Your echosounder could affect USBL performance so use the Acoustic Signal Analysis and Noise Plot tools available in Ranger to identify potential issues.
The Signal Analysis Tool, within you’re Ranger 2 software, allows you to identify and diagnose ‘False Detections’ caused by the echosounder and to then take steps to minimise this. The Noise Plot Tool allows you to analyse the background noise to which the USBL transceiver is exposed. Take various noise profiles under different operating configurations, for example, with the echosounder on and off. These will give you a good idea of the power and gain settings to use, the maximum range you can expect to achieve and the beacon power settings. If you are in any doubt, please feel free to send through the screenshots and we will look at them.
No.
there is no official support or testing for MODBUS although the Modem 6 supports binary data and will likely frame MODBUS messages correctly.
Modem 6 can send and receive data from multiple modems as long as the modem transfers are separated in time (i.e. simultaneous broadcasting of messages is not supported).
The desired actual acoustic data rate can be selected by picking from a set of telemetry schemes. The environmental conditions (SNR) will dictate what telemetry schemes can be used effectively.
Available telemetry schemes
The lower telemetry schemes are most robust whereas the higher schemes make better use of the battery life, allowing more data to be sent with the same amount of power. Supported telemetry schemes include:
• TS0 (100 bits/s)
• TS1 (200 bits/s)
• TS2 (400 bits/s)
• TS3 (900 bits/s)
• TS4 (3000 bits/s)
• TS5 (6000 bits/s)
• TS6 (3500 bits/s)
• TS7 (9000 bits/s)
What is meant by SNR?
SNR is an abbreviation for Signal-to-Noise Ratio and is a measure which describes the ratio of signal power to the noise power. A good signal to noise ratio helps when trying to achieve a reliable acoustic communications link.
What affects SNR?
The following all affect the ratio of signal to noise power:
• The acoustic channel (deep fading caused by reverberant geometries)
• The source level of the transmitting Modem 6
• The gain level used by the receiver electronics
• Electrical noise sources, e.g. noise conducted on the power lines or induced by modulated signals to control thrusters etc.
• Cable length and inadequate shielding of cables
All subsea Modem 6 variants have quiescent power less than 50 milliWatts. The transmission power level is configurable allowing the battery life to be optimized for the slant range. Typically, 1 megabyte of data can be transferred (at 9000 bps) using less than 1.5 Watt-hour.
A single topside modem can communicate individually with over 100 subsea modems, limited only by the number of unique acoustic addresses available. We recommend the Modem 6 Transceiver (Type 8182 & 8193) as a topside unit because it provides the most robust connection through a combination of increased SNR and superior processing gains.
All Modem 6 products utilize the same acoustic and serial protocol allowing a mix-and-match approach to suit a wide range of operating scenarios. The smaller Modems (Sub-Mini and the Mini) are suitable for vehicles and are both fitted with smaller rechargeable batteries. The standard Modem 6 is significantly larger but boasts increased transmission power and is suited to powering external equipment for long duration deployments.
While Modem 6 uses the same field proven technology as our core 6G range, it is aimed at users who do not require the more complex functions of our core 6G range, such as: precise positioning, on-board sensors or complex multi-node array telemetry. As such it is ideally suited for simple applications that require a dedicated point to point data (address to address) transmission capability, while our core 6G products, including OEM solutions, are available for more challenging applications. If you’re unsure, please get in touch so that we can identify the right solution for your project.
Yes you can.
The beacon, for example a WSM 6+, must be held vertical by a small float about 10 m above its transducer to prevent acoustic masking, with a (approximately) 1 m strop length from the beacon to a 20 kg clump weight (the strop length is important to reduce the possibility of the beacon hitting the weight and sustaining damage when it is lowered but not too long that the beacon ‘waves’ above it).
A second 20 kg clump weight (approximately twice the water depth away) acts as the tether point for a larger location buoy which will be at the surface well clear of the vessel’s turning circle. The surface float’s strop should be long enough to compensate for tidal variations to prevent it from being pulled below the surface.
Spin Test (DP Vessels):
Track the transponder on the seabed with the vessel directly over the target. Set a way point for the transponder position and set the measure tool from the way point to the transponder or increase the trail history, ensure GNSS is being fed to the system.
Slowly rotate the vessel over the top of the transponder, using the USBL pole as the centre of rotation whilst observing the snail trail on the Chart display for the mobile target.
If the transponder trail history draws a doughnut shape greater than expected from the 1DRMS value, an error may be present in the pitch and roll installation corrections.
Heading test:
Track the transponder on the seabed with the vessel directly over the target and set a way point as the transponder position. Set the measure tool to measure from the way-point to the transponders reported position and ensure GNSS is being fed to the system. Sail away from the transponder in any direction at a constant speed.
Watch the distance of the transponder from the way-point.
If the mobile target moves perpendicular to the vessel heading there is a possible heading alignment error between the USBL transceiver and the gyro.
Quick Track allows you to instantly start tracking a beacon with no other information required other than the unit’s address. You’ll no longer have to manually add the beacon to your job and go through the process of acoustically acquiring the beacon’s configuration. Ranger 2 takes care of everything, leaving you to get on with your subsea operations. Quick Track is particularly useful for checking system performance.