Technical Note: Where are my cattle at? – Part I: GPS Sensors
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Global positioning system (GPS) technology has been implemented into the agriculture world in numerous ways. It is a satellite navigation system based on real-time geolocation and time information. GPS data can be a useful tool to maximize production, manage more efficiently, and reduce costs. Farmers have proven the positive benefits of integrating GPS technology in their operations, such as tractor guidance, planting, application rates, and yield mapping. Recently, livestock producers are looking for ways to use GPS technology to observe cattle behavior in correlation with field topography, pasture management, and resource allocation. A study was conducted at the UNL feedlot near Mead, NE to evaluate two types of GPS tracking sensors placed on yearling steers grazing a smooth bromegrass pasture for a one-month duration.
What is GPS and how does it work?
GPS stands for “global positioning system” and is comprised of three main components: satellite fixing, ground stations and receivers. Surrounding the Earth, satellites function as the central hub held at an absolute known location. A ground station interacts with the satellite calculating the distance between the two. Receivers such as smartphones and GPS sensors constantly measure distance and signaling connections from the satellites. After verifying the distance between the receiver and multiple satellites, GPS data, including timestamp, latitude, and longitude are generated. Because consecutive GPS data are received, the relative velocity representing the GPS sensor’s movement can be calculated. The headed degree between two consecutive GPS fixes can also be obtained in newer GPS sensors with built-in accelerometer components.
Types of GPS sensors
GPS technology emerged during the early 2000s. The initial cost of GPS sensors was relatively expensive, ranging from $1,500 - $2,000 each. Thanks to modern technological advancements, numerous types of GPS sensors are available on the market today varying in multiple features at an affordable price. Price per sensor depends on accuracy and functionality. An average cost for a sensor to accurately measure a position within 10 feet can range from $75-$300, while others with capabilities measuring sub-inch measurements can easily exceed thousands of dollars. GPS sensors coupling the state-of-art Internet of Things (IoT) technology also provide the benefits of real-time monitoring and convenient data acquisition. What is IoT? A simple example is how are you reading this BeefWatch article right now! You may be reading it through your desktop computer, laptop, smartphone, or tablet. Whichever you find most convenient to use, it is connected to the internet. Thus, IoT can be simply defined as things that can be connected to the internet. Our objective was to assess GPS sensors from two generations and find a sensor suitable for cattle tracking providing us with reliable and accurate location data associated with a justifiable cost.
The first sensor we evaluated was a GPS travel logger that utilizes the SiRF GPS chipset and built-in memory card (Figure 1), costing $75-100. This type of GPS sensor was first available in 2010 and was popular for travel and sports use. This logger is powered by six 3.7 lithium-ion rechargeable batteries and has a mean location fix accuracy between 30-35 ft. The longevity of the battery depends on the fixing interval, meaning how often you want a location recorded. Battery life was evaluated by observing how long the logger would record from the initial turn-on time with a 10-minute fixing rate until the battery was unable to supply enough power to record data at a stationary location. Set at this interval, our battery life test lasted approximately four weeks. The battery charging duration was four days prior to monitoring. Other capabilities the travel logger featured but were not evaluated included distance traveled, elevation, and rate of speed.
The second sensor observed was an IoT GPS sensor that utilizes the Long-range and wide-area (LoRaWAN) communication protocol (Figure 2). LoRaWAN sensors came to debut only a few years ago and have gained increased interest and usage in multiple disciplines such as fleet tracking, factory environment monitoring, and agricultural business. The retail prices for the LoRaWAN GPS sensors vary between $50 – $100. This sensor operates on commercially available lithium batteries and has a configurable location fix accuracy between 15 – 65 ft. It was also tested for battery longevity prior to initial use set at the same time interval of 10 minutes that lasted on average for 5 weeks. A unique option this sensor came equipped with was the ability to access the sensor’s location via computer or phone in real-time while the sensors were actively monitoring (Figure 3).
Each GPS sensor was turned on and placed inside a plastic housing mounted on a polymer collar. One sensor was assigned to one collar, with each steer being assigned both sensors mentioned above for comparison (Figure 4). After a four-week recording period, the collars were removed from the steers for GPS sensor performance analysis. Computer software specific to each sensor was used to download the data.
Here is a summary of the highlight features of each GPS unit. The LoRaWAN GPS unit has clear benefits and conveniences over the SiRF GPS unit. Accessing data from SiRF sensors requires connecting each sensor to a computer to view/download data, while the LoRaWAN technology allows for user-friendly features such as remotely accessing the data in near-real-time. Data retrieval of the SiRF unit or confirming the status of the datalogger was not possible during active monitoring. For the LoRaWAN units, we were able to visually see where the cattle were located throughout the day, time spent in certain areas of the pasture, and obtain data files per user preference (e.g., every day, every week), along with an indication of battery life. On the other hand, the SiRF units allow battery recharging, while the LoRa units take retail available AA or AAA batteries.
How can GPS be implemented in the livestock sector?
The ability to locate cattle grazing actively and accurately could benefit ranchers and producers in improving grazing management decisions. Rangeland can greatly differ in size and pasture composition, which can pose a challenge to locate cattle, particularly with limited labor available. GPS technology has evolved to where we can monitor real-time or near-real-time locations. This tool can be utilized by operations to locate livestock in relation to pasture boundaries, accurately manage resources, and cut down labor costs by reducing time spent checking cattle. It can also detect the amount of time animals spend grazing in certain areas of pasture and further investigate its relationship with water availability and forage quality. GPS technology has various uses within the cattle industry and will continue to expand with ongoing research.
Did you enjoy reading this article? Stay tuned for the July issue featuring: Where are my cattle at? – Part II: Virtual Fencing.
Interviews with the authors of BeefWatch newsletter articles become available throughout the month of publication and are accessible at https://go.unl.edu/podcast.