Environmental Monitoring Using Unmanned Vehicles

Response to the article: Development and validation of a UAV based system for air pollution measurements by Villa, Salimi, Morton, Morawska, & Gonzalez (2016).

Environmental monitoring is one of the numerous applications that have yet to reach their full potential in the unmanned realm.  Villa, Salimi, Morton, Morawska & Gonzalez (2016) researched the possibility of using unmanned systems for pollution measurement and developed an unmanned aerial vehicle optimized for this task.  While the selection criteria of the vehicle itself is not covered extensively in this journal, the writer discussed some of the challenges faced when it comes to sensor placement on the vehicle due to the interference experienced from the wash of the propeller system on the vehicle.  For their vehicle platform, they chose the DJI S800 EVO, a hexacopter that can carry up to a 20-kilogram payload (Figure 1).  After modifications, the S800 EVO was able to sustain flight for about 12-13 minutes with the payload required for the study (Villa, Salimi, Morton, Marawska & Gonzalez, 2016).

Figure 1: S800 EVO Hexacopter (Villa et al., 2016)

For sensors, the S800 EVO was fitted with four exteroceptive gas sampling sensors, three for detection of CO, NO and NO₂ and one for the detection of CO₂ (Figure 1).  For CO, NO and NO₂ sensing, the Alphasense gas sensor was selected, which utilizes electrochemical cells to detect gas levels.  For CO₂ detection the SprintIR sensor was selected.  This sensor utilizes non-dispersive infrared (NDIR) technology to detect gas levels.  To evaluate the readings from the probes, the DISCmini was selected.  This monitoring system can detect gas concentrations from 10³ to 10⁶ p/cm³, while remaining small and light enough to fitted to the S800 EVO UAV platform (Villa et al., 2016).

            During the two tests conducted by these researchers, they explored the effects of the propeller wash on the readings of the probes as well as the best placement location for the sensors to minimize the effects that the vehicle had on the readings.  The first test explored the best positioning for the gas probes.  Using a boom with the gas sensors attached, experiments were conducted using 3 different locations for the boom: to the side, above and below the UAV.  During each of these tests the aimed to find where the effects of propeller air mixing a turbulence would be the lowest.  Figure 2 shows the results of the 4 variations that were completed during test one.  The results shown clearly indicate that the lowest effect was experienced to along the X-axis of the vehicle at distances between 1000 mm and 1200 mm. 

Figure 2: Results from test 1 (Villa et al., 2016)

            

          The second test the conducted was to determine the effect of the propeller wash on the concentration of the gases.  They conducted several variations of the test with the sensor placed in various positions relative to the gas and with the vehicles propellers on and off.  Figures 3 ad 4 describe the test results.  As expected, the propellers do have a significant effect on concentration levels.  Additionally, when the sensors are positioned within the gas plume the concentration levels rise (Villa et al., 2016).

Figure 3: Gas concentration comparison with UAV propellers on and off (Villa et al., 2016)

Figure 4: Gas concentration with sensor above, below and inside gas plume (Villa et al., 2016)

           

          While the results of these test are only conclusive for the gases that were tested, the results show that environmental monitoring using UAVs is a possibility.  There will be several limitations such as gas type, wind speed, and UAV design, but with further research some of these challenges could be overcome (Villa et al., 2016).  There are many developers and companies that have begun similar work.  The EPA has expressed interest in the use of UAV for many different types of environmental monitoring, highlighting the potential of these systems to revolutionize the industry.  There interests range from gas and pollutant monitoring to wildlife and wildfire monitoring as well as industrial emission monitoring (The Role, 2015).  This technology, once properly researched and perfected could have a profound effect on the health of our planet and the steps that we as humans take to protect it.

References:

The Role of Unmanned Aerial Systems-Sensors in Air Quality Research. (2015, November 16). Retrieved July 7, 2018, from https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=310260

Villa, T. F., Salimi, F., Morton, K., Morawska, L., & Gonzalez, F. (2016). Development and validation of a UAV based system for air pollution measurements. Sensors, 16(12), 2202. doi:http://dx.doi.org.ezproxy.libproxy.db.erau.edu/10.3390/s16122202