5th Workshop on "SMART Cable Systems: Latest
Developments and Designing the Wet Demonstrator
Project"
(Dubai, UAE, 17-18 April 2016)
Contribution of SMART cable systems to
Ocean and Climate Science
Jerome Aucan,
Research Scientist, IRD France
Jerome.aucan@ird.fr
Contribution of initial sensors
• Spatial and temporal variability of deep-ocean
temperatures.
• Temporal variability of tides, which impacts tidal
corrections for satellite missions.
• Ocean circulation response to wind forcing.
• Impact of infragravity waves on high-precision
altimetry missions.
Contributions to existing earth observing systems :
space/time coverage
Initial sensors :
• Temperature
– Initial accuracy : ±0.001ºC; Stability: 0.002ºC / year.
• Pressure
– Accuracy : ±1mm H2O relative to recent measurements;
Maximum allowable drift after a settling-in period :
0.2m H2O/year (much better can be achieved ?).
• Accelerometers
Accuracy and stability value from functional requirement
(http://www.itu.int/en/ITU-T/climatechange/task-forcesc/Documents/Functional-requirements-2015-05.pdf)
Contributions to existing earth observing systems
Deep ocean temperatures
• SMART cable temperature measurements could detect current
deep warming trends (0.003-0.010 ºC / year.) within several years :
– Much higher temporal sampling (thus, less aliasing problems) than
other arrays
– Much higher spatial sampling as well (20,000 nodes at 50 km spacing,
compared to projected 1,000 deep global ARGO floats)
Contributions to existing earth observing systems
Deep ocean temperatures
SMART temperature measurements will also allow unprecedented
exploration of temporal variability of deep ocean temperatures due to
tides, eddies, mixing, etc.
Contributions to existing earth observing systems
Sea level
• Sea level, a fundamental property of the ocean, is measured by satellite
altimetry.
• Bottom pressure measurements along cables provide ground truth for
models of tides and other high-frequency motions that must be
subtracted accurately from altimeter records.
Latitude
cm
Longitude
Seasonal amplitude (cm) of the principal lunar semi-diurnal tide M2 along cable routes, sampled
along cable routes in the Pacific and Atlantic from the STORMTIDE model forced by both
atmospheric fields and the astronomical tidal potential (Müller et al., 2014). Courtesy Malte
Müller.
Contributions to existing earth observing systems
Gravity
• Bottom pressure observations
– Proportional to total water mass above.
– Will be valuable ground truth for remotely sensed gravity
missions.
– Could provide an alternative ground truth method for windstress measurements and large-scale ocean circulation.
From Landerer et al. 2016
Contributions to existing earth observing systems
Long surface waves
• Infragravity waves are expected to be a significant
source of error in the planned NASA/CNES SWOT
mission.
• SMART cable bottom pressure data combined with
modeling will improve our ability to remove errors
due to infragravity waves.
Mean seasonal IG wave height
from the DART network
(Aucan& Ardhuin 2014)
• What happens when repeater is buried :
– Temperature data will have to be corrected for
sediment heat flux.
– Pressure data should be unaffected.
• What happens if repeater sinks :
– Effect on temperature will need to be accounted for.
– Induced pressure signal will be monotonic (increasing).
It will need correction for long-term trends but not for
high-frequency and short-term signals.
Wave-induced sinking of a
pressure sensor in the sand.
Thank you