Cranberry Frost Protection using Wireless Sensors

What is the connection between cranberry farming, sensor technology, and computer networks? That is the question I posed to Michael Lange, president of Lange Installations in British Columbia. I now know more than I ever thought I would about how those flavorful little berries grow. It is quite a story, and it revolves around cold and moisture, two phenomena that Canadians in general, and cranberry growers specifically, know a lot about.

“The biggest concern for cranberry growers is frost protection,” Michael told me. A cranberry plant is quite hardy, but when it buds out, it is vulnerable to frost damage. Everyone working for a grower puts in long hours during the frost season to make sure the future cranberry crop is protected by irrigation against future frost damage.

Image: FreeDigitalPhotos.net

Image: FreeDigitalPhotos.net

“From March 1st through June 30th, the cranberry plants are like a mat on the ground, called a ‘canopy’ in the trade,” Michael said. “At least once a year, they ‘mow’ it to control the thickness of the mat. During this time, the plant wakes up and begins to produce buds. That’s the time when pollination must occur. The danger to the plants occurs at night, when the temperature can go below freezing. The sub-freezing temperature can burn off new growth in as little as 20 minutes. It can take the plants—and the grower—up to three years to recover from that short exposure.”

Growers go to great lengths to protect the plants with irrigation. They use irrigation water with a temperature a bit higher than ambient. Then, something counterintuitive occurs. The instant the irrigation water hits the cranberry plants, the air temperature freezes it. You would think that such an exposure would kill the plant; instead, it protects the cranberry buds. “It freezes over the plant buds like a cocoon. The growers use ice to protect the buds from freezing,” Michael said.

This is where the technology comes in. When growers protect cranberries against frost, they need to know the exact bog temperature on the canopy. Traditionally they used sensors, hardwired from the bogs to a pump station to transmit environmental information. But, broken cables often disrupt transmissions. Hard wired sensor connections are also challenging because of long distances between the sensors to the pump station. Lange knew there had to be a better way. He found it with Spinwave Systems (www.spinwavesystems.com).

“I ran across Spinwave while researching how to run multiple sensors in a congested RF environment,” Michael said. “Spinwave gave us a way to use what they call Frequency Agility based on the IEEE  802.15.4 standard. Spinwave provides a receiver module that hard-wires directly into our controller, which is ideal for a small, low-density wireless sensor integration project. For larger networks, Spinwave also offers a receiver supporting a choice of open protocols (e.g.  ModBus, BACnet and LON) to support up to 31 wireless sensors per network. This solution is in use now on Grafton Farms.”The Lange-Spinwave project showcased the speed of design and delivery for which Spinwave is known. “From start to finish took six weeks!”Michael said. “The best thing for customers is that we can offer 10 times the data and monitoring capabilities of alternative approaches.”

Science and technology help optimize the growing environment

Lange developed a connection with a co-op started by some area growers and Ocean Spray. Scientists at the co-op help optimize the growing environment, managing pest control and diseases that affect productivity. For example, some growers water the canopy too often, producing a wet environment conducive to insect growth.

“When the sensors show us a temperature rise, we can manage moisture levels,” said Michael. “For example, if we have 32°F as a starting setpoint and the ambient temperature reaches 34°F, you can safely stop watering. With accurate sensors and optimized programming, we can manage the watering cycle. Sensor placement is critical, but with the Spinwave sensors we read temperatures accurate to 2/10ths of a degree F between what the plant feels and what’s read by the sensor.”

Over time, the information reported by the Spinwave wireless sensor mesh produces useful trend data. “We use the system in two ways, as a controller and a data logger,” Michael continued. “We can trend the temperature sensors and then, over time, see a pattern of how the cold moves in on the canopy. Software ‘senses’ when we have a frost ‘request’ or that the diesel or electric pump has started, so we can monitor the system’s water pressure and measure/monitor temperature differentials across filters. This is important because irrigation water comes from a reservoir that can get silted up. Turbines throw a lot of turbinated water and the filters screen out debris down to 40 microns, but over time they get clogged.

“For example, a user screen may show four-six pump stations on a typical farm. Overnight, we want to know the lowest temperature, the median temperature, and any pressure differential in any filter system. We’ll watch the pressure differential and hold it on the screen. In the morning, when the shift operator arrives, he’ll see when an event occurred, and send workers out to clean the filters.

“Information like this helps a farmer reduce expenses because it saves the cost of overnight labor when an automated system transmits 24/7/365,”Michael continued. “Growers feel secure that they’re protected because they get actionable data reliably.  The Spinwave wireless approach resolves all sorts of potential problems. Say, for example, there’s a physical tree line. You can’t run sensor cable over 1,000 feet at that point because of built-up capacitance and resistance. Also, a lot of cranberry bogs are near AM transmitters, which means there’s a interferes with wired sensor operation that cannot be filtered out.”

Another successful project for Lange & Spinwave

To illustrate his points, Lange talked about the work his firm did for The Acquilini Group, which farms over 1,000 acres of cranberry bogs. The challenge:  Integrate four pump stations on one property with nine stations on another plot. Here’s how Lange approached it:

“We experimented with 2.4 GHz wireless Ethernet technology to create a wireless LAN with an IP connection. We also used the very reliable Spinwave radio technology which matched our sensor specification, a 10K type 3 industry-standard thermistor. Before we developed this approach, farmers would bury wires in their dikes to get simple on/off remote control, but the wires kept getting cut or otherwise disabled. The Spinwave wireless concept eliminated these problems, so a grower could answer questions like: How do I know when to start frost protection if the temperature at the tree line is different than what the sensor registers in a different microclimate.

Future plans

Looking ahead, Lange hopes to have technology to determine the moisture content of the growing medium using a remote sensor location with a temperature and moisture sensor. This is important because Phase 2 in cranberry frost protection uses irrigation to maintain the moisture content of the growing medium. At present, it’s done by manual watering schedule, but Lange hopes to integrate this capability into the wireless solution so it can be automated and managed from a terminal.

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