Low Cost Autonomous Field-Deployable Environment Sensors

An Autonomous Environmental Sensor (AES) is a miniature electronic package combining position location capability (using the Global Positioning System (GPS)), communications (packet or voice-synthesized radio), and environmental detection capability (thermal, gas, radiation, optical emissions) into a small, inexpensive, deployable package. AESs can now be made with commercial off-the-shelf components. The AES package can be deployed at a study site by airdrop or by workers on the ground, and operates as a data logger (recording data locally) or as a sentry (transmitting data real-time). Using current low-power electronics technology, an AES can operate for a number of weeks using a simple dry battery pack, and can be designed to have a transmitting range of several kilometers with current low power radio communication technology. A receiver to capture the data stream from the AES can be made as light, inexpensive and portable as the AES itself. In addition, inexpensive portable repeaters can be used to extend the range of the AES and to coordinate many probes into an autonomous network. We will discuss the design goals and engineering restrictions of an AES, and show a design in a particular application as a wildland fire sentry. INTRODUCTION AND CONCEPT Studies in ecology, biology, geology and other fields often require collection of data in widely dispersed remote locations. The recent attack on the United States by extremist groups has created new requirements for remote and sometimes clandestine monitoring of radiation, airborne chemicals and microbes. Current data collection methods are cumbersome, expensive and manpower intensive and do not usually provide measurements over an extended period of time. For example, monitoring the surface temperature of a body of water to study its hydrodynamic and biologic properties is commonly done by field biologists, most often by crews collecting data manually from boats. A system that could automatically measure and process a number of physical parameters in a remote setting would thus be embraced by workers in a large number of fields. A tremendous advantage is obtained if such a system could be built inexpensively and adapted for a variety of applications without extensive redevelopment. We call such a low cost environmental re-configurable data collection system an autonomous environmental sensor (AES). Recently, advances in positioning capability (using the global positioning system), electronics design, component packaging, networking and radio communication technology have made it possible to construct the AES in lightweight, compact inexpensive packages. The AES has the ability to record and analyze data and report the data and the position of the device by radio to a collection station. These devices can be deployed using a variety of means, and could collect data continuously, periodically or on command. The collected data can be reported immediately, stored and forwarded at a known time, or stored and retrieved later if the AES is recovered. Technology is available for recording a wide variety of physical parameters using inexpensive, compact sensors. Some of the environmental parameters and the corresponding sensors suitable for monitoring by AES are shown in Table 1. An AES can be constructed using commercially available off-the-shelf components and software, speeding development time and minimizing the cost of the devices. Many of the devices and software developed over the last ten years for the cellular telephone and Internet computer infrastructure can be applied directly to the AES concept. The savings in development time and cost are substantial allowing simple AES systems to be deployed for as little as $100 each. (US$2002) AN EXAMPLE APPLICATION: WILDLAND FIRE SENTRY One of the major problems in combating wildland fires is monitoring the time history of the fire [1]. Understanding the size, location, and progression of the fire front is critical to optimal allocation of fire fighting resources and maintaining safety of the fire crew. Investigation of major wildland fire accidents involving loss of life indicates that the crews became imperiled because of insufficient or untimely information about the location and progression of the fire [2]. An AES can be used as a field deployed fire alarm that has the ability to report its location and whether a fire is in the vicinity. A fire can be detected by one or more inexpensive sensors in the AES that detect smoke, carbon monoxide, methyl chloride or temperature. These devices may also be equipped to record and transmit other data affecting fire spread like humidity and wind speed. The data gathered by the AES can be recorded locally to get a post-fire time history and is also transmitted by radio to individual firefighters equipped with appropriate receivers or to a central control receiver. At present, once firefighters are on the ground near the fire site, they are effectively blind to the activity of the fire. Spotter planes and other aircraft may periodically over Table 1. Environmental measurements suitable for monitoring with inexpensive sensor systems. Environmental Parameter Sensor Cost (US$2002) Temperature Thermistor and signal conditioning (+/0.2K) 3 40 Humidity Capacitive humidity sensor 10 Solar Flux Cosine-corrected photodiode and signal conditioning 30 Radioactivity (α,β,γ) Large area PIN photodiode and signal conditioning 50 Wind Speed Thermistor cooling-rate monitoring 30 Water Turbidity, Particulate Smoke IR 90 scattering cell 5 Gas Detection Catalytic or electrochemical sensor and signal conditioning 5 30 fly the area and report the movement and location of the fire to the incident commander, but often even this rudimentary data is lacking. In its simplest use model, AESs provide direct real time voice data to firefighters on the ground. The time history of the fire can be kept manually by the incident commander by recording the position and time of AES fire alarms on paper maps. Much effort has been expended in modeling the movement of fires in wildland settings [3,4] but these models are only as good as the detailed weather, terrain and fuel load information. Lacking precise information of the fire site, these complex fire models can predict fire behavior for short time periods, but must then be 'tuned' with actual data to obtain long-term accuracy. These fire models are similar to modern weather simulations that are similarly adjusted periodically with weather data to provide long-term modeling. Using AESs, and armed with handheld computers running these fire models, firefighters will have accurate real-time data for model 'tuning', and may be able to more accurately predict the behavior based on past fire movement even when only very imprecise weather, fuel and terrain information is initially available. The ability to predict the movement of the fire is a powerful advantage to fire logistics and firefighter safety. The use of satellites to obtain fire data for model tuning is feasible, but complications are imposed by limited satellite spatial resolution, complicated ground link equipment, and short satellite loiter time (for low Earth orbit satellites) over the target area. Real time data can be obtained using unmanned or remotely controlled unmanned flying vehicles (UFVs) flying over the fire site, but this solution is both FIGURE 1. Deployment and communication between AESs and base units, other AESs and firefighters in a fully networked system. complex and difficult to support in the field, and would require additional worker training to operate and maintain the UFV. A small number of AESs that are located in the forest could provide this data at low cost and with little additional effort in training or support. We present both advanced and simple AES communication concepts and show the initial design of a prototype. OPERATIONAL CONSIDERATIONS In use, AESs can be dropped from an aircraft or unmanned airborne vehicle (UAV) or placed manually by crews in a study area. The mechanical package of the AES can be designed for any of a number of applications, including urban environmental monitoring, wildland monitoring, or as drifters on bodies of water. The devices periodically report their position and status to each other, to a central receiver, or to radio receiving equipment carried by individuals. After they are deposited in the fire area, AESs will find their location (via their internal GPS receiver) and report their initial position and fire alarm status via a radio link.