Autonomous Monitoring of River Level with Real Time Event Prediction

Observation of water level at various river sites could provide valuable insight about probable disaster in advance to initiate disaster management protocol as early as possible. We have developed an autonomous remote river water level monitoring network with event prediction algorithm at the server while maintaining a substantially low manufacturing cost. The WSN is comprised of several chosen sites based on their statistics with intelligent sensors for water level measurement. The sensors are autonomous in nature to account for any disturbance in node environment and also within the network. The real time data are transmitted to a remote server through GPRS for further processing. Server extracts information and simulates various real time parameters such as water level rise rate, time remaining to exceed the critical level for a particular site etc. A prediction algorithm running on the server side predicts the measured level values for each node over a period of time. A prototype system is implemented with six nodes at different points and has yielded satisfactory results.


Introduction
In coastal countries where rivers are flowing everywhere through lands, flood is considered to be one of the most common natural disasters.About 100,000 persons are killed and over 1.4 billion people are affected during the last decade of the 20th century as described by S. N. Jonkman (Jonkman, 2005).Continuous monitoring of river water level at alarming points could provide with valuable information that can be utilized to warn authorities and inhabitants well ahead in time.A review on conventional river water level measuring showed that river level monitoring by constructing piezometer on the location under investigation is somewhat costly and requires human presence for data collection (Winter, LaBaugh, & Rosenberry, 1988).Therefore, information cannot be gathered ahead in time.The modern sensor network for this purpose has pressure sensors installed at different points to acquire data with high precision.But the use of this kind of networks is limited by the cost involved with installation and maintenance.For developing and under developed countries where such costly method is not a viable option, the threat of mass destruction by sudden flood is still at large.The only solution is to find a low cost system that could provide a near precision measurement and timely warning so that if water level is about to exceed the critical level, concerning authorities might be able to be prepared to minimize the figure of flood caused deaths and immense harms.This paper illustrates such an autonomous wireless sensor network (WSN) for twenty four hour river water level surveillance and alarming tasks.This article is a revised and expanded version of a paper entitled Design and Deployment of a Robust Remote River Level Sensor Network, presented at IEEE Sensors Applications Symposium, TX, USA, February 22-24, 2011 (Chowdhury et al., 2011).The sensor network architecture is illustrated using a block diagram shown in figure 1.At the heart of this network, a server collects data periodically sent from installed nodes (Node 1, Node 2… Nodes N) placed at different sites along the rivers.The nodes are responsible for raw data collection, storage and transmission to the server after initial processing.Existing GSM (Global System for Mobiles) network is Along with these sections, a few voltage divider networks are used to feed voltage signals to MCU.This section actually monitors different parameters from other sections, e.g.node battery voltage.The voltage is converted by MCU and sent to the server along with other data.

Explanation of Acquisition Process
When the system is switched on, MCU initializes the modules necessary for system operation.After the initializations are being done, GLOBAL interrupt is enabled to allow the external interrupts.The contents of count register of TIMER1 and capture register are cleared.MCU starts sending 40 KHz pulse whose transmission length can be varied from the firmware.After a transmission pulse is sent, there is a chance that the transmitted signal could directly fall on the receiver.This could trigger a wrong detection.To avoid this scenario, the signal from the echo detector is disregarded until a certain period of time is elapsed which ensures the avoidance of reception of the transmitted pulse directly instead of the echoed signal.MCU waits 1 ms and then enables the detector circuit.Just prior to this, the capture module and timer modules are turned on.TIMER1 starts to count the number of pulses between the turn on and another pulse to indicate the end.When an echo is received, the capture module turns off the timer module and the count value is stored.From the timer count, the time taken by the echoed signal to traverse the length of the tube above water is calculated.If the time taken by the sound wave to return to the module is t seconds, the one way distance traversed by the transmitted wave before being captured by R X will be: l = (v × t )/2, where v = velocity of sound at a specific temperature.If the clock of TIMER1 is configured as to count 1µs/count, the value of the TIMER1 count register will indicate the number of instances elapsed since US wave is being transmitted.It takes k microseconds to execute one instruction for a PIC MCU with an F MHz clock where, k=1/F.This count value is used as the value of t.Hence, the TIMER1 module must be configured very carefully depending on the system clock.Before transmitting the signal, MCU samples the temperature sensor data to get the instantaneous temperature value and sets the value of v to be used in that calculation.The dependency of velocity of sound on temperature is governed by this formula: Where T is temperature in degree Celsius.A lookup table (LUT) containing values of velocity for every 1 °C increase in temperature between the range 5 °C-50 °C is used by firmware after acquiring temperature revision data for appropriate value of v.The actual water column height is determined afterwards which is stored and sent to remote server.The whole system process is illustrated in Figure 5.

Node firmware
The software works in two successive steps: one is for acquiring column height and another for storing and sending the data over internet.MCU is loaded with software to carry on the signal generation, reception, data acquisition, data storage and data transmission tasks.The coding steps can be visualized with the help of a flow chart which is shown in the Figure 6.After the system is switched on, built-in timer module TIMER0 is initialized with a calculated pre-scalar so that the timer counts up to 65535 which indicates a timeout of 65 ms at 4 MHz clock speed used for controlling purpose of transmission period.TIMER1 is initialized to capture the echoed signal from the slab surface.Capture module CCP1 is turned off to prevent the module from capturing noise.A temperature revision data is input to A/D channel which is used to get the current velocity of sound from a LUT.As the river surface should have some disturbances in terms of current and waves, there must be situations when the successive readings will yield data which are different from each other significantly.To mitigate this effect, multiple reading are taken during a single measurement and then averaged to get a value that lies in between the maximum and minimum values with minimum aberration from the true value.A variable r is declared to have a null value that indicates the number of readings taken.Enabling the interrupts, MCU declares another variable k which is also assigned a null value at the beginning of a process.The limiting value of k defines the number of readings per measurement cycle to be made.Signal transmission is initiated by MCU and continues for a period of 0.5 ms.

Measu
The screen   Morita, & Okuma, 2001) could be proved to be a solution.USB modem can be a great replacement in this system for utilizing 3G (Third Generation) connectivity for faster and more reliable networking.Firmware for USB connected modem could also reduce the power and spatial concerns for RS232 supported modems.The data analyzed by the server can find additional uses in other applications and researches also.The nature of water level of any particular river in each season can be taken into account to plan for the agricultural aspects of the nearby localities.Architects can decide whether the place under consideration is reachable to flood and design structures accordingly.Geographically important information such as time of high tide, low tide and any behavior other than normal could be extracted from the analyzed data.Using multi sensor-multi node technique in single installation site, change in depth of river bed can be understood.Advanced statistical analysis of the information could provide pattern of river level rise and fall over a long period of time which could be useful understanding the effects on sea level by phenomenon like global warming.With sufficient data, a database could be built to observe the current scenario of the water level rise over a period of time which could give us a fair idea about the effect of global warming over a particular geographical area.
Real Time Clock (RTC) generation: To stamp the events in real time, there is a real time generation section.This is actually a RTC integrated circuit (DS1307) employed to operate in I 2 C slave mode over a two-wire serial bus with MCU acting as the master.The design is done according to the application note provided byMaxim  Integrated Products (2006).Timing information is stored in 56 bytes of NV (Non-Volatile) SRAM from where it is fetched by master when necessary.
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