James D. Lyden

Characterization of sea ice types using synthetic aperture radar

The results of an investigation into the use of synthetic aperture radar (SAR) imagery for sea ice-type discrimination are presented. X- and L-band dual-polarization SAR data of Beaufort Sea ice were examined using manual interpretation techniques to determine which channel provides the most information. Quantitative methods for ice-type discrimination also were explored by statistical parameterization of these data. Various statistical tests, both parametric and nonparametric, were applied to evaluate the utility of the parameters for machine interpretation of SAR ice data. The results obtained indicate that, under winter ice conditions, X-nband is superior to L-band for discriminating various ice types. Also, imagery obtained at small incidence angles shows greater tonal variation between ice types than that obtained at larger angles. Of the quantitative measures evaluated, mean and standard deviation appear to be the most valuable. Examination of quantities involving higher order moments indicates that a better understanding of the SAR imaging process is required before these measures can be utilized successfully.

Estimates of ocean wavelength and direction from X-and L-band synthetic aperture radar data collected during the Marineland experiment

Simultaneously obtained X - and L -band synthetic aperture radar (SAR) data collected during the Marineland Experiment were spectrally analyzed by fast Fourier transform (FFT) techniques to estimate ocean wavelength and direction. An eight-sided flight pattern was flown over the same ocean area in order to study the sensitivity of the spectral estimate on radar look direction. These spectral estimates were compared with in situ wave measurements made by a pitch-and-roll buoy. The comparison revealed that the X -band SAR detected all gravity waves independent of radar look direction, while the L -band SAR detected all range-traveling gravity waves but failed to detect waves in three of four cases in which the waves were traveling within 25° of the azimuth direction. The analysis also indicates that azimuth-traveling waves appear longer and more range-traveling in the SAR imagery than observed by in situ instrumentation. It is postulated that degraded azimuth resolution due to scatterer motion is responsible for these observations.

Analysis of Spotlight Synthetic Aperture Radar Ocean Wave Imagery

During1 the November 1990 SAXON-FPN Experiment, Synthetic Aperture Radlar (SAR) data was collected of ocean waves in the North Sea. The primary objective of this experiment was to investigate SAR imagery of ocean waves at a variety of microwave frequencies under high sea staite conditions. One of the SAR SAXON-FPN wais the P-3/SAR which consists of a three-frequency (X-,C-, and L-band), fully-polarimetric SAR system which is jointly operated by ERIM and the Naval Air Development Center (NADC) and is flown in an NADC P-3 aircraft. instrumented1 tower at several altitudes to collect data which could be used to rigorously evaluate existing SAR ocean wave imaging theories. In addlition to conventional stripmap data, the P-3/SAR collected data at L-balnd in a spotlight mode. Recall that in a stripmap SAR, the antenna pattern illuminates a region perpendicular to the flight path while the forward motion of the aircraft creates the doppler history. In1 the spotlight mode, the radar antenna is continuously repositioned as the aircraft progresses so as to collect data at the same spatial location. For the L-band spotlight mode of the P-3/SAR, the antenna tracks the targeted area over squint angles +45O from broadside and the imaged area on the sea surface is approximately 1 by B km. Spot1 ight data of ocean waves provides several interesting analysis capabilities. directional sensitivity of the wave imaging mechanisms to be studied at a finer scale than conventional stripmap data and without the uncertainties of collecting data at different times. The dwell time over which spotlight data is collected is nominally 60 seconds. this period, the ocean waves propagate into, through, and out of the spotlight scene. wavelengths can be used as a check on water depth. In addition, the longer dwell time allows us to examine both the spatial and temporal frequency of breaking wave events under higher sea states. The results from these analyses and others will be reported in this paper. systems utilized during