IN-SITU OBSERVATIONS
195
2. In-situ techniques and platforms
As also highlighted in the chapter by I. Robinson in this volume, a very
tightly integrated approach is needed between remote sensing and in-situ
observations, in order to provide the data necessary for the modelling
procedures in operational ocenography and ocean forecasting. None of the
two methodologies alone can acquire the ocean data required with sufficient
accuracy, 4-D coverage and 4-D resolution. This section is organized on a
platform basis for clarity, but the guiding principle in all cases will be the
way in which in-situ data are indispensable for providing information
impossible to obtain with remote sensing, or for complementing, validating
and calibrating remote sensing data.
At the end of this section, Table 1 provides an overview of the platforms
with their costs, strengths and weaknesses. This can help in guiding through
the following sections, comparing the different methods. More importantly,
however, the table is meant to emphasize the complementarity between all
these elements and technologies.
2.1 Profiling floats
Description:
These are platforms that passively follow the horizontal flow in the ocean
interior and periodically rise to the surface for satellite positioning and to
collect profile data on the way up. Originally designed to give the current
field (e.g. a deep reference flow for geoid estimation), they are presently
used more for the T/S profiles they provide. The original rationale was to
have a platform that is so cheap and long-lived (while requiring no other
infrastructure) that it can be used in large numbers anywhere around the
globe. This is still the philosophy, now implemented in the ARGO program,
so most of the floats have only standard sensors. Heavy or power-hungry
sensors cannot be incorporated. ARGO plans to deploy and sustain such
floats on a 3qx3q grid globally, which needs a total of over 3000 instruments
(see also the chapter by S. Pouliquen in this volume). The standard drift
depth is 1000m in ARGO, but for profiling the floats dive down to 2000m
before ascending to the surface. The cycle period is 10 days, and with a
targetted capacity of 180 cycles, the floats are designed to last for 4-5 years.
Application:
Profiling floats in the ARGO approach are intended to complement
satellite altimetry in two ways. From the latter, anomalies of sea surface
height (SSH) can be derived which consists of the steric (dynamic height)
contribution of T and S (H dyn ) and a reference level pressure (P ref ) related
to a barotropic flow component. Symbolically (strictly these are different
quantities which cannot be added), the contributions are
195
2. In-situ techniques and platforms
As also highlighted in the chapter by I. Robinson in this volume, a very
tightly integrated approach is needed between remote sensing and in-situ
observations, in order to provide the data necessary for the modelling
procedures in operational ocenography and ocean forecasting. None of the
two methodologies alone can acquire the ocean data required with sufficient
accuracy, 4-D coverage and 4-D resolution. This section is organized on a
platform basis for clarity, but the guiding principle in all cases will be the
way in which in-situ data are indispensable for providing information
impossible to obtain with remote sensing, or for complementing, validating
and calibrating remote sensing data.
At the end of this section, Table 1 provides an overview of the platforms
with their costs, strengths and weaknesses. This can help in guiding through
the following sections, comparing the different methods. More importantly,
however, the table is meant to emphasize the complementarity between all
these elements and technologies.
2.1 Profiling floats
Description:
These are platforms that passively follow the horizontal flow in the ocean
interior and periodically rise to the surface for satellite positioning and to
collect profile data on the way up. Originally designed to give the current
field (e.g. a deep reference flow for geoid estimation), they are presently
used more for the T/S profiles they provide. The original rationale was to
have a platform that is so cheap and long-lived (while requiring no other
infrastructure) that it can be used in large numbers anywhere around the
globe. This is still the philosophy, now implemented in the ARGO program,
so most of the floats have only standard sensors. Heavy or power-hungry
sensors cannot be incorporated. ARGO plans to deploy and sustain such
floats on a 3qx3q grid globally, which needs a total of over 3000 instruments
(see also the chapter by S. Pouliquen in this volume). The standard drift
depth is 1000m in ARGO, but for profiling the floats dive down to 2000m
before ascending to the surface. The cycle period is 10 days, and with a
targetted capacity of 180 cycles, the floats are designed to last for 4-5 years.
Application:
Profiling floats in the ARGO approach are intended to complement
satellite altimetry in two ways. From the latter, anomalies of sea surface
height (SSH) can be derived which consists of the steric (dynamic height)
contribution of T and S (H dyn ) and a reference level pressure (P ref ) related
to a barotropic flow component. Symbolically (strictly these are different
quantities which cannot be added), the contributions are