SAR Observations Research Articles

Monitoring Surface Deformations over Siberian Gas Deposit Areas Using ALOS PALSAR Interferometry

Japan and Russia cooperated in performing a study to monitor ground surface deformations over gas deposit areas in Siberia using the phased array type L-band synthetic aperture radar (PALSAR) of the Advanced Land Observing Satellite (ALOS). The studied areas had permafrost and surface subsidence due to gas extraction, both of which would afiect gas facilities and infrastructure. The observation sites were located in a tundra that had widespread permafrost, bogs, and a thin layer of mosses and lichens. Difierential interferometry analysis was conducted independently by both NEC and GASPROM Space Systems using PALSAR data. The results clearly showed widespread ground subsidence with block structures over the past two years. Also, small hills and dips apparently formed by permafrost were detected by high spatial resolution (25m) interferometry analysis. This study demonstrates that L-band SAR observation using a satellite provides a wide area instrumental technique for gathering information to support fleld and pipeline operation and for observing the resulting impact on the environment. The results also show the technical and economic e-ciency of surveying and performing geodesic monitoring of gas fleld areas using ALOS PALSAR.

Extreme wind conditions observed by satellite synthetic aperture radar in the North West Pacific

In this paper some recent results on SAR observation of extreme surface wind conditions are summarized. Particular emphasis is put on the investigation of typhoons occurring in the North West Pacific. The study is based on the use of ENVISAT ASAR wide swath images (400 km×400 km), which allow synoptic measurements of the complete mesoscale system at high resolution (150 m). Surface wind speed for typhoon cases is determined from SAR measurements using the geophysical model function CMOD5. Further structures observed in the image like streaks indicating wind direction and the ring of maximum wind speed are additionally taken into account to reconstruct the typhoon wind field. The influence of heavy rain on the radar cross section is estimated from an existing radiative transfer model and compared to the SAR measurements. A new technique for the estimation of typhoon intensity from SAR data is presented, which makes use of a parametric type model. The main goal of the paper is the improvement of the estimation of maximum typhoon intensity using SAR data.

SAR Observation and Modeling of Gap Winds in the Prince William Sound of Alaska.

Alaska's Prince William Sound (PWS) is a unique locale tending to have strong gap winds, especially in the winter season. To characterize and understand these strong surface winds, which have great impacts on the local marine and aviation activities, the surface wind retrieval from the Synthetic Aperture Radar data (SAR-wind) is combined with a numerical mesoscale model. Helped with the SAR-wind observations, the mesoscale model is used to study cases of strong winds and relatively weak winds to depict the nature of these winds, including the area of extent and possible causes of the wind regimes. The gap winds from the Wells Passage and the Valdez Arm are the most dominant gap winds in PWS. Though the Valdez Arm is north-south trending and Wells Passage is east-west oriented, gap winds often develop simultaneously in these two places when a low pressure system is present in the Northern Gulf of Alaska. These two gap winds often converge at the center of PWS and extend further out of the Sound through the Hinchinbrook Entrance. The pressure gradients imposed over these areas are the main driving forces for these gap winds. Additionally, the drainage from the upper stream glaciers and the blocking effect of the banks of the Valdez Arm probably play an important role in enhancing the gap wind.

Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data

Only a few impact craters have been unambiguously detected on Titan by the Cassini‐Huygens mission. Among these, Sinlap is the only one that has been observed both by the RADAR and VIMS instruments. This paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition, topography, and surface roughness. Several units appear in VIMS false color composites of band ratios in the Sinlap area, suggesting compositional heterogeneities. A bright pixel possibly related to a central peak does not show significant spectral variations, indicating either that the impact site was vertically homogeneous, or that this area has been recovered by homogeneous deposits. Both VIMS ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket. Since the Ku‐band SAR may see subsurface structures at the meter scale, the difference between infrared and SAR observations can be explained by the presence of a thin layer transparent to the radar. An analogy with terrestrial craters in Libya supports this interpretation. Finally, a tentative model describes the geological history of this area prior, during, and after the impact. It involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact, followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind. Subsequent evolution is then driven by erosional processes and aeolian deposition.

Investigation of the spatial variations in synthetic aperture radar backscatter in western Dronning Maud Land, Antarctica

C-band SAR observations show that backscatter varies significantly across small scales (tens of kilometers) in western Dronning Maud Land. Generally, backscatter was found to diminish with altitude reflecting lower accumulation and reduced ice inclusions in the firn of the percolation zone at higher elevations. Reference to (incomplete) mass balance data suggests an anticorrelation between backscatter and net balance, although more data are needed to confirm the trend. Even within the percolation zone, areas of low backscatter (<-12 dB) exist. These are uncorrelated with altitude above sea level. Using a Rayleigh backscatter model, we show that backscatter over such regions may represent differences in grain sizes. The application of a buried-layers model did not accurately estimate backscatter from these regions. We suggest that these regions occupy exposed positions subject to increased wind sublimation which, in turn, results in smaller grain sizes in the firn and therefore reduced backscatter. The Radarsat Antarctica Mapping Mission SAR mosaic indicates such regions occur in Coates Land, near the edge of the Antarctic Plateau, and on exposed promontories elsewhere in East Antarctica. More information regarding the structure of the firn and the mass balance of the region is needed before we can definitively explain controls on backscatter and understand the climatology of the low backscatter zones.

Identification of 2-amino-5-(thioaryl)thiazoles as inhibitors of nerve growth factor receptor TrkA

2-Amino-5-(thioaryl)thiazoles are potent inhibitors of TrkA (e.g., 20h, TrkA IC 50 = 0.6 nM) that show anti-proliferative effect in cellular assays. A proposed inhibitor binding mode to TrkA active site is consistent with key SAR observations.

Global inundation dynamics inferred from multiple satellite observations, 1993–2000

Wetlands and surface waters are recognized to play important roles in climate, hydrologic and biogeochemical cycles, and availability of water resources. Until now, quantitative, global time series of spatial and temporal dynamics of inundation have been unavailable. This study presents the first global estimate of monthly inundated areas for 1993–2000. The data set is derived from a multisatellite method employing passive microwave land surface emissivities calculated from SSM/I and ISCCP observations, ERS scatterometer responses, and AVHRR visible and near‐infrared reflectances. The satellite data are used to calculate inundated fractions of equal area grid cells (0.25° × 0.25° at the equator), taking into account the contribution of vegetation to the passive microwave signal. Global inundated area varies from a maximum of 5.86 × 106 km2 (average for 1993–2000) to a mean minimum of 2.12 × 106 km2. These values are considered consistent with existing independent, static inventories. The new multisatellite estimates also show good agreement with regional high‐resolution SAR observations over the Amazon basin. The seasonal and interannual variations in inundation have been evaluated against rain rate estimates from the Global Precipitation Climatology Project (GPCP) and water levels in wetlands, lakes, and rivers measured with satellite altimeters. The inundation data base is now being used for hydrology modeling and methane studies in GCMs.

SAR/InSAR observation by an HF sounder

Application of SAR imaging algorithm to spaceborne HF sounder observation was studied. Two types of image ambiguity problems were addressed in the application. One is surface/subsurface image ambiguity arising from deep penetration of HF wave, and another is mirror image ambiguity that is inherent to dipole antenna SAR. A numerical model demonstrated that the surface/subsurface ambiguity can be mitigated by taking a synthetic aperture large enough to defocus subsurface objects. In order to resolve the mirror image ambiguity problem, an image superposition technique was proposed. The performance of the technique was demonstrated by using simulation data of the HF sounder observation to confirm the feasibility of HF SAR and HF InSAR observation.

Information Retrieval and Reconstruction Based on High-Resolution SAR Observation over Urban Area

A novel approach for information retrieval and 3D-object reconstruction using multi-aspect high-resolution SAR imagery of urban area is briefly introduced.It includes CFAR edge detection of SAR images,automatic extraction of building images and Maximum-likelihood estimation of building parameters.The fidelity of this approach is demonstrated by a building reconstruction experiment on a set of square-path Pi-SAR images.

Satellite SAR observations of atmospheric and oceanic vortex structures in the Black Sea coastal zone

ERS-2 SAR and Envisat ASAR images of the north-eastern coastal zone of the Black Sea have revealed frequent manifestation of dynamic upper ocean and atmospheric boundary layer structures. In 1999–2004, IKI RAS carried out a series of experiments in the region of Novorossiisk–Gelendzhik to investigate the dominant processes associated with such dynamic features. Special focus was on oceanic vortices of small and medium scales at 2–20 km which are difficult to register by ship measurements or satellite optical instruments. Meanwhile, they play a significant role in circulation and mixing processes in the coastal zone. Atmospheric synoptic vortices and local mushroom flows are also discussed.

航空機搭載SAR（Pi-SAR）による網走湖氷の多偏波観測

航空機搭載SAR（Pi-SAR）による網走湖氷の多偏波観測

Analysis of coupled oceanographic and acoustic soliton simulations in the Yellow Sea: a search for soliton-induced resonances

The area south of the Shandong peninsula has been of great interest to both oceanographers and underwater acousticians due to the measurements of Zhou et al. [J. Acoust. Soc. Am. 90 (1991) 2042]. Over a period of years, in the summer, they observed anomalous losses in shallow water acoustic signals. They attributed the losses to acoustic mode conversions produced by solitary internal waves (solitons). Their hypothesis remains unsubstantiated due to a scarcity of oceanographic measurements in this area. In this simulation study the non-hydrostatic, 2.5-dimensional Lamb model was used to generate solitons in an adjacent, deeper area than that examined by Zhou et al. [J. Acoust. Soc. Am. 90 (1991) 2042]. Topographic variations and semi-diurnal tidal strength magnitudes were obtained from digital atlases and published data. For summer conditions, the Lamb model simulations showed that the existing semi-diurnal tidal flow over the topographic variations could lead to the formulation of internal bores and solitons. SAR observations of solitons near this region were used to select parameters and initialize the Lamb model. The resulting soliton simulations were comparable to the two-dimensional surface spectra seen in the SAR data. Soliton amplitudes of 2–7 m were indicated. Acoustic studies were made using the highly accurate finite element parabolic equation (FEPE) acoustic model applied to the initial soliton state data generated by the Lamb model. Mode decomposition of the acoustic fields in the deeper region showed that the mode conversions necessary for anomalous signal losses were present. These findings are consistent with the soliton hypothesis made by Zhou et al. [J. Acoust. Soc. Am. 90 (1991) 2042].

Fully polarimetric airborne SAR and ERS SAR observations of snow: implications for selection of ENVISAT ASAR modes

Snow cover has a substantial impact on processes involved in the interaction between atmosphere and surface, and the knowledge of snow parameters is important in both climatology and weather forecasting. With the upcoming launch of Advanced Synthetic Aperture Radar (ASAR) instruments on Envisat, enhanced snow-mapping capabilities are foreseen. In this paper fully polarimetric C- and L-band airborne SAR data, ERS SAR and auxiliary data from various snow conditions in mountainous areas are analysed in order to determine the optimum ASAR modes for snow monitoring. The data used in this study are from the Norwegian part of the snow and ice experiment within the European Multi-sensor Airborne Campaign (EMAC'95) acquired in the Kongsfjellet area, located in Norway, 66° N, 14° E. Fully polarimetric C- and L-band SAR data from ElectroMagnetic Institute SAR (EMISAR), an airborne instrument operated by the Danish Center for Remote Sensing (DCR), were acquired in March, May, and July 1995. In addition, several ERS SAR, airborne photos, field and auxiliary data were acquired. A larger separation between wet snow and bare ground in EMISAR C-VV polarisation data was found at high incidence angle (55°) compared to lower incidence angle (45°). Cross-polarized observations from bare ground, dry and wet snow in the incidence angle range 35° to 65° are below the specified Envisat ASAR noise floor of –20–22 dB. The backscattering angular dependency for wet snow and bare ground derived from EMISAR C-VV and ERS SAR data corresponds well, and agrees to some extent with volume and surface scattering model results. The C-band is more sensitive to variation in snow properties than the L-band.

Tropospheric delay estimation and analysis using GPS and SAR interferometry

Spatially localized refractivity variations, mainly due to water vapor, are a major source of error in high-precision positioning techniques such as GPS and SAR interferometry. Refractivity induced delay variations can be misinterpreted as, e.g., crustal deformation signals or positioning biases. In this study, signal delay estimates based on SAR observations and simultaneous GPS time series are quantitatively compared. Wind speed and wind direction estimates are used to relate the temporal zenith delays derived from GPS with the spatial slant delays observed by SAR interferometry, assuming a static refractivity distribution transported by the wind. Five case studies show significant correlation between both techniques, mainly limited by the GPS epoch length, zenith averaging, and the degree of similarity in wind direction during the two SAR acquisitions. RMS differences varied between 2 and 10 mm, while the total delay variability spanned 15–60 mm. The results show that it can be possible, under suitable atmospheric circumstances, to approximate the amount of delay variation with wavelengths >5 km in a strip of a SAR interferogram using GPS, wind speed, and wind direction measurements.

Deriving sea-ice thickness and ice types in the Sea of Okhotsk using dual-frequency airborne SAR (Pi-SAR) data

AbstractDual-frequency, multi-polarization airborne synthetic aperture radar (Pi-SAR; developed by the Communications Research Laboratory and National Space Development Agency of Japan) observations of the seasonal sea-ice region off the Okhotsk coast of Hokkaido, Japan, were carried out in February 1999 using X- and L-band radar frequencies with a resolution of 1.5 and 3.0 m. In conjunction with the SAR observations, the sea-ice thickness (draft) and velocity were measured by a moored Ice Profiling Sonar (IPS) and an Acoustic Doppler Current Profiler (ADCP). Tracks of the sea ice passing over the IPS were estimated from the time series of the ADCP ice-velocity and -direction data. Along these tracks, the SAR backscattering coefficient profiles were compared with the IPS ice-draft profiles. The results showed that the L-band SAR backs cattering profiles correlated well with the IPS ice-draft data, particularly in the thicker part (a few meters thick) of the rim of first-year ice, which had a large backscattering coefficient. Although the X-band SAR backscattering profiles did not correlate well with the IPS data, thin ice (&lt;10 cm thick) showed a large backscattering coefficient. The L-band SAR and IPS data did not distinguish thin ice from open water.

Analysis of temporal radar backscatter of rice: A comparison of SAR observations with modeling results

In this study an established microwave backscatter model is used to predict the radar backscatter behavior of rice and to understand the interaction between backscatter and the rice canopy during its growth cycle. The emphasis of this study is to understand the effect of physical plant parameters on the backscatter signatures as a function of polarization and how these signatures vary during a complete growth cycle of rice. Inputs to the backscatter model included the physical parameters of rice as obtained through field measurements. These measurements were acquired within a few days of multiple RADARSAT acquisitions of the Zhaoqing test site in southern China. RADARSAT observations and the modeling results were then compared and analyzed. The results show that the interaction mechanisms change during the rice growth cycle and polarimetric and (or) multi-polarization measurements at C band will contribute to rice monitoring programs.

Enols as Potent Antibacterial Agents

This paper describes the discovery of α-trifluoroketoacetamides as potent antibacterial agents against Gram-positive organisms. The initial SAR indicates that the aryl ethyl side chain is essential in maintaining antibacterial activity. The SAR observations have been utilized to design a bioisostere for the α-trifluoroketoacetamide with good activity against Gram-positive organisms.

Sodium adsorption ratios and salinity levels in nine texas aquifers: implications for irrigated agriculture

This study evaluated sodium and salinity irrigation hazards for Texas’ nine major aquifers. Sodium adsorption ratios (SAR's) and electrical conductivity levels (EC's) were calculated at 5,442 water wells. Aquifer median SAR's varied widely, from 0.3 (Edwards Balcones Fault Zone) to 8.5 (Carrizo‐Wilcox). The percentage of SAR observations exceeding 17.5 ranged from 0.0 (Seymour Aquifer) to 36.3 (Carrizo‐Wilcox Aquifer). There was a significant positive correlation between SAR and well depth in four aquifers and a significant negative correlation in four aquifers. Median EC's ranged from 545 umhos/cm (Edwards Balcones Fault Zone Aquifer) to 2,280 umhos/cm (Cenozoic Pecos Alluvium Aquifer). Respectively, 12.1% and 95.1% of the observations exceeded 750 umhos/cm in the Edwards Balcones Fault Zone and Cenozoic Pecos Alluvium Aquifers. EC and well depth were significantly positively correlated in two aquifers and significantly negatively correlated in five aquifers. Several factors control SAR's and EC's in Texas aquifers, including rock/sediment composition, groundwater chemical evolution, and seepage from nearby formations. Probable human controls include irrigation return flow, oil field brine, and pumping‐induced saltwater intrusion. The Trinity, Carrizo‐Wilcox, Gulf Coast, Cenozoic Pecos Alluvium, Seymour, and Hueco‐Mesilla Bolson Aquifers have the greatest potential for sodium or salinity irrigation problems.

Coherence Characteristics of Radar Signals from Rough Soil

To understand the mechanisms of decorrelation in interfer- ometric SAR (InSAR) images of bare soil, a model has been developed. Under the Kirchhoff and stationary phase approximations, coherence can be related to the statistical variations of dielectric constant and roughness parameters of surfaces. With the help of an empirical model for the dependence of dielectric constant on soil moisture, coherence due to the inhomogeneity of soil moisture is numerically demonstrated. It has been shown that the decorrelation of the radar signal from rough soil is mainly due to the moisture variability within the resolution cell. The effect of roughness on decorrelation is complex. The effect is neg- ligible compared to that of the dielectric variability for homogeneous resolution cells (no dielectric variability within a resolution cell). How- ever, the coherence depends strongly on the roughness parameters for resolution cells with large moisture variability. It is concluded that the loss of coherence induced by variability of dielectric constant can be related to the relative variation of moisture expressed by the ratio of standard deviation and mean value, and that large relative variations of moisture could lead to much decorrelation. If the moisture variabil- ity is small the coherence will be very high even if the values of mean moisture of the two SAR observations are different, which means that coherence can be high in spite of much backscatter differences.

Repeat-Pass Interferometric Coherence Measurements of Disturbed Tropical Forest from JERS and ERS Satellites

The phase coherence between repeat-pass SAR observations of a tropical forest region was investigated as a source of information for biophysical characteristics in regenerating and undisturbed areas of forest. SAR imagery was acquired and interferometric coherence maps were derived for a 1-day repeat pair at C-band, using ERS-1 and ERS-2, and for 44-day and 132-day repeats at L-band, using JERS. The backscattering coefficient and coherence characteristics were analyzed in conjunction with biomass density estimates determined from field measurements and land cover characteristics derived from an annual sequence of Landsat TM imagery. The results demonstrate that repeat-pass coherence adds significantly to the information available from SAR imagery of tropical forest.