Here are the results of two AUV missions performed on 5/16 and 5/17 to observe the offshore extent of the river plume during max ebb using elevated CDOM signatures to define the boundaries of the plume. The 5/16 mission was performed during strong southerly wind conditions (blowing directly into the inlet) while the 5/17 mission was performed during minimal wind conditions. Both missions extend to 1km offshore. You’ll notice how defined the river jet is during the 5/17 mission and how the plume extends beyond our survey lines. In contrast, it appears the strong wind conditions during the 5/16 mission suppressed the offshore extent of the plume and pushed it in a southwesterly direction. It’s also interesting to see the impact the wind conditions have on the mixing of the plume. The high wind event on 5/16 diluted the plume significantly (colorbar range: 6 to 10 ppb) when compared to the low wind event on 5/17 where the river plume saw consistent CDOM levels of ~13 ppb as it is advected offshore.
Hello everyone, just wanted to pass along some of the work the SIO CORDC group has been performing offshore with the REMUS AUV. On 5/8/2012 we ran a REMUS mission supporting the Guza dye release. We’ve overlaid the Rhodamine signature observed by our AUV on the hyperspectral image taken at 17:39UTC (courtesy of Luc Lenain and Nick Statom). The REMUS was deployed at 17:20UTC and started near the entrance to the new channel and went in a southwesterly direction towards the beach. It reached the end of this leg at ~17:40UTC(when the image was taken). You can see from the image that this first leg was outside of the dye signature which corresponded with our observations The REMUS then performs a mow the law pattern across the inlet. We first encountered dye at ~17:46UTC and continued measuring the plume until the end of the mission at ~19:00UTC.
Since there has been a bit of discussion about bedforms recently I thought would post a kmz of sidescan imagery from May 5th. This survey started at the end of flood tide and the bedforms in the dredged channel were asymmetrical in flood oriented direction, by the end of the survey, 2 hrs later at the beginning off ebb tide flow, they had reversed asymmetry to ebb oriented.
The bedforms are generally bigger in the dredged channel on the southwest side of the inlet. This is especially noticeable in the inner portions of the inlet.
Not sure how to make post the images big enough here to see what is going on. Either click & download the images here or the kmz to see more detail
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.
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.
The ‘Maple’ group from BIO, Dalhousie and UMaine arrived Tuesday. Our objective is to characterize suspended particles (size distribution and composition) and relate it to ocean color. We have already scouted the river, taken grab samples and water samples for grain size, and have completed a drift station with a LISST and Digital Floc Camera through
the mouth of the inlet. In the next few days we plan to occupy a 13h station near the river mouth (Friday) and perform a transect along the river (Saturday). With the arrival of Emmanuel Boss, in addition to the in situ particle size spectrum, our measurements now include spectral absorption, attenuation and backscattering of both dissolved and
particulate material and hyper-spectral upwelling radiance and irradiance. Our observations will help link the in-water optical properties to remote observations.
Tim Milligan, Brent Law, Gary Bugden (BIO/DAL) and Emmanuel Boss (UMaine)
Posting on behalf of Rocky Geyer: These are near-surface velocity vectors from the WHOI REMUS at max ebb on May 4th in the north channel. Maximum ebb currents are well over 1 m/s. Lots of bathymetric steering, but some interesting free lateral shear zones as well.
Here is a composite image from 12 days of SWIFT drifter runs through the inlet spanning many different tide/wind/wave conditions. The color scale is the surface turbulence dissipation rate, which is generally correlated with strong wave-current interactions in the two channels. Preliminary turbulence metrics and bulk wind, wave, and current values are posted for each day at http://herschel.apl.washington.edu/darla/SWIFT/, along with an xls table listing available data. More to come!
The imagery above is a preliminary mosaic of the New River inlet plume on May 2, at about 1150 EDT (the companion data to Gordon Farquaharson’s microASAR data in his May 4 post). Brightness in the image indicates relatively warmer temperatures, and I’ve adjusted the contrast to highlight the plume, making the warmer land white. The plume on this day (due to wind) was shooting north and the plume front(s!) are complicated – including prominent transverse features at N = 3822.5km, E = 286 to 288km. Note there are still kinks in the mapping, so image overlap is not exact, and the camera drift and angular emissivity effects have not been corrected.