Shelf Sea Biogeochemistry blog

Saturday, 18 April 2015

Ship's inbuilt equipment that science uses on the cruise

Jon Seddon, National Oceanography Centre, Southampton

I look after the science equipment that is permanently fitted to Discovery. I am also responsible for the storage of all the data that we record and the satellite system that we use for communicating with the shore.

On this cruise we’re using several of the instruments that are permanently fitted to the RRS Discovery. We have a weather station that every second records the air temperature, humidity, air pressure, the intensity of the light coming from the sun, and the wind speed and direction. Every second we also measure the properties of the sea 5 metres under the surface. We record the temperature, salinity, how much the phytoplankton in it fluoresce and also how clear the water is, from which we can work out how much is growing in the water (see picture with measurements below). The whole cruise is looking at how the phytoplankton start to grow in the Celtic Sea in spring. The data from the ship allows us to continuously observe how much phytoplankton there is at the surface throughout all of the sea that we pass through.

A screenshot of the underway data that is continuously logged aboard 24-7.  Since 7 am this morning temperatures have increased and fluorescence (chlorophyll) has decreased.
We’re using the echo sounders on the ship to make a profile of how deep the sea underneath us is. There’s more information about how echo sounders work here. We’re using two types of echo sounder on this cruise. The single beam system sends a single pulse of sound down from the bottom of the ship to measure the water depth directly under the ship. We’re also using the multibeam system, which sends out 400 beams of sound out in a triangular pattern to measure the water depth underneath and out to the side of us. We’re currently on the flat shelf and so the sea bed is uniform and 118 metres deep. When we dropped off the edge of the shelf during the iron transect the water went as deep as 2650 metres. There were lots of canyons flowing from the shelf into deeper water that showed up in the multibeam data. 

Multi-beam data from the iron transect showing increasing depth with colours going from red (shallow) to deep blue (deep). Below the ship is a deep canyon running east to west.

This is the unprocessed multibeam data from the deepest part of the iron transect.  The yellow line is the course that the ship took. The blues show the deepest areas of the sea and the reds are the shallower parts that are on the edge of the shelf. The navigation charts that we have for this part of the sea are not that detailed. The echo sounder data allows us to know how deep to lower the CTD to make sure that we measure all of the sea but that we don’t bump the CTD into the sea bed.

There’s a 2.4 metre wide satellite dish on top of the ship that connects us to the Internet and gives us four phone lines (see picture below). Satellite data is very expensive and so our system only works at 256 KBits per second. This is about one-eighth of the speed of the data on a mobile phone and we have to share this amongst the 50 scientists, crew and technicians onboard. There are nine computers around the ship that we can use to access the Internet. You have to be very patient though – the BBC Sport page takes 30 seconds to load and even longer if all nine computers are in use at once.

Picture of the bridge of the RRS Discovery with satellite dome and lots of other aerials and instruments. Photo: Chata Seguro.

Everyone has a phone in their cabin and the ship has four lines with Aberdeen phone numbers because that’s where our satellite ground station is. Friends and family can call us on these numbers or we can call them using phone cards that we’ve bought in advance. Because of the Aberdeen number it only costs the same as a UK phone call and so is very affordable but there is a bit of delay on the line, which can be confusing if you’re not used to it. 

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