GB2063003A - Methods of remotely sensing the state of a body of water and devices for carrying out such methods - Google Patents
Methods of remotely sensing the state of a body of water and devices for carrying out such methods Download PDFInfo
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- GB2063003A GB2063003A GB8035902A GB8035902A GB2063003A GB 2063003 A GB2063003 A GB 2063003A GB 8035902 A GB8035902 A GB 8035902A GB 8035902 A GB8035902 A GB 8035902A GB 2063003 A GB2063003 A GB 2063003A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/95—Radar or analogous systems specially adapted for specific applications for meteorological use
- G01S13/951—Radar or analogous systems specially adapted for specific applications for meteorological use ground based
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
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- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
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- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Radar Systems Or Details Thereof (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Geophysics And Detection Of Objects (AREA)
- Length Measuring Devices With Unspecified Measuring Means (AREA)
Abstract
A method of remotely sensing of the state (i.e. the amplitude and frequency of the waves) of a selected zone (Z) of a body of water comprises: transmitting successive radar pulses ( DELTA ); receiving corresponding echoes ( beta ) returned by the waves of the selected zone; forming series of samples of said echoes ( beta ), each series having a different time shift ( delta 1, delta 2, delta 3) and corresponding to a different sector of the selected zone; keeping one of these series, corresponding to a reference sector, unchanged; applying to the other series correction factors for eliminating therefrom the influence of the difference in distance and/or azimuth, with respect to the transmission point, between the sectors corresponding to the series in question and the reference sector; and summing the so-corrected series or the corresponding frequency spectra with that corresponding to the reference sector, thereby improving the signal-to-noise ratio of the signals emanating from the reference sector, which are representative of the state of the selected zone. <IMAGE>
Description
SPECIFICATION
Methods of remotely sensing the state of a body of water and devices for carrying out such methods
This invention relates to methods of remotely sensing the state of a body of water and to devices for carrying out such methods. More particularly, the invention relates to methods of remotely sensing the state of the body of water by determining the frequency spectrum of successive echoes, from the waves of the body of water, of sequentially transmitted radar pulses; and to devices for carrying out such methods.
It is known that electromagnetic waves transmitted from a radar device towards a selected zone of the ocean, sea or other body of water subjected to wave motion are selectively reflected and/or backscattered by the waves, in particular towards the radar device. The electromagnetic waves are backscattered in particular by sea waves whose wavelength is one half of the wavelength of the transmitted electromagnetic waves.
The backscattered waves are subjected to a Doppler frequency shift corresponding to the velocity of motion of the sea waves in the direction of observation and their spectrum comprises two discrete components, called 'Bragg lines', respectively corresponding the sea waves approaching or moving away from the radar device. The ratio of the amplitudes of the two Bragg lines may be used to determine the direction of the wind and, under certain conditions, the directional spectrum of the waves. The direction of the wind may, for example, be ascertained by determining the direction of reception of the electromagnetic waves for which the ratio between the amplitudes of the lines is a maximum or minimum.By making use of the Doppler frequency spectrum, and particularly of the so-called second order spectrum, it is also possible to determine the significant height of the waves, i.e. the average height of the highest third of the waves, this significant height being related to the wind velocity over the sea. It is also known that the accuracy of the frequency which may be obtained when measuring the frequency spectrum will be better as the measuring period is longer.
As is explained hereinbelow, in view of the Doppler frequency shift resulting from the motion of the sea waves, which shift is small (of the order of 0.2 Hz, for example), it is necessary, in order to obtain a good resolution in the frequency measurement (for example of the order of 1 of2 Hz), for the measuring period of the spectrum to be at least one hundred seconds. This total period of measurement is distributed over successive echoes backscattered by the waves of the selected (surveyed) zone, these echoes corresponding to a sequence of sucessively transmitted radar pulses.
If the direction of the wind were constant in the zone surveyed by radar, it would be possible to extend at will the duration of the measuring period as as to obtain optimum accuracy. However, in practice, the total period of measurement must be limited to the estimated period of stability of the wind, since any change in its direction would induce a modification of the direction of the wave crests and modify the relative amplitude of the Bragg lines.
On the other hand, though a method consisting of multiplying the number of measurements carried out during this limited period, by increasing the recurrence frequency of the transmitted pulses, would result in an improvement of the signal-to-noise ratio, it would not provide for a significant increase in the measurement accuracy. As a matter of fact, measurements carried out within too short a time interval are liable not to be independent of one another in view of the very low frequency of the motion of the waves; accordingly, it is necessary that two measuring steps be separated by a certain period of time in order to detect significant variations in the same zone.
According to the invention there is provided a method of remotely sensing the state (i.e. the amplitude and frequency of the waves) of a selected zone of a body of water, including determining the frequency spectrum of echoes, from the waves of said zone, of sequentially transmitted radar pulses, wherein the following steps are performed;
a) a plurality of series of samples of the successive echo signals are taken, each of which series
corresponds to a separate sector of the selected zone;
b) one of the series, which corresponds to a sector which is used as a reference sector, is kept
unchanged;
c) the frequency spectrum of each series of signal samples is determined;;
d) corrections are applied to the or each other series or to the corresponding frequency spectrum or
spectra to adjust its or their values to values which would have corresponded to the reference sector,
by applying thereto (i) a correction factor related to the difference in distance from the trasnmission
point of the sector corresponding to the series in question and of the reference sector, in order to take
into account the different degree of weakening of the radar signals in relation to the propagation
distance, or (ii) a correction factor related to the difference in azimuth with respect to the transmission
point of the sector corresponding to the series in question and of the reference sector, in order to take
into account the different angles of incidence of the wind, resulting from the different orientation of
the sector corresponding to the series in question and of the reference sector, with respect to the wind
direction, or (iii) both of the above-mentioned correction factors, in a cumulative manner; and
e) the corrected spectrum or spectra or the spectrum or spectra of the corrected series are combined with
that of the series corresponding to the reference sector.
Methods embodying the invention and described hereinbelow make it possible to obtain an optimum accuracy and an improved signal-to-noise ratio in the determination of the frequency spectrum of the successive echoes, from the selected zone of the sea, ocean or other body of water, of sequentially transmitted radar pulses.
An important advantage of the methods embodying the invention and described hereinbelow consists essentially in the fact that, inside the limited time during which the direction of the wave crests on survey is stable, which time depends on the wind direction, it is possible to multiply the number of significant measurements by making use of samples whose characteristics are always independent on one another, since they correspond to echoes from different sectors of the selected, (surveyed) zone.
The invention also provides a device for carrying out the method of the invention, the device comprising:
means for sequentially transmitting radar pulses;
a system for receiving echoes, from the waves of the selected zone, of the transmitted pulses, said system comprising directional and orientable receiving means to selectively receive the echoes along a predetermined direction;
a reception chain comprising demodulation means and variable gain amplification means;
a system for recording and processing the received signals; and
control elements operative to modify the gain of the amplification means and/or to modify the orientation of the receiving means, the recording and processing system being operative to actuate the control elements in relation to the geographical location of the different sectors of the selected zone with respect to the reference sector.
The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:
Figure 1 shows an angular sector of a surveyed zone Z of the surface of a body of water, e.g. the sea, from which transmitted radar pulses are backscattered to form echo pulses;
Figure 2 shows chronograms (i.e. variations of level with time t) showing (a) the transmitted radar pulses and (b) corresponding echo pulses of which unique samples are taken;
Figure 3 shows a portion of a curve representing the variation, versus time, of the amplitude A(6) of the samples of the echoes at fixed sampling instants;;
Figure 4A is a very diagrammatic view of a frequency spectrum of the received echo signals, showing in particular the backscattering phenomenon resulting in the formation of Bragg lines, the direction of the radar being oriented with respect to the wind direction by an angle equal to 90"C; Figure 4B is a view similar to that of Figure 4A, but corresponding to the case where the wind is directed towards the earth and where the angle of orientation of the radar with respect to the wind direction is 1200; Figure 4C is a view similar to that of Figure 4A, but corresponding to the case where the wind is directed towards the sea and the angle of orientation of the radar with respect to the wind direction is 1200;; Figure 5 shows a surveyed zone Z located in an angular sector corresponding to a fixed reception azimuth and sectors of the zone corresponding to three different sampling instants;
Figure 6shows chronograms of (a) transmitted pulses A and (b) corresponding echoes ss received along a fixed reception azimuth, each of which echoes is subjected to three samples with different time shifts (61, 2, Figure 7 shows several adjacent angular sectors z1, z2, Z3, Z4 of a surveyed zone Z corresponding to several different reception azimuths which are close to each other, and elementary portions of the zone corresponding to a sample of echoes received along serveral azimuths;;
Figure 8 shows chronograms of (a) transmitted pulses and (b) echoes received along several reception azimuths, each of which is subjected to a unique sample corresponding to a time shift identical for all the azimuths;
Figure 9 illustrates the general case of an angular sector of a surveyed zone Z sub-divided into adjacent portions corresponding to different reception azimuths oo, Oi, 02, 03, and elementary portions corresponding to several successive samples of successive echoes !3o, ssl, t32, ss3 at different instants shifted respectively by time intervals 6 2, Figure 10 shows chronograms of (a) transmitted pulses and (b) received echoes for the general case of
Figure 9; and
Figure 11 diagrammatically illustrates a device for carrying out methods embodying the invention.
A measuring method previously used to remotely sense the sea state by ascertaining the frequency spectrum of signals transmitted by a transmission/reception radar device and backscattered by the sea waves will now be described with reference to Figures 1 and 2. In this method, a unique sample is taken of each of the echoes of a series of echoes received along a fixed azimuth. More specifically, the method comprises taking a series of samples of the successive echoes or of some of them for detecting the slow deformation of their envelope resulting from the motion of the sea waves.
Figure 1 shows an angular sector of the operative angle of the radar device, the sector containing a hatched zone Zfrom which the echoes are emitted at a given time, the echoes being sensed by a receiving antenna of the radar device oriented along a selected azimuth. The radar device transmits pulses of duration
A with a recurrence period T. Inside a reception angular sector, reflection or backscattering zones of the transmitted pulses, whose radial depth is proportional to the duration A, corresponds to the pulses. For example, if the duration A of the transmitted pulses is equal to 100 microseconds, the depth of the hatched zone Z, from which the echoes of each pulse are emitted, is 15 km, taking into account the return journey of the radar waves and their propagation velocity through the air.An echo pulse ss is sampled for a duration which is very short with respect to A, the sample being shifted by a time interval with respect to the instant of transmission of the middle of the corresponding transmitted pulse (Figure 2). The amplitude and the phase of the sample are then determined. All or some of the futher pulse echoes are sampled with the same time shift 6 with respect to the instant of transmission of the middle of the corresponding transmitted pulse and the amplitude and phase of each such further sample are determined. The resultant series of amplitude and phase values makes it possible to plot a curve (Figure 3) representing the variations of amplitude and phase of the samples versus time, these variations being due to the motion of the waves in the surveyed or measuring zone.A fast Fourier transform (FFT) of the series of discrete samples is made in order to obtain the coresponding frequency spectrum. This frequency spectrum comprises, in particular (Figures 4A, 4B, 4C), two lines A+ and A- corresponding to Doppler frequency shifts which are generally small and which depend on the frequency of the transmitted electromagnetic wave, and which it is advisable to measure with a sufficiently high frequency resolution (lower than 1/100 Hz, for example, for a Doppler frequency shift of 0.2
Hz of a transmitted wave whose frequency is 4 MHz) to obtain a good measurement accuracy. It is accordingly necessary for sampling to take place over a sufficiently long time, desirably a minimum of one
hundred seconds and preferably more.Futhermore, in a manner known in the art, it is preferable in practice to carry out several successive independent measuring cycles (each lasting at least one hundred seconds)
and to sum the moduluses of the corresponding frequency spectra so as to decrease the effect of
background noise.
As previously mentioned, the whole measurement period must be limited to the period of stability of the sea surface. As the stability period within the measuring zone is not generally well known, it is appropriate to
reduce the measuring time as much as possible to enable a frequency spectrum which accurately depicts the sea state to be obtained.
According to a first method embodying the invention (Figures 5 and 6), an echo pulse ss from inside a surveyed zone Z, corresponding to a fixed reception azimuth of the echo pulses, is subjected to three successive samples having respective time shifts b 62, 63. (The number of samples is not limited to three: any number of samples may be taken.) The samples correspond to three portions of the surveyed zone
located at different distances from the radar wave source of the radar device. The three zone portions may be separate (as illustrated), adjacent or partially overlapping. The three samples, corresponding to portions of the reflecting zone at least partly different from one another, are accordingly independent of one another.
The same is true for the frequency spectra obtained from the different samples of each echo or from different series of samples taken with the same time shift 6i, 62 or 63 from the successive echoes. However, in order to effect a useful combination at the end of each measuring cycle of the samples taken with different time shifts, or of the frequency spectra determined from these samples or series of samples, it is necessary to take into account weakening and modifications of the signals due to the propagation of the electromagnetic waves.Taking the central portion of the zone (time shift 62) as a reference, the frequency spectra determined from the samples or series of samples taken with time shifts 61 and 63, and associated with zone portions respectively nearer to and farther from the radar wave transmission reception device, have their moduluses multiplied by coefficients respectively lower and higher than unity. In this way, the moduluses of the frequency spectra associated with portions of the zone on opposite sides of the central reference portion are given the same amplitude as if the corresponding samples were samples of the central portion. In this way, variations due to the geographical dispersion of the different portions of the zone are cancelled, but the corrected frequency spectra remain independent of one another as far as noise is concerned.The two corrected frequency spectra are then combined with the frequency spectrum corresponding to the central portion of the zone so as to obtain a frequency spectrum having a better signal-to-noise ratio. The corrections are preferably performed on the amplitudes of the frequency spectra, but may also be performed on the amplitudes of the samples or of the series of samples taken with time shifts 61 and 63 before determining the frequency spectra corresponding thereto, and the results obtained are identical.
According to a second method embodying the invention (Figures 7, 8) the surveyed zone Z comprises several different angular sectors or portions, each of which has an apex angle equal to the angular width of a radar beam employed. Rotation of the beam is obtained by pivoting the radar transmission/reception device mechanically or electronically. The different sectors may be adjacent (as shown), partially overlapping or separate according to the amplitude of the rotation to which the radar transmission/reception device is subjected. In the illustrated case the surveyed zone Z comprises, for example, four angular sectors zq, Z2, Z3, and Z4 having respective azimuths 00, 8,, 02 and 03. The number of angular sectors is not limited to 4.The values of the azimuths may be, for example, O, 100 and 15". Pulses of duration A are transmitted sequentially with a reccurrence period T, and it has been decided to successively sense echoes Po, Pi, P2, P3 along the four different azimuths 00, Or, e2 and 03. Each echo of the series of echoes sensed along the same azimuth is sampled, the sample being shifted by the same time interval 6 with respect to the instant of transmission of the middle of the corresponding pulse returning from a portion of the zone formed by an annular sector Z centred on the reception point. From each series of samples corresponding to the same angular sector, the associated frequency spectrum is determined. As the relative amplitude of the Bragg lines varies in accordance with the angle between the direction of reception and the direction of the wind (Figures 4A, 4B, 4C for example), summing of the frequency spectra obtained along the different reception azimuths can be correctly performed only after the application of corrections taking into account these amplitude variations.
Reference is then made to a directional diagram model representing the energy transported by the waves
about the wind direction, which was previously determined, for example, on the basis of the direction of
reception for which the ratio between the respective intensitites of the Bragg lines is a maximum or
minimum. The model may be a theoretical model or a model resulting from previous calibrations performed
in the surveyed zone.The wind direction being known, the model is used to determine multiplication
coefficients to apply to the moduluses of the frequency spectra associated with the sample series
corresponding to the reception azimuths 0o, 02, and 03, for example, in order to take into account the fact that
the angles aO, a2 and a3 formed between the axes of these angular sectors and the wind direction are
different from the angle a1 formed between the angular sector of the azimuth 87 (taken as a reference sector)
and the wind direction.
After application of these corrections, the moduluses of the corrected spectra may be added to the
modulus of the uncorrected spectrum associated with the series of samples corresponding to the sector
having the azimuth Oi, preferably, although they correspond to angular sectors of different orientations.
When the sea zone including the different angular sectors is homogeneous, which is generally the case, the
frequency spectrum resulting from the summing of the four mutually independent spectra will have a better
signal-to-noise ratio.
For the reasons already mentioned, the echoes corresponding to a certain azimuth are sampled
periodically, taking into account the frequency of change of phenomena on the sea. In the particular case
illustrated, the sequences of examining the four reception azimuths are linked with one another without
interruption, a sample of the echo Po corresponding to the azimuth 0o immediately following a sample of the
last echo P3 corresponding to the aximuth 03 of the preceding sequence.
A third method embodying the invention (Figures 9 and 10) comprises a combination of the two preceding
ones, i.e. it comprises taking series of samples corresponding to portions of the surveyed zone which are at
different distances from the reception point and/or are emitted from angular sectors having different
azimuths. Puises of duration A are sequentially transmitted with a recurrence period T and the
corresponding echoes are successively sensed along four different azimuths 00,131, 02 and 03.Each of the
echoes Po Pi, P2, P3 emitted along the same azimuth, 00 for example, is subjected to at least one sample
shifted with respect to the transmission time of the middle of the corresponding transmitted pulse by a time
interval 6,. Preferably, several samples are taken: in the illustrated case there are three samples with time
shifts 61, 62, 63- Series of samples are thus formed, each of which corresponds to reflection from the same
portion of the surveyed zone, and the corresponding frequency spectra are determined.The moduluses of
the frequency spectra respectively associated with the series of samples shifted by time intervals b and 63
and corresponding to portions of the surveyed zone located on opposite sides of the central portion, taken as
a reference portion of the zone, have correction coefficients, similar to thos mentioned in the description of
Figures 5 and 6, applied thereto in order to take into account the weakening of the waves during their
propagation. The same operations are repeated with the series of samples of echoes received along the
other azimuths Oi, 02 and 03. The corrections relating to the distance may, of course, also be applied to the
amplitudes of the samples before determining the frequency spectra.Also performed are the operations
mentioned in the description of Figures 7 and 8, which operations comprise:
applying correction coefficients to the moduluses of the frequency spectra associated with series of
samples of echoes emitted from zone portions located within the angular intervals of the angular sectors
having the azimuths 81, 02, and 03, in order to take into account the orientation of the axes of these angular
sectors with respect to the wind direction (angles aO, a2, and a3, respectively) which differe from that of the
azimuth O taken as a reference (angle a1 with respect to the wind direction); and,
after application of the corrections relating to the distance and to the azimuth, allocating to the moduluses
of the frequency spectra associated with series of samples corresponding to zone portions different from
the reference portions, amplitudes equal to those they would have if the samples all corresponded to the
reference portion. However, the frequency spectra remain, so far as noise is concerned, independent of
one another, since they correspond to reflections from different but homogeneous zone portions and,
accordingly, their summing will increase the signal-to-noise ratio.
In the selected example, where sequences of four pulses are transmitted, twelve independent and
significant samples, i.e. samples issued from independent portions of the surveyed zone, are available.
In this embodiment also, the selected angular sectors may be adjacent, separate or partially overlapping.
Figure 11 shows a device for carrying out a method embodying the invention. The device comprises a
directional or non-directional transmission antenna 1 operative to transmit radar pulses that propagate
through the atmosphere, for example in the vicinity of the water/air interface (surface wave), and directional
and orientable reception means comprising a fixed directional receiving antenna 2 provided with a certain
number of antenna elements (2a, 2b, 2c. . .2n) which are spaced apart at regular intervals, oriented along the
same determined direction, and'have a fixed directivity lobe. The axis of the lobe of the receiving antenna 2 is electronically orientable by means of a group 3 of phase shift means (delay) lines 3a to 3n. Each antenna
element (21,2b,... 2n) is connected to a particular delay line (3a,3b,3c... 3n) of the group 3, which delay line
is operative to apply a variable predetermined delay to the signals received by the corresponding antenna
element. As is already known in the radar art, by suitably selecting delays applied to the repective signals
received by the antenna elements and summing these signals, conveniently delayed, it is possible to obtain
an overall signal similar to that which would have been obtained with an orientable reception antenna.
The different resultant signals received by the antenna 2 in response to sequentially transmitted pulses are introduced into a reception chain 4 comprising a reception element 5, a demodulator 6 operative to mix the received signal from the reception element 5 with a signal generated by a synthesizer 7, a low-pass filter 15 operative to filter the signal from the demodulator 6, and a variable gain amplifier 8 connected to the output of the low-pass filter 15. The low frequency signal from the amplifier 8 is passed to an analog-to-digital converter 9 and from there to a recording and processing system 10. The system 10 records the received signals, controls the gain of the amplifier 8, and changes the orientation of the receiving antenna.The recording and processing system 10 generates control signals and transmits them to the assembly 3 through a means 14 for controlling the delay lines 3, 36 ... 3n in order to impart a predetermined orientation to the receiving antenna 2. The gain of the amplifier 8 is controlled by the recording and processing system 10 through the intermediary of control elements comprising a digital memory 11, wherein a computer transfers a determined gain program, and a digital-to-analog converter 12 for converting to analog form the digital signals transferred to the digital memory. This analog signal is applied to a gain control input of the amplifier 8. The synthesizer 7 is connected to a transmission means 13 operative to generate pulses at the frequency of the signals of the synthesizer and to amplify the pulses before supplying them to the transmission antenna 1.
The effect of weakening of the signals in accordance with their propagation distance may be cancelled by transferring to the digital memory 11 a set of digital gain values whose sequential reading permits the gain of the amplifier 8 to be varied during the reception of each of the echoes.
Similarly, if successive samples are to be taken from echoes received along different azimuths of the antenna, the recording and processing system 10 is operative to generate, between the reception of two successive echoes, signals for varying the length of each delay line 3a, 3b .. 3n, thereby to modify the directional diagram of the antenna 2 to orient it successively along the selected directions.
The recording and processing system 10 is also operative to average the values of the samples or the series of samples obtained at the end of each measuring cycle and to compute the fast Fourier transform for obtaining the corresponding frequency spectra. The system 10 is also operative to correct the spectra obtained from application of the Fourier transforms to the echoes received from the different directions.
Before the beginning of the measuring cycles, a preliminary calibration of the reception chain 4 is carried out. A signal of known amplitude is introduced into the reception chain 4 and the recording and processing system 10 is operated to adjust the gain program so that the output voltage is close to an optimum value.
The gain curve is then calibrated by measuring the variation in level of the received signals in relation to their propagation distance, and then summing samples respectively corresponding to several intervals of propagation time, so that each sum is of the same order of magnitude. Data acquisition is then performed.
Claims (5)
1. A method of remotely sensing the state (i.e. the amplitude and frequency of the waves) of a selected zone of a body of water, including determining the frequency spectrum of echoes, from the waves of said zone, of sequentially transmitted radar pulses, wherein the following steps are performed;
a) a plurality of series of samples of the successive echo signals are taken, each of which series
corresponds to a separate sector of the selected zone;
b) one of the series, which corresponds to a sector which is used as a reference sector, is kept
unchanged;
c) the frequency spectrum of each series of signal samples is determined;;
d) corrections are applied to the or each other series or to the corresponding frequency spectrum or
spectra to adjust its or their values to values which would have corresponded to the reference sector,
by applying thereto (i) a correction factor related to the difference in distance from the transmission
point of the sector corresponding to the series in question and of the reference sector, in order to take
into account the different degree of weakening of the radar signals in relation to the propagation
distance, or (ii) a correction factor related to the difference in azimuth with respect to the transmission
point of the sector corresponding to the series in question and of the reference sector, in order to take
into account the different angles of incidence of the wind, resulting from the different orientation of
the sector corresponding to the series in question and of the reference sector, with respect to the wind
direction, or (iii) both of the above-mentioned correction factors, in a cumulative manner; and
e) the corrected spectrum or spectra or the spectrum or spectra of the corrected series are combined with
that of the series corresponding to the reference sector.
2. A method according to claim 1, wherein the combination of spectra of step (e) comprises summing the spectra.
3. A method according to claim 2, wherein the summing of the spectra comprises summing with weighting coefficients.
4. A method of remotely sensing the state of a selected zone of a body of water, the method being substantially as herein described with reference to Figures 5 and 5, Figure 7 and 8 or Figures 9 and 10 of the accompanying drawings.
5. A device for carrying out a method according to any one of claims 1 to 4, the device comprising
means for sequentially transmitting radar pulses;
a system for receiving echoes, from the waves of the selected zone, of the transmitted pulses, said system comprising directional and orientable receiving means to selectively receive the echoes along a predetermined direction;
a reception chain comprising demodulation means and variable gain amplification means;
a system for recording and processing the received signals; and
control elements operative to modify the gain of the amplification means and/or to modify the orientation of the receiving means, the recording and processing system being operative to actuate the control elements in relation to the geographical location of the different sectors of the selected zone with respect to the reference sector.
5. A device for carrying out the method of the invention, the device comprising:
means for sequentially transmitting radar pulses;
a system for receiving echoes, from the waves of the selected zone, of the transmitted pulses, said system comprising directional and orientable receiving means to selectively receive the echoes along a predetermined direction;
a reception chain comprising demodulation means and variable gain amplification means;
a system for recording and processing the received signals; and
control elements operative to modify the gain of the amplification means and/or to modify the orientation of the receiving means, the recording and processing system being operative to actuate the control elements in relation to the geographical location -of the different sectors of the selected zone with respect to the reference sector.
6. A device according to claim 5, wherein the control elements comprises a digital memory arranged to receive a series of digital values and means for converting the digital values to an analog signal for controlling the gain of the amplification means.
7. A device according to claim 5 or claim 6, wherein the directional and orientable receiving means comprises a plurality of fixed receiving elements arranged in line and connected to a plurality of phase shifting means operative to apply a variable delay to signals received by each receiving element, and the control elements comprise means for transmitting, to the plurality of phase shifting means, control signals generated by the recording and processing system.
8. A device for carrying out a method according to any one of claims 1 to 4, the device being substantially as herein described with reference to Figure 11 of the accompanying drawings.
New claims or amendments to claims filed on 29 Jan 1981.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7927629A FR2469717A1 (en) | 1979-11-07 | 1979-11-07 | METHOD FOR REMOTE DETECTION OF THE SEA STATE AND DEVICE FOR IMPLEMENTING SAME |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2063003A true GB2063003A (en) | 1981-05-28 |
| GB2063003B GB2063003B (en) | 1984-05-31 |
Family
ID=9231466
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8035902A Expired GB2063003B (en) | 1979-11-07 | 1980-11-07 | Methods of remotely sensing the state of a body of water and devices for carrying out such methods |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5693007A (en) |
| CA (1) | CA1157131A (en) |
| FR (1) | FR2469717A1 (en) |
| GB (1) | GB2063003B (en) |
| IT (1) | IT1133755B (en) |
| NL (1) | NL8006069A (en) |
| NO (1) | NO149365C (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2117595A (en) * | 1982-03-19 | 1983-10-12 | Smiths Industries Plc | Marine radar |
| GB2128833A (en) * | 1982-10-13 | 1984-05-02 | Emi Ltd | Improvements relating to the measurement of directional wave spectra |
| US4509048A (en) * | 1982-03-18 | 1985-04-02 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method and apparatus for ΔK synthetic aperture radar measurement of ocean current |
| WO1987004258A1 (en) * | 1986-01-13 | 1987-07-16 | Gjessing Dag T | System for marine seismic exploration |
| WO1991013373A1 (en) * | 1990-02-22 | 1991-09-05 | Jan Gateman | Electrooptical sensor system for marine seismic data acquisition |
| WO1992021041A1 (en) * | 1991-05-16 | 1992-11-26 | The Commonwealth Of Australia | Oceanographic and meteorological data |
| GB2320829A (en) * | 1996-12-04 | 1998-07-01 | Lockheed Martin Tactical Sys | Predicting future motion |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4999586B2 (en) * | 2007-07-19 | 2012-08-15 | 三菱電機株式会社 | Radar equipment |
| KR100971767B1 (en) * | 2009-11-13 | 2010-07-21 | 엘아이지넥스원 주식회사 | Automatic gain control apparatus and method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3731306A (en) * | 1972-01-24 | 1973-05-01 | Us Navy | Sea state analyzer using radar sea return |
| JPS5350881A (en) * | 1976-10-20 | 1978-05-09 | Hitachi Ltd | Measuringmethod for wave |
-
1979
- 1979-11-07 FR FR7927629A patent/FR2469717A1/en active Granted
-
1980
- 1980-11-05 NO NO803316A patent/NO149365C/en unknown
- 1980-11-06 IT IT25819/80A patent/IT1133755B/en active
- 1980-11-06 NL NL8006069A patent/NL8006069A/en not_active Application Discontinuation
- 1980-11-07 CA CA000364294A patent/CA1157131A/en not_active Expired
- 1980-11-07 JP JP15678980A patent/JPS5693007A/en active Granted
- 1980-11-07 GB GB8035902A patent/GB2063003B/en not_active Expired
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4509048A (en) * | 1982-03-18 | 1985-04-02 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method and apparatus for ΔK synthetic aperture radar measurement of ocean current |
| GB2117595A (en) * | 1982-03-19 | 1983-10-12 | Smiths Industries Plc | Marine radar |
| GB2128833A (en) * | 1982-10-13 | 1984-05-02 | Emi Ltd | Improvements relating to the measurement of directional wave spectra |
| WO1987004258A1 (en) * | 1986-01-13 | 1987-07-16 | Gjessing Dag T | System for marine seismic exploration |
| US4843597A (en) * | 1986-01-13 | 1989-06-27 | Gjessing Dag K T | System for marine seismic exploration |
| WO1991013373A1 (en) * | 1990-02-22 | 1991-09-05 | Jan Gateman | Electrooptical sensor system for marine seismic data acquisition |
| AU654124B2 (en) * | 1990-02-22 | 1994-10-27 | Bertil Gateman | Electrooptical sensor system for marine seismic data acquisition |
| WO1992021041A1 (en) * | 1991-05-16 | 1992-11-26 | The Commonwealth Of Australia | Oceanographic and meteorological data |
| US5469168A (en) * | 1991-05-16 | 1995-11-21 | The Commonwealth Of Australia, C/O The Secretary, Department Of Defence | Oceanographic and meteorological data |
| GB2320829A (en) * | 1996-12-04 | 1998-07-01 | Lockheed Martin Tactical Sys | Predicting future motion |
| GB2320829B (en) * | 1996-12-04 | 1998-10-21 | Lockheed Martin Tactical Sys | Method and system for predicting the motion e.g. of a ship or the like |
| US6064924A (en) * | 1996-12-04 | 2000-05-16 | Lockheed Martin Corporation | Method and system for predicting ship motion or the like to assist in helicopter landing |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0213275B2 (en) | 1990-04-03 |
| IT1133755B (en) | 1986-07-09 |
| FR2469717B1 (en) | 1983-11-10 |
| IT8025819A0 (en) | 1980-11-06 |
| JPS5693007A (en) | 1981-07-28 |
| NO803316L (en) | 1981-05-08 |
| CA1157131A (en) | 1983-11-15 |
| NO149365B (en) | 1983-12-27 |
| FR2469717A1 (en) | 1981-05-22 |
| NL8006069A (en) | 1981-06-01 |
| NO149365C (en) | 1984-04-04 |
| GB2063003B (en) | 1984-05-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |