Satellite method and system for detecting a floating layer on a sea surface to be monitored

Abstract

A method and system for detecting a floating layer on a surveillance area of the sea surface, a site of interest being placed in or around the surveillance area. The method comprises the following steps: a) satellite measurement of a radar feedback return, the radar signal being emitted by a satellite toward the sea surface of the surveillance area; b) recognition of at least one swell profile of the sea surface in accordance with the satellite measurements; c) identification of the fluid properties corresponding to the recognized swell profiles; and d) emission of a warning when the fluid properties identified for one of the recognized profiles correspond to a sea surface that includes undesirable elements for the site of interest.

Claims

1. A method for detecting a floating layer on a surveillance area of a sea surface, a site of interest being located in or at the edge of the surveillance area, the method comprising: a) satellite measurements of a returned radar signal, the radar signal being transmitted by a satellite toward the sea surface of the surveillance area; b) recognition of a swell profile of the sea surface, based on the satellite measurements; c) identification of fluid properties corresponding to the recognized swell profile; and d) emission of a warning when the fluid properties identified for one of the recognized profiles correspond to a sea surface comprising elements belonging to a predefined set of elements that are undesirable for the site of interest, wherein, in b), a boundary of the swell profile is further recognized in the surveillance area, the boundary corresponding to localized variations in levels of the satellite measurements greater than a predefined variation threshold; wherein the recognized swell profile corresponds to a set of measurements among the satellite measurements whose level varies according to a same wavelength and a same amplitude, the set of measurements being delimited at least in part based on the recognized boundary; and wherein, in c), the fluid properties of the recognized swell profile are identified by: determining a volume fraction as a function of: a damping coefficient of swell amplitude at the boundary, a number of waves at the boundary, determined from the wavelength of the recognized swell profile, identifying a first volume fraction among predefined volume fractions that is closest to the determined volume fraction, the predefined volume fractions being associated with predetermined fluid properties; and associating the recognized swell profile with the predetermined fluid properties of the identified first volume fraction.

2. The method according to claim 1, wherein dimensions of the surveillance area are based on at least one parameter among: speeds of the ocean currents; a tidal coefficient; weather conditions; a predetermined surveillance frequency; and frequency at which the satellite passes over the surveillance area.

3. The method according to claim 1, wherein the recognized swell profile corresponds to a subset of measurements among the set of measurements having substantially a same level.

4. The method according to claim 3, wherein, in the surveillance area: a first swell profile is recognized from a set of measurements among the satellite measurements of substantially a same first level, a second swell profile is recognized from a set of measurements among the satellite measurements of substantially a same second level, wherein the first level and the second level are compared, and wherein the swell profile corresponding to a lower of the compared levels among the first swell profile and the second swell profile is associated with the fluid properties of a sea surface having elements belonging to a predefined set of elements that are undesirable for the site of interest.

5. The method according to claim 1, wherein the volume fraction is also a function of a surface tension of the sea surface corresponding to the recognized swell profile.

6. The method according to claim 1, wherein the predefined volume fractions correspond to volume fractions observed, in known weather conditions, for sea surfaces having identified floating bodies.

7. The method according to claim 1, wherein the recognized boundary is compared to a bathymetric mapping of the surveillance area.

8. The method according to claim 1, further comprising: determining movement of the swell profile corresponding to a sea surface comprising elements belonging to a predefined set of elements that are undesirable for the site of interest, the movement determination being based on pre-established hydrodynamic models of the surveillance area or on hydrodynamic models from sources of information about the hydrodynamic conditions of the surveillance area.

9. A detection system for detecting a floating layer in a surveillance area of a sea surface, a site of interest being located in or at the edge of the surveillance area, the system comprising at least: a satellite configured to: transmit a radar signal toward the sea surface of the surveillance area; measure a return signal of the transmitted radar signal; communicate data concerning the measurement levels of the measured return signals; a management unit comprising: a communication interface configured to receive data communicated by the satellite, and a data processing unit configured to implement a method for detecting a floating layer on a surveillance area of a sea surface, a site of interest being located in or at the edge of the surveillance area, the method comprising: a) satellite measurements of a returned radar signal, the radar signal being transmitted by a satellite toward the sea surface of the surveillance area; b) recognition of a swell profile of the sea surface, based on the satellite measurements; c) identification of fluid properties corresponding to the recognized swell profile; and d) emission of a warning when the fluid properties identified for one of the recognized profiles correspond to a sea surface comprising elements belonging to a predefined list of elements that are undesirable for the site of interest; wherein, in b), a boundary of the swell profile is further recognized in the surveillance area, the boundary corresponding to localized variations in levels of the satellite measurements greater than a predefined variation threshold; wherein the recognized swell profile corresponds to a set of measurements among the satellite measurements whose level varies according to a same wavelength and a same amplitude, the set of measurements being delimited at least in part by the recognized boundary; and wherein, in c), the fluid properties of the recognized swell profile are identified by: determining a volume fraction as a function of: a damping coefficient of swell amplitude at the boundary, a number of waves at the boundary, determined from the wavelength of the recognized swell profile, identifying a first volume fraction among predefined volume fractions that is closest to the determined volume fraction, the predefined volume fractions being associated with predetermined fluid properties; and associating the recognized swell profile with the predetermined fluid properties of the identified first volume fraction.

10. The detection system according to claim 9, further comprising a database configured for storing data relating to: predefined volume fractions corresponding to volume fractions observed, in known weather conditions, for sea surfaces having identified floating bodies; and/or a bathymetric mapping of the surveillance area.

11. A non-transitory computer readable storage medium, having stored thereon a computer program comprising program instructions, the computer program being loadable into a data-processing unit and adapted to cause the data-processing unit to carry out a method for detecting a floating layer on a surveillance area of a sea surface, a site of interest being located in or at the edge of the surveillance area, the method comprising: a) satellite measurements of a returned radar signal, the radar signal being transmitted by a satellite toward the sea surface of the surveillance area; b) recognition of a swell profile of the sea surface, based on the satellite measurements; c) identification of fluid properties corresponding to the recognized swell profile; and d) emission of a warning when the fluid properties identified for one of the recognized profiles correspond to a sea surface comprising elements belonging to a predefined set of elements that are undesirable for the site of interest; wherein, in b), a boundary of the swell profile is further recognized in the surveillance area, the boundary corresponding to localized variations in levels of the satellite measurements greater than a predefined variation threshold; wherein the recognized swell profile corresponds to a set of measurements among the satellite measurements whose level varies according to a same wavelength and a same amplitude, the set of measurements being delimited at least in part based on the recognized boundary; and wherein, in c), the fluid properties of the recognized swell profile are identified by: determining a volume fraction as a function of: a damping coefficient of swell amplitude at the boundary, a number of waves at the boundary, determined from the wavelength of the recognized swell profile, identifying a first volume fraction among the predefined volume fractions that is closest to the determined volume fraction, the predefined volume fractions being associated with predetermined fluid properties; and associating the recognized swell profile with the predetermined fluid properties of the identified first volume fraction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the invention will become apparent from the following detailed description and from the attached figures in which:

(2) FIGS. 1a and 1b illustrate an example of a system for detecting a floating layer according to the invention;

(3) FIG. 2 illustrates an exemplary satellite image of a coastline where a thermal power plant is installed, with a floating layer close to the plant;

(4) FIG. 3 is an exemplary sectional view of the swell of the sea surface at the floating layer;

(5) FIG. 4 is an exemplary graphical representation of the levels of measurements obtained by the satellite at the floating layer located in the surveillance area;

(6) FIG. 5 is an illustrative example of a floating layer of crude oil as seen from the sky;

(7) FIG. 6 is an example of a graphical representation of the levels of measurements obtained by the satellite at the floating layer of crude oil located in the surveillance area; and

(8) FIG. 7 is a flowchart composed of an exemplary sequence of steps in the detection method according to the invention.

(9) For clarity, the dimensions of the various elements represented in these figures are not in proportion to their actual dimensions. In the figures, identical references correspond to identical elements for the various embodiments described.

DETAILED DESCRIPTION

(10) We first refer to FIG. 1a which illustrates an embodiment of the system for detecting a floating layer according to the invention.

(11) In this example, the system S comprises a satellite SAT configured to: send a radar signal toward the sea M, and in particular toward a sea surface to be monitored; measure a return signal of the transmitted radar signal; communicate data concerning the measurement levels of the measured return signals.

(12) To this end, the satellite SAT may comprise a radar altimeter transmitter operating in a non-visible frequency range, emitting signals for example within a frequency between 12 and 18 GHz. The accuracy of the altimetric measurements is preferably 10 centimeters vertically and 1 meter horizontally in order to correctly detect the different swells at the water surface.

(13) In addition, the satellite SAT may include a communication module for sending measurement data to a management center CG. The center CG processes the data sent by the satellite in order to detect floating layers on the surface of the sea M.

(14) In this embodiment, the center CG is a separate entity. However, in other possible embodiments, the center CG may be directly embedded in the satellite or installed in a power plant.

(15) We first refer to FIG. 1b which represents the management center CG of the system S. The center CG may be a computer, comprising memory 102 for storing: instructions for implementing the method, satellite data received, and temporary data for implementing the various steps of the method as described above and as detailed below.

(16) The memory MEM may also store a database containing: predefined volume fractions corresponding to volume fractions observed in known weather conditions, for sea surfaces having identified floating bodies; and/or a bathymetric mapping of the surveillance area.

(17) The computer further comprises a data processing unit 104. This data processing unit may be a circuit, for example such as: a processor capable of interpreting instructions in the form of a computer program, or a circuit board in which the steps of the inventive method are defined in the silicon, or a programmable chip such as an FPGA (Field-programmable Gate Array).

(18) This computer has an input interface 106 for receiving satellite data, and an output interface 108 for supplying alerts to a remote device 110 upon detection of a floating layer. Finally, the computer may include a screen 112 and a keyboard 114, for easy user interaction. The keyboard is of course optional, for example in the context of a tablet computer with touchpad.

(19) The input interface 106 may receive hydrodynamic models from sources of information about the hydrodynamic conditions of the surveillance area, such as a server of an ocean monitoring center.

(20) Typically, the remote device 110 may be a monitoring platform of a power plant or a client terminal capable of receiving alerts from the center GC via the interface 108. To this end, the device 110 may comprise a communication interface capable of receiving data from the center CG and a data processing unit for interpreting them. Alerts received by the remote device 110 can thus be used by said device to anticipate potential clogging and/or blockages. As an illustrative example, a user can receive telephone alerts for a power plant he or she oversees. The user can then implement preventive actions to forestall the possibility of blockages (and thus the need to shut down the production of power by the plant). Various services may further be offered to users according to various possible interpretations of alerts by the remote device 110.

(21) In addition, the interface 106 may receive qualitative and quantitative data concerning weather conditions and winds. These data may, for example, come from an anemometer placed at or near the management center CG, or at least close to the region of the sea to be monitored and to the thermal power station. This data can be taken into account to refine the determination of the volume fraction corresponding to the altimetric measurements sent by the satellite.

(22) FIG. 2 shows an exemplary satellite image of a coastline where a thermal power station CT has been installed. The area monitored by the satellite is the surveillance area ZS, located close to the intake E to the cooling system of the plant CT.

(23) Using satellite measurements received by the management center CG, it is possible to detect altimetric variations at the surface of the sea M. A floating layer NF is currently present on the sea M. In this example, the layer NF is a cluster of jellyfish.

(24) At the edges of the layer NF, the swell of the sea M changes abruptly. The sudden variations in the swell at the edges form the distinctive boundaries LS.

(25) In FIG. 3, an exemplary cross-sectional view of the swell is represented on the surface of the sea M at the floating layer NF. The swell of the sea M has a regular wavelength and amplitude. The swell in the layer NF is different because of the presence of the floating bodies (jellyfish). In this example, there is almost no swell in the layer NF. The swell of the sea is rapidly dampened at the edges of the layer NC, forming distinctive boundaries which separate the swell profile of the sea from the swell profile of the layer.

(26) The distinctive boundaries LS are areas at the edges of the layers NF where a more pronounced damping of the swell is observed. This distinction is caused by a greater local viscosity of the fluid due to the presence of floating bodies (for example jellyfish or other).

(27) In FIG. 4, a graph shows the variation in the detection level N of the measurements as a function of the position x of the measurements in the surveillance area ZS. Satellite measurements of the returned radar signal have variations in the detection levels corresponding to the altimetric variations at the water surface.

(28) From the satellite measurements, the management center CG can recognize: a first swell profile and a second swell profile for sets of measurements P1 and P2 having levels respectively corresponding to the same swell characteristics (same wavelength and same amplitude); and distinctive boundaries LS that correspond to strong localized variations in the satellite measurement levels.

(29) Using the measurements made, a map of the mechanical properties of the swell is obtained for the surveillance area ZS.

(30) We now refer to FIG. 5 in which a floating layer NF of crude oil is illustrated.

(31) The layer of oil formed on the surface of the sea M affects the viscosity and surface tension, thereby altering the apparent roughness at the water surface.

(32) The layer NF has a lower roughness than the sea. The swell profiles can be differentiated by their respective roughnesses, which differ.

(33) In FIG. 6, a graph is represented which also shows, as in FIG. 4, the variation in the detection level N of the measurements as a function of the position x of the measurements in the surveillance area ZS.

(34) The variations in measurement levels oscillate between a first level N1 and a second level N2, depending on the location of the measurements in the area ZS. The first and second levels correspond to different roughnesses (surface wavelets of the swell) of the sea surface. As mentioned above, areas of high roughness return a strong radar echo to the satellite, and conversely, areas of low roughness reflect very little radar signal to the satellite.

(35) The swell profiles of the sea M and of the layer NF can thus be recognized via: a first set of measurements P1 substantially at the first level N1, corresponding to the swell profile of the sea M, and a second set of measurements P2 substantially at the second level N2, corresponding to the swell profile of the layer NF.

(36) We now refer to FIG. 7, which illustrates a flowchart composed of an exemplary sequence of steps in the method for detecting a floating layer.

(37) In step 700, the dimensions and location of the surveillance area ZS are defined (DEF (ZS)). The dimensions of the surveillance area may be determined based on parameters among the following: speeds of the ocean currents; a tidal coefficient; weather conditions; a desired surveillance frequency; and frequency at which the satellite passes over the surveillance area.

(38) The surveillance area is located above a site of interest such as power plant CT or at least at the edge of this site (for example at sea, off the coast near the power plant CT).

(39) In a step 702, the satellite SAT transmits radar signals to the sea surface of the surveillance area ZS and measures the level of the return signal (MES). Satellite measurements by radar allow obtaining a real-time spatial mapping of the sea surface (geometry of the waves). The raw information obtained from the satellite is the altimetry of the sea surface in the surveillance area. The resolution of this mapping is directly related to satellite performance. The choice of satellites used may consider as a parameter the desired resolution for the analysis of swell characteristics (amplitude and wavelength of the waves).

(40) In a step 704, the management center CG receives the satellite data concerning the measurements and interprets them so as to recognize at least one swell profile P of the sea surface (REC(P)). A swell profile may be recognized for a set of measurements corresponding to similar swell characteristics.

(41) To better differentiate between the different swell profiles that are present, rapid transition areas are identified in the surveillance area. These rapid transition areas form the distinctive boundaries LS of the swell profiles and correspond to pronounced localized variations in the satellite measurement levels. The identified distinctive boundaries define the transition between two different swell profiles.

(42) In addition, to ensure that the areas of rapid transition are not those inherent to shallow seas in the surveillance area, the recognized distinctive boundaries may be compared to a bathymetric mapping of the surveillance area. Cross-checking with the bathymetric mapping allows identifying and isolating changes to the swell caused by bathymetric refraction.

(43) This step of identifying distinctive boundaries from changes in the swell may be performed on the basis of visual examination, by an operator, of the altimetric mapping obtained using the satellite measurements for the surveillance area. This step may also be carried out by automatic processing that identifies the distinctive boundaries on the basis of the mechanical properties of the swell exceeding a spatial gradient criterion.

(44) Swell profile recognition may be carried out by identifying: a set of measurements of substantially the same level, the set of measurements being defined at least in part by the recognized distinctive boundaries, or a set of measurements for which the level varies by a same wavelength and a same amplitude, the set of measurements being defined at least in part by the recognized distinctive boundaries.

(45) In a step 706, the fluid properties PF corresponding to the swell profiles are identified (ID(PF)).

(46) When at least two swell profiles correspond to sets of measurements of substantially the same levels respectively, the first and second levels can be compared. Typically, in the example of FIG. 6, the first swell profile (corresponding to a set of measurements P1) is identified as the set of measurements of substantially the first level N1, and the second swell profile (corresponding to a set of measurements P2) is identified as the set of measurements of substantially the second level N2.

(47) Depending on the comparison of the levels, the first or second swell profile corresponding to the lower of the compared levels can be associated with fluid properties PF of a sea surface that includes undesirable elements for the site of interest. The other among the first and second profiles (corresponding to the higher of the levels) can be associated with fluid properties typically observed for an ocean surface in the open sea.

(48) When the swell profile corresponds to a set of measurements in which the level varies by a same wavelength and a same amplitude, the fluid properties of the at least one recognized swell profile are identified by: determining a volume fraction as a function of: a damping coefficient of amplitude a of the swell at the distinctive boundaries, a number of waves k at the distinctive boundaries, determined from the wavelength of the recognized swell profile, identifying the fraction among predefined volume fractions that is closest to the determined volume fraction, the predefined volume fractions being associated with predetermined fluid properties; and associating the recognized swell profile with the predetermined fluid properties of the predefined volume fraction identified as being closest to the determined volume fraction.

(49) The approach consists of linking the variations in the mechanical properties of the swell (swell damping) to the fluid properties of the sea surface, and for this purpose it may use fluid mechanics equations that are based on: the laws of conservation of energy (in the form of the relation between wave damping at the distinctive boundaries and fluid viscosity), an empirical relation, for mixtures in suspension, between the apparent viscosity and the concentration of solid particles.

(50) As for the laws of conservation of energy, swell damping by viscous dissipation can be determined using the following exponential law:
A=A.sub.0e.sup.x

(51) This relation allows calculating wave damping as a function of the amplitude of the waves detected for the recognized swell profile, a reference amplitude A.sub.0, and the width x of the distinctive boundaries LS.

(52) In practice, the damping coefficient is thus obtained by graphically measuring the damping of wave amplitude on the mapping of altimetric measurements.

(53) From the damping calculated at the separating boundaries, the viscosity of the swell profile can be calculated using a relation for gravity waves of the type:
=(4k.sup.3).sup.1

(54) In this relation, k is the number of swells k detected at the distinctive boundaries LS, corresponds to the damping calculated using the above relation, is the density of the fluid, and corresponds to the angular frequency of the swell.

(55) For some swell types (in particular low amplitude and low wavelength), the effects of surface tension are not insignificant and must be taken into account. According to another possible embodiment, the viscosity can then be calculated based on the effects of surface tension , as follows:

(56) $=\left(\frac{}{2k^2}\right)\left(\frac{g+3\frac{k^2}{}}{2{\left(\mathrm{kg}+\frac{k^3}{}\right)}^{1/2}}\right)$

(57) The viscosity of the sea surface corresponding to the swell profile can be used to characterize the viscosity of the mixture in suspension at the surface of seawater.

(58) To this end, one can use the case of a mixture in suspension with a density between the fluid (seawater) and the solid particles (marine organisms) that is considered to be constant. The viscosity of such a mixture in suspension (seawater/marine organisms) can be defined by:
.sub.s=.sub.r*.sub.l

(59) In this relation, .sub.s corresponds to the viscosity of the mixture, .sub.l corresponds to the viscosity of the seawater, and .sub.r is a relative viscosity (dimensionless).

(60) There are several empirical models for defining .sub.r as a function of the volume fraction of solid particles. For example, the Thomas empirical model is as follows:
.sub.r=1+2.5+10.05 .sup.2+Ae.sup..sup., where A=0.00273 and =16.6.

(61) There is also the Kitano model in which:

(62) ${}_r={\left(1-\left(\frac{}{A}\right)\right)}^{-2},$
where A=0.68 for spherical particles.

(63) Other similar models may also be used, such as the Krieger-Dougherty empirical model.

(64) From the relative viscosity .sub.r, one can thus determine the volume fraction of the mixture at the sea surface having the recognized swell profile. This volume fraction describes the fluid properties of the recognized profile.

(65) In addition, qualitative and quantitative data on the winds and weather may be taken into account in order to refine the volume fraction determination.

(66) The determined volume fraction may be compared to a database of predefined volume fractions.

(67) As mentioned above, the fluid properties of the determined volume fraction are considered as corresponding to the predetermined fluid properties of the most similar fraction among the predefined volume fractions.

(68) Using the fluid properties PF identified for the swell profile P, step 708 verifies whether or not the swell profile has fluid properties that correspond to the fluid properties of a sea surface comprising undesirable elements EP for the plant CT (PFEP?).

(69) When the fluid properties correspond to a floating layer containing floating bodies (Y arrow exiting step 708), then an alert is issued in step 710 (ALERT), for example to the remote device 110 mentioned above.

(70) This alert provides warning of the possibility of drum screen clogging for example. It is then possible to implement preventive measures to avoid such obstruction.

(71) Otherwise, as indicated by the arrow N exiting step 708, the fluid properties do not correspond to a floating layer, or at least not to a floating layer posing a threat to the plant CT. The method then ends in step 712 (END) and can be repeated to obtain new measurements and recheck for the presence of a threatening floating layer in the surveillance area.

(72) In addition, in order to overcome the temporally discontinuous nature of information from satellites (which is dependent on how frequently a satellite passes over the area of interest), the detection of a layer of marine organisms may be coupled with digital hydrodynamic models. The principle consists of injecting detected floating layers into the hydrodynamic models, and modeling the drift of these layers over the following days based on ocean currents. Weather forecasts may also be considered, in particular to include the influence of winds on the ocean currents.

(73) This allows estimating the future movement of a swell profile corresponding to a floating layer posing a threat to a nuclear power plant, which allows taking pre-emptive measures for example to protect the cooling system of the plant.

(74) The database of predefined volume fractions may be constructed from: a history of prior clogging events at the plant CT, a known volume fraction for identified floating bodies, ranges of damping coefficients or viscosities that are typically observed for the concentrations of clusters of clogging organisms or other bodies, behaviors specific to biological species, characteristics of floating bodies on an immiscible free surface, or other.

(75) The database may be in the form of a multidimensional table that includes volume fractions of floating bodies classified by time of year, water temperature, etc.

(76) The inclusion of behaviors specific to biological species helps to distinguish between species in the identification of fluid properties. For example, the water column of some jellyfish species changes with the light levels, resulting in a detectability that is dependent on the time of day (fluid properties evolve with the behavior of the floating organisms over the course of a day).

(77) This database allows refining the empirical relationship between apparent viscosity and particle content of a mixture in suspension, and assigning specific empirical coefficients to each type of marine organism (by types of algae, types of jellyfish, etc.).

(78) It is therefore understood that the invention is based on the principle that sea waves can be modified/damped when they encounter a cluster of marine organisms (for example jellyfish, algae, etc.).

(79) Detection of a floating layer allows triggering an early warning when one or more clusters of marine organisms or slicks of crude oil are approaching a nuclear power plant (and more particularly the filtering drum screens of the cooling system).

(80) The proposed detection method and system advantageously: offer extensive coverage spatially, and are operational day and night, regardless of cloud cover.

(81) Potentially, the proposed detection method and system may also allow detection of vessels releasing oil at sea, particularly at night.

(82) The invention has been described with reference to particular embodiments, which are non-limiting. The invention is of course not limited to the embodiment described by way of example, and extends to other variants. For example, the detection method and system may also be implemented for facilities such as offshore wind farms, to verify their accessibility during maintenance operations.