Yield Monitoring and Mapping in Precision Agriculture
Combine Harvester Components
Yield Monitor Console
The yield monitor console (Figure 11.1) is a data collection unit and computer that records data from the yield sensor, moisture sensor, and DGPS receiver. The display is also used by the grower to input information, such as the header width, swath width, ground speed, field name, crop type, cultivar, and electronic flags manually set by the operator. For instance, the data collected from a field could all be tagged with, or referenced by, a user-supplied name such as “Field A” or “North Forty.” Electronic flags are often used to record the location of weeds (known to be highly correlated with yield reductions). These flags may locate and identify other problems or obstacles, such as rocks, terrace failures, standing water, etc. In addition to sensor inputs, the display console receives inputs from the combine operator. This permits the operator to provide data for which no sensor is installed (width of cut, for example) or field or load information to permit tagging or referencing of the yield and moisture data that is being collected.
Data Collection and Storage
Yield monitors create files containing large amounts of spatial information, including the type of monitor, longitude, latitude, field name, object ID, track, swath width distance, elevation, header switch status, GPS differential status, time Y and X offset material flow rate harvester speed, productivity (acre/hr), grain moisture content type of crop harvested, and date. This data is compiled to produce a yield map.
Grain Yield Flow Sensors
Although there are many types of sensors for measuring mass flow, the most common is the impact-plate sensor located on the inside of the grain tank at the top of the clean grain elevator just before the grain enters the loading auger (Figure 1). As the grain presses against the impact plate, a load cell converts the applied pressure into a voltage signal that increases with higher pressure. The voltage is sent to the computer, where it is converted from an analog to a digital signal. Combined with travel speed, cut width, and GPS location, it calculates instantaneous yield (e.g., bu/ac or t/ha).
Grain Moisture Sensors
Grain moisture levels in a single field can vary significantly due to factors like soil type, growing conditions, ear size, and test weight, potentially resulting in fluctuations of around ten percent. Additionally, the moisture content of crops in the field naturally decreases during the harvest season. Since most grain crops are sold on a wet basis, accurate estimation of grain moisture is important for accurately estimating grain yield. Moisture sensors are often located in the clean grain elevator or the clean grain auger. Grain moisture content is generally calculated based on the dielectric properties of the harvested grain.
Protein Sensors
A grain yield combine protein sensor is a device mounted on a combine that measures the protein and oil content of grain while it's being harvested. These sensors use near-infrared spectroscopy (NIRS) to analyze the chemical bonds within the grain. The sensors emit light, which interacts with the grain and is then recorded. A calibration algorithm is used to calculate the grain's protein, moisture, and oil content.
Ground Speed Sensors
Ground speed is required to compute grain yield. Ground speed can be calculated using a GNSS receiver or alternatively using a sensor that monitors ground speed, such as the shaft speed type found on John Deere and Case IH combines. Most systems use GNSS for primary ground speed calculations and utilize a ground speed sensor as a secondary input.
Secondary Sensors
Several secondary sensors exist on a complete yield monitoring system to help ensure quality data collection. First, a header height sensor is required to start and stop data collection when entering or leaving headland areas.
Task Computer
A task computer located in the cab of the combine serves several functions: it integrates and calibrates the sensors; converts their output signals into data for storage, display, and later use; contains the DGPS receiver interface, external data storage devices, and user interface (display and keyboard); and controls the interaction of these devices.
Differential GNSS Receiverss
To generate a yield map, a positioning system is required to record the locations as yield is being measured across the field. The GPS receiver facilitates creating a yield map by providing a physical location for each crop flow reading. The accuracy of GPS receivers will vary based on the type of correction service used, but WAAS GPS correction is suitable for yield monitoring. Typically, the GNSS receiver is mounted in the center of the vehicle on top of the cab. It is critical that proper machine measurements are entered into the user interface when prompted for the machine configuration offsets so that proper material handling and flow delay can be correctly calculated.
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