IN-SITU OBSERVATIONS
199
2.3.2 Volunteer observing ships
Description:
Volunteer observing ships (VOS) are merchant vessels which are willing
to collect underway sampling (or deploy instruments) for free as they transit
along their most economical paths (which are not always the same, and they
do not stop or slow down for measurements). Thus they are useful for
performing repeat section measurements on trans-basin paths, with a repeat
interval of usually 2-4 weeks. Most measurements are only at the surface of
the ocean (sampling water from the engine intake), but this is done for an
increasing number of variables. For example complete CO 2 analyzers are
now installed on various ships. Depth profiles are limited to temperature, for
which the expendable XBT probes are used (normal profile depth is 800m),
employing automatic launching system. XCTDs to measure also
conductivity are used more rarely because of their high cost.
Application:
The so-called low-density sampling of the GOOS XBT program is
carried out on 70 VOS on 26 transects in the three ocean basins at a density
of usually 4 profiles per day (note that commercial vessel are usually twice
as fast as research ships). These data are used operationally for
weather/climate forecasting (e.g. by NCEP) and for climate research. Further
VOS sampling is organized by the Ship of Opportunity Program (SOOP).
These include high-resolution XBT lines, which sample every 50km in the
open ocean and every 10-30km in boundary currents, some ADCP
measurements, and pumped surface observations of temperature, salinity,
pCO 2 , and chlorophyll.
Strengths and weaknesses:
This is a cost-effective methods for collecting data with high resolution
along repeated trans-oceanic tracks. For the surface layer, a wide range of
variables can be measured now. However, the initial installation of
equipment may be difficult, and then there is no guarantee that a ship
operator will not change ship routes or destinations. Spatial coverage is
limited to commercial ship routes, and subsurface sampling (profiles) is
restricted to temperature and usually not deeper than 800m.
Further readings: Smith at al (2001), Upper ocean thermal center website,
SOOP website.
2.4 Moorings and fixed platforms
Description:
199
2.3.2 Volunteer observing ships
Description:
Volunteer observing ships (VOS) are merchant vessels which are willing
to collect underway sampling (or deploy instruments) for free as they transit
along their most economical paths (which are not always the same, and they
do not stop or slow down for measurements). Thus they are useful for
performing repeat section measurements on trans-basin paths, with a repeat
interval of usually 2-4 weeks. Most measurements are only at the surface of
the ocean (sampling water from the engine intake), but this is done for an
increasing number of variables. For example complete CO 2 analyzers are
now installed on various ships. Depth profiles are limited to temperature, for
which the expendable XBT probes are used (normal profile depth is 800m),
employing automatic launching system. XCTDs to measure also
conductivity are used more rarely because of their high cost.
Application:
The so-called low-density sampling of the GOOS XBT program is
carried out on 70 VOS on 26 transects in the three ocean basins at a density
of usually 4 profiles per day (note that commercial vessel are usually twice
as fast as research ships). These data are used operationally for
weather/climate forecasting (e.g. by NCEP) and for climate research. Further
VOS sampling is organized by the Ship of Opportunity Program (SOOP).
These include high-resolution XBT lines, which sample every 50km in the
open ocean and every 10-30km in boundary currents, some ADCP
measurements, and pumped surface observations of temperature, salinity,
pCO 2 , and chlorophyll.
Strengths and weaknesses:
This is a cost-effective methods for collecting data with high resolution
along repeated trans-oceanic tracks. For the surface layer, a wide range of
variables can be measured now. However, the initial installation of
equipment may be difficult, and then there is no guarantee that a ship
operator will not change ship routes or destinations. Spatial coverage is
limited to commercial ship routes, and subsurface sampling (profiles) is
restricted to temperature and usually not deeper than 800m.
Further readings: Smith at al (2001), Upper ocean thermal center website,
SOOP website.
2.4 Moorings and fixed platforms
Description: