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)

A method is presented for the analysis and modeling of the 3-D physical structure of a seawatervolume using CTD-STD oceanographic measurements, along with some issues for its generalization andexamples of application in two areas in the NW Adriatic Sea, which present coastal fronts generated byfreshwater inputs into the basin. The procedure accepts on input x(lon),y(lat),z,v points (where v is thephysical parameter, for example salinity) and it produces on output a set of 2-D grids for any selected zinterval, which are integrated to a 3-D volume and bounded with the more appropriate masking operationsto avoid function discontinuities. Several seawater volume estimations can therefore be obtained for anyparticular range of ?and made available for the calculations of budgets of other biogeochemical parametersmeasured in the same areaa, e.g. nutrients. The procedure (a mix of PERL,C and GMT software) wasmade as automated as possible and it can supposedly be generalized for other physical properties. Theapplication presented in this repoort is based on the CTD dataset (n=500000) collected by the undulatingtow-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 inputto the procedure, the data were statistically filtered to remove spikes and navigation problems. and theywere afterwards re-calibrated against CTD profile obtained from ship's station. The 3-D salinity fields werereproduced in 7 boxes with surface ranging from 554 up to 1089 Km2 where the corresponding volumesranged from 11.6 to 27.4 Km3.