Download pptx - SUNA V2 Data Processing Temperature & Salinity Compensation Geoff MacIntyre May 15, 2014

SUNA V2 Data Processing

Temperature & Salinity CompensationGeoff MacIntyre

May 15, 2014

©2014 Sea-Bird Scientific Inc.

Outline

• SUNA V2 technology overview• Principles of operation• Temperature & salinity compensation• Data processing and analysis


SUNA V2 overview

Submersible ultra-violet spectrophotometer• Developed from the original MBARI ISUS technology• Measures dissolved NO3 concentration directly through UV absorbance• Integrated wiper for anti-biofouling

UV LIGHT SOURCE UV SPECTROMETER


Two versions

Deep SUNA• 2000 m pressure rating• Integrated with Argo floats• Anodized aluminum housing

SUNA V2• 200 m pressure rating• Integrated bio-wiper• Acetyl housing, titanium coupler


Configurations

Moorings

GlidersCTD’s

Profilingfloats


UV spectroscopy

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

200 210 220 230 240 250

wavelength (nm)

exti

nct

ion

NO3

Br

Extinction coefficients for NO3 and Br

Compounds that absorb strongly in UV


Absorbance spectroscopy

Reference spectrum – ultrapure deionized water

Sample spectrum – water containing nitrate

Absorption due to Nitrate


Nitrate calculationBeer-Lambert law

Relates the concentration of dissolved materials in water to the absorption of light travelling through the water

Absorbance = -log10(I/Io)

… where I = reference spectrum and I0 = sampled spectrum

SUNA calculates absorption spectrum 217 – 240 nm (~ 35 channels) SUNA calibration file has extinction coefficients for NO3 and Br-

Absorption spectra de-convolved to individual absorbers using the MBARI method Br- is a conservative component of seawater (i.e. relative proportion is consistent

regardless of salinity) Therefore, if salinity is known, [Br-] can be calculated accurately


Temperature salinity correction

Seawater is known to have temperature-dependent absorption properties (Sakamoto et al 2009)

Extinction properties of Br- change with temperature

This adds a 4th variable into the equation i.e. NO3, Br, T, baseline

Both the temperature effect and the absorption by Br can be mitigated by providing temperature and salinity data (e.g. SBE CTD) for the nitrate calculation

Only have to solve for NO3 and baseline

Baseline absorption includes as absorption that cannot be attributed to calibrated species


Temperature salinity correction

• TS correction algorithm from Sakamoto et al 2009 has been added to SUNACom

• Only valid for instruments that are calibrated for use in seawater• Requires TS data either from:

• SUNA data frames that were recorded in APF operating mode • float controller sends TS data to SUNA for real-time TS processing

• External TS data file


SUNACom

Dashboard area

Main view area

Output area

Menu bar


Reprocess data


Reprocess dashboard

Load instrument XML fileLoad calibration file

Load data file(s)

Choose output directory

Process


Temperature & salinity correction

Temperature & Salinity correction option appears

when calibration file with Br coefficients is loaded….


Temperature & salinity data

Click on down arrows and options appear…

1. Check box next to “Activate Temperature & Salinity…”

2. Choose eithera. TS data from SUNA APF

Mode framesor

b. Data from external file

3. Load external file

4. Apply time offset (if applicable)


External TS data file

The data in that file must be in the following ASCII format:

YYYY-MM-DD hh:mm:ss,Temperature[C],Salinity[PSU] 2012-11-10 09:08:07,12.3,34.567

Example of TS data from a .csv file…

15/08/2012 18:21 26.4376 0.0264

15/08/2012 18:22 26.4523 0.0262

15/08/2012 18:23 26.449 0.0253

15/08/2012 18:24 26.4236 0.0247

15/08/2012 18:25 26.3614 0.0242


APF mode TS correction

Only available on the Deep SUNA

In APF mode, AUV controller sends TS data to Deep SUNA in real-time

TS data used in onboard calculation of nitrate

TS data stored in Deep SUNA data files


All files loaded

XML file loaded

CAL file loaded

Data file(s) loaded

TS correction selected

TS data file loaded

Process!


Graph results

Original nitrate

Reprocessed nitrate

Absorption due to Br-

Absorption due to NO3-


Common problems

TS data file must follow defined format• Saved as .CSV file

Time stamp has to be in the following format• YYYY-MM-DD hh:mm:ss

Time stamps in both files must overlap• If the clocks were offset, inset time offset

No additional formatting info associated with file• Manipulating file with some programs adds formatting

information that may not be visible• Difficult to detect


Questions

Thank you!