Measurements are made using a YSI 6600 water quality sonde with internal datalogging capabilities. YSI Sonde water level sensor uses a non-vented** level depth sensor (stainless steel strain gauge).

**Depth values needed corrections factors applied due to using a non-vented cable with the YSI. Pressure/depth readings needed a post deployment correction to account for changes in ambient atmospheric pressure. Marshview Farm (MFM) weather station 15 minute barometric pressure data was used to compute correction factors at the same time intervals as the 6600 sonde time intervals.
Ambient pressure changes correspond to the following water level changes, 1 mb = 0.0102 meters of water.

To correct our non-vented sonde depth readings for atmospheric pressure effects, we correct the sonde to 1 standard atmosphere (1013 millibars or 760 mm Hg) when we calibrate it, then apply an offset to the depth data (post collection) based on simultaneous measures of barometric pressure

2009 Depth Correction factor calculations for Middle Rd
Sonde is calibrated in air at ambient pressure and should be calibrated to the corresponding depth at pressures relative to 1 ATM (760torr or 1013.25 mBar. 1mB = 0.0102 meters of water, 1 Torr = 1.333224 mB.

If ambient air is 1014.58 mB pressure then sonde should be calibrated to 0.0136 m.
Example table is below.

Ambient ATM (Torr) Ambient ATM (mB) Offset meters
755 1006.58 -.0.0680
756 1007.92 -0.0544
757 1009.25 -0.0408
758 1010.58 -0.0272
759 1011.92 -0.0136
760 1013.25 0.000
761 1014.58 0.0136

For 5/12/2009 the sonde depth was incorrectly calibrated to 0.000(m) instead of 0.0816(m). The error has been corrected/accounted for in the data file.

2009 Sonde Depth calib (m) Offset (m) Calib ATM (mB) Date
0.000, should have been (0.0816m) 0.0816 1021.25 5/12/2009
0.014 0.000 1014.58 6/8/2009
-0.163 0.000 997.65 6/29/2009
0.082 0.000 1021.25 7/23/2009
0.0272 0.000 1015.92 8/18/2009
-0.150 0.000 998.58 9/28/2009
0.136 0.000 1026.58 10/26/2009

Using the table above and measured depth data for the corresponding time intervals with pressure units in mB
Corrected depth (m) = (Measured depth + Offset) - ((Measured BAR- std ATM or 1013.25) x 0.0102)