Comparison of a self-processed EM3000 multibeam echosounder dataset with a QTC view habitat mapping and a sidescan sonar imagery, Tamaki Strait, New Zealand

A methodology for automatically processing the data files from an EM3000 multibeam echosounder (Kongsberg Maritime, 300 kHz) is presented. Written in MatLab, it includes data extraction, bathymetry processing, computation of seafloor local slope, and a simple correction of the backscatter along-track banding effect. The success of the latter is dependent on operational restrictions, which are also detailed. This processing is applied to a dataset acquired in 2007 in the Tamaki Strait, New Zealand. The resulting maps are compared with a habitat classification obtained with the acoustic ground-discrimination software QTC View linked to a 200-kHz single-beam echosounder and to the imagery from a 100-kHz sidescan sonar survey, both performed in 2002. The multibeam backscatter map was found to be very similar to the sidescan imagery, quite correlated to the QTC View map on one site but mainly uncorrelated on another site. Hypotheses to explain these results are formulated and discussed. The maps and the comparison to prior surveys are used to draw conclusions on the quality of the code for further research on multibeam benthic habitat mapping

Mercury Bay Coastal Processes Study: Data Report for 2014 & 2015.

Two month-long hydrographic and sedimentation field campaigns were conducted from July 15th, 2014 to August 13th, 2014 and from April 9th, 2015 to May 8th, 2015 within the Mercury Bay-Whitianga Inlet-northern Whitianga Estuary system to fulfill the field data needs of the Waikato Regional Council towards the goal of producing a hydrodynamic model of Mercury Bay. The purpose of this data report is to summarize the instrument deployment locations,durations, and settings that were used during the field campaign. This document also aims to aid the modeler (or other Waikato Regional personnel) in the locating of the desired instrument data files from the accompanying data discs. In all cases, the raw data files have been provided for each instrument. In the instance that a raw data file is in a data format that requires proprietary software from the instrument manufacture to process, an export of the data files to a universally-readable file format has been included (e.g., .txt, .dat, .csv, .etc.) or to a MATLAB file format when necessary. Clarification has been provided for instruments that export data files without headers

Water flow between Ohau Channel and Lake Rotoiti following implementation of a diversion wall.

The water quality in Lake Rotoiti has become increasingly degraded since the 1950s. Water from Lake Rotorua, with elevated phytoplankton and nutrient concentrations, has entered Lake Rotoiti via the Ohau Channel. To help improve water quality in Lake Rotoiti, a constructed wall was completed in July 2008, to divert water from the Ohau Channel towards Okere Arm in Lake Rotoiti, with the objective to transport this water into the Kaituna Rivr instead of entering the main basin of Lake Rotoiti. This report has been produced in response to a request from the Rotorua Lake Technical Advisory Group to determine water velocities in the region of the constructed wall, in order to consider the effectiveness of the diversion

Water flow between Ohau Channel and Lake Rotoiti following implementation of the diversion wall part B

To help improve water quality in Lake Rotoiti, a diversion wall was completed in July 2008, to divert the water emanating from the Ohau Channel towards Okere Arm in Lake Rotoiti. The objective was that this water would be directly transported into the Kaituna River instead of entering the main basin of Lake Rotoiti. A report was produced in response to a request from the Rotorua Lakes Technical Advisory Group to determine water velocities in the region of the wall, to consider the effectiveness of the diversion. This subsequent report has been written to follow-up on the recommendation that vertically resolved measurements of water current and direction in Lake Rotoiti should be investigated. The timing of the data collection was April to May when an underflow is more likely to be present

Quantitative experimental comparison of single-beam, sidescan, and multibeam benthic habitat maps

Map comparison is a relatively uncommon practice in acoustic seabed classification to date, contrary to the field of land remote sensing, where it has been developed extensively over recent decades. The aim here is to illustrate the benefits of map comparison in the underwater realm with a case study of three maps independently describing the seabed habitats of the Te Matuku Marine Reserve (Hauraki Gulf, New Zealand). The maps are obtained from a QTC View classification of a single-beam echosounder (SBES) dataset, manual segmentation of a sidescan sonar (SSS) mosaic, and automatic classification of a backscatter dataset from a multibeam echosounder (MBES). The maps are compared using pixel-to-pixel similarity measures derived from the literature in land remote sensing. All measures agree in presenting the MBES and SSS maps as the most similar, and the SBES and SSS maps as the least similar. The results are discussed with reference to the potential of MBES backscatter as an alternative to SSS mosaic for imagery segmentation and to the potential of joint SBES–SSS survey for improved habitat mapping. Other applications of map-similarity measures in acoustic classification of the seabed are suggested

Evidence for directed fishing effort in North sea cod and haddock

Fishing mortalities at age in North Sea cod, haddock, and whiting are examined in relation to biomass of fish at each age. For cod and haddock highest fishing mortalities are associated with high biomasses. For haddock this means the exploitation pattern changes from year to year because recruitment is very variable. For cod more stable recruitment results in a consistent exploitation pattern. The implications for stock assessment are discussed