Long Reach - Optical Backscatter Results

Multi-Sensor, Underway Oceanographic Profiling
C.S.L. Heron - Long Reach, Saint John River
October 20^th 2003

John E.Hughes Clarke and Nicole Delpeche
Ocean Mapping Group
Dept. Geodesy and Geomatics Engineering
University of New Brunswick

Herein, we present the results of simultaneous underway oceanographic data collection using a combination of a Brooke Ocean MVP-30 undulating instrument (with CTD and optical backscatter probe), an RDI 600 kHz monitor ADCP and a Knudsen 320 digital 200 kHz echosounder. All instrumentation is deployed simultaneously from CSL Heron, the primary research platform of the Ocean Mapping Group at the University of New Brunswick. Processing, integration and presentation software was written by JEHC. These data were collected as part of an ongoing investigation into the estuarine dynamics of the lower Saint John.

As an example of the capabilities of the instrumentation and processing software, a single transect of Long Reach (Saint John River) is presented showing the different views available. Long Reach is one of the most oceanographically active sections of the estuarine part of the river system. Depending on the time of year, a salt wedge/brackish mixed layer, penetrates up this section and exhibits remarkable mixing dynamics (the current MScEng thesis of Nicole Delpeche).

All plots below represent data projected into the long axis of the chartlet above. For all plots, the depth range 0-25m, 5m grid intervals, horizontal units 50m per grid mark

Salinity - (colour range blue: 0ppt, pink: 20ppt)
derived from Brooke MVP-30 using AML smart CTD
dipping ~ every 500m (125 seconds at 8 knots) interpolated

Temperature - (colour range blue: 11.75degC, pink: 14degC)
derived from Brooke MVP-30 using AML smart CTD
dipping ~ every 500m (125 seconds at 8 knots), interpolated

Optical Backscatter - (colour range black: 100mV, white: 700mV)
derived from Brooke MVP-30 using ?an optical backscatter sensor ?
dipping ~ every 500m (125 seconds at 8 knots) interpolated

ADCP current vectors - (azimuths red: downstream, green-upstream, blue-out_of_screen, yellow-into_screen)
derived from 600kHz RDI Monitor ADCP, pole mounted - 50cm bins vertically
pinging ~ 1Hz (4m at 8knots), but ensemble averaged over 100m metres

600 kHz Acoustic Volume Backscatter - (black - high intensity (linear range))
derived from 600 kHz RDI Monitor ADCP, pole mounted - 50cm bins vertically
pinging ~ 1Hz, averaged in 10m bins horizontally,

200 kHz Acoustic Volume Backscatter - (black - high intensity (logarithmic range))
derived from Knudsen 320BP - 200 kHz 6 deg. beam, over-gained
pinging at ~ 10Hz, stacked in 10m bins, 10cm vertically (0.1ms pulse)

The data illustrated above, provide an opportunity to make remarkable insights into the dynamics of the salt-water fresh-water mixing in this section of the estuary. At this point I will refrain from interpreting it (Nicole's job!), but clearly the availability of all these simultaneous views markedly improves our ability to observe and understand these gorgeous estuarine processes.

last updated by John E. Hughes Clarke , August 2004