Ramapriyan Pratiwadi

1
AquaNet Ultrasonic Measurement of Oil Spills
Transducer Operation
Apparatus
Group 21 Ramapriyan Pratiwadi Sameer
Qudsi Sandip Saha Advisor Dr. Jay
Zemel Presentation Times April 22, 2004
930 AM 1000 AM 1130 AM 1200 PM
100 PM 130 PM
An ultrasonic transducer forms one component of
each node. The transducer is used as an actuator
for transmitting, as well as a receiver for
detecting the reflected pulses. Given an
electrical signal at its resonant frequency, the
transducer transmits a pulse of high frequency
sound. The pulse reaches the oil-water boundary,
and gets partially reflected back to the
receiver. The rest of the pulse passes through
the oil-water boundary, and reaches the oil-air
interface. In this region, virtually all of the
signal undergoes total internal reflection, and
returns to the transducer. This phenomenon is
depicted in the figure below. The time
difference between the two pulses is used to
calculate the thickness of the oil layer.
Abstract Without a doubt, oil spills pose a
significant threat to the aquatic environment. It
is common to think that the most hazardous spills
are those on the scale of Exxon Valdez, where 11
million gallons were lost. However, there are
equally perilous spills occurring daily, albeit
on a smaller scale leakage from commercial and
recreational watercraft in harbors. The
individual discharges are difficult to detect
when compounded, however, they are qualitatively
identifiable. The challenge, therefore, is the
design of a semi-permanent system to accurately
quantify the thickness of an oil layer on water,
independent of the magnitude of the calamity. The
information provided by such a system could be
used to determine the environmental impact of the
spill and the measures necessary to avert
disaster. Current procedures of oil spill
analysis are classified into two categories
optical and physical. Primarily, satellite image
analysis or optical reflections are used to
detect the presence of an oil slick. However,
they are incapable of providing accurate
information regarding the quantity of oil
present. The second method is the immersion of
giant buoys into the water to obtain liquid
samples. This method is quite costly and time
intensive as it requires the use of complex
hydrocarbon sensors and a lab to analyze the
results. AquaNet provides a reliable,
cost-effective method of determining and relaying
oil spill information in real-time. This
technique involves using a small underwater
transducer to generate an ultrasonic pulse and
receive the reflected pulses, one from the
oil-water interface and another from the air-oil
interface. A microcontroller is then used to
calculate the time of flight of these signals and
determine the thickness of the oil layer. The
data is then sent from each node to a central
server capable of modeling the entire the spill.
Thus, the user has real-time spatial information
regarding the concentration of oil spills, as
well as historical data to determine gradients
and other behavioral properties.
Diagram and photograph of apparatus
Waveform of reflected signals and processed signal
Aggregate Modeling
Signal Processing
A pulse generator is used to control the behavior
of an analog switch. When the generator output
is high, 10 pulses of the 200 kHz oscillating
signal is passed to the transducer. When the
signal is low, the transducer is momentarily
forced to ground before it switches to receive
mode. The received signals are amplified and then
demodulated. The result is then fed to a Schmidt
trigger in order to generate a 5V pulse
output. This pulse will in turn generate an
interrupt on the HC11 microcontroller, which
calculates the time between transmission of the
original pulse and the interrupt.
Each node collects data and maintains a running
average of the oil height at a specific spatial
location. This data is then sent to a central
server which can aggregate the data from each
node and model the entire oil spill. The
simplest model of an oil spill assumes a
perfectly lenticular shape with this assumption,
it is possible to interpolate the results from
each node and create an accurate model of the
spill. In the AquaNet system, the data is
extracted from each node into a text file. This
file is then analyzed with Matlab to generate
multiple plots of the oil spill. A Visual Basic
interface is subsequently used to allow quick and
efficient visualization of the spill. The user
has the option of either viewing the raw data and
individual node plots, or can view the entire
spill in multiple plot types.
Preliminary Results
The measurement of oil can be divided into two
modes of operation. In the first mode, the oil
layer is thick enough to ensure that the
reflected signals do not overlap. In this
domain, the software is able to correctly predict
the amount of oil present. As the graph shows,
the time difference between the reflections from
the water-oil and oil-air interfaces is linearly
related to the amount of oil present. The
experiment predicted the speed of sound in oil to
within 10 of the true value of approximately
1550 m/s, and the oil thickness to within 5
millimeters. The second mode of operation
represents sub-wavelength oil heights. In this
scenario, it is possible to manually determine
the amount of oil present via the interference of
the two received pulses. Oil heights can thus be
calculated within 1 millimeters.
Interface displaying user choices and outputs.
Shown here is a surface plot of the oil spill and
bar graphs for the individual sensors.
Graph of oil height vs. time between reflections
Patent Pending