© Valeport Limited 2003
MIDAS Surveyor Operating Manual
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0420805d.doc
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INTRODUCTION
This manual describes the operation of the Valeport MIDAS Surveyor GPS Echosounder, and its associated PC software
SurveyLog.
The MIDAS Surveyor is a hydrographic survey system, logging a time series of position and depth data. Real time data
is displayed on the integral graphics LCD screen and output in a variety of industry standard formats, and all logged data
may subsequently be uploaded to PC. More advanced features of the MIDAS Surveyor include the ability to take
corrective data from external instruments, including Valeport tide gauges & sound velocity sensors, together with heave
sensors and gyrocompasses. Additionally, a second echosounder transducer may also be used.
The system logs data asynchronously. That is to say, it will log all incoming data regardless of the update rate or exact
timing of each data channel, and will log each data input in sequence. The onboard microprocessor applies an accurate
time stamp to each data point, ensuring that a complete time series record of each data input can be generated, together
with interpolated position and depth information. Any corrective data received from a heave sensor or tide gauge can be
applied in real time to the depth data, and the user may choose whether to log or output either the corrected or
uncorrected data.
The instrument may be supplied with or without an integral GPS receiver. Valeport offer a choice of two industry
standard GPS receivers – an Ashtech A12 twelve channel DGPS receiver or a high accuracy Ashtech DG16 sixteen
channel DGPS receiver. Both receivers feature SBAS differential correction as standard, and the DG16 also features
Marine Beacon differential correction. The scope of this manual does not include a detailed discussion of the SBAS
(Satellite Based Augmentation System) systems, but they can be simply described as a free differential GPS correction,
transmitted from geostationary satellites. There are currently three SBAS systems active in different geographical areas:
WAAS in North America, EGNOS in Europe and the Middle East, and MSAS in the Far East. The accuracy of the
differential corrections obtained from the SBAS systems varies depending on the receiver’s position within the footprint,
but can typically be relied upon to give overall accuracy levels in the region of 1 – 5m, depending on receiver type.
Valeport has developed its own single beam echosounder system, which utilises advanced Digital Signal Processing
techniques to give high levels of accuracy and consistent performance. The system is integral to the MIDAS Surveyor,
which thus requires only a standard analogue transducer to be connected. The system has two channels as standard,
optimised for 210kHz and 33kHz transducers respectively. The user may choose to use either or both of these channels,
using Valeport’s standard supply transducers or their own choice. Alternatively, the MIDAS Surveyor can accept digital
transducer inputs, or single / dual channel data from any standard third party echosounder system.
