Observation and inversion of seismo-acoustic waves in a complex Artic ice environment

Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990The propagation of low frequency seismo-acoustic waves in the Arctic Ocean ice canopy is examined through the analysis of hydrophone and geophone data sets collected in 1987 at an ice camp designated PRUDEX in the Beaufort Sea. Study of the geophone time series generated by under-ice explosive detonations reveals not only the expected longitudinal and flexural waves in the ice plate, but also an unexpected horizontally-polarized transverse (SH) wave arriving at a higher amplitude than the other wave types. The travel paths of all three observed wave types are found to be refracted in the horizontal plane along a line coincident with a known ridge separating the ice canopy locally into two distinct half-plates, the first of thin first year ice and the second of thicker multi-year ice. The origin of the SH wave appears to be near the detonation and not associated with the interaction of longitudinal, flexural or waterborne waves with the ridge line. The need to determine the exact location of each detonation from the received time series highlights the dramatic superiority of geophones over hydrophones in this application, as does the ability to detect the anomalous SH waves and the refracted ray paths, neither of which are visible in the hydrophone data. Inversion of the geophone data sets for the low frequency elastic parameters of the ice is conducted initially by treating the ice as a single homogeneous isotropic plate to demonstrate the power of SAFARI numerical modeling in this application. A modified stationary phase approach is then used to extend SAFARI modeling to invert the data sets for the elastic parameters of the two ice half-plates simultaneously. The compressional/shear bulk wave speeds estimated in the half-plates, 3500/1750 m/s in the multi-year ice and 3000/1590 m/ s in the new ice, are comparable to previously obtained values; however, the compressional/shear attenuation values in the two half-plates, 1.0/2.99 d/Bλ. and 1.0/2.67 dB/λ, respectively, are somewhat greater than previously measured values and four times greater than estimates extrapolated from high frequency data

Participant motivation and satisfaction with off-campus agricultural credit programs

The off-campus credit programs in agriculture at Iowa State University were evaluated to determine the motivation for participation and to gain knowledge of the degree to which participant\u27s needs and expectations were being met. The target population was participants in off-campus credit programs in the College of Agriculture;The Education Participation Scale (EPS) was used to determine the motivation for participation. The EPS has been factor analyzed. The factors were: social contact, social stimulation, professional advancement, community service, external expectations, and cognitive interest. The study revealed the cognitive interest factor mean score to be rated highest. All factor mean scores, with the exception of that for professional advancement, were statistically significantly lower than the normative group. Government service organization personnel (Extension, Soil Conservation Service, etc., employees) were found to be more motivated by professional advancement opportunities and external expectations of supervisors than individuals in other occupations. Government Service personnel also had the lowest mean factor score for cognitive interest. The study concluded that Master of Agriculture degree-seekers were more socially motivated than other participants. The factor means of the social contact factor and the social stimulation factor were found to be higher among this group of participants;Participant satisfaction was also studied. A researcher-developed instrument was used. The instrument was comprised of three parts. Part I assessed personal benefits derived through participation in the off-campus programs. Part II included statements with respect to institutional and programmatic functions of the off-campus programs. Part III gathered demographic information. Composite scores from Part I, Part II, and a total score were used data analysis;A high statistically significant difference was observed on the Part II composite score when data were grouped by occupation and also registration status (graduate vs undergraduate). A statistically significant difference in the overall composite mean scores was observed when grouped by program involvement. In general, the researcher felt that the data in this section of the study were quite consistent among participants. Participants were satisfied with the off-campus programs; however, a relatively low level of agreement with the satisfaction indicator statements was observed

Hypervelocity Impact of Composite Overwrap Pressure Vessels

There is a limited amount of hypervelocity impact (HVI) data on pressurized composite overwrapped pressure vessels (COPV). In recent years, NASA has performed HVI tests to characterize impact conditions resulting in either leak or burst of the COPVs representative of spacecraft hardware. This paper reports on the results of 40 tests that have been conducted on several types of COPV configurations, pressurized by inert gas to near the vessels rated maximum expected operating pressure (MEOP). These tests were used to better understand COPV response under HVI conditions and develop ballistic limit equations (BLE) related to these tests

Use of aerial survey and aerophotogrammetry methods in monitoring manatee populations

We evaluated the use of strip-transect survey methods for manatees through a series of replicate aerial surveys in the Banana River, Brevard County, Florida, during summer 1993 and summer 1994. Transect methods sample a representative portion of the total study area, thus allowing for statistical extrapolation to the total area. Other advantages of transect methods are less flight time and less cost than total coverage, ease of navigation, and reduced likelihood of double-counting. Our objectives were: (1) to identify visibility biases associated with the transect survey method and to adjust the counts accordingly; (2) to derive a population estimate with known variance for the Banana River during summer; and (3) to evaluate the potential value of this survey method for monitoring trends in manatee population size over time. (51 page document