Rescuing Seasat-A from 1980

Seasat-A was NASA’s first ocean observing satellite mission. It launched in June 1978 and operated continuously until it suffered a power failure 106 days later. It contained an altimeter (ALT), scatterometer (SASS), SAR, microwave radiometer (SMMR), and a visible/infrared radiometer (VIRR). These instruments allowed Seasat to measure sea surface height, ocean winds and both brightness and sea surface temperatures. The data, except for the SAR, are archived at PO.DAAC. Since these are the only oceanographic satellite data available for this early period of remote sensing, their importance has grown for use in climate studies. Even though the datasets were digitized from the original tapes, the Seasat data have since still been maintained in the same flat binary format technology of 1980 when the data were first distributed.

In 2013 PO.DAAC began a project to reformat the original data into a user friendly, modern and maintainable format consistent with the netCDF data model and Climate Forecast (CF) and Attribute Conventions Dataset Discovery (ACDD) metadata standards. A significant benefit of using this data format includes the improved interoperability with tools and web services such as OPeNDAP, THREDDS, and various subsetting software, such as PO.DAAC’s HiTIDE. Additionally, application of such metadata standards provides an opportunity to correctly document the data at the granule level.

The first step in the conversion process involved going through the original documentation to understand the source binary data format. Documentation was found for processing levels 1 and 2 for ALT, SASS and SMMR. Software readers were then written for each of the datasets using Matlab , followed by regression tests performed on the newly outputted data in order to demonstrate that the readers were correctly interpreting the source data. Next, writers were created to convert the data into the updated format. The reformatted data were also regression tested and science validated to ensure that the data were not corrupted during the reformatting process. The resulting modernized Seasat datasets will be made available iteratively by instrument and processing level on PO.DAAC’s web portal http://podaac.jpl.nasa.gov, anonymous ftp site, ftp://podaac.jpl.nasa.gov/allData/seasat and other web services.