Mobile version

Frequently asked questions

Registration/data access

/

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 MSS (Mean Sea Surface) is a mean of several years of altimetry data, eventually using several satellites. It is a reference surface (thus you have values on a lon/lat grid).
The MDT (Mean Dynamic Topography) is the previous surface minus the geoid. It is the ocean topography due to the mean currents. It is also a reference surface.
The Mean profile is the mean of an 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.


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-Timegridded 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 2019So 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+.

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.

Could you send me an explanation of the times associated with your gridded data?

The gridded data are computed for a given day. Each map represents the situation on the day indicated in its name. It is not a mean over a period, definitely not a "weekly mean" (as often written, erroneously deduced from the fact that at some point the data were computed only for every 7 days).
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 preceding the given day are considered.

In the gridded data, to which point lat/lon refer to?

Each value has been computed exactly on the Lat/Lon values
defined by LatLonMin and LatLonStep , as specified in the metadata of the NetCDF file.

Explanation is given is section 4.3 of the handbook "Ssalto/Duacs User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time products" that you can find here

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.

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 1st 1950, 0h0min0s for Cnes Julian days, January 1st 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.

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.
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).

What are Jason1&2, 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 and Topex / Poseidon , the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.
Gridded Aviso data are available at 1/3° on a Mercator grid.

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
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).
Note that T/P GDR -Ms are coded in little endian format and Jason -1 GDRs in big endian format.

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 Data access services.
  2. Use OPeNDAP tool: refer to OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Data and processing questions

/

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 MSS (Mean Sea Surface) is a mean of several years of altimetry data, eventually using several satellites. It is a reference surface (thus you have values on a lon/lat grid).
The MDT (Mean Dynamic Topography) is the previous surface minus the geoid. It is the ocean topography due to the mean currents. It is also a reference surface.
The Mean profile is the mean of an 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.


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-Timegridded 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 2019So 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+.

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.

Could you send me an explanation of the times associated with your gridded data?

The gridded data are computed for a given day. Each map represents the situation on the day indicated in its name. It is not a mean over a period, definitely not a "weekly mean" (as often written, erroneously deduced from the fact that at some point the data were computed only for every 7 days).
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 preceding the given day are considered.

In the gridded data, to which point lat/lon refer to?

Each value has been computed exactly on the Lat/Lon values
defined by LatLonMin and LatLonStep , as specified in the metadata of the NetCDF file.

Explanation is given is section 4.3 of the handbook "Ssalto/Duacs User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time products" that you can find here

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.

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 1st 1950, 0h0min0s for Cnes Julian days, January 1st 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.

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.
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).

What are Jason1&2, 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 and Topex / Poseidon , the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.
Gridded Aviso data are available at 1/3° on a Mercator grid.

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
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).
Note that T/P GDR -Ms are coded in little endian format and Jason -1 GDRs in big endian format.

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 Data access services.
  2. Use OPeNDAP tool: refer to OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Altimetry questions

/

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 MSS (Mean Sea Surface) is a mean of several years of altimetry data, eventually using several satellites. It is a reference surface (thus you have values on a lon/lat grid).
The MDT (Mean Dynamic Topography) is the previous surface minus the geoid. It is the ocean topography due to the mean currents. It is also a reference surface.
The Mean profile is the mean of an 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.


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-Timegridded 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 2019So 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+.

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.

Could you send me an explanation of the times associated with your gridded data?

The gridded data are computed for a given day. Each map represents the situation on the day indicated in its name. It is not a mean over a period, definitely not a "weekly mean" (as often written, erroneously deduced from the fact that at some point the data were computed only for every 7 days).
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 preceding the given day are considered.

In the gridded data, to which point lat/lon refer to?

Each value has been computed exactly on the Lat/Lon values
defined by LatLonMin and LatLonStep , as specified in the metadata of the NetCDF file.

Explanation is given is section 4.3 of the handbook "Ssalto/Duacs User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time products" that you can find here

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.

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 1st 1950, 0h0min0s for Cnes Julian days, January 1st 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.

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.
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).

What are Jason1&2, 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 and Topex / Poseidon , the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.
Gridded Aviso data are available at 1/3° on a Mercator grid.

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
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).
Note that T/P GDR -Ms are coded in little endian format and Jason -1 GDRs in big endian format.

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 Data access services.
  2. Use OPeNDAP tool: refer to OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Applications questions

/

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 MSS (Mean Sea Surface) is a mean of several years of altimetry data, eventually using several satellites. It is a reference surface (thus you have values on a lon/lat grid).
The MDT (Mean Dynamic Topography) is the previous surface minus the geoid. It is the ocean topography due to the mean currents. It is also a reference surface.
The Mean profile is the mean of an 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.


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-Timegridded 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 2019So 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+.

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.

Could you send me an explanation of the times associated with your gridded data?

The gridded data are computed for a given day. Each map represents the situation on the day indicated in its name. It is not a mean over a period, definitely not a "weekly mean" (as often written, erroneously deduced from the fact that at some point the data were computed only for every 7 days).
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 preceding the given day are considered.

In the gridded data, to which point lat/lon refer to?

Each value has been computed exactly on the Lat/Lon values
defined by LatLonMin and LatLonStep , as specified in the metadata of the NetCDF file.

Explanation is given is section 4.3 of the handbook "Ssalto/Duacs User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time products" that you can find here

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.

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 1st 1950, 0h0min0s for Cnes Julian days, January 1st 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.

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.
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).

What are Jason1&2, 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 and Topex / Poseidon , the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.
Gridded Aviso data are available at 1/3° on a Mercator grid.

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
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).
Note that T/P GDR -Ms are coded in little endian format and Jason -1 GDRs in big endian format.

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 Data access services.
  2. Use OPeNDAP tool: refer to OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Doris questions

/

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 MSS (Mean Sea Surface) is a mean of several years of altimetry data, eventually using several satellites. It is a reference surface (thus you have values on a lon/lat grid).
The MDT (Mean Dynamic Topography) is the previous surface minus the geoid. It is the ocean topography due to the mean currents. It is also a reference surface.
The Mean profile is the mean of an 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.


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-Timegridded 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 2019So 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+.

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.

Could you send me an explanation of the times associated with your gridded data?

The gridded data are computed for a given day. Each map represents the situation on the day indicated in its name. It is not a mean over a period, definitely not a "weekly mean" (as often written, erroneously deduced from the fact that at some point the data were computed only for every 7 days).
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 preceding the given day are considered.

In the gridded data, to which point lat/lon refer to?

Each value has been computed exactly on the Lat/Lon values
defined by LatLonMin and LatLonStep , as specified in the metadata of the NetCDF file.

Explanation is given is section 4.3 of the handbook "Ssalto/Duacs User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time products" that you can find here

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.

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 1st 1950, 0h0min0s for Cnes Julian days, January 1st 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.

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.
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).

What are Jason1&2, 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 and Topex / Poseidon , the distance is up to 315 km at the Equator; for ERS and Envisat, it is about 80 km.
Gridded Aviso data are available at 1/3° on a Mercator grid.

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
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).
Note that T/P GDR -Ms are coded in little endian format and Jason -1 GDRs in big endian format.

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 Data access services.
  2. Use OPeNDAP tool: refer to OPeNDAP details, in particular go to the OPeNDAP website or OPeNDAP support.

Figures marked " Aviso ", are copyright Cnes/CLS, but please feel free to use them, conditional on the figures not being altered, and their source being acknowledged, and with a link to this site where possible.
All other figures are copyrighted. Please do not copy without the owner's permission.

EnglishFrançaisEspañol
Rss feedsContactSitemapPartners FAQGlossaryLexiconMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso + features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

The new home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!