CN102565767A - Ground verification instrument of satellite-based marine radar height gauge - Google Patents
Ground verification instrument of satellite-based marine radar height gauge Download PDFInfo
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- CN102565767A CN102565767A CN2011104394808A CN201110439480A CN102565767A CN 102565767 A CN102565767 A CN 102565767A CN 2011104394808 A CN2011104394808 A CN 2011104394808A CN 201110439480 A CN201110439480 A CN 201110439480A CN 102565767 A CN102565767 A CN 102565767A
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Abstract
The invention provides a ground verification instrument of a satellite-based marine radar height gauge, which is used for performing absolute calibration, performance examination and function test on the satellite-based marine radar height gauge in a laboratory. The ground verification instrument of the satellite-based marine radar height gauge comprises a time service unit, a transceiving control unit, a transmitting unit, a receiving unit, a frequency heald unit and a numerical control unit. The frequency heald unit utilizes an ultra-stable crystal oscillator signal provided by a radar height gauge to be verified as a clock. The time service unit takes charge of providing accurate synchronous time service for the numerical control unit and the radar height gauge. The transceiving control unit takes charge of respectively and simultaneously sending signals transmitted by the transmitting unit to the receiving unit and the radar height gauge and also controlling the receiving unit to receive the signals transmitted by the radar height gauge or the signals transmitted by the transmitting unit. The numerical control unit takes charge of eliminating channel influences of a verification instrument system, generating calibration signals, simulating echo signals of various target scenes and controlling the transceiving control unit, the receiving unit, the transmitting unit and the frequency heald unit.
Description
Technical field
The present invention relates to the calibration of ground experiment chamber, service check and function test system before the spaceborne ocean radar altimeter emission are specifically related to a kind of spaceborne ocean radar altimeter ground calibrating instrument.
Background technology
Spaceborne ocean radar altimeter is a kind of very important ocean microwave remote sensing device, and it is high accurately to measure global mean sea level, and the degree of accuracy of measurement reaches a centimetre magnitude.Along with the development of microwave remote sensing technique in recent years, the measurement that spaceborne ocean radar altimeter is high to mean sea level at the 2m significant wave height, under 1 second average situation, can reach 2 centimetres.Dividing the design objective of first spaceborne ocean radar altimeter of China of emission in August, 2011 is 4 centimetres.Because the principle of spaceborne ocean radar altimeter is to calculate the distance of sea and radar through the delay of measuring electromagnetic wave transmission in the space; Therefore; Before emission; Must accurately measure the path delay of electromagnetic signal in spaceborne ocean radar altimeter internal transmission with quite high precision, this part postpones usually about 1 meter.Therefore, in the path delay of spaceborne ocean radar altimeter internal transmission, must before emission, come out by the absolute calibration experiment measuring through ground.
Because the survey high target of spaceborne ocean radar altimeter is very high, reaches 2～4 centimetres, and since the needs of marine monitoring need in orbit for a long time, so need before emission, carry out service check and system evaluation spaceborne ocean radar altimeter.
In order to realize high-precision measurement, spaceborne ocean radar altimeter must be predicted and the tracking lock sea echo signal more accurately.Therefore a critical function of spaceborne ocean radar altimeter is exactly to launch under the situation about changing in the object height characteristic, still the tracking lock echoed signal.Because the wave height of ocean and mean sea level height change in the world; And satellite orbital altitude also changes; And satellite also can fly over the non-marine environment sky such as land; Therefore spaceborne ocean radar altimeter might be followed the tracks of losing lock in the flight measurement process, and this just requires spaceborne ocean radar altimeter when tracking lock is failed, and can get into acquisition mode; When acquisition success, can change the tracking lock pattern over to.Before spaceborne ocean radar altimeter emission, must test this function.When this just required that spaceborne ocean radar altimeter carried out functional test, the echo of simulation must be able to reflect the variation of scene echoes.
In the world, European Space Agency is at ERS-1, and ERS-2 is equipped with spaceborne ocean radar altimeter on Envisat and the Cryosat satellite, and has carried out functional test on ground; The Topex of the U.S. and France's cooperation, the spaceborne ocean radar altimeter of Jason series have also carried out functional test, and have carried out Performance Evaluation before emission.But, all do not see detailed absolute calibration and survey high-performance check report.These functional tests and Performance Evaluation all are that the echo simulator with documents claim carries out, but do not disclose any equipment or method that can realize absolute calibration and service check.
It is at home, existing that what be used for spaceborne ocean radar altimeter is carried out functional test is echo simulator.Because the echo simulator channel latency can not be separated with the radar altimeter channel latency, thereby can't provide the radar altimeter channel latency.In addition; The frequency of existing echo simulator is combined the used ultra stable crystal oscillator in unit and the ultra steady crystal oscillator oscillator of radar altimeter is two oscillators, thereby makes the statistical nature of echo simulator and each self-recording echo of radar altimeter be difficult to keep in full accord.Existing echo simulator uses digital circuit to confirm echo delay, and present electronic circuit technology can't be eliminated the time jitter of 1 nanosecond, promptly can't eliminate the shake of 15cm.There is existing echo simulator data recording not keep therefore also just can not testing synchronously again, can't confirms also whether the markers of radar altimeter is correct with radar altimeter to the markers function of radar altimeter.The structure of the echo simulator of prior art is shown in Fig. 1-a.
Because above-mentioned defective; Make present existing echo simulator to carry out absolute calibration to radar altimeter; The echo simulator that is prior art can only compare rough Performance Evaluation to radar altimeter, can not carry out absolute calibration, service check and the system evaluation of centimetre-sized to the radar altimeter range performance.
Summary of the invention
The objective of the invention is to, can not carry out the problem of absolute calibration and service check on ground to spaceborne ocean radar altimeter emission is preceding for solving prior art, thereby a kind of spaceborne ocean radar altimeter ground calibrating instrument is provided.
For realizing above-mentioned purpose; The invention provides a kind of spaceborne ocean radar altimeter ground calibrating instrument; It is that spaceborne ocean radar altimeter to be examined and determine carries out absolute calibration, service check and functional test that this calibrating instrument is used in the laboratory; Comprise: receiving element, transmitter unit, frequently comprehensive unit and numerical control unit is characterized in that said calibrating instrument also comprises: the transmitting-receiving control module; Said transmitting-receiving control module transmits simultaneously, gives respectively said receiving element and spaceborne ocean radar altimeter to be examined and determine with said transmitter unit; Also be responsible for the signal that the said receiving element of control receives spaceborne ocean radar altimeter emission to be examined and determine, the signal of perhaps said transmitter unit emission.
In the technique scheme, the ultra steady oscillator clock that the comprehensive unit of said frequency uses spaceborne ocean radar altimeter is as work clock.Said calibrating instrument also comprises a time service unit, and this time service unit is used for carrying out time service for said numerical control unit and spaceborne ocean radar altimeter to be examined and determine simultaneously.
Said transmitting-receiving control module further comprises: first waveguide switch 1, second waveguide switch 2 and a power splitter; Said power splitter, first waveguide switch 1 and second waveguide switch 2 are connected successively, and said first waveguide switch is used for and spaceborne ocean radar altimeter two-way signaling transmission to be examined and determine; And an output terminal of said power splitter also is connected with second waveguide switch, 2 one input ends; The output terminal of said transmitter unit links to each other with the input end of said power splitter, and the output terminal of said second waveguide switch 2 links to each other with the input end of said receiving element; And said numerical control unit also is used for to said first waveguide switch 1 and second waveguide switch 2 control signal being provided.
In the technique scheme, said numerical control unit further comprises:
The AD sampling module, the signal that is used for the spaceborne ocean radar altimeter emission that reception is to be examined and determine carries out the AD sampling, obtains the sampled value sequence of calibrating instrument channel response function or analogue echo;
Simulate signal sequence acquiring unit is used to obtain the Serial No. of simulation objectives echoed signal, and wherein simulate signal directly reads from local mass storage;
Convolution unit; The sampled value sequence that is used for sampling unit is obtained and the Serial No. of simulation objectives echoed signal carry out convolution; Generation is used for to the baseband signal of ocean radar altimeter to be examined and determine calibration and produces the analog echo signal that the ocean radar altimeter that is used to treat calibrating carries out service check; (wherein, said simulate signal sequence acquiring unit and convolution unit are closed and are called " analogue echoes unit ", perhaps are " digital echo acquiring unit ", and both can realize in the DSP device) and
DA conversion and transmitter module, the signal that is used for that convolution unit is finally obtained carry out sending to radio frequency unit and sending to ocean radar altimeter to be examined and determine through the transmitting-receiving control module after the digital-to-analog conversion, are used for ocean radar altimeter is calibrated and service check;
Wherein, said convolution unit can be with fast convolution unit replacement, and this unit by using Fourier transform uses the sampled value sequence that fast convolution obtains sampling unit and the Serial No. of simulation objectives echoed signal to carry out convolution algorithm.
Optional, said numerical control unit is through USB2.0 interface and computing machine communication, and this computing machine is provided with the running parameter of calibrating instrument through USB2.0, and downloads emulated data and receive measurement data.Said time service unit further comprises and is connected in series successively: ultra steady oscillator, counter and RAM storer.Said frequency is combined the unit and is further comprised: frequency synthesizer, linear FM signal generator, frequency multiplier and/or frequency mixer.
Based on the described spaceborne ocean radar altimeter of technique scheme ground calibrating instrument, the present invention also provides a kind of calibrating method, and said calibrating method comprises following steps:
The spaceborne ocean radar altimeter t0 of step 1) is emitting radio frequency signal constantly, after the delay through transmission channel Δ t1, gets into the cable that connects spaceborne ocean radar altimeter and ground calibrating instrument; After passing through the delay of Δ tx1 again, arrive second waveguide switch 2, get into the receiving cable of calibrating instrument; After through the delay of Δ t2, get into the mixing unit and go oblique local oscillator mixing to obtain intermediate-freuqncy signal constantly at t2; Wherein to go the time of oblique frequency mixer be t2+ δ t2 to the actual arrival of signal; Wherein t2 is obtained by the crystal oscillator clock; δ t2 can be obtained by Tracking Estimation, and intermediate-freuqncy signal is carried out quadrature demodulation, filtering and A/D conversion, and the digital signal that obtains deposits in the data-carrier store;
Step 2) numerical control unit is used the digital quadrature signal and the synthetic digital echo signal of the scene echoes signal of emulation in advance that obtains in the step, is stored in the data-carrier store again;
Step 3) under the control of the microprocessor of numerical control unit, digital echo signal synthetic in last step behind suitable time-delay, by D/A converter convert to the analogue echo orthogonal signal and with up-conversion Chirp signal mixing, be the t3 moment this moment; After delay, arrive power splitter, get into the cable that connects spaceborne ocean radar altimeter and ground calibrating instrument through transmission channel Δ t3; Again through arriving the antenna port of radar altimeter after the delay of Δ tx2 and getting into the receiving cable of radar altimeter; After the delay through Δ t4, but gone the actual arrival of oblique mixing signal to remove the time t4+ δ t4 of oblique frequency mixer by the spaceborne radar altitude gauge constantly at t4, thereby and be converted into digital signal and be locked tracking;
Step 4) simultaneously, the signal of calibrating instrument emission is given own receiving cable through power splitter loopback after the delay of Δ tx3, at t5+ δ t5 constantly by self receiver reception and be stored as digital signal;
Step 5) is repeatedly tested according to following formula, can obtain absolute delay E [the Δ t of altitude gauge system
1+ Δ t
4], i.e. the average of absolute delay, thus realize absolute calibration, obtain comprising the spaceborne radar altitude gauge system delay of radar altimeter track algorithm deviation;
Δt
1+Δt
4＝(t
4-t
0+δt
4)-(t
5-t
2+δt
5-δt
2)-Δt
x1-Δt
x2+Δt
x3；
Wherein, Δ t
X1, Δ t
X2With Δ t
X3It is the corresponding delay of concentric cable; t
0, t
2, t
4And t
5Be the high stability crystal oscillator timing of spaceborne ocean radar altimeter, δ t
2, δ t
4With δ t
5Be that the track algorithm error is estimated to obtain by tracker.
Optimize, the digital signal of the analogue echo before the said D/A calculates according to following formula:
Wherein, s
r(t) be the analog echo signal that calibrating instrument will send to spaceborne ocean radar altimeter and this calibrating instrument receiving element, S
r(f
t) be its corresponding frequency-region signal; S (f
t) be the sea-surface target echo simulation signal of frequency domain; S
Rvs(f
t) be the calibrating instrument emission coefficient response of frequency domain,
Be its conjugation, | S
Rvs(f
t) |
2It is its power spectrum.
Compared with prior art, technical advantage of the present invention is:
1, calibrating instrument of the present invention use radar altimeter ultra stable crystal oscillator clock as work clock, thereby make calibrating instrument to keep clock homology and clock synchronization with altitude gauge.
2, calibrating instrument of the present invention adopts three branch road calibration technologies based on the transmitting-receiving control module (calibrating instrument transmitter unit-spaceborne ocean radar altimeter, calibrating instrument transmitter unit to calibrating instrument receiving element, spaceborne ocean radar altimeter to the calibrating instrument receiving element) can eliminate the influence of calibrating instrument channel to the test signal path delay when making that calibrating instrument carries out absolute calibration to altitude gauge; And can calculate the channel latency of spaceborne ocean radar altimeter, realize absolute calibration spaceborne ocean radar altimeter.
3, according to three branch road measuring-signals of calibrating instrument, numerical control unit can calculate the system responses of calibrating instrument, thereby eliminates the influence of calibrating instrument system responses function to guinea pig altitude gauge echoed signal.
4, calibrating instrument of the present invention adopts independently the time service unit identical, high-precision time service to be provided simultaneously for calibrating instrument numerical control unit and altitude gauge.Thereby markers function and system performance to altitude gauge are tested.
Description of drawings
Fig. 1-a is the composition frame chart of the echo simulator of prior art;
Fig. 1-b spaceborne ocean radar altimeter of the present invention ground calibrating instrument principle composition frame chart;
The spaceborne ocean radar altimeter of Fig. 2 employing of the present invention ground calibrating instrument carries out the principle schematic of absolute calibration;
The time service unit composition frame chart of Fig. 3 spaceborne ocean radar altimeter of the present invention ground calibrating instrument;
The transmitting-receiving control module composition frame chart of Fig. 4 spaceborne ocean radar altimeter of the present invention ground calibrating instrument;
The numerical control unit composition frame chart of Fig. 5 spaceborne ocean radar altimeter of the present invention ground calibrating instrument;
Fig. 6 is the process flow diagram of the calibration process of spaceborne ocean radar altimeter of the present invention ground calibrating instrument;
The frequency of Fig. 7 spaceborne ocean radar altimeter of the present invention ground calibrating instrument combine the unit each frequency signal obtain synoptic diagram.
Embodiment
Below in conjunction with accompanying drawing and specific embodiment the present invention is done further description.
Spaceborne ocean radar altimeter according to the invention ground calibrating instrument comprises the time service unit, the transmitting-receiving control module, and transmitter unit, receiving element is combined unit and numerical control unit, frequently shown in accompanying drawing 1-b.Wherein, the transmitter unit in the echo simulator of said transmitter unit, receiving element and prior art and the similar of receiving element are not done at this and to be given unnecessary details; Described frequency combines the unit and numerical control unit can improve based on comprehensive unit of the frequency on the echo simulator of prior art and numerical control unit.Wherein, the basic improvement of frequently combining the unit is: combining the unit frequently is the frequent rate signal of each point that calibrating instrument provides, and such as 2870MHZ, 12.48GHz etc. obtain by the clock multiplier/frequency division of ultra steady oscillator of examining and determine radar altimeter of waiting of input.The sequential control of DDS generator and frequency of operation also thus clock provide.The basic improvement of numerical control unit is: sequential control with its on the device frequency of operation (it < and can not be any delay that the integral multiple that is actually the work clock of radar altimeter to be examined and determine postpones by combine the clock sent here the unit through overfrequency; Because the randomness of signal transmission path Design of length in the side circuit, this is easy to be left in the basket >).In addition, numerical control unit is frequently combined the unit except control, and transmitter unit is with beyond the receiving element work, the also waveguide switch switching of control transmitting-receiving control module (switching sequence of waveguide switch should according to the system works timing Design).
The principle of work of spaceborne ocean radar altimeter according to the invention ground calibrating instrument is shown in accompanying drawing 2.Wherein the C1 point is represented waveguide switch 2, C2 point expression power splitter; The antenna port of B1 point and B2 point expression radar altimeter (for easy analysis, draws their differentiations, respectively as altitude gauge emission port and receiving port.Physically they are that same port is an antenna port).Calibration process is following:
The radiofrequency signal that the spaceborne ocean radar altimeter t0 of step 1) launches constantly after the delay through transmission channel Δ t1, gets into the cable that connects spaceborne ocean radar altimeter and ground calibrating instrument.After passing through the delay of Δ tx1 again, arrive waveguide switch 2, get into the receiving cable of calibrating instrument.Get into down-converter unit after through the delay of Δ t2 and go oblique local oscillator mixing (but to go the time of oblique frequency mixer be t2+ δ t2 to the actual arrival of signal, wherein t2 is obtained by the crystal oscillator clock, δ t2 can be obtained by Tracking Estimation) constantly, obtain intermediate-freuqncy signal at t2.It is carried out quadrature demodulation, filtering and A/D conversion, and the digital signal that obtains deposits in the data-carrier store.
Step 2) the digital echo signal synthesis unit is stored in the data-carrier store with digital quadrature signal that obtains in (1) step and the synthetic digital echo signal of scene (such as the sea) echoed signal of emulation in advance again.
Step 3) under the control of numerical control unit microprocessor, digital echo signal synthetic in (2) step behind suitable time-delay, by D/A converter convert to the analogue echo orthogonal signal and with up-conversion Chirp signal mixing, be the t3 moment this moment.After delay, arrive power splitter, get into the cable that connects altitude gauge and ground calibrating instrument through transmission channel Δ t3.Again through arriving the antenna port of radar altimeter after the delay of Δ tx2 and getting into the receiving cable of radar altimeter.After the delay through Δ t4, gone oblique mixing (the time t4+ δ t4 of oblique frequency mixer is removed in the actual arrival of signal) by the spaceborne radar altitude gauge constantly at t4 thus and be converted into digital signal and be locked tracking.Step 4) simultaneously, the signal of calibrating instrument emission is given own receiving cable through power splitter loopback after the delay of Δ tx3, at t5+ δ t5 constantly by self receiver reception and be stored as digital signal.
Δ t wherein
X1, Δ t
X2With Δ t
X3Be the corresponding delay of concentric cable, be easy to definite and highly stable; t
0, t
2, t
4And t
5Be the high stability crystal oscillator timing of spaceborne radar altitude gauge, corresponding range error can not surpass 0.1mm; δ t
2, δ t
4With δ t
5It then is the track algorithm error.Can obtain comprising the spaceborne radar altitude gauge system delay of radar altimeter track algorithm deviation according to above-mentioned calibration process:
Δt
1+Δt
4＝(t
4-t
0+δt
4)-(t
5-t
2+δt
5-δt
2)-Δt
x1-Δt
x2+Δt
x3 (1)
Therefore, radar altimeter is repeatedly tested, can be obtained absolute delay E [the Δ t of altitude gauge system according to following formula
1+ Δ t
4] (average of absolute delay) thus realize absolute calibration.After repeatedly testing, can also utilize D [Δ t
1+ Δ t
4] (standard deviation of absolute delay) carry out service check to radar altimeter, so that check it whether to reach design objective.
The time service unit of spaceborne ocean radar altimeter according to the invention ground calibrating instrument comprises independently ultra steady oscillator, counter and a RAM storer.The time service unit can be that the numerical control unit of ground calibrating instrument carries out accurate time service with spaceborne radar altitude gauge to be examined and determine simultaneously.Shown in accompanying drawing 3.
The transmitting-receiving control module of spaceborne ocean radar altimeter according to the invention ground calibrating instrument comprises power splitter and waveguide switch.The transmitting-receiving control module is responsible for giving receiving element and spaceborne ocean radar altimeter simultaneously, respectively with the signal of transmitter unit.The transmitting-receiving control module is controlled by numerical control unit, is responsible for the control receiving element and receives, the signal or the receiving radar altitude gauge signal of transmitter unit emission.Shown in accompanying drawing 4.Because ocean radar altimeter generally adopts Ku frequency range and C frequency range double frequency system, so accompanying drawing 4 provides is that Ku and C double frequency are received and dispatched the control module block diagram.
The frequency of spaceborne ocean radar altimeter according to the invention ground calibrating instrument is combined the unit, and its overstable crystal oscillator signal is provided by radar altimeter to be examined and determine, shown in accompanying drawing 1.
The numerical control unit of spaceborne ocean radar altimeter according to the invention ground calibrating instrument is shown in accompanying drawing 5.There is a radical word signal communication line to link between the numerical control unit of numerical control unit and radar altimeter, so that radar altimeter notice calibrating instrument, frequency that current radar altimeter transmitted and bandwidth.The digital signal of the analogue echo before the D/A calculates according to following formula:
S wherein
r(t) be the analog echo signal that calibrating instrument will send to radar altimeter and calibrating instrument receiving element, S
r(f
t) be its corresponding frequency-region signal; S (f
t) be the sea-surface target echo simulation signal of frequency domain; S
Rvs(f
t) be the calibrating instrument emission coefficient response of frequency domain,
Be its conjugation, | S
Rvs(f
t) |
2It is its power spectrum.
The generation method of the echo simulation signal of sea-surface target had had description in a lot of documents and materials, here not as claim, therefore also repeat no more.But, in the process of spaceborne radar altitude gauge analog echo signal, except the speed and attitude of satellite platform, also need consider earth rotation.Considering under the earth self-rotation, using following formula to carry out the echo simulation of sea-surface target:
Wherein s (t) is the sea-surface target echo simulation signal of time domain; s
i(t) be the time-domain signal of sea point target echo simulation, f
iBe that earth rotation causes, the Doppler frequency that the sea point target is corresponding.
Spaceborne ocean radar altimeter according to the invention ground calibrating instrument, to the workflow of radar altimeter calibration and service check shown in accompanying drawing 6.
Embodiment
Spaceborne ocean radar altimeter according to the invention ground calibrating instrument is on the basis of radar system and radar echo simulator, to form.Identical such as transmitter unit and receiving element with associated cell structures in the echo simulator, can repeat no more here with reference to existing document.
The ground calibrating instrument of present embodiment comprises: transmitting-receiving control module, frequently comprehensive unit, time service unit and numerical control unit specifically describe as follows to each unit:
The transmitting-receiving control module of calibrating instrument, the concrete realization block diagram of the transmitting-receiving control module of spaceborne ocean radar altimeter according to the invention ground calibrating instrument is as shown in Figure 4, and the technical indicator example is as shown in the table, the C frequency range is similar):
| The Ku frequency range | The C frequency range | |
| Centre frequency | ?13.58GHz | ?5.25GHz |
| Bandwidth | ?400MHz | ?400MHz |
| Switching time | ?≤1us | ?≤1us |
| The switch control level | Transistor-Transistor Logic level | Transistor-Transistor Logic level |
| Interface shape | ?SMA | ?SMA |
| Waveguide switch | Isolation＞50dB, Insertion Loss＜1.2dB | Isolation＞50dB, Insertion Loss＜1.2dB |
| Power splitter | Isolation＞15dB, Insertion Loss＜1.3dB | Isolation＞15dB, Insertion Loss＜1.3dB |
The frequency of ground calibrating instrument is combined the unit; The frequency of spaceborne ocean radar altimeter according to the invention ground calibrating instrument is combined the unit; The overstable crystal oscillator signal of the radar altimeter that use is to be examined and determine is as its crystal oscillator signal, and promptly the concrete meaning of Fig. 7 is to point out that it all is to obtain according to external source clock (being the ultra steady oscillator clock signal of radar altimeter) that calibrating instrument is combined each frequency signal of unit frequently.Frequently combine the FM signal of unit output, the radiofrequency signal of Ku, C-band is used for each tone signals such as intermediate-freuqncy signal of mixing, all is through this crystal oscillator signal being carried out frequency multiplication and frequency division obtains; The work clock of numerical control unit and needed incoming frequency also are that crystal oscillator signal provides thus.
The overstable crystal oscillator of radar altimeter described here is that radar altimeter is realized precision distance measurement key foundation parts.
Frequently combining unit and overstable crystal oscillator is the core component of calibrating instrument.In order to guarantee calibrating instrument and altitude gauge clock synchronization, and the frequency homology, the crystal oscillator signal is produced by spaceborne ocean radar altimeter and introduces through concentric cable.Frequently the technical indicator example of combining the unit is (can succinctly describe the major technique characteristic for asking here, deletion technical indicator, and it is as shown in the table only to provide the technical indicator of a frequency range of Ku, the C frequency range is similar) as follows:
The time service unit of ground calibrating instrument, the time service unit of spaceborne ocean radar altimeter according to the invention ground calibrating instrument, example is as shown in Figure 3.Ultra steady oscillator is that frequency is the ultra steady oscillator of atomic clock of 10MHz.Atomic clock is present state-of-the-art frequency source, and its frequency accuracy and degree of stability are high, helps to realize accurate time service.Frequency accuracy is superior to ± and 1 * 10
-10, short-term stability is superior to ± and 1 * 10
-11, long-term stability (3 years) is superior to ± and 1 * 10
-6The time service per second once.The time service unit is identical with the transmission delay that arrives ground calibrating instrument numerical control unit to the transmission delay of spaceborne ocean radar altimeter, and is postponed to confirm by read-write control lag and transmission line, is 100ns.
The numerical control unit of ground calibrating instrument, the numerical control unit of spaceborne ocean radar altimeter according to the invention ground calibrating instrument, example is as shown in Figure 5.Numerical control unit can pass through USB2.0 interface and computing machine communication.Computing machine is downloaded emulated data and is received the calibration data through the running parameter that USB2.0 is provided with calibrating instrument.Wherein FPGA is responsible for the work schedule of numerical control unit as processor controls, supports 1024 FFT computings of 10000 times/per second simultaneously; DSP is responsible for the floating point arithmetic of digital control system; A/D is responsible for gathering simultaneously I, the Q signal that the two-way bandwidth is 20MHz; D/A is responsible for generating simultaneously I, the Q signal that the two-way bandwidth is 40MHz.Specific targets are as shown in the table, and the C frequency range is similar):
| AD | | |
| Quantization digit | ||
| 10 | 12 | |
| Sampling rate | 60MSa/s | 80MSa/s |
| Bandwidth | 20MHz | 40MHz |
| The amplitude imbalance coefficient | ≤1∶1.2 | ≤1∶1.2 |
| Phase imbalance | <=5 degree | <=5 degree |
| Rise and fall in the band | ≤0.5dB | ≤0.5dB |
| Level | ±1V | ±1V |
| Interface | SMA | SMA |
The workflow of the described ground of technique scheme calibrating instrument specifically describes as follows shown in accompanying drawing 6:
After spaceborne ocean radar altimeter ground calibrating instrument and the radar altimeter start, the running parameter of computer installation calibrating instrument.Then, radar altimeter transponder pulse signal is given calibrating instrument, notifies the carrier frequency and the signal bandwidth of this pulse signal of calibrating instrument simultaneously with an independent digital signal.Calibrating instrument is according to the carrier frequency and the bandwidth information of the radar altimeter that receives, and the RF pulse signal of receiving radar altitude gauge emission also is converted into digital signal, and calculates the calibrating instrument system responses.The calibrating instrument numerical control unit utilizes the object scene simulate signal and the calibrating instrument system responses function of download, the digital echo signal of simulated target scene subsequently.After through the delay of setting, through the D/A conversion and with the FM signal mixing of combining the unit frequently, pass through again after the up-conversion mixing, send to the transmitting-receiving control module through transmitter unit.The transmitting-receiving control module is divided into the two paths of signals of constant amplitude, homophase with signal, presents respectively to radar altimeter and receiving element.Spaceborne ocean radar altimeter receives analogue echo remote sensing signal and the laggard line item storage of digitizing, and simultaneously, the calibrating instrument receiving element also carries out digitizing and record with the analog echo signal that receives.In the process of recorded and stored remotely-sensed data, the time that radar altimeter and calibrating instrument numerical control unit send according to calibrating instrument time service unit, data recorded is packed and preserved (perhaps being uploaded to computing machine).
Should be noted that at last above example only is used to explain the summary of the invention of claim part of the present invention.It should be appreciated by those skilled in the art,, and do not break away from the technical scheme block diagram scope of technical scheme of the present invention, all should be encompassed in the claim of the present invention even ins and outs are wherein implemented to make amendment or replacement on an equal basis.
Claims (9)
1. spaceborne ocean radar altimeter ground calibrating instrument; It is that spaceborne ocean radar altimeter to be examined and determine carries out absolute calibration, service check and functional test that this calibrating instrument is used in the laboratory; Comprise: receiving element, transmitter unit, frequently comprehensive unit and numerical control unit; It is characterized in that said calibrating instrument also comprises: the transmitting-receiving control module;
Said transmitting-receiving control module transmits simultaneously, gives respectively said receiving element and spaceborne ocean radar altimeter to be examined and determine with said transmitter unit; Also be responsible for the signal that the said receiving element of control receives spaceborne ocean radar altimeter emission to be examined and determine, the signal of perhaps said transmitter unit emission.
2. spaceborne ocean radar altimeter according to claim 1 ground calibrating instrument is characterized in that, the ultra steady oscillator clock that the comprehensive unit of said frequency uses spaceborne ocean radar altimeter is as work clock.
3. spaceborne ocean radar altimeter according to claim 1 and 2 ground calibrating instrument; It is characterized in that; Said calibrating instrument also comprises a time service unit, and this time service unit is used for carrying out time service for said numerical control unit and spaceborne ocean radar altimeter to be examined and determine simultaneously.
4. spaceborne ocean radar altimeter according to claim 3 ground calibrating instrument is characterized in that said transmitting-receiving control module further comprises: first waveguide switch 1, second waveguide switch 2 and a power splitter;
Said power splitter, first waveguide switch 1 and second waveguide switch 2 are connected successively, and said first waveguide switch is used for and spaceborne ocean radar altimeter two-way communication to be examined and determine; And an output terminal of said power splitter also is connected with second waveguide switch, 2 one input ends;
The output terminal of said transmitter unit links to each other with the input end of said power splitter, and the output terminal of said second waveguide switch 2 links to each other with the input end of said receiving element;
And said numerical control unit also is used for to said first waveguide switch 1 and second waveguide switch 2 control signal being provided.
5. spaceborne ocean radar altimeter according to claim 4 ground calibrating instrument is characterized in that said numerical control unit further comprises:
The AD sampling module, the signal that is used for the spaceborne ocean radar altimeter emission that reception is to be examined and determine carries out the AD sampling, obtains the sampled value sequence of calibrating instrument channel response function or analogue echo;
Simulate signal sequence acquiring unit is used to obtain simulation objectives echoed signal Serial No.;
Convolution unit; The sampled value sequence that is used for sampling unit is obtained and the Serial No. of simulation objectives echoed signal carry out convolution; Generation is used for to the baseband signal of ocean radar altimeter to be examined and determine calibration and produces the analogue echoes signal that the ocean radar altimeter that is used to treat calibrating carries out service check;
DA conversion and transmitter module; The signal that is used for that convolution unit is finally obtained carries out sending to transmitter unit and being transmitted to ocean radar altimeter to be examined and determine via said transmitting-receiving control module after the digital-to-analog conversion, is used for ocean radar altimeter is calibrated and service check;
Wherein, said convolution unit can be with fast convolution unit replacement, and this unit by using Fourier transform uses the sampled value sequence that fast convolution obtains sampling unit and the Serial No. of simulation objectives echoed signal to carry out convolution algorithm.
6. spaceborne ocean radar altimeter according to claim 1 ground calibrating instrument is characterized in that, said time service unit further comprises and is connected in series successively: ultra steady oscillator, counter and RAM storer.
7. spaceborne ocean radar altimeter according to claim 2 ground calibrating instrument; It is characterized in that; Said frequency is combined the unit and is used the ultra steady running clock of spaceborne ocean radar altimeter to be examined and determine as work clock and reference frequency; And further comprise: frequency synthesizer, linear FM signal generator, frequency multiplier and/or frequency mixer.
8. calibrating method that adopts aforesaid right to require 7 described spaceborne ocean radar altimeter ground calibrating instruments, said calibrating method comprises following steps:
The spaceborne ocean radar altimeter t0 of step 1) is emitting radio frequency signal constantly, after the delay through transmission channel Δ t1, gets into the cable that connects spaceborne ocean radar altimeter and ground calibrating instrument; After passing through the delay of Δ tx1 again, arrive second waveguide switch 2, get into the receiving cable of calibrating instrument; After through the delay of Δ t2, get into the mixing unit and go oblique local oscillator mixing to obtain intermediate-freuqncy signal constantly at t2; Wherein to go the time of oblique frequency mixer be t2+ δ t2 to the actual arrival of signal; Wherein t2 is obtained by the crystal oscillator clock; δ t2 can be obtained by Tracking Estimation, and intermediate-freuqncy signal is carried out quadrature demodulation, filtering and A/D conversion, and the digital signal that obtains deposits in the data-carrier store;
Step 2) numerical control unit is used the digital quadrature signal and the synthetic digital echo signal of the scene echoes signal of emulation in advance that obtains in the step, is stored in the data-carrier store again;
Step 3) under the control of the microprocessor of numerical control unit, digital echo signal synthetic in last step behind suitable time-delay, by D/A converter convert to the analogue echo orthogonal signal and with up-conversion Chirp signal mixing, be the t3 moment this moment; After delay, arrive power splitter, get into the cable that connects spaceborne ocean radar altimeter and ground calibrating instrument through transmission channel Δ t3; Again through arriving the antenna port of radar altimeter after the delay of Δ tx2 and getting into the receiving cable of radar altimeter; After the delay through Δ t4, but gone the actual arrival of oblique mixing signal to remove the time t4+ δ t4 of oblique frequency mixer by the spaceborne radar altitude gauge constantly at t4, thereby and be converted into digital signal and be locked tracking;
Step 4) simultaneously, the signal of calibrating instrument emission is given own receiving cable through power splitter loopback after the delay of Δ tx3, at t5+ δ t5 constantly by self receiver reception and be stored as digital signal;
Step 5) is repeatedly tested according to following formula, can obtain absolute delay E [the Δ t of altitude gauge system
1+ Δ t
4], i.e. the average of absolute delay, thus realize absolute calibration, obtain comprising the spaceborne radar altitude gauge system delay of radar altimeter track algorithm deviation;
Δt
1+Δt
4＝(t
4-t
0+δt
4)-(t
5-t
2+δt
5-δt
2)-Δt
x1-Δt
x2+Δt
x3；
Wherein, Δ t
X1, Δ t
X2With Δ t
X3Be the corresponding delay of concentric cable, stable and measurement easily; t
0, t
2, t
4With t5 be the high stability crystal oscillator timing of spaceborne ocean radar altimeter, δ t
2, δ t
4With δ t
5Be that the track algorithm error is estimated to obtain by tracker.
9. calibrating method according to claim 8 is characterized in that, the digital signal of the analogue echo before the said D/A calculates according to following formula:
Wherein, s
r(t) be the analog echo signal that calibrating instrument will send to spaceborne ocean radar altimeter and this calibrating instrument receiving element, S
r(f
t) be its corresponding frequency-region signal; S (f
t) be the sea-surface target echo simulation signal of frequency domain; S
Rvs(f
t) be the calibrating instrument emission coefficient response of frequency domain,
Be its conjugation, | S
Rvs(f
t) |
2It is its power spectrum.
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