Aircraft Synthetic Aperture Radar Research Articles

Methods of obtaining offshore wind direction and sea-state data from X-band aircraft SAR imagery of coastal waters

X -band synthetic aperture radar (SAR) imagery of the Goto Islands of Japan was digitally analyzed to extract air-sea interaction parameters and to assess the potential of texture measures in analysis of SAR ocean imagery. Wind direction is extracted from wind rows, wind streaks, and random turbulence patterns observed in the SAR imagery. Sea-state parameters are either extracted directly from the imagery or estimated using the extracted information in previously established empirical formulas. A convenient method of digitally presenting imagery, local power spectra, and the extracted/estimated parameters is presented. Texture analysis based on gray-level co-occurrence (GLC) matrices is applied to SAR ocean imagery. The inertia measure is shown to extract similar information to the power spectrum. The cluster-shade measure is shown to be sensitive to image phase.

Applications of Digital Terrain Data to Multisensor Image Analysis: ABSTRACT

Some of the key factors for detection of facies changes in sedimentary environments, such as changes in surface composition and texture, are parameters that can be detected using the remote sensing techniques presently available. For example, multipolarization aircraft synthetic aperture radar (SAR), Landsat 4 Thematic Mapper (TM), and airborne Thermal Infrared Multispectral Scanner (TIMS) images were acquired over the Deadman Butte area of the Wind River basin, Wyoming. The SAR images were acquired at L-band (wavelength = 24.6 cm) simultaneously in 4 polarization states (HH, HV, VV, VH). The 6 visible and near infrared TM bands range in wavelength from 0.45 to 2.35 µm. Thus, reflected and emitted radiation, and radar backscatter from geologic targets can be simultan ously analyzed using a coregistered image data set. In this way, lithologic variations can be mapped based on compositional information derived from the TM and TIMS data and detailed surface scattering information derived from the multipolarization SAR data. In addition, coregistration of the image data set to digital terrain data results in the ability to generate a stratigraphic column based on the remote sensing data, and to perform detailed structural analyses. End_of_Article - Last_Page 254------------

Interpretation of synthetic aperture radar measurements of ocean currents

Synthetic Aperture Radar (SAR) experiments have been performed over the last few years to measure ocean currents inferred from shifts in the Doppler spectral peak. Interpretations of aircraft SAR measurements, when compared with limited surface values, tend to underestimate the currents by about 25%. A theory is developed that modifies the classical Doppler expression showing that the radar measurements are dependent on the radar processor (system) bandwidth and the received signal bandwidth. Measured bandwidths give a correction that increases the inferred current values by about 25%, bringing the measurements into good agreement. This new correction lends credence to the theory and increases the potential for application of SAR systems to future ocean current measurements. SAR measurements should include the determination of processor and signal bandwidths such that this correction can be applied.

A Review of the Utility of Remote Sensing in Alaskan Permafrost Studies

This paper reviews the uses of remote sensing techniques for studies of permafrost related features and processes in Alaska. Remote sensing is ideally suited for studying the Arctic because of the inherent problems associated with obtaining in situ measurements in the harsh Arctic environment. Aircraft thermal infrared imagery, aircraft SAR (Synthetic-Aperture Radar), and helicopter-borne shortpulse radar data are also discussed. It is shown that thermal infrared, aircraft SAR, and Landsat data are all useful for qualitative determination of lake depth of the thaw lakes in northern Alaska. Lakes frozen to their beds can be distinquished from lakes not frozen to their beds using thermal infrared and aircraft SAR imagery. Summer Landsat imagery has been used to monitor lake ice cover dissipation, a relative measure of ice thickness and lake depth. Landsat data have also been used to study the distribution and interannual variability of stream aufeis on the Arctic Slope of Alaska. In addition, break-up characteristics and floods have been studied using Landsat data. Shortpulse radar data are being used experimentally to study subsurface permafrost features, and to examine subsurface homogeneity for construction purposes. In addition, Landsat digital data have been used to measure the one year recovery of tundra following a wildfire in northwestern Alaska. Use of remotely sensed data has substantially increased our understanding of processes operating in Arctic land areas as evidenced by the variety of studies that have been undertaken using data from different parts of the electromagnetic spectrum.