GB2529934A - Method for absolute radiometric calibration of the radar cross-section of radar targets - Google Patents
Method for absolute radiometric calibration of the radar cross-section of radar targets Download PDFInfo
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- GB2529934A GB2529934A GB1512481.1A GB201512481A GB2529934A GB 2529934 A GB2529934 A GB 2529934A GB 201512481 A GB201512481 A GB 201512481A GB 2529934 A GB2529934 A GB 2529934A
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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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
- G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
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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
- G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
- G01S13/75—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors
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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
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
-
- 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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4004—Means for monitoring or calibrating of parts of a radar system
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
- G01S7/4082—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder
- G01S7/4091—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder during normal radar operation
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- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Radar, Positioning & Navigation (AREA)
- Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
Method for radiometric calibration of the radar cross section of at least 3 radar targets, at least one of which operates in a transponder mode (fig. 1, 220) and another one of which may be passive. In a first step 101, a signal is emitted from a first radar target with a transmission power PT, this signal is received by a second radar target, and then the received signal is emitted or reflected by the second target to the first target, and received by the first target with receiving power PR. In a second step 102, this initial step is repeated for each different pairing of targets. In a third step 103, the radar cross section of the second radar target is determined based on a given relationship (radar equation) between ascertained ratio of PR/PT and other known values of gain, distances and wavelength. Each of the 3 steps may be executed for different transmitting frequencies of the transmitters, different distances of the targets, or different polarisations of the signal.
Description
METHOD FOR ABSOLUTE RADIOMETRIC CALIBRATION OF THE RADAR
CROSS-SECTION OF RADAR TARGETS
FTELD OF INVENTION
The invention relates a method for absolute radiometric calibration of the radar cross-section RCS of a N number of radar targets T1 with i = 1, 2, ..., N and N »= 3. The invention is used in the aerospace industry for absolute radiometric calibration of the radar cross-section, in particular of active reference targets, so-called transponders.
BACKGROUND
Due to a constantly rising demand for remote sensing data of the earth, in particular for remote sensing data obtained with the aid of satellite-supported SAR systems such as TerraSAR-X or Sentinel-i, the quality of so-called SAR data products is becoming increasing more important. It is only when the quality of the SAR data products is guaranteed that useful information for earth observation cam be derived (such as for example when observing glacier movements, the pack ice or flooding, the cutting down of tropical rain forest, the derivation of the world-wide bio mass etc.).
However, a high quality of SAR data products can only be achieved if the satellite-supported SAR systems are accurately calibrated, and since future SAR systems are to be tuned to higher accuracy, the accuracy of the reference targets required for this, and thus a sufficiently accurate calibration of these reference targets, is becoming more and more important.
The main application of the described method initially is the absolute radiometric calibration of active reference targets, the so-called (radar) Transponders, which are subsequently used for the calibration of satellite-supported SAP. systems. In principle the method can be used in all cases where radar cross-sections ROS of in particular active calibrating targets shall be measured.
This includes for example transponders such as used for the callbraticn of weather radars.
In principle, there are currently three different variants of the method for determining the radar cross-section ROS of active radar targets. In the first variant, individual transponder components such as antennae and amplifiers, are measured In the laboratcry follcwed by the calculation cf the resulting radar cross-section RCS of the respective transponder. With this variant the problem lies in the high systematic measuring uncertainty of the method, which results from the multitude of individual measurements. In addition uncertainties arise from the series connections of individual components of the transponder (antennae, converters, amplifiers etc.) after measuring, because the interfaces are not part of the original measurements.
In a second variant of the method, the transponder is measured as a radar target in a suitable ROS measuring station (inside and outside) . Here the transponder is regarded as a black box, the inner workings of which are unimportant. A particular problem with this variant, apart from the usual challenges, such as the suppression of undesirable backscatter from the measuring environment, which is caused, for example, by mountings, a rotating tower etc., is the fact that this measuring system is a comparison, for which an additional reference target with a known radar cross-section ROS is reguired. The uncertainty, for which this last-mentioned radar cross-section ROS is known, immediately puts a limit on achieving calibrations which are still accurate. In addition, with transponders with a high radar cross-section ROS and thus high amplification, an undesirable upswing may happen, if these are operated in a shielding chamber. As a result an accurate absolute radicmetric calibraticn of the transponders in a shielding chamber is prevented.
In a third variant of the methcd the transponder is operated as a radar device, i.e. with an active transmitter and receiver, which is used for measuring a reference target with known radar cross-section P03 at a known distance. A problem with this variant lies in the fact that apart from the same problems as with the previcus seccnd variant, adeguate filtering of the background within the time range is nct possible due to the typically limited transponder band width.
In total it is true to say of the said calibration of SAP systems that the measuring uncertainty in calibrating a reference transponder has a direct influence upon the achievable radiometric accuracy of the SAP systems to be calibrated. The more acourate the calibration standard is, the more accurately the SAP system can be calibrated.
BRIEF SUFNARY OF THE INVENTION
The invention is based on the characteristics cf the independent claims. Advantageous further develcpments and designs are the subject cf the dependent claims. Further features, possible applications and advantages of the invention are found in the description below as well as the explanation of exemplary embodiments of the invention shown in the figures.
According to a first aspect of the invention there is proposed a method for absolute radicmetric calibration of the radar cross-section cf three or mcre radar calibration targets.
There is proposed a method for absolute radiometric oalibration of the radar oross-seotion ROS1 of a N number of radar targets T1 with i = 1, 2, ..., N and N »= 3. The proposed method is based on the fact that at least one radar target comprises a radar transmitter Si with a transmitting antenna SAi and a radar receiver Ei with a receiver antenna EA1, wherein the radar receiver E1 and radar transmitter Si operate independently of each other.
Thus the radar target I can be operated in a radar mode, wherein the radar target Ii can transmit radar signals and can receive radar signals independently thereof.
Further, the proposed method is based on the fact that a second radar target 11=2 exists, which comprises a radar transmitter S2 with a transmitting antenna SA2, a radar receiver F2 with a receiver antenna EA2, and a unit D2, with which the radar transmitter S2, in a transponder mode TM of the radar target T2 is connected with the radar receiver E2, so that a signal S received by the radar receiver E2 is again (actively) emitted by the radar transmitter S2 (almcst immediately) , and with which the radar transmitter 52, in a radar mode RN of the radar target Tc, is not connected with the radar receiver F2, so that the radar transmitter S2 and the radar receiver F2 operate independently of each other.
Further, the proposed method is based on the fact that a third radar target Tl3 exists, which comprises a radar transmitter S with a transmitting antenna SA3, a radar receiver E3 with a receiver antenna EA3, and a unit D3, with which the radar transmitter 3; is connected with the radar receiver F3, so that a signal S received by the radar receiver F1 is again emitted by the radar transmitter 5?., or the radar target I? is a passive radar target, which reflects an incoming signal S. A passive radar target I and a radar target T operated in transponder mode here have in common, that they reflect an incoming radar signal (in the first case this happens in a passive manner, in the second case in an active manner and possibly with a time delay) The above-mentioned properties of the at least three radar targets T are minimum reguirements. For example all three of the radar targets T1 may be realised in such a way that they can be operated both in radar mode and in a transponder mode, and thus conprise the properties of the above-mentioned second radar target T2.
The proposed method comprises the following steps: The method begins with the radar transmitter Sk of the radar target Ik with a transmission power PTR1 sending a signal S to another radar target I-j. The sent signal S is received by the other radar target T1. This radar target T sends or reflects the received signal S back to the radar target Tk. The signal S emitted by the radar target T is received by the radar receiver Ek of the radar target Tk with the receiving power PRk1, wherein k, j a {l, 2,..., N} and k j. These sequences are summarised for the following
statements as a "first step" of the method.
Furthermore in a second step previously defined as the "first step", N different pairings TkTJ of radar targets Tj and T are executed, wherein the pairings T1T and TJTk are assumed to be identical. The variables: transmission power PIk,j and receiving power PRk,j are recorded, respectively.
Furthermore the distances Dk,1 = (Pk -F1) of the radar transponders Tk and T, on which measuring is based, are recorded, i.e. accurately determined.
Then, in a third step, the radar transponder Tj is ascertained based on known distances Dk, of the radar transponders Tk and T during execution of the first and second step as well as based on ascertained ratios of PRk,j/PTk,j of the radar cross-sections RCS, on the basis of the following relationship: iL.G22.RCS.
(1) f'R=PT -It S (4rD with GR: antenna gain of the receiver antenna EAk, GT: antenna gain of the transmitter antenna SA1, and A wavelength of the radar signal S. Advantageously, in performing the "first step", the main beam direction of the radar transmitter Sk is aligned exactly with the radar target I-j or its receiving antenna.
This alignment may for example be effected by means of laser measuring.
Advantageously the distances Dk,J result from the accurate detection of the positions Pk and P of the radar targets Ik and T1 while taking the measurements: Dk,-j = I (Pi -Ph), wherein, respectively, measurements are taken from the phase centre of the respective antenna. Accurate detection of these positions is effected for example, by means of a differential GPS device. Advantageously the distances Dk,J may also be detected by means of a laser distance measuring means.
It should be noted that the radar cross-section RCS± is defined in a meaningful way only for a distant field. Based on an antenna dimension D the distant field condition D
I
applies to a distance Dk of A. wherein A is the wavelength of the signal S. If the radar targets used are, for example, radar transponders with two antennae (transmitter antenna, receiver antenna), the antenna apertures of which have a diameter of 20 cm and where the antenna feed lines are separated from each other by approx. 40 cm, then this means for a D of 60 cm and a wavelength A = 5.6 cm, that the
distant field begins at distances of Dk,J > 13 m.
Provided N> 3, the further radar targets 11>3 may be realised at random, i.e. they may be passive radar targets, radar targets working as transponders, or optionally radar targets operable in the radar or transponder mode.
For absolute calibration of the radar cross-sections RCS1],2,7 of three generic radar targets T1,2,3 the proposed method merely requires that the ratio PRk,l/PTk,l for radar target combinations, e.g. T1T2, 1113 und T2T7, is measured for known distances Di,2, Di,3 and D>,3. This data is inserted into a linear and easily solvable equation system resulting from the equation (1) with three equations and three unknowns (radar cross-sections P051=i,2,3) This means that determination of the radar cross-sections of N radar targets Th requires at least N measurements for N different pairings.
One advantageous further development of the method is oharacterised in that the radar target Ii comprises a unit Di, with which the radar transmitter Si in a transponder mode TM of radar target Ii is connected with the radar receiver Ei, so that a signal S received by the radar receiver Ei is again emitted by the radar transmitter Si, and with which the radar transmitter Si in a radar mode RM of the radar target Ti is not connected with the radar receiver Ni, so that the radar receiver Et and the radar transmitter Si operate independently of one another. In other words, the radar target Ii in this further development can be used both in transponder mode and in radar mode, so that in total two of the at least three radar targets I can be operated in both modes, whilst the third radar target T can only be operated as a transponder or represents a passive radar target.
One advantageous further development of the method is characterised in that the radar target 13 comprises a unit D3, with which the radar transmitter S in a transponder mode TM of the radar target 17 is connected with the radar receiver F3, so that a signal S received by the radar receiver F3 is again emitted by the radar transmitter Si, and with which the radar transmitter S in a radar mode PM of the radar target T3 is not connected with the radar receiver E, so that the radar receiver E and the radar transmitter S7 operate independently of each other. This variant of the method together with the above further development includes the combination that all three radar targets Ii are operable in both modes (transponder mode and radar mode) One advantageous further development of the method is characterised in that the entire method, i.e. from the first to the third step, is performed for different transmitting freguencies f of the radar transmitters S or the signal 5, wherein ultimately the radar cross-sections RCS of the radar targets Ij are ascertained as frequency-dependent radar cross-sections RCS(f) . Thus as a result of the method absolute calibrated frequency-dependent radar cross-sections RCS(f) are obtained.
Furthermore it is advantageous to perform the entire method from the first to the third step for each pairing TkT-j for different distances Dk,J for the radar targets I< and I, wherein the measured distance-dependent ratios (PR],/PTkj) (Di,) are utilised for the correction of multipath effects when ascertaining the radar cross-sections P051. Interferences or inaccuracies occurring due to the multipath propagation of the signals S or due to stationary waves can thereby be compensated for to a large extent, which ultimately improves accuracy of the ascertained radar cross-sections P051.
Furthermore it is advantageous to perform the entire method from the first to the third step for different polarisations P of the signal S, wherein as a result the radar cross-sections P051 of the radar targets T are ascertained as being dependent on the polarisation P. It is advantageous to repeatedly perform the entire method from the first to the third step g-times, wherein the radar cross-sections P051 are ascertained as mean values <R0S>0, wherein q {2, 3, 4...}. Furthermore it is advantageous if only the "first step" is repeatedly performed q-times for a pairing of radar targets Ik und I-j, wherein the transmission powers P1k,1 and receiving powers PRk,i measured during the process are averaged, and the means values: <PTj,j> and <PRj,> generated are used for ascertaining the ratio PRki/PIk,i = <PRi,k>c/<PTk,i>c and for respectively ascertaining the radar cross-sections P051.
An advantageous further development of the method is characterised in that the units D1, in transponder mode of the radar target T, amplify and/or filter and/or delay over time the signals S received from the radar receiver F1, before these are forwarded to the radar transmitter S for emitting them. In particular by emitting the signals with a time delay, interference effects from multipath signals and further environment-dependent effects such as upswings can be very largely excluded.
An advantageous further development of the method is characterised in that the distances Dk,j of the radar targets Ik and I from each other satisfy the following condition: (2) Dk,i > (2*D2)/A with D: antenna diameter of the transmitter antenna SA1 and A: wavelength of the signal S. This corresponds to the
distant field condition already addressed.
Advantageously the transmitting antenna SAk of the radar target Ik and the receiving antenna BA1 of the radar target I are aligned in a co-polar manner.
The at least three measurements of transmission power PIij and receiving power PR],1 permit an eguation system to be developed, from which the radar cross-section RCS of each radar target T can be unequivocally calculated, provided the distance Dk,-j between the radar targets Tk and T1 is known with sufficient accuracy.
In contrast to the known methods an additional radar target with known backscatter cross-section is not required, resulting in higher calibrating accuracies being achieved.
Besides the radar targets T1 are measured in their final configurations (as a black box), i.e. cable connections and corresponding internal interfaces need not be altered again after measuring, which would subsequently falsify the radar cross-section ROS. In addition radar targets T, which operate as transponders with a digital delay, allow the decoupling, over time, of the transmitting and receiving of signals. Any upswings, as may happen with previous measurements of transponders in a shielding chamber, may thereby be prevented. A further advantage consists in that when taking measurements there is no need for additional high-frequency measuring equipment, such as for example a network channel analyser. This will result not only in cost savings, but also in additional measuring uncertainties being avoided. Finally the traceability of the proposed RCS calibration is limited to standards for a comparatively simple length measuring system, whilst up to now the radar cross-section ROS had to be ascertained either by a detour via a further calibrated reference target or by measuring the individual components of a respective radar target.
Thus the present method allows to trace the calibration back to different standards in a simple way.
Acoording to a further aspect of the invention, there is provided a computer system with a data processing device, wherein the data processing device is realised in such a way that a method as described above is executed on the data processing device.
According to a further aspect of the invention, there is provided a digital storage medium with electrically triggered control signals, wherein the control signals can interact with a programmable computer system in such a way that a method as described above is executed.
According to a further aspect of the invention, there is provided a computer program product with a program code stored on a machine-readable medium for executing the method as described above, when the program code is executed on a data processing device.
According to a further aspect of the invention, there is provided a computer program with program codes for executing the method, as described above, when the program is run on the data processing device. To this end the data processing device may be designed as a random or arbitrary computer system known from the state of the art.
Further advantages, features and details are revealed in the following description, in which -possibly with reference to the drawing -at least one exemplary embodiment is described in detail. Identical, similar and/or functionally identical parts are provided with the same reference symbols.
BRIEF SUMMARY OF THE DRAWINGS
The invention will be described in more detail by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a schematic exemplary representation of a radar target operated solely as a radar, and a radar target operated here in transponder mode and which can be switched between transponder mode and radar mode, and Fig. 2 shows a schematic flow diagram of an exemplary embodiment of the proposed method.
DETAILED DESCRIPTION OF THE INVENTION
Example methods embodying aspects of the invention will now be described with reference to Fig. 1 and Fig. 2.
In the following an exemplary embodiment of the proposed method is described in detail, in which the radar cross-sections RCSi, RCS2, and ROS3 are absolutely calibrated for three radar targets Ii, 12, and I-. Iwo of the three radar targets, that is T1 and 12, may be operated both in radar mode and in transponder mode, i.e. they comprise a unit, which can switch between these two modes. The radar target 13 here can be operated only as a radar, i.e. receiving and emitting of radar signals S is effected independently of each other.
Fig. 1 schematically shows a radar target 201 operated only as a radar, and a radar target 220 operated here in transponder mode, and which can be switched between transponder mode and radar mode.
The radar target 201 comprises a radar transmitter 202 with an amplifier 204 (operating in the digital range) , a digital-analogue converter 205 and a transmission unit 206 with a transmitting antenna 207. A signal is provided to the radar transmitter 202 at the amplifier 204, which signal is ultimately emitted via the transmitting antenna 207 as a signal S. Further the radar target comprises a radar receiver 203 with a receiving antenna 210, an amplifier 209 and an analogue-digital converter 208. A signal S received by the radar receiver travels from the receiving antenna 210 via the shown signal path to the analogue-digital converter and is provided there for further processing. It is easily recognisable that the radar transmitter 202 is not connected with the radar receiver 203, i.e. a signal S received by the radar receiver 203 is not provided for emission at the radar transmitter 202.
The radar target 220 comprises a radar transmitter 222 with an amplifier 225 (operating in the digital range) , a digital-analogue converter 224 and a transmitting unit 223 with a transmitting antenna 226. The radar target 220 further comprises a radar receiver 221 with a reiving antenna 227, an amplifier 228 and an analogue-digital converter 229. Furthermore the radar target 220 comprises a unit 230, with which the radar transmitter 222, in the transponder mode TM of radar target 220 shown, is connected with the radar receiver 221, so that a signal S received by the radar receiver 221 is again emitted by the radar transmitter 222, and with which the radar transmitter 222, in a radar mode RN (not shown) of the radar target 220, is not connected with the radar receiver 221, so that the radar transmitter 222 and the radar receiver 221 operate independently of each other, i.e. as radar.
The present three radar targets of the exemplary embodiment respectively correspond to the principal construction of the radar targets 201 and 220 generally described above.
For absolute radiometric calibration of the radar cross-seotion P051=1,2,3 of the above defined radar targets T, with i = 1, 2, 3, the measurements described below are taken for the following pairings: T3T1, T3T2 and 1112, wherein in the first two pairings: 1311, 1312 the radar targets Ti and 12 are operated in transponder mode, so that the radar target 17 emits respective signals S to the radar targets Ii and 12 and records the respective signals returned from there. With the pairing 1112 one of the two radar targets Ti or 12 must operate in radar mode and the respectively other target must operate in transponder mode.
Let it be assumed in this case that Ti operates in radar mode and I? operates in transponder mode.
For each of these pairings: a signal S is emitted by the radar transmitter Sk of a radar targets Ik with a transmission power PIk,J, a signal S is received by the respectively other radar target T of the pairings, the received signal S is emitted by the other radar target I-and the signal S coming from the radar target TI is received by the radar receiver Ek of the radar target Ik with a receiving power PRR,I with k, j c {l, 2, ..., N} and k :1.
All measurements are taken for an identical frequency of signal 5, or by utilising a sinus signal. Subsequently the measurements are repeated preferably for gradually changed frequencies f of signal 5, in order to ascertain the frequency-dependent radar cross-section P051 (f) For each measurement the transmission power PIi and the receiving power PRi, are measured on the radar target lic operated as radar. In total therefore, following the measurements, the transmission powers present are: PIk3,-i, l2 and PTkI, l2 and the receiving powers are: PRk.7, Ii, 1=2, and PRk=1,j=2. Furthermore, for each pairing, the distance 20 Dk,-j present between the respective radar targets K and T is ascertained by means of laser range measuring.
Furthermore based on known distances Dk,J of the radar transponders Ik and T during the measurements, and the ascertained ratios PRk,/PTk,: PRk.,jI /PTk,j1, PRk7,i2/PIky,i2 and PRkl,jr/PTkl,1r, the radar cross-sections P031 of radar transponders Ij are ascertained based on the following radar equation: (1) PR =PL. 2 A'.j (4)3 D:j4 with C: antenna gain of the receiving antenna EA, Cr: antenna gain of the transmitter antenna 3A1, and A wavelength of the radar signal.
This equation (1) describes the receiving power PRK,1 received from a radar target Ii with an antenna gain Cr of the receiving antenna EAK as a function of the radar cross section RCS; of the radar target I at a distance DR,J, and the transmission power PIk,1 of the radar transmitter Sk with a transmitting antenna SAic comprising an antenna gain Gt, for a wavelength A of the emitted signal S. The radar cross-section RCS may also be expressed as the total gain G1 ("loop gain") of the radar target 1j. This results in: (3) RCS. = wherein the loop gain can he typically expressed as follows: G = Gs*GekGr, i.e. as a product of the antenna gain G5 of the transmitting antenna SA1 of the radar target T, the antenna gain Gr of the receiving antenna EA of the radar target Ij, and the gain Ce of the electrical amplification of the received signal at the radar target T. Equations (2) and (3) result in: (4) RCS, wherein Gtx and Crx are the gains of the transmission path / the receiving path in the radar target I-j, i.e. a combination of antenna gain and gain by electrical amplification in the respective path. The transmission path / the receiving path, with reference to fig. 1, results from the signal path in the radar receiver 221 such as the radar transmitter 222.
Equations (2) and (3) can be combined to form one equation.
Here it is presumed as explained above, that the radar target Ik is operated as a radar, and the radar target T is operated as a radar transponder. This results in: PJL. 4 (5) = RCS1RcS.
PL, (4irYD.4 L For the proposed three pairings three equations are thus obtained. These equations can be transformed by a logarithmic transformation into a linear equation system.
This is possible because all expressions are larger than zero.
For simplification, the same symbols are then used for the radar cross-section RCS-j, however, it is pointed out that following the logarithmic transformation: 10 log(...) they now refer to values which are indicated in decibel.
Equation (5) can then be expressed as follows: (6) RCSk ±RCS, =1-C CD 0. H ci-ci-HOt H OH 0 ci-i--U OH H-0 00 H Cu H H H-(Ci 0. CD 0. OH ci-H H-C (DO OH HOC LCD CD (D H-o C ci-ci-H-ct (DO LQ CDt* 0 Ft HO H.-CD H Hi H-H H-C/) Cl) H (DO OH C C/) 0 CD CD CD <H d I CnN) H HF-C H 00 t H L HH CD CD t'"-. 0 HO C/JOt H-CD H-' C/JO H-HN)(D aDi 0 CD HLCD 0 CD t (j H H LCD ci-C H-r --. r-CD &-. CD H CD CD H ctH C H -CD H CD 0.0 fl CD 00 0 ci-oOO H-CD H-cl-(D ci--a 0H CD H HO LCD 0 OH-CD CD. CD 00 CD II t CD Cu C/JO ci-H H-I a -0 a H H ct H-ao CD C/J Z 00 a I CD H-CD CD 00 H /)j a tC)I-H-CD 000 t CD 0 H-H HO H-H 0. ---H-C ci-H HiC C H-HO Cl) CuCD Hi H. CD H a ci-CD H-H OH-H- 0 -C o ----.-*----------. a -, a CD 0 LCD OH-Hi 0 P. H H-H 0 ci-H H H CD t-Di 0 H CD H-H H->-. Dl (D Q CDLC H -Cu H-H-H K I -CD CD C (U CD HH LCD 0 CD CD Dl C K 0 ci-, --0 ci-ci-GO > b/CD P.CD H c) trC> CD OLO A t CD) k Cu H-C ci-F ci-H H Cl) \/ ci-OH 0. aH-o 0. -I -CD P.ci-kQ o-a (DO CD H-CD C. CD t H OH 0 H II H ao H H-- 0 CD CD a 1 5ci-0 -H Hci--+-H H-wC H H ci-H- H ci-Dl ci-OH Dl H H 000 H CD H-H-H 1)'" K CC/JO H-Fc H-0H 000 C C -L HO H-H H 00. HO CD H II ii I I H H-CD C/i H-0.0 H 00 I? --4 OH -H a CD CD H-CD a H 000 M I I CD -I 0 (DO OH HiHCD rm -F-) H) a CDDJ -HH H-H CD a H H ci-H-H --I.. -CD CD CD CD CD CD H- H H-CD 0 ci H-H aC/it a H CD 0H H I 0 OH CD H0 CD CD (DC/I Cl) H HaCD C/i H HCD H CD H H H H OH 0 pCD H-H H-HH CD C/I o a Cl) CD 0H HK H-H-Cl) H CD H aCD H H CD HO K H-ci- 000 CD ci c-i-H-0 CD a OH-H H-OH ci-0 Cl) Di ci-CD CDH CD CD H CD H 0H0 H-H H-0 HctK H-H- FiG 0 0(00 * Hi H OT Cu HO Hi H H CD H C/i i--CD H C/i CD CD H-H ci-H-H Dli 00 0 H C/I H-H-H H-0 H-C/i, H H-H-00 CD 0ci-H-o H Di CD 00 00 ao C/JO CD H ci-a H-0 i Hi H-H-ci-H 0 H C/i CD CD.° H-receiving antenna EA2, and a unit D2, with which the radar transmitter S2. in a transponder mode TM of the radar target 12, is connected with the radar receiver F2, so that a signal S received by the radar receiver F2 is again emitted by the radar transmitter 52, and with which the radar transmitter 52, in a radar mode P.M of the radar target 12 is not connected with the radar receiver E2, so that the radar transmitter 52 and the radar reoeiver F2 operate independently of each other, and a radar target T3 comprises a radar transmitter 53 with a transmitting antenna SA3, a radar receiver F2. with a receiver antenna EA3, and a unit D3, with which the radar transmitter S is connected with the radar receiver F7, so that a signal S received by the radar receiver F3 is again emitted by the radar transmitter 53, or the radar target T is a passive radar target, which reflects an incoming signal S. The method comprises the following steps: In a first step 101 a signal S is emitted by the radar transmitter Sk of one of the radar targets Ik with a transmission power PIk,i, a signal S is received by another of the radar targets T, the received signal S is emitted or reflected by the other radar target Ii, and a signal S emitted by the radar target T is received by the radar receiver Fk of the radar target Ij< with a receiving power PRj,], withk, j a {1, 2,..., N} andk!=j.
In a second step 102 step 101 is executed for N different pairings IkIj of radar targets Tk and I-j, wherein the pairings IkIj and T1Tk are considered identical.
In a third step 103, based on known distances D],J of the radar transponders and Ii during execution of steps 101 and 102 and based on the ascertained ratios PR,k/PIk,, the radar cross-sections RCS1 of radar transponders Th are ascertained based on the following relationship: G.GA*RCS, (1) PR=PT,, " 1 $ * D. with CR: antenna gain of the receiver antenna EAk, C1: antenna gain of the transmitter antenna SAk, and A wavelength of the radar signal.
Although the invention has been illustrated and described in detail by way of preferred exemplary embodiments, the invention is not limited by the disclosed embodiments, and other variations may be derived therefrom by the expert without deviating from the scope of the invention. It is therefore clear that a multitude of possible variations exists. It is also clear that embodiments cited as examples really only represent examples, which should not be understood in any way as limiting the protective scope, the passible applications or the configuration of the
invention. Rather, the above description and the
description of the figures enable the expert to translate the exemplary embodiments into practice, wherein the expert, in the knowledge of the disclosed inventive idea, can make various changes, for example as regards the function or the arrangement of individual elements named in an exemplary embodiment, without deviating from the protective scope which is defined by the claims and their legal equivalents such as the extended explanation in the
description.
Claims (11)
- CLAIMS1. A method for radiometric calibration of the radar section RCS1 of a number N of radar targets T, with ± = 1, 2, ..., N, and N »= 3, wherein at least: one radar target Ti comprises a radar transmitter Si with a transmitting antenna SA1 and a radar receiver F1 with a receiver antenna EA1, wherein the radar receiver F1 and the radar transmitter Si operate independentiy of each other; one radar target T2 comprises a radar transmitter 52 with a transmitting antenna 5A2, a radar receiver F2 with a receiver antenna EA2 and a unit D2, with which the radar transmitter 52, in a transponder mode TM of the radar target Ic, is connected, so that a signal S received by the radar receiver F2 is emitted again by the radar transmitter S2, and with which the radar transmitter 52, in a radar mode FM of the radar target I>, is not connected with the radar receiver F2, so that the radar transmitter S2 and the radar receiver Fc operate independently of each cther; and one radar target T3 comprises a radar transmitter Si with a transmitting antenna SA3, a radar receiver F3 with a receiver antenna FA3, and a unit D3, with which the radar transmitter Si is connected with the radar receiver F3, so that a signal S received by the radar receiver Fi is again emitted by the radar transmitter Si, or the radar target 13 is a passive radar target, which reflects an incoming signal 5, wherein the method comprises: a) emission of a signal S by the radar transmitter Sic of one of the radar targets Ik with a transmission power PIk,i, reception of the signal S by another of the radar targets T1, emission or reflection of the received signal S by the other radar target T1, and reception of the signal S coming from the radar target Ij by the radar receiver Ek of the radar target Tk with a receiving power PR1,j, with k, j c {1, 2, ..., N} and k!= j; b) execution of step a) for N different pairings TkTj of radar targets Tk and T, wherein the pairings k'j and IIj are considered identical; and c) based on known distances Dk,j of the radar transponders Tk and T during execution of steps a) and b) and based on ascertained ratios PRk,j/PTk,j, determination of radar cross-sections RCS1 of radar transponders T1 based on the following relationship: c.c; -Rcc Pit =PF T in which Gk is an antenna gain of the receiver antenna EA1, CT is an antenna gain of the transmitter antenna SAk, and A is a wavelength of the radar signal.
- 2. The method of claim 1, wherein the radar target Ii comprises a unit Di, with which the radar transmitter Si, in a transponder mode TM of the radar target Ti, is connected with the radar receiver Fi, so that the signal S received by the radar receiver Fi is again emitted by the radar transmitter Si, and with which the radar transmitter Si, in a radar mode PM of the radar targot Ti, is not oonncctcd with thc radar receiver Ei, so that the radar receiver Fi and the radar transmitter Si operate independently of one another.
- 3. The method of claim 1 or claim 2, wherein the radar target T3 comprises a unit D?., with which the radar transmitter S, in a transponder mode TM of the radar target 13, is connected with the radar receiver F3, so that a signal S is again emitted by the radar transmitter S, and with which the radar transmitter 5?:, in a radar mode PM of the radar target I?:, is not connected with the radar receiver E, so that the radar receiver E7 and the radar transmitter S operate independently of one another.
- 4. The method of any of claims 1 to 3, wherein the steps a) , b) and c) are executed for different transmitting frequencies f of the radar transmitters S, wherein the radar cross sections RCS1 of radar targets T1 are ascertained as frequency-dependent radar cross-sections RCS1(f)
- 5. The method of any of claims 1 to 4, wherein the steps a) , b) and c) for each pairing IiIj are executed for different distances Dk,-of the radar targets Ik and T1, wherein the measured distance-dependent ratios (PRk,1/PIk,l) ( D,j) are utilised for the correction of multipath effects during determination of the radar cross-sections R053.
- 6. The method of any of claims 1 to 5, wherein the steps a) , b) and c) are executed for different polarisations P of the signal 5, wherein the radar cross-sections RCS of radar targets I are ascertained as polarisation-P-dependent radar cross-sections RCS1(P)
- 7. The method of any of claims 1 to 6, wherein the steps a) , b) and c) are repeated g-times and the radar cross-sections P053 are ascertained as mean values <RCSi>q.
- S. The method of any of claims 1 to 7, where the units D1, in transponder mode TM of the radar target T, amplify and/or filter and/or delay over time, signals S received by the radar receiver F1, before these signals are forwarded to the radar transmitter Sj.
- 9. The method of any of claims 1 to 8, wherein the distances Dk,j between the radar targets Ik and I satisfy the condition: > (2*Dl)/A in which D is an antenna diameter of the transmitting antenna SA1 A is the wavelength of signal S
- 10. The method of any of claims 1 to 9, wherein the transmitting antenna SAK of the radar target K and the receiving antenna FA of the radar target I are aligned in a ocpclar manner.
- 11. A method as herein described with reference to the accompanying description and/or to the accompanying drawings.
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| Application Number | Priority Date | Filing Date | Title |
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| DE102014110079.4A DE102014110079B3 (en) | 2014-07-17 | 2014-07-17 | Method for absolute radiometric calibration of the radar backscatter cross section of radar targets |
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| CA (1) | CA2897569C (en) |
| CH (1) | CH709940B1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109541560A (en) * | 2018-11-14 | 2019-03-29 | 辽宁工程技术大学 | A kind of Calibration Method based on communication signal tower |
| US10908258B2 (en) | 2016-02-03 | 2021-02-02 | Deutsches Zentrum für Luft- und Raumfahrt e. V. | Method for calibrating an active sensor system |
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| CN105466365B (en) * | 2015-11-12 | 2017-11-17 | 中国科学院光电研究院 | The method for obtaining radar corner reflector RCS precision |
| CN110146859B (en) * | 2019-05-30 | 2021-07-06 | 中国人民解放军63921部队 | Method and device for radar scattering cross section RCS calibration |
| CN111551904A (en) * | 2020-04-03 | 2020-08-18 | 北京无线电计量测试研究所 | Method and device for measuring radar scattering cross section parameter field calibration |
| CN113281710B (en) * | 2021-05-11 | 2023-04-11 | 北京无线电计量测试研究所 | Darkroom calibration method for measuring radar scattering cross section parameters |
| CN113534150B (en) * | 2021-06-08 | 2022-04-05 | 国家卫星海洋应用中心 | Satellite-borne synthetic aperture radar ocean scene observation radar gain setting method and system |
| CN117392549B (en) * | 2023-12-08 | 2024-04-09 | 齐鲁空天信息研究院 | Target characteristic extraction method and system based on high-resolution SAR image |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2221590A (en) * | 1987-12-02 | 1990-02-07 | Plessey Co Plc | Radar system calibration apparatus |
| US20040246169A1 (en) * | 2003-06-03 | 2004-12-09 | Fujitsu Ten Limited | Target determination apparatus, target judgement apparatus, and determination aid apparatus |
| US20140002297A1 (en) * | 2012-06-27 | 2014-01-02 | Government Of The United States, As Represented By The Secretary Of The Air Force | Low Clutter Method for Bistatic RCS Measurements |
-
2014
- 2014-07-17 DE DE102014110079.4A patent/DE102014110079B3/en active Active
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2015
- 2015-07-16 CA CA2897569A patent/CA2897569C/en active Active
- 2015-07-16 GB GB1512481.1A patent/GB2529934B/en active Active
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2221590A (en) * | 1987-12-02 | 1990-02-07 | Plessey Co Plc | Radar system calibration apparatus |
| US20040246169A1 (en) * | 2003-06-03 | 2004-12-09 | Fujitsu Ten Limited | Target determination apparatus, target judgement apparatus, and determination aid apparatus |
| US20140002297A1 (en) * | 2012-06-27 | 2014-01-02 | Government Of The United States, As Represented By The Secretary Of The Air Force | Low Clutter Method for Bistatic RCS Measurements |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10908258B2 (en) | 2016-02-03 | 2021-02-02 | Deutsches Zentrum für Luft- und Raumfahrt e. V. | Method for calibrating an active sensor system |
| CN109541560A (en) * | 2018-11-14 | 2019-03-29 | 辽宁工程技术大学 | A kind of Calibration Method based on communication signal tower |
| CN109541560B (en) * | 2018-11-14 | 2023-05-23 | 辽宁工程技术大学 | Radiation calibration method based on communication signal tower |
Also Published As
| Publication number | Publication date |
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| GB2529934B (en) | 2018-11-14 |
| CA2897569C (en) | 2023-03-21 |
| GB201512481D0 (en) | 2015-08-19 |
| DE102014110079B3 (en) | 2015-07-09 |
| CH709940B1 (en) | 2020-03-13 |
| CA2897569A1 (en) | 2016-01-17 |
| CH709940A2 (en) | 2016-01-29 |
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