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How can I register?

Please, to register for AVISO+ products, fill the registration form available here.

Please give us some details about your motivation. Insert A-Z letters, numbers, '.', '-', '_' and spaces only!. Note especially that the character ',' (comma) is not allowed for the moment in the motivation field.

Category: Registration/data access

Once I have registered, how do I have information about the products?

Once you have filled the form, you have received emails for the connexion. Please note that the AVISO+ service desk will manually validate your registration (it can take 1-2 days) and then you will access the data (an email is sent for the validation).

With your account identifiers, connect on the MY AVISO+ personal page

You will find information on the 'Help & Contact' page. The products to which you are subscribed are listed in the 'products' page.

you will have access to the services available for each product

 

Category: Registration/data access

Can I reset my password?

You can reset your password on www.aviso.altimetry.fr/en/my-aviso-plus/reset-password.html

Note that your account login is your email address

An email will be sent with your new password

Category: Registration/data access

How could I log on with my ftp/sftp account?

Symptoms:

• I could not connect to ftp/sftp with my browser.
• I could not download the data from the authenticated ftp/sftp folders.
• I don't see any place to enter my username/password.

To access to data from authenticated ftp/sftp site, firstly you must have a personal account provided by the Aviso Users Services after you have properly filled the registration form available online.

There are two different accesses for the following services

• Aviso+ Cnes Data Center
• ftp / sftp / Thredds Data Service / Opendap / Gridded Data Extraction Tool

Once you have your access to the ftp / sftp/ Thredds Data Service / Opendap / Gridded Data Extraction Tool, you have to connect with your personal account information by proceeding as follows:

1/ On your dedicated My Aviso+ web page (see FAQ "Once I have registered, how do I have information about the products"

2/ With a web browser: The FTP/SFTP protocol may not be supported by your web browser anymore. The alternative is to use a FTP client such as WinSCP, FileZilla, MobaXterm.

3/ Otherwise, see below the other ways to log in:

• by using a FTP/SFTP client (FileZilla for example): enter 'ftp-access.aviso.altimetry.fr' in the hostname, then your login and password in the appropriate boxes. If you use the SFTP protocol, you need to enter the port 2221.
• By using Unix commands: write 'ftp ftp-access.aviso.altimetry.fr' (and then enter your login/password). You can also use the command line "wget --no-proxy" with the suitable options (--user=YOUR_LOGIN  --password=YOUR_PASSWORD).

Some parameters settings have maybe to be checked: passive mode, proxy settings...

Category: Registration/data access

Access to the ftp/sftp/Opendap/Thredds Data Server/Gridded Data Extraction tool

There are two different accesses for the following services

• Aviso+ Cnes Data Center
• ftp/sftp/Opendap/Thredds Data Server/Gridded Data Extraction Tool

Once you have registered on https://www.aviso.altimetry.fr/en/data/data-access/registration-form.html 

the login/password has been sent by email for the access to the ftp/sftp/Opendap/Thredds Data Server/Gridded Data Extraction Tool. After validation by the Service Desk, this account gives you the access (see FAQ "Once I have registered, how do I have the information about the products" in the FAQ for the complete access to the products).

Category: Registration/data access

Access to the Aviso+ Cnes Data Center

There are two different accesses for the following services

• Aviso+ Cnes Data Center
• ftp/Opendap/Thredds data server/ Gridded Data Extraction Tool

To get the access to the Aviso+ Cnes Data Center, 

log on https://aviso-data-center.cnes.fr/

and click on the button 'registration' on top right as indicated below

Category: Registration/data access

How can I request new products?

Once you are registered to a list of products you can ask for a new products:

Go on your dedicated MY AVISO+ web page

Go on your dedicated 'products' page

Go in the section 'Other products you may want to access':

And then select one or more products and click on 'Continue'. PLEASE, SELECT ALL THE PRODUCTS YOU NEED IN ONE STEP, AND NOT ONE BY ONE, OUR SYSTEM IS NOT YET ADAPTED TO SUCH REQUESTS.

You will have to sign the licence and submit.

The Service Desk will validate your request manually.

 

Category: Registration/data access

What are the conditions to get Aviso data?

Please refer to the Licence agreement for the conditions of use of Aviso+ products. 

When a product is requested, please, justify by a short text explaining how you plan to use the data. This helps Aviso in refining the available data to be better tuned to the users' needs.

For a first level of education, the best is to work with online maps (gif format), e.g. the one available through the Argonautica project, or with the Live Access Server.

Category: Registration/data access

I'd like data over a precise area (data extraction)

- for some gridded NetCDF data, an online extraction tool is available, please refer to your dedicated products page
- for the other dataset, users have to perform their own extraction from the global or regional datasets

Category: Registration/data access

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Mean Dynamic Topography, Mean Sea Surface, Mean Sea Level or mean profile?

There are several means used in altimetry processing or altimetry-based studies.
The altimeter measures the ‘Altimeter Range’ which is the distance between the center of mass of satellite to the surface of the Earth (see Figure below). This allows computing the ‘Sea Surface Height’ (SSH) which is the height of the sea surface above the reference ellipsoid. The ‘Satellite Altitude’ refers to the distance of the center of mass of the satellite above a reference point. The reference point will usually be either on the reference ellipsoid or the center of the Earth.
SSH = Satellite Altitude - Altimeter Range – Corrections

The ‘Corrections’ due to environmental conditions need to be applied in order to retrieve the correct ‘Sea Surface Height’. 

The Mean Sea Surface (MSS_N) is the temporal mean of the SSH over a period N. It is a mean surface above the ellipsoid of reference and it includes the Geoid.
MSS_N=<SSH>_N

The Sea Level Anomaly (SLA_N) is the anomaly of the signal around the time-mean component. It is deduced from the SSH and MSS_N :
SLA_N = SSH – MSS_N

The Mean Dynamic Topography (MDT_N) is the temporal mean of the SSH above the Geoid over a period N.
MDT_N = MSS_N – Geoid

The Absolute Dynamic Topography (ADT) is the instantaneous height above the Geoid. The geoid is a gravity equipotential surface that would correspond with the ocean surface if ocean was at rest (i.e. with no currents under only the gravity field). Then, when the ocean is also influenced by wind, differential heating and precipitation and other sources of energy, the ocean surface moves from the geoid. Thus, the departure from the geoid (MDT) provides information on the mean effect on SSH from ocean dynamics.
The ADT is the sum of the SLA_N and MDT_N:
ADT= SLA_N + MDT_N = SSH - MSS_N + MDT_N

The reference period N considered can be changed as described in Pujol et al. (2018). Currently it is 1993-2012.

The Mean profile is the mean of altimeter measurements along the satellite's tracks. It can be used as reference for computing SLA for the same satellite. It is an along-track data (not distributed)
The MSL (Mean Sea Level) is a trend (a number of mm/year), often given with respect to time as a curve.

Reference:
Pujol, M.-I., Schaeffer, P., Faugère, Y., Raynal, M., Dibarboure, G., & Picot, N. (2018). Gauging the improvement of recent mean sea surface models: A new approach for identifying and quantifying their errors. Journal of Geophysical Research: Oceans, 123. https://doi.org/10.1029/2017JC013503 .

Category: Data and processing questions

Wave L4 gridded products now disseminated by CMEMS

The Copernicus Marine Environment Monitoring Service CMEMS is now in charge of the processing and distribution of the gridded (L4) NRT wave products. Indeed in the frame of the Transition AVISO+ to CMEMS, AVISO+ focuses on the distribution of innovative products whereas CMEMS is dedicated to the operational products and services.
Since July 2019, gridded L4 wave NRT products (called WAVE_GLO_WAV_L4_SWH_NRT_OBSERVATIONS_014_003) have been added to the CMEMS catalogue. 
Therefore the CMEMS catalogue disseminates Near-Real-Time gridded L4 wave products as well as two along-track L3 wave products (altimetry and spectral). 

Compared to AVISO+, the CMEMS gridded L4 wave products on a 2°x2° grid are based on several up-to-date missions and benefit from an improved processing fully described in the CMEMS QUality Information Document: QUID. 
You will find the list of AVISO+ and CMEMS wave products in the document Migration AVISO+ to CMEMS and AVISO+ to C3S (section 8) and a brief overview of the differences between the two L4 NRT wave products in section 8. Note that for the moment on CMEMS, only the NRT products are distributed beginning on July 2019. It is planned to disseminate a Delayed-time product on CMEMS by the beginning of 2021.

Thus, the production of the AVISO+ gridded L4 NRT wave products will stop by December 2019. So the user is invited to register to CMEMS as soon as possible: the useful links to CMEMS are indicated in the  document Migration AVISO+ to CMEMS and AVISO+ to C3S.

Note that for the moment, the gridded L4 NRT wind products are still disseminated by AVISO+.

Category: Data and processing questions

Why latest Pistach data are from May 2017 ?

Following Jason2 satellite Safe Hold Mode in May 2017, Pistach data processing has been stopped. Last data are from May 17th with few passes between July 11th and 13th for cycle 500 when the satellite was on a new orbit. 

Pistach Coastal and Hydro products remain available from cycle 001 to cycle 327 pass 111.

Category: Data and processing questions

Where can I find tables showing the correspondance date / cycle and pass number?

On-line tools on this website make the correspondance between hour and calendar date and cycle and pass number.

Category: Data and processing questions

How to convert measurement time in local time ?

• For T/P, 86400xTim_Moy_1 + 10^-3xTim_Moy_2 + 10^-6xTim_Moy_3 = time (in seconds)
• For Jason-1&2, 86400xTime_day + 10^-3xTime_sec + 10^-6xTim_microsec = time (in seconds)

Time is given in UTC (Universal Time Coordinate, linked to Greenwich meridian), date in Julian day, which is the elapsed time between a reference epoch (January 1^st 1950, 0h0min0s for Cnes Julian days, January 1^st 1958, 0h0min0s for Nasa Julian days) and measurement date. To convert UTC time in local time, you have to convert it in date, hours, minutes, seconds, then in solar time and finally in your local time. We haven't got any conversion procedure.

Category: Data and processing questions

What is the impact of missing data in the Duacs products?

When one satellite is missing for a while, due to an incident example, the impact on the products is twofold:

• the along-track files are missing if the incident lasts for more than one day

• the impact on the generation of the map depends on the gap in the data: to generate these maps, computing methods based on objective analysis allow us to interpolate data in time and in space. In delayed time, the processing window used is centered, e.g. 6 weeks of data before and after the given date are taken into account. In near-real time, only the 6 weeks of data preeceding the given day are considered. The maps of formal errors (in the directory "err") will give an overview of the error induced by the missing data in the generation of the maps.

Category: Data and processing questions

We haven't receive T/P cycles 118/431/432, Jason-1 cycles 178 and 375 to 500

There were no data processed for Topex/Poseidon cycles 118, 431, 432 and for Jason-1 cycle 178, due to incidents.

The cycles 375 to 500 for Jason-1 are missing because the mission ended the repeat orbit phase (until 374) and began geodetic phase from cycle 500 (the cycles have been recomputed).

Category: Data and processing questions

What are Jason1&2&3, Topex/Poseidon data resolution?

Spatially, along the track, data are available every 7 km (measurements averaged on 1 second, or "1 Hz data"). GDR 10 or 20 Hz data also exists (depending on the satellite), but those are more noisy. Between tracks, for Jason-1&2&3 and Topex/Poseidon, the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.

Category: Data and processing questions

What are the characteristics of the reference ellipsoid you are using?

The Aviso products are referenced to the Topex/Poseidon ellipsoid (see the references below). So the Sea Surface Height of the MSS, CorSSH products are referenced to T/P ellipsoid, even for ERS-1, ERS-2, Envisat and Cryosat products. The SLA and MSLA products are not concerned since they are anomalies.

The reference ellipsoid is the first-order definition of the non-spherical shape of the Earth. For the GDRs, concerning Jason-1&2 GFO and Topex/Poseidon, the reference ellipsoid is:

• radius : 6378136.3
• inverse Earth flattening coefficient : 298.257

For ERS-1, ERS-2, Envisat, Cryosat-2:

• radius : 6378137
• inverse Earth flattening coefficient : 298.257223563

Category: Data and processing questions

On which platform/Operating system can I use Aviso data?

You can use Aviso data on every platform and Operating system, but the reading software may not be available for your precise configuration (see the available software).

Category: Data and processing questions

How get/exploit Aviso products available in NetCDF format (.nc)?

Firstly, to get Aviso data in NetCDF format, download the corresponding files via FTP client (for example FileZilla the Open Source FTP client filezilla-project.org). After downloading, in order to get the corresponding NetCDF files ('.nc'), extract the files with a 'gunzip' command if extension is '.gz' , use the 'tar -xzvf' commande for extensions '.tar.gz'

Aviso proposes two ways to directly work with Aviso NetCDF data :

1. Use Aviso data extraction tool: see <link en data data-access-services data-extraction-tool index.html>Data access services.
2. Use OPeNDAP tool: refer to <link en data data-access-services opendap index.html>OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Category: Data and processing questions

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ABC of Altimetry: SSH, SLA, ADT, MSS, MDT

The altimeter measures the ‘Altimeter Range’ which is the distance between the center of mass of satellite to the surface of the Earth (see Figure below). This allows computing the ‘Sea Surface Height’ (SSH) which is the height of the sea surface above the reference ellipsoid. The ‘Satellite Altitude’ refers to the distance of the center of mass of the satellite above a reference point. The reference point will usually be either on the reference ellipsoid or the center of the Earth.
SSH = Satellite Altitude - Altimeter Range – Corrections

The ‘Corrections’ due to environmental conditions need to be applied in order to retrieve the correct ‘Sea Surface Height’. 

The Mean Sea Surface (MSS_N) is the temporal mean of the SSH over a period N. It is a mean surface above the ellipsoid of reference and it includes the Geoid.
MSS_N=<SSH>_N

The Sea Level Anomaly (SLA_N) is the anomaly of the signal around the time-mean component. It is deduced from the SSH and MSS_N :
SLA_N = SSH – MSS_N

The Mean Dynamic Topography (MDT_N) is the temporal mean of the SSH above the Geoid over a period N.
MDT_N = MSS_N – Geoid

The Absolute Dynamic Topography (ADT) is the instantaneous height above the Geoid. The geoid is a gravity equipotential surface that would correspond with the ocean surface if ocean was at rest (i.e. with no currents under only the gravity field). Then, when the ocean is also influenced by wind, differential heating and precipitation and other sources of energy, the ocean surface moves from the geoid. Thus, the departure from the geoid (MDT) provides information on the mean effect on SSH from ocean dynamics.
The ADT is the sum of the SLA_N and MDT_N:
ADT= SLA_N + MDT_N = SSH - MSS_N + MDT_N

The reference period N considered can be changed as described in Pujol et al. (2018). Currently it is 1993-2012.

The Mean profile is the mean of altimeter measurements along the satellite's tracks. It can be used as reference for computing SLA for the same satellite. It is an along-track data (not distributed)
The MSL (Mean Sea Level) is a trend (a number of mm/year), often given with respect to time as a curve.

Reference:
Pujol, M.-I., Schaeffer, P., Faugère, Y., Raynal, M., Dibarboure, G., & Picot, N. (2018). Gauging the improvement of recent mean sea surface models: A new approach for identifying and quantifying their errors. Journal of Geophysical Research: Oceans, 123. https://doi.org/10.1029/2017JC013503 .

Category: Altimetry

Does sea state influence the measurement of the satellite-sea surface range?

Sea state influences the measurement of the satellite-sea surface range because the altimeter is sensitive to sea surface elements perpendicular to the target line. These elements are more frequently in the wave trough than in the crest, so the mean height of these elements doesn't match the geometric mean height of all sea surface elements that make the mean sea level (electromagnetic bias). In this way, the altimetric-measured mean is shifted toward wave trough, and moreover if waves are high.

 

Category: Altimetry

About the radiometer, how brightness temperature is defined, and why 3 frequencies are used?

The brigthness temperature of a surface is equal to the product of the emissivity of this surface by its physical temperature.
The radiation measured by the radiometer depends on the ocean surface emissivity, its physical temperature and water vapour and cloud absorption in the atmosphere. If you want to know precisely the atmospheric water vapour contents, you have to substract surface and cloud contribution from the signal received by the radiometer. That's why several frequencies (3 in most cases) are used, each one being more sensitive than the other to one of these contributions. By combining measurements done at each frequencies, you can extract the water vapor signal.

Category: Altimetry

What are the differences between ADT and SLA products?

Absolute Dynamic Topography (ADT) and Sea Level Anomaly (SLA) are defined by:
ADT=MDT+SLA
where MDT is Mean Dynamic Topography.

Category: Altimetry

What is the difference between SSH and ADT?

SSH is what the altimeter system measures, and the quantity from which everything else is deduced (with also some in situ data for the MDT).
SSH = (satellite altitude with respect to reference ellipsoid) - (satellite-to-surface distance)
(see altimetry pages)
Thus, in altimetry (it's not the case in all oceanography), SSH can be defined as the sea surface height with respect to the reference ellipsoid, which means that, compared to ADT, there's also the geoid height in it.
You can say that : SSH = SLA + MDT + geoid = ADT + geoid
with SLA computed from SSH and a mean sea surface over several years

Category: Altimetry

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Is it possible to estimate geostrophic currents from altimetry data?

Satellite altimetry allows to measure the Sea Surface Height (SSH) with a few centimeters precision. Appart from the equatorial band (ie, 5°N,5°S), the geostrophy can be assumed with a good certainty: it means that the slope of the sea surface measured by the altimeter along the satellite track is assumed to be DYNAMIC TOPOGRAPHY. In other word, it means that this slope is directly related to the pressure gradient at the sea surface, and thus, to a GEOSTROPHIC VELOCITY at the surface.

Category: Altimetry and Doris applications

I'd like to have some information about ocean bottom cartography.

You can have a look at our "Geophysics" section (in the "Applications"). Here are some websites with more information on this subject :

• Legos
• Noaa/Scripps Institute of Oceanography or Scripps Institute of Oceanography/Noaa

 

Category: Altimetry and Doris applications

I would like some information about El Niño.

On this subject, you can consult our web pages (including an extensive list of websites)

Category: Altimetry and Doris applications

I would like some information about tide time-tables.

We suggest you to consult these websites:
Tides and Altimetry
http://tbone.biol.sc.edu/tide/sitesel.html

Category: Altimetry and Doris applications

Where can I find information about sea waves (satellite imagery and also lectures)?

On this website
  - Wind and wave maps
  - Applications: Wind and waves: marine meteorology 

 

Category: Altimetry and Doris applications

I'm doing a report about currents (physical aspect, modelisation). Could you give me some adresses?

You can look at the Ocean application section

ocean circulation model :
- Southampton Oceanography Centre
- Ocean Surface Currents

Category: Altimetry and Doris applications

Can you give me anything about troposphere?

We do not study troposphere as such but only since troposphere crossing disrupt the radar wave of the altimeter
We rather suggest you to contact meteorological centers (ex. CNRM, UK met. office, ECMWF), atmospheric studies centers (ex. CETP), or dedicated satellite missions (Nasa's TES).

Category: Altimetry and Doris applications

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How the Doppler effect with Doris can give the distance between the satellite and the Earth?

Doris can give the position of a satellite because it compares a model of orbit (giving position and velocity) with its measurements:
Measurement data for permanent network beacons are processed to yield the satellite's precise trajectory. This processing includes modelling of forces acting on the satellite (terrestrial gravitation, etc.) in order to determine its precise trajectory.

Category: Doris system