OCSv2 Description:
The Ocean Carbon System version 2 (OCSv2) consists of 4 sensors, 1 pump, 1 submersible data logger, a solar power package, and cellular telemetry package. The equipment models and serial numbers (s/n) are: Pro-Oceanus CO2-Pro CV (s/n 37-398-75) for measurement of carbon dioxide concentration; Sea-Bird/Satlantic SeapHOx sensor (s/n PSH-1008) for measurement of pH on the total scale; Sea-Bird SBE 37-SMP-ODO MicroCAT C-T-ODO (P) Recorder (s/n 37-15715) for measurement of dissolved oxygen, salinity, temperature and depth; Sea-Bird/WET Labs ECO-PAR (s/n PARS-529) for measurement of photosynthetically active radiation (PAR); Sea-Bird/Satlantic STOR-X data logger (s/n StorX-210) and a Sea-Bird SBE-5P submersible pump (s/n 9272). Sensor resolution is as follows: Pro-Oceanus CO2-Pro 0.01 ppm; 1 mbar for PRESS(IRGA); SeapHOx 0.004 pH; Sea-Bird SBE 37-SMP-ODO MicroCAT C-T-ODO (P) Recorder 0.0001 degrees C for temperature; 0.00001 siemens for conductivity (used by the instrument to calculate salinity) and 0.002% of full scale range; 0.001 mg/L for dissolved oxygen; and ECO-PAR 14-bit digital output resolution.
The sensors were packaged as a single unit in a custom designed platform that was mounted on a navigational mooring. The Sea-Bird SBE-5P submersible pump pulls water through a stainless copper mesh strainer and pumps the water to the CO2-Pro CV for pCO2 measurement. The sensors not requiring flow are located in close proximity to the pump intake and measure ambient water. The STOR-X and sensors are powered by a 90 watt solar panel and rechargeable battery system.
The STOR-X distributes power to the attached sensors according to a custom schedule. The OCSv2 operates 24 hours per day, with a sampling acquisition period once every hour at the half-hour mark prefaced by a 20-minute warm up period for the CO2-Pro CV. The sampling acquisition period runs for approximately 00:01:10. The CO2 sensor re-zeros every 8 hours and collects approximately 35 CO2 and PRESS(IRGA) measurements during each sampling period. The ECO-PAR sensor collects approximately 51 PAR measurements per sample period. The SeapHOx collects 3 pH measurements per sample period. The SBE 37 collects 3 conductivity, temperature, dissolved oxygen and pressure measurements per sampling period.
Data Storage and Preprocessing:
Data are managed and stored by the STOR-X data logger. Acquired data are saved into sensor-specific .raw files that contain the information for each Julian day. Downloading this data from the site occurs at regular intervals to ensure the sensors operational status. Downloading these .raw files from the STOR-X requires the use of STORXCom software to communicate between the STOR-X and a computer. Once the data are downloaded, SatCon version 1.5 Data Conversion program converts the .raw files into .dat files and applies any processing required. Individual sensor Julian day .dat files are then combined into one large multi-day dataset per sensor. These files are opened in Microsoft (MS) Excel 2010 and saved in the .xlsx format. The combined multiday files contain headers for each individual day file that are strung together; these must be manually removed in MS Excel leaving only the top header line. Multi-day files are then processed through a custom averaging code written in Pearl, designed by David Zawada (USGS). This code averages the multiple measurements from each sensor per sampling period to generate a single averaged value for each sensor per sampling period, reported at the start time of the sampling period and day. In addition to averaging parameter values, the code also provides the mean, standard deviation, minimum and maximum for each sampling period. Averaged data for each sensor parameter are then manually merged into a single .xlsx file for further processing. Data files are deleted from the STOR-X after confirmation of successful download and storage of parameter data. Additionally, processed data are transferred hourly from the STOR-X through a Satlantic Land/Ocean Biogeochemical Observatory (LOBO) cellular telemetry system and are available online at
http://tampabay.loboviz.com/.
Advanced Data Processing:
Preliminary QA/QC of sensor data are performed after averaged data are compiled into .xlsx files and after advanced data processing is performed. The SeapHOx pH data are corrected for salinity and temperature, using Sea-Bird SBE 37-SMP-ODO MicroCAT C-T-ODO (P) Recorder data through a MS Excel macro provided by Satlantic. The Satlantic macro is also used to perform a single point calibration of the SeapHOx pH data using discrete pH measurements determined in- situ and concurrently with OCS sample acquisition. Discrete pH measurements are performed using spectrophotometric pH methods. Once corrections have been completed, parameter data are plotted to examine sensor performance and identify non-trending outliers. Cross validation of sensor parameters is performed to further analyze outliers and identify questionable or bad data points. Further validation of pH and CO2 sensor data is performed by comparing sensor values to values measured in discrete water samples. Discrete pH is measured using spectrophotometric measurements. CO2 is calculated from discrete measurements of pH and dissolved inorganic carbon (performed using carbon coulometry methods). Measurement of sensor data is validated with discrete data approximately every 3 weeks.
