A new processing technique, i.e., ground cancellation, which removes the ground signal from a pair of interferometric synthetic aperture radar (SAR) images, is used to emphasize the response from ...above-ground targets. This technique is of particular interest when studying forest canopies using low-frequency signals able to reach the underlying ground, in which case the portion of the signal coming from the ground interferes with the recovery of information about the vegetation. We demonstrate that the power in ground-canceled P-band HV SAR data gives significantly higher correlations with above-ground biomass (AGB) than the interferometric images considered separately. In addition, a significant increase in the sensitivity of backscatter to AGB is observed. Ground-canceled power may then be modeled or regressed to estimate AGB; these possibilities are not discussed here as they will be the topic of forthcoming publications. The effectiveness of this technique is proven through simulations and analysis of real data gathered on tropical forests. The stability of the technique is analyzed under the digital terrain model and baseline control errors, and compensation strategies for these errors are presented.
One of the limitations of the interferometric synthetic aperture radar (InSAR) is its one‐dimensional measurement capability. Although three‐dimensional (3‐D) deformation can be studied if there are ...three or more measurements with different viewing geometries, it has not been executed because almost all SAR data are acquired using a right‐looking geometry. For the Sakurajima volcanic activity on 15 August 2015, ALOS‐2 conducted SAR observations from four different viewing directions, ascending/descending and right‐/left‐looking, enabling the retrieval of 3‐D deformation data only from the InSAR results. We have retrieved 3‐D deformation with high precision and resolution by a weighted least squares approach. Expansive deformation of over 10 cm has been observed with standard errors of 0.8, 3.4, and 0.7 cm for east‐west, north‐south, and up‐down components, respectively. It is inferred that a dike of 1.7 × 106m3 volume intruded beneath the Showa crater at a depth of 0.4–1.2 km.
Key Points
Sakurajima volcano promptly studied by right‐ and left‐looking InSAR
Precise and high‐resolution 3‐D deformation retrieved from four interferograms
A dike intrusion of 1.7 × 106m3 volume has been identified
The effects of both system additive and multiplicative noise on the X-, C-, and L-band synthetic aperture radar (SAR) data covering oil slicks are examined. Prior studies have attempted to ...characterize such oil slicks, primarily through analysis of polarimetric SAR data. In this article, we factor in system noise that is added to the backscattered signal, introducing artifacts that can easily be confused with random and volume scattering. This confusion occurs when additive and/or multiplicative system noise dominates the measured backscattered signal. Polarimetric features used in this article are shown to be affected by both additive and multiplicative system noise, some more than others. This article highlights the importance of considering specifically multiplicative noise in the estimation of the signal-to-noise ratio (SNR). The SNR based on additive noise should at least be above 10 dB and the SNR involving both additive and multiplicative noise should at least be above 0 dB. The SNR from TerraSAR-X (TS-X) and Radarsat-2 (RS-2) is below 0 dB for the majority of the oil slick pixels when considering both the additive and multiplicative noise, rendering these data unsuitable for any analysis of the scattering properties and characterization. These results are in contrast to the reduced impact of noise on oil slicks detected by the L-band UAVSAR system. In particular, we find that there is no need to invoke exotic scattering mechanisms to explain the characteristics of the data. We also recommend a noise subtraction for any polarimetric scattering analysis.
Precipitable water vapour (PWV) is a primary factor that affects climate and weather. The accurate retrieval of PWV is crucial for weather prediction and meteorological research. Interferometric ...Synthetic Aperture Radar (InSAR) has been rapidly developed in recent years and proven effective in PWV retrieval in the regions of good coherence. However, there are large areas of natural terrain where signals decoherence that limit the precision of PWV retrieval. Besides, due to the differential interference processing of InSAR data, the results of its retrieval are differential PWV (ΔPWV). In this study, the StaMPS-InSAR was used to overcome the problem of weak detection ability in low coherence regions. A series of 11 Sentinel-1A images were selected to retrieve space-continuous ΔPWV. Beidou Satellite Navigation System (BDS) can retrieve high-precision PWV. Hence, the BDS data was utilized to convert the InSAR-derived ΔPWV to PWV. Compared with the BDS-derived PWV, the root mean square error (RMSE) of the experimental results is 1.3 mm with a spatial resolution as fine as 20 m. The correlation coefficient between the deviations and Liquid Cloud Water is 0.65, indicating a positive correlation. We demonstrate the advantage of the proposed method for retrieving PWV in computational efficiency by comparing it with the SBAS-InSAR. With the increasing stack size of the SAR images, our method can reduce the taking time for processing. The proportion can reach 12.6% when the stack size of SAR images is 20. By the spatio-temporal analysis of the results, we found some characteristics of PWV in mountain areas especially. The results have certain reference value for the space-continuous PWV retrieval and the study of PWV spatio-temporal characteristics.
LuTan-1 (LT-1), i.e., TwinSAR-L, mission is an innovative spaceborne bistatic synthetic aperture radar (SAR) mission that is based on two satellites operating at L-band with flexible formation ...flying, which is planned to launch in 2020. The primary objective of LT-1 is to generate a highly accurate global digital elevation model (DEM). Beyond that, LT-1 will serve for the demonstration of some state-of-the-art technologies in radar field and some applications, such as biomass inversion, disaster forecasting, and climate and environmental monitoring, and phase synchronization is a technical challenge in realizing the highly accurate topography and deformation measurements. The pulsed alternate synchronization scheme, which is proposed to solve the synchronization problem of TerraSAR-X add-on for Digital Elevation Measurements (TanDEM)-X, is an efficient and accurate method. However, it interrupts the normal work of the TanDEM-X, accordingly flowing a series of problems. For LT-1, a novel synchronization scheme, in which the phase synchronization signal is exchanged by virtue of a time slot between radar signals, is applied. Thus, the working efficiency and synchronization accuracy can further be improved. Furthermore, the performance prediction and phase synchronization experiment for this synchronization scheme is presented, which verifies the feasibility of the proposed scheme. Finally, in order to guarantee the transmission quality of the synchronization signal, the illumination combinations and gain variation of the synchronization antenna in an orbital period are detailed.
Satellite interferometric synthetic aperture radar (InSAR) is emerging as a viable low-cost alternative method to airborne laser scanning (ALS) for forest inventory though little research has ...examined its efficacy for plantation forests located in temperate regions on steep terrain. InSAR and ALS data were collected from Geraldine Forest which is located on rolling to very steep topography in the southeast of New Zealand. These data were combined with an extensive set of plot measurements from which mean top height (H), basal area (G), stem density (N), and total stem volume (TSV) were calculated. InSAR and ALS-based Random Forest models of each variable were developed and compared.
Using the ALS data as a reference, the mean RMSE of the InSAR DSM and DTM surfaces were, respectively, 4.58 and 8.09 m and these errors increased to mean values of, respectively, 6.02 and 10.17 m for slopes of 40–50°.
ALS-based models were substantially more precise than those developed from InSAR for H (R2 = 0.86 vs. 0.60; RMSE% = 5.47 vs. 10.8%), G (R2 = 0.56 vs. 0.32; RMSE% = 21.5 vs. 30.4%), N (R2 = 0.47 vs. 0.09; RMSE% = 32.3 vs. 43.2%), and TSV (R2 = 0.70 vs. 0.41; RMSE% = 19.4 vs. 30.7%). The base metrics (i.e. ALS height and canopy cover variables) accounted for most of the variance in the ALS models with addition of further metrics providing ≤ 1% reduction in the RMSE%. Base metrics (i.e. InSAR observables) also accounted for most of the variation in InSAR models. Addition of metrics from a mixed Canopy Height Model (CHM), derived from InSAR Digital Surface Model (DSM) and ALS Digital Terrain Model (DTM), resulted in reductions in RMSE% of 3.1–5.4% for H, G, and TSV models with addition of textural metrics providing further reductions of 0.2–0.3% for H and G models. Addition of metrics from the radar CHM, derived from the InSAR DTM and DSM, and texture metrics reduced the RMSE% of the base model for N by 2.3% and 0.5%, respectively.
The results were generated using a SAR image pair with a height of ambiguity (HOA) that was higher than ideal, which reduced the sensitivity of results to changes in terrain. Despite this limitation, and the steep slopes throughout the forest, the InSAR models described here had comparable precision to developed InSAR models for key inventory metrics from previous studies.
•Models using InSAR data provided a reasonable level of precision for H and TSV.•CHM derived from InSAR DSM and ALS DTM significantly improved the predictions.•InSAR DSM and DTM errors were within the WorldDEM™ target but increased with slope.•CHM errors increased with slope but the final InSAR models were invariant to slope.
Ship classification in synthetic-aperture radar (SAR) images is of great significance for dealing with various marine matters. Although traditional supervised learning methods have recently achieved ...dramatic successes, but they are limited by the insufficient labeled training data. This letter presents a novel unsupervised domain adaptation (DA) method, termed as discriminative adaptation regularization framework-based transfer learning (D-ARTL), to address the problem in case that there is no labeled training data available at all in the SAR image domain, i.e., target domain (TD). D-ARTL improves the original ARTL by adding a novel source discriminative information preservation (SDIP) regularization term. This improvement achieves an efficient transfer of interclass discriminative ability from source domain (SD) to TD, while achieving the alignment of cross-domain distributions. Extensive experiments have verified that D-ARTL outperforms state-of-the-art methods on the task of ship classification in SAR images by transferring the automatic identification system (AIS) information.
To increase the image quality of synthetic aperture radar (SAR) is one of the hot issues for high-performance detection/reconnaissance. With this interest in the SAR technique, it generates various ...techniques according to the purposed platforms (Auto-SAR, ViSAR, InSAR, and PolSAR). In this article, we introduce high-efficiency and useful techniques, which can be applied to various SAR applications for generating high-quality images in the Ka -band. We proposed the stretched deramping hardware system applicable in the Ka -band, and design the Range-Doppler algorithm which well matches the proposed radar system with the modified signal parameters. Thus, we can extend the integration time of the convolution process in slow time and it leads to the improvement of the SAR image quality. To verify the performance of our proposed technique, we process the practical experiments in conventional outdoor fields. Furthermore, the proposed method is operated on the range Doppler algorithm (RDA), which is mostly used for standard SAR.
Thanks to the vigorous development of smart logistics and warehouse applications, many scholars have made outstanding contributions to indoor object positioning, among which indoor positioning ...algorithms mediated by radio frequency identification (RFID) systems are particularly prominent. However, the phase information of RFID has the characteristics of high precision, and the state-of-art algorithm generally uses phase information to achieve localization. Inspired by the synthetic aperture radar (SAR) method that uses phase information, this article first proposes a rotating SAR (RSAR) method for harnessing received signal strength indicator (RSSI) information. This method establishes a functional relationship between RSSI information and angle and virtually synthesizes reader antenna arrays at different angles at the same point by rotating the reader antenna. By combining the RSAR method using RSSI information with the SAR method using phase information, a 3-D positioning system with mobile robots as the carrier is proposed. After that, this article proposes a position estimation algorithm named sort cluster algorithm with threshold (SCWT) to improve positioning accuracy. Finally, we evaluate the performance of the three aspects of our proposed algorithm through multiple experiments. First, experiments show that the RSAR method can achieve high-precision positioning. Second, the RSAR method and the SAR method are independent of each other when realizing 3-D positioning. Third, comparative experiments show that the time complexity of the proposed position estimation algorithm is more dominant.
Observations from satellites provide high-resolution images of ground deformation allowing to infer deformation sources by developing advanced modeling of magma ascent and intrusion processes. ...Nevertheless, such models can be strongly biased without a precise model of the internal structure of the volcano. In this study, we jointly exploited two interferometric techniques to interpret the 2011–2013 unrest at Campi Flegrei caldera (CFc). The first is the Interferometric Synthetic Aperture Radar (InSAR) technique, which provides highly-resolved spatial and temporal images of ground deformation. The second is the Ambient Noise Tomography (ANT), which images subsurface structures, providing the constraints necessary to infer the depth of the shallow source at CFc (between 0.8 and 1.2 km). We applied for the first time a tool to delineate the deformation source boundaries from the observed deformation maps: the Total Horizontal Derivative (THD) technique. The THD processes the vertical component of the ground deformation field detected through InSAR applied to COSMO-SkyMed data. The patterns retrieved by applying the THD technique show consistent spatial correlations with (1) the seismic group-velocity maps achieved through the ANT and (2) the distribution of the earthquakes nucleated during the unrest at ~1 km. High-velocity anomalies, the retrieved geometrical features of the deformation field, and the spatial distribution of seismicity coincide with extinct volcanic vents in the eastern part of the caldera (Solfatara/Pisciarelli and Astroni). Such a coincidence hints at a significant role of the extinct plumbing system in either constraining or channeling the eastward propagation of magmatic fluids. Here, we demonstrated that a joint analysis of the InSAR patterns, seismic structures, and seismicity allows us to model in space and time the characteristics and nature of the shallow deformation source at CFc. Using published literature, we show that the effects of structural heterogeneities at shallow depths may have a more significant early-stage impact on the evolution of the surface displacement signals than deeper magmatic sources: these secondary structural effects may produce local amplification in the deformation records which can be mistakenly interpreted as early signals of impending eruptions. The achieved results are particularly relevant for the understanding of the origin of deformation signal at volcanoes where magma propagation within sills is expected, as at CFc.
•The joint exploitation of InSAR and ANT allow to detect the source features.•Interferometric technique is Synthetic Aperture Radar to the surface analysis.•The Ambient Noise Tomography to analyze the internal structures.•We analyze di Campi Flegrei caldera during the 2011–2013 unrest episode.
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