Aspect Land & Hydrographic Surveys

Aspect Land & Hydrographic Surveys operate throughout the UK and continental Europe. In-house survey vessels capable of single beam surveys range from an open workboat capable of operating effectively in the shallowest and most hazardous coastal and riverine environments through a 6.1m rigid inflatable to an 8m catamaran. The RIB in particular is easy to deliver to site by road and capable of high sea transit speeds. This selection of platforms and the ability to fit our survey equipment to other contracted vessels offer the client flexibility and us the ability to react quickly to client needs.

Our single beam (SBES) bathymetric surveys are primarily conducted using survey grade Kongsberg Maritime EA400 dual frequency echosounders. Other equipment may be utilized to suit the client's needs and the operating environment as required. RTK GPS positioning is preferred and heave compensation is applied to all surveys. Tidal data is either processed from the RTK GPS or obtained from the deployment of a fully calibrated and referenced tide gauge. High quality survey planning, real time quality assurance and stringent post survey quality control assure appropriate survey standards are met. We adhere to nationally and internationally accepted hydrographic survey standards including the International Hydrographic Organisation's S44.

The Kongsberg Maritime EA400 dual frequency echosounder emits acoustic pulses from a composite transducer which propagates into two, narrow cones of energy directed toward the sea floor in 38 and 200kHz frequencies.

The transducer "listens" for the reflected energy from the sea floor and records both the high and low frequency depth measurements directly beneath the transducer. The water depth is calculated by using the travel time of the emitted pulse, the time taken for the sound wave to travel from the transducer, to the sea floor and back. The individual depth values are subsequently processed to generate bathymetric models, maps and chartlets.

It is essential that the speed of sound in seawater is accurately understood in the area and at the time of the survey. This includes any temporal or geographical variation during the survey to assure the required standards are achieved. Bar checks are conducted daily on SBES systems to ensure that these are correctly calibrated.

The benefit of the dual frequency transducer is seen in areas of high silt deposition where conventional single, high frequency units only record the top of the silt level. By utilising both the low and high frequencies on the EA400 unit the low frequency pulse can be configured to penetrate the silt layers and record a level on the harder seafloor beneath. This can be particularly beneficial to dredging companies and civil engineers who need to ascertain seabed levels for marine construction works.

The use of these dual frequencies allows interpretation of the seabed texture, and when coupled with a sampling strategy to ground truth, these observations can be effective in the wide scale mapping of seafloor habitats.

Single beam surveys benefit greatly from the addition of side-scan imagery between the lines of sounding to ensure that the seabed is fully insonified. This ensures that all significant features, and in particular any dangers to navigation, are located. Particular side-scan systems for individual surveys are selected, dependent upon the client's object detection requirements and the depth of water in the area of survey.

Reporting