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Proceedings ArticleDOI

Requirements on the calibration of Hybrid-Compact SAR

13 Jul 2014-pp 1109-1112
TL;DR: The state of the art in compact SAR calibration is reconsidered and it is shown that all the existing Compact calibration methods are built on the assumption that the Compact transmits a perfect circular polarization (CP).
Abstract: The state of the art in compact SAR calibration is reconsidered. It is shown that all the existing Compact calibration methods are built on the assumption that the Compact transmits a perfect circular polarization (CP). Unfortunately, the actual technology does not permit the generation of a perfect CP wave. The impact of non circularity of the transmitted polarization on Compact polarization information is assessed. The variations with incidence angles of the helicity and ellipticity of the transmitted polarization are simulated for C-band and L-band Compact SAR using Radarsat-2 and Alos data. This permits quantification of the resulting radiometric error on RH and RV dual-pol measurements. The impact of the non circularity of the transmitted polarization on the degree of polarization (DoP) and Compact polarization synthesis is also quantified. The requirements on the calibration of compact SAR for the extraction of a meaningful polarimetric SAR information from compact, are then setup.
Citations
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Journal ArticleDOI
TL;DR: Results confirm model prediction, showing that differences mainly apply when polarimetric features are estimated over slick-free sea surface using different SAR architectures, with the π/4 mode behaving closer to FP SAR.
Abstract: In this paper, a theoretical and experimental analysis of polarimetric synthetic aperture radar (SAR) architectures is undertaken for sea oil slick observation purposes. Reference is made to the conventional full-polarimetric (FP) SAR that is here contrasted with new-generation polarimetric SAR architectures, known as compact-polarimetric (CP) SAR. Two CP modes are considered, i.e., the hybrid-polarity and π/4 modes, whose measurements are emulated from actual L- and C-band FP SAR data. Polarimetric sea surface scattering is predicted according to an extended version of the Bragg scattering model (X-Bragg) in order to point out the differences exhibited between FP and CP SAR architectures and among CP SAR modes. Theoretical predictions are then contrasted with experiments undertaken on actual polarimetric SAR data collected over well-known oil slicks and weak-damping surfactants. Results confirm model prediction, showing that differences mainly apply when polarimetric features are estimated over slick-free sea surface using different SAR architectures, with the π/4 mode behaving closer to FP SAR. Although CP SAR architectures measure only a subset of the FP information content, they represent an interesting operational alternative for both detecting oil slicks and discriminating them from weak-damping surfactants.

66 citations


Cites background from "Requirements on the calibration of ..."

  • ...This matter is not detailed here, but the interested reader can find useful hints in relevant literature [11], [12]....

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Journal ArticleDOI
TL;DR: The proposed hybrid polarimetric soil-moisture inversion algorithm works well for bare soils (rmse = 3.1-8.9 vol%) with inversion rates of around 30-70%.
Abstract: In this paper, the capabilities of hybrid polarimetric synthetic aperture radar are investigated to estimate soil moisture on bare and vegetated agricultural soils. A new methodology based on a compact polarimetric decomposition, together with a surface component inversion, is developed to retrieve surface soil moisture. A model-based compact decomposition technique is applied to obtain the surface scattering component under the assumption of a randomly oriented vegetation volume. After vegetation removal, the surface scattering component is inverted for soil moisture (under vegetation) by comparison with a surface component modeled by two physics-based scattering models: The integral equation method (IEM) and the extended Bragg model (X-Bragg). The developed algorithm, based on a two-layer (random volume over ground) scattering model, is applied on a time series of hybrid polarimetric C-band RISAT-1 right circular transmit linear receive data acquired from April to October 2014 over the Wallerfing test site in Lower Bavaria, Germany. The retrieved soil moisture is validated against in situ frequency-domain reflectometry measurements. Including the entire growing season (all acquired dates) and all crop types, the estimated soil moisture values indicate an overall rmse of 7 vol.% using the X-Bragg model and 10 vol.% using the IEM model. The proposed hybrid polarimetric soil-moisture inversion algorithm works well for bare soils ( $\mbox{rmse}=3.1$ –8.9 vol.%) with inversion rates of around 30–70%. The inversion rate for vegetation-covered soils ranges from 5% to 40%, including all phenological stages of the crops and different soil moisture conditions.

59 citations


Cites background from "Requirements on the calibration of ..."

  • ...Unfortunately, the antenna technology of RISAT-1 does not allow the generation of a perfect circular polarization due to a phase shift that occurs during the quadrature phase combination of H and V polarizations to form the circular polarization [42]....

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Journal ArticleDOI
TL;DR: The results indicate a similar separability between the sea ice types identified within the real HP system in RISAT-1 and the simulated HP system from Radarsat-2, and the HP features that are sensitive to surface scattering and depolarization due to volume scattering showed great potential for separating variousSea ice types.
Abstract: Utilizing several Synthetic Aperture Radar (SAR) missions will provide a data set with higher temporal resolution. It is of great importance to understand the difference between various available sensors and polarization modes and to consider how to homogenize the data sets for a following combined analysis. In this study, a uniform and consistent analysis across different SAR missions is carried out. Three pairs of overlapping hybrid- and full-polarimetric C-band SAR scenes from the Radar Imaging Satellite-1 (RISAT-1) and Radarsat-2 satellites are used. The overlapping Radarsat-2 and RISAT-1 scenes are taken close in time, with a relatively similar incidence angle covering sea ice in the Fram Strait and Northeast Greenland in September 2015. The main objective of this study is to identify the similarities and dissimilarities between a simulated and a real hybrid-polarity (HP) SAR system. The similarities and dissimilarities between the two sensors are evaluated using 13 HP features. The results indicate a similar separability between the sea ice types identified within the real HP system in RISAT-1 and the simulated HP system from Radarsat-2. The HP features that are sensitive to surface scattering and depolarization due to volume scattering showed great potential for separating various sea ice types. A subset of features (the second parameter in the Stokes vector, the ratio between the HP intensity coefficients, and the α s angle) were affected by the non-circularity property of the transmitted wave in the simulated HP system across all the scene pairs. Overall, the best features, showing high separability between various sea ice types and which are invariant to the non-circularity property of the transmitted wave, are the intensity coefficients from the right-hand circular transmit and the linear horizontal receive channel and the right-hand circular on both the transmit and the receive channel, and the first parameter in the Stokes vector.

19 citations


Cites background from "Requirements on the calibration of ..."

  • ...As highlighted in [20], the non-circularity of the transmitted wave increases with incidence angle [21]....

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  • ...It is well known that an AR of 0 dB indicates perfect circular, while values above 0 dB corresponds to elliptical, and values of infinity is linear polarization [20]....

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  • ...[20], it is not possible to generate perfect circular polarization using current technology due to the phase errors in combining the horizontal and vertical with 90◦ phase difference when...

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  • ...At the target, there might be an uncertainty associated with the actual transmitted wave, due to the non-circularity of a HP system in general, which was pointed out in [20] and tested in [14] for RI-1....

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  • ..., [14,20] when discussing the non-circularity in general for a HP system....

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Journal ArticleDOI
TL;DR: In this paper, a dual-frequency Synthetic Aperture Radar (SAR) was used for a science payload on Chandrayaan-2, ISRO's second moon mission.

19 citations

Proceedings ArticleDOI
10 Jul 2016
TL;DR: The resolution and PSLR/ISLR are better than the specification of the product and the large difference in sigma-0 is observed for water and sand features due to high value of noise-equivalent-sigma-zero of RISAT-1.
Abstract: Synchronous with RISAT-1 and RADARSAT-2 passes, corner reflectors (CR) were mounted for the evaluation of radiometric calibration of RISAT-1 compact polarimetric SAR data. Based on the CRs response on SLC images, RISAT-1 calibration constant, PSLR/ISLR, resolution, channel imbalance and cross-talk were analyzed and compared with that of product specifications. A difference of 0.5 to 1.5 dB is observed between product and estimated calibration constant K. The resolution and PSLR/ISLR are better than the specification of the product. Backscattering coefficient and compact polarimetric parameters of RISAT-1 were compared with RADARSAT-2 simulated compact polarization. The large difference in sigma-0 is observed for water and sand features due to high value of noise-equivalent-sigma-zero of RISAT-1. Similarly, some differences are observed between RISAT-1 estimated compact polarimetric parameters (m, m c , δ, χL, axial ratio, CPR) and that of RADARSAT-2 simulated compact data.

11 citations


Cites methods or result from "Requirements on the calibration of ..."

  • ...The received wave axial ratio may change with incidence angle as reported by [7]....

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  • ...According to Touzi and Charbonneau [7], the present technology does not allow to generate perfect circular polarization due to phase errors in combining H and V waves with π/2 phase difference....

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References
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Proceedings Article
01 Apr 1983
TL;DR: The energy o f the observed signal may contain frequencies a l l t h e way from 1 h e r t z t o above 100 Mhz and the presence o f such atmospheric energy needs to be understood.
Abstract: I n t h e c o n t e x t o f t h i s "handbook" o f f e r i n g , a tmospher ics re fer to e lect romagnet ic s ignals that rad iate or are produced by l ightn ing and r e l a t e d e lec t r i ca l d ischarge phenomena. Sometimes these sign a l s a r e c a l l e d s f e r i c s and the i r ex i s tence was known s ince the ea r l y days o f r a d i o . The energy o f the observed signal may contain frequencies a l l t h e way from 1 h e r t z t o above 100 Mhz. Needless t o say, the presence o f such atmospheric energy i n .ou r env i ronment needs t o be understood. I n s p i t e o f observat ional research spanning hal f a century, we r e a l l y do n o t have a c l e a r p i c t u r e o f what i s going on n o t t o mention our lack o f t h e o r e t i c a l i n s i g h t . More recent ly , inves t iga tors have examined t h e s u b j e c t i n the contex t o f the e lec t romagnet ic s igna ls tha t can be produced ind i rect ly f rom the prompt gama radiat ion associated wi th nuc lear detonat ions.

660 citations


"Requirements on the calibration of ..." refers background or methods in this paper

  • ...The non circularity of the transmitted polarization is measured with the polarization axial ratio (AR) [11]; with AR = 0 dB for a “perfectly” AR = +∞ for a linear polarization....

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  • ...It is also admitted that the non circularity of the transmitted wave increases with incidence angle [11]....

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Journal ArticleDOI
01 Jul 2006
TL;DR: Data from a CL-pol SAR yield to decomposition strategies such as the m-delta method introduced in this paper, which is the architecture of choice for two lunar radars scheduled for launch in 2008.
Abstract: A synthetic aperture radar (SAR) often is constrained to transmit only one polarization. Within this constraint, two aggressive measurement objectives are 1) full characterization and exploitation of the backscattered field, and 2) invariance to geometrical orientations of features in the scene. Full characterization implies coherent dual-polarization to support the four Stokes parameters. These are rotationally invariant with respect backscatterer orientation if and only if the transmission is circularly polarized. Given that the data products are the Stokes parameters, the receivers can use any orthogonal polarization basis. A SAR in hybrid-polarity architecture (CL-pol) transmits circular polarization and receives two orthogonal mutually coherent linear polarizations, which is one manifestation of compact polarimetry. The resulting radar is relatively simple to implement, and has unique self-calibration features and low susceptibility to noise and cross-channel errors. It is the architecture of choice for two lunar radars scheduled for launch in 2008. Data from a CL-pol SAR yield to decomposition strategies such as the m-delta method introduced in this paper.

490 citations


"Requirements on the calibration of ..." refers background or methods in this paper

  • ...The Hybrid-Compact mode concept firstly introduced in the 1960th [1], [2], has been recently resuscitated [3], [4]....

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  • ...More focus was assigned in [4] to the Compact mode with CP transmission....

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  • ...The information provided by the hybrid Stokes vector parameters, and in particular the DoP (named m in [4]) and the channel phase difference, was shown to be very promising for target scattering classification [4], [6]....

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  • ...This can be a significant advantage for operational use of Compact SAR in large swath applications [4], [6]....

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Journal ArticleDOI
TL;DR: The polarization uniqueness in transmission of this mixed basis mode, hereafter referred to as the /spl pi//4 mode, maintains the standard lower pulse repetition frequency operation and hence maximizes the coverage of the sensor.
Abstract: We assess the performance of synthetic aperture radar (SAR) compact polarimetry architectures based on mixed basis measurements, where the transmitter polarization is either circular or orientated at 45/spl deg/(/spl pi//4), and the receivers are at horizontal and vertical polarizations with respect to the radar line of sight. An original algorithm is proposed to reconstruct the full polarimetric (FP) information from this architecture. The performance assessment is twofold: it first concerns the level of information preserved in comparison with FP, both for point target analysis and crop fields classification, using L-band SIRC/XSAR images acquired over Landes forest and Jet Propulsion Laboratory AIRSAR images acquired over Flevoland. Then, it addresses the space implementation complexity, in terms of processed swath, downloading features, power budget, calibration, and ionospheric effects. The polarization uniqueness in transmission of this mixed basis mode, hereafter referred to as the /spl pi//4 mode, maintains the standard lower pulse repetition frequency operation and hence maximizes the coverage of the sensor. Because of the mismatch between transmitter and receiver basis, the power budget is deteriorated by a factor of 3 dB, but it can partly be compensated.

322 citations

Journal ArticleDOI
TL;DR: A synthetic aperture radar (SAR) with hybrid-polarity (CL-pol) architecture transmits circular polarization and receives two orthogonal, mutually coherent linear polarizations, which is one manifestation of compact polarimetry as mentioned in this paper.
Abstract: A synthetic aperture radar (SAR) with hybrid-polarity (CL-pol) architecture transmits circular polarization and receives two orthogonal, mutually coherent linear polarizations, which is one manifestation of compact polarimetry. The resulting radar is relatively simple to implement and has unique self-calibration features and low susceptibility to noise. It also enables maintenance of a larger swath coverage than fully polarimetric SAR systems. A research team composed of various departments of the Government of Canada evaluated this compact polarimetry mode configuration for application to soil moisture estimation, crop identification, ship detection, and sea-ice classification. This paper presents an overview of compact polarimetry, the approach developed for evaluation, and preliminary results for applications important to the Government of Canada. The implications of the results are also discussed with respect to future SAR missions such as the Canadian RADARSAT Constellation Mission, the American DESD...

253 citations

Proceedings ArticleDOI
26 Jun 1989
TL;DR: An algorithm is derived to reduce required storage space for multipolarimetric synthetic aperture radar data which preserves signal integrity and operations with polarimetric data are greatly facilitated and are now within reach of small research groups.
Abstract: The authors derive an algorithm to reduce required storage space for multipolarimetric synthetic aperture radar data which preserves signal integrity. The data reduction operation reduces the required storage by 12.8. The image synthesis process applied to a reduced data set can be applied to a standard image in two minutes on a VAX 785 when the compressed data format is used. This is ten times faster than image synthesis of the corresponding original data, due to the smaller volume of the compressed data (10 Mb compared with 128 Mb per image). The errors introduced in the output images are on the order of 10/sup -3/. Thus, operations with polarimetric data are greatly facilitated and are now within reach of small research groups. >

83 citations


"Requirements on the calibration of ..." refers background in this paper

  • ...Since one of the important aspect of Compact exploitation is polarization synthesis for the various received polarization, the requirements admitted for fully polarimetric (FP) SAR [12], [13], [5] can be adopted for the Compact....

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