Bathymetric data is used for a lot more than safety of navigation. The list below gives a quick summary.

• Safety of navigation of ships and small craft
• Ports and harbours
• Government - determining boundaries of territorial waters
• Marine spatial planning, e.g. Marine Protected Areas and Marine Conservation Zones
• Marine energy, e.g. oil and gas, offshore wind, tide and wave power
• Coastal and offshore engineering, e.g. coastal defences, sewage outfalls, underwater cables and pipelines
• Mineral resource management, e.g. dredging, underwater mining, oil and gas
• Coastal erosion and sedimentation, and areas of mobile sea beds like the Thames Estuary and entrance to San Francisco Bay
• Hydrodynamic modelling for tides and currents, surges and tsunami modelling
• Habitat and ecosystem mapping to understand where fish and other marine animals will live, feed and breed - both for conservation and for fishing
• Understanding the effects of the volumes of water in the oceans, and their circulation, on the weather and climate
• Health - modelling sewage outfalls, algal blooms etc,
• Leisure activities, e.g. sailing, diving, cruise liners
• Marine archaeology

 For more information, good starting points are "The Use of Bathymetric Data in Society and Science: A Review from the Baltic Sea"and "Report on the Economic Benefits of Hydrography".

Not very is the short answer. The more emotive one is that we know the surface of the moon and of Mars better than we know the depths of our seas and oceans. Globally, only about 5 - 10% is surveyed to modern standards - most of the oceans are surveyed by satellite, giving an average depth over a 20km square area, give or take 100m or thereabouts of depth. In coastal waters around Europe, about 50% is fully surveyed, and the USA is considerably worse. In the developing world, in many areas there is just a lead line survey from when they were occupied by one of the Western powers in the era of colonialism, and in the Pacific there are still charts with soundings taken by Captain Cook (1728 - 1779).

Indeed there is a significant mismatch between some of the statements about mapping the seas, and the reality. At GEBCO's Forum for Future Ocean Floor Mapping the scientists and their funders, the Nippon Foundation, stated that they will have the world's oceans mapped to 100m resolution by 2030. And in the EU, the Directorate General of Maritime Affairs and Fisheries (DG Mare) are continuing to develop their EMODnet portal, aiming to complete their European Map of the Seas by 2020. Yet, in both these cases, there are huge areas where the available data does not meet the standards of the mapping product being produced, but no significant resourced are being put into this huge data gap. 

To understand the developments and challenges in surveying the seas, have a look at Hydrographic survey methods. 

As with so many interesting questions, the answer can be summed up as "it's complicated"! There are a number of factors involved, briefly listed here:

• Most of our oceans lie in international waters, where there is no organisation with a duty to survey them. Countries have a strong interest in surveying their territorial waters (up to 12nm offshore), and often their Exclusive Economic Zone (EEZ) as well (up to 200nm offshore), but there is little motivation to survey further offshore
• Conventional hydrographic surveying is expensive. An oft quoted figure for a multibeam survey in coastal waters is £3000 per square kilmometre. The world has 3,600,000,000 sq.km. of seas and oceans!
• In many of the less developed parts of the world, there is not the resources to carry out any extensive hydrographic surveying
• In a significant amount of coastal waters the sea bed is soft sand or mud, and is quite mobile, e.g. the underwater sand dunes off the entrance to San Francisco, or the moving channels of the Thames Estuary and WaddenSea in the North Sea. These require regular resurveying to keep the data up to date.
• National hydrographic offices generally have their primary tasks as meeting the needs of commercial ships and national defence, so they do not see it in their remit to publish data on other areas, especially if, like the UKHO, they are also tasked with maximising their profits
• Hydrographic offices are all very conservative when considering newer, lower cost methods of surveying, due to the effect of a ship going aground - this generally over rides any considerations of other uses of the data
• Many national hydrographic offices are part of the country's navy, and so tend to see depth data as a state secret that should be guarded to hinder possible invasion of their shores by their enemies
• Although a number of newer, lower cost methods of surveying are becoming established, they all have their own limitations, so there is no magic bullet in new technology
• Whilst many surveys are carried out for commercial customers, e.g. oil and gas, the data is seen as commercially sensitive, and so is typically only released when this is made a requirement by the government issuing the licences
• Many scientists have carried out surveys, but have not made the data available either through their own institution's web servers or through repositories of research data such as the IHO DCDB. Sometimes this is exacerbated by the funding body claiming ownership of the data, and then doing nothing with it.
• Commercial chart publishers with products for small craft generally base their products on hydrographic office data, partly because this requires minimal effort, and partly to reduce their exposure to liability if there is an error in a chart. Thus they seldom initiate their own surveys, though some do source other existing survey data where available.

For more information on the various ways of conducting surveys, and their strengths and weaknesses, have a look at Hydrographic survey methods.

There are some 10 million seagoing vessels of all sizes that are capable of carrying a GPS and depth sounder. If even 1% of these logged data, it would go a long way to filling the data gap in may areas. Most of these vessels are small craft, whose depth sounder works to about 100m, so these are relevant for coastal waters. Offshore there are under 100,000 vessels in all - ships' echo sounders will work to about 2000km depth, whereas only a few hundred research vessels and deep sea fishing vessels will be able to plumb deeper depths.

The data that can be produced is not as good as a professional multibeam survey, but is significantly better in accuracy and coverage than a lead line or early echo sounder survey, and is on a par with newer methods such as optical satellite derived bathymetry, but with a greater depth range. To get the required accuracy we need many tracks covering an area, ideally from a number of boats, so that the inherent inaccuracies can be dealt with statistically. Also, to cover as many waters as possible, we need to recruit a wide range of vessel types, as each has their own habitat, sailing in specific parts of the oceans.

The data is perfectly adequate for creating a baseline bathymetry that fills the data gap and is good enough for many applications. In critical areas, such as where safety of shipping is involved (with ships often working to under keel clearances of a few centimeters), or for detailed plans for offshore engineering, crowd sourced data can be used as a pre-survey tool to better target the use of a multi-beam survey of the area, which should always be seen as the gold standard of current survey techniques, but also the most expensive by far.

We are steadily building up a data repository, both of data contributed to us from our own fleet of loggers, and also data from other sources, such as the IHO DCDB. This is held both as track data and as output data, either contoured or gridded. Here is how we make this data available:

• The web site shows the track data, and is just being upgraded to show contoured data, updated in near real time
• Active loggers will always have free access to the contoured data for their own use, at present as an (admittedly limited) number of PDFs, but these will also soon be available in a number of marine chart formats as well, e.g. BSB, S-57 and others
• Where we have a project that fully funds us in an area, such as the BASE Platform project, we can make the data available as Open Data, free for all to use
• We are providing free data to the GEBCO and EMODnet projects producing Open Data maps of the sea bed
• For other users of the data, we can provide the data in a variety of formats for both GIS and marine communities. We do require a financial contribution to help cover our running costs.

We do not generally make our track data available, as many users want to retain their privacy, or see this as commercially sensitive data. However, when the IHO's crowd sourced bathymetry portal becomes active we will be one of their "Trusted Nodes", and will give all of our loggers the option of having their tracks uploaded to this Open Data repository.

Whilst TeamSurv started off by just looking at bathymetry, comig at things from a navigational interest and then realising that bathymetry is used in many more areas, as we engage with the wider marine and maritime communities we have come to realise that this data gap is just as wide in many other areas. So, given that we have an increasing fleet of vessels engaged in recording data, what else can be achieved? Whilst we are only just beginning to move in this direction, here are some initial thoughts.

From the instruments carried on most boats, we can generally get wind speed and direction and also derive surface currents. Sea surface temperature is also available, but initial investigations show that the accuracy is not that good. We can easily and cheaply add meteorological sensors for things like barometric pressure and sunlight/cloud cover, and by measuring boat motions we can probably determine wave data.

For additional parameters we need to look at adding sensors, and for large scale deployment they need to be low cost. We have done some work in this area within the SeaFront project, where we have extended TeamSurv to gather water quality data such as pH, dissolved Oxygen and chlorophyll. Also, the X Prize had a competition that ended in 2015 for low cost sensors for pH, as a measure of acidification, so there is room for collaboration in that area. We are now looking for opportunities to take this further.