Abstract-We describe the use of a multi-metal electrochemical cell for measuring ocean pH. The sensor was designed to be robust, inexpensive, and capable of 0.02 sensitivity to pH in the narrow ranges required for marine pH monitoring. A prototype sensor has undergone an extended ocean deployment with promising results.Ocean Sensors; pH Sensors; Metal electrochemistry; Arduino.
I. TECHNOLOGY APPROACHThe idea behind the sensor comes from the very low cost unpowered sensors used for soil pH measurements [1]. These simple meters use two metals to generate a potential that is read on an analog meter and are surprisingly accurate at measuring soil pH. We purchased and tested many of these sensors and were very impressed with the accuracy and repeatability of this simple technology. Based on this idea we measured the potential across Zinc and Copper in pH buffered solutions of Instant Ocean. We found that we could calibrate the electrochemical cell to approximately 0.02 pH for the pH 7-9 range. This led to the idea that we could use metals for a useful low cost ocean pH sensor.
II. POTENTIAL PROBLEMSBiofouling and corrosion will alter the metal surfaces over time [2], and the metal surface potentials will be sensitive to chemical potentials other than just pH. To overcome this we propose using metal diversity. We are currently using 9 different ¼ inch metal rods in our prototype sensor (Figure 1). These are all mass produced and available at low cost.
A damaging earthquake of Mw 7.7, which struck the Bhuj region of India on January 26, 2001, was followed by a large number of aftershocks. The aftershock data available at Gauribidanur Seismic Array Station (GBA), India, till 869 h following the main shock were compiled. The plot of the aftershocks rate with time was found to be oscillatory decay. There was a sharp decrease of the aftershocks rate in the initial 144 h from the main shock and this paper presents the analysis of the temporal characteristics of aftershock activity during this period. A statistical best fit for the rate of aftershocks is performed using the generalised Omori's law and the exponential decay law. The statistical errors for the exponential fit are found to be lower than that of the generalised Omori's fit. The superimposed oscillations present in the aftershock activity are extracted by differencing the observed aftershock activity from the statistical fits. The frequencies of these oscillations are found to be 0.062 h -1 , 0.078 h -1 , 0.102 h -1 , 0.118 h -1 , 0.141 h -1 , 0.164 h -1 , 0.233 h -1 and 0.476 h -1 . Some of the plausible causes for this kind of oscillations present in the aftershock activity are also discussed in this paper.
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