Sea Surface Temperature Sensors for Australian Vessels

Summary

Remotely sensed sea surface temperature (SST) data are important inputs to ocean, weather, seasonal and climate models.  In order to improve validation of satellite SST and ocean models in the Australian region, there is a need for high quality in situ SST observations with greater  spatial and temporal coverage than is currently available from moored and drifting buoys.  

Prior to 2008, SST observations from ships in the Australian region, available via the Global Telecommunications System (GTS), were either of significantly poorer accuracy than those available from buoys or difficult to access in a timely manner.  Commencing in 2008, as part of the IMOS project, new streams of high quality, near real-time (within 24 hours), SST observations from 20 vessels in the Australian region have become available on the Global Telecommunications System (GTS) and the AODN Portal.  

The amount of IMOS ship SST data on the GTS now significantly exceeds that available from other vessels in the Australian region.  During 2015 twelve ships of opportunity provided near real-time, quality controlled SST from the IMOS SST Sensors Sub-facility.

Cruise tracks of 18 vessels providing SST data to IMOS and the GTS between 4 February 2008 and 3 June 2013.
Cruise tracks of 18 vessels providing SST data to IMOS and the GTS between 4 February 2008 and 3 June 2013.

Instrumentation and Data

As part of the IMOS Project, eleven commercial vessels have been fitted with a hull-contact temperature sensor (SeaBird SBE48), attached by magnets to the inside of a ship’s hull.  These calibrated sensors have supplied real-time, high-quality sea surface temperature data every hour, transmitted via satellite to the Bureau of Meteorology in Melbourne for processing.  

In addition, since 2008 seven research vessels and two fast passenger ferries already instrumented with through-hull ocean temperature sensors (SeaBird SBE 38) have supplied 1-minute averaged SST data every few hours to the IMOS Ocean Portal. A list of ships and SST sensors can be found here.

The SeaBird SBE 48 Hull Contact Temperature Sensor (left) installed against the exterior hull of the PV Spirit of Tasmania II in the bow thruster room, and (right) covered with the custom-made insulating pad.
The SeaBird SBE 48 Hull Contact Temperature Sensor (left) installed against the exterior hull of the PV Spirit of Tasmania II in the bow thruster room, and (right) covered with the custom-made insulating pad.

Comparisons with sea surface temperature (SST) observations from satellites indicate that the IMOS ship SST data streams from the calibrated SBE48 and SBE38 sensors provide SST data in the top few metres of the ocean ('SSTdepth') with comparable errors to those available from drifting buoys – see Beggs et al. (2012) and IMOS SST validation web pages.  It was therefore concluded that that these IMOS ship SST data will benefit the validation of satellite SST products, and validation of ocean models, over regions lacking in buoy observations such as coastal areas and the Southern Ocean.

Although the SSTdepth measurements from ships can be used for validation of remotely sensed SST measurements, this application is limited by the thermal stratification of the top few metres of the ocean, particularly in regions of high solar insolation and low winds.  

In October 2014, an Infra-red Autonomous Radiometer (ISAR) was installed on the RV Investigator, and has supplied 1 minute averaged observations of 'skin' SSTs in the top 10 to 20 microns of the ocean ('SSTskin'), the same depth sampled by infra-red radiometers on satellites.  More information about the ISAR SST calibration, quality control, data format and data access can be found here.

The benefits of sustaining these SSTdepth and SSTskin data streams from ships are:

  • Improved validation of satellite SST and ocean models, particularly over coastal regions where other in situ SST data are lacking
  • Enhanced input into operational SST analyses, particularly over data sparse areas such as cloudy coastal regions
  • Significantly improved accuracy of ship SST over the Australian region input into long-term, global in situ SST data sets (eg. HadSST3, ICOADS)
  • The SST radiometer on RV Investigator will provide the first ever sustained data stream in the Southern Hemisphere of in situ skin SST, traceable to NIST temperature standards and capable of validating satellite SST to climate quality.

Applications of Data

The National Oceanographic and Atmospheric Administration (NOAA) provides all IMOS SOOP SST (available from the IMOS Ocean Portal) via its In Situ Quality Monitoring (iQuam) web site.  The IMOS SOOP SST data are quality controlled by the iQuam system using comparisons against two daily global SST analyses (NCDC Reynolds and Canadian Meteorological Centre).  

These comparisons indicate that the IMOS ship SST are significantly more accurate (less RMS error) than those available from non-IMOS ships and comparable in RMS error to Argo SST.  NOAA analysis of the IMOS ship SST data sets also indicated that the Bureau quality flags in the IMOS ship SST data files “add value” (i.e. identified an additional 2.1% of anomalous SST values not identified by the NOAA iQuam QC procedure).  For the period Jan 2008 to Dec 2014 a combination of iQuam QC and Bureau QC applied to the Bureau’s IMOS ship SST data sets resulted in a bias of 0.05°C and standard deviation of 0.42°C when compared with the Canadian Meteorological Centre daily 0.2° resolution SST analyses.

 

 

Number of observations of in situ SST from ships available from the Global Telecommunications System (dark green) and IMOS ships of opportunity (lime green), quality controlled and provided via the NOAA In Situ Quality Monitoring (iQuam) web site (http://www.star.nesdis.noaa.gov/sod/sst/iquam/v2/).
Number of observations of in situ SST from ships available from the Global Telecommunications System (dark green) and IMOS ships of opportunity (lime green), quality controlled and provided via the NOAA In Situ Quality Monitoring (iQuam) web site (http://www.star.nesdis.noaa.gov/sod/sst/iquam/v2/).

The Bureau of Meteorology uses the near real-time SOOP SST data for ingestion into operational SST analyses of satellite and in situ data (RAMSSA and GAMSSA - www.bom.gov.au/marine/sst.shtml) and for routine validation of real-time (fv01) and reprocessed (fv02) IMOS HRPT AVHRR SST data.