GNSS Metadata Information

Each site where we have extracted GNSS-IR data has a dedicated site page (e.g. Newlyn) containing the following information:

Metadata Information


Our identifier for the site. We have given each site a unique identifier, which is used to access information on that site, and also in file names. We're using a five digit code, to make it clear these are distinct from the IDs used in our traditional mean sea level from tide gauge dataset, which have a 1-4 digit ID.

The site page for a station can be accessed using this number, for example the page for Newlyn (ID 10049) is:

In the future we hope to also link to a persistent, uniquely defined identifier for each GNSS receiver to make identifying where the data comes from easier.

IGS Type Code

A four character code used commonly used to represent a GNSS installation.

These codes are listed on GNSS data sites such as SONEL and the Nevada Geodetic Laboratory. Unfortunately, some codes have been used for more than one site, so these identifiers aren't unique. Where there is a disagreement, we have used SONEL's.

The site page for a station can be also accessed using this code, for example the page for Newlyn (ID 10049, Code newl) is: . Just be aware you may not end up on the site you were looking for.

If required, you can download a CSV file linking IDs to Codes

Latitude and Longitude

Note that supplied latitude and longitudes quoted are only approximations: the primary purpose of continuous GNSS installations is to measure the movement of the installation over time, hence the actual latitude and longitude will change - the SONEL and NGL sites have visualisations of how this varies over time.

Ellipsoidal Height

This is the height of the receiver's phase centre (the point where measurements are taken) above the reference ellipsoid used by GNSS systems - that's the imaginary surface of all points across the globe given a height of zero.

Note this value is an estimate - as with latitude and longitude the actual value varies over time and is the main reason the sensor has been installed in the first place. See original data, and the visualisations on the SONEL and NGL sites for more information on how the ellipsoidal height is changing at a site.

Ellipsoidal Height Epoch

This is the date at which the value of Ellipsoidal Height is estimated.

This is expressed as a decimal, so for example 2017.0000 would mean the height was estimated for midnight (UTC) at the start of 1st January, 2017.

Reflector Height

This is an estimate of the average height of the receiver's phase centre above the water below. The estimate we use is the mean sea level (Z0) from a tidal analysis of the heights we obtain through our processing.

Additional data sources

Here we have provided for convenience a list of tide gauge data available from nearby instruments.

Maps and plots

Site Map

Each site page contains an interactive map showing the location of the site, along with an illustration of the portion of the GNSS footprint that produces good data.

These are based on the first Fresnel zone of the L1 band of GPS, and considering the mean azimuth and elevation of each satellite pass producing good data. Passes are grouped by mean azimuth, and the most common minimum and maximum elevation for each azimuth are shown.

Daily data plot (example)

We have included a plot of daily data at the site, and where possible included data from a nearby tide gauge. Heights are expressed in metres above the reference ellipsoid.

Please note that the tide gauge data comes from a variety of sources with a range of quality control applied, and in some cases only real time data with no quality control is available, and is only present to show how the GNSS-IR data compares with data from a traditional tide gauge. If you are after the tide gauge data, please obtain it from the usual sources listed on the site pages (e.g. links for Newlyn)

Inventory plot (example)

This plot illustrates which GNSS constellations and signals provide data on each day throughout the length of the series

Daily observations plot (example)

This plot shows the number of observations available each data throughout the series, and will vary with the number of constellations and signals available