Integrated Distributed Acoustic Sensing (iDAS)

Last modified by robert on 2024/05/17 16:52

What is iDAS?

iDAS stands for Integrated Distributed Acoustic Sensing. This advanced system utilizes the principle of Rayleigh backscattering in optical fibers to measure strain rates along the fiber's length. It's a cutting-edge technology predominantly used in fields like geophysics, where it's crucial for monitoring seismic activities, as well as in industrial applications like pipeline monitoring and security systems.

Safety first!

The iDAS uses a Class 1 laser, which is generally considered safe for most applications. However, direct exposure to the eye should be avoided to prevent any risk of eye injury.

Cables and fibers may create tripping hazards. Ensure that the routing of cables is done in a way that minimizes the risk of accidents.

System Components

The iDAS system consists of the following components:

Interrogator unit: This unit houses the laser, detector, and electronics for processing the backscattered light signal. It records various settings such as the optical system configurations, spatial sampling rates, and the duration of data acquisition. More than one interrogator may be used in an experiment. Each unit should have a unique identifier and is described in its respective metadata block.
Optical fiber: The optical fiber is the sensor that is used to measure strain rate.
Data acquisition software: This software is used to control the interrogator unit and to acquire and process the data. It records various settings such as the optical system configurations, spatial sampling rates, and the duration of data acquisition.

DAS Data Collection System

1. Surface Installation

Cable Arrangement: The optical fiber cable can be a single long continuous cable or multiple cables with connectors, used across different installation environments.
Cable Types: Cables may vary in construction types based on the installation environment.
Geographical Metadata: Parameters related to geographical location are specified for easy searchability in databases.

2. Installation Environments

Shallow Burial: The cable can be shallowly buried.
In-Conduit Installation: The cable can also be installed within a conduit.
Water Installation: Suitable for underwater environments.

3. Channels

Sensor Distribution: Channels represent sensors distributed along the fiber array at fixed intervals.
Physical Location Determination: The physical locations of these channels are ascertainable through methods like tap tests and GPS tracking.
Metadata for Channels: Each channel or group of channels has its own metadata block, detailing specifics like location and properties.

DAS Metadata Schema

1. Interrogator

Required: Interrogator ID, manufacturer, model.
Optional: Serial number, firmware version.

2. Acquisition Parameters

Required: Interrogator ID, acquisition ID, unit of measure, acquisition start and end time, acquisition sample rate, gauge length, number of channels, spatial sampling interval.
Optional: Pulse rate, pulse width.

3. Overview

Required: Network code, location, start date, end date, point of contact.
Optional: Digital Object Identifier (DOI), purpose of data collection, funding agency.

4. Cable Information

Required: Cable ID, cable bounding box.
Optional: Cable owner, cable installation date, cable characteristics.

5. Fiber Information ('Native format')

Required: Cable ID, fiber ID, fiber geometry, fiber mode, fiber refraction index.
Optional: Fiber optical length, fiber start and end location, fiber one-way attenuation, fiber winding angle.

6. Channel Group

Required: Interrogator ID, acquisition ID, channel group ID, cable ID, fiber ID, coordinate generation date.
Optional: Location method, coordinate reference frame, first/last usable channel ID, uncertainty of various coordinates (x, y, latitude, longitude, elevation, depth, strike, dip).

7. Channel

Required: Channel group ID, channel ID, coordinates (x, y, latitude, longitude).
Optional: Elevation above sea level, depth below surface, distance along fiber, strike, dip.

Pre-processing Steps for DAS Data (2.5 months, 90 TB)

Create a Deployment Log
- Document key details like photonics settings, duration of data collection, instances of hard disk failure, power outages, etc.
Generate Geographic Coordinates
- Assign latitude and longitude coordinates to each DAS channel for spatial referencing.
Data Conversion
- Convert the raw DAS time series data from counts to strain rate, which is more meaningful for seismic analysis.
Data Decimation
- Reduce the sampling rate from 1000 Hz to 100 Hz. This step is essential to manage data volume and focus on frequencies of interest for seismic activities.
Extract Specific Time Series
- Isolate time series data of special interest, such as those related to earthquake events, for detailed analysis.
Data Hosting
- Store the processed data on Research School of Earth Sciences (RSES) clusters and the National Computational Infrastructure (NCI) for accessibility and further analysis.
Extract Data and Instrument Response from Seismic Nodes
- Retrieve both the raw data and the corresponding instrument response characteristics for accurate interpretation of the seismic signals.
Long-term Archiving and Data Sharing
- Ensure that the data is archived in a format and location that supports long-term preservation and accessibility, such as the AuScope Distributed Acoustic Sensing (DAS) Collection.
Data Access and Record Keeping
- Maintain records and access paths (e.g., NCI local file path) for the data, including metadata and other associated records, to facilitate future research and data sharing.

iDAS Software Overview

Operating System Compatibility:

The iDAS system software is designed to run on the Windows operating system, with the current version compatible with Windows 7.

Accessing the System:

User Login: The system is set up to log in automatically as "User", without requiring any credentials.
Software Shortcut: A shortcut to access the iDAS software is conveniently placed on the desktop for easy access.

Data Acquisition Controls

Start / Stop: Easily control the start and stop of data acquisition using the current settings.
Calibrate Reference: Recalibrate reference levels as needed.
Exit: Safely exit the iDAS software.

Configuration iDAS Setup Wizard:

Provides a guided, step-by-step process for setting up the iDAS system.

iDAS Configuration: Access the iDAS configuration window for advanced settings.
Trigger Mode: Opens the trigger configuration window for specific acquisition needs.

Operating Modes

Available Modes: Acoustic, Waterfall, Stacking, Security, and OTDR.
Functionality: Each mode presents the acoustic data from iDAS in unique formats.
Detailed Information: See pages 19-23 of the Standard iDAS manual for comprehensive details on each mode.

Application Type Options

Diagnostic Setup Only:
- Retrieves current settings for a basic diagnostic overview.
Seismic Application:
- Sets Data Output Frequency to 1000 Hz.
- Adjusts Data Output Spatial Resolution to 2 meters.
Flow Monitoring:
- Changes Data Output Frequency to 10,000 Hz.
- Sets Data Output Spatial Resolution to 0.25 meters.
Security Monitoring:
- Configures Data Output Frequency to 1000 Hz.
- Sets Data Output Spatial Resolution to 2 meters.

Detailed Parameter Information

Time Decimation and Output Decimation:
- These values are calculated based on the physical fiber length.
Measure Length (m):
- Generated value: 10176 meters.
- Note: 'Measure Length' includes the reference fiber inside the iDAS unit, differentiating it from 'Physical Fibre Length'.
Pulse Width (ns):
- Generated value: 50 nanoseconds.
- Spatial Extent: A 50ns pulse corresponds to a 10m spatial extent.

Optimal Light Management

Objective: Achieve balanced light distribution across the region of interest in the iDAS system.

Adjustment Guidelines

Setting Optical Power:
- Aim to have the start of the region of interest around or below +4000 units.
- Ensure the far end of the region of interest does not enter a non-linear response scheme.
Consideration for Short Fibers:
- In cases where the fiber length is short and non-linear effects are not observed, set the Optical Power to its maximum.
- Power Scale: The adjustment slider ranges from 0-100, representing the percentage of maximum power available.

Note on Optical Power Control

Control Mechanism: The slider provides a precise control mechanism to manage the intensity of light sent through the fiber.
Monitoring and Adjustment: Continuously monitor and adjust as necessary to ensure optimal performance.

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Integrating GPS Antenna for Accurate Timing

Installation and Connection Process

Connecting the GPS Antenna:

Connect one end of a coaxial cable with SMB female connectors to the GPS antenna.
If you plan to mount the antenna, do so before connecting the cable.
Connect the other end of the cable to the 'GPS Ant.' port located on the output panel at the front of the iDAS unit.

Monitoring GPS Status and Time

GPS Information Display: The GPS status and time are displayed on the Tool Bar of the iDAS software.
Status Indicators:
- Red: Antenna is not connected.
- Amber: Antenna connected, but self-survey not completed.
- Green: Antenna connected, self-survey completed, and timing is accurate.

Primary Configuration Settings in iDAS

These settings are integral to the operation of the iDAS system, significantly influencing aspects like the rate of data streaming. They encompass:

Sampling Frequency: Determines how often data is captured.
Spatial Resolution: Defines the level of detail in spatial data.
Fiber Length: Impacts the range over which data is collected.

In configuring these parameters, a balance must be struck. This involves aligning the system's physical capabilities, such as fiber length and spatial resolution, with the practical limits of data collection, including the volume of data generated. Adjusting these settings correctly is crucial for optimizing data quality while managing the data volume effectively. This balance ensures that the system meets the specific needs of each application without overwhelming storage or processing capabilities.

Silixa iDAS Setup Manual for Reoccupying/Duplicating Experiment

General Information

Experiment Name: _______________________________________
Local Date: ____/___/202
Local Time: ___________________________________________
Personnel: ____________________________________________
Site Condition Notes:
- [Space for detailed notes about the site condition, any upkeep performed, and changes made since the last visit.]

Setup Procedure

Open iDAS Box
- Serial Number: _________________
- IP Address: ____________________
Check Laser Lock
- Ensure the lever on the LASER/RIGHT side of the iDAS is in the locked position (LEVER UP).
Placement of iDAS
- Position the iDAS on a stable surface.
- Ensure clear air flow around the fan vents.
UPS Setup (If applicable)
- Connect the UPS to a power source.
- Plug the NAS into the UPS using the special cable with a rectangular connector.
- Connect the monitor to the UPS.
Peripheral Connections
- Connect a computer monitor, mouse, and keyboard to the iDAS.
GPS Antenna Connection
- Connect the GPS antenna to the left-side socket on the front of the iDAS using a special adapter.
Fibre Optic Connection
- Clean both the fibre optic cable and the socket with a 1-click cleaner before connection.
- Use the guide/tip for cleaning the fibre and clean the socket without it.
Powering the iDAS
- Connect the iDAS to a power socket or UPS.
- Note: The iDAS turns on automatically when connected to power. Use the power button at the bottom left if it does not.
Network Drive Mapping
- Open File Explorer and select 'This PC' from the left pane.
- On the File Explorer ribbon, select 'More' > 'Map network drive'.
- Choose a drive letter from the 'Drive' list.
Open iDAS Software
- Use the link/shortcut on the Desktop.
GPS Satellite Confirmation
- Check for a green light in the top row of the software interface indicating GPS satellite detection.
Lever/Interlock Adjustment
- Lower the lever/interlock (as mentioned in step 2) before starting data acquisition.
Configuration File Duplication
- Use 'current.cfg' for duplicating previous setup.
- The file is located at C:/Silixa/Data/current.cfg.
- Copy this file to the desktop and save it with a new filename.
iDAS Configuration Settings
- Navigate to the 'Configuration' tab and click 'iDAS configuration'.
- Check all values under 'system'.
- Under 'application', enable error messages.
- In 'saving', select 'acoustic saving', choose 'tdms', and set the file save location and identifier.
- Leave default parameters in 'measure'.
Mode Selection
- Toggle between Acoustic mode, Waterfall mode, and OTDR mode to check data recording.
Photograph OTDR Mode
- Document the OTDR mode settings with a photograph.
Photograph Waterfall Mode
- Similarly, take a picture of the Waterfall mode settings.
Configuration File Saving
- Save the configuration file in .cfg format in a separate location without overwriting the existing one.
Software Check
- Ensure QFinder, Teamviewer, and Microsoft Remote Desktop are installed.
Remote Access Setup
- Open Teamviewer or Microsoft Remote Desktop.
- For Teamviewer, photograph the ID and password and ensure it remains open.
- For Microsoft Remote Desktop, record the IP address and test remote access with a separate laptop.
Final Mode Setting
- Switch to OTDR mode for ongoing operation (avoids excessive memory usage of Waterfall mode).

Important Reminders

Always ensure that the iDAS is connected to a suitably earthed power socket or UPS for safety.
Regularly check the condition of all cables and connectors.
Before leaving the setup, confirm that data saving is active if required.
Keep a log of all actions taken during the setup for future reference and troubleshooting.