Seasonal and Vertical Distributions of Planthoppers (Homoptera: Fulgoroidea) Within a Black Walnut Plantation

Information on the seasonal and vertical distributions of 34 species (eight families) of planthoppers was obtained from window trap collections in a North Carolina black walnut plantation in 15 and 1978. The most commonly collected species were Acanalonia conica (Acanaloniidael. Liburniella ornata (Delphacidae), Oliarus ecologus (Cixiidae), and O. quinquelineatus

Space Shuttle Proximity Operation Sensor Study

The performance of the Kuband radar was analyzed in detail, and the performance was updated and summarized. In so doing, two different radar design philosophies were described, and the corresponding differences in losses were enumerated. The resulting design margins were determined for both design philosophies and for both the designated and nondesignated range modes of operation. In some cases, the design margin was about zero, and in other cases it was significantly less than zero. With the point of view described above, the recommended solution is to allow more scan time but at the present scan rate. With no other changes in the present configuration, the radar met design detection specifications for all design philosophies at a range of 11.3 nautical miles

Split-beam echosounder observations of natural methane seep variability in the northern Gulf of Mexico

A method for positioning and characterizing plumes of bubbles from marine gas seeps using an 18 kHz scientific split-beam echo sounder (SBES) was developed and applied to acoustic observations of plumes of presumed methane gas bubbles originating at approximately 1400 m depth in the northern Gulf of Mexico. A total of 161 plume observations from 27 repeat surveys were grouped by proximity into 35 clusters of gas vent positions on the seafloor. Profiles of acoustic target strength per vertical meter of plume height were calculated with compensation for both the SBES beam pattern and the geometry of plume ensonification. These profiles were used as indicators of the relative fluxes and fates of gas bubbles acoustically observable at 18 kHz and showed significant variability between repeat observations at time intervals of 1 h–7.5 months. Active gas venting was observed during approximately one third of the survey passes at each cluster. While gas flux is not estimated directly in this study owing to lack of bubble size distribution data, repeat surveys at active seep sites showed variations in acoustic response that suggest relative changes in gas flux of up to 1 order of magnitude over time scales of hours. The minimum depths of acoustic plume observations at 18 kHz averaged 875 m and frequently coincided with increased amplitudes of acoustic returns in layers of biological scatterers, suggesting acoustic masking of the gas bubble plumes in these layers. Minimum plume depth estimates were limited by the SBES field of view in only five instances

Acoustic Scattering from Mud Volcanoes and Carbonate Mounts

Submarine mud volcanoes occur in many parts of the world’s oceans and form an aperture for gas and fluidized mud emission from within the earth’s crust. Their characteristics are of considerable interest to the geology, geophysics, geochemistry, and underwater acoustics communities. For the latter, mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar. Close-range (single-interaction) scattering measurements from a mud volcano in the Straits of Sicily show scattering10–15dB above the background. Three hypotheses were examined concerning the scattering mechanism: (1) gas entrained in sediment at/near mud volcano, (2) gas bubbles and/or particulates (emitted) in the water column, (3) the carbonate bio-construction covering the mud volcano edifice. The experimental evidence, including visual, acoustic, and nonacoustic sensors, rules out the second hypothesis (at least during the observation time) and suggests that, for this particular mud volcano the dominant mechanism is associated with carbonate chimneys on the mud volcano. In terms of scattering levels, target strengths of 4–14dB were observed from 800to3600Hz for a monostatic geometry with grazing angles of 3–5°. Similar target strengths were measured for vertically bistatic paths with incident and scattered grazing angles of 3–5° and 33–50°, respectively

Excited-state absorption in ZBLAN:Er3+: implications for a diode-pumped 3-µm fiber laser

Effective excited-state absorption (ESA) cross-sections are measured in ZBLAN:Er3+ at 780-840 nm. Pump losses by ESA are present over the whole absorption band. Diode pumping at 979 nm seems more favorable for high-power 3-µm fiber lasers