Low-Frequency SAR Radiometric Calibration and Antenna Pattern Estimation by Using Stable Point Targets

Guccione, Pietro; Scagliola, Michele; Giudici, Davide

doi:10.1109/tgrs.2017.2752228

Cited by 10 publications

(8 citation statements)

References 34 publications

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“…Permanent Point Scatterers (PPS): Because there are so few multi-temporal P-band datasets, it has only been possible to assess the value of PPSs in BIOMASS calibration using PALSAR data. From this analysis [3], the most useful types of target appear to be desert with isolated rocks, savanna with isolated trees and urban areas. Radiotelescope antennas are unlikely to be useful as calibrators unless they are pointed towards the satellite.…”

Section: Absolute Radiometrymentioning

confidence: 99%

“…Using a transponder or specially designed passive polarimetric calibrators, it is possible to provide 4 independent scatterers in which only one of the elements of the true scattering matrix is non-zero. Using (11), this leads to an over-determined set of equations for the system errors, Ω and system noise, which also allows for imperfections in the calibrators [3]. The solution scheme derived in [5] led to the conclusion that extremely accurate estimates of Ω were needed to give adequate estimates of system errors, and this required the calibration devices to be located almost exactly where Ω = 0 (near the magnetic equator) or provision of a separate estimate of Ω.…”

Section: Estimating System Errors Using a Transpondermentioning

confidence: 99%

See 1 more Smart Citation

Calibration Challenges for the Biomass P-Band SAR Instrument

Quegan¹,

Lomas²,

Papathanassiou³

et al. 2018

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium

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The BIOMASS mission gives completely new challenges in external calibration arising from the orbital pattern needed for the tomographic and Pol-InSAR phases of the mission, the strong effects of the ionosphere at P-band, and the lack of pre-existing P-band data except over very limited parts of the globe. Together these create problems that can only be solved by combining infrequent visits to instrumented calibration sites with systematic exploitation of the properties of distributed targets and targets of opportunity. Proposed approaches to performing radiometric and polarimetric calibration are described, together with meeting geolocation accuracy requirements.

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Section: Absolute Radiometrymentioning

confidence: 99%

Section: Estimating System Errors Using a Transpondermentioning

confidence: 99%

Calibration Challenges for the Biomass P-Band SAR Instrument

Quegan¹,

Lomas²,

Papathanassiou³

et al. 2018

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium

View full text Add to dashboard Cite

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“…Furthermore, the MEO-SAR systems tend to have a lower working frequency and stronger signal penetration compared with LEO-SARs [17]. Therefore, the Amazon rainforest may no longer be assumed as homogeneous, as the radar signal is not solely scattered at the canopies of the trees, which makes traditional elevation antenna pattern determination using homogenous distributed targets, such as the Amazon rainforest, inapplicable [18].…”

Section: Introductionmentioning

confidence: 99%

An In-Orbit Measurement Method for Elevation Antenna Pattern of MEO Synthetic Aperture Radar Based on Nano Calibration Satellite

et al. 2022

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The medium-Earth-orbit synthetic aperture radar (MEO-SAR) is deployed at orbit altitude above low-Earth-orbit synthetic aperture radar (LEO-SAR, around 2000 km) and below the geosynchronous orbit SAR (GEO-SAR, near 35786 km) to cover a wide swath, which is four to five times larger than LEO-SAR. Therefore, the measurement method for the LEO-SAR elevation antenna pattern using the SAR data acquired over the Amazon tropical rainforest (ground-based method), where the typical width of rainforest area is approximately 150 km, can hardly meet the requirement of a wide swath to determine the MEO-SAR antenna elevation pattern. Moreover, several new MEO-SAR systems are now proposed that will use low frequency, and the low frequency penetration characteristics may affect the elevation antenna pattern determination using homogenous distributed targets such as the Amazon rainforest. This paper proposes a novel space-based method for the in-orbit measurement of the elevation antenna pattern of MEO-SAR based on one nano calibration satellite mounted with a receiver. Through appropriate orbit design, the nano calibration satellite can fly across the entire MEO-SAR swath along the range direction, and the elevation antenna pattern envelope can be extracted from the data recorded by the receiver. Simulation work is performed to verify the feasibility of the proposed space-based method, and the measurement accuracy of this method is analyzed.

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“…Manmade calibrators, like transponders, corner reflectors, and ground receivers, are commonly used to measure the calibration constant. They have known radar cross sections (RCSs) with a high radiometric accuracy (better than 0.2 dB) [5][6][7]. The calibrators are usually placed in a uniform and low noise field.…”

Section: Introductionmentioning

confidence: 99%

“…The calibration constant is calculated as the difference between the calibrator's true RCS and its image intensity. However, the layout and maintenance of calibrators is costly; therefore, the calibrator-based method can only be conducted a few times in the whole lifetime of the SAR [5], which influences the measurement accuracy of the constant. Monitoring of the constant is usually undertaken by the measurement of Amazon rainforest, which is a temporal stable and azimuthally isotropic natural target [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Identification of Stable Backscattering Features, Suitable for Maintaining Absolute Synthetic Aperture Radar (SAR) Radiometric Calibration of Sentinel-1

et al. 2018

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Measuring the absolute calibration constant is crucial for the radiometric calibration of synthetic aperture radar (SAR) systems. However, it is expensive to monitor the calibration constant continuously using manmade calibrators, and it is regionally restricted using the rainforest as the calibration field. In this study, the stability of SAR backscattering for common objects on the earth surface was analyzed, expecting to find the stable backscattering feature that could be used for maintaining absolute radiometric calibration. A database was established using Sentinel-1 dataset, and a classification model based on neural networks was proposed to extract the image slices of proper objects. Based on these, a temporal stable backscattering feature with a standard deviation of 0.19 dB was obtained from urban areas, and it was proved to be even more stable than the rainforest. Finally, the calibration scheme was given using this stable feature as a reference, which provided a new means of monitoring the SAR radiometric calibration constant. illuminated in the intervals of the observation tasks. Thus, the frequency of the constant measurement cannot be guaranteed.Besides the manmade calibrators and rainforests, the researches about calibration reference mainly focus on deserts, oceans, and permanent scatters (PSs). The study about the Simpson Desert shows that its backscattering coefficients are consistently 12 dB with a root mean square error (RMSE) of 0.2 dB as time changes and the accuracy when it is used to cross-calibrate radar altimeters is about 1 dB [12]. However, the desert's backscattering stability depends on the surface topography and soil moisture. Oceans can also be used to derive the calibration constant, using the empirical models of the relationship between the oceans' backscatter coefficient and the wind speed. The accuracy is about 0.5 dB when it is used to calibrate ERS-2 SAR images [13]. Nevertheless, this method needs massive images to fit the model and then to obtain model parameters; so its accuracy is susceptible to the quantity and selection of dataset. Moreover, these two methods cannot resolve the regional-restricted problem and the accuracy is relatively low. The method based on PS has also been studied. PSs usually appear in urban areas, rocky areas, and some P-land forests [14]; they can be detected in SAR images by the coherent or noncoherent methods in D' Aria, D et al. and Iannini, L et al. [14,15]. Since the RCSs rarely change with time, they can relatively calibrate multi-temporal images. If their RCSs are calibrated by corner reflectors or transponders, they can be used in absolute calibration. It has been proved that the stability of this method is better than 0.1 dB and the calibration difference between this method and the transponder method is less than 0.2 dB [1,16]. However, this method requires repeated-pass images with highly similar imaging geometry, such as the images that were used for differential interferometric applications [14].Given the above, the existing methods...

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Low-Frequency SAR Radiometric Calibration and Antenna Pattern Estimation by Using Stable Point Targets

Cited by 10 publications

References 34 publications

Calibration Challenges for the Biomass P-Band SAR Instrument

Calibration Challenges for the Biomass P-Band SAR Instrument

An In-Orbit Measurement Method for Elevation Antenna Pattern of MEO Synthetic Aperture Radar Based on Nano Calibration Satellite

Identification of Stable Backscattering Features, Suitable for Maintaining Absolute Synthetic Aperture Radar (SAR) Radiometric Calibration of Sentinel-1

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