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Geosynchronous synthetic aperture radar: design and applications

Geosynchronous synthetic aperture radar: design and applications

Typically, EO satellites are placed in Low Earth Orbit (LEO), to take advantage of the shorter slant range. The key limitation of LEO for remote sensing is the difficulty of providing frequent timely images of an area. A single satellite typically images a swath 100-200 km wide steerable within a field of view 500 km across. LEO orbit periods are approximately 100 minutes, and in this time, the Earth has turned almost 3000 km at the equator: it thus takes ~3000/500=6 days to obtain complete access. Envisat actually uses a 35-day repeat orbit, which means a repeat period of 5 weeks for interferometry, and 1-2 weeks (at mid-latitudes) for imaging. Processes with timescales shorter than these periods are difficult to measure usefully. Satellites in geosynchronous orbit, on the other hand, have a permanent view of 1/3 of Earth’s surface so that, as soon as one image is complete, the next can be started. Allowing for the time required to acquire the image this means that a geosynchronous satellite could provide in principle several images each day of any location in the field of view. An inconvenience caused by the geosynchronous orbit is its fixed longitude. This implies that only a constellation of at least three satellites can guarantee a nearly global coverage. Even so, polar zones cannot be imaged with nominal resolution. However, global coverage is not always an essential requisite for a space system. The problem that many satellite service providers have to tackle is that the request for satellite products is concentrated in the most industrialised regions of the globe therefore a system that is able to provide nearly continuous imaging of a certain region may prove to be advantageous for certain customers.
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Interferometric Synthetic Aperture Radar (SAR) Missions Employing Formation Flying

Interferometric Synthetic Aperture Radar (SAR) Missions Employing Formation Flying

4) Bistatic SAR Imaging: Bistatic SAR imaging provides additional observables for the extraction of important scene and target parameters [65]. TanDEM-X allows for the simultaneous acquisition of bistatic and monostatic images in a single data take to obtain a highly informative set of multiangle observations. A quantitative evaluation of the bistatic radar cross-section and a comparison with its monostatic equivalents facilitates the detection and recognition of targets. The segmentation and classification in radar images is expected to be substantially improved by comparing the spatial statistics of mono- and bistatic scattering coefficients. This is also supported by the results from an airborne bistatic radar campaign performed in close collaboration between DLR and ONERA [66]. This joint experiment, which was conducted in early 2003 in Southern France, revealed significant changes of the scattering behavior for both artificial and natural targets even in case of rather small bistatic angles [67]. A joint evaluation of mono- and bistatic SAR images could furthermore be used to isolate different scattering mech- anisms like, e.g., a distinction between highly directive dihedral returns from more isotropic volume scattering. Bistatic SAR imaging has moreover potential for the retrieval of sea state parameters, the estimation of surface roughness and terrain slope, as well as stereogrammetric, meteorological, and atmospheric applications [68]. Inno- vative processing algorithms will be required to exploit all these capabilities. The bistatic data acquired with TanDEM-X will hence provide a unique data source to improve our understanding of bistatic imaging and its exploitation for future remote sensing applications. Data takes with large bistatic angles are planned at the begin-
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Laplace plane and low inclination geosynchronous radar mission design

Laplace plane and low inclination geosynchronous radar mission design

For the QGS GEO SAR concepts there may only be a single beam which stares continuously at the target area. The footprint may be large enough for these missions to cover a wide area on the order of 1 000 km in size using L-band. However, for higher inclination orbits than QGS the antenna is likely to be larger resulting in a smaller beam footprint. In these cases it will be necessary to use multiple beams to cover a large region. The beams may be simultaneous by using multiple feeds for the antenna or an electronically-steered antenna, or may be imaged sequentially. Figure 6 shows the RF power demand timeline for two representative applications from Table 1: in both cases the power demand for three sequential beams is shown. It can be seen that the RF power demand is modest (about 500 W RF for the snow mass case and less than 50 W for the APS measurements). With the orbit speed assumed (200 m s −1 ) the images are acquired quickly leaving time to increase the total area covered by steering the beam to new areas before repeat images are needed.
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A Tutorial on Synthetic Aperture Radar

A Tutorial on Synthetic Aperture Radar

Symmetry assumptions about the distribution of ele- mentary scatterers within the resolution cell simplify the scattering problem and reduce the number of independent parameters of [ ] T (or [ ] C ) allowing qualitative and quanti- tative conclusions about the scattering behavior [35], [42], [43]. Besides reciprocity, three special cases of symmetry are important in radar remote sensing applications: Reflection, rotation and azimuthal symmetry. Reflection symmetric media are characterized by a symmetry plane that contains the line-of-sight so that for any scatterer located at one side of the plane a mirrored scatterer at the other side of the plane exists. In this case the correlation between the co- and cross- polarized elements becomes zero. The resulting [ ] T matrix contains only five independent parameters in form of three real diagonal elements and one single non-zero complex off-diagonal element (i.e., the correlation between the co- polarized elements). The majority of natural distributed scatterers is reflection symmetric. In the case of rotation symmetry, the spatial distributions of elementary scatterers do not change when rotated about the line-of-sight (LOS) axis. Accordingly, the scattering behavior of such media is invariant under the line-of-sight rotations and the resulting coherency matrix contains only three independent parame- ters in form of two independent real diagonal elements and one non-zero imaginary off-diagonal element. This is typi- cal for gyrotropic random media, as given for example by a random distribution of helices. When both, reflection and rotation symmetry applies, the medium is said to be azi- muthally symmetric: All planes including the line-of-sight are reflection symmetry planes. Consequently, all three off- diagonal elements of the coherency matrix become zero, and only two diagonal elements are independent, the num- ber of independent parameters reduces to 2. This is the case for volumes consisting of random distributions of ellipsoids.
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Relativistic Effects in Bistatic Synthetic Aperture Radar

Relativistic Effects in Bistatic Synthetic Aperture Radar

The relativistic phase and time offsets from this paper are not only of high importance for DEM generation with a formation flying SAR cross-track interferometer. Formations with multiple satellites have also been suggested for a wide range of further remote sensing applications, ranging from along-track interferometry for moving object and ocean current measurements over sparse aperture ambiguity suppression and super resolution for enhanced high-resolution wide-swath SAR imaging up to single-pass SAR tomography for vertical struc- ture measurements [38]–[44]. Due consideration of relativistic effects from varying along-track baselines is again of essential importance for these advanced bistatic and multistatic SAR systems to avoid mutual range and phase offsets between the received SAR signals. The phase accuracy requirements for the combination of the different receiver signals are typically in the order of 1° or a few degrees. For comparison, an along-track baseline of 100 m causes in an X-band system a relativistic phase shift in the order of several tens of degrees. Future multistatic SAR satellite missions should therefore take into account relativistic effects in the design of the radar synchronization system and/or the SAR processor to avoid a possible performance loss.
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Hurricane Monitoring With Spaceborne Synthetic Aperture Radar

Hurricane Monitoring With Spaceborne Synthetic Aperture Radar

The German X-band SAR TS-X was launched successfully on 15 June 2007 from Baikonur, Kazakhstan. The satellite is in a near-polar orbit around the Earth, at an altitude of 514 km. Using its active radar antenna, TS-X is able to produce image data with a resolution down to one meter, independent of weather conditions and daylight. It has been fully operational since January 7, 2008. Main technical parameters of TS-X are briefed in Table 6.1 . The detailed information of TS-X mission, design, as well as ground segment is available in [ 16 , 17 ]. Figure 6.1 illuminates three different imaging modes of TS-X, i.e., Spotlight, Stripmap and ScanSAR modes. For both Stripmap and ScanSAR modes, the radar beam can be electronically tilted within a range of 20–45 ◦ perpendicular to the flight direction without having to move the satellite itself. For Spotlight mode, the radar beam can be further tilted to 55 ◦ . Scenes sizes and resolutions of the three imaging modes of TS-X are listed in Table 6.2 .
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Multidimensional Waveform Encoding for Spaceborne Synthetic Aperture Radar

Multidimensional Waveform Encoding for Spaceborne Synthetic Aperture Radar

Digital beamforming on transmit allows furthermore a flexible distribution of the RF signal energy on the ground. This enables not only a switching between different SAR modes like Spotlight, ScanSAR and HRWS stripmap, but it allows also for the simultaneous combination of multiple imaging modes in one and the same data acquisition. An example for such an interleaved operation is a spotlight imaging of an area of high interest in combination with a simultaneous wide swath SAR mapping for interferometric applications. This can be achieved by enhancing the multi- dimensional waveform encoding with additional sub- pulses that steer highly directive transmit beams to some specific areas on the ground. By this, one obtains a high Tx gain and a longer illumination time along the synthetic aperture, which will improve both the radiometric and the geometric resolution for the local areas of high interest. This is illustrated in Fig. 7 and such a hybrid mode is well suited to satisfy otherwise contradicting user requirements like the conflict between a continuous interferometric background mission and a high-resolution imaging request. The data acquisition in such a hybrid system could even be made adaptive where more system resources are devoted automatically to areas of high interest and/or low SNR, thereby maximizing the overall information content for a given RF power budget. By this, a closed loop will be formed which connects the recorded data directly to the transmitted waveform by an appropriate real-time raw data evaluation of the scattered signals from the environment (cf. Fig. 3). As a simple opportunity one may consider the adaptive use of a longer sub-pulse and/or a higher Tx an- tenna gain for a spatially restricted area with lower back- scatter, thereby enhancing the overall signal-to-noise ratio for a given amount of system resources. Such an adapta- tion can e.g. be performed in real-time via a multiple beamforming processor which evaluates the spatial power distribution of the scattered and recorded radar data. The output from this processor is then directly fed back to the waveform encoding system. Another opportunity is the use of longer azimuth illumination times and higher range bandwidths for selected regions with high contrast and/or fast changes. Such features could be indicators for areas of high interest, therefore calling also for a higher spatial and/or radiometric resolution. A potential application sce-
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Onboard Quantization for Interferometric and Multichannel Synthetic Aperture Radar (SAR) Systems

Onboard Quantization for Interferometric and Multichannel Synthetic Aperture Radar (SAR) Systems

In the last decades, the radar system technology has experienced significant advance- ments, which will very likely revolutionize radar system concepts [151]. Recent studies demonstrate that multi-static SAR missions will pave the way for unprecedented poten- tials in radar remote sensing [152]. In particular, in [153] the new MirrorSAR system concept is proposed, consisting of a fractionated SAR system where the scene illumi- nation and the spatial sampling of the scattered radar signal is carried out by different platforms. The functionality of the receiver satellites is limited to a transponder-like routing of the received radar echoes to the active transmitter(s), hence significantly re- ducing the hardware and downlink requirements for an affordable implementation cost. The described system architecture can achieve very high resolution SAR imaging of ultra-wide swaths and allows, among other applications, for single-pass tomography for the three-dimensional imaging of volume scatterers, and for multi-baseline cross-track interferometric acquisitions for very high-resolution DEM generation and the monitor- ing of vector deformation [153], [154]. For such systems, the resulting huge amount of data, collected by the multiple independent apertures, represents a critical challenge. However, the simultaneous availability of all received signals on a centralized node can be exploited by applying, e.g., a proper onboard preprocessing to exploit the mutual re- dundancy which characterizes multi-static radar signals from close satellite formations. More specific, the described data correlation can be conveniently represented by means of an appropriate three-dimensional “information cube”, where the three axes correspond to time, frequency, and direction of arrival of the recorded signals [155]. Thus, an ef- ficient bit-allocation in the transformed space may be derived by applying the general concept of rate distortion analysis to the multi-channel SAR system [87], [156].
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Multidimensional Waveform Encoding for Synthetic Aperture Radar Remote Sensing

Multidimensional Waveform Encoding for Synthetic Aperture Radar Remote Sensing

The HRWS system concept assumes a wide area illumination by a separate transmit antenna. This enables an independent electrical design and optimization of the transmit and receive paths, but it requires also the accommodation of an additional antenna on the spacecraft and reduces the flexibility to operate the radar system in different SAR imaging modes like ultra- wide-swath ScanSAR, high SNR spotlight, or new hybrid modes to be discussed later. It is hence worth to consider also the application of digital beamforming techniques in radar sys- tems that use the same antenna array for both the transmission and reception of radar pulses, thereby taking advantage of al- ready existing space-qualified T/R module technology. Since the high-resolution wide-swath SAR imaging capability is es- sentially based on a large antenna array, this poses in turn the question of how to distribute the signal energy on the ground. The trivial solution would be amplitude tapering, or as an ex- treme case, the use of only a part of the antenna for signal transmission, but this causes a significant loss of efficiency. Another possible solution is phase tapering, but the derivation of appropriate phase coefficients is an intricate task which re- quires in general complicated numerical optimization tech- niques.
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Multidimensional Radar Waveforms: A New Paradigm for the Design and Operation of Highly Performant Spaceborne Synthetic Aperture Radar Systems

Multidimensional Radar Waveforms: A New Paradigm for the Design and Operation of Highly Performant Spaceborne Synthetic Aperture Radar Systems

Digital beamforming on transmit allows furthermore a flexible distribution of the RF signal energy on the ground. This enables not only a switching between different SAR modes like Spotlight, ScanSAR and HRWS stripmap, but it allows also for the simultaneous combination of multiple imaging modes in one and the same data acquisition. An example for such an interleaved operation is a spotlight imaging of an area of high interest in combination with a simultaneous wide swath SAR mapping for interferometric applications. This can be achieved by enhancing the multi- dimensional waveform encoding with additional sub- pulses that steer highly directive transmit beams to some specific areas on the ground. By this, one obtains a high Tx gain and a longer illumination time along the synthetic aperture, which will improve both the radiometric and the geometric resolution for the local areas of high interest. This is illustrated in Fig. 7 and such a hybrid mode is well suited to satisfy otherwise contradicting user requirements like the conflict between a continuous interferometric background mission and a high-resolution imaging request. The data acquisition in such a hybrid system could even be made adaptive where more system resources are devoted automatically to areas of high interest and/or low SNR, thereby maximizing the overall information content for a given RF power budget. By this, a closed loop will be formed which connects the recorded data directly to the transmitted waveform by an appropriate real-time raw data evaluation of the scattered signals from the environment (cf. Fig. 3). As a simple opportunity one may consider the adaptive use of a longer sub-pulse and/or a higher Tx an- tenna gain for a spatially restricted area with lower back- scatter, thereby enhancing the overall signal-to-noise ratio for a given amount of system resources. Such an adapta- tion can e.g. be performed in real-time via a multiple beamforming processor which evaluates the spatial power distribution of the scattered and recorded radar data. The output from this processor is then directly fed back to the waveform encoding system. Another opportunity is the use of longer azimuth illumination times and higher range bandwidths for selected regions with high contrast and/or fast changes. Such features could be indicators for areas of high interest, therefore calling also for a higher spatial and/or radiometric resolution. A potential application sce-
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Orbital Effects in Spaceborne Synthetic Aperture Radar Interferometry

Orbital Effects in Spaceborne Synthetic Aperture Radar Interferometry

displacement, a parametric model like a linear rate of change or a seasonal oscillation is assumed. Preliminary estimation of displacement parameters has the clear disadvantage that a functional model has to be postulated, chosen either from a priori knowledge or by statistically testing the performance of different models (van Leijen and Hanssen, 2007). Whereas preliminary displacement estimation is included in most PS processing chains, it is disapproved by Hooper et al. (2004, 2007) who only estimate per PS an absolute height error δh (or look angle error, respectively) and a spatially uncorrelated contribution of the master image. Assuming the relative displacement of nearby PS to be small, their approach does not rely on the preliminary choice of a specific functional model. However, in contrast to other approaches, large spatial displacement gradients may be critical for successful unwrapping. The most critical issue inherent to all unwrapping approaches is the validity of the assumption that phase differences of PS adjacent in time or space are smaller than π. Taking into account the unseizable noise contribution, it is rather desirable that systematic signal components differ by distinctly less than π. Preliminary mitigation of atmospheric and orbital signals is usually neither performed nor required, because their local gradients are mostly sufficiently small. However, even though this assumption applies to the great majority of applications, it might prove invalid in some cases with very large orbit errors, where only a preliminary estimation enables successful unwrapping.
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Ocean wave measurements using complex synthetic aperture radar data

Ocean wave measurements using complex synthetic aperture radar data

As demonstrated in the previous chapters, the information SAR provides on the two-dimensional ocean wave spectrum has limitations in particular for shorter waves propagating in the azimuth direction. SAR look cross spectra have shown their capa- bility to resolve the ambiguity of wave propagation direction present in conventional SAR image variance spectra, but the information loss caused by nonlinear SAR imag- ing effects, like the azimuthal cut-off still exists. One can of course try to restrict the SAR measurement to the long wave regime, which is less affected by nonlinear mech- anism as shown in the previous chapter, however for practical applications like, e.g. wave model assimilation this approach is not really satisfactory. The main reason is the fact that due to the strong coupling of different wave components in the imaging process there is no obvious separation of the spectral regime in regions of linear and nonlinear wave mapping.
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Bathymetry using Synthetic Aperture Radar (SAR) satellites

Bathymetry using Synthetic Aperture Radar (SAR) satellites

In the maritime sector, SAR is currently being used for the detections of sea state, wind, oil spills, sea ice, icebergs and ships. These detection algorithms have been developed to run automatically in the receiving station to provide results in Near Real Time (NRT). Applications are the improvement of wave and wind models by providing data across large areas, the improvement of maritime domain awareness, and the support of vessels travelling through ice-infested waters.

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Passive Interferometric Ocean Currents Observation Synthetic Aperture Radar (PICOSAR)

Passive Interferometric Ocean Currents Observation Synthetic Aperture Radar (PICOSAR)

Aperture Radar), a concept consisting of two small, low-cost and low power spacecraft carrying a passive, receive-only SAR payload. PICOSAR enhances the functionality of a full SAR system such as Sentinel-1 or TerraSAR-X by adding a unique along-track interferometer dedicated to ocean surface current measurements. The passive nature of this system and the focus on a single application and single operation mode allows the implementation of PICOSAR using a very cost effective payload design and the use of a compact and low-cost micro-satellite bus. Besides the clear scientific value of PICOSAR, it would also foster the development of several key technologies: micro-satellite architectures, autonomous formation flying, and multi-static SAR constellations.
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Spaceborne MIMO Synthetic Aperture Radar for Multimodal Operation

Spaceborne MIMO Synthetic Aperture Radar for Multimodal Operation

to a considerable improvement in system performance when compared to the state-of-the-art SAR, and its benefits can be maximized when combined with digital beamforming (DBF) capability [5]. So, SAR systems with DBF functionality on receive are spotlighted as a promising way toward the next generation of SAR instrument [6]–[10]. The high-resolution wide-swath (HRWS) SAR is a representative example of the DBF SAR concept. The HRWS SAR system enables one to circumvent the fundamental limitation in the SAR design and produces high-resolution images over a wide area with the aid of DBF [11], [12]. The multiple channels of the HRWS system provide increased degrees of freedom that are fully exploited for the suppression of azimuth ambiguities caused by lower pulse repetition frequency (PRF) than the Nyquist sampling requirement. The DBF techniques make the ambiguity suppres- sion flexible and adaptive [7], [13]. In this paper, we attempt to build a reconfigurable SAR system concept in which the HRWS SAR imaging operation can be effectively combined with other operation modes, avoiding performance degradation. For this purpose, one needs to increase the spatial degrees of freedom. We achieve it by adding transmit antennas to the multiple receive antennas, the so-called multiple–input multiple–output (MIMO) SAR.
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Monitoring permafrost environments with Synthetic Aperture Radar (SAR) sensors

Monitoring permafrost environments with Synthetic Aperture Radar (SAR) sensors

The DInSAR and advanced time-series InSAR methods have been tested recently for monitoring permafrost thaw subsidence and frost heave [18], [20]–[26]. One of the main limitations of DInSAR applications is the signal loss caused by insuffi- cient interferometric coherence, which describes the degree of correlation between two SAR observations [17]. This feature indicates the quality of the DInSAR results. The loss of phase coherence can be explained by a number of reasons, including thermal noise from the antenna, large interferometric baseline, topographic effects, and misregistration between SAR images, and atmospheric effects; however, it can also be caused by land surface changes that occur between two SAR acquisitions [27]. Permafrost regions are usually difficult to access because of their remoteness and harsh environmental conditions; therefore, the availability of ground-truth data for these regions is lim- ited. Although quantitatively validating DInSAR displacements over permafrost is difficult, several efforts have been reported. Short et al. first used in situ thaw tubes [21], [28], [29] to obtain ground observation data to evaluate RADARSAT-2 DInSAR products at the Iqaluit Airport, Baffin Island, Canada [21]. The thaw/frost tube is a classical method used to record thaw set- tlements and frost heave in permafrost areas. In this method, a tube is anchored vertically in permafrost, a metal grill is placed on the ground surface, and a scriber scratches the tube when it moves with the upward and downward movement of the metal grill [21], [28], [29]. In the work undertaken by Short et al., DInSAR-derived seasonal ground displacement patterns aligned well with in situ measurements. In dry areas, the data showed subcentimeter consistency. However, in low-lying wet areas, the DInSAR stack significantly underestimated the true thawing settlement because the combination of high phase gra- dients and poor coherence over intermittently flooded surfaces increases the difficulty of preserving reliable phase measure- ments [21]. Subject to saturation and flooding, changes in soil moisture between two radar acquisitions can also influence DIn- SAR displacements [10], [30].
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Digital Beamforming Techniques for Multi-Channel Synthetic Aperture Radar

Digital Beamforming Techniques for Multi-Channel Synthetic Aperture Radar

In the last years a clear trend towards multi-digital-channel SAR systems has manifested itself. Examples are TerraSAR- X (two channels as a by-product of the redundancy concept), R ADARSAT -2 for ATI applications, ALOS-2 to increase the azimuth resolution. This step towards multi-channel SAR instruments marks a paradigm change as a consequence of research activity results in the last decade. The main inno- vative characteristic of forthcoming generations of SAR sys- tems is the use of multiple elevation and/or azimuth receiver channels combined with digital beamforming (DBF) capabil- ity [1, 2, 3]. This allows for the synthesis of multiple or dy- namic digital receiver beams. Further, multiple transmit chan- nels are being suggested as an extension to DBF systems.
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Very-High-Resolution Airborne Synthetic Aperture Radar Imaging: Signal Processing and Applications

Very-High-Resolution Airborne Synthetic Aperture Radar Imaging: Signal Processing and Applications

Airborne SAR sensors have been and are still used ex- tensively for the development and demonstration of new imaging techniques, often involving several repeated passes over the same area of interest, each being separated by certain spatial baselines. For Pol-InSAR and SAR tomog- raphy, predefined spatial baselines, typically separated by some tens of meters, are flown, whereas for change de- tection and differential SAR applications, the same nominal flight track is preferred. In each track, deviations from a straight flight path occur, which need to be compensated during processing. The RD and ECS algorithms typically implement a two-step motion compensation: a first-order, range-invariant correction at raw data level is performed prior to any presumming or azimuth resampling operation, while the second step is the range adaptive motion com- pensation, which is conveniently applied after range cell migration correction. Each compensation step needs to cor- rect phase and envelope of the signal according to the line-of- sight difference between the real and nominal tracks.
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System design for geosynchronous synthetic aperture radar missions

System design for geosynchronous synthetic aperture radar missions

System Design for Geosynchronous Synthetic Aperture Radar Missions Stephen Hobbs, Cathryn Mitchell, Biagio Forte, Rachel Holley, Member, IEEE, Boris Snapir, and Philip Whittaker Abstract—Geosynchronous synthetic aperture radar (GEO SAR) has been studied for several decades but has not yet been implemented. This paper provides an overview of mission design, describing significant constraints (atmosphere, orbit, temporal stability of the surface and atmosphere, measurement physics, and radar performance) and then uses these to propose an approach to initial system design. The methodology encompasses all GEO SAR mission concepts proposed to date. Important classifications of missions are: 1) those that require atmospheric phase com- pensation to achieve their design spatial resolution; and 2) those that achieve full spatial resolution without phase compensation. Means of estimating the atmospheric phase screen are noted, including a novel measurement of the mean rate of change of the atmospheric phase delay, which GEO SAR enables. Candidate mission concepts are described. It seems likely that GEO SAR will be feasible in a wide range of situations, although extreme weather and unstable surfaces (e.g., water, tall vegetation) prevent 100% coverage. GEO SAR offers an exciting imaging capability that powerfully complements existing systems.
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Physics-based clutter model for geosynchronous synthetic aperture radar

Physics-based clutter model for geosynchronous synthetic aperture radar

We propose a novel physics-based approach which prom- ises to provide a generic approach to clutter modelling suit- able for a wide range of incidence angles and wavelengths. It is based on observations of the true motion of vegetation (wheat, in the first case) in natural wind. These are combined with a focussing algorithm to assess how broadly the scattered power is smeared in azimuth across the image. Parametrisa- tions of the azimuth spread for a particular class of vegetation (wheat, representing short crops) are derived to allow image simulation for a range of landscapes and weather conditions. We expect that similar parametrisation could be developed for other landcover classes, for example rough water, long crops and trees / forest (probably the most important class needed to represent real landscapes).
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