Reports

Three PME miniDOT sensors (sn 1219, sn 1220, sn 1221) were installed at Mayberry since fall 2014 at different depths under the water level. On 2017-05-10, the three sensors were moved from a fence post in the middle of the channel to a fixed boom attached by guywire to the tower.  The three sensors were co-located 10cm under the water level (20 cm above the soil level). Two weeks later on 2017-05-25, Joe installed a floating boom and we adjusted the depth of the sensors. Two sensors (sn 1219, sn 1221) were located 17cm under the water level. The third sensors (sn 122) was located 62cm under the water level. These two periods provide a chance to quickly cross-compare the sensors.

2017-05-10 to 2017-05-25: sn 1219, sn 1220, sn 1221 at -10cm depth

2017-05-25 to 2017-06-05: sn 1219 and sn 1221 at -17cm depth (sn 1220 at -62 cm depth)

Conclusion: Comparison between sensors was messier than I expected. They generally follow the same diurnal pattern, but timing of rising/falling limb differ, and daily max/min values differ.

In fact, the sensor at -17cm and -62cm compared better than the two sensors at -17cm. Perhaps the funky sensor was affected by dead vegetation or insects inside the mesh, near the sensing foil.

Figure 1. Dissolved oxygen when all 3 sensors were co-located 10cm below water level. There seems to be something wrong with sn 1220 for most of this period--maybe gunk stuck inside the mesh? It clears up around 2017-05-23, about 2 days before we move it to the lower position. The other 2 sensors (sn 1219 and sn 1221) seem relatively well matched; the diurnal dynamics are similar, but sn 1219 sometimes had higher daily max and/or lower daily min value.

Figure 2. Scatter when 3 sensors were co-located 10cm below water level. Very messy scatter with sn 1220 (green line). Some scatter for sn 1219 (blue line), but at least R²~84%.

Figure 4. Dissolved oxygen when only 2 sensors were co-located. Surprisingly, sn 1221 (-17cm, green line) matches better with sn 1220 (-62cm, purple line) than with sn 1219 (-17cm, teal line). Again, sn 1219 had higher daily max and lower daily min values.

Figure 5. Scatter when only 2 sensors were co-located. A lot of scatter, but again, the two sensors that are NOT co-located match better (R²~67%) than with the two sensors that ARE co-located (R²~57%). Neither comparison is as good as the R²~84% when sn 1221 and sn 1219 were co-located at -10cm.

Figure 6. Temperature data from the whole comparison. The 3 sensors were co-located at -10cm depth from 2017-05-10 to 2017-05-25. Temperature data reinforces the conclusion from Fig. 1 (dissolved oxygen time series) where there was something weird about sn 1220 (purple line) for most of the comparison period, but the other 2 sensors match. Perhaps there was gunk blocking sn 1220 sensing foil, because it has muted daily max/min value compared to the other 2 sensors. After 2017-05-25, only 2 sensors were co-located. The two co-located sensors match with each other. The third sensor is very similar, but has some lower temperatures in the early morning--not sure if this is real or not.

Figure 7. Temperature scatter when 3 sensors co-located at -10cm depth. Generally well matched with slopes close to 1 and offset close to 0. More scatter (R2=77) with sn 1220 (green line), very well matched (R2=99) than with sn 1219 (blue line).

Figure 8. Temperature scatter when only 2 sensors were co-located. All sensors match well with slopes close to 1 and offset close to 0. Not much scatter with either sensor.