ESR Antarctic Tide Gauge Database

Laurence Padman, ESR
email: padman@esr.org 
Phone: +1 (541) 753-6695
Fax: +1 (541) 753-1999

Matt King, University of Newcastle
email: m.a.king@newcastle.ac.uk 
Phone: +44 191 222 7833
Fax: +44 191 222 6502

 
Funded by NSF Polar Programs
 

Go directly to map of tide height data sites.

Overview

Scientists at ESR, in collaboration with Matt King at the University of Newcastle Upon Tyne, U.K. (NCL), have created an Antarctic database of ocean tide harmonic coefficients (amplitude and phase) from a variety of measurement systems. These coefficients are primarily intended for users interested in validation of tide models for the Antarctic seas including the areas covered by the large floating ice shelves. For example King and Padman (2005) used a subset of this database to determine the present best model for Antarctic tide heights. Included in the database are coefficients for both ocean tide and ocean tide loading, the combination of which provides tides as frequently measured in geocentric coordinates (e.g., by GPS and satellite altimeters).

Data contributing to the database vary widely in quality, from short records of unknown accuracy, to very precise, long-term records from bottom pressure recorders (BPRs). This database provides sufficient information for a user to judge whether a tidal analysis at a particular site should be used for their application.

Data have been collected using a wide variety of measurement techniques. These include:

The highest-quality data come from CTG, BPR and modern GPS records. The major tidal constituents are best separated if more than 1/2-year of data are available. Many Antarctic records are less than 29 days long, so that they are difficult to analyze for a sufficient number of major tides to develop reliable predictive models for that site. Nevertheless, because so few tide records exist in the region, these shorter records (and, of course, the intermediate-length records between 29 days and 1/2 year long) may be valuable to some users.

More information on ocean tides around Antarctica comes from records from GPS sites installed on bedrock sites. The entire Antarctic continent experiences deformation by the tidal change in the weight of water over the adjacent ocean seabed: this is called "ocean tide loading" (OTL). The OTL term is typical a few centimeters amplitude over Antarctica (see Yi et al. 2000), and can easily be seen in onshore GPS data (King et al., 2005; and http://www.staff.ncl.ac.uk/m.a.king/GPS_OTL.htm).

Information on each site can be viewed from clickable maps, selected from the index in the left-hand frame or by clicking on the general locator map, below. Once in a clickable map, you can find the name of the nearest site by positioning the cursor over the site. Clicking on the site gives basic information below the map. For information on accessing the complete database as a single file, click here, or scroll to below Figure 1.

Ocean Tide, and Ocean Tide Loading

The principal data set provided here describes the ocean tide, the perturbation of the ocean free surface elevation relative to the seabed. This is the usual product from ocean tide models, thus a direct comparison between the ocean tide database and models is appropriate. Measurements made with bottom pressure recorders (BPRs) and coastal tide gauges (CTGs) are recorded with a seabed datum.

Many elevation measurements, however, are obtained using geocentric coordinates, which are relative to the Earth's center of mass. These measurements (GPS and satellite altimetry) must be corrected for Earth body tides (due to the direct attraction of the Sun and Moon on the Earth) and ocean tide loading (OTL) displacements, which is the deflection of the deformable seabed by the tide-induced anomalous weight of water above it; see, e.g., Baker (1984). Earth body tides are well known and accurately modelled in GPS and altimetry software and hence do not require further correction. A very coarse approximation for the OTL displacement is that it is about 5% of the amplitude of, and 180o out of phase with, the ocean tide, i.e., the geodetic amplitude for each tidal constituent is about 95% of the ocean tide amplitude. However, the OTL displacement has larger length scales than the ocean tide, and so, especially close to the coast, it can vary significantly from this simplification. Using ocean tide models, Green's functions and an Earth model, OTL displacements may be computed directly, as outlined below.

In addition, gravimetric measurements measure gravity changes induced by the ocean tide plus the those induced by the Earth body tides and OTL. Again, Earth body gravity tides are well known. The gravimetric records described here were originally converted from units of gravity (gals) to units of length using free-air and Bouger corrections; see, for example, Williams and Robinson (1980) or delta_h(m) = -3.768delta_g(mgal). To be self-consistent, the OTL corrections outlined below follow the same approach, with modelled gravity OTL values obtained and then converted to length units. Once corrected for OTL, the major remaining error in the gravity record will relate to the calibration of the gravity meters, possibly inducing biases as large as 3-4% (pers. comm. T. Baker, 2005) of the total observed tide (prior to correction for Earth body tides and OTL).

In this database we provide both ocean tide and OTL coefficients. The GPS and gravity records have been corrected for OTL, the tiltmeter records have not. Based on previous studies of GPS from near-coastal grounded stations (King et al., 2005; and http://www.staff.ncl.ac.uk/m.a.king/GPS_OTL.htm), the TPXO6.1 ocean tide model is the best available model for Antarctic OTL calculations. Thus, we use TPXO6.1 to generate OTL tidal coefficients for all sites for which we have ocean tide data using the SPOTL software (Agnew, 1997). In some cases the OTL values are the same as those used to convert observed tide (e.g., for GPS) to ocean tide. For BPR and CTG data, which are obtained from direct analyses of sea surface elevation, the OTL model provides a mechanism for converting ocean tide to the elevations that should be measured by satellite altimeters.



Figure 1: Map of Antarctic tide gauges (TGs). Click on image to display an interactive map. The magenta dashed line shows the TOPEX/Poseidon (T/P) satellite radar altimeter mission maximum latitude. Focus regions can be accessed from index (left-hand panel) or via the main interactive map.

Downloadable Database

Site information, and tidal coefficients for both ocean tide and OTL displacements (OTL modeled by TPXO6.1) are provided in ASCII text and Matlab *.mat files in file atg_database.zip. Ocean tide coefficients for a few sites (Recent GPS records from the Ross and Ronne ice shelves, and the AnSlope BPR in the northwest Ross Sea) are not yet public data. Potential users of these data should contact Matt King (for GPS) or Laurie Padman (AnSlope) for more information.

We hope to expand this site in future, to also make available the original time series on which the tidal analyses are based.

Please let us know about other public tide height data we have omitted! Email Laurie Padman.

Database Download Instructions

Download zipped database file (includes README)

If you prefer, the database file can be downloaded from our FTP site, as follows:

  1. ftp ftp.esr.org
  2. login: anonymous
  3. password: email address
  4. cd pub/datasets/atg
  5. binary
  6. get atg_database.zip (~... MB)

References for Tide Height Data

General Antarctic Tide References