Advanced UAS Mapping Missions

Date: 10/11/2024 

   In the field of UAS, there are various types of advanced sensor technology and ground control methods which all serve different purposes. In this week’s lab, the class was exposed to several different sensors and ground control methods with the goal of comparing the different technologies and ultimately gaining a further understanding of each system.

            This outing was conducted at the Purdue University Grass Turf Research Center which provides a consistent surface for which to compare the sensors, and an optimal field for flying with minimal obstructions. The weather on the day of the mission was 63 degrees Fahrenheit, lightly cloudy skies, winds north northeast at 5kts gusting 11kts, and nearby precipitation that had no impact on the flight.

            The chosen platform for this mission was the DJI M300. Being a heavy lift platform with improved battery life, the M300 was able to carry out consistent flights with all 4 sensors. To accurately compare each of the sensors, the M330 was flown in a lawn mower pattern with 80% overlap for each flight.

Flight 1: Thermal with RTK

            The first flight of this mission was conducted with the Zenmuse H20T (figure 1) thermal sensor using Real Time Kinematic (RTK) ground control. RTK operates using a base station which provides position data via Bluetooth to the UAS.A primary advantage of RTK over PPK is that (as the name implies) it provides real time position data and does not require corrections after the flight which can save time during a mission. As for the sensor, a thermal sensor may be more useful than an RGB sensor for certain applications or when trying to gather data related to the radiant energy being reflect by a surface and not just the visible light.

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Flight 2: RGB with RTK

            The second flight utilized the same ground control system as the first (RTK) but used the Zenmuse P1 (figure 2), an RGB sensor rather than a thermal sensor. RGB sensors capture energy on the visible light spectrum and can be used to generate 2D/3D images useful for conducting visual inspections of buildings or surfaces. One advantage of RGB imagery over thermal is the significantly smaller file size, which can in turn reduce processing times. It is also worth noting that the M300 flew a mission of the same area in five less minutes with the P1 than the thermal sensor indicating that the P1 sensor likely can produce more images per minute of battery life. This may not seem like much, but when imaging a larger area this could add up to many more minutes or even hours meaning more battery cycles are required to complete the scan.

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Flight 3: Sony A7 with PPK

            The third flight was conducted with the Sony A7 RGB camera and post processing kinematic (PPK) ground control (figure 3). This system consisted of ground control points GCPs placed throughout the scan area. A rover connected via Bluetooth to the base station was utilized to record the GPS data of each GCP. The base station was set up 3 hours ahead of the mission to send data to OPIS. Although PPK requires more set up and post processing, typically PPK offers a more reliable system for ground control as it does not rely on as many constant links between systems to operate as RTK.

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Flight 4: Mica Sense Red Edge with PPK

            The fourth and final flight was conducted with the Mica Sense Red Edge multispectral sensor (figure 4). While more expensive, multispectral sensors offer a new advantage over RGB sensors as they collect a wider range of bands of light. Multispectral sensors can provide an advantage in analyzing vegetation health by capturing how light reflects off plants on a wider spectrum. This flight also utilized PPK as a ground control system. While it has been established that RTK can save time in post processing, one potentially significant difference between RTK and PPK is the flight times of the mission. Flights 1 and 2 which utilized RTK took 17 and 12 minutes respectively, and flights 3 and 4 took 7 and 5 minutes respectively demonstrating that PPK may save time in data collection.

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            The data outcomes from these flights have not yet been released. Once the datasets are processed, comparing the orthomosaics may provide some insight on the quality and usefulness of data from each sensor. Additionally, the finished products may indicate which ground control system most accurately provided position data to the images.