Precision agriculture with Calian GNSS

An exclusive interview with Ken MacLeod, Director of Product Management and Gordon Echlin, Director of Business Development at Calian GNSS. Read the full story and additional exclusive interviews here.

What are the main challenges and issues for GNSS antennas in agriculture, as opposed to, say, surveying or construction? How do your products address them?

KM: Many agricultural applications use L-band GNSS corrections, which are broadcast from a geostationary satellite (located above the equator). If you’re close to the equator, the geostationary satellite is roughly above you. However, as you move away from the equator, the look angle gets lower and lower. In Canada and northern Europe for example, the look angle is low, and the signal path is longer than at the equator. Therefore, you need an antenna that has low elevation angle gain.  Calian has several antenna products that have great low elevation angle gain.

One of the other differences is antenna mounting. Agriculture requires positional accuracy, so mounting an antenna on a farm machine is not a trivial matter. On metallic machinery, radio frequency surface currents and reflections (multipath) will degrade the antenna radiation pattern, and RF noise coming from other electronics on the machine can interfere with GNSS.

Most GNSS applications now are full band. The challenge is designing antennas that are small and full band, and which also reduce local multipath on the machine.

You mentioned that these antennas are small, but on a tractor, size, weight and power (SWAP) is not a big concern. So, why is size an issue?

KM: As you mentioned, for most large farm machinery, SWAP it’s not a problem. It is, however, for UAVs, which are being used to spray crops with herbicides and pesticides where a small light weight antenna is beneficial.

Do most farm machines now use two antennas for their heading?

KM: Many agricultural applications use the moving base technique to estimate a precise heading which can be used to monitor pass to pass overlap. Calian GNSS have smart antennas that support the moving base application.

You also need to sense obstructions on the ground, but I guess that somebody else deals with integrating other sensors, such as inertial ones, with GNSS.

GE: Calian GNSS smart antennas (GNSS receiver built-in to the antenna) have built in Inertial Measurement Units (IMU). We also have smart antennas that employ the L1-L5 observation pair rather than L1-L2, since the L5 signal is stronger and performs better under cover. L5 uses an enhanced signal architecture with 10x faster chipping rate (10.23MHz) offering more precise standard localization and improved multipath mitigation for reflections exceeding 29.3m

[Shared a screen with eight antenna models.]

What are the key characteristics of your antennas regarding precision agriculture?

GE: Our GNSS agriculture antennas support centimeter level precision, have best in class lower elevation angle gain enabling L-Band correction reception (at northern and southern latitudes), and eXtended Filtering (XF), which creates very deep attenuation of nearby out of band radio frequency signals.

KM: We have deep GNSS antenna knowledge and we know how to integrate receivers into antennas. So, out of the box, you can buy from Calian GNSS a fully functional smart GNSS antenna that outputs a digital signal. Having a digital signal from the antenna to the smart ag controller simplifies and reduces the cost of the installation.  Many customers, especially in the autonomy space, know software very well but are not hardware specialists. We remove the problem of integrating an antenna and a receiver into their product, and customers can start solving their PNT application.

GE: There are many startups that don’t understand RF; there are not enough GNSS and RF guys around. Let us take care of the antenna rand receiver integration. Then customers just take the RS-422 or RS-232 signals and read the receiver’s messages or NMEA data and use our ROS2 driver.

Does the installation take place at the factory or at the dealership, or do growers do it themselves?

GE: We provide products to OEMs who designed our products into their machinery. There are also system integrators and aftermarket system providers that use our smart antennas. We offer advice and consulting services to customers who design the products and do the installs and ask us to recommend where they should place the antenna to get the best performance. Let’s say that you have a large metal roof with a patch antenna. The GNSS signal can bounce off the roof or run on top of a metal surface and reach the antenna and interfere with the direct signal. To mitigate these problems, we often provide installation advice.

What are some of the GNSS receivers that you use?

GE: Calian GNSS provides smart antenna products with Septentrio, uBlox or ST-Micro receivers built in. Our ceramic patch antennas typically use a ZED-F9P, which you can use as either a base or a rover. It can take in PPP-RTK corrections through L-band signals. We can also take commercial RTK services, such as those from Point One Navigation or from Swift Navigation. Or, if you have a big farm and many different pieces of equipment that need precise positioning, you could set up your own RTK base, which provide precise positioning for a radius of up to ~20 kilometers from the base station. The point is that we support correction services and are not bound to one service provider.