CN112083414B - Dual-frequency detection method for radar altimeter and satellite-borne equipment - Google Patents
Dual-frequency detection method for radar altimeter and satellite-borne equipment Download PDFInfo
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- 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
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- G01S13/882—Radar or analogous systems specially adapted for specific applications for altimeters
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Abstract
The invention discloses a double-frequency detection method for a radar altimeter and a satellite-borne device, wherein the method comprises the following steps: transmitting a first signal of a Ka frequency band and a second signal of a Ku frequency band; performing full deskewing receiving, collecting and spectrum analysis on the first echo signal; performing full deskewing receiving, collecting and spectrum analysis on the second echo signal; respectively carrying out synthetic aperture processing on the first echo signal and the second echo signal to obtain sea surface height information of the Ka frequency band and sea surface height information of the Ku frequency band; delay information is calculated according to the first signal, the second signal, the first echo signal and the second echo signal, sea surface height information is corrected according to the delay information, time sequence combination and working mode of Ka and Ku dual-frequency bands are reasonably planned, the effects of measuring height precision, resolution and effectively measuring height data proportion and improving the ratio can be achieved, ocean observation capacity can be improved, and near coast and sea ice polar ice observation capacity can be improved.
Description
Technical Field
The invention relates to the field of radar altimeters, in particular to a double-frequency detection method for a radar altimeter and satellite-borne equipment.
Background
The satellite-borne radar altimeter is a radar device which is based on a satellite platform and utilizes electromagnetic waves to realize active remote sensing detection of sea surface height, sea ice, near coast and the like, and the working frequency range is a key design factor of the radar altimeter, and the working mode, the signal processing mode, the error correction, the environmental adaptability, the ocean element inversion and the like are all related to the working frequency range.
Along with the development of marine research and the proposal of new application demands, higher requirements are put on the radar altimeter, and the radar altimeter has high altimeter accuracy, high resolution and high effective altimeter data proportion, and when the radar altimeter is applied in high sea conditions (above 4-level sea conditions), the altimeter accuracy is reduced, so that the effective altimeter data proportion is reduced.
The patent of the radar altimeter adopting Ka+Ku dual-frequency detection does not exist so far, paper literature of the Ka+Ku dual-frequency synthetic aperture radar altimeter is not studied, and the invention aims to fill the technical blank in the field.
Disclosure of Invention
The invention aims to provide a double-frequency detection method for a radar altimeter, which combines the advantages of Ka and Ku frequency bands and combines a synthetic aperture height measurement technology to reasonably plan a time sequence combination and a working mode of the Ka and Ku frequency bands, so that the effects of measuring height precision, resolution and effectively measuring height data proportion and improving the sea observation capacity can be achieved, and the near-coast and sea ice observation capacity can be improved.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a dual frequency detection method for a radar altimeter, comprising:
transmitting a first signal of a Ka frequency band and a second signal of a Ku frequency band;
performing full deskewing reception, acquisition and spectrum analysis on a first echo signal, wherein the first echo signal is generated by the first signal;
performing full deskewing reception, acquisition and spectrum analysis on a second echo signal, wherein the second echo signal is generated by the second signal;
respectively carrying out synthetic aperture processing on the first echo signal and the second echo signal to obtain sea surface height information of a Ka frequency band and sea surface height information of a Ku frequency band;
and calculating delay information according to the first signal, the second signal, the first echo signal and the second echo signal, and correcting the sea surface height information according to the delay information.
Optionally, the first signal and the second signal are sent through a preset rule, where the preset rule specifically includes:
judging whether the first echo signal is received in a first preset time, if not, carrying out cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band, and if so, carrying out a first echo signal judging step.
Optionally, the first echo signal judging step specifically includes:
s100, judging whether the signal-to-noise ratio of the first echo signal exceeds a threshold value, if so, performing step S101, otherwise, performing step S102;
s101, performing cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band;
s102, cluster transmitting and cluster receiving detection is carried out by taking a Ku frequency band as a main detection frequency band and a Ka frequency band as an auxiliary detection frequency band.
Optionally, the cluster transmitting and cluster receiving detection with the Ka frequency band as a main detection frequency band and the Ku frequency band as an auxiliary detection frequency band specifically includes:
s200, a first signal of a Ka frequency band is sent, and the time of a transmitting cluster of the first signal is a second preset time, wherein the number of pulses in the time of the transmitting cluster of the first signal is 32-64, and the pulse width is 40-60 us;
s201, a second signal of a Ku frequency band is sent, and the time of a transmitting cluster of the second signal is a third preset time, wherein the number of pulses in the time of the transmitting cluster of the second signal is 32-64, and the pulse width is 30-50 us;
s202, receiving a first echo signal of a Ka frequency band;
s203, receiving a second echo signal of the Ku frequency band;
s204, repeating the step S200.
Optionally, the cluster transmitting and cluster receiving detection by using the Ku frequency band as a main detection frequency band and using the Ka frequency band as an auxiliary detection frequency band specifically includes:
s300, transmitting a second signal of a Ku frequency band, wherein the time of a transmitting cluster of the second signal is a third preset time, and the pulse number in the time of the transmitting cluster of the second signal is 32-64 and the pulse width is 30-50 us;
s301, a first signal of a Ka frequency band is sent, wherein the time of a transmitting cluster of the first signal is a second preset time, the number of pulses in the time of the transmitting cluster of the first signal is 32-64, and the pulse width is 40-60 us;
s302, receiving a second echo signal of a Ku frequency band;
s303, receiving a first echo signal of a Ka frequency band;
s304, repeating the step S300.
Optionally, the threshold is 12dB.
Optionally, the synthetic aperture processing includes azimuth beam sharpening, doppler parameter estimation, echo delay correction, range compression, inter-Burst registration, multi-view processing, and re-tracking.
Optionally, the delay information is delay information generated by an ionosphere.
Optionally, the calculating step of the delay information specifically includes:
sea surface height information of the Ka frequency band and sea surface height information of the Ku frequency band are corrected respectively, and the sea surface height information is processed specifically through the following formula:
R_Ka＝Range_Ka+sea_state_bias_Ka (1)
R_Ku＝Range_Ku+sea_state_bias_Ku (2)
Range_Ka＝R_Ka+iono_Corr_Alt_Ka (3)
Range_Ku＝R_Ku+iono_Corr_alt_Ku (4)
wherein R_Ka is a ranging value (m) after Ka frequency band Sea state deviation correction, R_Ku is a ranging value (m) after Ku frequency band Sea state deviation correction, range_Ka is a Ka frequency band ranging value (m), range_Ku is a Ku frequency band ranging value (m), sea_state_bias_Ka is a Ka frequency band Sea state deviation correction value (m), sea_state_bias_Ku is a Ku frequency band Sea state deviation correction value (m); iono_Corr_Alt_Ka is Ka frequency band ionosphere correction value (m), and Iono_Corr_Alt_Ku is Ku frequency band ionosphere correction value (m); freq_ka and freq_ku represent frequencies of Ka and Ku bands, respectively, and TEC represents the total amount of free electrons in the propagation path.
On the other hand, the invention also provides a satellite-borne device for executing the double-frequency detection method.
Compared with the prior art, the invention has at least one of the following advantages:
(1) The scheme adopts double-frequency detection, can achieve high-precision height measurement and high-data effective rate
Firstly, the dual-frequency detection can improve the height measurement precision, so that the product precision is improved. In a non-rainfall area, ka is used as a main detection frequency band, ku is used as an auxiliary detection frequency band, and both Ku and Ka are treated by adopting synthetic aperture. Under the same accumulation time, the single-view resolution of the synthetic aperture is related to the wavelength, the shorter the wavelength is, the higher the single-view resolution is, so that under the condition of the same output resolution, the more the Ka frequency band is, the higher the distance measurement precision is relatively, the more the distance measurement precision can reach 1cm, and in addition, the resolution can reach about 200m, thereby being beneficial to the improvement of the product precision; meanwhile, the dual-frequency detection can improve the environmental adaptability and the effective height measurement data proportion. The method has the advantages that severe rainfall conditions are not considered, height measurement data can be obtained in dual frequency bands, wherein higher height measurement precision and resolution can be obtained in the Ka frequency band, tracking random errors in the Ka frequency band are lower than those in the Ku frequency band, on the other hand, under the condition that the same accumulation time is adopted, the single-view resolution of the synthetic aperture is related to the wavelength, the shorter the wavelength is, the higher the resolution is, and under the condition of the same output resolution, the more the multiview numbers in the Ka frequency band are, and the height measurement precision can be further improved.
With the increase of the rainfall rate, the performance comparison and judgment of Ka+Ku dual-frequency detection are switched to Ku main detection, and the radar altimeter can still obtain altimetry data at the moment, so that the influence of a single-frequency-band rainfall environment can be overcome, the environmental adaptability of the radar altimeter is improved, the effective altimetry data proportion is improved, and the effective altimetry data proportion of the global sea area can reach 99%.
(2) Dual-frequency detection for realizing ionosphere delay high-precision correction
The ionospheric correction accuracy of a conventional ku+c dual-frequency altimeter is typically 0.5cm. When Ka is used as a main detection frequency band and Ku is used as an auxiliary detection frequency band, high-precision correction of ionospheric delay is carried out through measurement values of two different frequencies. As the measurement precision of the Ka+Ku dual-frequency combination and the sea state deviation correction precision are superior to those of the Ku+C dual-frequency combination, the correction precision of ionospheric delay by using the Ka+Ku dual-frequency is superior to that of the Ku+C, and can reach 0.3cm.
When the detection performance of the Ka frequency band is reduced due to rainfall, the Ku is switched to the main frequency band, and the Ka is switched to the auxiliary frequency band. The ionospheric correction values measured by Ka+Ku double frequencies before and after a rainfall area are substituted into a global ionospheric model to restrain the ionospheric model of the rainfall area, so that the accuracy of the ionospheric model can be improved, and the ionospheric delay of the Ku frequency band is corrected by using the ionospheric model, so that the ionospheric delay correction accuracy of the Ku frequency band is improved, and effective measurement data of the sea surface of the rainfall area is obtained.
(3) The dual-frequency detection can obtain rainfall rate distribution
The absorption effect of rainfall can lead to the attenuation of echo energy received by the radar altimeter, meanwhile, the raindrops generate gravity capillary waves, subsurface vortex rings, vertical mixing and the like on the sea surface through the impact on the sea surface, further the roughness of the sea surface is changed, the backscattering coefficient of the sea surface is influenced, and the two effects can lead to the attenuation of the echo energy of the altimeter. In addition, the attenuation of the rainfall on the echoes of different frequency bands is different, and the attenuation coefficient is related to the rainfall, so that the distribution of the rainfall rate can be obtained through the data processing of the double-frequency echoes based on the difference of the attenuation of the rainfall on the echo energy of the Ka frequency band and the Ku frequency band.
(4) Multiple data can be acquired by double-frequency detection
The dual-frequency height measurement data, ionosphere correction data and rainfall rate distribution data can be obtained, and the comprehensive remote sensing detection of the marine environment is facilitated.
Drawings
FIG. 1 is a schematic diagram of a Ka+Ku dual-frequency detection operation in a first embodiment of the present invention;
FIG. 2 is a schematic diagram of a Ka+Ku dual-frequency detection combination timing diagram in accordance with an embodiment of the present invention;
FIG. 3 is a timing diagram of a Ka-band dominant sounding mode in accordance with an embodiment of the present invention;
fig. 4 is a timing chart of Ku band dominant probing mode in the first embodiment of the present invention.
Detailed Description
The method, system and computer readable storage medium for dual frequency detection of radar altimeter according to the present invention are described in further detail below with reference to fig. 1 to 4 and the detailed description. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for the purpose of facilitating and clearly aiding in the description of embodiments of the invention. For a better understanding of the invention with objects, features and advantages, refer to the drawings. It should be understood that the structures, proportions, sizes, etc. shown in the drawings are for illustration purposes only and should not be construed as limiting the invention to the extent that any modifications, changes in the proportions, or adjustments of the sizes of structures, proportions, or otherwise, used in the practice of the invention, are included in the spirit and scope of the invention which is otherwise, without departing from the spirit or essential characteristics thereof.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or field device that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or field device. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or field device that comprises the element.
Embodiment one:
referring to fig. 1-4, a dual-frequency detection method for a radar altimeter according to the present embodiment includes:
transmitting a first signal of a Ka frequency band and a second signal of a Ku frequency band;
performing full deskewing receiving, collecting and spectrum analysis on a first echo signal, performing mixing processing on a local oscillation signal coupled by the echo signal and a transmitting signal to form a difference frequency signal, wherein the process is full deskewing receiving; collecting the difference frequency signals according to the Nyquist sampling law, and converting echo analog signals into digital signals; carrying out FFT processing analysis on the acquired digital signals, wherein the process is spectrum analysis, and the first echo signals are generated by the first signals;
performing full deskewing receiving, collecting and spectrum analysis on the second echo signal, performing mixing processing on the echo signal and a local oscillator signal coupled with a transmitting signal to form a difference frequency signal, wherein the process is full deskewing receiving; collecting the difference frequency signals according to the Nyquist sampling law, and converting echo analog signals into digital signals; carrying out FFT processing analysis on the acquired digital signals, wherein the process is spectrum analysis, and the second echo signals are generated by the second signals;
respectively carrying out synthetic aperture processing on the first echo signal and the second echo signal to obtain sea surface height information of a Ka frequency band and sea surface height information of a Ku frequency band;
and calculating delay information according to the first signal, the second signal, the first echo signal and the second echo signal, and correcting the sea surface height information according to the delay information.
The height information of the two frequency bands are combined to carry out high-precision correction of ionospheric delay (see formulas 1-8), so that the height information of the two frequency bands is corrected by utilizing the high-precision ionospheric delay correction value.
Ionosphere delay information extraction is carried out by using Ka+Ku double frequency data, so that sea surface height information is corrected. The double frequency data specifically refer to Ka and Ku frequency band delay values, ka and Ku frequency band sea state deviation correction values, ka and Ku frequency band ionosphere correction values and Ka and Ku frequency band sea surface height values. In the following (equations (1) to (6)), the process of extracting ionospheric delay information from the data is described.
Because the influence of rainfall on the Ka and Ku frequency band altimetry is different, the rainfall condition can be estimated and judged by analyzing the data of the two frequency bands, so that the altimetry data with better quality is selected, and the proportion of the effective measurement data is improved. In addition, the ionosphere content of the point path under the satellite is measured in real time by utilizing the influence difference of the ionosphere on Ka and Ku double frequencies and through Ka and Ku double frequency detection, so that high-precision ionosphere delay correction can be performed, and the sea surface height measurement precision is improved.
In this embodiment, the first signal and the second signal are sent through a preset rule, where the preset rule specifically includes: judging whether the first echo signal is received in a first preset time, if not, carrying out cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band, and if so, carrying out a first echo signal judging step.
Ka is main Ku is auxiliary detection: the transmitting links and the receiving links of the two frequency bands (Ka frequency band and Ku frequency band) are mutually independent, a cluster transmitting and cluster receiving mode is adopted in time sequence, as shown in figure 2, TB1 and RB1 are main detection frequency band and are used for transmitting and receiving clusters, and 64 pulses are arranged in the clusters; TB2 and RB2 are transmitting cluster time and receiving clusters of the auxiliary detection frequency band, and 32 pulses are arranged in the clusters. The time interval between two adjacent TBs 1 is one Burst cluster period, denoted BRI. According to the change of the satellite orbit height and the change of the requirement of the resolution of the main frequency band and the auxiliary frequency band, the pulse number, the signal parameters, the BRI and the like in the main frequency band and the auxiliary frequency band can be adaptively adjusted.
When the radar altimeter starts to work, a mode which mainly takes a Ka frequency band and takes a Ku frequency band as an auxiliary mode, namely, a Ka frequency band leading detection mode is set, as shown in fig. 3, in a typical application occasion, the first 2.67ms of a time sequence design is Ka frequency band emission cluster time, the cluster has pulse number 64 and pulse width 40us, the next 1.8ms is Ku frequency band emission cluster time, and the cluster has pulse number 32 and pulse width 50us. After about 6ms, the radar altimeter receiving time is entered, the receiving echo sequence is sequentially Ka frequency band and Ku frequency band, and 4 cluster periods are one tracking period. Under different application occasions, according to the change of satellite orbit height, the transmission cluster time, the number of pulses in the cluster, the pulse width in the cluster, the receiving cluster time and the like of the main frequency band and the auxiliary frequency band are all adaptively adjusted.
Ka. The Ku receiving link carries out full deskewing receiving, collecting and orthogonal demodulation on echo signals received by the receiving clusters of the respective frequency bands, and outputs the echo signals to the signal processing unit, and the signal processing unit carries out synthetic aperture processing on the echo signals, wherein the synthetic aperture processing comprises the steps of azimuth beam sharpening, doppler parameter estimation, echo delay correction, distance compression, registration between bursts, multi-vision processing, re-tracking and the like, and sea surface height information is obtained by combining error correction.
Azimuth beam sharpening: the segmentation of the beam irradiation area strips in the azimuth direction of Ka and Ku detection data is realized through an FFT filter;
doppler parameter estimation: doppler center estimation is carried out to obtain an antenna mispointing angle, and the antenna mispointing angle is used for correcting a delay compensation coefficient;
echo delay correction: the Doppler phase of the strip in different periods is compensated by utilizing the relation between the Doppler frequency and the relative azimuth, and the influence of the distance change on the height measurement in the flying process is eliminated.
Distance compression: and performing FFT processing after deskewing the large bandwidth linear frequency modulation signal and the receiving local oscillator of each period to obtain distance information.
Registration between Burst: and correcting the influence of the change of the pitch in the flight on the azimuth accumulation, so that the processed scenes among different bursts correspond to the same scene on the sea surface.
Multi-view processing: and the data obtained by the same strip in different observation periods are coherently accumulated, so that the influence of wave noise is reduced, and the measurement accuracy is improved.
And (5) heavy tracking: and fitting an echo waveform obtained by echo signal processing by using the constructed echo model so as to improve the sea surface height measurement precision.
In this embodiment, the first echo signal determining step specifically includes:
s100, judging whether the signal-to-noise ratio of the first echo signal exceeds a threshold value, if so, performing step S101, otherwise, performing step S102;
s101, performing cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band;
s102, cluster transmitting and cluster receiving detection is carried out by taking a Ku frequency band as a main detection frequency band and a Ka frequency band as an auxiliary detection frequency band.
The Ka frequency band has the main defect that the influence of water vapor in a troposphere is larger, so that rainfall can interfere with the observation of a radar altimeter to a certain extent, even data failure can be caused when the rainfall is serious, the effective height measurement data proportion in global observation is influenced to a certain extent, and the global effective height measurement data proportion is about 90%.
In this embodiment, the threshold is 12dB. When the signal-to-noise ratio of the echo data is smaller than 12dB, cluster receiving detection is still performed according to the Ku-based main Ka-based auxiliary cluster, and when the signal-to-noise ratio of the Ka-based echo is larger than 12dB, the detection mode is switched to a detection mode with the Ka-based main and the Ku-based frequency band as the auxiliary.
In this embodiment, the synthetic aperture processing includes azimuth beam sharpening, doppler parameter estimation, echo delay correction, range compression, registration between bursts, multi-view processing, and re-tracking.
Referring to fig. 1, in this embodiment, two frequencies of ka+ku are used for simultaneous detection, and synthetic aperture processing is used for echo data of two frequency bands, so that the synthetic aperture processing results of the two frequency bands can be obtained simultaneously, and a traditional low resolution processing mode is considered. The detection method is characterized in that Ka is used as main detection, ka+Ku double-frequency synthetic aperture treatment, ka+Ku double-frequency ionosphere delay correction and meteorological environment autonomous judgment autonomous switching are used as auxiliary detection. And (3) extracting ionosphere delay information from the sea surface height information obtained in the previous step by using Ka+Ku double-frequency data, so as to correct the sea surface height information.
And respectively correcting sea state deviation of the measured values of the Ka+Ku frequency bands.
R_Ka＝Range_Ka+sea_state_bias_Ka (1)
R_Ku＝Range_Ku+sea_state_bias_Ku (2)
Wherein r_ka is a ranging value (m) after Ka band Sea state deviation correction, r_ku is a ranging value (m) after Ku band Sea state deviation correction, range_ka is a Ka band ranging value (m), range_ku is a Ku band ranging value (m), sea_state_bias_ka is a Ka band Sea state deviation correction value (m), and sea_state_bias_ku is a Ku band Sea state deviation correction value (m).
The ionosphere corrected Range value Range can be expressed by the following formula:
Range＝R_Ka+iono_Corr_Alt_Ka (3)
Range＝R_Ku+iono_Corr_alt_Ku (4)
wherein Iono_Corr_Alt_Ka is Ka band ionosphere correction value (m), and Iono_Corr_alt_Ku is Ku band ionosphere correction value (m).
Ionospheric corrections can be expressed by the following formula:
freq_ka and freq_ku represent frequencies of Ka and Ku bands, respectively, and TEC represents the total amount of free electrons in the propagation path.
Thereby obtaining ionospheric corrections.
Autonomous switching of meteorological environment judgment: when Ka is dominant and Ku is subordinate, judgment and autonomous switching are performed according to the influence of a meteorological environment (for example, rain fall) on echo. Under the condition of rain attenuation, a certain judgment threshold is set according to the signal-to-noise ratio of echo data, when the signal-to-noise ratio of Ka frequency band echo is larger than 12dB, cluster transmitting and cluster receiving detection is carried out still according to Ka as a main part Ku as an auxiliary part, when the signal-to-noise ratio of Ka frequency band echo is reduced to less than 12dB, the detection mode is switched to a detection mode which takes the Ku frequency band as a main part and the Ka frequency band as an auxiliary part, namely, the Ku frequency band main detection mode, broadband signal parameters, the number of pulses in clusters, BRI and the like can be adjusted while switching, and the time sequence mode can be switched before the next adjacent cluster period comes, so that the observation time is not occupied by switching is ensured.
When the switching condition is met, the double-frequency data are still valid, and the period result of the adjacent cluster is not invalid due to the frequency band switching. In a typical application, the time sequence is shown in fig. 4, the first 3.6ms is the Ku frequency band emission cluster time in the time sequence design, the cluster has a pulse number 64 and a pulse width 50us, the next 1.3ms is the Ka frequency band emission cluster time, and the cluster has a pulse number 32 and a pulse width 40us; after about 6ms, the radar altimeter receiving time is entered, the receiving echo sequence is in a Ku frequency band and a Ka frequency band, and 4 cluster periods are one tracking period. According to the change of the satellite orbit height and the change of the requirement of the resolution of the main frequency band and the auxiliary frequency band, the pulse number, the signal parameters, the BRI and the like in the main frequency band and the auxiliary frequency band can be adaptively adjusted.
In the mode, according to the relation between the echo energy and the rainfall rate of each of the Ka and Ku dual-band, the data processing of the dual-band echo is carried out, and the rainfall rate information is obtained.
The purpose of switching is to guarantee that during on-orbit operation, due to the influence of atmospheric attenuation such as rainfall, data loss can not be caused during on-orbit tracking, so that double-frequency effective echoes can be acquired and transmitted to the ground, and the effective altimetric data proportion is improved. And carrying out detailed treatments such as synthetic aperture, multi-view accumulation and the like on the ground to obtain the high-level data product meeting the application requirements.
Based on the same inventive concept, the embodiment also discloses a satellite-borne device for executing the dual-frequency detection method.
While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Many modifications and substitutions of the present invention will become apparent to those of ordinary skill in the art upon reading the foregoing. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims (9)
1. A dual frequency detection method for a radar altimeter, comprising:
transmitting a first signal of a Ka frequency band and a second signal of a Ku frequency band;
performing full deskewing reception, acquisition and spectrum analysis on a first echo signal, wherein the first echo signal is generated by the first signal;
performing full deskewing reception, acquisition and spectrum analysis on a second echo signal, wherein the second echo signal is generated by the second signal;
respectively carrying out synthetic aperture processing on the first echo signal and the second echo signal to obtain sea surface height information of a Ka frequency band and sea surface height information of a Ku frequency band;
calculating delay information according to the first signal, the second signal, the first echo signal and the second echo signal, and correcting the sea surface height information according to the delay information;
the calculating step of the delay information specifically includes:
sea surface height information of the Ka frequency band and sea surface height information of the Ku frequency band are corrected respectively, and the sea surface height information is processed specifically through the following formula:
R_Ka＝Range_Ka+sea_state_bias_Ka (1)
R_Ku＝Range_Ku+sea_state_bias_Ku (2)
Range_Ka＝R_Ka+iono_Corr_Alt_Ka (3)
Range_Ku＝R_Ku+iono_Corr_alt_Ku (4)
wherein R_Ka is a ranging value (m) after Ka frequency band Sea state deviation correction, R_Ku is a ranging value (m) after Ku frequency band Sea state deviation correction, range_Ka is a Ka frequency band ranging value (m), range_Ku is a Ku frequency band ranging value (m), sea_state_bias_Ka is a Ka frequency band Sea state deviation correction value (m), sea_state_bias_Ku is a Ku frequency band Sea state deviation correction value (m);
Iono_Corr_Alt_Ka is Ka frequency band ionosphere correction value (m), and Iono_Corr_Alt_Ku is Ku frequency band ionosphere correction value (m); freq_ka and freq_ku represent frequencies of Ka and Ku bands, respectively, and TEC represents the total amount of free electrons in the propagation path.
2. The method of claim 1, wherein the first signal and the second signal are transmitted by a preset rule, the preset rule specifically comprising:
judging whether the first echo signal is received in a first preset time, if not, carrying out cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band, and if so, carrying out a first echo signal judging step.
3. The method of claim 2, wherein the first echo signal determining step specifically includes:
s100, judging whether the signal-to-noise ratio of the first echo signal exceeds a threshold value, if so, performing the steps
S101, otherwise, performing step S102;
s101, performing cluster transmitting and cluster receiving detection by taking a Ka frequency band as a main detection frequency band and a Ku frequency band as an auxiliary detection frequency band;
s102, cluster transmitting and cluster receiving detection is carried out by taking a Ku frequency band as a main detection frequency band and a Ka frequency band as an auxiliary detection frequency band.
4. The method as claimed in claim 2 or 3, wherein the performing cluster-transmitting and cluster-receiving detection with the Ka band as a main detection band and the Ku band as an auxiliary detection band specifically comprises:
s200, a first signal of a Ka frequency band is sent, and the time of a transmitting cluster of the first signal is a second preset time, wherein the number of pulses in the time of the transmitting cluster of the first signal is 32-64, and the pulse width is 40-60 us;
s201, a second signal of a Ku frequency band is sent, and the time of a transmitting cluster of the second signal is a third preset time, wherein the number of pulses in the time of the transmitting cluster of the second signal is 32-64, and the pulse width is 30-50 us;
s202, receiving a first echo signal of a Ka frequency band;
s203, receiving a second echo signal of the Ku frequency band;
s204, repeating the step S200.
5. The method of claim 3, wherein the performing cluster-transmitted cluster-received detection with Ku frequency band as a main detection frequency band and Ka frequency band as an auxiliary detection frequency band specifically comprises:
s300, transmitting a second signal of a Ku frequency band, wherein the time of a transmitting cluster of the second signal is a third preset time, and the pulse number in the time of the transmitting cluster of the second signal is 32-64 and the pulse width is 30-50 us;
s301, a first signal of a Ka frequency band is sent, wherein the time of a transmitting cluster of the first signal is a second preset time, the number of pulses in the time of the transmitting cluster of the first signal is 32-64, and the pulse width is 40-60 us;
s302, receiving a second echo signal of a Ku frequency band;
s303, receiving a first echo signal of a Ka frequency band;
s304, repeating the step S300.
6. A method according to claim 3, wherein the threshold is 12dB.
7. The method of claim 1, wherein the synthetic aperture processing comprises azimuth beam sharpening, doppler parameter estimation, echo delay correction, range compression, inter-Burst registration, multi-view processing, and re-tracking.
8. The method of claim 1, wherein the delay information is ionosphere generated delay information.
9. A satellite-borne device for performing a dual-frequency probing method as claimed in any one of claims 1 to 8.
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| CN115184923A (en) * | 2022-06-24 | 2022-10-14 | 北京木牛领航科技有限公司 | A millimeter-wave radar altimeter and a method for calculating altitude by using a millimeter-wave radar |
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