Product History

April 30th 2015 — 

• The surface water level variation products have recently been upgraded (TPJO.3). They have been re-calculated based on updated altimetric parameters and a revised reference datum. End users are advised not to mix the TPJO.2/TPJO.3 product versions. Please discard the older products.
• The upgraded products now include two correction factors in the ascii text file header which enable end users to translate the satellite-based time series to i) an orthometric frame (approximating mean sea level) and ii) a WGS84 frame. At the lake product level there is also the option (left-hand panel) to view the new reference datum for each lake, and view the corresponding geoid profile. Details can be found in the Q&A link.
• Additional lake products at the 10-day resolution level and created with the NASA/CNES Jason-2/OSTM mission data sets are also now available.

• Please note that the water level product for Lake Mosul in Iraq (1534.Mosul) has recently been revised and now includes height information for additional dates. Users are advised to only use the variations displayed in this new product.

• The ENVISAT mission ended on May 9, 2012 and the ISRO/SARAL mission is now recording lake level variations in the same 35-day repeat cycle. The archive ENVISAT lake level products can now be found under the 'One Click Options" above. New operational SARAL products are expected to go on-line by early 2015.

• The lake level products derived from the NACA/CNES series of instruments (10-day temporal repeat) have been updated. The new JPJO.2 products are now available. Also note that the reference datum for each lake has now changed. It is no longer based on a 9-year mean level, but is based on full resolution (20Hz) data from a single fly-over date. In some cases the portion of the satellite track used over the lake has also changed to accommodate drought conditions. End-users should not mix the old TPJO.1 with the new TPJO.2.

• To aid users with converting the altimeter-derived relative time series of height variations into a series based on a mean sea level datum, additional products have now been made available. These new products are associated with the ENVISAT products and are in graph and text format. They show the geoid variation and lake reference datum across the lake. The lake reference datum is an elevation profile for a given date or satellite overpass cycle. The geoid profile has been constructed via interpolation of EGM2008. Details on how to use these reference datum and geoid profiles can be found in the FAQ section.

• 73 new ENVISAT lakes have been added and a total of 148 lakes are currently being monitored by ENVISAT.

• Users please note that a water-level product for the Kajakai reservoir is now available within the NASA/CNES series of satellite data. This product is Jason-2/OSTM only (i..e, post 2008) with a datum based on an individual (i.e., single-date) overpass within the OSTM timeframe. Based on a single overpass date (rather than 9year Topex mean datum) it therefore represents the start of the new TPJO.2 products which will emerge shortly and which will replace all existing TPJO.1 products.

• 18 new ENVISAT lakes have been added and a total of 75 lakes are currently being monitored by ENVISAT.

• 51 new ENVISAT lakes have been added and a total of 57 lakes are currently being monitored by ENVISAT.

• New ENVISAT products from the ESA satellite mission are in the process of being installed with 6 new lakes currently being monitored by ENVISAT.

• Users can now download all products at 1-click. See the option at the top left-hand side of this page. The 3 files are tar format and contain the text (raw and smoothed) and graphical products for all lakes currently in the database.

• An error in the surface elevation product for Lake Powell, USA has been identified and corrected this month. Users please note the new available time series is available for download.

• TIME SERIES: The time series provided for each lake is not based on a fixed (lat/long) location but is derived from height information along a specific stretch of lake water. The location and extent of this stretch are in the ascii text files. As several lakes, reservoirs, and inland seas (e.g. Aral Sea, Guri reservoir) are experiencing drought or low-level conditions, the original lake stretch may now be including multiple pools of water each surface varying differently with time. This may lead to an erroneous overall mean measurement. In the future we may change the location of the stretch of water to minimize these problems but will announce such changes in the bulletins.
• PRODUCT UPDATES: The lake products were modified in October 2009. Users should not mix the pre Oct 2009 product with the Nov 2009-2010 products as there are differences in reference datum and height corrections. Users should take the completely revised 1992-2010 product.
• WEEKLY UPDATES: The time resolution of the NASA/OSTM products is 10-days but products are updated on a weekly basis if the satellite data is available to us. The last height value in the product text file may thus be set to 999.99 indicating that the available data was not yet available. Users should therefore check the height entries the following week to note the replacement of the 999.999 value with a valid measurement.
• MISSING DATA: Note that the date/time/height parameters for Topex/Poseidon cycle118 and Jason-1 IGDR/cycle001 are all set to 999.999 default values. There was no lake data from these instruments during these periods.
• SMOOTHED PRODUCTS: The format of the filtered/smoothed product text file has been altered. The date/time parameters are now set to the same format as the raw-data text file. Note that the filtered file 999.999 height entries reflect the original 999.999 values in the raw files i.e. the smoothing was not allowed to interpolate over original data gaps to avoid interpolation across too large a time period. The smoothed product file contains data that are sorted in mission order, not time order. The order of satellite mission is Topex, then Jason-1, then OSTM. There are 6month time periods when Topex/Jason and Jason/OSTM were flying in tandem, being only ~1minute apart on the same orbit. The data recorded by both instruments during these tandem periods will therefore overlap in time.
• HEIGHT CORRECTIONS: The height of the lake is determined by applying a correction that takes into consideration the water vapor in the atmosphere. In cases where there is no such instrument-based or model-derived correction value, the water vapor correction field parameter (typically set to FMO=model or TMR=instrument) is now set to "N/A".
• RADAR BACKSCATTER COEFFICIENT: The estimation of the radar backscatter coefficient (sigma0) value in the product text files, which can depict periods of calm or frozen water, has been revised. Typical values are in the range 10-50dB. Any 999.999 or 99.99 are default values and should be rejected.

• http://sealevel.jpl.nasa.gov/mission/ostm.html
• http://smsc.cnes.fr/JASON2/index.htm
• http://www.osd.noaa.gov/ostm/
• http://www.eumetsat.int/HOME/Main/What_We_Do/Satellites/Jason/index.htm