geostrophic calculations, together with an estimate
of the reference velocity based on any or all of several considerations: a priori assumptions; classical
water property analysis; conservation of mass and
other conservative properties within a fixed volume;
and direct measurements of velocity. Methods of
applying these considerations have become more
sophisticated and systematic in recent years, but the
conceptual basis for estimating ocean circulation in
WOCE has been essentially unchanged for perhaps
75 years since the Atlantic Expedition of the Meteor.
Even the best hydrographic section is unable to
resolve all the ocean variability. Geostrophic calculations implicitly average the currents between
stations; WOCE sections were not generally eddyresolving. The section is sampled once only, so
time variation is not resolved. Section analyses
generally assume that the observed section is representative of the mean circulation, although some
information about temporal variability over parts
of the section may be known from moored subsurface measurements, floats and drifters or spaceborne measurements.
3.1.1.1 The need for a global programme
At the start of WOCE, far more was known about
the North Atlantic than any other basin. There
were a number of reasons for this. First, its accessibility to the oceanographic institutions of western Europe and eastern North America. Second, its
size, compared with the Pacific for example, made
trans-oceanic sections practical. Third, in comparison with the Indian Ocean and the Pacific, the
Atlantic has the greatest variety of water types and
the most vigorous water mass formation regions,
so it has been the natural first target for surveys of
water properties. During the International Geophysical Year (IGY) only the Atlantic was covered
with a systematic, high-quality, top-to-bottom, continent-to-continent grid of hydrographic stations
(Fuglister, 1960).
In the other oceans, the database was largely
the result of uncoordinated surveys, leaving large
gaps in coverage in one or more of the essential
fields. Any substantial progress in understanding
the global circulation would require a description
of the distributions of heat, fresh water, chemical
tracers, relative geostrophic currents and surface
forcing in the other basins that would permit their
discussion with the same confidence that existed
for the North Atlantic.
WOCE planning defined three Core Projects.
Core Project 1 – ‘The Global Description’ – was to
include a hydrographic and chemical tracer survey,
measurements of sea surface height, especially
from altimeters, wind stress and direct current
measurements.
The shipboard hydrographic programme of
WOCE, known as the WOCE Hydrographic Programme, or WHP, was one of the central elements
of Core Project 1. The WHP consisted of a network of trans-oceanic sections, occupied with highquality CTD (Conductivity-Temperature-Depth)
and bottle sample measurements, with a nominal
along-track spacing of 50 km. Direct measurements of upper ocean currents were made continuously along the ship track with shipboard Acoustic
Doppler Current Profilers (ADCPs). In the latter
stages, these were supplemented with Lowered
ADCPs (LADCPs): self-contained ADCPs lowered with the CTD package, which provide top-tobottom profiles of ocean current at the station.
The fundamental purpose of the WHP was to provide a complete global map of property distributions, and to enable the calculation of fluxes of
those properties across sections. At the start of
WOCE, shipboard ADCP data were not required
observations, though many research ships were
fitted with the instruments. But as the technology
and data quality developed, high-quality data
returns became routine.
This chapter describes the organization and
success of the WHP. Section 3.1.2 covers CTD and
the basic sample measurements: salinity, oxygen
and nutrients. Shipboard and lowered ADCP are
discussed in Section 3.1.3. Shipboard meteorology
measurements are discussed in Section 3.1.4.
A summary of XBT (Expendable Bathythermograph) measurements from research ships and
Voluntary Observing Ships is given by Lindstrom
and Legler (Chapter 3.5). Transient tracers measured from bottle samples are beyond the scope of
this chapter, and are discussed by Schlosser et al.
(Chapter 5.8). Measurements of parameters in the
inorganic carbon system are described by Wallace
(Chapter 6.3).
While it has been pointed out that the WHP
was a central element of Core Project 1, it also
underpinned the other core projects. The overall
WOCE Goals and Core Projects are described by
Thompson et al. (Chapter 1.3). Hydrography provides the dynamical link between the surface and
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
100
of the reference velocity based on any or all of several considerations: a priori assumptions; classical
water property analysis; conservation of mass and
other conservative properties within a fixed volume;
and direct measurements of velocity. Methods of
applying these considerations have become more
sophisticated and systematic in recent years, but the
conceptual basis for estimating ocean circulation in
WOCE has been essentially unchanged for perhaps
75 years since the Atlantic Expedition of the Meteor.
Even the best hydrographic section is unable to
resolve all the ocean variability. Geostrophic calculations implicitly average the currents between
stations; WOCE sections were not generally eddyresolving. The section is sampled once only, so
time variation is not resolved. Section analyses
generally assume that the observed section is representative of the mean circulation, although some
information about temporal variability over parts
of the section may be known from moored subsurface measurements, floats and drifters or spaceborne measurements.
3.1.1.1 The need for a global programme
At the start of WOCE, far more was known about
the North Atlantic than any other basin. There
were a number of reasons for this. First, its accessibility to the oceanographic institutions of western Europe and eastern North America. Second, its
size, compared with the Pacific for example, made
trans-oceanic sections practical. Third, in comparison with the Indian Ocean and the Pacific, the
Atlantic has the greatest variety of water types and
the most vigorous water mass formation regions,
so it has been the natural first target for surveys of
water properties. During the International Geophysical Year (IGY) only the Atlantic was covered
with a systematic, high-quality, top-to-bottom, continent-to-continent grid of hydrographic stations
(Fuglister, 1960).
In the other oceans, the database was largely
the result of uncoordinated surveys, leaving large
gaps in coverage in one or more of the essential
fields. Any substantial progress in understanding
the global circulation would require a description
of the distributions of heat, fresh water, chemical
tracers, relative geostrophic currents and surface
forcing in the other basins that would permit their
discussion with the same confidence that existed
for the North Atlantic.
WOCE planning defined three Core Projects.
Core Project 1 – ‘The Global Description’ – was to
include a hydrographic and chemical tracer survey,
measurements of sea surface height, especially
from altimeters, wind stress and direct current
measurements.
The shipboard hydrographic programme of
WOCE, known as the WOCE Hydrographic Programme, or WHP, was one of the central elements
of Core Project 1. The WHP consisted of a network of trans-oceanic sections, occupied with highquality CTD (Conductivity-Temperature-Depth)
and bottle sample measurements, with a nominal
along-track spacing of 50 km. Direct measurements of upper ocean currents were made continuously along the ship track with shipboard Acoustic
Doppler Current Profilers (ADCPs). In the latter
stages, these were supplemented with Lowered
ADCPs (LADCPs): self-contained ADCPs lowered with the CTD package, which provide top-tobottom profiles of ocean current at the station.
The fundamental purpose of the WHP was to provide a complete global map of property distributions, and to enable the calculation of fluxes of
those properties across sections. At the start of
WOCE, shipboard ADCP data were not required
observations, though many research ships were
fitted with the instruments. But as the technology
and data quality developed, high-quality data
returns became routine.
This chapter describes the organization and
success of the WHP. Section 3.1.2 covers CTD and
the basic sample measurements: salinity, oxygen
and nutrients. Shipboard and lowered ADCP are
discussed in Section 3.1.3. Shipboard meteorology
measurements are discussed in Section 3.1.4.
A summary of XBT (Expendable Bathythermograph) measurements from research ships and
Voluntary Observing Ships is given by Lindstrom
and Legler (Chapter 3.5). Transient tracers measured from bottle samples are beyond the scope of
this chapter, and are discussed by Schlosser et al.
(Chapter 5.8). Measurements of parameters in the
inorganic carbon system are described by Wallace
(Chapter 6.3).
While it has been pointed out that the WHP
was a central element of Core Project 1, it also
underpinned the other core projects. The overall
WOCE Goals and Core Projects are described by
Thompson et al. (Chapter 1.3). Hydrography provides the dynamical link between the surface and
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
100