Analysis of the seasonal stratification at the Acqua Alta Oceanographic Tower, northern Adriatic Sea LUIGI ALBEROTANZA*, JACOPO CHIGGIATO and GIULIANA PROFETI CNR-ISDGM, S. Polo 1364 - 30125 Venezia, Italy Abstract. Underwater biological, optical and physical measurements have been carried out at the Acqua Alta Oceanographic Tower (AAOT) in the northern Adriatic Sea on behalf of the European project ‘Coastal region long- term measurements for colour remote sensing development and validation’ (COLORS). This project is aimed at studying the variability of bio-optical properties and testing existing bio-optical algorithms for the major water parameters. In particular, this paper deals with the analysis of underwater profiles of optical and physical parameters, which are aimed at studying the seasonal development of stratification in the water column. The first part of this paper describes the analysis of long-term series of physical measurements, such as temperature, salinity and conductivity, to enhance the development of stratification. The influence of stratification on the optical properties of the water column is discussed in the second part of the paper, and illustration is made of the application of the previous results to the analysis of the underwater profiles of downwelling irradiance and upwelling radiance. 1. Introduction The Adriatic Sea is a basin semi-enclosed by the Italian and the Balkan peninsulas (see figure 1). The Acqua Alta Oceanographic Tower (AAOT) is located in its northern part, at 45.3139‡ latitude and 12.5083‡ longitude, approximately 15 km east of the city of Venice. The average bottom depth at the tower site is 17 m. The tower and its instrumentation are described in detail in Cavaleri (2000). The tower is currently used as a test site on behalf of the European project ‘Coastal region long-term measurements for colour remote sensing development and validation’ (COLORS). Biological, optical and physical measurements along the water column have been carried out since October 1998, in order to study the bio-optical properties of the water. As the biological properties of water are strictly related to their physical characteristics, data analysis has been aimed first at studying inter-annual and intra-annual variability of temperature and salinity profiles and then relating them to the coastal dynamic processes in the North Adriatic. Among these, the seasonal development of stratification is particularly International Journal of Remote Sensing ISSN 0143-1161 print/ISSN 1366-5901 online # 2004 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/01431160310001592472 An updated version of a paper originally presented at Oceans from Space ‘Venice 2000’ Symposium, Venice, Italy, 9–13 October 2000. *e-mail: luigi.alberotanza@ismar.cnr.it INT. J. REMOTE SENSING, 10–20 APRIL, 2004, VOL. 25, NO. 7–8, 1473–1480