Images

Frame from video of Cowells Beach in Santa Cruz, California, showing “pixel instruments” measured continuously during the video and used to estimate different coastal processes. The blue dots represent an array of pixels used by a computer program called cBathy to estimate seafloor depths (bathymetry).

USGS ocean engineer Gerry Hatcher (left) and USGS postdoctoral oceanographer Shawn Harrison make adjustments to a computer controlling two video cameras on the roof of the Dream Inn, a 10-story hotel overlooking Monterey Bay in Santa Cruz, California. One camera looks eastward over Santa Cruz Main Beach and boardwalk, and the other southward over Cowells Beach.

Snapshot, or first frame of from a 10-minute video taken May 6, 2017, in Santa Cruz, California.

Time-averaged image, or “timex,” created by averaging the intensity of light recorded at each spot, or “pixel,” during a 10-minute video taken at Santa Cruz, California, on May 6, 2017. Blurred white zones show where waves are breaking. Line between wet and dry sand shows the maximum height on the beach reached by the waves (“runup”).

“Variance” image produced from video shot at Cowells Beach in Santa Cruz, California, on May 6, 2017. The more the light intensity changes at a given spot, or “pixel,” during the video, the brighter the value assigned to that pixel. Motion tends to produce changes in light intensity. Note bright areas along and beyond the shore where waves were breaking.

Provisional data subject to revision. From the USGS Remote Sensing Coastal Change Project, illustration describes how the USGS measures topographic change with 4D photogrammetry utilizing the techniques of Warrick et al., 2017. A digital terrain model of a coastal cliff is shown with its ground control points.

After mixing about 20 grams of a sediment sample with distilled water, we add strong hydrogen peroxide to break down or "digest" organic matter that may be in the sample. Organic matter makes clay particles stick together and we need them separate in order to calculate accurate particle size fractions of the sample.

Tips of Brazilian waterweed (Egeria densa) break the surface at low tide in Lindsey Slough in the northern Sacramento-San Joaquin River Delta. More commonly, this invasive plant is completely submerged.

On March 21, 2017, the sediment trap from this instrument package (deployed the previous October into Monterey Canyon) is gone and the mounting frame is mangled, having been exposed to several significant turbidity currents in one deployment. 

We take most cores and samples straight from the loading dock into a large walk-in refrigerator (about 780 square feet), kept at the international core curation standard of 4° C plus or minus 2° C. Each core and sample must be labeled with an identifier and metadata, which follows the material through processing and analysis.

The back door of the refrigerator connects to our core and sample processing labs.

Each half of a split sediment core is wrapped in plastic to prevent drying and contamination. For long-term storage, we can shrink-wrap one half with a thick film that prevents moisture loss.

Lab technicians create written descriptions of sediment cores, referencing Munsell chart colors and standard phrases.

Sediment cores may be subsampled for further processing and analysis in other labs, like the Sediment Lab which is across the hall from the Core Lab.

The first stop for many sediment cores is the Geotek MSCL or multi-sensor core logger. The logger automatically measures P-wave velocity, magnetic susceptibility, electrical resistivity, and gamma density at intervals from 1 millimeter to 1 centimeter along cores up to 1.5 meters long.

This is the Pacific Coastal and Marine Science Center's Sediment Prep Lab, where sediment samples and core subsamples are prepared for analyses.

We spin down a sample of sediment that's mixed with distilled water in a centrifuge. This separates the sediment from the water at the bottom of the sample bottle, and we pour off most of the water. This process removes dissolved salts.

Washing a sediment sample through two sieves with distilled water lets us measure the fractions of gravel (bigger than 2 millimeters or -1 phi) and sand (2 millimeters to 63 microns, -1 phi to 4 phi). Smaller sediment passes through the sieves into a standard 1-liter graduated cylinder.

After adding a little sodium hexametaphosphate dispersant, we use a plunger to carefully stir the cylinder then let it settle, to ensure good mixing and standardized suspension of the sediment.

Lab technician Angela Tan takes a sample of the sediment suspended in liquid, for analysis in one of several ways.

We can use the tried-and-true method of washing samples through finer and finer sieves, then weighing the sediment trapped in each sieve, to determine sediment size fractions.