STATE OF THE ART AND BEFORE

EVALUATION OF A SUBMERGED REMOTE SENSING (SRS) TECHNIQUE

Trees, Charles C.¹; Pennucci, Giuliana¹; Austin, Ros²; Petzold (Deceased), Ted<sup>3

1</sup>NATO Undersea Research Centre Viale San Bartolomeo 400, 19126 La Spezia, Italy, --, 19126, Italy; ²Center for Hydro-Optics & Remote Sensing/SDSU , San Diego, CA, 92120, United States; ³Visibility Laboratory/ SIO, San Diego, CA, 92120, United States

Currently, there are efforts at using autonomous underwater vehicles, gliders and moorings to extend the spatial and temporal measurement capabilities in oceanographic research. These platforms either operate at fixed depths, programmed to change depths, sea saw, undulated or profile through the water column. Sensor data collected by these platforms is usually internally recorded and then transmitted via satellite-based communications when at the surface or dump via a cable when retrieved by a vessel. A variety of optical instruments have been deployed on these observing platforms with most of them measuring inherent optical properties (IOPs) because day/night illumination differences does not affect these measurements, they can be directly related to in situ properties and are not sensitive to vehicle orientation. Fluorescence sensors also have provided very valuable information related to the biological and dissolved components in the ocean. Disadvantages of IOP measurements, such as absorption, scattering and attenuation measurements as well as fluorescence, are that they measure a small volume and in order to obtain a vertical distribution the platform must profile or undulate. The ability to measure integrated optical properties from the surface to the depth of a platform would be highly advantageous for moorings and AUVs. The Submerged Remote Sensing (SRS) technique takes downwelling irradiance at two wavelengths at a known depth below the ocean surface, and given time, date, position and the extra-terrestrial solar spectral irradiance, computes the total water and atmospheric attenuation above the sensor. Using irradiance profiles from the North Atlantic, the integrated diffuse attenuation (490 nm) was predicted for depths from 20 to 120 m. Mean K(490) ranged from 0.028 to 0.4 m-1 with the average ratio between the SRS to measured K(490) being 0.986 m-1, with a standard deviation of 0.073 m-1. The SRS technique was only published as an SIO Technical Memo 87-18 and is not easily available to the optical community. We plan to explore the robust nature of SRS algorithm using a much larger optical database that has been collected since 1988 at the Visibility Laboratory/SIO and Center for Hydro-Optics and Remote Sensing/SDSU, as well as attempt to extraplote this in to coastal areas.

DIAPHANOUS: OR DAYS OF FLY FISHING IN A SHORT CONVERSATION. WITH SOME ACCOUNT OF THE HABITS OF WHITE SUBMERSIBLE OBJECT OPERATORS BELONGING TO THE GENUS CAPTAIN OR SCIENTIST

Wernand, Marcel Robert<sup>1

1</sup>Royal Netherlands Institute for Sea Research Landsdiep 4, Den Hoorn, Texel, --, 1797 SZ, Netherlands

A standardized method to determine the water clarity (transparency) was adopted at the end of the nineteenth century. This method, lowering a white painted disc into the water until it disappeared out of sight, was described in 1865 by Alessandra Cialdi and Angelo Secchi . However, before 1865 there were several others who experimented, like Cialdi and Secchi, with white and coloured submersible objects to quantify water transparency. Why was it then that this method became known as the Secchi depth method?