ABSTRACT

Optical sensors for scattering plus chlorophyll fluorescence were added

to APEX Float 0005 to demonstrate the complementary information

such instruments could provide to future deployments. Float 0005 was

METHODS

Vicarious Calibration. Float 0005 measurements of chlorophyll and

backscatter were vicariously calibrated by comparing the optical

measurements with in-situ data obtained from a bio-optical mooring

(ASIS buoy) co-deployed in the Labrador Sea during the summer of 2004

(Fig. 2). Chlorophyll data were measured at night to avoid non-

photochemical quenching of fluorescence.

Much of this effort has been funded by NASA.

Comparison with Ocean Color. Chlorophyll data from Float 0005 were

compared with satellite imagery obtained from MODIS and SeaWIFS for a

portion of the period during which the float has operated. In general, we

observe good agreement between chlorophyll estimated from the float

and that obtained from remotely sensed ocean color. Both the MODIS and

float data sets show the spring blooms and decline in algal activity during

the winter months, while the SeaWIFS and float data sets mutually

delineate the smaller 2004 fall bloom (Fig. 4).

released in the North

Atlantic at the mouth

of the Labrador Sea in

2004 (Fig. 1). To date,

we have received 168

profiles, one every five

days, each including 50

discrete measurements

from 1,000 m to the

surface. Here we

describe an

experiment designed

to test the

SUMMARY

Good agreement between chlorophyll derived from the float and

that estimated from remotely sensed ocean color.

No significant instrument drift to date, suggesting sensor stability

and lack of fouling.

Physical measurements appear not to have been compromised by

the addition of optical sensors.

After 25 months of operation, Float 0005 has collected and trans-

mitted more than 8,000 measurements for chlorophyll fluorescence,

backscattering, and the physical parameters measured on ARGO floats.

The annual cycle is clearly visible in all parameters, as are the inter-

annual differences in both the physical and optical data (Fig. 5).

RESULTS

Stability. The potential for instrumental drift was evaluated with

respect to measurements obtained at 900-1,000 m below the surface.

Optical sensor stability can be inferred from the consistency of the

deepest measurements, which are not expected to vary appreciably

over time. The measured parameters appear relatively constant (Fig.

3), which suggest that little or no significant drift has occurred to date.

Figure 1. Surface positions of Float 0005 (including drift) as a function of time.

stability of the measurements on such a platform in the hope of con-

veying the usefulness of this approach to the oceanographic community.

Figure 2. Distribution of chlorophyll and bb from Float 0005 and the ASIS buoy as a function of time.

Comparison plots were constructed using the average buoy data collected within 24 hours of float

data. We expected agreement between the data sets to degrade over time as the float and buoy

drifted farther apart.

Figure 5. Distribution of physical and optical properties as a function of time and depth. Data from the top 100-

200m or so show variations typical of near-surface conditions, while the constant measurements at depth

demonstrate that the sensors are stable. Each dot represents a single measurement.

Figure 4. Comparison of chlorophyll obtained from Float 0005, MODIS, and SeaWIFS. The satellite data derive

from a 51km by 51km grid around the float. There is good agreement between chlorophyll estimated from the

float and that estimated from remotely sensed ocean color.

Figure 3. Value of properties from 900-1,000 m as a function of time. Data are stable at this depth, which

suggests that the float’s optical and physical sensors have not drifted appreciably over time.

APEX Float 0005

Float Description

Constructed by Dr. S Riser’s laboratory at the University of Washington (UW).

First AFP9 board deployed with UW firmware.

First use of active optics on profiling floats.

First use of lithium batteries in APEX profilers.

FLSS Scattering & Chlorophyll Fluorescence Sensor

Small, newly-developed, solid-state, active optical sensor developed by WET Labs.

Uses an infrared LED as a source for light scatter and a blue LED to excite chlorophyll fluorescence, both of which are detected with the same red-infrared sensitive detector.

Size: 5 cm in diameter, 3 cm thick.

Power consumption: <10 milliwatts.

Sampling interval: 4 seconds.

Data transmitted as 12-bit integers from the FLSS to the float controller via a serial stream.

Developed by WET Labs under a NOPP contract to Dr. M.J. Perry and C. Ericksen.

Seabird CTD

CONCLUSIONS

A variety of existing and future sensors capable of measuring a

multitude of biogeochemical parameters could be added to APEX

floats in the ARGO program without compromising their original

mission requirements.

Chlorophyll fluorescence and backscattering data can be collected

year-round, in both the vertical and horizontal directions, for

systematic delineation and tracking of particulate organic carbon

and phytoplankton pigment distribution in time and space.

Data can be collected in areas inaccessible by ship, at

significantly less cost than would be required where expeditions

are possible.

Data can be collected under cloudy skies when satellite imagery is

unavailable (thus expanding global coverage), while affording a

means for filling in the gaps in data obtained from remote sensing

platforms such as MODIS and SeaWIFS.

FUTURE WORK

Compare bb data obtained from the float with satellite imagery.

Analyze the science of the data.

Compare Float 0005 results with data obtained from other, similar

floats.

ACKNOWLEDGEMENTS

Visit us at http://misclab.umeoce.maine.edu or contact: emmanuel.boss@maine.edu

Long Term Measurements of Physical and Optical Properties with Profiling FloatsLisa Taylor1, Emmanuel Boss1, Peter Brickley1, Dana Swift2, Ron Zaneveld3, and Peter Strutton4

1School of Marine Sciences, University of Maine, 2School of Oceanography, University of Washington, 3WET Labs,4College of Oceanic and Atmospheric Sciences, Oregon State University