The Nortek Signature 1000, 500, 250 and 100 are equipped with ability to capture Echosounder data. This is an optional feature that enables the instruments to measure the magnitude of the echo generated by the instrument pinging in high resolution. The echosounder collects data along the center beam to gain information about scattering particles in the water column.
This article summarizes the most important considerations when configuring this application. For a comprehensive guide to Echosounder measurements, please see the articles found under the Oceanography - Documentation section: Introduction to Echosounder measurements.
Requirements
To collect echosounder data, no hardware change is required. The application is activated by purchasing the corresponding license from you local sales representative. There are two licenses available:
- Echosounder (This enables the base functionality.)
- Multifrequency (This is an additional feature, allowing the simultaneous collection of echograms at 1000, 500 and 250 kHz. This is currently only available for the 1000kHz Signature!)
The license key(s) can be uploaded to the instrument using the configuration software Signature Deployment (Instrument -> Licenses -> Add).
Calibration
It is essential to calibrate the echosounder gain if you intend to (1) compare data from a specific site over extended periods or (2) compare data from multiple instruments at a given location. The calibration needs to be carried out by the user! For detailed guidelines of the procedure, please see this article: Echosounder calibration.
Configuration using the Deployment wizard
Open Signature Deployment and connect to the instrument. Open the Deployment Wizard to create a configuration. This can also be done without having an instrument connected to test out various deployment configurations in preparation. Refer to the software's Help section for detailed descriptions of each parameter.
Follow the below guide for relevant steps in each section.
Instrument
Ensure that the correct instrument type is displayed and the instrument is equipped with the echosounder license.
Application
Depending on your instrument type, there will be a different selection of applications to choose from:
Signature 1000 & 500 kHz:
If you are solely interested in collecting echosounder data, choose Burst with Echosounder. This application will allow you to collect 3 independent echograms using the center beam. No current data is collected!
If you are interested in collecting current or wave data at the same time as the Echosounder, choose one of the standard burst/wave configurations and select the Echosounder that will become available under Extension. The echosounder and the other burst measurements will follow the same time schedule.
For a detailed overview of the available applications for you instrument, see these articles:
- Which application should I use for my Signature 1000 measurements?
- Which application should I use for my Signature 500 measurements?
Signature 250 kHz:
If you are solely interested in collecting echosounder data, choose Burst with Echosounder. This application will allow you to collect 3 independent echograms using the center beam. No current data is collected!
If you want to collect wave data in addition to the echosounder, select Wave height and direction as well as the Echosounder under Extension.
Signature 100 kHz:
Select Echosounder. If you want to sample currents in addition, you need to work with a concurrent plan.
Environment
Consider each parameter and make the appropriate choice for you deployment location.
Echosounder
Range
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Start and End of profile
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Choose the blanking distance or distance from the instrument head at which you want the echosounder profile to start as well as the end of the profile you want to capture. If you are uncertain of the final deployment depth of the instrument and want to capture cells close to the sea surface, we generally recommend to configure a too long profile to ensure that the entire water column is captured. |
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Cell size [m]
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Cell size is the vertical size of the individual cells in the profile, in meters. This parameter will therefore determine the spatial resolution of your echosounder profile. A larger cell size will make the instrument transmit more energy for a given power level. |
Echograms
It is possible to collect up to 3 individual echograms with the Signature. All echograms will capture the same profile and use the same cell size (spatial resolution), but their individual settings can be used to fine tune data collection to the particle type you are trying to capture.
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Pulse compression
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Enabling pulse compression alters the way in which the pulse is transmitted and processed. Its use is limited to one of the three echograms. The advantage of the Pulse compression is the noise reduction, higher accuracy and longer range due to the combination of long- and high energy pulses. However, Pulse compression is not ideal for shallow water as it can yield side lobe effects near the boundary and may come at a cost of higher power usage. Please see this article for a detailed description and guide on choosing the appropriate setting: Introduction to Echosounder measurements. If you are collecting multiple echograms, it can be a good idea to enable one echogram without pulse compression and another echogram with pulse compression enabled. Then you get both results at the same time and can decide later which one to use. |
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Frequency
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The used frequency is limited to the instruments frequency by default. For specific Signature types, a multifrequency license is available, which allows the configuration of multiple frequencies at once. If your instrument is equipped with the appropriate license, you need to decide whether to collect multiple echograms using the same frequency or if you would like to for example use 1000kHz for Echogram1 and 500khz for Echogram 2. As with any other ADCP, the selection of the instrument frequency depends on the target under study. High-frequency instruments can discern smaller targets than lower frequencies, whilst having higher water absorption (\(\alpha\)). For more details on choosing the appropriate frequency, please see this FAQ: What are the steps to collect Echosounder data? |
| Transmit Length [ms] |
With pulse compression: Changing the transmit pulse length when using pulse compression can increase the SNR at the expense of the power consumption. The resolution is not affected at the bin size will be equal to the configured value (cell size). Without pulse compression: The length of the transmit pulse affects the bandwidth of the pulse according to \(\Delta f \approx \frac{1}{t}\). In combination with the cell size, this value determines the spatial resolution and thereby the cell over which the signal is averaged. The smaller the transmit length and cell size, the higher the spatial resolution. For more details, please see this FAQ: What are the steps to collect Echosounder data? |
| Power level | The Power level determines the amount of energy that the instrument transmits. It is given in a relative dB scale, where maximum power level is 0 dB. The higher the power the higher the range, particularly in low scatterer conditions. This of course comes at the downside of high power consumption. |
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Bins (only Signature 100) |
The user has the choice to select the data to be processed into single beam (centered at 90 kHz) or five frequency bins, centered at 73.8, 82.3, 90.9, 99.4 and 107.9 kHz. With five frequency bins, the user gets a broader range of data points, which can be useful for more detailed analysis. |
Burst
Sampling
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Measurement Interval
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The measurement interval determines how often the measurement is repeated. Use the number of samples and sampling rate to determine the burst duration, which is the amount of time for which the instrument collects data each measurement interval. \( \text{Burst duration} = \text{Number of samples} \times \frac{1}{\text{sampling rate [Hz]}} \) |
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Sampling rate
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The echosounder will be sampled at the same rate as the burst measurements. The maximum sampling rate depends on the instrument type and application. If only the echosounder application is used, a higher sampling rate is selectable compared to a combination of waves and echosounder. |
Raw echosounder data
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Raw data interval
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It is possible to enable the storge of raw echo data on the recorder. The frequency or interval at which the raw profile is stored can be determined using the Raw data interval (s). Keep in mind that storing raw echo data significantly increases memory usage and should only be used if needed. |
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