Figure 1.
Overview of the UAV landscape, from insect-sized drones to military aircrafts, classified according to the approximate weight and size. The graphic shows the large range of UAV sizes, which spans seven orders of magnitude.
Figure 1.
Overview of the UAV landscape, from insect-sized drones to military aircrafts, classified according to the approximate weight and size. The graphic shows the large range of UAV sizes, which spans seven orders of magnitude.
Figure 2.
Gas source localization strategies. (left) Reactive plume tracking; (center) Plume modelling; (right) Map-based.
Figure 2.
Gas source localization strategies. (left) Reactive plume tracking; (center) Plume modelling; (right) Map-based.
Figure 3.
The CrazyFlie 2.0 equipped with the MOX deck and the UWB tag (center) gets its 3D position from an external localization system composed of six ultra-wide band anchors (left). The location and sensor data are communicated to the ground station (right) over the 2.4 GHz ISM band.
Figure 3.
The CrazyFlie 2.0 equipped with the MOX deck and the UWB tag (center) gets its 3D position from an external localization system composed of six ultra-wide band anchors (left). The location and sensor data are communicated to the ground station (right) over the 2.4 GHz ISM band.
Figure 4.
Schematic of the conditioning electronic circuit for each MOX sensor in the MOX deck, using PWM for powering and a voltage divider for read-out.
Figure 4.
Schematic of the conditioning electronic circuit for each MOX sensor in the MOX deck, using PWM for powering and a voltage divider for read-out.
Figure 5.
Experimental arena. (left) Frontal picture; (right) Schematic top view. The green squares indicate the position of the UWB anchors, which are positioned along two inverted triangles (green lines).
Figure 5.
Experimental arena. (left) Frontal picture; (right) Schematic top view. The green squares indicate the position of the UWB anchors, which are positioned along two inverted triangles (green lines).
Figure 6.
Gas source location in the three experiments. (a) Experiment 1: inside small room; (b) Experiment 2: hidden in suspended ceiling; (c) Experiment 3: hidden in a power outlet box.
Figure 6.
Gas source location in the three experiments. (a) Experiment 1: inside small room; (b) Experiment 2: hidden in suspended ceiling; (c) Experiment 3: hidden in a power outlet box.
Figure 7.
Flow diagram of the improved bout computation. The meaning of each symbol is given in the text.
Figure 7.
Flow diagram of the improved bout computation. The meaning of each symbol is given in the text.
Figure 8.
Setup for assessing the effect of the rotors on the MOX sensor signals. (a) Top view of the stand used to hold the drone at different heights while minimizing interference with the rotors air flow; (b) Photo of an experiment with the drone placed 25 cm above an ethanol bottle (gas source), overlaid with an illustration of a gas cloud.
Figure 8.
Setup for assessing the effect of the rotors on the MOX sensor signals. (a) Top view of the stand used to hold the drone at different heights while minimizing interference with the rotors air flow; (b) Photo of an experiment with the drone placed 25 cm above an ethanol bottle (gas source), overlaid with an illustration of a gas cloud.
Figure 9.
Predefined navigation strategy based on zig-zag sweeping at two heights (0.9 and 1.8 m). The green squares indicate the location of the UWB anchors.
Figure 9.
Predefined navigation strategy based on zig-zag sweeping at two heights (0.9 and 1.8 m). The green squares indicate the location of the UWB anchors.
Figure 10.
(A) 2D map of MOX sensor response during 15 min of random exploration of the target area without gas; (B) Histogram of blank readings, with a Gaussian curve Ν(, ) superimposed.
Figure 10.
(A) 2D map of MOX sensor response during 15 min of random exploration of the target area without gas; (B) Histogram of blank readings, with a Gaussian curve Ν(, ) superimposed.
Figure 11.
(A) Calibration line in the range 1–50 ppm (log-log plot), with blank variability superimposed at each concentration level (see inset). The LOD is estimated using Equation (2); (B) Histogram of amplitudes of bouts detected in the calibrated blank signals. (Equation (5)) is indicated by a red dashed vertical line.
Figure 11.
(A) Calibration line in the range 1–50 ppm (log-log plot), with blank variability superimposed at each concentration level (see inset). The LOD is estimated using Equation (2); (B) Histogram of amplitudes of bouts detected in the calibrated blank signals. (Equation (5)) is indicated by a red dashed vertical line.
Figure 12.
Sensor signals (log scale) near an evaporating source. (A) Propellers switched off; (B) Propellers switched on. The ethanol bottle is opened at t = 2 min.
Figure 12.
Sensor signals (log scale) near an evaporating source. (A) Propellers switched off; (B) Propellers switched on. The ethanol bottle is opened at t = 2 min.
Figure 13.
Smoothed derivative (i.e.,
in
Figure 7) of the sensor signals at 50 cm in front of the source (blue line), 65 cm above the source (yellow line) and 25 cm above the source (green line). Bouts with amplitude higher than
are highlighted in red. In the left column, the propellers are switched off whereas in the right column they are switched on. The ethanol bottle is opened at
min.
Figure 13.
Smoothed derivative (i.e.,
in
Figure 7) of the sensor signals at 50 cm in front of the source (blue line), 65 cm above the source (yellow line) and 25 cm above the source (green line). Bouts with amplitude higher than
are highlighted in red. In the left column, the propellers are switched off whereas in the right column they are switched on. The ethanol bottle is opened at
min.
Figure 14.
Aerodynamics of Crazyflie 2.0 when the four rotors are spinning, visualized using a Deskbreeze wind tunnel (Courtesy of Bitcraze AB). The drone is fixed to one of the walls of the tunnel using a 3D printed stand and dry ice fog is emitted from (A) below the drone or (B) above the drone. It shows the downwash of the propellers and how part of the fog reaches the MOX gas sensor (red arrow). The MOX deck has been overlaid to the original images for visual clarity.
Figure 14.
Aerodynamics of Crazyflie 2.0 when the four rotors are spinning, visualized using a Deskbreeze wind tunnel (Courtesy of Bitcraze AB). The drone is fixed to one of the walls of the tunnel using a 3D printed stand and dry ice fog is emitted from (A) below the drone or (B) above the drone. It shows the downwash of the propellers and how part of the fog reaches the MOX gas sensor (red arrow). The MOX deck has been overlaid to the original images for visual clarity.
Figure 15.
Results of Experiment 1. (A) 2D map of the instantaneous concentration (ppm) in log scale, with bouts represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the leftmost panel. The box plot below the map represents the instantaneous concentration along the x-axis; (B) Trajectory of the drone along the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm) on a log scale, with detected bouts highlighted in red (the black star indicates the start of a bout). The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum instantaneous concentration and the maximum bout frequency are indicated by a green star and a blue triangle, respectively.
Figure 15.
Results of Experiment 1. (A) 2D map of the instantaneous concentration (ppm) in log scale, with bouts represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the leftmost panel. The box plot below the map represents the instantaneous concentration along the x-axis; (B) Trajectory of the drone along the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm) on a log scale, with detected bouts highlighted in red (the black star indicates the start of a bout). The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum instantaneous concentration and the maximum bout frequency are indicated by a green star and a blue triangle, respectively.
Figure 16.
Effect of the bout amplitude threshold in the results of Experiment 1. The blue circles represent bouts with amplitude higher than 0.04 ppm/s ( threshold) and the green circles represent bouts with amplitude higher than 1.0 ppm/s. In each case, a hand-drawn ellipse outlines the approximate plume shape based on the location of the bouts. The green and blue stars indicate the source location estimate in each case, according to the maximum bout frequency.
Figure 16.
Effect of the bout amplitude threshold in the results of Experiment 1. The blue circles represent bouts with amplitude higher than 0.04 ppm/s ( threshold) and the green circles represent bouts with amplitude higher than 1.0 ppm/s. In each case, a hand-drawn ellipse outlines the approximate plume shape based on the location of the bouts. The green and blue stars indicate the source location estimate in each case, according to the maximum bout frequency.
Figure 17.
3D map of the instantaneous concentration (ppm) in Experiment 2. The black square indicates the gas source location (x,y,z) = (14.0, 5.2, 2.7) m, the black arrow the wind direction (positive x-axis) and the letter ‘S’ the starting point of the drone (x,y,z) = (13.5, 5.2, 0.0) m.
Figure 17.
3D map of the instantaneous concentration (ppm) in Experiment 2. The black square indicates the gas source location (x,y,z) = (14.0, 5.2, 2.7) m, the black arrow the wind direction (positive x-axis) and the letter ‘S’ the starting point of the drone (x,y,z) = (13.5, 5.2, 0.0) m.
Figure 18.
Results of Experiment 2. (A) 2D map of the instantaneous concentration (ppm), with odor hits represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the panel on the left. The box plots below the map represents the instantaneous concentration along the x-axis; (B) Drone trajectory in the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum instantaneous concentration and the maximum bout frequency are indicated by a green star and a blue triangle, respectively.
Figure 18.
Results of Experiment 2. (A) 2D map of the instantaneous concentration (ppm), with odor hits represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the panel on the left. The box plots below the map represents the instantaneous concentration along the x-axis; (B) Drone trajectory in the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum instantaneous concentration and the maximum bout frequency are indicated by a green star and a blue triangle, respectively.
Figure 19.
Results of Experiment 2 when is increased to 0.18 ppm/s. (top) 2D map of the instantaneous concentration (ppm), with odor hits represented by blue circles. A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. (bottom) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The maximum bout frequency is indicated by a blue triangle.
Figure 19.
Results of Experiment 2 when is increased to 0.18 ppm/s. (top) 2D map of the instantaneous concentration (ppm), with odor hits represented by blue circles. A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. (bottom) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The maximum bout frequency is indicated by a blue triangle.
Figure 20.
Results of Experiment 3. (A) 2D map of the instantaneous concentration (ppm), with bouts represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the leftmost panel. The box plot below the map represents the instantaneous concentration along the x-axis; (B) Drone trajectory in the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum of the instantaneous concentration and the bout frequency are indicated by a green star and a blue triangle, respectively.
Figure 20.
Results of Experiment 3. (A) 2D map of the instantaneous concentration (ppm), with bouts represented by blue circles ( ppm/s). A hand-drawn ellipse outlines the approximate plume shape based on the location of bouts. The average bout frequency along the y-axis is shown in the leftmost panel. The box plot below the map represents the instantaneous concentration along the x-axis; (B) Drone trajectory in the z-axis. (C) Temporal evolution of the instantaneous concentration (ppm), with detected bouts highlighted in red (the black star indicates the start of the bout). The bout frequency (gray line) is computed using a sliding window of 5 s. The identifiers R1–R4 between panels (B) and (C) indicate the area of the map in which the drone is flying at each moment. The maximum of the instantaneous concentration and the bout frequency are indicated by a green star and a blue triangle, respectively.
Table 1.
Characterization of MOX signals at different distances of the source under two conditions: propellers switched on or off.
Table 1.
Characterization of MOX signals at different distances of the source under two conditions: propellers switched on or off.
Distance | Propellers | Mean (ppm) | Variance (ppm2) | Bout Frequency (Bouts/min) | Bout Amplitude (ppm/s) |
---|
Above 25 cm | OFF | 10.05 | 60.46 | 3.52 | 0.39 |
ON | 9.22 | 29.97 | 7.69 | 0.084 |
Above 65 cm | OFF | 1.39 | 0.053 | 0.48 | 0.027 |
ON | 2.67 | 0.53 | 7.74 | 0.015 |
Front 50 cm | OFF | 1.68 | 0.59 | 1.13 | 0.10 |
ON | 1.45 | 0.12 | 0.47 | 0.10 |
Table 2.
Gas source localization error (m) in the three experiments, using the instantaneous concentration, the bout frequency with threshold or the bout frequency with optimum threshold.
Table 2.
Gas source localization error (m) in the three experiments, using the instantaneous concentration, the bout frequency with threshold or the bout frequency with optimum threshold.
Experiment | Instantaneous Concentration | Bout Frequency | Bout Frequency (Optimum Threshold) |
---|
1 | 0.94 | 4.32 | 1.16 |
2 | 4.0 | 3.31 | 2.22 |
3 | 1.22 | 5.07 | 0.77 |
Mean | 2.05 | 4.23 | 1.38 |