argo profilers missions, sampling rates, accuracy etc

Argo Profilersmissions, sampling rates, accuracy etc

Howard FreelandD.F.O. Science/Pacific Region, Canada

Tel: (250)-363-6590Email: [email protected]

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Argo Profilersmissions, sampling rates, accuracy etc



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The Argo community plans to deploy 3000 floats

And we very nearly are there!

How does an Argo float work?

SOLO Float

Courtesy of the animation wizards at Woods Hole and Scripps.

APEX FloatPROVOR Float

How many of each float type?

20th Nov. 2006

How are floats being launched?

Floats are most commonly launched from research vessels

Dropped from aircraft….

Or deployed from container vessels

The Air Launch is so neat, you’ve got to see this…

Finally, what does a mission look like

X

Alternate missions exist….

Ocean surface

1000 db

2000 db

1) Launch

2) Dive

3) 10-d drift

4) Diveto 2000

5) Profile to 0

6) Transmit data

Etc.

The standard mission repeats 1) to 6) until batteries expire.


Ocean surface

1000 db

2000 db

1) Launch

2) Dive

3) 10-d drift

4) Diveto 2000

5) Profile to 0

6) Transmit data

Etc.

This is Park and Profile, PnP = 2I use PnP = 2, Riser is using 3 or 4

a recent addition is DPF = Deep Profile First

7) Dive

8) 10-d drift

9) Profile to 0


Ocean surface

1000 db

2000 db

1) Launch

2) Dive

to 2000

3) Profile to 0

4) Transmit data

Etc.

a recent addition is DPF = Deep Profile Firstthis enhances quality control if the float was launched

from a research vessel & doing CTDs

5) Dive

6) 10-d drift

7) Profile to 0

New sensors are appearingWater intake and platinum resistance thermometer.

Conductivity cell

Aanderaa optode sensor, for dissolved oxygen which has gained acceptance because of perceived high value for the data return, and has minimal impact on the primary Argo mission.

Wet Labs FLNTU fluorometer & turbidity sensor.

New sensors are appearing

How do we get the critical information?

Two critical items about float performance1) Accuracy, from manufacturer

Resolution

Sensor Accuracy Reported

Pressure 2.4 dbar 0.1

Temperature 0.002 0.001

Salinity 0.005 0.001Analysis of floats recovered with various times at sea shows that these are being met and that sensors usually show little drift.

Two critical items about float performance2) Float energetics

Energy stored on an APEX = 2350 kJ (alkaline cells)=> 220 profiles via Argos

kJ/Profile

Controller 0.71

Buoyancy 4.19

SBE-41 1.55

Argos Communications 2.19

Self discharge 1.67

Total 10.31

The messages are broadcast to a satellite


02442 25410 65 32 J 3 2006-11-17 06:09:37 44.963 233.944 0.000 401652016 2006-11-17 06:03:37 1 72 05 11 A7 85 E2 1B 51 12 6B 85 BB 19 5D 12 B0 85 87 17 6A 14 00 85 79 15 73 14 A2 85 59 13 81

This is message number 5, messages were received in the order:- 7, 8, 7, 9, 10, 11, 1, 10, 2, 5, 7, 9, 10, 8 etc11A7 (hex) = 4519 (decimal) = pressure 451.985E2 (hex) = 34274 (decimal) = salinity 34.274

1B51 (hex) = 6993 (decimal) = temperature 6.993


Floats in the Gulf of Alaska get 24 passes/day and it takes 8 hours to get a profile home.

Floats in the Gulf of Guinea get 12 passes/day and it takes 16 hours to get a profile home, also costs kJ and total profiles.

The consequence is:-

An easy exercise, count the floats in the Gulf of Mexico!

A tightly integrated system A typical Canadian float uses the same parameters that Steve Riser uses, he has advised many nations.

Average latitude = 50°N – 8 hours at sea surface

We use PnP = 2 (i.e. drift at 1000 dbars, profile from 2000 every second profile)

Transmit data from 72 levels

Accuracy as specified by the manufacturer

We have floats running with >170 profiles completed we think 200 profiles/float is likely.

What can we improve or change? Very little it seems….

How can we escape these constraints? Argos

kJ/profileIridium

kJ/profileController 0.71 0.38Buoyancy 4.19 4.14SBE-41 1.55 4.21Communications 2.19 0.40Self discharge 1.67 1.61Total 10.31 10.75Energy stored on an APEX = 2350 kJ (alkaline cells)220 Argos profiles or 208 Iridium profiles – this may change too!

From Webb Research, and I assume Martec/Metocean will follow -

Energy stored on an APEX = 2350 kJ (alkaline cells)220 Argos profiles or 208 Iridium profiles WRC is experimenting with a carbon-fibre hull for their floats.

Lighter material means more batteries can be carried.

Slightly compressible hull implies less energy needed to move from 2000 dbars to the surface.

We can use lithium batteries, but that poses serious operational issues.

In Canada we are not rushing to adopt Iridium communications or lithium batteries, for a variety of reasons, including shipping inflexibility.

How can we escape these constraints? Switching to Iridium has immediate benefits:-1) Only 3 minutes at the sea surface, so grounding risk is greatly

reduced and fouling risk is greatly reduced.2) Much larger files are transferred easily.3) The fraction of profiles passing DMQC will increase.

But, switching to Iridium is not without costs:-1) Iridium does not supply positions, so increased capital cost.2) With only 3 min at the surface we lose surface trajectories.3) Adding Iridium to a standard float does cost energy and,

therefore, profiles.

An Iridium antenna needs care

Standard patch configuration Mai-tai configurationthis IS sub-optimal for communications, but….

An Iridium antenna needs care

Standard patch configuration in tow tank dye testMai-tai configuration in

tow tank dye test

What of the future?

One obstacle for the objective of global coverage is the difficulty of operating in ice-infested waters.

Three approaches have been designed……

1) JAMSTEC/Metocean

2) Germany – ice detection algorithms – store profiles for future transmission

3) US (WHOI – Breck Owens) approach of probing for openings in the ice.

JAMSTEC Under-Ice sampling….

Arctic Argo started this year

German Under-Ice sampling system….

German Under-Ice sampling….

1) Each float has a built-in ice-detection algorithm. If a float detects close approach to the freezing point of sea-water then the ascent is aborted and the profile saved for future transmission.

2) When ice clears the float delivers a set of profiles. This sometimes happens during the ice-covered season if a float is lucky to find a hole in the ice.

3) Profiles are of no value without positions, so each float carries a Rafos receiver that allows it to determine its position underwater.

WHOI Under-Ice sampling system….

1) Use Iridium communications to detect the presence of ice, algorithm is simple:-

a) Have I stopped rising, if yes, can I hear Iridium satellites?

b) If “yes” then the float is in water, if “no” it is under ice.

2) If the float is not under ice, transmit 1 or more profiles.

3) If the float is under ice, descend 50 metres, wait 1 hour and try again, then again, then again.

4) After 50 probes descend to drift depth and wait 10 days.

This system is still experimental but shows great promise. It will work best in marginal ice zones.

Argo is a global ocean sampling program available to anyone anywhere. It is yours, to use as you see fit, but please, please we have

written a data manual, read it…



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argo profilers missions, sampling rates, accuracy etc

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