UK: Low Cost GNSS Tide & Sea Level Measurements for Intertidal Public Safety (LoCTIPS)

A recent NERC-funded proof of concept award successfully demonstrated that Global Navigation Satellite System (GNSS) signals reflected off the sea surface and received by very low cost (<£30) GPS receivers can be used to estimate the difference in height between the receiver and the water. This represents a method of remotely sensing tidal elevations and, if averaged over time, mean sea level. These could be routinely and remotely measuring sea level at a cost that would allow unprecedented numbers of systems to be deployed around the world by organisations of all sizes and levels of funding.
Here we propose to take the initial proof of concept from TRL 3 up to TRL 7 by designing a self-contained unit that receives, records and processes the required signals to output a tidal water level in near real time and at a target hardware and assembly cost of less than £100. The demonstration units will be tested and used by our project partners, the RNLI, initially to provide tidal information at an intertidal causeway with a history of RNLI rescues of members of the public who have become stranded by the rising tide.
The technology has the potential to be rolled out not only across the UK but globally, potentially as open source designs & firmware, revolutionising the ability to collect tidal and sea level data at an unprecedented price point and operational simplicity.

To help reduce rescues and thus call-outs the RNLI currently provide two different tidal services for the general public; Text for Tide and live tide signage. Text for tide is a free text service that provides the user with safe crossing times for a specific location. It is operational in two locations, Crammond Island and Coney Island; both of these locations feature causeways to islands that cover mid-tide. Text for tide is based on predicted tide data, some of which is provided by the NOC. Live tide signage is currently only operational in one location. Deployment at a second location is planned but is being hampered by issues relating to tidal data access. The signs give the general public safe causeway crossing times based on local tide gauge readings. The projected cost for a new live tide signage installation with tide gauge is around £20,000, access to the proposed GNSS system could to reduce this significantly.
The Text for Tide service at Crammond Island runs year round without issue. However, the service at Coney Island is seasonal and is switched-off from October until April. This is because the weather effects (e.g. atmospheric pressure, storm surges) are more influential during the winter, and tidal predictions alone do not give sufficiently accurate information. Local measurements at Coney Island would remedy this situation; however the cost basis of a conventional system is prohibitive. Access to low-cost live tidal information would make text for tide a viable service in almost any location. This would greatly improve the reach of the RNLI's prevention work. The two-fold effect of this would be to reduce both the numbers of people needing to be rescued, and the use of RNLI resources. Not only does every lifeboat launch cost money, but every crew member (almost all of whom are volunteers) leaving their day-job draws on the goodwill of their employer.
Beyond the RNLI's immediate requirements for low cost sea level measurement systems, there are many other scientific and practical applications. Sea level rise is one of the most important, and one of the most publicised impacts of climate change. In the UK for example, the public is mostly concerned with extreme sea level changes, which determine the frequency and severity of flooding and are a major factor in coastal erosion. In many other regions of the world coastal hazards associated with sea level changes can be much more severe. Impacts such as inundation, floods, storm damage, wetland loss, habitat change, coastal erosion and saltwater intrusion have the potential to negatively impact socio-economic development efforts. In the Western Indian Ocean, a region that experiences significant cyclone activity, and associated surge events, there is a paucity of observational data. Madagascar, for example, has only 1 operational tide gauge and more than 4000km of coastline; Mozambique has only 3 tide gauges over a coastline of more than 7000km. Equipment cost is one of the barriers that is preventing the deployment of additional tide gauges. The availability of in-situ sea level data in Madagascar and Mozambique is representative of many countries on the DAC List.
The ability to deliver low cost systems, providing real-time or near real time information on sea level is a potential game changer for coastal resilience. Real time data are needed to support operational flood warning in areas prone to storm surges and tsunamis. Vastly greater spatial coverage could be achieved and the information made available to reduce risks to communities and to support a range of socio-economic activities including tourism, artisanal fishing, gleaning (gathering food on foot from the coastal zone), and non-primary ports and harbours.