Hydrographic Surveys: Cooler Than They Sound!
Our Megan’s experience of supporting a marine project in Queensland, Australia
As a geography research fellow, I am a little bit obsessed with anything to do with our planet – or even our universe (I’m not picky!). So I get somewhat over-excited when I get to experience something new. In this case, I recently got to be involved in a hydrographic survey in Queensland, Australia. These aren’t conducted that often, and involve highly trained and specialised professionals – so it was a bit of a coup to get invited along.
I thought that my experience would be a good story to tell to others that are either considering this exciting field of study or are thinking of branching out into a more specific area of maritime science, engineering or surveying – all of which are related fields.
What is a hydrographic survey?
Just as land is surveyed for a variety of reasons – mapping, real estate, government etc, water needs to be surveyed too. A hydrographic survey measures, describes and maps features that can be found underwater.
There are several reasons why hydrographic surveys are important, with the main purpose being for navigation. When ships or fishing boats are out on the water, they use hydrographs to establish whether an area is safe to head into, either in advance or while on the water. The hydrographs are also used by those involved with dredging, oiling and environmental impact assessors.
During a hydrographic survey, those involved collect all the data needed for maritime cartographers to put together an accurate underwater topographical map.
In Australia, hydrographic surveys are conducted by the Australian Hydrographic Survey – who I joined. But around the world there are hundreds of different agencies – both government and private – that regularly conduct surveys.
It is important to know the difference between a hydrograph and a hydrographic survey. Hydrographs measure the flow of the water, as well as discharge left behind over time. Many people do simple hydrographs at a local river during high school geography or science classes. Hydrographic surveys, on the other hand, measure and describe the shape of the land under water – as opposed to the water itself.
People involved in a hydrographic survey
There isn’t just one ‘hydrography expert’ that does all the work – there are numerous different experts across varying fields of study that work together to get the job done. In fact, this was one of the most fascinating parts of the experience – you get to mingle with people outside of your usual crowd and learn things from a completely new angle.
Hydrographic surveyors are the key players involved – they have specialist knowledge on conducting the surveys, and afterwards the maritime cartographers play an important role in interpreting and mapping the data collected.
On the day
Hydrographic surveying is getting increasingly advanced. In the past, measurements had to be taken by hand – dropping lines into the water and bringing back spot results. Now, specialised water vessels with sonar equipment on board are most commonly used, and in some cases low-flying aircraft are also used. The size of the vessel depends on the size of the area being surveyed, as well as the depth of the water – for deep ocean surveys a large ship is often used, whereas areas closer to the shore may even use inflatable rafts.
In my particular case, we were on board a boat. On board we had access to two types of sonar equipment – sidescan and multibeam sonar. Combined, these two forms of sonar (an acronym for sound navigation ranging), provide a detailed look at the surface below the water. Sonar works by sending sound waves to the bottom of the ocean floor and bouncing them back up to the vessel. The echo of that sound wave is then measured to give a depth in that particular area.
A huge amount of measurements need to be taken – so it’s no easy task! Several scans are taken per square foot, so it can take several days or even weeks to cover a significant area.
After the survey
Although I wasn’t personally involved in this part, it’s interesting to know what is done with all the data that is collected. During the survey, a ridiculously huge amount of data is collected and not all of it can be used. Also, the sonar equipment can sometimes bring back bad scans, so it’s important to manually go through all the data to eliminate these bad results – otherwise it can skew the final map.
Maritime cartographers also need to adjust the results to account for tides, waves and so on – to ensure a consistent and accurate map. While conducting the survey, tides were noted to assist the cartographers.
I haven’t seen the final product yet – but I look forward to seeing it! It was a fantastic and fun experience to be part of and I have no doubt I will be moving my career into that direction.