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

©2014 Sea-Bird Scientific Inc. Outline SUNA V2 technology overview Principles of operation Temperature & salinity compensation Data processing and analysis

©2014 Sea-Bird Scientific Inc. 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

©2014 Sea-Bird Scientific Inc. 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

©2014 Sea-Bird Scientific Inc. Configurations Moorings Gliders CTD’s Profiling floats

©2014 Sea-Bird Scientific Inc. UV spectroscopy Extinction coefficients for NO3 and Br Compounds that absorb strongly in UV

©2014 Sea-Bird Scientific Inc. Absorbance spectroscopy Reference spectrum – ultrapure deionized water Sample spectrum – water containing nitrate Absorption due to Nitrate

©2014 Sea-Bird Scientific Inc. Nitrate calculation Beer-Lambert law Relates the concentration of dissolved materials in water to the absorption of light travelling through the water Absorbance = -log 10 (I/I o ) … where I = reference spectrum and I 0 = sampled spectrum  SUNA calculates absorption spectrum 217 – 240 nm (~ 35 channels)  SUNA calibration file has extinction coefficients for NO 3 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

©2014 Sea-Bird Scientific Inc. 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 4 th 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

©2014 Sea-Bird Scientific Inc. 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

©2014 Sea-Bird Scientific Inc. SUNACom Dashboard area Main view area Output area Menu bar

©2014 Sea-Bird Scientific Inc. Reprocess data

©2014 Sea-Bird Scientific Inc. Reprocess dashboard Load instrument XML file Load calibration file Load data file(s) Choose output directory Process

©2014 Sea-Bird Scientific Inc. Temperature & salinity correction Temperature & Salinity correction option appears when calibration file with Br coefficients is loaded….

©2014 Sea-Bird Scientific Inc. Temperature & salinity data Click on down arrows and options appear… 1.Check box next to “Activate Temperature & Salinity…” 2.Choose either a.TS data from SUNA APF Mode frames or b.Data from external file 3.Load external file 4.Apply time offset (if applicable)

©2014 Sea-Bird Scientific Inc. 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] :08:07,12.3, Example of TS data from a.csv file… 15/08/ : /08/ : /08/ : /08/ : /08/ :

©2014 Sea-Bird Scientific Inc. 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

©2014 Sea-Bird Scientific Inc. All files loaded XML file loaded CAL file loaded Data file(s) loaded TS correction selected TS data file loaded Process!

©2014 Sea-Bird Scientific Inc. Graph results Original nitrate Reprocessed nitrate Absorption due to Br - Absorption due to NO 3 -

©2014 Sea-Bird Scientific Inc. 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

©2014 Sea-Bird Scientific Inc. Questions Thank you!