Author Contributions
Conceptualization, C.H. and C.B.; methodology, C.B.; software, Z.X.; validation, C.H.; formal analysis, C.B.; investigation, C.B., C.H., T.P., and Z.X.; resources, C.H.; data curation, C.B., T.P, and Z.X.; writing—original draft preparation, C.B.; writing—review and editing, C.B. and C.H.; supervision, C.H.; project administration, C.H.; funding acquisition, C.H. All authors have read and agreed to the published version of the manuscript.
Figure 1.
(a) Leddar and SR50A sonic ranging device co-located on a tower. Approximation of sensor beam footprint; not to scale. Leddar segment 1 orientation is the north side of the tower. The sensor emits defuse LED light and receives return signals for 16 segments. The ground surface footprint is dependant on the height of the sensor above the target, and the beam length and depth. (b) LeddarTech IS16 pulsed based time of flight LED LIDAR sensor logging to a Raspberry Pi 3.
Figure 1.
(a) Leddar and SR50A sonic ranging device co-located on a tower. Approximation of sensor beam footprint; not to scale. Leddar segment 1 orientation is the north side of the tower. The sensor emits defuse LED light and receives return signals for 16 segments. The ground surface footprint is dependant on the height of the sensor above the target, and the beam length and depth. (b) LeddarTech IS16 pulsed based time of flight LED LIDAR sensor logging to a Raspberry Pi 3.
Figure 2.
The West Castle Field Station tower and snow depth monitoring sensors (Leddar and SR50A), the totalizing precipitation gauge located south of the tower, and the meteorological sensors for the 2017–2018 snow season collecting wind speed, wind direction, air temperature (temp), barometric pressure (BP), relative humidity (RH), and incoming and reflected shortwave (SW) and longwave (LW) radiation. A temperature sensor was located at the ground surface to collect ground temperature.
Figure 2.
The West Castle Field Station tower and snow depth monitoring sensors (Leddar and SR50A), the totalizing precipitation gauge located south of the tower, and the meteorological sensors for the 2017–2018 snow season collecting wind speed, wind direction, air temperature (temp), barometric pressure (BP), relative humidity (RH), and incoming and reflected shortwave (SW) and longwave (LW) radiation. A temperature sensor was located at the ground surface to collect ground temperature.
Figure 3.
Data flow diagram of the Leddar-Raspberry Pi for the 2017−2018 Snow Season. TS refers to timestamp, Seg# refers to segment number, DTT-F# is the distance to target for flag number, Int-F# is the intensity for flag number, Cnt-F# is the number of returns received for the status flag number, Tot-Flags is the total count of both flag numbers, and %F1 is the percentage of Flag = 1 returns for the segment.
Figure 3.
Data flow diagram of the Leddar-Raspberry Pi for the 2017−2018 Snow Season. TS refers to timestamp, Seg# refers to segment number, DTT-F# is the distance to target for flag number, Int-F# is the intensity for flag number, Cnt-F# is the number of returns received for the status flag number, Tot-Flags is the total count of both flag numbers, and %F1 is the percentage of Flag = 1 returns for the segment.
Figure 4.
Leddar snow depth 15 December 2017 to 27 April 2018.
Figure 4.
Leddar snow depth 15 December 2017 to 27 April 2018.
Figure 5.
Leddar intensity return signal from 15 December 2017 to 27 April 2018. Before the implementation of all of the quality control steps.
Figure 5.
Leddar intensity return signal from 15 December 2017 to 27 April 2018. Before the implementation of all of the quality control steps.
Figure 6.
Leddar “noise” in the data from 14 December 2017 to 27 April 2018. The noise is the proportion of the data per time step that received noisy returns in relation to the total number of returns. Time series of readings culminated in
Table 3a—proportion of noisy returns.
Figure 6.
Leddar “noise” in the data from 14 December 2017 to 27 April 2018. The noise is the proportion of the data per time step that received noisy returns in relation to the total number of returns. Time series of readings culminated in
Table 3a—proportion of noisy returns.
Figure 7.
Leddar intensity (mean all segments), air temperature, sample precipitation events. Initial examination of the Leddar intensity signal suggests an LED light output sensitivity to air temperature.
Figure 7.
Leddar intensity (mean all segments), air temperature, sample precipitation events. Initial examination of the Leddar intensity signal suggests an LED light output sensitivity to air temperature.
Figure 8.
Proportion of clean signals (a) and mean hourly Leddar signal intensity (b) by month from December to April. The box delineates the lower 25th and upper 75th percentiles. The dashed T-lines are the minimum and maximum values and open circles to the left and right of the dashed T-line are outliers. The black dot inside the box is the mean.
Figure 8.
Proportion of clean signals (a) and mean hourly Leddar signal intensity (b) by month from December to April. The box delineates the lower 25th and upper 75th percentiles. The dashed T-lines are the minimum and maximum values and open circles to the left and right of the dashed T-line are outliers. The black dot inside the box is the mean.
Figure 9.
Reflective target placed on the ground under the Leddar unit. SR50A footprint and Leddar Segment 16 were not contained within the target surface. (a) Boxplot of Leddar and SR50A DTT, (b) boxplot of Leddar Intensity. (Note: SR50A does not return intensity signal measurements).
Figure 9.
Reflective target placed on the ground under the Leddar unit. SR50A footprint and Leddar Segment 16 were not contained within the target surface. (a) Boxplot of Leddar and SR50A DTT, (b) boxplot of Leddar Intensity. (Note: SR50A does not return intensity signal measurements).
Figure 10.
(a) Plot of Leddar segment mean against SR50A mean snowpack depth. (b) Plot of Leddar segment depth range (bars) and mean (blue square) against manual field measurements.
Figure 10.
(a) Plot of Leddar segment mean against SR50A mean snowpack depth. (b) Plot of Leddar segment depth range (bars) and mean (blue square) against manual field measurements.
Table 1.
Leddar and SR50A sonic ranger manufacturer technical specifications [
24,
29].
Table 1.
Leddar and SR50A sonic ranger manufacturer technical specifications [
24,
29].
Sensor | Leddar IS16 | SR50A Sonic Ranging Device |
---|
Type | Leddar LED Multichannel LIDAR sensor, built-in processing chip performing proprietary temperature adjusted Full-Waveform analysis for multi-object detection distance measurement | SR50AA Sonic Ranging Sensor with independent temperature compensation |
Manufacturer | LeddarTech Inc. | Campbell Scientific (Canada) Corp. |
Distance | 0 to 50 m | 0.5 to 10 m |
Operating Temp | −40 °C to +50 °C | −45 °C to +50 °C |
Accuracy | ±50 mm Quoted for a moving target | ±10 mm or 0.4% of DDT (greater value) |
Precision | 6 mm (manufacturer specification if intensity > 15) | |
Resolution | 10 mm | 0.25 mm |
Measurement Rate | Up to 50 Hz | Less than 1.0 second |
Emitter | Single LED diffused light source beam | Sonic Ranging ultrasonic pulses |
Receiver | Measurement of backscatter on a 16-Channel photodetector array | Listening for return echoes |
Beam Length | 48° (Distance from sensor * 0.8905) | 30° (Radius = 0.268 * Height) |
Segment Length | 1/16 of the Beam Length (Beam Length / 16) | N/A |
Beam Depth | 8° (Distance from sensor * 0.1402) | N/A |
Wavelength | 940 nm (infrared) | 50 kHz (Ultrasonic) electrostatic transducer |
Table 2.
Leddar measurement configuration settings used for the 2017–2018 snow season.
Table 2.
Leddar measurement configuration settings used for the 2017–2018 snow season.
Parameter | Configuration | Description |
---|
Distance Units | cm | Unit of measurement for distance to target |
Accumulations | 1024 | Range: 0 to 1024. Higher values enhance the range for DTT below 10 m, reduce the measurement rate and noise |
Measurement Rate | 1.5625 Hz | Range: 1.5625 to 50 Hz. Rate of signal measurement. Lower values give highest accuracy and precision (also known as Refresh Rate) |
Oversampling | 8 | Range: 1–8. High values reduce measurement rate and increase accuracy |
Point Count | 12 | The number of base sample points |
Threshold Offset | 0.00 | Range: −5% to 100%. Modifies intensity threshold. At 100%, no detections. Negative values increase likelihood of false measurements. |
LED Control | Automatic | LED power level setting |
Change Delay | 1 (640 ms) | Number of measurements before sensor changes LED power level |
Object Demerging | Enabled | Indicates detection of multiple objects in return signal |
Crosstalk Removal | Enabled | Degradation compensation from object detections in other segments |
Useful Range | 21.3 m | Leddar sensor computed value based on configuration settings |
Table 3.
From 14 December 2017 to 27 April 2018, n = 3211 (1-hour timestep) per segment (SEG) for the entire data collection period. (a) Leddar data series proportion of clean and noise returns. (b) The proportion of timestep observations with no clean returns refers to the amount of data for all 15-minute measurement cycles where the sensor did not detect any clean readings. (c) Leddar intensity signal minimum, maximum, mean, and range.
Table 3.
From 14 December 2017 to 27 April 2018, n = 3211 (1-hour timestep) per segment (SEG) for the entire data collection period. (a) Leddar data series proportion of clean and noise returns. (b) The proportion of timestep observations with no clean returns refers to the amount of data for all 15-minute measurement cycles where the sensor did not detect any clean readings. (c) Leddar intensity signal minimum, maximum, mean, and range.
SEG | Proportion of Clean Returns | Proportion of Noisy Returns | Proportion of Timestep Observations with no Clean Returns | Intensity |
---|
Min | Max | Mean | Range |
---|
1 | 99.2% | 0.8% | 0.0% | 10.0 | 45.2 | 29.3 | 35.2 |
2 | 99.7% | 0.3% | 0.0% | 13.7 | 61.6 | 40.8 | 47.9 |
3 | 97.5% | 2.5% | 0.0% | 18.6 | 82.0 | 55.0 | 63.4 |
4 | 96.4% | 3.6% | 0.1% | 24.8 | 105.1 | 70.9 | 80.3 |
5 | 94.6% | 5.4% | 0.1% | 26.0 | 123.2 | 83.4 | 97.2 |
6 | 91.1% | 8.9% | 2.1% | 30.3 | 128.0 | 87.8 | 97.6 |
7 | 88.9% | 11.1% | 2.2% | 32.1 | 134.0 | 92.6 | 101.9 |
8 | 84.9% | 15.1% | 5.6% | 31.6 | 131.7 | 92.7 | 100.1 |
9 | 81.7% | 18.3% | 5.5% | 31.3 | 134.5 | 94.8 | 103.1 |
10 | 33.4% | 66.6% | 38.5% | 29.2 | 135.3 | 105.1 | 106.1 |
11 | 87.5% | 12.5% | 1.2% | 29.3 | 136.1 | 94.3 | 106.8 |
12 | 84.8% | 15.2% | 5.9% | 24.6 | 118.8 | 83.9 | 94.2 |
13 | 88.4% | 11.6% | 0.3% | 20.4 | 96.1 | 66.3 | 75.7 |
14 | 97.0% | 3.0% | 0.0% | 17.6 | 75.6 | 51.9 | 58.0 |
15 | 98.5% | 1.5% | 0.4% | 12.9 | 57.8 | 39.7 | 44.8 |
16 | 96.9% | 3.1% | 1.4% | 7.7 | 38.3 | 26.0 | 30.6 |
(a) | (b) | (c) |
Table 4.
Pearson’s Correlation coefficient (r) for the Leddar (mean of all segments) sensor and other meteorological variables for the given timestep. “% Clean” is the proportion of clean returns.
Table 4.
Pearson’s Correlation coefficient (r) for the Leddar (mean of all segments) sensor and other meteorological variables for the given timestep. “% Clean” is the proportion of clean returns.
| Daily Albedo | Air Temperature | Leddar VT | Leddar Intensity |
---|
| r | r | r | r |
---|
Leddar Intensity | 0.77 | −0.77 | −0.43 | - |
Leddar % Clean | 0.59 | −0.57 | −0.13 | 0.74 |
Table 5.
Maximum snowpack depth occurred on 8 April 2018 10:00. Leddar segments and SR50A snow depth. From 14 December 2017 to 27 April 2018 winter season 1-hour dataset, n = 3211.
Table 5.
Maximum snowpack depth occurred on 8 April 2018 10:00. Leddar segments and SR50A snow depth. From 14 December 2017 to 27 April 2018 winter season 1-hour dataset, n = 3211.
SR50A | Leddar Segment (m) |
---|
(m) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
---|
0.83 | 0.81 | 0.79 | 0.80 | 0.77 | 0.75 | 0.75 | 0.75 | 0.76 | 0.77 | 0.75 | 0.78 | 0.78 | 0.81 | 0.85 | 0.85 | 0.85 |
Table 6.
Manual field measurement, SR50A, Leddar (all 16 segments), mean air temperature, and daily albedo. Manual snow depth measurements taken from behind the tower out of the sensor footprints under the Leddar unit, but exact location varied with each visit. All data collected on calm days with no precipitation.
Table 6.
Manual field measurement, SR50A, Leddar (all 16 segments), mean air temperature, and daily albedo. Manual snow depth measurements taken from behind the tower out of the sensor footprints under the Leddar unit, but exact location varied with each visit. All data collected on calm days with no precipitation.
Site Visit Date | 21-Dec | 05-Jan | 20-Jan | 21-Feb | 04-Mar | 09-Apr | 15-Apr | 19-Apr | 26-Apr | 27-Apr | 27-Apr |
---|
Start Time | 18:30 | 11:00 | 15:00 | 10:45 | 14:45 | 14:00 | 14:00 | 18:15 | 06:00 | 07:00 | 11:15 |
End Time | 22:30 | 15:00 | 19:00 | 14:45 | 18:45 | 18:00 | 18:00 | 21:45 | 10:00 | 11:00 | 12:30 |
Snow Depth (m) | | | | | | | | | | | |
Manual Field Sample | 0.35 | 0.40 | 0.36 | 0.70 | 0.74 | 0.77 | 0.53 | 0.58 | 0.28 | 0.20 | 0.17 |
SR50A Mean | 0.31 | 0.44 | 0.36 | 0.66 | 0.72 | 0.71 | 0.59 | 0.57 | 0.29 | 0.21 | 0.17 |
SR50A Min | 0.29 | 0.42 | 0.35 | 0.65 | 0.72 | 0.70 | 0.59 | 0.56 | 0.28 | 0.20 | 0.06 |
SR50A Max | 0.31 | 0.45 | 0.36 | 0.69 | 0.72 | 0.73 | 0.60 | 0.58 | 0.29 | 0.22 | 0.20 |
| | | | | | | | | | | |
Leddar Mean | 0.28 | 0.36 | 0.31 | 0.61 | 0.66 | 0.65 | 0.54 | 0.53 | 0.23 | 0.14 | 0.12 |
Leddar Min | 0.24 | 0.32 | 0.27 | 0.54 | 0.61 | 0.59 | 0.48 | 0.46 | 0.16 | 0.08 | 0.06 |
Leddar Max | 0.38 | 0.40 | 0.37 | 0.70 | 0.74 | 0.75 | 0.62 | 0.61 | 0.32 | 0.24 | 0.21 |
Proportion clean returns | 92% | 83% | 81% | 93% | 93% | 59% | 47% | 49% | 79% | 63% | 28% |
Air Temperature (°C) | −6.2 | 3.2 | −0.3 | −13.4 | −7.4 | 7.4 | 7.5 | 5.0 | 4.8 | 5.1 | 16.8 |
Daily Albedo | 0.84 | 0.83 | 0.80 | 0.81 | 0.85 | 0.77 | 0.69 | 0.73 | 0.59 | 0.58 | 0.58 |
Table 7.
Leddar and SR50A sensor snow depth data from 20:00 26 December 2017 to 06:00 27 December 2017 nighttime sampling period meeting the minimum specifications.
Table 7.
Leddar and SR50A sensor snow depth data from 20:00 26 December 2017 to 06:00 27 December 2017 nighttime sampling period meeting the minimum specifications.
Leddar | Snow Depth (m) |
---|
Segment | Mean | STDev | Min | Max | Range |
---|
1 | 0.191 | 0.001 | 0.190 | 0.194 | 0.004 |
2 | 0.181 | 0.001 | 0.180 | 0.183 | 0.003 |
3 | 0.189 | 0.001 | 0.188 | 0.190 | 0.002 |
4 | 0.179 | 0.001 | 0.178 | 0.181 | 0.003 |
5 | 0.157 | 0.001 | 0.156 | 0.158 | 0.002 |
6 | 0.162 | 0.001 | 0.161 | 0.164 | 0.003 |
7 | 0.161 | 0.001 | 0.160 | 0.163 | 0.003 |
8 | 0.174 | 0.001 | 0.173 | 0.176 | 0.003 |
9 | 0.179 | 0.001 | 0.178 | 0.182 | 0.003 |
10 | 0.169 | 0.001 | 0.168 | 0.172 | 0.003 |
11 | 0.173 | 0.001 | 0.172 | 0.175 | 0.003 |
12 | 0.176 | 0.001 | 0.175 | 0.178 | 0.003 |
13 | 0.191 | 0.001 | 0.189 | 0.193 | 0.003 |
14 | 0.212 | 0.001 | 0.211 | 0.215 | 0.004 |
15 | 0.197 | 0.002 | 0.195 | 0.200 | 0.005 |
16 | 0.211 | 0.001 | 0.210 | 0.214 | 0.004 |
SR50A (m) | 0.174 | 0.008 | 0.164 | 0.185 | 0.021 |