Sensors

Tender description

The following specifications of the iDAS unit of Silixa Ltd are essential for our research and no other supplier provides equipment that achieves all these requirements: • phase coherent system with a linear response to acoustic energy to measure flows; • real time measurements; • ability to measure strain changes; • spatial resolution down to 1 m and sampling down to 25 cm; and • the signal to noise ratio needs to be at least 100 dB when measured with phase sensitivity 10-4 for a seismic bandwidth of 100 Hz, with 50 kHz laser repetition rate, 45 ns pulse width and 10 m gauge length. Silixa Ltd is the supplier of the world’s highest performing distributed acoustic sensing (DAS) units that can be used to create distributed fibre optic monitoring arrays with the highest levels of accuracy in the industry (https://silixa.com/). It has 33 patents for fibre optic sensing equipment (https://patents.justia.com/assignee/silixa-ltd). The distributed acoustic sensing (DAS) unit will be part of the Birmingham Urban Observatory (https://birminghamurbanobservatory.com) and used for research on ambient noise, ground soil conditions (including crucially soil moisture changes – for example for water, sewer or drainage pipeline leakage detection) and flows in urban areas. The equipment needs to have high spatial resolution and sensitivity so that it can measure the very detailed temporal and spatial variability of the urban environment.Using DAS for sensing the urban environment is a relatively new area of research and very few peer reviewed academic papers have so far been published, all of these being within the last few years. Those most relevant to our research are Dou et al. (2017) and Ajo-Franklin et al. (2018), which report on calibrating the use of DAS for sensing of ambient noise, soil ground conditions, moisture changes and flows in urban areas, and Zeng et al. (2017) and Jousset et al. (2018) on utilising fibre optic cable of existing networks. These studies used an iDAS unit supplied by Silixa Ltd and, crucially for our research, we are not aware of any equivalent published research on ground conditions and ambient noise in urban areas that has used a DAS unit from a different supplier. Our measurements using DAS must be directly comparable with these previous studies so that, without enormous additional cost and effort (most likely including the need to hire a Silixa iDAS unit), we can compare our measurements with their calibrated findings to validate our results. If we were to use equipment with a different specification there would be uncertainty over whether differences between our findings and these previous studies are due to environmental factors or the sensitivity of the equipment. The measurements also need to be in real time so that results can be instantaneously updated on the Birmingham Urban Observatory website, correlated with other real time measurements and contribute to the collaboration between the six UK-wide UKCRIC Urban Observatories. Finally, we need to have close collaboration with the equipment supplier to check that the equipment is functioning appropriately in each of its novel applications – the user and supplier need to ‘advance together by learning’. Silixa Ltd have already successfully collaborated with University of Birmingham on the use and development of an earlier generation of acoustic sensing equipment (Bense et al., 2016), so we know that they are prepared to act in this way and we can build on the existing relationship. Silixa have agreed to include free training for university staff on using the iDAS unit. While this might not appear exceptional, Silixa staff have co-authored three of above references and thus their knowledge and research experience will be uniquely valuable for the success of our project – we have one year remaining on the capital grant that is funding the equipment and in which to obtain robust datasets; we simply do not have time to make ‘learning to use the equipment in previously untried applications’ on the way. We also have a limited research budget and Silixa Ltd have included a generous discount on the normal cost of this equipment on the condition that we use it collaboratively and only for academic research. The research funding awarded by the Engineering and Physical Sciences Research Council for purchasing this equipment is a maximum of GBP 200 000 plus VAT.