Advancements in the U.S. army corps of engineers hydrographic survey capabilities: The SHOALS system

In an effort to modernize its hydrographic survey capabilities, the U.S. Army Corps of Engineers has undertaken a joint development program with Canada to construct and field test an operational prototype airborne lidar bathymeter system. The construction and field verification effort of this program began March 1990 with field tests scheduled for winter 1993. The system will be built by Optech, Inc., based on their design of the LARSEN 500, the only commercial lidar system currently producing bathymetric surveys.

The Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) system will operate out of a medium‐sized helicopter such as the Bell 212 at approximately 200 meters altitude where the laser scanning system generates a swath width of just over 140 meters. System requirements dictate a laser operating at 200 Hz in both the blue‐green wave length for maximum water depth penetration and the infrared for surface interface recognition. Each laser shot strikes the water surface at a known location where its energy is partially reflected back to the receiver and partially transmitted through the water column. Transmitted energy undergoes scattering and absorption along its path to the bottom where the remaining energy is then reflected back to the receiver.

The Transceiver, Positioning, Acquisition, Control and Display, and Ground Based Data Processing subsystems make up the SHOALS system. These subsystems have been designed, constructed, and currently are being laboratory tested prior to total system integration and field testing. This article presents the system's design and discusses system use following development.     

Subduction factory processes beneath the Guguan cross-chain, Mariana Arc: no role for sediments, are serpentinites important?

We need to understand chemical recycling at convergent margins and how chemical interactions between subducted slab and the overlying mantle wedge affect mantle evolution and magmagenesis. This requires distinguishing contributions from recycled individual subducted components as well as those contributed by the mantle. We do this by examining magmatic products generated at different depths above a subduction zone, in an intra-oceanic arc setting. The Guguan cross-chain in the intra-oceanic Mariana arc overlies subducted Jurassic Pacific plate lithosphere at depths of ~125--230 km and erupts mostly basalt. Basalts from rear-arc volcanoes are more primitive than those from the magmatic front, in spite of being derived by lower degrees of melting of less-depleted mantle. Rear-arc magmas also show higher temperatures and pressures of equilibration. Coexisting mineral compositions become more MORB- or OIB-like with increasing height above the subduction zone. Trace element and isotopic variations indicate that the subduction component in cross-chain lavas diminishes with increasing depth to the subduction zone, except for water contents. There is little support for the idea that melting beneath the Mariana Trough back-arc basin depleted the source region of arc magmas, but melting to form rear-arc volcanoes may have depleted the source of magmatic front volcanoes. Enrichments in rear-arc lavas were not caused by sediment melting; the data instead favor an OIB-type mantle that has been modestly affected by subduction zone fluids. Our most important conclusion is that sediment fluids or melts are not responsible for the K--h relationship and other cross-chain chemical and isotopic variations. We speculate that an increasing role for supercritical fluids released from serpentinites interacting with modestly enriched mantle might be responsible for cross-chain geochemical and isotopic variations. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

The distant beat of my father’s drums: Contemporary Aboriginal music and NCI-FM broadcasting, Manitoba, Canada

Contemporary Aboriginal music in Manitoba fuses the traditional and modern. Aboriginal songwriters address social and economic issues faced by their communities through a variety of genres ranging from country to hip hop. Native Communications Incorporated (NCI) is an Aboriginal-owned and operated enterprise that addresses the broadcasting needs of Manitoba’s Aboriginal population. It broadcasts a high proportion of contemporary Aboriginal music that mirrors Aboriginal concerns and perceptions. NCI also plays a significant role in developing and promoting Aboriginal music and reflects the challenges of catering to a culturally diverse and geographically dispersed Aboriginal population.     

Uptake of estradiol from sediment by hornyhead turbot (Pleuronichthys verticalis) and effects on oxidative DNA damage in male gonads

Male and female hornyhead turbot (Pleuronichthys verticalis) were exposed to four concentrations (0, 0.75, 14.7 and 46.5 ng/g dry weight) of E2-amended sediment for 7 days. Sediment-derived E2 was bioavailable to the flatfish, though the route of uptake was unclear. A concentration of 46.5 ng/g E2 in sediment led to a significant increase in vitellogenin concentrations in the plasma in both sexes after 7 days of exposure. Though plasma E2 concentrations increased significantly in males at sediment E2 concentrations of 0.75 ng/g dry weight and above, a dose-dependent increase was not observed. There was also no correlation between sediment E2 concentrations, plasma E2 concentrations, and oxidative DNA damage in male gonads. The results suggest that the DNA damage previously seen in the gonads of feral hornyhead turbot at a sewage outfall is likely not caused by acute exposure to exogenous E2 from sediments.     

Evidence that biological activity affects Ocean Bottom Seismograph recordings

Brief and impulsive signals of uncertain origin appear regularly on records from Ocean Bottom Seismographs (OBS) of several institutions. These signals have been recorded on nearly all deployments of the Texas OBS, including sites at depths greater than 7000 m. At some sites, they account for over 90% of the events recorded. They are of short duration (usually 0.5–4.0 s) and have a characteristic frequency (usually in the range of 4–18 Hz) that differs from site to site. When networks of OBS instruments are deployed, the signals are not recorded simultaneously by different instruments. Neither the frequency content nor the distribution of durations of these signals is similar to what is observed for known earthquake events.We present evidence suggesting that the signals are of biological origin, perhaps caused by animals touching the OBS units. (1) The distribution of these signals on instruments deployed at depths shallower than 1000 m shows a 24 h periodicity, while there is a 24 h periodic pattern on instruments deployed at sites deeper than 1000 m (where there is no visible light). (2) The frequency of occurrence of signals is similar to the vertical distribution of biomass in the oceans, i.e., they appear most frequently on OBS instruments deployed at very shallow depths. (3) Biological material has been found attached to several OBS units upon recovery.University of Texas Institute for Geophysics contribution number 468.     

Smoothing GPS carrier phase double differences using inertial measurements for high performance applications

This paper will describe an enhancement to the GPS double difference carrier phase measurements on a single airborne platform by smoothing them with inertial measurements while preserving the dynamic bandwidth. This enhancement will reduce the impact of carrier phase multipath and carrier phase noise on baseline determination between multiple antennas on an aircraft when in flight. This type of measurement system has numerous applications where platform pointing and relative body motion must be determined at the mm-level for applications such as sensor stabilization, Synthetic Aperture Radar, long range RADAR (i.e. angle-of-arrival measurements). Lower noise levels (mm-level and below) enable more performance to the stabilized system such as increased aperture for longer range, operation at higher frequencies, and more image resolution. The focus of this paper will be on a technique to provide this enhanced performance for these various applications using the available navigation systems. Additionally, this type of smoothing can effectively remove the additional noise induced by carrier phase measurement differencing. The noise level of a double or triple difference can be reduced below that of the raw measurement. A complimentary synthesized double difference quantity with ultra-low-noise characteristics will be used to smooth the GPS carrier phase double difference measurements without losing dynamic bandwidth since it follows the airborne dynamics. Flight test data will be presented to demonstrate the performance improvement in the midst of aircraft dynamics. Results will show that the noise reduction follows the theoretical prediction.     

Monitoring Partitioning Tracer Testing and Surfactant Flooding by In-Line Gas Chromatography Techniques

An automated in-line analytical system has been developed to provide near real-time results for partitioning interwell tracer testing (PITT) and surfactant enhanced aquifer remediation (SEAR). The analytical methodology is based on gas chromatography (GC) with flame ionization detection and direct aqueous injection. The system was constructed from both commercially available and custom-manufactured components that are linked electronically to facilitate autonomous operation. For the field trials presented herein, the in-line GC method provided superior or comparable PITT and SEAR data compared to conventional sample collection followed by shipment and analysis at a commercial analytical laboratory. Analytical precolumns were shown to effectively safeguard the integrity of the analytical column, despite the consecutive analysis of more than 1000 samples per PITT or SEAR. Additionally, the use of the in-line GC resulted in an 85% and 74% reduction in analytical costs per PITT and SEAR, respectively.     

Coastal failures during the 1999 Kocaeli earthquake in Turkey

During the 1999 Kocaeli earthquake (M_w=7.4) in Turkey, coastal failures and sea inundation were observed and were particularly concentrated along the margins of Izmit Bay and Lake Sapanca, in pull-apart basins created by stepovers in the fault rupture. Geotechnical site characterization, geologic mapping, liquefaction evaluation, and slope stability analysis were carried out to identify the principal contributing factors of the coastal failures. Results from this study indicate that both liquefaction and tectonic subsidence contributed to the failures and sea inundation within the pull-apart basins. Most of the liquefaction sites were situated at the prograding nose of active delta fans, where the presence of steep slopes coupled with the loose sediments found within young active delta fan deposits resulted in liquefaction-induced slope failures and sea inundation. Liquefaction in other coastal deposits outside the actively prograding delta fans caused limited lateral spreading and only minor sea inundation. Outside the delta fans, where soils were not liquefiable, tectonic subsidence associated with normal faulting was the cause of the observed sea inundation. Generally, tectonic subsidence caused the most severe sea inundation. Based on these observations, the identification of regions susceptible to both tectonic subsidence and liquefaction are important when evaluating seismic hazards.