All posts by robholman

West side bed forms

Below is a movie made by Cassia Pianca showing changes in low-tide morphology during the experiment. Focus on the short-scale features right along the shoreline – you will see them steadily move toward the inlet at a rate of about 50 m in 8 days (6 m/day).  Hmm.  If this doesn’t show up in the blog, I’ll email it.

movieSmallLowTide

(Falk also put the video on youtube to simplify thing. See video below).

Inlet Currents??

Today I tried initial analyses on “vBar” pixel instruments to measure tidal currents in the inlet. These are based on Chris Chickadel’s work and seemed potentially applicable to this situation of co-aligned waves and currents in the inlet. Below shows the locations of estimates.

The figure below shows ebb current estimates for each of the three lines. Locations of zero current are mostly where pixel resolution has degraded. The cross-inlet structure and along-inlet gradients seem interesting. Of course, I have not compared against any ground truth (but hope to).
These are initial experimental results that we will work further on.  We collected these data for one transect every half hour since 04/29 and added the two other transects on 05/10.  We will begin bulk analysis soon-ish.

If you are interested, here are four plots illustrating the method. The first is just an example stack and shows the mix of waves propagating into the inlet (down left) and current streaks showing ebb flow (down right).  This is a moderately easy case with strong current signatures.

The second figure shows the corresponding f-k spectrum (using a convention of +/- frequency and positive wavenumber). The ridge of energy going down right corresponds to the current. The curved shape in the upper half corresponds to the gravity waves and would normally be roughly parabolic but the current turns the dispersion curve. The analysis exploits the current ridge but could also exploit the wave Doppler shift (later???).  (This is my coolest plot).  Streaks at high k are from aliasing and are not included in the analysis.

The third figure transforms the f-k spectrum to V-k space, a al Chickadel.

The fourth figure integrates through k to give a variance versus V curve. The peak (Gaussian fitted) is the estimated current.  This case is the landward-most point in west transect, so V ~ 95 cm/s.

West Side Bedforms

Attached is a higher resolution local merged timex from today’s low tide showing detailed bedforms on the western side of the inlet.  I’m amazed by the amount of structure.  Also, we have posted a first draft web description of Argus at RIVET at cil-www.oce.orst.edu/rivet.  It includes description of our geometry set up procedure and the location of a decent 3D benchmark by the OSU house that Tom Lippmann helped us set up.

Merge Images available

I’m not sure if this is well known yet, but Argus merged images are available on the web at http://cil-www.oce.orst.edu/RIVETmerge.  They are posted as they are collected and consist of snap, timex, var, bright and dark images for every 1/2 hour.  The upper half of the page is rectifications for the large inlet area at 2.5 m resolution.  If you continue down you will see equivalent images for the west side area at 1.0 m resolution.  Click on thumbnails to see full res images.  Further explanations will be posted soon (after I teach), but a nice example snap from 1100 today is attached below (with luck) – check the small scale features in very shallow water around x=-150, y = -450.  Tres cool (and it looks like people are surveying based on dark image tracks).

Example Merged Rectifications

Here are example merged Argus products that we will be putting on the web. If you have suggestions for changes, let us know. For example, we will add instrument locations as we learn them. The first is a large area time exposure showing the shoal configuration. The second in a small area snap that shows fierce crossing wave patterns.

Initial Timex Images

Attached (with luck) are initial time exposure images from today at 1700 EST (1800 EDT??). We surveyed this evening and will be doing image geometries tomorrow then will run routine rectification maps thereafter. But we thought people might be interested in the shoal geometries.