CHARACTERIZING THE VARIABILITY IN THE INHERENT AND APPARENT OPTICAL PROPERTIES DURING THE LEO-15 1998 COASTAL PREDICTIVE SKILL EXPERIMENTS

By Mark M. Moline & Oscar M. Schofield
Presented at ASLO-99, on February 5, 1999, in Santa Fe, NM
Our phenomenological focus during the 1998 Coastal Predictive Skill (CPS) experiments was to characterize the impact of coastal upwelling in shallow waters (5-30 m) on nearshore bulk optical properties. Shipboard data was complemented by ocean color data collected by the SeaWiFs satellite. The timing and location of the shipboard transects were adaptively adjusted based upon real-time data collected from the LEO-15 profilers, satellites and physical shipboard surveys. Optical properties on the ships were measured using a Wetlabs absorption/attenuation meter (ac-9), a Wetlabs submersible fixed wavelength spectrofluorometers (SAFIRE), a profiling Satlantic spectroradiometer, and a BioSpherical spectroradiometer. A short summary of what we learned is shown below.

Figure 1. The upwelling eddy and front are clearly visible in AVHRR, surface current radar, and SeaWiFs imagery. According to the ocean color data, pigment concentrations were clearly enhanced within the upwelling waters. Prior to the upwelling, satellite imagery indicated low pigment concentrations in these nearshore waters. In collaboration with Dr. Robert Arnone (Naval Research Laboratory) efforts are underway to test ocean color algorithms being developed for Case 2 coastal waters.




Attenuation at 440 nm

Figure 2. The in situ inherent optical properties varied in space in time. This figure shows several cross shelf transects of light attenuation at 440 nm as measured with an ac-9 during the 1998-CPS experiments. Prior to upwelling, the optical loads in these coastal waters were low, except for very nearshore. The heavy optical loads here reflected the material being transported out of the local estuaries. Upon initiation of upwelling, the optical front was extended further offshore. The edge of the offshore optical front agreed well with the satellite and radar imagery. The optical front moved inshore as the upwelling ended.




Figure 3. A) The offshore extent of the optical front was clearly extended offshore by the coastal upwelling.
B) There was good agreement between the apparent and inherent optical properties.



Figure 4. Other then the optical front, there was significant vertical variability in the inherent and apparent optical properties. This variability could largely be accounted for by the local current patterns. This figure illustrates local current patterns as measured an ADCP mounted on the Majid tow vehicle. Overlaid on the hydrography is the absorption as measured by an ac-9 at 676 nm. Optical loads were clearly enhanced within water flowing to the south in the nearshore waters. These optical loads were dominated by particulate matter and had fluorescence loads indicating the presence of phytoplankton.


Conclusions

1) The optics prior to upwelling is low in offshore waters and the nearshore waters are dominated by material being transported out of the local estuaries.
2) Upwelling results in enhanced phytoplankton concentrations, which is clearly visible in both satellite and in situ optical data.
3) Upwelling extends the optical front further offshore. The optical front moves inshore as upwelling ends.
4) Vertical variability in the inherent optical properties is driven by local current patterns.


I hope you enjoyed this annotated presentation on optical properties at LEO-15. If you have any questions email Oscar Schofield at the address below.
Questions???

oscar@ahab.rutgers.edu