LiAir V: Fundamentals of Operation
The fundamentals of LiAir V operation have assigned to one of three general categories in this GreenValley International (GVI) Product Article: planning, setup, and execution. Planning can be the most time-consuming stage of any LiAir V operation, but it is essential to success. Knowing what you think will happen and what to do if hazardous situations arise sets the stage for safe and effective UAV LiDAR data collection. It is during the execution of LiAir V operations where poor planning and faulty setups will cause projects to fail.
All LiAir V projects present their own unique challenges that must be overcome. While no two LiAir V projects are ever the same, there exist some basic operational best practices that, when correctly followed, can increase the likelihood of a successful outcome. This article will touch on only some of those best practices and operators of this GVI solution are encouraged seek out other sources of information when planning or executing UAV-LiDAR surveys. As the collective experience of the LiAir V user community grows and new supporting technologies emerge, the complete list of best practices is expected to change and become more detailed over time. However, many of the fundamentals of operation discussed in this article should continue to hold their relevance into the future as they are core to the way UAV-LiDAR technologies function. For more in-depth information on the LiAir V system itself please refer to the LiAir V: What is It? article.
Planning
The amount of time that should be allocated to the planning phase of LiAir V operation will vary depending on the scope and scale of the survey project being undertaken. At a minimum planning should include the identification of potential hazards (natural and man-made) within the survey area as well as the strategies that will be used to mitigate them, the selection of a UAV model that will be used carry the LiAir V payload, the construction of a flight path(s) the UAV auto-pilot will take to capture information needed to directly or indirectly satisfy specific data collection objectives, criteria, and constraints as well as a quantification of the staffing and auxiliary equipment resources needed to successfully conduct the proposed operation.
Planning activities may also be extended to include the assessment of one’s personal and professional liability coverages for conducting a specific mission, at a specific location, at a particular moment in time, with the LiAir V. Purchasing of additional insurances when deemed appropriate to do so, may be a necessary expense to consider. Here, however, LiAir V etches a clear edge over other 3D LiDAR systems as its low replacement cost keeps inland marine insurance policies for this payload affordable and, more importantly, easy (in most cases) to obtain. Acquisition and scheduling of resources including the drone(s), accessories, transportation, power supply, and supporting personnel as well as the securing of any waivers or permission needed to operate in specific areas or under certain conditions are all activities that fit under the broad umbrella of planning.
Local weather patterns and predictions should be investigated before committing resources to the field. Check with the UAV manufacturer to see what the maximum wind speed that the drone can be safely operated in with the LiAir V payload mounted to it. In general, sustained winds and greater than 8-12 miles per hour (7 to 10 knots) can make it difficult to safely takeoff and land the system. The rate of power consumption also increases as the UAV must use more energy to stabilize itself in flight. The LiAir V should not be used in snow, rain, or fog. The device is also sensitive to ambient air temperature and humidity. Check the product specifications for more information on the exact limits to safe storage and operation are.
Persons who will be charged with operating the UAS/UAV during data acquisition (the pilots) should be involved in the planning stages so that they can be made aware of any potential hazards that may be present in the survey area. The drone operators will also want to verify the there are no permanent or temporary flight restrictions in place where the survey flights are to take place. Operators can rely on apps like B4UFLY from the US Federal Aviation Administration or AIRMAP to alert them when/where no-fly conditions are in place. However, these apps are not perfect and do not provide the same amount of coverage globally. It is good for the operator to have knowledge of the local area when the survey flights will be conducted. It may be necessary for the operator to monitor aviation radio traffic while operating in specific locations so having an understanding of which frequencies should be monitored is also important.
UAV operators must also have an in-depth understanding of the proposed flight plan so that they quickly identify deviations from intended course of flight if they are to occur while the mission is being executed. Operators will want to study the flight route and make contingency plans particular to the local flight area that can be relied upon in the case an unlikely fly-away event or air space conflict.
Special waivers that allow drone operators (pilots) to operate their system beyond visual line-of-sight (BVLOS) can be difficult and expensive to obtain. The time and financial barriers standing in the way of easily obtaining an exemption (BVLOS waiver) mean that LiAir V operators will more often than not need to actively seek out areas where they can as easily take off and land the system as they can keep eyes on it as it executes is pre-programed flight route.
Computer programs like Google Earth can be very useful during the planning stage as they offer 3D representations of the terrain, and in some cases surface objects, that can be visually inspected in order to determine places where the operator will be able to safely take off, to maintain line-of-sight on the drone from, and successfully land. However, these 3D models of project areas should not always be trusted since they may be constructed from stale imagery lacking features that have been added to or removed from the site (e.g. radio towers built, trees harvested, buildings erected, etc.) since the photos were taken.
It is generally true that UAV operators should position themselves above the survey area as this will help them maintain situational awareness during data aerial data collection. The 3D perspective that Google Earth offers can be an extremely helpful planning tool but it is no substitute for a visit to the actually site that will be flown. When operating in steep and hilly terrain or in regions where there are tall surface features such as trees and buildings that can easily obstruct an operator’s view, getting eyes on the site before planning exact autonomous flight paths may be essential. Since this may not always be a viable option, operators may elect to carry out the actual flight planning activities once they have scouted the survey area in-person.
Access to takeoff and landing areas as well as base station setup locations should also be investigated before heading out to the field. It may be necessary to contact local landowners and obtain permission to cross or operate on private property. When working in remote areas where cell service is limited it is a good idea to have the coordinates of key locations so that they can be found with a GPS navigation device.
Many an hour and dollar of field work can be saved by knowing how to best access and depart from pre-determined LiAir takeoff and landing areas as well as GNSS Base Station setup locations. Time should be taken during the planning stage laying out the routes that ground transportation will take to get to and from the operation. Here, again, LiAir V has a distinct advantage over other UAV LiDAR systems. Its lightweight and compact design make it easy for one person to carry, with one hand, across rugged terrain. The hard case the LiAir V is delivered in can easily fit in a plane’s overhead compartment so it travels well. It is not an overstatement to say that a single person can easily carry everything that is needed for data collection, including one of the more compact DJI consumer drones like the MATRICE M210, on their back. This level of system portability opens new frontiers to UAV LiDAR data collectors who were previously bound to their vehicles (or areas they can dive a vehicle to) by heavy and cumbersome equipment.
Automated Flight Planning
Popular drone control apps like UgCS for DJI, MapsMadeEasy, or DJI Ground Station Pro can be used to plan and conduct automated flight missions. GVI is also developing its own mission planning and flight control software, LiPlan, which has functions that make it particularly useful when planning and executing LiDAR data collection flights. Many of these applications also allow users to import or build terrain-following ( aka adaptive) flight plans.
Automated flight speeds ranging from 4 to 6 meters per second are recommended when capturing LiDAR measurements with the LiAir V. Flight speeds should not exceed 10 meters per second during data collection. Assuming the flight height and surface characteristics do not vary, LiDAR point (measurement) density decreases as speed increases. The hypothetical mean number of LiDAR measurements (points) per square meter that one can expect to capture with the LiAir V ranges from approximately 1,100 at 2 meters/sec to around 200 at 10 meters/second (see chart below). These density figures also assume that three (3) returns are generated per lase pulse from objects that reflect at least 80 percent of the incoming LiAir V laser light.
It is important to understand that realized point cloud densities will vary across most UAV-LiDAR survey areas. Changes in topography will move the surface objects that reflect the LiAir V laser light closer and at different angles to the LiDAR sensor. In certain situations, terrain-following flights can improve the consistency of point cloud metrics like density per unit area as well as measurement accuracy however these flight plans are subject to the harmful effects of bad elevation data. When using software to build new terrain following flight plans it is a good practice to first execute them on a less-expensive drone or at lease on a drone without the LiAir V payload installed in order to confirm that they are error free and safe to fly.
Due to size and equipment constraints, LiAir V survey areas must often be broken up into separate flights. It is important for the flight planner to understand the rate at which battery power will be consumed by the drone and LiAir V payload at a specific location so that they can properly monitor power use during data collection. Flight endurances for drones carrying the 1.0 kg LiAir V (without optional camera) vary widely between drone make and models. Operators must also build in time buffers during which fine-calibration figure-8 maneuvers will be performed after take-off and before landing. The anticipated battery consumption time-buffer should also include allotments for flying the drone to the start of a mission and then back to the landing area at the end of a mission.
Having a highly accurate base station set-up location and GNSS antenna height information on hand when processing LiAir V data is extremely important. Point-clouds generated without entering accurate and precise GNSS base station set up locations can have meter-level absolute accuracies. This amount of error in the geographic coordinates of individual LiDAR points will present difficulties when attempting to align point clouds collected at different moments in time (e.g. separate flights) or with other geospatial datasets (e.g. photogrammetrically-derived, RGB textured digital ortho-mosaic raster models of surface color).
Moreover, it is important that 3D-survey points used to denote the GNSS base station set up locations are made available as WGS84 Geographic Coordinates attributed with WGS84 Ellipsoid Heights in meters when LiAir captures are used as inputs to the LiNav module found in GVI’s LiGeoreference. In many instances the GNSS base station must be set up in places where appropriate survey monuments have not yet been established. When this occurs, RTK/PPK surveying technologies are typically used to collect LiAir Base Station setup location information.
Setup
Out-of-the-box setup of the LiAir V takes just a few minutes to complete. Certain setup tasks do not need to be done every time the system is used, including the mounting the GNSS antenna’s to the top of the UAS/UAV as well as the setting up an ethernet/LAN connection which allows users to access the system’s firmware interface, set data collection parameters, download data to their laptop or desktop computer, and more. GVI and its partners have produced many detailed manuals and video guides that users can rely on when setting up their LiAir V.
LiAir V is a versatile UAS/UAV LiDAR solution in that it can be mounted to a variety of commercially available and custom body designs. To date, users have typically favored DJI’s MATRICE 210/RTK, MATRICE 600 Pro, or the newly released MATRICE 300 RTK. The LiAir V has been designed with these users in mind as it features a Skyport adaptor that can pull power directly form the DJI platform. In the case of the M600 Pro, GVI makes a special adapter and power cable that can be used to integrate the LiAir V into this widely used DJI model. When non-DJI drones are used some level of custom integration is needed to safely integrate and supply power to the payload. These integrations are typically made possible through GVI partners that have custom mounting kit fabrication capabilities.
Installing the LiAir V into the Skyport of a DJI system is as simple as inserting the adapter located at the top of the payload into the socket and then rotating it clockwise until the red dots printed on both side the connection joint align. The user will then connect the GNSS 1 and GNSS 2 connector cables to the appropriate port located on the side of the LiAir V unit. The DJI Pilot app can then be used to enable the external power supply port on the M210/RTK or M600 platforms. When other drones besides the DJI models discussed are used to carry the LiAir V payload there may be additional steps to follow but the core setup concepts will be the same: mount the GNSS antennas, secure the payload to the underside of the UAS/UAV, and supply power from an external source. Please contact GVI directly for more information on how LiAir V mounting kit and power inputs can be customized to fit a specific UAS/UAV make or model.
Once the LiAir V has been successfully mounted to the drone and powered on, users can connect their computer to the LiAir V via the Ethernet/LAN connection and access the system’s firmware interface through LiAcquire Web to view the number of visible satellites at a given site. LiAcquire Web can also be used to check the status of the integrated components, configure data collection parameters, such as the height or speed at which LiDAR sensor data recording will start/stop, update firmware or stored system calibration parameter values, and import device activation files. Again, users do not need to connect to the LiAir V before each flight as the control parameters will be logged in memory and the LED panel on the front of the device will indicate if there are any issues that need to be addressed before executing data collection.
Other setup procedures that should be paid attention to relate to the drone itself. Manufactures often require software updates that are troublesome to deal with in the field. Users should always check to see that their software and hardware are up to date before carrying out a LiAir V data collection flight. It may also be necessary to calibrate the navigation devices (IMU and GPS) that the drone’s flight controller relies upon before the system can be safely operated. In many instances these updates will require an internet connection. Make sure to review the manuals for the UAV, the controller, and the batteries before heading into the field to make sure you are not caught off guard by a show-stopping (i.e. drone-grounding) required software or firmware update.
Execution
It is a good idea for operators to develop a mental or written checklist that will guide them through each the execution phases of LiAir V operation. Making sure that specific actions are taken in the proper order is critical to any successful data collection. This section will describe checklist items that are most important to include while also providing some technical background on the technologies that support the LiAir V. Users should refer to the LiAir V, LiAcquire Web, and LiGeoreference user manuals when questions about specific product features arise.
After arriving at the survey site, the recommended first step involves setting up a GNSS base station within 10 kilometers of the flight area. LiAir users are required to start GNSS base station data logging at least 15 minutes before a starting LiAir V data acquisition period. GVI manufactures its own GNSS base station which can be purchased separately from the LiAir V system. Third-party GNSS base stations can also be used to gather the required satellite information, if a RINEX file can be exported from the device.
When setting up the GNSS base station, it is important to make sure that the space directly above the antenna is unobstructed. It should also be placed away from tall objects, such as buildings, or sources of electromagnetic interference, such as powerlines. Users must measure the height of the base station antenna once it has been set up and leveled. Antenna height refers to the vertical distance between the GNSS antenna’s L1 phase center and the survey control point that it has been centered over. For the GVI GNSS base station antenna, a diagram is printed near its base to help users determine where the L1 phase center lies relative to the antenna’s connection point to a survey tripod or threaded rod. GVI base station users should measure to the bottom edge of the rubber ring on the GNSS antenna.
While tasks surrounding LiAir V data collection may be quite involved the actual operation of the system is very straight forward and easy to learn. LiAir V is powered up by pressing and holding the ON/OFF button until the LED lights on the front panel illuminate. If the optional LiAir V camera is not installed then the CAM light will remain red. The unit should then sit undisturbed for a couple of minutes while the IMU, LIDAR sensor, and other integrated components finish initializing. Once the LED lights have all turned solid blue, users will again press and hold the ON/OFF button for approximately two seconds. The RECORD LED light will turn solid blue indicating a new LiAir Project has been created on the device’s internal storage unit and IMU+GNSS data collection has begun. LiVox sensor data will then start being collected after user-specified Control Mode requirements are met. The Control Mode parameters must be set prior to data collection using the LiAcquire Web App. It is critical that operators make sure to not move or disturb the LiAir V for five (5) minutes once data recording has started.
Once the five-minute period has elapsed the UAV operator can take off and perform two (2) mandatory figure-8 flight maneuvers at a height that is just-below or at that of the pre-determined route for data collection. Most UAV operators will choose to control the drone manually during this stage of the flight since building these turning patterns into the programmed route can be an awkward and time consuming using many of the common flight control software/apps. It is important that operators do not fly the UAV in reverse while the LiAir V is recording. Abrupt changes in speed or direction may jeopardize the quality of the results so all turns and accelerations should be smooth. When building turns into the automated flight plan it is best not let the turning radius to fall below five (5) meters.
After completing the figure-8 maneuvers, UAV operators will typically start executing their automated flight plan. While the automated flight is being conducted operators should be on the lookout for airborne hazards that may require them to take manual control of the drone and fly it safely to a predetermined landing area. Hazards that are commonly encountered while in the field range from birds to other aircraft. Flight-tracking apps and websites allow users to track aircraft in the skies in real time. Unfortunately, wildlife cannot be monitored in this way so operators need to continuously scan the flight area and horizons for birds that may display aggressive behavior towards the UAS/UAV. Operators should also keep a close eye on their battery life to make sure consumption rates are normal and sufficient reserves exist to safely complete the mission and land the system.
Once the mission has completed or the trigger point for bringing the system back to refresh the batteries has been reached the operator will typically take manual control of the UAV/UAS and fly it back to the landing area. Before begging their decent to land the system the operator will again perform two figure "8" flight maneuvers. Once the LiAir V is safely on the ground it should again sit undisturbed for five minutes. The operator can then press ON/OFF button until RECORD indicator LED light turns off. At this point IMU data collection has stopped the system has closed the LiAir Project. Before powering off the payload and drone it is a best practice to download the LiAir Project via the ethernet connection and store it on a local device for subsequent data processing routines. The LiAir V can be turned off by holding the ON/OFF button until all of the lights on the LED indicator panel go dark. At this point images from the LiAir V’s optional RGB camera should also be copied from the removable SD card and stored in the “…/Cam/Images” directory of the corresponding LiAir V project folder copied to an external storage device.
Operators should end GNSS base station data collection and copy the file(s) to the “Base” directory located in the LiAir V project folder. It is possible to use the same base station file for multiple flights.
When the project requires an assessment of accuracy, it is a good practice to collect reference data such as GNSS survey control and check points during or near the time that the LiAir V data collection is taking place. Survey crews should also collect the location (WGS84 lat., long., and ellipsoidal elevation) of the ground point that the GNSS base station was setup over during data collection.
Data collected during LiAir V operations must then be processed. For more information on and descriptions of required and recommended data processing workflow please refer to LiAirV: Data Processing article.
Contact us
For additional information on LiAir V or any topics discussed in this Product Article, please contact GVI at info@greenvalleyintl.com.