IN-SITU OBSERVATIONS
201
moorings are already able to provide other biogeochemical variables, like
nutrients and O 2 which are critical for biogeochemical models (see chapter
by A. Oschlies in this volume) but are not available from remote sensing.
Strengths and weaknesses:
Moorings are expensive to build and maintain, need a lot of technical
effort, and require regular visits by research vessels. Therefore, only a
limited number of distinct locations can be monitored by moorings. They
have no x-y coverage or resolution, thus normally should be complemented
with other techniques. On the other hand, they are ideal for sampling in the
time domain, covering many multidisciplinary variables, and measuring in
difficult fixed locations (straits, boundary currents). Moored instruments can
be re-calibrated so may serve as in-situ reference stations both for satellite
data and other types of sensors like floats and drifters.
Further readings: Tupper et al (2000), Dickey et al (2001), Dickey (2003),
OceanSITES website.
2.5 Gliders and AUVs
Description:
A new class of platforms are autonomous gliding or self-propelled
vehicles. These navigate under water and can be programmed (or “steered”)
to sample along specific mission tracks. AUVs have propellers, usually not a
very long range or endurance (order of days) and need support ships. Gliders
on the other hand propel themselves by buoyancy changes and wings, thus
they undulate up/down through the ocean. They are still in the prototype
stage. Current versions have a limited speed of 20-25cm/s, a depth range of
1000m, and endurance of 6-12 months. Like floats they are very restricted in
terms of additional payload mass and energy consumption, but usually carry
more sensors than floats. Therefore they have the potential to provide
biogeochemical data like fluorescence (for chlorophyll) and other optical
measurements in a spatial mode and thus to greatly complement timeseries
data from moorings.
Application:
Gliders can be used for repeat transects in remote areas or to complement
VOS lines, either on orthogonal tracks or by providing additional variables.
Every 2 weeks a glider could cover the equivalent of a 300 km XBT section
(though not synoptic, i.e. not a snapshot, but for assimilation into models
this makes little difference). Useage under the ice is also imaginable. Apart
from running along repeat sections, holding position like a “virtual mooring”
is also possible, and even entering a float mode may be feasible soon.
201
moorings are already able to provide other biogeochemical variables, like
nutrients and O 2 which are critical for biogeochemical models (see chapter
by A. Oschlies in this volume) but are not available from remote sensing.
Strengths and weaknesses:
Moorings are expensive to build and maintain, need a lot of technical
effort, and require regular visits by research vessels. Therefore, only a
limited number of distinct locations can be monitored by moorings. They
have no x-y coverage or resolution, thus normally should be complemented
with other techniques. On the other hand, they are ideal for sampling in the
time domain, covering many multidisciplinary variables, and measuring in
difficult fixed locations (straits, boundary currents). Moored instruments can
be re-calibrated so may serve as in-situ reference stations both for satellite
data and other types of sensors like floats and drifters.
Further readings: Tupper et al (2000), Dickey et al (2001), Dickey (2003),
OceanSITES website.
2.5 Gliders and AUVs
Description:
A new class of platforms are autonomous gliding or self-propelled
vehicles. These navigate under water and can be programmed (or “steered”)
to sample along specific mission tracks. AUVs have propellers, usually not a
very long range or endurance (order of days) and need support ships. Gliders
on the other hand propel themselves by buoyancy changes and wings, thus
they undulate up/down through the ocean. They are still in the prototype
stage. Current versions have a limited speed of 20-25cm/s, a depth range of
1000m, and endurance of 6-12 months. Like floats they are very restricted in
terms of additional payload mass and energy consumption, but usually carry
more sensors than floats. Therefore they have the potential to provide
biogeochemical data like fluorescence (for chlorophyll) and other optical
measurements in a spatial mode and thus to greatly complement timeseries
data from moorings.
Application:
Gliders can be used for repeat transects in remote areas or to complement
VOS lines, either on orthogonal tracks or by providing additional variables.
Every 2 weeks a glider could cover the equivalent of a 300 km XBT section
(though not synoptic, i.e. not a snapshot, but for assimilation into models
this makes little difference). Useage under the ice is also imaginable. Apart
from running along repeat sections, holding position like a “virtual mooring”
is also possible, and even entering a float mode may be feasible soon.