RUNTI

RUNTI: Remote Unit for Nearshore Transport Investigation

RUNTI The RUNTI (Remote Unit for Nearshore Transport Investigation) quadrapod was developed in order to obtain time series of water elevation, current speed and suspended sediment transport. RUNTI is a small benthic lander quite different from similar designs, being specifically thought for deployments in shallow lagoon environments, taking into account logistical constraints. The main strongpoint of the lander is its size (about 1.2 high) and weight (less than 100 kg in air). The quadrapod is designed to be completely balanced in order to avoid its leaning on one side during the deployment. The structure is lowered from a boat using a small crane with a diver in the water to assist the operation and make sure that the equipment is levelled and oriented correctly. The sensors on the quadrapod are a Valeport 800 series bi-axial electromagnetic current meter (EMCM), a Sensym pressure transducer (PT) and a D&A OBS 3-A Optical Back-scatter Sensor (OBS). RUNTI is self logging, with a data logger that can be programmed either for burst or for continuous sampling at frequencies between 1 and 8 Hz. It is also self powered through a battery pack. The OBS and EMCM are mounted at the same height (50 cm) to allow computation of sediment fluxes while the PT is at 27 cm above the sea bed. A diver's compass is mounted on the frame to measure the relative alignment of the EMCM axes referred to the magnetic north. The kit is concluded with a sea switch, a battery pack and a data logger which can be programmed for both burst and continuous recording of data. During deployment, RUNTI can be lowered to the sea/lagoon bed from the side of a barge or boat. Once in place, a diver checks the levelling of the structure and its orientation.

Software development

For analysis of the raw data from RUNTI, they first need to be downloaded from the datalogger to a computer. The next stage involves the conversion of the downloaded data from binary into ASCII formats. At this stage, it was required for the data to be analysed and the various physical parameters extracted. It was hence necessary to write an extensive suit of programmes in Matlab, which has formed a major part of the work so far. The first stage involves a programme for the conversion of the existing ASCII data to a form readable into Matlab. The converted data is then calibrated, given the specific calibration constants for each test, and then plotted. The plots for each burst of data include the parameters of depth, suspended particle matter (SPM), directional currents, resultant current, and current direction, all against time. In addition, separate graphs are plotted which show the burst means and STDs of each parameter against overall time of RUNTI deployment. The Matlab programmes are written in such a way so that the various functions are carried out using a mouse. On execution of the main programme, the user is given options on the screen which include: data conversion, data calibration, time plots for individual bursts, and time plots for the mean and STD of bursts. Hence with a new set of RUNTI data, the user can analyse the results by following the steps and view the plots within minutes of completion of the experiment. The programmes are also written in such a way that they are transportable on a floppy disk and hence the results analysis can be carried out on any computer with the only requirement being the Matlab software. The next stage in the data analysis software is the spectral analysis of the results and its incorporation into the existing suit of programmes with an extra option for the user. The lander has already been deployed on several occasions like for instance in the Gironde from the 25th to the 29th September 1999.