1. Instrument related problems with optical backscatter sensors
Joan Backers
Royal Belgian Institute of Natural Sciences, OD Natural Environment,
3de & 23ste Linieregimentsplein, B-8460 Ostend, Belgium

2. Introduction 1. Short history of the OD Nature tripod moorings.
2. Calibration procedures.
3. Problems with an OBS-3+ sensor connected to a LISST-100X. 2

3. 1. Short history of the OD Nature tripod moorings.
First tripod deployment in 2003 with R/V Belgica.

6. 23 May 2011: Tripod ready for deployment near MOW1 pile.

7. 11 July 2011: Tripod recovered after diver intervention (surface buoy disappeared).

8. First considerations:
For continuous moorings you need a good planning:
Man power
Vessel availability
Sufficient number of instruments
Weather conditions play an important role in the recuperation of the tripod
What if surface buoy is gone? Need for Navy divers
Real-time data transmission
Virtual AIS for the protection of the mooring

9. 2. Calibration procedures
2.a. In the lab with AmcoClear
Use same data acquisition system as during field measurements.
Used for veryfying sensors.

10. 2.b.Watersampling and in-situ measuring
A typical configuration for turbidity calibration measurements:
2 Sea-Bird SBE09 data acquisition systems
6 turbidity sensors
6 five litre Niskin bottles
Procedure:
13h cycle
during all seasons
water sampling every 20 minutes (2 bottles)
vertical cast every 30 minutes at low speed
bottles are emptied at the hour
immediate filtration

11. Configuration table of both SBE09 CTD systems
SBE09 SN
parameter
Instrument
Model
Serial Number
Remarks
792
C1, T1
Sea-Bird
N/A -
C2, T2 D
86815
Voltage V0-V1
Campbell Scientific
OBS-3
1811
0 – 2000
Voltage V2-V3
OBS-3+
T8730
: 2000
Voltage V4-V5
T8849
0 – 500 : 2000
Voltage V6-V7
T8557
206
04:03
1857:2306
39867
None
DataSonics
PSA-100
altimeter
1801
Seapoint
0-25
12755
range * 5 (0 – 125)

12. Results of the comparison of the analysed water samples (SPM) and the turbidity measurements (NTU).

15. Considerations:
Is the filling of the Niskin bottles during calm weather conditions and low current flow fast enough?
A test is planned with one OBS-3+ inside a bottle and one OBS-3+ at the outside of the Niskin bottle.
The distance of the carousel to the bottom is not constant during a 13 hour cycle. Do we have to take this variation into account?
Would it be better to sample with horizontal mounted Niskin bottles? Does a multiple bottle system exist on the market?

16. 3. Problems with a OBS-3+ sensor connected to a LISST-100X
Upper graph: OBS-3+ low range (LR) connected to LISST-100X
Middle graph: OBS-3+ high range (HR)connected to LISST-100X
Lower graph: 2 OBS-3+ connected to a SonTek hydra system

17. Data values of previous slide sorted from high to low.
The values of the OBS-3+ connected to the LISST-100X are much to low.

18. Analysis of the problem let to a correction factor.

19. Measuring configuration for the determination of the correction values.

20. The reason for bad data values of OBS-3+ connected to LISST-100X: LISST power to external instruments is insufficient.
6 Volt DC
1 Volt DC
Turbidity = 0 NTU, MA = 10

21. 6 Volt DC
1 Volt DC
Turbidity = 2000 NTU, LR analogue channel, MA = 10

22. 6 Volt DC
1 Volt DC
Turbidity = 2000 NTU, HR analogue channel, MA = 10

23. 6 Volt DC
1 Volt DC
Turbidity = 0 NTU, MA = 50

24. 6 Volt DC
1 Volt DC
Turbidity = 2000 NTU, LR analogue channel, MA = 50

25. 6 Volt DC
1 Volt DC
Turbidity = 2000 NTU, HR analogue channel, MA = 50

26. 6 Volt DC
1 Volt DC
Turbidity = 0 NTU, MA = 150

27. 6 Volt DC
1 Volt DC
Turbidity = 2000 NTU, LR analogue channel, MA = 150

28. How does an OBS3+ react to a power shortage

29. Considerations:
The problem is that neither the LISST-100X neither the OBS-3+ gives a warning for a low voltage.
How are other data acquisition systems working? With a Sea-Bird you can set a pre-measurement period (eg. 4 seconds for warming up a sensor)