Ekaterina Vsemirnova

Estimating movement of reflectors in the water column using seismic oceanography

The observation of spatial and temporal dynamics of the ocean is fundamental to understand global and regional aspects of water mixing. Physical oceanography has traditionally observed ocean structures with in situ measurements, often limited in temporal and/or spatial resolution. In exploration seismology a set of techniques has been developed over the last decades to image and characterize the physical properties of sub-seafloor structures by inversion methods at high horizontal resolution. The two different fields have made contact in seismic oceanography where the well developed methods of marine reflection seismology have been applied to the dynamic ocean. However, one aspect, so far ignored in seismic oceanography, is the dynamical, temporally varying nature of water structures. Here we show that it is possible to estimate temporal variations of reflectors in water structures as an inversion parameter. The new dynamic property reflector movement velocity gives an additional parameter to characterize ocean water dynamics.

Estimating internal wave spectra using constrained models of the dynamic ocean

Multi-Channel Seismic method (MCS), with its ability to image events down to a lateral resolution of 10 m has been successfully applied to address questions in physical oceanography. However, to date, these analyses have overlooked an important detail; the imaged boundaries are dynamic and move on a timescale that can be resolved by the MCS method. An important step in understanding the effect of the movement is calibration against constrained models. We demonstrate in this paper that it is possible using careful interpolation to take high resolution models of dynamic water (160 m x 2 m spatial resolution and 15 min temporal resolution) and generate models for synthetic seismic simulations (20 m x 4 m spatial resolution and 20 sec temporal resolution). We show that moving water, when ignored, will distort analyses of wavenumber spectra estimated from seismic data since the relative movement of water masses and the seismic acquisition vessel will change the apparent slope of spectra. Citation: Vsemirnova, E., R. Hobbs, N. Serra, D. Klaeschen, and E. Quentel (2009), Estimating internal wave spectra using constrained models of the dynamic ocean, Geophys. Res. Lett., 36, L00D07, doi: 10.1029/2009GL039598.

Mapping turbidity layers using a combination of high resolution seismic oceanographic and physical oceanographic data

Synchronized seismic and oceanographic data were acquired during the Geophysical Oceanography (GO) project cruise in the Gulf of Cadiz in April–May 2007. The small volume (117 cu-in.) mini GI-gun seismic source used during the GO calibration experiment provided high resolution seismic data, which unveiled new features of the internal structure of the ocean. The seismic acquisition design gave a usable bandwidth of 50–250 Hz with a vertical resolution of 1.25 m, which is similar to that achieved by co-located CTD casts. We focus on the reflections observed on seismic data covering the moorings area. To test the hypothesis that measurable reflections can be generated by suspended sediment, we perform forward modeling of seismic response based on the temperature, salinity, and light attenuation measurements, available from CTD casts. Forward modeling based solely on temperature and salinity profiles show that thermohaline structure does not always explain reflections in water column, but they are consistent ...