Synthetic aperture radar method
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- DEUTSCHES ZENTRUM FÜR LUFT UND RAUMFAHRT E V
- Filing Date
- 2024-05-06
- Publication Date
- 2026-08-03
Smart Images
Figure 2026525719000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a synthetic aperture radar method for remote sensing of the Earth's surface via a radar device, and to a corresponding synthetic aperture radar system.
Background Art
[0002] The synthetic aperture radar method, also known as the SAR method, enables remote sensing of the Earth's surface using radar pulses that are transmitted by a radar device and whose radar echoes are received again by this radar device after reflection from the Earth's surface. The radar device moves at a constant speed over the Earth's surface in a so-called azimuth direction. The radar echoes are detected along a so-called range direction that extends perpendicular to the azimuth direction. In the following, the term "Earth's surface" is understood in a broad sense and may include, in addition to the surface of the Earth, the surface of another celestial body, particularly a planet.
[0003] The SAR technique utilizes the fact that due to the movement of the radar device, the same area of the Earth's surface is captured from different positions of the radar device, thereby providing amplitude information and phase information of the Earth's surface, and ultimately a radar image (also known as a SAR image). This creates a synthetic aperture in the azimuth direction.
[0004] In conventional SAR methods, the radar device generates continuous radar pulses that irradiate the Earth's surface obliquely with a fixed radar beam in the transmission mode. The radar echoes from these radar pulses are then received by the same radar device in the reception mode. The associated problem is that the width of the swath detected by the Earth's surface is subject to range direction limitations. In particular, when detecting a swath that is too wide, the signal quality deteriorates. Furthermore, since the radar echoes that reach the radar device at the same time as the radar pulses are transmitted cannot be received by the radar device, gaps occur within each swath.
[0005] To cover a wider area of the Earth's surface, U.S. Patent No. 9,869,762(B2) describes how multiple SAR acquisitions of different swaths on the Earth's surface can be performed in parallel by interleaving different radar pulse sequences using a radar device.
[0006] A further development of conventional SAR methods is the so-called F-scan technique, which is described, for example, in the document WO2019 / 015911A1. In this method, the radar beam generated by the radar pulse moves along the range direction toward a shorter distance between the radar device and the Earth's surface. At the same time, the radar pulse is frequency-modulated within a predetermined frequency band, so that the position of the moving radar beam correlates with the corresponding frequency of the radar pulse. The F-scan method allows the radar echo signals of the radar pulse to reach the radar device essentially simultaneously, thereby significantly shortening the reception time interval of the radar echo compared to conventional methods. This, in turn, means that the width of the detected swath can be increased for a predetermined pulse repetition rate of consecutive radar pulses. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] U.S. Patent No. 9,869,762(B2) [Patent Document 2] WO2019 / 015911A1 [Overview of the project] [Problems that the invention aims to solve]
[0008] The objective of the present invention is to improve the synthetic aperture radar method based on the above-described F-scan technology in order to further increase the capture area of the Earth's surface. [Means for solving the problem]
[0009] This objective is achieved by the method described in claim 1 or by the apparatus described in claim 12. Embodiments of the present invention are defined in the dependent claims.
[0010] The synthetic aperture radar method according to the present invention uses a radar device for remote sensing of the Earth's surface, the radar device moves azimuthally over the Earth's surface, and the radar device can be operated in a transmit mode for transmitting radar pulses to the Earth's surface and in a receive mode for receiving radar echoes of radar pulses from the Earth's surface along a range direction perpendicular to the azimuthal direction. Preferably, the radar device includes a single antenna device adapted for both transmitting radar pulses and receiving radar echoes. In transmit mode, the antenna direction is not capable of receiving radar waves.
[0011] In the synthetic aperture radar method according to the present invention, the radar device transmits a series of radar pulses having associated pulse durations in transmission mode, the radar pulses generating a radar beam directed toward the Earth's surface and having a waveform within a frequency band. The frequencies contained within the waveform within the frequency band are varied over the pulse duration, and the radar beam simultaneously moves along the range direction over the pulse duration toward a shorter distance between the radar device and the Earth's surface to illuminate a section on the Earth's surface in the range direction.
[0012] The method according to the present invention therefore uses F-scan technology based on a moving radar beam and frequency-modulated radar pulses. The frequency of the radar pulses within the frequency band preferably changes linearly, and the frequency can increase or decrease over time depending on the embodiment.
[0013] The radar echo of each radar pulse is received by the radar device in receive mode after reflection in the illuminated section during the reception time interval assigned to each radar pulse. In other words, each radar pulse is assigned a reception time interval in which its radar echo is received, and this reception time interval can be assigned to multiple radar pulses if necessary. If necessary, each reception time interval may be temporarily interrupted by the transmission of one or more subsequent radar pulses, because it is generally not possible for the radar device to receive a radar echo while a radar pulse is being transmitted.
[0014] Unlike conventional F-scan techniques, the method according to the present invention is characterized in that each radar pulse belongs to a predetermined number of different pulse types (i.e., at least two different pulse types), thereby the pulse type is always changed between two consecutive radar pulses, and radar pulses of the same pulse type are transmitted at a predetermined pulse repetition rate. Radar pulses of the same pulse type also have waveforms in the same frequency band and generate a radar beam that illuminates the same section in the range direction on the Earth's surface. In contrast, radar pulses of different pulse types have waveforms in different frequency bands and generate radar beams that illuminate different sections in the range direction on the Earth's surface. The term "different frequency bands" is understood here and below to mean that for each pair of frequency bands of different frequency bands, at least a portion of the frequencies of one frequency band of the pair are different from the frequencies of the other frequency band of the pair. Preferably, each frequency band of different frequency bands includes at least a portion of frequencies that are not included in any other frequency band of different frequency bands. In a particularly preferred embodiment, the different frequency bands are separated from each other (i.e., they do not overlap). The term "different sections in the range direction" is understood here and below to mean that for each pair of sections among the different sections, at least one portion of one section of the pair does not overlap with the other section of the pair in the range direction. Preferably, each section among the different sections includes at least one sub-region in the range direction that is not included in any other section of the different section.
[0015] The method according to the present invention has the advantage that the use of different pulse types enables parallel detection of multiple sections of the Earth's surface in the range direction using F-scan technology. In this way, it is possible to detect a wide area on the Earth's surface.
[0016] In a preferred embodiment, the predetermined pulse repetition rate at which each pulse type of radar pulse is transmitted is the same for all pulse types. In other words, pulses of different pulse types are transmitted interleaved with each other at a constant offset.
[0017] In a further particularly preferred embodiment of the method according to the present invention, a sequence of consecutive radar pulses of all pulse types corresponding to a predetermined number of different pulse types is repeatedly transmitted without an intermediate reception time interval for radar echoes from the radar pulses of this sequence, thereby receiving radar echoes from all pulse types of the predetermined number of different pulse types in the reception time interval thereafter, and the received radar echoes belong to radar pulses from different temporally consecutive previous sequences. The number of radar echoes received in the reception time interval corresponds to a predetermined number of different pulse types. This means that there are no two radar echoes belonging to different radar pulses of the same pulse type in a single reception time interval. All previous sequences typically precede the sequence that follows the reception time interval in time. The number of radar pulses in a sequence therefore corresponds to a predetermined number of different pulse types, and each sequence contains one radar pulse of each pulse type. This embodiment is characterized in that radar echoes of all pulse types are received in parallel at a common reception time interval, thereby enabling detection of radar echoes in a shorter time. By using different frequency bands for the waveforms of different pulse types of radar pulses, radar echoes of different pulse types of radar pulses can be distinguished from one another.
[0018] In a further embodiment of the method according to the present invention, each reception time interval is provided exclusively for the radar echo of a single radar pulse. By using such separate reception time intervals, for each pulse type, a separately processable acquisition of SAR data for a section of the Earth's surface associated with that pulse type is generated.
[0019] In another preferred modification of the method according to the present invention, at least some, preferably all, of the different sections are isolated sections on the Earth's surface, i.e., sections that are separated in the range direction (i.e., without overlap). Preferably, the isolated sections are selected so that radar echoes arising from the gap between the two isolated sections in the range direction reach the radar device while it is in transmit mode, thereby preventing any reception of these radar echoes under normal circumstances.
[0020] In a further embodiment of the method according to the present invention, at least some of the different sections may overlap in the range direction.
[0021] In another preferred modification of the method according to the present invention, one or more of the different pulse types each belong to a stripmap SAR mode in which the pulse type radar pulse generates a radar beam having a main beam direction perpendicular to the azimuth direction. In other words, this embodiment implements a special modification of a known stripmap operating mode in which the stripmap operating mode detects the Earth surface along an elongated strip with radar pulses in a direction perpendicular to the azimuth direction.
[0022] In another variant of the method according to the invention, one or more of the different pulse types each belong to a spotlight SAR mode in which the radar pulses of the pulse type generate a radar beam that irradiates a fixed target area on the earth's surface. In other words, this embodiment implements a special variant of the conventional spotlight mode of operation, in which the radar beam is also tilted in the azimuth direction in order to obtain high-resolution SAR data from the corresponding target area in the spotlight mode of operation.
[0023] The two above-described embodiments relating to the strip map SAR mode and the spotlight SAR mode can also be combined with each other. In particular, one or more pulse types may belong to the strip map SAR mode, while one or more other pulse types may belong to the spotlight SAR mode.
[0024] In another preferred variant of the method according to the invention, the predetermined pulse repetition rate of the radar pulses of at least one of the predetermined number of different pulse types is changed one or more times during the execution of the method. Thereby, the effect is achieved that so-called blind ranges, in which the incident radar echo cannot be received due to the transmission of the radar pulses, are shifted over time. In this way, the data loss due to blind ranges can be significantly reduced. Depending on the embodiment, the pulse repetition rate can be changed in different ways. In particular, the pulse repetition rate can be kept constant for a plurality of pulse repetition intervals before the change is made. It is also possible for the pulse repetition rate to be changed after each pulse repetition interval.
[0025] In another preferred embodiment of the method according to the invention, for at least one of the different pulse types and, if necessary, for each of all of the different pulse types, the section in the range direction irradiated by the radar beam generated by the radar pulse of each pulse type is changed one or more times during the execution of the method. Preferably, when the section in the range direction irradiated by the radar beam generated by the radar pulse of each pulse type is changed for each pulse type, the pulse repetition rate of the radar pulse of each pulse type is simultaneously changed, whereby a gap, which refers to an area on the earth's surface where a radar echo cannot be received due to the transmission of the radar pulse before the change of the pulse repetition rate, is covered by the changed section. In other words, in the changed section, a radar echo is received from the area of the earth's surface that was a gap before the pulse repetition rate was changed. In this way, data loss due to gaps or blind ranges can be reduced.
[0026] In addition to the method described above, the invention relates to a synthetic aperture radar system for remote sensing of the earth's surface using a radar device that moves in the azimuth direction over the earth's surface during operation, the radar device being operable in a transmission mode for transmitting radar pulses to the earth's surface and a reception mode for receiving radar echoes of the radar pulses from the earth's surface along a range direction perpendicular to the azimuth direction, the synthetic aperture radar system being configured to execute a synthetic aperture radar method according to the invention or according to one or more preferred variants of the method during operation.
[0027] Embodiments of the invention are described in detail below with reference to the accompanying drawings.
Brief Description of the Drawings
[0028] [Figure 1] It is a schematic perspective view for explaining the principle of SAR used in the present invention. [Figure 2] This is a schematic diagram illustrating the difference between a conventional strip map SAR mode without F-scan and a conventional strip map SAR mode with F-scan. [Figure 3] This is a schematic perspective view of a conventional stripmap SAR mode using F-scan. [Figure 4] This is a schematic perspective view showing the SAR operating mode according to the first embodiment of the present invention. [Figure 5-6] This figure illustrates the characteristics of the pulse type used in the embodiment shown in Figure 4. [Figure 7] This is a schematic perspective view showing the SAR operating mode according to a second embodiment of the present invention. [Figure 8] This is a schematic perspective view showing the SAR operating mode according to a third embodiment of the present invention. [Modes for carrying out the invention]
[0029] The principle of SAR measurement will first be explained in general terms with reference to Figure 1. For this purpose, a SAR radar device 100 is used, which is equipped with a radar antenna, shown in Figure 1 as a rectangular antenna array. The radar device 100 moves in the so-called azimuth direction x at a flight speed v at an altitude h above the Earth's surface GR. The dashed line NT indicates the so-called nadir orbit, which is a projection in the azimuth direction perpendicular to the Earth's surface GR. To enable movement, the radar device is placed on a flying object (not shown), which is preferably a satellite, but may also be an aircraft. The radar device 100 is a combined transceiver that emits radar radiation in transmit mode and receives radar radiation in receive mode. It is not possible to receive radar radiation while in transmit mode.
[0030] In transmission mode, the radar device 100 emits a radar beam RB based on a radar pulse RP toward the Earth's surface GR at an angle β. The radar beam RB corresponds to the main lobe of the emitted antenna radiation and is directed toward the Earth's surface at an angle θ iThe radar pulse RP is directed toward the Earth's surface GR at a continuous pulse repetition interval with a predetermined pulse repetition frequency. Most of the energy of each radar pulse RP or radar beam RB is directed toward a roughly elliptical region FP on the Earth's surface. This region is usually referred to as the "footprint" of the radar device or its associated radar antenna.
[0031] In Figure 1, SR represents the inclined range from the radar device 100 to a point on the Earth's surface. This inclined range can be clearly converted to the so-called ground range, whose direction is indicated by y in Figure 1. The ground range corresponds to the projection of the inclined range SR onto the Earth's surface GR and extends perpendicular to the azimuth direction x. Hereafter, the direction of the ground range will also be generally referred to as the range direction. The footprint FP has a spread in the range direction corresponding to the width of the indicated swath SW. As the radar device 100 moves, radar echoes of radar pulses from the swath SW reflected off the Earth's surface are acquired. For this purpose, the radar device 100 is switched to receive mode.
[0032] The principle of SAR measurement is based on the fact that, due to the movement of the radar device, a point on the Earth's surface is acquired multiple times from different viewing angles. Due to the Doppler effect, a frequency shift occurs during the acquisition of radar echoes, which can be properly evaluated to ultimately obtain amplitude and phase information about the point on the Earth's surface to which the radar pulse is reflected, and thus the pixels on the Earth's surface. The corresponding calculation of the pixels on the Earth's surface from the acquired radar echoes is well known to those skilled in the art and will therefore not be described in further detail.
[0033] Figure 1 shows a conventional stripmap SAR mode in which a SAR radar device 100 acquires an elongated swath SW using a fixed radar beam RB emitted perpendicular to the azimuth direction (without using F-scan). A well-known variation of this stripmap SAR mode is the stripmap SAR mode using F-scan, which is illustrated in Figure 2 in comparison to the stripmap SAR mode without F-scan.
[0034] Figure 2 encompasses four diagrams DI1, DI1', DI2, and DI2', each of which represents a section in a plane perpendicular to the azimuth direction x shown in Figure 1. Diagram DI1 shows the transmission of the radar beam RB for a strip-map SAR mode without F-scan, while Diagram DI2 shows the transmission of the radar beam RB for a strip-map SAR mode with F-scan. Diagram DI1' shows the correspondingly transmitted radar pulse RP and resulting radar echo EC wavefronts for a strip-map SAR mode without F-scan, while Diagram DI2' shows the transmitted radar pulse RP and resulting radar echo EC wavefronts for a strip-map SAR mode with F-scan.
[0035] As can be seen from Figure DI1, in stripmap SAR mode without F-scan, the radar beam RB is emitted and irradiates the swath SW, and the radar beam does not change over time. Due to the fixed radar beam, the wavefront of the radar pulse RP is transmitted without any time delay, which means that the resulting radar echo EC returns to the radar device 100 with a time delay due to the different distances of its reflection points (see Figure DI1'). This means that a long reception time interval is required to receive the radar echo. Furthermore, conventional stripmap SAR methods have the disadvantage of using a wide radar beam, which results in so-called range ambiguity caused by radar echoes received simultaneously from different radar pulses.
[0036] To improve the stripmap SAR modes in Figures DI1 and DI1', a stripmap SAR operating mode using F-scan is known, which is shown in Figures DI2 and DI2' in Figure 2. Proper design of the radar antenna ensures that the linearly frequency-modulated pulse RP is combined with spatial control (beam steering) of the radar beam RB. In other words, the frequency of the radar pulse RP changes over time as it is transmitted, and simultaneously, the radar beam RB caused by the radar pulse moves along the range direction, i.e., along the width of the detected swath SW. The corresponding position of the moving radar beam then correlates with the frequency section from the frequency band of the transmitted radar pulse.
[0037] As can be seen from Diagram DI2 in Figure 2, the F-scan moves the radar beam RB in the direction of the indicated arrow P. According to Diagram DI2', this results in a time delay in the wavefront of the transmitted radar pulse RP. This time delay, in turn, compensates for the time delay of the radar echo EC that would occur without the F-scan. As a result, the radar echo EC of each pulse RP is received by the radar device 100 essentially simultaneously. In this way, the radar echoes can be detected with significantly shorter reception time intervals. In addition, the use of a narrow radar beam improves signal quality, while the movement of the radar beam ensures the detection of wide swaths on the Earth's surface.
[0038] Figure 3 again shows a perspective view of the stripmap SAR mode using F-scans from Figures DI2 and DI2' of Figure 2. As can be seen, radar pulses RP are transmitted continuously at pulse repetition interval PRI, and each radar pulse generates a radar beam RB that covers the swath SW on the Earth's surface by moving in the direction of arrow P.
[0039] The embodiments of the present invention described below are improvements to the F-scan SAR mode described above. For the improvement, the Earth's surface is detected using a moving radar beam that covers multiple different regions on the Earth's surface.
[0040] Figure 4 shows a first embodiment of the SAR operating mode according to the present invention. According to the method shown therein, a successive sequence of three radar pulses RP of different pulse types PT1, PT2, and PT3 is transmitted. In the sequence, pulse type PT1 is transmitted first, followed by pulse type PT2, and then pulse type PT3. Radar pulses of the same pulse type are transmitted at a fixed, predetermined pulse repetition interval PRI, which is the same for all pulse types. In other words, individual radar pulses of different pulse types in the sequence are transmitted at the same time offset from one another.
[0041] Figure 4 shows three temporally consecutive sequences of correspondingly transmitted radar pulses RP of different pulse types PT1, PT2, and PT3. The radar pulses of different pulse types differ in that, on the one hand, they are linearly frequency-modulated signals in separate frequency bands, and on the other hand, they cover different swaths SW1, SW2, and SW3 on the Earth's surface. Each pulse type generates a radar beam RB that travels within the corresponding swath along the range direction y toward the nadir orbit NT. Specifically, the radar pulse of pulse type PT1 generates a radar beam that illuminates swath SW1, the radar pulse of pulse type PT2 generates a radar beam that illuminates swath SW2, and the radar pulse of pulse type PT3 generates a radar beam that illuminates swath SW3. The gaps between swath SW1 and SW2, and between swath SW2 and SW3, are due to the fact that these gaps correlate with time intervals during which the radar device 100 is transmitting radar pulses and therefore no radar echoes can be received.
[0042] Each sequence of three radar pulses of different pulse types is followed by a reception time interval during which radar echoes of all pulse types are received by the receiving radar equipment. The radar echoes in the reception time interval belong to radar pulses from different, temporally consecutive, preceding sequences, which typically precede the subsequent reception time interval by several pulse repetition intervals. In other words, during the reception time interval, radar echoes of pulse type PT1 radar pulses belong to a preceding sequence preceding the sequence in which radar echoes of pulse type PT2 occur, while within the reception time interval, radar echoes of pulse type PT2 radar pulses belong to a preceding sequence preceding the sequence in which radar echoes of pulse type PT3 occur. Due to the moving radar beam, radar echoes arrive in a much shorter time than in conventional SAR operating modes without F-scan. By using separate frequency bands for different pulse types, radar echoes can also be assigned to corresponding radar pulses. In modified embodiments, such as the modification shown in Figure 7 below, where the stripmap SAR mode is combined with the spotlight SAR mode, it is sufficient that the frequency bands are different according to the definitions given above.
[0043] The embodiment shown in Figure 4 enables the detection of a wide area of the Earth's surface by multiple swaths through the successive transmission of moving radar pulses of different pulse types. In contrast, in the conventional F-scan operating mode, only one swath on the Earth's surface is detected at a time. In addition, the radar pulses in the sequence are received within a common reception time interval, thereby improving the time efficiency of the method. At the same time, the use of a narrow radar beam for each swath achieves a high signal-to-noise ratio and reduces the signal intensity of range ambiguity.
[0044] In the corresponding SAR image obtained from radar echoes captured using the method shown in Figure 4, gaps are observed between the illustrated swaths. These gaps can be compensated using known techniques. For example, individual pulse-type radar pulses can be transmitted in successive bursts, each burst differing in that the captured swaths are shifted from burst to burst. This ensures that all gaps occurring in one burst are covered by the corresponding swaths in another burst. In addition, the pulse repetition rate can be varied over time if necessary, thereby changing the location of the gaps and significantly reducing data loss caused by the gaps, which can then be reconstructed by interpolation.
[0045] Figure 5 shows the pulse shapes of the pulse types from Figure 4 along the vertical coordinate PU as a function of time t (horizontal coordinate). The dotted line L1 corresponds to pulse type PT1, the dashed line L2 corresponds to pulse type PT2, and the solid line corresponds to pulse type PT3. Each pulse type is a rectangular pulse transmitted sequentially. The pulse durations of the individual pulse types PT1, PT2, and PT3 are called PD1, PD2, and PD3, respectively. As can be seen from the figure, the pulses are of different lengths. A pulse is transmitted at the start of the pulse repetition interval PRI, which has a period of approximately 100 μs. The overall pulse interval PRI is approximately 390 μs long.
[0046] Figure 6 shows the frequency bands (vertical coordinate of frequency f) of individual pulses of pulse types PT1, PT2, and PT3 over time t (horizontal coordinate). The dotted line L1' represents the frequency band FB1 of pulse type PT1, the dashed line L2' represents the frequency band FB2 of pulse type PT2, and the solid line L3' represents the frequency band FB3 of pulse type PT3. As can be seen from the figure, the frequency bands are separated from each other, which makes it possible to distinguish between radar echoes of different pulse types that are received together at the same reception time interval.
[0047] Figures 7 and 8 illustrate second and third embodiments of the SAR operating mode according to the present invention, respectively. These embodiments differ from the first embodiment in that separate reception time intervals are used for each pulse type, rather than receiving radar echoes of consecutively transmitted radar pulses of different pulse types within a common reception time interval. This means that each pulse type of radar echo represents the acquisition of separate SAR data, each having independent SAR raw data, from which separate SAR images can be obtained.
[0048] In the second embodiment shown in Figure 7, two pulse types, PT1 and PT2, are used and transmitted alternately in succession. The radar pulse RP of the first pulse type PT1 performs a strip-map SAR mode using F-scan, that is, it generates a radar beam RB that moves along a wide swath SW1 on the Earth's surface in the range direction y in a plane perpendicular to the azimuth direction x. In contrast, the radar pulse RP of the second pulse type PT2 generates a radar beam RB that is directed entirely towards a fixed target region TR on the Earth's surface, so that this target region has a width SW2 in the range direction that is significantly smaller than the width of the swath SW1. The radar beam of the second pulse type PT2 is used to perform a SAR mode similar to the known spotlight SAR mode, so that, in contrast to the conventional spotlight SAR mode, the individual radar beams perform movement (i.e., F-scan).
[0049] Figure 8 shows a third embodiment of the SAR operating mode according to the present invention. Similar to the operating mode shown in Figure 7, this operating mode also includes two different pulse types PT1 and PT2 having separate reception time intervals for radar echoes. Similar to Figure 7, the first pulse type PT1 performs a strip map operating mode using F-scan at swath SW1. In contrast to Figure 7, in the embodiment of Figure 8, the second pulse type PT2 also performs a strip map operating mode using F-scan, but a swath SW2 on the Earth's surface is detected, separated in the range direction y from swath SW1 detected using the first pulse type PT1.
[0050] The embodiments of the present invention described above have several advantages. In particular, multiple pulse types that generate a moving radar beam for detecting the Earth's surface are interleaved with each other, so that each pulse type covers a different section in the range direction on the Earth's surface. This makes it possible to detect a wide area on the Earth's surface with high resolution and good signal quality. In one modification, radar echoes of all pulse types are detected within a common reception time interval. The radar echoes can be distinguished from one another due to the use of different frequency bands for the radar pulses. By using a common reception time interval for all pulse types, more SAR raw data can be obtained within the same period, which means that SAR acquisition can cover a wider area on the ground.
Claims
1. A synthetic aperture radar method for remote sensing of the Earth's surface (GR) via a radar device (100) moving over the Earth's surface (GR) in an azimuth direction (x), wherein the radar device (100) is capable of operating in a transmit mode for transmitting radar pulses (RP) to the Earth's surface (GR) and in a receive mode for receiving radar echoes (EC) of the radar pulses (RP) from the Earth's surface (GR) along a range direction (y) perpendicular to the azimuth direction (x), wherein the radar device (100) transmits a series of radar pulses (RP) having associated pulse durations (PD1, PD2, PD3) in the transmit mode, each radar pulse (RP) generating a radar beam (RB) directed towards the Earth's surface (GR) and having a waveform in frequency bands (FB1, FB2, FB3), and the frequency In a synthetic aperture radar method, the frequencies contained within the waveforms in several bands (FB1, FB2, FB3) are varied over the pulse duration (PD1, PD2, PD3), the radar beam (RB) moves along the range direction (y) over the pulse duration (PD1, PD2, PD3) toward a shorter distance between the radar device (100) and the Earth surface (GR) to illuminate a section (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR), and the radar echo (EC) of each radar pulse (RP) is received by the radar device (100) in the receiving mode after reflection in the illuminated section (SW1, SW2, SW3) at the receiving time interval assigned to each radar pulse (RP), Each radar pulse (RP) belongs to one of a predetermined number of different pulse types (PT1, PT2, PT3), the pulse type (PT1, PT2, PT3) is constantly changed between two consecutive radar pulses (RP), the transmission of radar pulses (RP) of the same pulse type (PT1, PT2, PT3) is performed at a predetermined pulse repetition rate, and radar pulses (RP) of the same pulse type (PT1, PT2, PT3) are in the same frequency band. Generates radar beams (RB) having waveforms in (FB1, FB2, FB3) and illuminating the same section (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR), and generates radar pulses (RP) of different pulse types (PT1, PT2, PT3) having waveforms in different frequency bands (FB1, FB2, FB3) and illuminating different sections (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR). A synthetic aperture radar method characterized by the following:
2. The method according to claim 1, characterized in that the predetermined pulse repetition rate is the same for all pulse types (PT1, PT2, PT3).
3. The method according to claim 1 or 2, characterized in that a sequence of consecutive radar pulses (RPs) of all pulse types (PT1, PT2, PT3) corresponding to a predetermined number of different pulse types (PT1, PT2, PT3) is repeatedly transmitted without an intermediate reception time interval for radar echoes (ECs) from the radar pulses (RPs) of this sequence, and then radar echoes (ECs) from the radar pulses (RPs) of all pulse types (PT1, PT2, PT3) of the predetermined number of different pulse types (PT1, PT2, PT3) are received at reception time intervals, and the received radar echoes (ECs) belong to radar pulses (RPs) from different temporally consecutive previous sequences.
4. The method according to claim 1 or 2, characterized in that each reception time interval is provided exclusively for the radar echo (EC) of a single radar pulse (RP).
5. The method according to any one of claims 1 to 4, characterized in that at least a portion of the different sections (SW1, SW2, SW3) are separate sections (SW1, SW2, SW3) on the Earth's surface (GR) in the range direction (y).
6. The method according to any one of claims 1 to 5, characterized in that at least some of the different sections (SW1, SW2, SW3) have overlap in the range direction (y).
7. The method according to any one of claims 1 to 6, characterized in that one or more of the different pulse types (PT1, PT2, PT3) each belong to a stripmap SAR mode in which the radar pulse (RP) of the pulse type generates a radar beam (RB) having a main beam direction perpendicular to the azimuth direction (x).
8. The method according to any one of claims 1 to 7, characterized in that one or more of the different pulse types (PT1, PT2, PT3) each belong to a spotlight SAR mode in which the radar pulse (RP) of the pulse type generates a radar beam (RB) that illuminates a fixed target area on the Earth's surface (GR).
9. The method according to any one of claims 1 to 8, characterized in that the predetermined pulse repetition rate of the radar pulse of at least one pulse type (PT1, PT2, PT3) from the predetermined number of different pulse types (PT1, PT2, PT3) is changed once or more times.
10. The method according to any one of claims 1 to 9, characterized in that, for each of at least one of the different pulse types (PT1, PT2, PT3), the section (SW1, SW2, SW3) in the range direction (y) irradiated by the radar beam (RB) generated by the radar pulse (RP) of each of the pulse types (PT1, PT2, PT3) is changed once or more times.
11. The method according to claim 10, characterized in that, for each pulse type (PT1, PT2, PT3), when the section (SW1, SW2, SW3) in the range direction (y) illuminated by the radar beam (RB) generated by the radar pulse (RP) of each pulse type (PT1, PT2, PT3) is changed, the pulse repetition rate of the radar pulse (RP) of each pulse type (PT1, PT2, PT3) is simultaneously changed, so that a gap in the region on the Earth's surface (GR) is covered by the changed section (SW1, SW2, SW3) where radar echoes (EC) cannot be received before the change in pulse repetition rate due to the transmission of the radar pulse.
12. A synthetic aperture radar system for remote sensing of the Earth's surface (GR) using a radar device (100) that moves over the Earth's surface (GR) in an azimuth direction (x) during operation, wherein the radar device (100) is capable of operating in a transmit mode for transmitting radar pulses (RP) to the Earth's surface (GR) and in a receive mode for receiving radar echoes (EC) of the radar pulses (RP) from the Earth's surface (GR) along a range direction (y) perpendicular to the azimuth direction (x), wherein the synthetic aperture radar system transmits a series of radar pulses (RP) having associated pulse durations (PD1, PD2, PD3) in the transmit mode, each radar pulse (RP) generating a radar beam (RB) directed towards the Earth's surface (GR) in a frequency band (FB1, FB2, F In a synthetic aperture radar system having a waveform in B3), the frequencies included in the waveform within the frequency band (FB1, FB2, FB3) are varied over the pulse duration (PD1, PD2, PD3), the radar beam (RB) moves along the range direction (y) over the pulse duration (PD1, PD2, PD3) toward a shorter distance between the radar device (100) and the Earth surface (GR) to illuminate a section (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR), and the radar echo (EC) of each radar pulse (RP) is received by the radar device (100) in the receiving mode at a receiving time interval after reflection in the illuminated section (SW1, SW2, SW3), Each radar pulse (RP) belongs to one of a predetermined number of different pulse types (PT1, PT2, PT3), the pulse type (PT1, PT2, PT3) is constantly changed between two consecutive radar pulses (RP), the transmission of radar pulses (RP) of the same pulse type (PT1, PT2, PT3) is performed at a predetermined pulse repetition rate, and radar pulses (RP) of the same pulse type (PT1, PT2, PT3) are in the same frequency band. Generates radar beams (RB) having waveforms in (FB1, FB2, FB3) and illuminating the same section (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR), and generates radar pulses (RP) of different pulse types (PT1, PT2, PT3) having waveforms in different frequency bands (FB1, FB2, FB3) and illuminating different sections (SW1, SW2, SW3) in the range direction (y) on the Earth surface (GR). A synthetic aperture radar system characterized by the following.
13. The synthetic aperture radar system according to claim 12, configured to perform the method described in any one of claims 2 to 11.