Group 21:

Ramapriyan Pratiwadi

Sameer Qudsi

Sandip Saha

Advisor: Dr. Jay Zemel

Presentation Times:

April 22, 2004

9:30 AM – 10:00 AM

11:30 AM – 12:00 PM

1:00 PM – 1:30 PM

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.

AquaNet: Ultrasonic Measurement of Oil Spills

Signal Processing Aggregate Modeling

Preliminary Results

Transducer OperationAn 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.

Patent Pending

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.

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.

Apparatus

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.

Waveform of reflected signals and processed signalTransducer output and reflected signalsDiagram and photograph of apparatus

Graph of oil height vs. time between reflections

Interface displaying user choices and outputs. Shown here is a surface plot of the oil spill and bar graphs for the individual sensors.

Time Between Reflected Pulses vs. Height of Oil

y = 1662x + 0.0253

R2 = 0.9927

0.000.100.200.300.400.500.600.700.80

0 0.0001 0.0002 0.0003 0.0004 0.0005

Time Between Reflected Pulses (s)

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