Geology topics

B.A. Stewart

Publications and source records attributed to B.A. Stewart.

3 recordsLinked to original sources

USGS2024

The Europa Imaging System (EIS) investigation

The Europa Imaging System (EIS) consists of a Narrow-Angle Camera (NAC) and a Wide-Angle Camera (WAC) that are designed to work together to address high-priority science objectives regarding Europa’s geology, composition, and the nature of its ice shell. EIS accommodates variable geometry and illumination during rapid, low-altitude flybys with both framing and pushbroom imaging capability using rapid-readout, 8-megapixel (4k × 2k) detectors. Color observations are acquired using pushbroom imaging with up to six broadband filters. The data processing units (DPUs) perform digital time delay integration (TDI) to enhance signal-to-noise ratios and use readout strategies to measure and correct spacecraft jitter. The NAC has a 2.3° × 1.2° field of view (FOV) with a 10-μrad instantaneous FOV (IFOV), thus achieving 0.5-m pixel scale over a swath that is 2 km wide and several km long from a range of 50 km. The NAC is mounted on a 2-axis gimbal, ±30° cross- and along-track, that enables independent targeting and near-global (≥90%) mapping of Europa at ≤100-m pixel scale (to date, only ∼15% of Europa has been imaged at ≤900 m/pixel), as well as stereo imaging from as close as 50-km altitude to generate digital terrain models (DTMs) with ≤4-m ground sample distance (GSD) and ≤0.5-m vertical precision. The NAC will also perform observations at long range to search for potential erupting plumes, achieving 10-km pixel scale at a distance of one million kilometers. The WAC has a 48° × 24° FOV with a 218-μrad IFOV, achieving 11-m pixel scale at the center of a 44-km-wide swath from a range of 50 km, and generating DTMs with 32-m GSD and ≤4-m vertical precision. The WAC is designed to acquire three-line pushbroom stereo and color swaths along flyby ground-tracks.

Space Science Reviews↗

USGS2018

Infection by Nanophyetus salmincola and toxic contaminant exposure in out‐migrating steelhead from Puget Sound, Washington: Implications for early marine survival

Out‐migrating steelhead Oncorhynchus mykiss from four Puget Sound rivers and associated marine basins of Puget Sound in Washington State were examined for the parasite, Nanophyetus salmincola in 2014 to determine whether recent trends in reduced marine survival are associated with the presence of this pathogen. A subset of steelhead from three of these river–marine basin combinations was analyzed for the presence of persistent organic pollutants (POPs) to assess whether exposure to these contaminants is a contributing factor to their reduced marine survival. The prevalence and parasite load of N. salmincola were significantly higher in fish from central and southern Puget Sound than in fish from river systems in northern Puget Sound. The proportion of steelhead samples with concentrations of POPs higher than adverse effects thresholds (AETs) or concentrations known to cause adverse effects was also greater in fish from the central and southern regions of Puget Sound than in those from the northern region. Polybrominated diphenyl ether concentrations associated with increased disease susceptibility were observed in 10% and 40% of the steelhead sampled from central and southern Puget Sound regions, respectively, but in none of the fish sampled from the northern region. The AET for polychlorinated biphenyls was exceeded in steelhead collected from marine habitats: 25% of the samples from the marine basins in the central and southern regions of Puget Sound and 17% of samples from northern Puget Sound region. Both N. salmincola and POP levels suggest there are adverse health effects on out‐migrating steelhead from one southern and one central Puget Sound river that have lower early marine survival than those from a river system in northern Puget Sound.

Washington↗

USGS2015

Study 8: Prevalence and load of Nanophyetus salmincola infection in outmigrating steelhead trout from five Puget Sound rivers

Nanophyetus salmincola is a parasitic trematode, or flatworm, that infects salmonid fishes in the Pacific Northwest, including Washington, Oregon, and portions of California. The adult worm lives in the intestine of fish-eating birds and mammals. Eggs shed into the water hatch into miracidia which penetrate the first intermediate host, one of two species of snail Juga plicifera or J. silicula . Asexual reproduction occurs within the snail. Free-swimming cercaria are released from the snail and penetrate the secondary intermediate host, often a salmonid fish, in fresh and brackish water. The cercaria encyst as metacercaria in various organs of the fish, including gills, muscle and heart, but favor the posterior kidney. Penetration and migration by the cercaria through the fish causes damage to nearly every organ system. Once encysted, metacercaria survive the ocean phase of salmonid life cycle. N. salmincola is a likely contributor to mortality of juvenile coho salmon ( Oncorhynchus kisutch ) during the early ocean rearing phase, and it is the most prevalent pathogen of outmigrating steelhead in the estuaries of the Pacific Northwest. A field survey was implemented from March-June 2014 to compare the prevalence and parasite load of N. salmincola infections in outmigrating steelhead from five Puget Sound watersheds and to assess changes in infection levels that occurred during the smolt out-migration through each watershed. N. salmincola infection prevalence and parasite loads were determined by counting metacercaria in posterior kidney samples. Tissue samples were collected and examined by standard histological methods.

Washington↗