In the year 2001, the company Desmar Ltd began to work with multibeam echosounders, introducing a whole new set of tools to assist where high-resolution and high accuracy bathymetric data and 100 per cent of sea floor coverage was needed. Three large, multibeam surveys have since been performed by Desmar.

Valparaiso
The first one of these was in Valparaiso and covered near 400 hectares of coastal zone. The aim was to acquire a complete and clear picture of the inner part of port of Valparaiso in order to employ the resulting hydrographic information as the main judging element in planning the future development of the port. The resulting bathymetric sheets, slope views, virtual videos and contour maps constituted information elements never before available to engineers. The amount and quality of the data, as well as the variety of ways it could be handled and displayed, allowed planners to look at the situation of the sea floor and its interrelation with the surrounding topographic area in unlimited ways.
Valparaiso is an old port where numerous wrecks exist. The high resolution of the multibeam echosounder used, Reson 8125, allowed perfectly survey of all the wrecks lying on the sea floor within the surveyed area. Some of these were preserved to a degree where skylights and other small details where clearly pictured when generating JPG images out of the bathymetric data.
Noticeable surprises were found when surveying 100 per cent of the seafloor. Due to the advantage of the slant beams, features under fixed and floating structures not usually possible to survey when working with single-beam echosounders also became 'visible'. One outstanding result coming from the slant beams was surveying and dimensioning large accumulations of sediment coming from a floating. These large piles of sediments were clearly and completely mapped, allowing the shipyard to plan their immediate removal, since several pollutant elements are present in the residuals from careening.
Along with the planning of new infrastructure for the port of Valparaiso, other studies were also conducted to oceanographically validate the designs; among these, was a comprehensive wave climate assessment. The support offered by multibeam data was incomparably superior to single beam data. The 100 per cent coverage of the seafloor allowed engineers to assess the impact of waves on the planned infrastructure with degree of certainty impossible to achieve without this type of data.

Valdivia
The second MB survey was conducted in 2002 along 17 kilometres of rivers, near the fluvial city of Valdivia. The purpose of the survey was to obtain large-scale nautical charts to support the navigation of barges transporting the multiple parts of a new pulp plant being built near Valdivia. The closer the barge could get to the plant site, the greater the degree of assembly of plant machinery in the factory in its country of origin. This in turn would allow much faster building of the pulp plant, saving a significant amount of money and time as well as putting the plant to work much sooner.
In contrast to the survey in Valparaiso, which was orientated towards support planning, this survey involved safety of navigation. For this reason, SHOA had to inspect and approve the survey in order for the resulting charts to acquire the condition of ‘officially approved’ bathymetric data. The survey was conducted with a party of four inspectors from SHOA on board of the surveying launch: one geodesist, one tide specialist, a multibeam expert and a hydrographer. Since this was the first multibeam survey conducted by the private sector and which had to be officially approved, a complete set of rules and tests had to be drafted by SHOA. All rules were adhered to and all tests satisfactorily passed both in the field and in the office.
A total of twelve sheets at the scale of 1:1,000 were produced from this survey. A preliminary evaluation of the route before the multibeam survey indicated that navigation was possible up to the end of the 17km route; however, no proper consideration of tidal influence or pluviosity were taken at that time. As a result of the MB survey and proper consideration of tides, it was concluded that the route was navigable up to 15km, the last 2km being too shallow for the barges draft. This complex survey was conducted in only three days and the
data processing done in a couple of weeks, despite the heavy sediment transport in the rivers which added a great deal of ‘noise’ to the data.
The support of Reson in California, where part of the data was processed, allowed the very rapid submission of bathymetric sheets to SHOA for approval. After fixing minor details, the sheets were approved by SHOA and given the quality of ‘Officially Approved’. They thus became the first multibeam surveying conducted by the private sector in Chile to attain such a condition.

San Vicente
The third survey was conducted in San Vicente Bay. This survey also required SHOA approval, since its purpose was supporting the detailed engineering development of two large oil and liquefied gas terminals in the Bay; in such conditions a certified survey is required by the Maritime Authority prior to the beginning of building the terminal. The survey covered nearly 800 hectares. Since this survey was conducted immediately after the one in the rivers, the same SHOA party inspected this survey, working alongside the company’s specialists during four days. San Vicente Bay has a shallow and monotonous underwater morphology, presenting no abrupt depth changes, with seafloor slopes between 1 per cent and 2 per cent.
This survey represented a whole new way of looking at bathymetric data collected for engineering purposes. The amount of data and its accuracy allowed the engineers to analyse several lay-outs for the infrastructure to be built, having always a complete and clear picture of the sea floor within and around the alternative solutions.
The Bay is widely open to the West, thus sea swell coming from this predominant direction freely enters into the Bay, having a great impact on surveying operations. Despite this, a precise motion sensor in line with the Reson System allowed the surveying party to completely filter its effects on the data. As in Valparaiso Bay, a wave impact assessment was also required in San Vicente Bay. The complete coverage of the sea floor and the surveying of two long ‘legs’ outwards from the Bay allowed engineers to objectively and precisely determine the way waves will impact the different solutions analysed. The survey was given ‘official value’ by SHOA shortly after its completion, allowing planners to carry out their studies based upon high-quality, high-accuracy and officially recognised data.

Conclusion
Many papers are written these days about multibeam surveys and thus falling into repetition is something very likely to happen. For this reason no major details are given here regarding these surveys and the contents are focused more on aspects where this technology clearly represents gigantic changes as compared to single-beam bathymetry. A completely new field has been opened up to private consulting, making this outstanding technology available to meet all sorts of requirements coming from the private sector.