High-resolution stripmap sar imaging

The present invention relates to a SAR image forming method which comprises performing N SAR acquisitions in band mapping mode of areas of the Earth's surface by means of a synthetic aperture radar which is transported by an aerial or satellite platform (30) which comprises a single, non-partitioned antenna and a single receiver coupled to said single non-partitioned antenna, N being an integer greater than one. Each SAR acquisition in band mapping mode is carried out using a respective observation angle relative to the direction of flight of the synthetic aperture radar, said respective observation angle being equal to, or different from the angles, used to perform the other Ν-1 SAR acquisitions in band mapping mode. Each SAR acquisition in band mapping mode is carried out using a respective altitude angle relative to the nadir of the synthetic aperture radar, said respective altitude angle being different from the altitude angles used to perform the Ν -1 SAR acquisitions in band mapping mode, and therefore, it follows that each SAR acquisition in the strip mapping mode relates to the respective swath of the Earth's surface which is different from the swaths observed through the other Ν-1 SAR acquisitions of the strip mapping mode. Each SAR acquisition

0 carried out in band mapping mode includes the respective radar transmission and reception operations which are interspersed in time, individually or in group, with a single or groups of radar transmission and reception operations of the others Ν- 1 SAR acquisitions in band mapping mode carried out, which include the transmission and reception of respective radar beams in the acquisition directions

5 which are defined by the respective viewing angle and by the respective altitude angle used for said SAR acquisition in strip mapping mode, which means that said respective acquisition directions are parallel to each other and are not parallel to the acquisition directions of the other Ν-1 SAR acquisitions carried out in band mapping mode. The method further comprises the generation, on the basis of each SAR acquisition in strip mapping mode carried out, of SAR images of the areas of the respective swath obseived via the SAR acquisition in strip mapping mode. All the SAR images generated have the same azimuth resolution which is

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- ح 2 equal to half the physical length or equivalent along the azimuth direction of the single antenna, not partitioned from the synthetic aperture radar.

(TWENTY SEVEN PAGES)

THALES ALENIA SPACE ITALIA

SPA CON UNICO SOCIO.

PP SABA & CO., Casablanca

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۴ ع ، ٠

MULTIPLE MOWDLE BAJOUS MAP IMAGING SAR: ر

TECHNICAL FIELD OF THE INVENTION

The present invention relates to remote sensing by means of a Synthesis of Aperture Radar (SAR) in general and, in particular, an innovative method of SAR imaging of mapping by multiple swath bands.

STATE OF THE ART

A typical reference geometry for generating SAR images of the surface of the Earth is represented in FIG. -after), the surface of the Earth is (and will be) shown plane only for the convenience and simplicity of illustration and description, without any loss of generality.

In particular, FIG. 1 schematically represents a synthetic aperture radar (hereinafter called SAR sensor, for the simplification of the description) 10 which moves along a flight direction d at an altitude h (relative to the surface of the Earth) assumed to be substantially constant. As is known, the altitude h of the SAR sensor 10 is measured along a direction of the nadir تم which passes through said SAR sensor 10 (in particular, it

0 passes through the phase center of the antenna of the SAR sensor 10) and is orthogonal to the surface of the Earth and to the direction of flight d. Ideally, the SAR sensor 10 is transported in flight / orbit by an air / space platform '(not shown in Figure 1 to simplify the illustration), such as, for example, an aircraft or an unmanned drone (UAV) ), or a satellite. the flight track d on the ground identifies an azimuth direction X which is

5 parallel to said direction of flight d and orthogonal to the direction of nadir Z, while a direction transverse to runway y, which is perpendicular both to the direction of nadir Z and to the direction of azimuth X, with the azimuth direction X, identifies an xy plane tangential to the surface of the Earth. In use, by means of a suitable antenna (not shown in FIG. 1 to simplify the illustration), the SAR sensor 10 transmits

0 radar pulses and receives the associated broadcast signals in a direction of acquisition sr which identifies the oblique distance and which forms an angle of altitude Θ with the direction of nadir Z and an angle of observation φ with the direction of flight d (or , equivalently, with the ^ A

38366Β1 azimuth direction -X) which, in the SAR acquisition geometry represented in FIG. 1, is equal to 90٥.

In particular, the SAR acquisition geometry represented in FIG. 1 relates to the mode called strip mapping, in which the SAR sensor 1'0 illuminates a strip of the surface of the Earth, known as a swath, with radar pulses and then receives the backscattered signals associated with them, said swath ؛ extends mainly in parallel with the direction of azimuth X and having a given width w along the transverse direction y. For clarity, Figure 2 shows the SAR acquisition geometry in band mapping mode in the xy plane, where ü is possible to observe how the observation angles φ are all the same (in particular, in l example shown in Figure 2, the observation angles φ are you right angles). !

SAR technology can be considered mature technology. In fact, these days, there are countless articles, manuals, patents and patent applications that describe the features and potential of it; in this regard, we can refer to:

The article by Josef Mittermayer et al. titled Bidirectional SAR Imaging Mode, IEEE Transactions on Geoscience and Remote'Sensing, vol. | 1, no. 1, January 1, 2013, pages 601614, which will be indicated below, for the simplicity of description, like Refl and which describes a mode for creating bidirectional SAR images; German patent application DE 103 19 063 A1, which will be indicated below, for the simplicity of the description, as Ref2 and which relates to a method and a SAR antenna system having a plurality of elements of antenna; to generate multiple SAR beams; \\ the article by A. Currie et al. titled Wideswath ؛ SA /? , IEE Proceedings of Radar and Signal Processing, vol. 139, no. 2, April 1, 1992, pages 122-135, which will be hereinafter indicated, for simplicity, by description, as Ref3 and which describes the various methods for enlarging the swath observable via SAR; ا ا VÉVe àedegev ةة \. n Advanced Concepts for High-Resolution WideSwath SAR Imaging, 8th European Conference on 'Synthetic Aperture Radar', 'June 7

2010, pages 524 to 527, which will be indicated below, for the simplicity of the description, as

Ref4 and which presents the different concepts concerning multi-channel SAR systems for

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38366Β1 ع create high resolution wide swath SAR images; , د. اخ د the book by JC Curlander and RN McDonough entitled Radar. '

Systems and Signal Processing ”, Wiley Series in Remote Sensing, Wiley-Interscience, 1991, which will be indicated below, for the simplicity of the description, as Ref5 and which is a manual on SAR systems; and the book by G. Franceschetti and R. lanarios entitled Synthetic Aperture RADAR Processing ”, CRC-Press, March 1999, which will be indicated below, for simplicity of description, as Ref6 and which is another manual on SAR systems .

As is known, the azimuth resolution for SAR acquisition in stripe mapping mode is a function of the angular aperture (or angular deviation - delta angle) with which a target is observed by the SAR sensor; or, equivalently, the azimuth resolution can also be considered as a function of the time difference (delta time), related to the speed of the SAR sensor, with which the target is observed. In particular, the resolution in azimuth can be expressed by the following equation (for more details, refer to Refi, Ref5 and Ref6):

0.8862.

res = -------------- 2 * delta _angle where res indicates the resolution in. azimuth, د indicates the wavelength used by the SAR sensor and deltajngle indicates the angular aperture (or angular deviation - delta angle) with

0 which the target is observed by the SAR sensor.

Assuming the angle as an opening 3 dB (one pass) of the antenna (= 0.8862Æ, where L indicates the physical length or equivalent along the azimuth direction of the antenna of the SAR sensor), the traditionally associated constraint at the azimuth resolution for the

5 band mapping mode can be obtained, which is equal to L / 2 (for more details, refer to Refi Ref5 and Ref6).

Currently, very large antenna beams are used to improve the azimuth resolution, these being achieved through the use of small antennas or a

0 lighting or amplitude and / or phase modulation subsystem so as to reduce the equivalent size, or by using what is called soptlight mode, the logic of acquiring this mode is illustrated schematically in FIG. figure 3.

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In particular, as shown in FIG. 3, the SAR acquisition logic in spotlight mode envisages using continuous or quasi-continuous piloting of the antenna beam during the flight movement of the SAR sensor 10 (by dynamically adjusting the value of the angle of observation φ) so as to illuminate the same area of ​​interest with the radar pulses, and then to receive the backscattered signals associated with these, in this way it is possible to increase the persistence time of the SAR sensor 10 on said area of ​​interest and thus improve the resolution in azimuth.

The two methods mentioned above used for improving the azimuth resolution have certain drawbacks. In particular, the use of very large antenna beams requires the use of very high transmission powers, while the spotlight mode introduces limitations on the length in azimuth of the mows.

As indicated in the literature, there exist mathematical relations which connect the parameters of the operating modes. In particular, the azimuth sampling requires that the repetition frequency of the emission / reception pulses (PRE) is linked to the size of the beam and to the speed of the SAR sensor (for more details, see Refi Ref5 and Ref6):

L where a is a parameter depending on the level of ambiguity desired, V indicates the speed of the SAR sensor and L indicates the physical or equivalent length along the azimuth direction of the antenna of the SAR sensor.

The PRE value limits the extension of the measured area (mown) in the range (for more details, refer to Ref3 Ref5 and Ref6):

AÆ &lt;

P RF

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where AR indicates the extension of the measured area (mown) in the range, τ indicates the time interval (or duration) of the emitted pulse and c indicates the speed of light.

0 In order to make the most of the capabilities of a SAR system, in addition to the band and spotlight mapping modes, various other techniques have been proposed over the years.

38366Β1 years for the use .: of SAR sensors. These techniques can be grouped into three main modes:

burst mode (segment);

space division mode; and

٠ angle division mode.

The main burst mode is the ScanSAR mode, which divides time into synchronous bursts (i.e. with a regular rate). Part of the scene at the nominal PRE of the antenna is acquired in each segment, so that the spectrum of the azimuth is correctly sampled (for more details, refer to Refi Ref5 and Ref6), but for a shorter time (and therefore a smaller delta angle). This division of time allows the beam to pass, in subsequent segments, in other directions in order to increase the swath in the range. In practice, the time of the azimuth is divided into Nb segments and a different band is acquired in each segment. The biggest indication of this mode is that, by reducing the acquired delta angle, the azimuth resolution deteriorates. In particular, the constraint of the continuous cover which guarantees the absence of holes in the bands implies that the best azimuth resolution cannot be less than (better than) a certain quantity (for more details, refer to Refi Ref4 , Ref5 and Ref6); in particular, we note that:

res ScanSar ^ ٢N_b١ \ ؛ l-eS Strip

WHERE resscanSar indicates the resolution ScanSAR and resstrip indicates the resolution of mapping reference by bands (ie L / 2).

TOPS mode (for more details, refer to Ref4) is also counted among the burst modes; this mode exploits the azimuth direction capability and requires a scanning direction opposite to that of the spotlight mode, that is to say comparable to a scanning rather than a recentering. In other words, in each segment, the initial azimuth direction ensures that the SAR sensor looks backward and then points forward at the end of the segment.

This ensures that, unlike the conventional ScanSAR mode, each target is illuminated by the entire antenna pattern, which allows for equalization of the radiometric response and ambiguities in azimuth. As happens with the prescribed ScanSAR mode, in the mode

38366Β1 try to deduce these critical areas, such as the high resolution wide mown technique (HRWS), which also provides for altitude partitioning in order to follow the beam in altihide, thus increasing the directivity and therefore the sensitivity of the product. The purpose of the techniques which use angle division modes is similar to that of the techniques which use space division modes, but the additional samples are acquired by sampling in different directions. In particular, there are two main logics: the angular division in altitude and the angular division in azimuth.

The angular division in altitude (with regard to this, one can refer, for example, to the technique Beam in Altitude Multiple (MEB) described in Ref4) envisages the simultaneous acquisition with multiple systems of antenna / reception and a single transmitter (with wide, mown), 'or several directive transmissions (for more details, refer to Ref3 and Ref4). In this way, a plurality of acquisitions is obtained in strip mapping mode with nominal resolutions of the azimuth (approximately L / 2). To reduce the problems of ambiguity in the range, the literature suggests observing the individual beams at altitude.

-Instead, the angular division in azimuth (in relation to this, one can refer, for example, to the Multi-Beam Single-Center Center technique (SPCMB) described in Ref3) envisages the emission via a single wide beam and simultaneous reception via M narrow beams. In this way, the wide beam is obtained (improved resolution), but similarly to the spotlight mode, the only reception channels correctly sample a part of different angle. These channels will then be recombined during processing in order to obtain a synthesized delta angle M times greater, consequently improving the resolution (for more details, refer to Ref3 and Ref4). In general, the angular division in azimuth techniques has many critical areas with respect to the level of ambiguity; indeed, the interaction of the side lobes of the transmitting antenna and the simple receiving antennas increases the level of ambiguities.

In this case also, the biggest contraindication of angular division techniques is complexity; in fact, these techniques envisage the simultaneous use of M receivers' and M small antennas (or a large antenna partitioned into M sub-blocks) and require

ΜΑ 38366Β1 ί- · therefore the power of emissioh٠. High to obtain an adequate sensitivity of the product.

The concepts of space and angle division are well summarized in Ref4, whose section 2 states: Several proposals solve the vast dilemma of resolution in azimuth against 5 'wide swath by combining a multi-channel radar receiver with a transmitter. small opening illuminating a large area on the ground. Examples are the observable multiple beam SAR, the displaced phase center antenna technique (DPCA), the quadrangle network SAR system, etc., and the high resolution wide swath SAR system (HRWS).

Although the objective is different, the bidirectional SAR imaging mode (BiDi - for more details, see Refl) 'should also be counted among the angle division techniques. By exploiting the azimuth grid lobes of a phased array antenna or working at different times, this mode simultaneously acquires two different images: 15! 'One relating to the scene from the front and the other relating to!' back of the stage. The angular difference in azimuth is the equivalent of a time difference, namely the same scene seen at different times, and it is therefore possible to identify moving objects in the scene by comparing the images, n is important to emphasize that this technique expects the two acquisitions to be angularly separated in azimuth, that is, it is impossible to combine the data from the two channels to reconstruct an image with higher resolution.

In the conclusion of Refl, it is stated: Short-term BiDi series can be used for speed change and detection. ... The possibilities of the BiDi imaging mode in terms of speed measurement are the subject of future research. Other possible applications of BiDi include high precision measurement of a longitudinal displacement by the exploitation of widely separated Doppler spectra.

Finally, although SAR technology can be developed with different types of antenna, the one which offers the greatest flexibility of use is the so-called de-phase network type, which allows rapid switching of the acquisition direction. Other types of antenna can be used, such as those described in Ref2, for example.

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-ب 9 ^—

OBJECT AND SUMMARY OF THE INVENTION Aim of the present invention is to provide a method of SAR imaging by mapping of the 5 bands which makes it possible to observe several swaths.

The above-mentioned object is achieved by the present invention insofar as it relates to a SAR image forming method and a SAR system, as defined in the appended claims.

In particular, the SAR image forming method in accordance with the present invention comprises the realization of N -SAR acquisitions in band mapping mode of the zones: '.٠ of the Earth's surface by means of a radar. aperture asynthesis which is transported by an aerial or satellite platform and which comprises a single, non-partitioned antenna and a single receiver couples to said single non-partitioned antenna, where N is an integer greater than one.

Each SAR acquisition in strip mapping mode is carried out using a respective observation angle relative to the direction of flight of the synthetic aperture radar, said respective observation angle is either equal to or different from the angles d 'observation used 2 0 to carry out' the other Ν-1 SAR acquisitions in band mapping mode.

Each SAR acquisition in the band mapping mode is carried out using a respective altitude angle relative to the nadir of the synthetic aperture radar, said respective altitude angle being different from the altitude angles used to perform the others. Ν-1 SAR acquisitions in band mapping mode, resulting in each

5 SAR acquisition in the strip mapping mode is linked to the respective swath of the Earth's surface which is different from the swaths observed via the other Ν-1 acquisitions made in the strip mapping mode.

In addition, each SAR acquisition carried out in band mapping mode includes the respective radar transmission and reception operations which:

٠ are the interleaved times, individually or in group, with a single one, or groups of operations, transmission and radar reception of the other Ν-1 SAR acquisitions carried out in band mapping mode; and understands the emission and reception of the respective radar beams in the directions

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- 10 respective acquisition which are defined by the respective observation angle and by the respective altitude angle used for said SAR acquisition in strip mapping mode, which means that said respective acquisition directions are parallel to each other and are not parallel to the acquisition directions of the other Ν-1 SAR acquisitions carried out in strip mapping mode.

The method further comprises the generation, on the basis of each SAR acquisition carried out in the strip mapping mode, of SAR images of areas of the respective swath, observed via said SAR acquisitions in strip mapping mode.

In particular, all the SAR images generated have the same azimuth resolution, which is equal to half the physical length or equivalent along the azimuth direction of the single antenna, '' not partitioned from the synthetic radar 'opening.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, certain preferred embodiments, given by way of nonlimiting example, will now be described with reference to the attached drawings (which are not to scale), where:

Figures let 2 schematically show a typical geometry for acquiring SAR images in stripe mapping mode;

FIGS. 3 schematically show a typical geometry for acquiring SAR images in spotlight mode;

FIG. 4 schematically shows an example of the logic for SAR acquisition in stripe mapping mode according to a first aspect of the present invention;

FIGS. 5 and 6 schematically represent the effects of the application of a first acquisition strategy in carrying out a SAR acquisition technique in strip mapping mode according to a second aspect of the present invention; and * Figures 7 and 8 schematically represent the effects of the application of a second acquisition strategy in carrying out the technique of SAR acquisition in band mapping mode according to the second aspect of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

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-11The following description is provided to enable ؛ .an expert in the field of ealiseriet to use the invention. Various modifications to the embodiments shown will be immediately apparent to experts and the generic principles described herein can be applied to other embodiments and applications without departing from the scope of protection of the present invention.

Thus, the present invention is not intended to be limited only to the embodiments described and shown here, but should be given the widest scope compatible with the principles and characteristics described here and defined in the appended claims.

The present invention arises from the applicant's insight into exploiting the directional capability of the antennas used in SAR sensors in an unconventional manner. The applicant then designed a multi-beam and multi-time SAR acquisition technique which exploits the transmission and reception characteristics of a timeshare SAR sensor.

In particular, the basic idea of ​​the present invention is the division of a SAR acquisition in band mapping mode into N elementary acquisitions in band mapping mode (with Ν&gt; 1) and combine these in order to obtain N SAR image sets, in

0 -which each game is linked to the respective swath (ie, we can observe N distinct swaths with the same resolution in azimuth).

In the detail, a first aspect of the present invention relates to the realization of N different SAR acquisitions using N different altitude angles so as to observe N

5 different mows.

In particular, the idea on which said first aspect of the present invention is based consists in carrying out several SAR acquisitions interspersed at a level of pulse repetition interval (PRI), which represents the time between two consecutive transmitted pulses, in particular SAR acquisitions, in which the acquisition management

0 antenna altitude changes with PRI level. In order to achieve this, a pulse repetition frequency (PRL where PRF = 1 / PRI) is used and which is N times greater than the nominal PRE associated with the antenna of the receiver 'SAR used. Returning

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38366Β1 .- 12 briefly in the figure, for the clarity of the description 11 it should be remembered that the altitude angle is an angle θ between the direction of pointing sr of the antenna of the SAR receiver and the nadir direction of the receiver SAR.

By increasing the PRF by a factor N, the N different bands having N times less time available and therefore, in general, they will have a swath reduced by a factor N; however, by adding the N different swaths observed together, the typical size of the swath of the strip mapping mode is still obtained. As the individual bands are reduced by an N factor, it is possible to use an antenna N times wider in altitade, and consequently, the increase in the directivity of the product, that is to say the sensitivity. In general, the antenna can be used in several ways.

In addition, by increasing the PRE by an N factor, N acquisitions in band mapping can be obtained, individually presenting PRFs compatible with the size of the antenna (in this mode, the values ​​of the azimuth ambiguity are not altered).

Although the SAR acquisition technique in band mapping mode according to the first aspect mentioned above of the present invention can be used with a generic integer N greater than one, thereafter, to simplify the description and without loss of generality, examples will be displayed for N = 2, it being understood that the concepts explain. below with regard to the case N = 2 are also applicable mutatis mutandis in the case of a generic integer N greater than one.

For a better understanding of the second aspect of the present invention, FIGS. 4 schematically illustrates an example of the logic for SAR acquisition in band mapping mode according to said first aspect of the present invention in the case of N = 2, and in the case of the satellite application (it is understood that this SAR acquisition logic can also be advantageously used in the case of an aerial platform such as an aircraft, a drone or a helicopter).

In particular, Figure 4 (in which the Cartesian reference system used corresponds substantially to that previously introduced for Figures 1 to 3). shows, a satellite 30 which moves along a flight direction d and is equipped with a SAR sensor (not shown in FIG. 4 for the sake of illustration) is equipped with a

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- 13 unpartitioned single antenna (not shown in FIG. 4 to simplify the illustration) which is coupled to a single receiver (not shown in FIG. 4 to simplify the illustration), and is associated with a given nominal pulse repetition frequency PREnom.

In the example shown in Figure 4, the SAR sensor is used with an operational pulse repetition frequency PRFop twice that of the nominal pulse repetition frequency of the antenna PRFnom (i.e., PRFop = 2PRFnom) ١ so as to transmit successive pulses at a time distance PRIop = l / (2PRFn0m). In particular, as shown in FIG. 4, the SAR sensor on the satellite 30 performs a series of first SAR acquisitions using a first angle of elevation and a series of second SAR acquisitions using a second angle of altitude, in which said first and second SAR acquisitions are interspersed at a PRI level (i.e., the first SAR acquisition is always altered with a second SAR acquisition) and said first and second altitude angles are different from each other. In other words, the first SAR acquisition is carried out using the first angle of altitude, then, at a time distance PRl £, n = l / PRF_notn = l / (2PRF_nnm) ٩ a second SAR acquisition is performed using the second angle of elevation, always at a time distance PRl٤١n = l / PRF „, 2 = l / (2PRFno_m)_٦a first SAR acquisition is performed once again using the first altitade angle and so on, always alternating the execution of the first SAR acquisition with the execution of the second SAR acquisition while separating the different acquisitions ا by PRInpzl / PRFniflÆZPRFnom). In this sense, the SAR sensor on board the satellite 30 is capable of observing two separate swaths (as shown in Figure 4).

It is important to note that the acquisitions which concern the same swath are carried out - with the repetition frequency of nominal pulse PRFnom of the antenna, that is to say the first SAR acquisitions are carried out with the repetition frequency - antenna nominal PRFnom pulse rate and the second SAR acquisitions are also effected by the antenna PRFnom nominal pulse repetition frequency. In this sense, the ambiguity values ​​of the azimuth are altered.

<img file="MA38366B1_D0003.tif" />

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- 14 ، ق, Still in general, since the operational pulse repetition frequency PRFop 'used is N times (twice for example in Figure 4,) greater than the required / nominal PRFnom, the individual acquisitions will have PRF nominal, and therefore, all product quality parameters will not be altered.

For all these intentions and all these objectives, the technique of SAR acquisition in strip mapping mode according to the first aspect of the present invention allows the separation of the swath in the range of reduced swaths in N (approximately 1 / Ν ) without the other parameters being altered, such as the azimuth resolution.

All N SAR acquisitions can be performed using the same viewing angle, or each SAR acquisition can be performed using a respective viewing angle different from that used to perform the other Ν-1 acquisitions: SAR, such so as to obtain, for each acquisition, an integration time equal to standard time of the strip mapping.

1.5 Consequently, the SAR acquisition technique in band mapping mode according to the first aspect of the present invention allows to serve two (or N in the generic case) users who are interested in the areas of medium extension and separated the each other in the plane of altitude. With the traditional strip mapping technique, these requests would be in conflict and therefore would not be possible to serve them simultaneously.

In order not to alter the image quality parameters, the PRF used with the technique according to the first aspect of the present invention is greater than the natural frequency of the antenna. By increasing the FRP, the mows in the range where they can be acquired are smaller. Thus, a second aspect of the present invention relates to a SAR acquisition technique in band mapping mode which does not use an increased PRF, or in any case is not increased by a factor of N, so as to control the effects on the product and manages the induced degradation.

In particular, said second aspect of the present invention relates to what is called a band mapping technique in burst mode which is not interspersed at the PRI level, that is to say where the N acquisitions of band mapping are not -not done by

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-.15.variate the direction of altitude acquisition of the antenna at iPRI level, but by varying the direction of altitude acquisition of the antenna in PRL blocks

More precisely, the second aspect of the present invention is a burst mapping strip technique in which the N strip mapping acquisitions are carried out without increasing the PRP and by varying the altitude acquisition direction from the antenna, i.e. the altitude angle used, in PRI blocks.

The strip mapping technique in burst mode with unenhanced PRP and the variation of the altitude angle according to the second aspect of the present invention makes it possible to extend the swath in the range, and even to double it .

In order to divide the acquisition in half (N in the generic case) and assuming that the use of the natural nominal PRP of the antenna used, holes are introduced into the acquisition system. If these holes do not have the periodic characteristics, the effect will be a distributed increase of all the lateral lobes, i.e. the ISLR (Integrated Lobe Ratio) parameter deteriorates, but the PSLR (Lateral Pic Lobe Ratio ). Vice versa, using periodic execution patterns for two (N in the generic case) acquisition types, even echoes in a known position are created. Depending on the needs, 20 different solutions can be chosen and then a given pattern will be applied in the acquisition logic. 'As a smaller number of samples will be integrated, the product will have a reduced NESZ (Sigma Zero Noise Equivalence) parameter.

By way of example, FIGS. 5 and 6 show the effects of the application of a pattern of periodic execution of the N types of acquisition with the technique of strip mapping in burst mode with a PRP not increased according to the second aspect of the present invention, while the figures. 7 and 8 show the effects of applying a random execution pattern of the N types of acquisition with the band mapping technique in burst mode with a non-augmented -PRP according to the second aspect of the present invention.

Compared to the technique according to the first aspect of the present invention, the technique according to the second aspect introduces less technological constraints because the switching

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The antenna beam takes place at a much lower frequency. 'ن

Briefly summarizing, the present invention relates to:

the use of a PRF increased by a factor of N and the intercalated use of N different altitude angles at PRI level to observe N separate swaths with the same azimuth resolution (in particular, each of the N swaths is observed with the nominal azimuth resolution of the traditional band mapping mode, (i.e. L / 2,)); and the use of an unincreased PRF and the use of the segmentation of N different angles of altitude to 'extend the swath in the range by a factor of N (i.e. allow observation of N swaths, where each has a size comparable to that of swaths observed through acquisitions in conventional band mapping mode) with the resolution in azimuth (in particular, each swath is observed with the nominal azimuth resolution of the traditional band mapping mode (i.e. 172)).

It is important to mention that the fact that the present invention makes it possible to carry out N continuous acquisitions in strip mapping (that is to say with integration times equal to those of the traditional strip mapping mode), and consequently obtaining, for each swath, the nominal-maximum azimuth resolution of the traditional band mapping mode (that is to say L / 2)); in particular, according to the first aspect of the present invention, each acquisition is carried out with the nominal PRF of the antenna of the SAR sensor used.

In conclusion, the present invention exploits the multi-beam acquisition logics which make it possible to simultaneously acquire areas which are not contiguous in the orthogonal direction of the flight direction of the SAR sensor, unlike traditional techniques of spotlight and strip mapping which, on the other hand, do not allow several mows to be observed simultaneously.

The present invention therefore relates not only to the increase in the range of products 30 for the systems already produced, but, above all, the introduction of a new methodology for the design of new SAR systems.

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-17 -... ؛ Finally, after having compared the present invention with the Spotlight and traditional band mapping modes, the main differences compared to the known techniques for generating high resolution wide swath SAR image described above will now be described in detail. .

In particular, unlike the present invention, the burst techniques (for example ScanSAR and TOPS) provide for a deterioration of the resolution in azimuth in order to increase the swath in the range.

Unlike the present invention, which works with a single receive channel (i.e. with a single receiver), space division techniques (eg DPC and.: ... HRWS) and those of d division angle (for example MEB and SPCMB) envisage the use of M tracking systems for simultaneous reception and also envisage the use of a small antenna (typically, an antenna is divided into M smaller antennas).

The BiDi mode described in Refl has a different objective, which is the identification of the Moving Target (MTI) 'and therefore does not have the objective of observing several swaths in the range. In addition, the acquisition geometry is different from that of the present invention;

the beam openings currently take place on the azimuth plane and not in altitude plan.

In addition, it should also be noted that Ref2 has an implementation logic at the antenna level and not as a logic for acquiring the present invention. Furthermore, as can be inferred from Figure 3 of Ref2, the acquisitions are separated by a significant space with respect to the swath of the antenna and they have repeatability characteristics. The segments do not guarantee continuous sampling of the spectrum of the azimuth with the natural frequency (PRE) of the antenna, that is, there is no. of temporal continuity in the. segments about the same mown and therefore, contrary to what is provided by the present invention, the best resolution, in achievable azimuth is worse than the nominal value of the strip mapping mode (this is say L / 2). In particular, the geometry shown in Figure 3 of the RefZ is typical of the 'ScanSAR mode, which, as

38366Β1

- 18 mentioned just before, makes it possible to observe several swaths, but with mediocre azimuth resolutions compared to the nominal resolution of the strip mapping mode (i.e. 172) and consequently mediocre compared to those obtained by the mowed variables of the present invention.

Finally, it should also be noted that section 5 of the ReS also presents the ScanSAR mode, that is to say a mode which acquires multiple sub-swaths in a range with segments which are not contiguous in time. The segments are sequential and of shorter duration compared to those obtainable in band mapping mode, and consequently, contrary to what is provided by the present invention, there is a degradation of the resolution in azimuth relative to at the nominal resolution of the band mapping mode (i.e. L / 2). In addition, the figure 10 of the Refi does not show the acquisition logic, but only describes the values ​​of the PRE which can be chosen as a function of the distance from the scene. In particular, according to what FIG. 10 of Ref3 shows, synchronous and spaced segments are provided on the individual zones in the range, thus forcing the degradation of the resolution in azimuth. In addition, the figure s of Ref3 illustrates the traditional mode ScanSAR which, as indicated previously, which makes it possible to observe several swaths, but with a resolution in azimuth poor compared to the nominal resolution of the mode in strip mapping (c ' i.e. L / 2) and, therefore, poor compared to those obtained for the multiple mows of the present invention.

In conclusion, it is clear that various modifications can be made to the present invention without departing from the scope of the invention, as defined in the appended claims.