As part of the Office of Naval Research's Environmental and Ship-Motion Forecasting project, we have developed a four-antenna vertically-polarized coherent X-band radar to measure the orbital Doppler velocities of the sea-surface. This Advanced Wave-Sensing Radar (AWSR) initially used a gated CW pulse to radiate the scatterers using a traveling-wave tube amplifier (TWT) in full-saturation. To improve the performance of the system under low wind conditions, we implemented a pulse compression scheme to increase the average transmitted power. In this application, the range-sidelobes associated with compressed waveforms was required to be less than 40dB. Nonlinear FM chirp were considered but these waveforms require larger time-bandwidth products than the near-range requirements of the wave-sensing application would allow. A weighted linear FM chirp was chosen but linearization of the pulsed TWT is required. In this paper we will demonstrate the AWSR pulse-compression scheme detailing the waveform generation, real-time IF correlation and averaging, and digital predistortion.

We introduce a phase calibration scheme for an interferometric frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) to correct range-dependent phase errors in FMCW SAR interferograms. We demonstrate that the receiver filters operating on the FMCW beat frequency signal account for most of the phase mismatch between the different receiver channels. The scheme presented estimates the phase error in each channel. We present results of the scheme for three estimation approaches (curve fitting, joint least squares, and maximum likelihood) for two different phase models. The results are quantified by computing the reduction in spectral energy associated with the phase mismatch. We find that phase error can be reduced by 14 dB using the approach.

A radiometric calibration scheme that exploits time-domain backprojection is evaluated using a squinted frequency-modulated continuous wave radar and corner reflectors. We find that the calibration scheme compensates for most of the variation in image intensity due to changes in aircraft attitude, and that for good signal to clutter ratios, the return from the corner reflectors varies by for most cases by around 1 dB, although a 3 dB difference was observed in one case.

The concept of using orthogonal flight tracks to measure two components of surface velocity with along-track interferometric (ATI) synthetic aperture radar (SAR) has existed since the first ATI SAR measurements by Goldstein and Zebker in 1987. While this approach is geometrically optimal for measuring surface currents, it is limited in that the measurement can only be made over the intersecting area of the two SAR images. Furthermore, it is not feasible for a space-based implementation. To overcome these limitations, a single-platform dual-beam ATI SAR approach was evaluated, and first implemented at the University of Massachusetts, and subsequently during the Wavemill proof of concept project and as a miniaturized ATI SAR by the Applied Physics Laboratory at the University of Washington. In this paper, we present dual-beam ATI SAR measurements in a tidally-driven estuary, and compare the estimated surface velocity field with in situ drifter measurements.

Results from measurements of nearshore ocean processes with an frequency-modulated continuous wave along-track interferometric synthetic aperture radar are presented. Surface flow measured with the radar in a tidally-driven inlet compares well with in situ measurements by drifters. Data from a larger inlet system, in which stratification is important, shows regions of strong mixing and dramatic changes in the velocity field that are associated with bathymetric features.

In this paper we present the findings of an effort to create a millimeter-wave radar system to image the internal structure of a kraft recovery boiler as well as measure the dielectric coating on the pipes. A kraft boiler is used by the paper industry to reclaim inorganic salts used in the pulping of wood. The bio-mass and salt structure of the fuel combusted in the boiler causes rapid deposition on the boiler pipes reducing the efficiency of the heat-transfer mechanism. A large portion of the generated steam is used to mitigate the build-up of the salts (using sootblowers), commonly referred to as saltcake. The steam used for maintenance consumes a substantial portion of the energy generated in the boiler. A millimeter-wave radar system capable of measuring the saltcake could add a feedback path for an intelligent sootblower mechanism. We investigate the optimal center frequency as well as required bandwidth for an effective imaging/measuring device.