Rain gauge simulator and first tests with a new mobile climate alert system in Brazil
© Xavier et al. 2016
Received: 22 December 2015
Accepted: 11 May 2016
Published: 6 June 2016
Recent national developments in alert systems are the main motivation of this work. The aim is to provide an account on the development and first tests of a new Meteorological Alert System—MAS for mobile devices to deliver alert signals. The fundamentals encompass a summary description of the Brazilian government towards the installation and maintenance of a national wide climate sensor network where the new Meteorological Alert System can be integrated. The main challenges in installing and maintaining such a network in face of its continental scope are presented.
The method describes the emulation of rain precipitation, which requires (a) the development of a data model for rain gauges (called DCP, or Data Collection Platforms) and (b) a data interface with the existing network. After testing several rain simulation models, the DCP system is converted into a signal server to provide parametric regulated data. The emulator facilitates the creation of pluviometric surrogate data and therefore the test of extreme situations. The MAS system is completed by the development of a front-end mobile application where the alerts are received by end users. We discuss classes and metrics used to evaluate the emulator performance and its integration to the alert system. We describe the DCP data structures, the rain simulator functions, and its interface with the MAS.
Rain gauge emulated data sets for several parametric conditions and test performance results of the mobile application integrated to the rain emulator are discussed. We present and discuss an interface to easily access the entire rain gauge network using mobile devices.
Alert acquisition by the end user is a complex sequence of commands and integrated hardware involving a considerable amount of numerical work in weather forecasting. Consequently, modeling the information flow, and performing tests of a mobile application, justifies our initiative as a set-up stage prior to massive dissemination of an alert system fed by real data.
It is hard to estimate the value of information prior to a weather disaster or a significant risk situation caused by nature. Currently, advanced information is the only solution readily available against an imminent risk state. The term disaster implies a situation of increasing or fatal vulnerability while the word, as defined by , is “the characteristics of a person or group and their situation that influence their capacity to anticipate, cope with, resist, and recover from the impact of a natural hazard.” Information is however a simple word which encompasses several ideas such as validity, trustfulness, and accuracy. Such ideas are all important to the advanced recognition of a distressful incident often endangering countless lives and causing substantial economic and social damage. Another relevant requirement of a good warning system is easiness of access; otherwise, all benefits conveyed by such “highly precise, valid and trustful information system” are unreachable.
The idea of automatic meteorological alert systems exists since the availability of communication networks [2–7]. In particular, the demand for Disaster Alert Systems or DAS and, more specifically, Flood Alert System (or FAS, see  and ) have grown substantially both with population increase [9, 10] and the occurrence of climate change [11, 12]. The issuing of an (useful) alert is understandably a complex activity involving arrays of sensor networks and data on one side and much work in processing and analyzing data on the other, so as to have a minimum degree of reliability. Moreover, the issuing act is a decision problem  which naturally involves authority validation . The planning, development, and implantation of a national FAS for the entire country require a network covering about 8 million square kilometers. As such, there are several advantages in planning the system by the use of computer simulations [15, 16]. This task may be undertaken by setting up a simulation environment where all sensor network components and issue subsystems are conveniently modeled  and their performance analyzed. In particular, long time reliability of remote sensors—whose link is only possible via cabled or wireless links—should be taken into account as a network performance parameter. For wireless sensors (devices whose physical layer involves radio links), the influence of climate is a crucial factor since it is known  that water can attenuate electromagnetic wave propagation. Therefore, the effectiveness of the final alert signal may be severely impaired when it is most needed: at the imminence of a disaster.
The project of planning and integrating a large network of remote sensor data to render trustful alerts is a formidable task. There are application opportunities for both theoretical and practical aspects of computer science and software development, from sensor choice to programming the end user mobile interface. Moreover, it involves legal aspects related to the responsibility of delivery and sustaining a continuous service of information that becomes vital with the ongoing threat of climate change. This paper also emphasizes the importance of software engineering in the Brazilian context .
Research design and methodology
Technically, an alert system using CEMADEN data is in fact a FAS with additional landslide signals  for restricted areas. DCPs are autonomous systems (Fig. 1 (left) shows one type) installed on both urban and rural areas which communicate via GSM/GPRS links . DCP installation and maintenance are an ongoing process and involve detailed analysis of the target spot often recruiting specialized personnel and demanding transportation planning, since many DCPs should be located in remote areas like dense forests and other inhabited zones. Since GPRS links are privately owned and may suffer from link suppression for a variety of reasons [26, 27], efforts have been made by our group to find network alternatives. These may involve, for example, the use of satellite links (which, depending on the frequency used, is also prone to rain attenuation, see  and ) or alternative government-operated networks.
Regarding pluviometric DCPs, data are sent to SGRP via FTP regularly, depending on the weather, in the form a file using a protocol specified by CEMADEN. The file contains georeferenced information about the DCP spot (pluviometric temporal data and maintenance information). If there is no rain, files are dispatched hourly while the update rate falls to 10 min in case of severe rain. An internal buffer saves rain gauge countings and promptly delivers an updated file with all accumulated measures as soon as communication is restored after an event of link suppression. Therefore, although a single or groups of DCPs may be unreachable at a given moment during rain extremes, data are never lost but suffer a natural delay due to the intermittent status of the communication link. Present reports of DCP availability in time are 92 ± 4 % on average for all Brazilian states.
On the social level, there are several challenges of installing and supporting the variety of DCP types and their configurations across 8.5 million square kilometers. Data provided by ANATEL (Brazilian Telecommunication Agency, see also http://opensignal.com/ ) estimate that over 90 % of the Brazilian area are serviced by mobile connections, so natural choice for each DCP communication is the GSM/GPRS channels. CEMADEN network is therefore served by four major mobile carriers in the country: Vivo (Telefonica), the largest one responsible for 29 % of the Brazilian market share, TIM (Telecom Italia) with 27 %, CLARO (Amrica Movil) with 25 % and the remainder served by OI (CorpCo), a joint venture with Portugal Telecom. Thus, data communications employs packet data transport via GPRS (General Packet Radio Services) which is a packet-oriented mobile data service on the 2G and 3G GSM cellular global system . A major advantage of GPRS is its simplified access to the packet data networks like the internet. The packet radio principle is employed by GPRS to send user data packets in a M2M way between GSM DCP stations and external data networks. These can be directly routed to the packet-switched networks from the automatic hydro-meteorological stations. As is well known, GPRS throughput and latency are variables that depend on the user number simultaneously sharing the service. The GSM/GPRS transponders installed in every DCPs provide data rates up to the third generation (3G). Although the feasibility of such communication system has been demonstrated, there are clearly limits for both quality of service delivered (QoS; national coverage area of the GSM/GPRS network, service call time) and sensitivity to climate change (service loss during heavy rainfall).
In order to test a platform, for a massively distributed FAS, the following section describes a DCP numerical model, which emulates CEMADEN-formatted file flow as a surrogate data generator, a simplified dispatch system, and DTR-ADS (DTR Alert Dissemination System) specially designed for the purpose of disseminating alerts to the population. In this sense, our works integrates with the already existing network resources, readily allowing alert dispatch.
Emulation of DCP data generation is justified by the need of debugging a DAS prior to system delivery to final usage and by the difficulty of testing the real system. Accordingly, the output of the emulation system is the input of the alert system. With such scheme, it is possible to push the DAS to extreme and improbable situations when all DCPs (amounting to thousand units) would signal critical events at the same time, i.e., generalized rain gauge above a certain threshold. This scheme allows to test the resulting performance of the message delivery system as a DAS component without using real data. Another interesting feature of a simulation environment is the possibility of integrating DCP data into clusters and testing the incidence of network delays upon the efficiency of the delivered message.
Construction of a DCP data class;
Programming the class methods;
Definition, programming, and calibration of rainfall thresholds for alarm delivery;
Construction of an output interface (which in our case is integrations to the DAS system).
Network parameters can be added to the DAS interface as, for example, DCP-dependent link rates. Of particular importance is phase 4 where signals are triggered on the base of rainfall thresholds. In order to keep the model simple in a first approach, each DCP has its geographical position referenced as a simple attribute. Real alert signals may be created by integrating information over vast catchment areas in the cases where the network sensor density is below a certain value. Alert signals should ideally take into account soil features such as topology, porosity, and permeability, along with the need of solving hydrological models on real time . For simplicity, our model allows the reproduction of real cases by proper calibrations of statistical rain distributions instead of using first principle modeling.
Input: DCP identification number associated to an address
Input: DCP type
Input: DCP or alert zone latitude
Input: DCP or alert zone longitude
Input: DCP alert zone radius (in kilometers)
Input: DCP initial working date in Julian dates
Input: complete DCP simulation period
Input: percent of simulation time covered by rainfall
Simulation input parameter (see Eq. 1)
Simulation input parameter (see Eq. 1)
Input: rain generation rate within the simulation period
Input: alert time-out period
Input: critical volume triggering an alarm
Output: tipping times as a vector of dates
Output: rain volume in millimeters
Output: date of the DCP alert issuing
Output: integer returning alert severity
Output: total amount of rain
Input data for a collection of DCPs (see
Input of simulation-dependent variable
Output vector of tipping times in Julian
Date for a given DCP
Integrated output pluviograph of a
Sequence of issued alert types and times
for a given DCP
Function name (Fig. 5)
Responsible for fitting a stochastic model
to generate gauge tippings
Collects tipping times in Julian dates for
a given DCP
Integrates rain volumes within a given time
Write output of CalculatePluviographs()
Responsible for running the simulator logic
of alert generation
Responsible for dispatching a sequence of
alerts to the user alert zone
Each DCP is the geographic center of an “alert zone” which defines the area where potential targets (DAS users) may be associated by their maximum radius distance from the DCP. As a consequence of model simplicity, the so defined alert defined is a circle of a predefined radius where a specific alert type may be issued.
where β and γ are two positive parameters (see Table 1). The distributions of rain showers (say, their frequency in 1-month interval over a given DCP) as well as rain duration (how long a shower lasts) were generated by uniform distributions. Within each shower interval, however, the distribution of tipping time intervals was modeled by Eq. 1.
DTR-ADS scores and standard deviation according to Nielsen methodology 
DTR-ADS application software represented on the bottom left of Fig. 5 was integrated to the emulator program in order to test the delivery of alert signals to mobile devices. In the currently installed DCP network, massive alert relies on radio frequency broadcasting to distribute messages. The popular use of cell phones gave rise to a plethora of applications which greatly improve public dissemination. In particular, it is possible to generate specific alerts, that is, warning messages targeting a specific region at delivery time . Therefore, the only additional information required is location, which does not need to be fixed, since most modern cell phones are integrated to GPS units  or access their position using GPRS . DTR-ADS is a cell phone delivery message system which implements an alert server, a mechanism for users to visualize the entire network map status, and a way to register their location and receive alerts. The emulation version associates a circular zone around each DCP. Every time an alert is issued to that specific alert radius, all pertinent users receive a warning either through a Short Message Service (SMS, ) or an interaction with the phone alert software as described in this section.
Android platform [41–43] was chosen as the base operational system (OS) in accordance to the overall number of mobile devices per OS users in Brazil . DTR-ADS was built using FOSS guidelines (Free and Open Source Software)  and their fundamental programming tools are Android Studio SDK , Java SDK , and WAMP (Windows, Apache, MySQL, and PHP, ). HTTP (HyperText Markup Language, ) was used as the data control and access protocol.
An “administrator” who can access all system functions and is responsible for its operability and maintenance;
A “monitor” or agent responsible for situation registration (a situation is the state of a potential alert issuing for a given region), monitoring, alert issuing, and canceling;
An “end user” or the final and public entity interested in the alert and associated to at least a target zone.
Results and discussion
As for the adequacy to the user, the DTR-ADS testing used four cell phone brands (with different versions of of Android OS installed) and involved the distribution of cell phones for several testers (< 10 individuals). Users were invited to register themselves at predefined physical locations. The integration of the DCP emulator and ADS was tested together with an evaluation of the ADS interface in three different mobile brands using Nielsen methodology [53, 54]. From 0 to 10, usability, utility, and satisfaction were scored as shown in Table 3. The metrics used in assessing satisfaction consist of asking users to execute each of the software functions—without knowledge of its objective—before filling out a questionnaire. A complete test sequence was also run including downloading, installing, validating, and executing the application on each of the three mobile devices.
The advantage of using a circular area and the scheme adopted for the emulator is apparent for treating landslide alerts , which does not involve rain gauges. Although a strong correlation between heavy rain and landslides has long been established [56, 57], the problem of landslide alert is much more complex since it also depends on geological processes.
This paper describes a meteorological network emulator system that simulates data from thousand sensors and their integration to a mobile alert system application designed to end users. Rain data, produced by a stochastic rain generator, emulates the average volumes expected for a given place. Rain gauge data structures follow a DCP modeling that associates a given alert to a circular zone region centered on the DCP position. The area of one alert zone may be modeled by using arbitrary shapes . The resulting system is able to generate real-time alerts. It can test the effect of impairing factors on the overall performance of the communication process of a massive network of sensors.
Real data from CEMADEN DCP network can feed the alert system in this way by substituting outputs from the emulator by the gauge data associated to a specific radius centered on a real DCP. This procedure was implemented after the first emulator tests. Just as in the case of an emulated DCP, differential pluviometric volumes trigger flood alerts. In this model, each DCP is an alert source of pluviometric data. This is a simplified approach, since the real issuing of an alert is the result of a complex analysis involving decision taking and data processing. Nonetheless, the correct DCP risk degree can be set by changing the alert threshold for each sensor unit. Therefore, we have completed the development cycle as far as the alert interface is concerned. The mobile application can be improved by allowing users to provide real-time feedback such as images or describing the local status by sending messages. In fact, a simple questionnaire could be filled in by users after receiving an alert. In this way, the population would also understand the importance of actively participating in the alert system, which should not be limited to the automated network. Data collected by the population could be integrated, processed, and used to “tune” (or train) the alert dispatch system in a positive way so as to optimize its trustfulness and signal reliability (to access and confirm the performance of the dispatched signals, which is obviously impossible to be emulated by any automated method). The challenge of closing this positive cycle is big in Brazil, given the continental size and the variety of socio-economic contexts.
AD, analog-digital; ADS, Alert Dissemination System; ANA, Agência Nacional de Águas (National Water Agency); CEMADEN, Centro Nacional de Monitoramento de Alertas e Desastres Naturais (Center for Natural Disaster Monitoring and Alerts); CENAD, Centro Nacional de Gerenciamento de Riscos e Desastres (National Centre for Disaster and Risk Management); CPU, central processing unit; CTI, Center for Technology of Information; CURL, client uniform resource locator; DAS, Disaster Alert System; DCP, Data Collecting Platform; EGSM, Extended Global System for Mobile Communications; FAS, Flood Alert System; FOSS, free and open source software; FTP, file transfer protocol; GPRS, General Packet Radio Services; GSM, Global System for Mobile Communications; HTTP, hypertext markup language; KML, keyhole markup language; MAS, Meteorological Alert System; RS, recommended standard; SDK, Software Development Kit; SGRP, Sistema de Gerencialmento Remoto de Plataforma (Stations Remote Management System); SMS, Short Message Service; WAMP, (Windows, Apache, MySQL, PHP).
We are grateful to Dr. Carlos A. Nobre, Dra Regina C.S. Alvalá, from CEMADEN, Marcos A. Rodrigues, and Germano Beraldo from CTI for important discussions. This work is supported by the MCTI—the Brazilian Ministry of Science, Technology and Innovation. Special thanks to Silvestre R. de Aguiar Jr, from Coordenação Geral de Meteorologia, Climatologia e Hidrologia—SEPED/MCTI—Secretaria de Políticas e Programas de Pesquisa e Desenvolvimento.
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