Variations in sea level have a great environmental impact. They modulate coastal deposition, erosion and morphology, regulate heat and salt fluxes in estuaries, bays and ground waters, and control the dynamics of coastal ecosystems. Sea level variability has importance for coastal navigation, the building of coastal infrastructure, and the management of waste. The challenges of measuring, understanding and predicting sea level variations take particular relevance within the backdrop of global sea level rise, which might lead to the displacement of hundreds of millions of people by the end of this century. Sea level measurement relies primarily on the use of coastal tide gauges and satellite altimetry. Tide gauges provide sea levels at fine time resolutions (up to one second), but collect data only in coastal areas, and are irregularly distributed, with large gaps in the southern hemisphere and at high latitudes. Satellite altimetry, in contrast, has poor time resolution (ten days or longer), but provides near global coverage at moderate spatial resolutions (10-to-100 kilometres). Altimetric sea level products are problematic near the coast for reasons such as uncertainties in applying sea state bias corrections, errors in coastal tidal models, and large geoid gradients. The complicated shoreline geometry means that the raw altimeter data have to either undergo special transformations to provide more reliable measurements of sea level or be rejected. Developments in GPS measurements from buoys are now making it possible to determine sea surface heights with accuracy comparable to that of altimetry. In combination with coastal tide gauges, GPS buoys could be used as the nodes of a global sea level monitoring network extending beyond the coast. However, GPS buoys have several downsides. They are difficult and expensive to deploy, maintain, and recover, and, like conventional tide gauges, provide time series only at individual points in the ocean. This proposal focuses on the development of a unique system that overcomes these shortcomings. We propose a technology-led project to integrate Global Navigation Satellite Systems (GNSS i.e. encompassing GPS, GLONASS and, possibly, Galileo) technology with a state-of-the-art, unmanned surface vehicle: a Wave Glider. The glider farms the ocean wave field for propulsion, uses solar power to run on board equipment, and uses satellite communications for remote navigation and data transmission. A Wave Glider equipped with a high-accuracy GNSS receiver and data logger is effectively a fully autonomous, mobile, floating tide gauge. Missions and routes can be preprogrammed as well as changed remotely. Because the glider can be launched and retrieved from land or from a small boat, the costs associated with deployment, maintenance and recovery of the GNSS Wave Glider are comparatively small. GNSS Wave Glider technology promises a level of versatility well beyond that of existing ways of measuring sea levels. Potential applications of a GNSS Wave Glider include: 1) measurement of mean sea level and monitoring of sea level variations worldwide, 2) linking of offshore and onshore vertical datums, 3) calibration of satellite altimetry, notably in support of current efforts to reinterpret existing altimetric data near the coast, but also in remote and difficult to access areas, 4) determination of regional geoid variations, 5) ocean model improvement. The main thrust of this project is to integrate a state-of-the-art, geodetic-grade GNSS receiver and logging system with a Wave Glider recently acquired by NOC to create a mobile and autonomous GNSS-based tide gauge. By the end of the project, a demonstrator GNSS Wave Glider will be available for use by NOC and the UK marine community. The system performance will be validated against tide gauge data. Further tests will involve the use of the GNSS Wave Glider to calibrate sea surface heights and significant wave heights from Cryosat-2.