Norbert E. Yankielun

Extensive measurements of snow depth using FM-CW radar

A sled-mounted X-band FM-CW radar and field data reduction system was developed and field tested. An integral part of the measurement program was the use of a computer algorithm to pick peak radar amplitudes, which were needed to convert radar data into depths in the field. A set of field protocols, designed to collocate radar and hand-probe depth measurements, were used with the algorithm to locally calibrate the radar because, without local calibration, depths were unreliable. Mean snow depths determined using the calibrated radar agreed with mean depths determined by hand to within 3% but had a consistently larger variance because of radar measurement errors. An analysis of the errors indicates that they are random and can be removed by filtering using an Optimal (Wiener) filter, thereby producing both the same mean and variance in snow depth from the radar as that obtained by hand-probing.

Snow cover characterization using multiband FMCW radars

The use of radars to characterize the physical properties of a snow cover offers an attractive alternative to manual snow pit measurements. Radar techniques are non-invasive and have the potential to cover large areas of a snow-covered terrain. A promising radar technique for snow cover studies is the frequency modulated continuous wave (FMCW) radar. The use of a multiband radar approach for snow cover studies was investigated in order to fully exploit the capabilities of FMCW radars. FMCW radars operating at and near the C-, X- and K a -bands were used to obtain radar profiles over a wide range of snow cover conditions. These frequency-dependent radar signatures were used to identify important snow cover features such as ice and depth hoar layers. Snow grain size information was also obtained from the frequency-dependent scattering losses that were observed in the snow cover. Several case studies of FMCW radar profiles are presented in order to demonstrate the advantages of a multiband radar approach for monitoring the spatial and temporal variability of snow cover properties and/or processes over an extended area.

Passive Resonance Roof Moisture Detector

A new, simple, and inexpensive prototype moisture sensor (patent pending) has been developed and tested in a small mockup of a low-sloped roof. The sensor comprises an inductor and a moisture-sensitive capacitor; it reqmres neither batteries nor wire connections. It is intended to be placed at locations within low- sloped roofs that might become wet from a leak, and remain operational for the life of the roof and automatically reset if the roof becomes dry again. The moisture state of the sensor can be detected by a simple electronic circuit that is passed within 30 cm of the sensor. Preliminary tests have been performed that indicate the potential for electromagnetically and remotely polling the sensor to determine moisture state. Further instrumentation to poll remotely the assemblage of sensors to detect the presence of some that are wet has been proposed and the principle tested; however, a practical implementation has not yet been developed.

Development of an instrument to electronically measure, record, and image washover of a towed body

Abstract Washover is the condition of occasional, partial, or complete inundation of the surface of a body floating in water. Washover is typically caused by wave and wind action. A knowledge of the three-dimensional spatial and temporal parameters of seawater washover of low-profile towed bodies, buoys, and other maritime towed, tethered, and free-floating bodies is extremely helpful in the understanding and improving of their hydrostatic and hydrodynamic performance under a wide variety of sea states. Here we discuss the theory, implementation, and initial testing of a newly developed electromagnetic measurement technique and system (patent pending). This system provides real-time three-dimensional spatial and temporal detection, measurement, and visualization of washover. Data can be acquired and displayed in real time, as well as stored for later post-processing and analysis. The system has been successfully tested in a seawater wave tank and shows promise for open-ocean washover testing of low-profile buoyant towed bodies. This washover assessment measuring system is expected to provide an empirically based benchmarking process for computational fluid dynamic assessments of turbulent flow around arbitrarily shaped surface-towed bodies.