation 52 successive.

The distance between the two successive observation bands 52 may correspond to the rotation of the planet 4 observed between the two passages of the first observation satellite 6.

Thus, by considering a first area of ​​interest 50 located in this unobserved band 54, no first data 16 has been acquired for this first area of ​​interest 50 in a time period situated between the two successive passages of the first satellite d. observation 6. On the other hand, second data 18 were acquired by the second observation satellite 8.

The observation method implemented by the prediction algorithm 32 makes it possible to predict first predicted observation data 46 corresponding to what could have been observed by the first observation satellite 16, as a function of the second data of observation 18 acquired by the second observation satellite 8 during the time period considered.

A prediction can be made for first zones of interest 50 located in the second fixed observation zone 12 and which have not been observed by the first observation satellite 6 during successive passages from the first observation satellite 6 to the above this second observation zone 12, so as to predict first predicted observation data 46 for these first zones of interest 50 and thus reconstruct first observation data 16, 46 acquired or predicted for the whole of the second fixed observation zone 12.

Thus, although the first observation satellite 6 does not cover the whole of the second observation zone 12 in a determined time period, it is possible to obtain first observation data 16, 46 acquired or predicted for the whole of the second observation zone 12 fixed.

As illustrated in FIG. 4, it is possible that the frequency of acquisition of the first observation data 16 by the first observation satellite 6 is such that two first observation zones 10 observed successively by the first observation satellite 6 along its scrolling orbit is spaced apart by a first zone of interest 50 not observed by the first observation satellite 6 in the first time period situated between the observations of the two successive first observation zones 10.

In other words, the first observation satellite 6 observes the planet surface 4 by acquiring first observation data 16 for a succession of first discrete observation zones 10 alternating with unobserved zones, during the same revolution of the first observation satellite 6 around planet 4.

It is also possible that the acquisition of first data 16 by the first observation satellite 6 is momentarily interrupted, so that there is a first unobserved area of ​​interest 50 separating two first observation areas 10 observed successively by the first observation satellite 6 during the same revolution of the first observation satellite 6 around planet 4.

Also, in an exemplary embodiment, the observation method comprises the calculation of first predicted observation data 46 for a first area of ​​interest 50 located between two first observation areas 10 successively observed by the first observation satellite. 6 during the same revolution of the first observation satellite 6 around the planet 4, the first area of ​​interest 50 not having been observed by the first observation satellite 6.

As also illustrated in Figure 4, the observation method alternatively or optionally comprises the calculation of first predicted observation data 46 for a first area of ​​interest 51 which is located in the second observation area 12, which was not observed by the first observation satellite 6 during a first period of time during which the first observation satellite 6 observed first observation zones 10 located in the second observation zone 12, the first zone of interest 51 not being located in any of the alignments of first observation zones 10 of the successive passages of the first observation satellite 6 above the second observation zone in the first time period.

The first observation zones 10 are located along lines corresponding to the successive passages of the first observation satellite 6 above the second observation zone 12, the first zone of interest 51 being located outside these lines.

The observation method thus makes it possible, by combining first areas of interest 50 and 51, to reconstitute what the first observation satellite 6 would have observed during a determined period of time over an extended area for which the first observation satellite 6 acquired first observation data 16 only in first observation zones 10 located in the extended zone by being spaced from each other.

In other words, from parcel data in the extended area, it is thus possible to predict first observation data for the whole of the extended area.

As illustrated in FIG. 5, the first observation satellite 6 observes first observation zones 10 which are located outside the second fixed observation zone 12 observed continuously by the second observation satellite 8, and for which the second observation satellite 8 does not acquire first observation data 18.

In an exemplary embodiment, the observation method comprises the calculation of second predicted observation data 48 for a second area of ​​interest 55, 57 not observed by the second observation satellite 8 during a second time period considered, in function:

- on the one hand, first observation data 16 acquired by the first observation satellite 6 during the second time period considered, for example for the second area of ​​interest 55, and

- on the other hand, of reference observation data previously recorded in the database 38, in particular of joint reference observations 40 previously recorded in the database 38.

This makes it possible to calculate second predicted observation data 48 in second areas of interest 55 not observed by the second observation satellite 8, and thus to virtually enlarge the second observation area 12 covered by the second satellite d. observation 8.

As illustrated in Figure 5, an area of ​​interest 55 may coincide with an observation area 10 of the first observation satellite 6 observed by the latter during the second time period, in which case the second predicted observation data 46 is calculated as a function of first observation data acquired for the area of ​​interest 55, or an area of ​​interest 57 may be distinct from the observation areas 10 of the first observation satellite 6 observed by the latter during the second time period .

As illustrated in FIG. 6, in a first time period, the first observation satellite 6 acquires first observation data 16 for first observation zones 10 which are situated in an extended zone 60. The first zones of observation 10 are here aligned along parallel observation lines 62 corresponding to successive passages of the first observation satellite 6 above the extended zone 60. The observation lines 62 are spaced apart from each other. The first observation zones 10 of each observation line 62 are spaced apart (as illustrated) or contiguous.

In an exemplary embodiment, the observation method comprises the calculation of first predicted observation data 46 for at least one area of ​​interest 64 adjacent to one or more observation areas 10 and for the time period considered, as a function of first observation data 16 acquired by the first satellite and reference observation data previously recorded in the database 38.

In one embodiment, the reference observation data previously recorded in the database 38 and taken into account for the calculation of the first predicted observation data 46 are exclusively first reference observation data. In this case, the database 38 can only include first reference observation data.

As a variant, the reference observation data previously recorded in the database 38 and taken into account for the calculation of the first predicted observation data 46 comprise first observation data of

reference and second reference observation data. This makes it possible to have more data which allows better learning.

In a particular exemplary embodiment, the reference observation data previously recorded in the database 38 and taken into account for the calculation of the first predicted observation data 46 comprise or consist of joint reference observations 40. This is favorable to the learning and the reliability of the prediction.

This calculation is carried out in particular without taking into account the second observation data 18 acquired by the second observation satellite 8 during the same time period as the first observation data 16 acquired for the first observation zones 10. The extended zone 60 is for example separate from the second observation zone 12.

Indeed, the collection of joint reference observation data 40, in particular associated with machine learning, makes it possible to predict first predicted observation data 46 for areas of interest not observed solely from first data d. observations acquired 16 for adjacent observation areas 10.

The method makes it possible to reconstruct first observation data for the extended area 60 from first observation data acquired for first observation areas 10 located in the extended area 60 and covering only a part of the extended area 60.

The first observation satellite 6 and the second observation satellite 8 each comprise one or more sensor (s) configured to acquire the observation data.

In an exemplary embodiment, the first observation data 16 are acquired by at least one radar sensor 56 on board the first observation satellite 6, for example a synthetic aperture radar sensor.

In an exemplary embodiment, the first observation data 16 make it possible to determine a wind field at the surface of the planet. Indeed, a radar sensor, in particular a synthetic aperture radar sensor makes it possible for example to determine the surface state of a body of water, for example the sea, which makes it possible to deduce the direction and / or the force of the winds circulating on the surface of this body of water.

In an exemplary embodiment, the second observation data 18 are provided by at least one image sensor 58 on board the second observation satellite 8.

Each image sensor 58 can operate in any wavelength range.

Each image sensor 58 operates for example in one or more wavelength ranges from visible wavelengths, infrared wavelengths and microwaves.

The second observation data 18 make it possible to determine the presence of meteorological phenomena in the atmosphere. A meteorological phenomenon is characterized, for example, by the shape, the dimensions, the rate of variation of the shape and / or the rate of variation of the dimensions of clouds present in the atmosphere above the observed zone.

Indeed, certain forms and / or areas of clouds are characteristic of particular meteorological phenomena. For example, the Cumulonimbus, which are generally the seat of thunderstorms, are clouds having a characteristic shape (anvil) with a large vertical extent evolving rapidly.

In addition, the presence of certain meteorological phenomena is associated with particular winds on the surface of the planet. For example, a Cumulonimbus cloud generates ascending and descending winds, with areas of strong horizontal wind.

The joint reference observations 40 crossing first wind observation data 42 and second observation data 44 relating to meteorological phenomena make it possible to associate the winds with the meteorological phenomena which generate them.

It is then possible to predict a wind field on the surface of the planet 4 as a function of second data 18 acquired by the second observation satellite 8 and relating to the meteorological phenomena acquired by the second observation satellite 8 in a first zone of interest 50 and in a first time period for which the first observation satellite 6 has not provided first observation data 16.

Conversely, it is possible to predict a meteorological phenomenon as a function of first observation data 16 relating to the winds acquired by the first observation satellite 6 in a second area of ​​interest 55 and in a second time period for which the second satellite Observation 8 did not provide second observation data 18.

In a preferred embodiment, the observed planet is Earth. In this case, the first observation satellite is for example an observation satellite of SENTINEL, TerraSAR, CloudSat ... type and / or the second observation satellite is for example an observation satellite of Meteosat, Himawari type , Goes ...

The invention is not limited to the observation of winds and meteorological phenomena on the surface of the Earth.

The invention applies to other observable phenomena, for example phenomena of erosion of coastlines or mountain ranges, the evolution of vegetation, the type of soil, the phenomena and waves of seismic origins, changes altitude of land by settlement, collapse or eruption, etc., on the surface or inside the Earth or any other planet.

Thus, the first observation data and / or the second observation data make it possible, for example, to determine variations in the composition of the atmosphere, variations at the surface or inside the planet and variations in electric fields. , electromagnetic, gravitic and quantum, whatever the wavelengths.

For such phenomena whose evolutions are more or less rapid, the duration of the temporal period of joint observation is for example between one second (gust of winds, seismic waves) to several hours (wet surfaces), to several days ( vegetation, erosion, changes in elevation of land by settlement, collapse or eruption) or years (variation of magnetic fields for example).

The invention is based on machine learning from reference observation data previously recorded in the database 38. These reference observation data may comprise first reference observation data, second observation data. baseline observation and / or joint baseline observations. In particular embodiments, each calculation step is performed as a function of first reference observation data, second reference observation data and / or joint reference observations.

CLAIMS

1.- A method of observing a planet implemented by computer, the method comprising:

- a step of calculating first predicted observation data (46) for a first area of ​​interest (50, 51, 64) and a first time period during which the first area of ​​interest has not been observed by a first observation satellite (6) in scrolling orbit, depending on:

- second observation data (18) acquired by a second observation satellite (8) in stationary orbit, for the first area of ​​interest (50, 51, 64) and during said first time period, and / or first observation data (16) acquired by the first observation satellite (6), for first observation areas (10) located near the first area of ​​interest (50, 51, 64) and during said first time period, and;

- reference observation data (40) previously recorded in a database; and or

- a step of calculating second predicted observation data (48), for a second area of ​​interest (55) and a second time period during which the area of ​​interest (55) was not observed by the second observation satellite (8) in stationary orbit, depending on:

- first observation data (16) acquired by the first observation satellite (6) in scrolling orbit and during said second time period, and

- reference observation data (40) previously recorded in the database.

2.- An observation method according to claim 1, comprising updating the database (38) with observation data (16, 18) made by the first observation satellite (6) and / or the second observation satellite (8).

3.- The observation method according to claim 1 or 2, wherein the reference observation data (40) contain joint reference observations, each joint reference observation comprising first observation data and second data d. 'observation acquired for the same area

joint observation and one in the same time period of joint observation.

4.- Observation method according to any one of the preceding claims, each calculation step is carried out by a predictive algorithm updated by machine learning as a function of the reference observation data pre-recorded in the database for at least an area of ​​interest observed jointly by the first observation satellite (6) and the second observation satellite (8)

5.- Observation method according to any one of the preceding claims, in which the second observation data (16, 46) make it possible to detect meteorological phenomena in the planet's atmosphere, variations in the composition of the planet. atmosphere, variations on the surface or inside the planet, and variations in electric, electromagnetic, gravitic and quantum fields whatever the wavelengths.

6.- Observation method according to any one of the preceding claims, in which the first observation data (18, 48) make it possible to detect meteorological phenomena at the surface of the planet, variations in the composition of the atmosphere. , variations on the surface or inside the planet and variations in electric, electromagnetic, gravitic and quantum fields whatever the wavelengths.

7. Observation method according to any one of the preceding claims, in which an observation satellite (8) comprises at least one onboard image sensor (58).

8. Observation method according to claim 7, wherein each image sensor operates in any wavelength range, for example one or more of visible wavelengths, infrared wavelengths and microwaves.

9. Observation method according to any one of the preceding claims, in which an observation satellite (6) has at least one radar sensor (56) on board, for example a synthetic aperture radar sensor.

10. Observation method according to any one of the preceding claims, in which the planet is Earth.

1 1 .- Observation system of a planet configured for the implementation of the observation method according to any one of the preceding claims, the observation system (4) comprising a first observation satellite (6) in scrolling orbit and a second observation satellite (8) in stationary orbit, a database (38) in which the reference observation data (40) are stored, and a computer (30) on which is installed a prediction algorithm (32) configured to implement each calculation step as it is executed by the computer (30).

12. A computer program product comprising code instructions for implementing an observation method according to any one of claims 1 to 10.