expanding the capabilities of argo-type floats stephen c. riser university of washington
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EXPANDING THE CAPABILITIES OF ARGO-TYPE FLOATS Stephen C. Riser University of Washington Seattle, Washington USA [email protected]. Longevity of US Argo floats as a function of deployment year; the US longevity is consistently 5-10% higher than for non-US float programs. - PowerPoint PPT PresentationTRANSCRIPT
EXPANDING THE CAPABILITIES OF ARGO-TYPE FLOATS
Stephen C. RiserUniversity of WashingtonSeattle, Washington USA
Longevity of US Argo floats as a function of deployment year; the US longevity is consistently 5-10% higher than for non-US float programs
Presently: 2 types of US Argo floats
APEX(UW; PMEL)
SOLO(SIO; WHOI)
Argos antenna
Cowling(air and oil bladders inside)
SeaBirdCTD unit
Configuration:T, S, p sensors
ARGOS70 samples, 0-2000 m
Up to 275 profiles10-day sampling
Air bladder outside, oil bladder inside
Float technology, communications, and new sensors…
Low latitude profiling
A new type of float: SOLO-II Communications: Iridium
Other sensors: O2 , nitrate, wind speed, rainfall, SST, SSS
Profiling under sea ice
Displacement volume (cm3) necessary to profile to 2000 m for a float with the volume and mass of APEX 260 ( 240 cm3 usable).
Note the lack of necessary displacement volume for profiles to 2000 m at low latitudes. There are now remedies for this problem.
[ Note: problems within 13 of the Equator ]
Main Piston
Oil
Piston
Oil
N2 Gas
Oil Bladder
[ 200 dbar ]
Result: 330 cm3 displacement
For N2 floats, the additional oil and piston connected to the gas canister provide a means to store energy as the gas is compressed during the float descent and recover this energy and use it to increase the float’s buoyancy during the ascent phase.
An APEX N2 float…
N2 APEX float showing the main piston and pump assembly and N2 canister
[ marginal cost $400]
N2 canister
Main piston
Cowling(bladder inside)
[ see Argonautics No. 10 for more details ]
2000 m profiles….
t = 20.76
[data from 71 levels]
Solo-II Profiling Float
• Compact, lightweight, efficient.• Reduced labor for assembly. • 2000 m profiles anywhere.• Long life (~6 years).• No air bladder.• Reciprocating pump (same as
Spray glider)• Scalable (in length, batteries,
sensors).• Pumping system adaptable for
deep-ocean profiling.
Prototype SOLO-2 floats are now undergoing lab-testing; deployments soon.
SOLO-I and SOLO-II
SOLO-I SOLO-II
# of dive cycles ~180 ~200
Energy (kJ)/divew/SBE-41cp 22.5 10.3
Max depth (dBar) 2300 2300
Ocean coverage @ Max depth ~45% 100%
Telemetry ARGOS Iridium
Surface time (hr) 14 0.25
Mass (kg) 30.4 18.6
Main pressure-case length (in) 41 26
Seek capability Bidirectional Bidirectional
SOLO Version Comparison
SOLO-II internal view, SOLO-I in back
Dissolved oxygen measurements from profiling floats
UW float 894, with SBE O2 sensor, operated for more than 3 years in the N. Pacific and showed evidence of blooms and net O2 production (Riser and Johnson, Nature, 2008; Martz et al., L-O, in press).
2 types of O2 sensors:SBE and Aanderaa Optode
Float 8948/02 – 7/0599 profilesThe first SBE O2 sensor
worked well for nearly3 years, showing onlysmall instrument drift over that time.
[ now more than 150 floats with O2
deployed in Argo; 2 types of sensors;see O2 White Paper for details ]
Profiling float end capwith PAL hydrophone addedthat can be used to make acoustic measurements of wind speed and rainfall, ason UW float 0006
Year-long trajectory of float 0006 in the Bay of Bengal
h
2h
Wind speed and rainfall (PAL)…
[ h 650 m ]
The wind speed from the float and from QwikScat agree well at speeds below about 10 m/sec.
[similar good comparisons between float/PAL and TRMM rainfall]
Surface salinity in the Bay of Bengal can be very low due to rain events and large river input
Surface salinity in the Bay of Bengal is correlated to both position of the float in the basin and rain input events (Riser et al., L-O, in press)
TRMM
2004 2005
5 m SALINITYWIND SPEED
RAIN RATE
rivers/near coast
rainfall effect
SW
mo
nso
on
(w
et)
SW
mo
nso
on
(w
et)
NE
mo
nso
on
(d
ry)
Faster communications: IRIDIUM
2-way communication with floats (mission changeable after deployment; many downloadable commands: profile depth,interval between profiles, sampling interval, etc.)
Fast communication compared to ARGOS ( 180 byte/seccompared to < 1 byte/sec)
Short times on the surface ( 6 minutes for a 55 KB, high resolution deep profile, compared to 9 hours for a low resolution 0.8 KB profile with ARGOS)
Use of new sensors and high-resolution experiments become possible
Cost per profile greater than ARGOS; cost per byte << ARGOS (in the US only)
Iridium floats (approximately 150 deployed):
An antenna suitable for both Iridium and GPS communications is required for Iridium floats, as well as numerous changes to internal electronics.
CTD data from UW Iridium float 5037, showing high resolution T and S data (p = 2 dbar) over a 2000 m profile (1000 T/S/p samples); surface time 6 minutes
✭
1000 m parking depth
[data from 1000 levels]
CTD and O2
data from float5209 in the Bayof Bengal
Uses of Iridium….
Drift-phase sampling
More complex sensors that require shore-based processing
Applications requiring 2-way communication
Operation under sea-ice
Aug 1 2007
Antarctic sea ice cover: recent seasonal extremes
There are now over 75 UW Argo floats in the Antarctic ice zone, with more to be deployed late in 2008. The data from these will yield new clues to the nature of ocean/atmosphere/ice interaction and climate change in the Antarctic.
Polarstern 2/25/08
Argo float positions in and around the seasonal ice zone in the Antarctic.
For the first time, large amounts of data can be collected under the Antarctic ice in winter.
These floats store profile data internally while under ice and transmit the saved profiles during ice-free periods.
The floats are programmed with an ice-avoidance algorithm.
Water properties in Oct. 2007
Water properties in Feb. 2008
Research questions: heat budget;fresh water budget; seasonal variabilityin the ice zone; oxygen uptake/production; nutrient (NO3) variability; long-term changes?
Nitrate Sensors on Profiling Floats:A collaboration between UW and MBARI
Iridiumantenna
CTD unit
Optode
Carbon fiber hull
ISUS
Spectro- photometer
UV light source
ISUSelectronics
ISUS sensor
ISUS electronics
ISUS sensor
Sensor guard
The NO3 sensor (ISUS) consists of a spectrophotometer and a light source. With3 Li battery packs, this float should be capable of about 275 profiles. If a good pH sensor was added, a nearly complete carbon budget could be constructed from a single float.
Profile 21, 3/10/08[near Hawaii]
T/S
T/O2
T/NO3
(WMO 5901468)
To examine the relationship between the near surface (5 m)salinity and the true sea surface salinity, we have recentlydeployed an Argo-type float with a 2nd CTD sensor thatcan continue to collect CTD data all the way to the sea surface,known as the STS (surface temperature/salinity) unit.
The data stream from theSTS float is designed to allowthe STS sensor to be comparedand recalibrated to the mainSBE41CP CTD unit on eachprofile, thus insuring thespecified accuracy.
This is an example of typical temperature and salinity profilesfrom the STS sensors. Note that the measurments continue to be collected until the float breaks the sea surface during its ascent.
SUMMARY:
There are a number of new technical developments taking place with profiling floats, including new float designs, new sensors, and faster communications. Some of these new features are already commercially available.
When planning for the observing system of the future, the utility of these developments should be taken into consideration, both globally and regionally.