Temperature and Salinity Inverted for a Mediterranean Eddy Captured With Seismic Data, Using a Spatially Iterative Markov Chain Monte Carlo Approach

Ocean submesoscale dynamics are thought to play a key role in both the climate system and ocean productivity, however, subsurface observations at these scales remain rare. Seismic oceanography, an established acoustic imaging method, provides a unique tool for capturing oceanic structure throughout the water column with spatial resolutions of tens of meters. A drawback to the seismic method is that temperature and salinity are not measured directly, limiting the quantitative interpretation of imaged features. The Markov Chain Monte Carlo (MCMC) inversion approach has been used to invert for temperature and salinity from seismic data, with spatially quantified uncertainties. However, the requisite prior model used in previous studies relied upon highly continuous acoustic reflection horizons rarely present in real oceanic environments due to instabilities and turbulence. Here we adapt the MCMC inversion approach with an iteratively updated prior model based on hydrographic data, sidestepping the necessity of continuous reflection horizons. Furthermore, uncertainties introduced by the starting model thermohaline fields as well as those from the MCMC inversion itself are accounted for. The impact on uncertainties of varying the resolution of hydrographic data used to produce the inversion starting model is also investigated. The inversion is applied to a mid-depth Mediterranean water eddy (or meddy) captured with seismic imaging in the Gulf of Cadiz in 2007. The meddy boundary exhibits regions of disrupted seismic reflectivity and rapid horizontal changes of temperature and salinity. Inverted temperature and salinity values typically have uncertainties of 0.16°C and 0.055 psu, respectively, and agree well with direct measurements. Uncertainties of inverted results are found to be highly dependent on the resolution of the hydrographic data used to produce the prior model, particularly in regions where background temperature and salinity vary rapidly, such as at the edge of the meddy. This further advancement of inversion techniques to extract temperature and salinity from seismic data will help expand the use of ocean acoustics for understanding the mesoscale to finescale structure of the interior ocean.

Satellite-Derived Bathymetry Using Landsat-8 Imagery for Safaga Coastal Zone, Egypt

Satellite-Derived Bathymetry (SDB) modeling is used to derive bathymetric data needed for enriching several applications including nautical charting. The nautical charts of Safaga port, Egypt, contains significant gaps as they are based on 50-years old hydrographic survey data and it needs an update. We applied the SDB algorithm (log-ratio approach) using multispectral Landsat-8 OLI images for extracting bathymetry to update the nautical charts of SAFAGA port. The results are verified against the old nautical chart of SAFAGA with a coefficient of determination (R2) varies between 0.42 to 0.71 in areas where hydrographic data are old, unavailable or costly to obtain.

Variability of Net Primary Productivity and Associated Biophysical Drivers in Bahía de La Paz (Mexico)

The use of information of net primary productivity (NPP) from remote ocean color sensors is increasingly common in marine sciences. The resulting information has been used to explain variations in productivity at different spatio-temporal scales and in the presence of climate phenomena, such as the El Niño Southern Oscillation, and global warming. Satellite remote sensing data were analyzed in Bahía de La Paz (BLP), Mexico, to determine the spatio-temporal variation in NPP. In addition, in situ hydrographic data were obtained to characterize the water properties in the bay. The satellite data agree with in situ measurements, validating the satellite observations over this region. The NPP generally presented seasonal variation with maximum values in winter-spring and minimum values in summer–autumn. The variance explained by NPP from the measured variables was ranked as Chl-a < DEN < SST < PAR < WSC. The highest NPP values generally occurred when subtropical subsurface (SsStW) water was relatively shallow. Due to divergence and mixing processes, this water provided nutrients to the euphotic zone, and consequently an increase in NPP and changes in plankton biomass were observed. The annual trends of the variation in hydrographic data with respect to that of remote sensing data were similar; however, it is necessary to increase the number of data validation studies. The remote sensing and in situ measurements allowed for the main biophysical variables that modulate NPP in different time scales to be identified. The satellite-derived NPP data classifies the BLP as a high productivity zone with 432 g C m−2 year−1. The use of satellite NPP data is satisfactory and should be incorporated into marine primary productivity studies.

Filtering method based on cluster analysis to avoid salinity drifts and recover Argo data in less time

Currently there is a huge amount of freely available hydrographic data and it is increasingly important to have access to it efficiently and easily provided with as much information as possible. Argo is a global collection of around 4000 active autonomous hydrographic profilers. Argo data goes through two quality processes, real time and delayed mode. This work shows a methodology to filter profiles within a given polygon using the odd-even algorithm, this allows analysis of a study area, regardless of size, shape or location. Also, gives two filtering methods to discard only the real time quality control data that present salinity drifts, thus taking advantage of the largest possible amount of valid data within a given polygon. In the study area selected as an example, it was possible to recover around 80 % in the case of the first filter and 30 % in the case of the second of the total real time quality control data that are usually discarded due to problems such as salinity drifts, this allows researchers to use any of the filters or a combination of both to have a greater amount of data within the study area of their interest in a matter of minutes, unlike waiting for the delayed mode quality control that takes up to 12 months to be completed.

Meridional overturning circulation at 30ºS in the Pacific Ocean: 1992, 2003, 2009 and 2017.

&lt;div&gt; &lt;p&gt;&lt;span&gt;The meridional circulation and transports at 32&lt;sup&gt;o&lt;/sup&gt;S in the Pacific Ocean in 1992 and 2017 are compared with analogous data from 2003 and 2009. The hydrographic data comes from the GO-SHIP database and an inverse box model has been applied with several constraints. In 1992, 2003 and 2017 the pattern of the overturning streamfunction is similar, but in 2009 the pattern of the circulation changes in the whole water column. The horizontal distribution of mass transports at all depths in 1992 and in 2017 changes notably from the &amp;#8220;bowed gyre&amp;#8221; found in 2009 and resembles that regular shape of 2003. The hydrographic data have also been compared with analogous data obtained from the numerical modelling output of GFDL, ECCO, and SOSE. Results show that the numerical modelling output in the upper layers (&lt;/span&gt;&amp;#947;&lt;sup&gt;&lt;span&gt;n&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;&lt;27.58 kg/m&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;) have a roughly similar pattern as hydrographic data. This is not the case, however, for deep and bottom layers (&lt;/span&gt;&amp;#947;&lt;sup&gt;&lt;span&gt;n&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;&gt;27.58 kg/m&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;), where noticeable differences are found. Furthermore, the temperature transport in 2009 &lt;/span&gt;&lt;span&gt;(0.16 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.12 PW&lt;/span&gt;&lt;span&gt;)&lt;/span&gt;&lt;span&gt; is significantly lower than in 1992 &lt;/span&gt;&lt;span&gt;(0.42 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.12 PW&lt;/span&gt;&lt;span&gt;), &lt;/span&gt;&lt;span&gt;2003 &lt;/span&gt;&lt;span&gt;(0.38 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.12 PW&lt;/span&gt;&lt;span&gt;) and &lt;/span&gt;&lt;span&gt;2017 &lt;/span&gt;&lt;span&gt;(0.42 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.12 PW&lt;/span&gt;&lt;span&gt;). In addition, &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;freshwater transport result in 2009 (0.50 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.03 Sv&lt;/span&gt;&lt;span&gt;) is significantly higher than in 1992 (0.26 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.08 Sv&lt;/span&gt;&lt;span&gt;), 2003 (0.25 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.02 Sv&lt;/span&gt;&lt;span&gt;) and 2017 (0.34 &lt;/span&gt;&lt;span&gt;&amp;#177; 0.08 Sv&lt;/span&gt;&lt;span&gt;). Westward Rossby waves are presumably the dynamical forcing that changes the circulation pattern in 2009. &lt;/span&gt;&lt;/p&gt; &lt;/div&gt;

Hydrographic data inspection and disaster monitoring using shipborne radar small range images with electronic navigation chart

Shipborne radars cannot only enable navigation and collision avoidance but also play an important role in the fields of hydrographic data inspection and disaster monitoring. In this paper, target extraction methods for oil films, ships and coastlines from original shipborne radar images are proposed. First, the shipborne radar video images are acquired by a signal acquisition card. Second, based on remote sensing image processing technology, the radar images are preprocessed, and the contours of the targets are extracted. Then, the targets identified in the radar images are integrated into an electronic navigation chart (ENC) by a geographic information system. The experiments show that the proposed target segmentation methods of shipborne radar images are effective. Using the geometric feature information of the targets identified in the shipborne radar images, information matching between radar images and ENC can be realized for hydrographic data inspection and disaster monitoring.

GOANA, a Global Ocean Atlas, Neutrally Averaged

&lt;p&gt;Isopycnally averaged hydrographic data gives results that are significantly different to the standard method of averaging at constant depth. The act of averaging isopycnally ensures that water masses are neither created or destroyed.&amp;#160; We average using the weighted least squares quadratic (or LOESS) fitting method of Chelton and Schlax (1994) and Ridgway et al. (2002) along appropriately defined density surfaces.&amp;#160; This produces an gridded oceanographic atlas that is composed of the Fourier coefficients of the mean temporal trend, the strength of the semi-annual and seasonal cycle allowing the user to reconstruct a climatology at any temporal resolution. Initially we are producing an atlas consisting of Absolute Salinty and Conservative Temperature but in the future we aim to include nutrient data.&lt;/p&gt;