Inside Unmanned Systems

OCT-NOV 2018

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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33 October/November 2018  unmanned systems inside PRECISION NAVIGATION Poss noted that not very long ago, the U.S. military would consider a really good GPS fix to be about nine meters maybe down to three meters, on a really good day, which was great for the Air Force using GPS-guided munitions. At the time he felt three meters accuracy would have been sufficient for civilian applications. "Imagine my surprise when I really started dig- ging into this webinar talking with people like Jay Tilley and Visual intelligence to find that really the accuracy that you're talking about with RTK dual channel systems is not three meters anymore it's more like three centimeters and below, sometimes down to the millimeter levels," Poss said. "So I've been absolutely fascinated." Riley, who has been with Trimble in Sunnyvale, Calif. since the end of 1995, is currently a Director of Engineering responsible for the precision GNSS based technology used across Trimble. He addressed error sources/challenges, compared dual frequency and single frequency GNSS, discussed why the pseu- dorange is so important, and also explored beyond dual frequency to a triple band and some of the in- tegration tools that are helpful when you're putting these types of product into a UAS. "So if you look at GNSS or GPS, what are the over- all error sources?" Riley asked. "Well, you start with the atmosphere. The ionosphere is a delay and it's fre- quency dependent so if you have L1 and L2 you can actually correct it at least to a first order. There are tropospheric delays, the big atmospheric effects. And the satellites deliver ephemeres that tell us where the satellite is or allows us to calculate where the satellite is at any point in time and what state of the clock is." Because of errors and biases on the satellites, using just plain GNSS then inertial is not a consideration, he explains. Riley described the role played by iner- tial measurement units (IMU), how temperature ef- fects age and the importance of the GNSS hardware in different use cases. "The antenna is really, really critical to the perfor- mance. What are its age effects characteristics? Where is the electrical phase center?" he said. "That's where you're going to get the measurements that may not be where you think it is on the physical UAV; what is this HAT ATTENDEE ANTED TO KNO Participants had the chance to ask questions during the webinar. Here are a few of those questions: • Given the fact you're in a highly dynamic environment in a UAS and you're constantly yanking and banking and turning, how does that affect the PLL phase lock on some of these high precision receivers? If you're constantly turning you're constantly moving. Is it really going to affect your position this much? • Can you explain the difference in accuracy between DGPS (Differential GPS) and RTK precision navigation? • What are the considerations in integrating precision GNSS into UAS? In particular, antenna placement. • Do you have any advice for someone designing or confi guring UAS platforms on how to get the best accuracy from their system? • Can you explain how high-end receivers can mitigate multipath? • How does a dual frequency receiver compare to a single frequency receiver in an RF jamming environment, something where they're purposely putting RF energy in their device to devise multipath? • How do you see specifi cally 3-D models versus 2-D models as becoming more valuable in the UAS markets? How does better data accuracy improve the customer value? FOR MORE INFORMATION • Visit and • Visit • Connect with Trimble via LinkedIn: trimble-integrated-technologies/ TO WATCH THE FULL WEBINAR, GO TO: https://register. Howard W. Loewen Owner, founder and CEO of MicroPilot Inc. Stuart Riley Director of Engineering, Trimble General Jim Poss Maj Gen (Ret.) USAF, the CEO of ISR Ideas Jay Tilley President and CTO of Visual Intelligence THE PANELISTS

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