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 m 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 or contact: Long Term Measurements of Physical and Optical Properties with Profiling Floats Lisa Taylor 1, Emmanuel Boss 1, Peter Brickley 1, Dana Swift 2, Ron Zaneveld 3, and Peter Strutton 4 1 School of Marine Sciences, University of Maine, 2 School of Oceanography, University of Washington, 3 WET Labs, 4 College of Oceanic and Atmospheric Sciences, Oregon State University