An experimental ultrawideband (UWB) radar, designed and implemented by the Radar Division of the Naval Research Laboratory (NRL), is being used to develop techniques for the detection, imaging, and ultimately the identification of buried objects. This dual-frequency, dual-polarization, UWB radar has collected ultra-high resolution measurements (2-cm range resolution) of land mines and other objects in a laboratory setting. Initial free-space measurements are currently being used to develop and test imaging algorithms, as well as to explore the feasibility and limitations of various synthetic-aperture-radar (SAR) configurations. In this paper we describe the buried-object test bed and demonstrate the ability of the UWB radar to image several different types of objects. At the conclusion of the free-space measurements and analysis, the objects of interest will be buried and measured in various media.
This paper presents an experiment description, along with data examples, for ultrawideband radar measurements of low grazing angle forward scatter associated with a test target mounted above a wind-disturbed sea surface. The measurement radar used sub-nanosecond transmit pulses (0.15 ns and 0.25 ns 3 dB pulse widths) at center frequencies of 9 and 4 GHz to achieve resolutions finer than 3 cm in the range dimension. This resolution was sufficient to fully resolve direct and multipath (both single and double bounce) contributions to the signal reflecting from a tower-mounted retro reflector. The geometry produced a nominal 3 degree grazing angle for forward scatter. Dual frequency measurements for a wind-disturbed ocean surface highlight changes in the magnitude and the location of the scatter components with time.
An ultrawideband, dual polarized, dual waveform, instrumentation radar has been described and experimental measurements of fixed test objects and of a disturbed sea surface have been presented. The two cm range resolution of the system separates the contributions of individual scattering features on the ocean surface and is providing an increased understanding of the composition and behavior of radar sea clutter at low grazing angles. The experimental results have emphasized fundamental differences in the character of the clutter as a function of both polarization and radar resolution
This paper presents an experiment description, along with data examples, for ultrawideband radar measurements of low grazing angle forward scatter associated with a test target mounted above a wind disturbed sea surface. The measurement radar used subnanosecond transmit pulses (0.15 ns, 3 dB pulsewidth) at a 9 GHz center frequency to achieve resolutions as fine as 2 cm in the range dimension. This resolution was sufficient to fully resolve direct and multipath (both single and double bounce) contributions to the signal reflecting from a tower mounted retro reflector. The geometry presented a nominal 3 degree grazing angle for forward scatter. Dual polarized data examples, taken for a variety of wind conditions, highlight changes in the magnitude and the location of the scatter components with time.
This paper presents a system description, along with data examples, for an ultrawideband instrumentation radar which has been used by the Radar Division of the Naval Research Laboratory to measure low grazing angle sea clutter at X-band frequencies (3 cm wavelength). The radar system employs a video impulse excited traveling wave tube (TWT), dual wideband horns and multiple head, digital sampling oscilloscope circuitry. In its highest resolution mode, the system utilizes sub-nanosecond transmit pulses (0.15 ns, 3 dB pulsewidth) at a 9 GHz center frequency to achieve resolutions as fine as 2 cm in the range dimension. Multiple resolution waveforms, combined with dual polarization, provide insights into the varied and dynamic character of the radar sea clutter. Upwind data examples, measured at a 4 degree grazing angle in 20 knot winds, are examined
Microwave radar scatter from the sea surface at small grazing angles and moderate resolutions often exhibits a behavior which is termed as being "spikey" or composed of "sea spikes". Sea spikes appear to the radar as sporadic target like echoes which are localized in range and angle and which exhibit strong but deeply fluctuating amplitudes. For a given range cell, the sea spikes may persist for time spans of the order of seconds then disappear for tens of seconds before reappearing. This paper presents some data examples of sea spikes seen with a variety of instrumentation radar systems and points out some common characteristics of their time histories.
