by Ensign Sarah Chappel, NOAA Ship Rainier
NOAA Ship Rainier recently surveyed Whale Passage, which separates Whale Island from Kodiak Island, Alaska. The area has never been surveyed with modern full bottom coverage methods, and some project areas were last surveyed by lead lines around a hundred years ago. The area frequently experiences 7 knot currents, making rocky or shoal areas particularly treacherous. Whale Passage is a high traffic area for fishing vessels, U.S. Coast Guard cutters, barges, ferries, and small boats, which is why updating the area’s nautical charts is so important.
Strong currents push around Ilkognak Rock daymark at the entrance of Whale Passage. (Photo by LTJG Damian Manda)
The dynamics of the passage and surrounding area create several challenges for the hydrographic survey teams. The local tidal and current models are not well-known. To resolve this, Rainier was instructed to install four tide gauges in the greater project area, compared to a typical requirement for one gauge. Two of these gauges are a mere 4.5 nautical miles apart, in and just outside of Whale Passage itself. Some areas are so narrow and experience such high currents that it is only possible to survey in one direction in order to maintain control of the launch. The coxswain must plan each turn carefully, to avoid being pushed into dangerous areas. Ideally, these areas would be surveyed at or near slack tide. However, the slack in this survey area is incredibly brief and the predicted slack periods did not match what survey crews saw in the field.
The bathymetry is so dynamic that, even in relatively deep water, boat crews must remain alert for rocks and shoals. The survey teams found several large rocks in locations significantly different from where they were charted. Furthermore, the presence of large kelp beds increases the difficulty of surveying: they can foul the propellers on the launches, add noise to the sonar data, and can also obscure the presence of rocks.
While the work within Whale Passage, and the neighboring Afognak Strait on the north side of Whale Island, is challenging, it is also high-value. In addition to correcting the positions of known rocks and hazards, Rainier and her crew found a sunken vessel. Most importantly, though, they found areas that were charted twice as deep as they actually are. When the chart reads 8 fathoms (48 feet) and the actual depth is only 4 fathoms (24 feet), commercial traffic utilizing the passage could be in serious danger of running aground. Thus far, Rainier has submitted two DTON (danger to navigation) reports for depths significantly shoaler than charted. These new depths are already published on the latest version of chart 16594.
Rainier‘s multibeam sonar data shows a sunken fishing vessel in the vicinity of Whale Passage.
NOAA Ship Rainier will continue to survey the vicinity of Whale Passage, as well as the waters near Cold Bay out in the Alaskan Peninsula, for the remainder of the survey season before heading home to Newport, Oregon.
NOAA Ship Rainier recovers a survey launch after a morning of surveying and data collection. (Photo by LTJG Damian Manda)
by Marcus Cole, Coast Survey’s Cartographic & Geospatial Technology Program
Many are familiar with hydrographic surveys used to update nautical charts.
It isn’t enough, however, to collect just bathymetry during a survey. Without the context, such as when the data was collected, what instrumentation was used, or which tide stations were used to adjust the bathymetry to a particular datum, the data can’t be compiled into a chart update. The data can’t be discovered for a fish habitat study, or an analysis of coastal erosion, or tsunami inundation modeling. And, until two years ago, this metadata (data about data) was collected in a paper document that hadn’t changed much during the last century.
Experts from NOAA’s National Geophysical Data Center (NGDC) and Coast Survey’s Hydrographic Surveys Division recently ramped up the intensive process of overhauling their hydrographic survey metadata system ‒ an investment in resources that has increased efficiency, reduced errors, improved access, and enabled data discovery for anyone accessing the publicly available files.
Find descriptive reports from NGDC’s interactive map.
This particular effort centered on a new metadata format for descriptive reports (DR) that accompany every hydrographic survey. The report is a critical document that supplements and helps characterize the hydrographic data itself. For example, the DR lists the conditions under which the survey was performed, factors that might affect the survey’s adequacy and accuracy, who collected the data, how it was collected and processed, the equipment and procedures used, and the results. This metadata is essential for evaluating the survey, updating charts, and contributing to NOAA’s historical and legal archive.
Coast Survey’s new method of tracking metadata for DRs uses a format readable by both humans and computers: eXtensible markup language (XML). XML defines a set of rules for encoding documents that enables automation for many metadata-related processes:
- producing, editing, and transferring survey metadata;
- searching for text in a document;
- transforming data formats; and
- publishing standards-compliant metadata to multiple data warehouses from a single record.
Automation reduces the errors that may come from manual data entry, decreases the time needed to generate a DR, and enables data to be linked to other information pipelines. The biggest benefit from all these improvements in automation, however, is consistency. Just as datums are consistently defined and used in hydrographic surveys, metadata in the new XML DR architecture will be consistently generated and applied, leading to greater intercomparability between surveys. Furthermore, this change aligns with NGDC, where hydrographic survey data is archived. NGDC is adapting its data archiving and management infrastructure to take advantage of XML DR.
Not only does the new XML architecture make it easier to share data between Coast Survey and NGDC; it also helps integrate information from other branches of NOAA and the wider survey-interested community. Some of that information includes:
XML DR may also help Coast Survey integrate survey planning and ship resource management, extending its impact and utility even further.
A team of NOAA Corps officers, CIRES/University of Colorado contract staff, and Coast Survey experts worked together to foster these technology changes. As a result of their efforts to make data more consistent and accessible, it is as easy to learn something about H00001, the first survey conducted in 1837 in Long Island Sound, as it is to view H12381, a modern LIDAR survey from the Florida Keys.
–By Christy Fandel, Coast Survey physical scientist
Have you ever wondered what lies beneath the charted soundings on a nautical chart? While surveying Alaskan waters during the 2013 hydrographic field season, collecting bathymetry to update NOAA’s nautical charts, hydrographers revealed many interesting geologic features on the seafloor.
NOAA focuses a significant portion of our ocean mapping effort along the Alaskan coast. The Alaskan coastline represents over 50% of the United States coastline and dated nautical charts are inadequate for the increasing vessel traffic in this region. NOAA surveys are essential for providing reliable charts to the area’s commercial shippers, passenger vessels, and fishing fleets.
This past season, NOAA-funded hydrographic surveys in Alaska revealed many interesting geological features on the seafloor. Three surveys, in particular, took place in southeastern Alaska in the Behm Canal, along the Aleutian Chain within the coastal waters surrounding Akutan Island, and around Chirikof Island.
These three areas were among the areas surveyed by the NOAA Ship Rainier and surveying contractor Fugro-Pelagos during the 2013 field season.
In May, hydrographic surveying conducted by NOAA Ship Rainier in the Behm Canal revealed two distinct geological features. In the northern region of the canal, scientists identified a long, meandering ancient river. This ancient submarine river is nearly 40 km in length with up to 50 m in relief. Further south, Rainier surveyed a large volcanic-like feature. The surveyed volcano appears to have a distinct caldera, or collapse-feature that most likely formed after the volcanic eruption.
Multibeam bathymetry of the northeastern portion of the Behm Canal shows a large, meandering submarine river. The cross-sectional inset highlights the relief of the channel, nearly 50 m, as shown by the red box.
Multibeam data acquired by NOAA Ship Rainier shows a large volcanic feature in the southern portion of the Behm Canal.
Directly following the Behm Canal survey, Rainier transited west to survey the coastal waters surrounding Chirikof Island. The acquired bathymetric data revealed a stark northeast-trending fault in the southeastern portion of the survey area. This surveyed fault is distinguished by a clear misalignment across the fracture.
The red box outlines the northeast-trending fault along the coast of Chirikof Island, shown with bathymetry acquired by the Rainier.
Concurrently, an Office of Coast Survey hydrographic surveying contractor – Fugro-Pelagos – was surveying off the western coast of Akutan Island. Fugro’s hydrographers identified a large volcanic feature within the acquired bathymetric data. The surveyed volcanic feature is believed to be either a volcanic vent or cinder cone volcano. The multiple circular rings outlining this feature may represent the successive lava flows that formed the volcano.
Multibeam bathymetry acquired by Fugro, around Akutan Island, shows a large volcanic vent or cinder cone volcano, marked by multiple circular rings that represent the successive lava flows that formed the volcano.
With the upcoming 2014 hydrographic field season quickly approaching, the number of geologic discoveries will only increase. Extending all along the Aleutian Chain, from Kodiak Island to Bechevin Bay, the planned surveys for the 2014 field season will surely reveal many interesting and previously unknown geologic features.