A METHOD FOR SURFACE AND VOLUME ANALYSIS
OF A 3-D FUNCTION
WITH AN APPLICATION TO SALINITY DATA
ACQUIRED BY THE TOW-FISH SARAGO
DURING CRUISES U1-U2-U3-U4
(PRISMA2 PROJECT, ADRIATIC SEA)

Giovanni Bortoluzzi
Stefano Cozzi
Antonia Di Maio
Marco Marcelli

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IGM-CNR Cataloging-In-Publication data: TECHNICAL REPORT IGM-CNR N.68

A METHOD FOR SURFACE AND VOLUME ANALYSIS OF A 3-D FUNCTION WITH AN APPLICATION TO SALINITY DATA ACQUIRED BY THE TOW-FISH SARAGO DURING CRUISES U1-U2-U3-U4 (PRISMA2 PROJECT, ADRIATIC SEA)

by G. Bortoluzzi, S. Cozzi, A. Di Maio, M. Marcelli

Includes bibliographical reference and index.
1. 3-D functions 2. Adriatic Sea 3. Physical Oceanography 4. Coastal front 5. Undulating Vehicles 6. Tow-fish 7. SARAGO

Abstract - A method is presented for the analysis and modeling of the 3-D physical structure of a seawater volume using CTD-STD oceanographic measurements, along with some issues for its generalization and examples of application in two areas in the NW Adriatic Sea, which present coastal fronts generated by freshwater inputs into the basin. The procedure accepts on input x(lon),y(lat),z,v points (where v is the physical parameter, for example salinity) and it produces on output a set of 2-D grids for any selected z interval, which are integrated to a 3-D volume and bounded with the more appropriate masking operations to avoid function discontinuities. Several seawater volume estimations can therefore be obtained for any particular range of $v$ and made available for the calculations of budgets of other biogeochemical parameters measured in the same areaa, e.g. nutrients. The procedure (a mix of PERL,C and GMT software) was made as automated as possible and it can supposedly be generalized for other physical properties. The application presented in this repoort is based on the CTD dataset (n=500000) collected by the undulating tow-fish SARAGO during four winter and summer cruises (from June 1996 to February 1998) in two areas: South of the Po River Delta and along the Italian coast between Cattolica and Ancona. Before being input to the procedure, the data were statistically filtered to remove spikes and navigation problems. and they were afterwards re-calibrated against CTD profile obtained from ship's station. The 3-D salinity fields were reproduced in 7 boxes with surface ranging from 554 up to 1089 Km2 where the corresponding volumes ranged from 11.6 to 27.4 Km3.

Sommario - Viene presentata una procedura per la determinazione della struttura fisica 3-D di un volume di acqua di mare, basata su dati oceanografici, insieme alla sua applicazione in alcune aree dell'Adriatico nord-occidentale interessate dalla presenza del fronte costiero generato dall'advezione di acque fluviali. La procedura riceve dati di x(lon),y(lat),z,v (dove v e' il parametro fisico considerato, per esempio la salinita') e genera una serie di grigliati 2-D (superfici) che, integrati lungo z, ne producono uno 3-D (volume) delimitabile con appropriati contorni. Su questa base si possono ottenere stime dei volumi relativi ad un particolare intervallo di v, che rappresentano uno strumento utile per una eventuale successiva quantificazione di altri parametri bio-geochimici nella stessa area. L'interpolazione tridimensionale e' stata ottenuta usando programmi e pacchetti software liberamente disponibili, tra i quali Perl, C e procedure GMT, attraverso operazioni di interpolazione, filtraggio a mascheramento dei dati. La procedura e' stata resa piu' automatica possibile e puo' essere anche estesa ad altri parametri fisici. L'applicazione del calcolo utilizza i dati (n=500000) campionati mediante l'uso di una sonda CTD ondulante (il tow-fish SARAGO) durante quattro campagne invernali ed estive, condotte negli anni 1996, 1997, 1998 in due aree: a sud del Delta del fiume Po nella zona prospicente la costa italiana tra Cattolica ed Ancona. I dati sono stati filtrati con metodo statistico e ricalibrati usando profili CTD tradizionali acquisiti in stazioni fisse. Alla fine, il campo di salinita' e' stato riprodotto in 7 aree, di superficie compresa tra 554 e 1089 Km2, corrispondenti a volumi di acqua di mare compresi tra 11.6 e 27.4 Km3.

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