The Environmental Research Division's Data Access Program aggregates scientific data from diverse local and remote sources and offers a simple, consistent way to download subsets of the data in common file formats and make graphs and maps. In particular ERDDAP enables easy access to oceanographic data from satellites and buoys.
The Problems that ERDDAP Tries To Solve
Without ERDDAP, when a person (or a computer program) looks on the Internet for a specific type of scientific data (for example, oceanographic data like satellite sea surface temperature data), there are problems ...
- The datasets of interest are hard to find because they are at many different web sites.
- Each site requires a different protocol to request the data (for example, HTTP GET, XML, SOAP+XML, DAP, WCS, WFS, SOS, or an HTML form).
- Each site returns the data in a different format (for example, XML, SOAP+XML, DAP binary data stream, ASCII text, HDF 4, HDF 5, NetCDF, ...) and it isn't the common file format that you want (for example, .html table, ESRI .asc, Google Earth .kml, .mat, .nc, .csv, .tsv, .json, .xhtml, WMS).
- Data from different sites is hard to compare because the dates+times are expressed in different formats (for example, "Jan 2, 1985", "02-JAN-1985", "1/2/85", "2/1/85", "1985-01-02", or days since has Jan 1, 1980, or ...).
- ERDDAP aggregates data from diverse local and remote sources.
- ERDDAP offers several ways to search for datasets of interest.
- ERDDAP lets you make requests in a standardized way, regardless of the data source's request protocol.
- Gridded data is available via the DAP hyperslab protocol and WMS.
- Tabular data is available via the DAP constraint protocol.
- ERDDAP also provides Data Access Forms (web pages) which help humans create the DAP requests. OPeNDAP's DAP is the recommended IOOS DMAC data transport mechanism and a NASA EOSDIS standard. (DAP is great!)
- ERDDAP lets you choose the file format for the results (for example, .html table, ESRI .asc, Google Earth .kml, .mat, .nc, .csv, .tsv, .json, .xhtml, .png).
- ERDDAP standardizes the dates+times in the results, either as:
- UDUNITS-compatible "seconds since 1970-01-01T00:00:00Z" numbers, or
- ISO 8601:2004 "extended" format strings (YYYY-MM-DDThh:mm:ssZ, for example, "1985-01-02T00:00:00Z").
- To avoid time zone and daylight savings confusion, time values are always converted to the UTC time zone.
- ERDDAP lets you request .png and .pdf image files with graphs and maps of the data, in addition to the raw data. Three special uses of these images are:
- Web page authors can embed a graph with the latest data in a web page using an HTML <img> tag.
- Anyone can use ERDDAP's Slide Sorter to build a personal web page that displays graphs with the latest data (or other images or HTML content), each in its own, draggable slide.
- Anyone can use or make Google Gadgets to display images with the latest data on their iGoogle home page.
- ERDDAP offers email/URL and RSS subscriptions, so you can be notified whenever a dataset changes.
- ERDDAP is a web application (for humans with browsers) and a web service (for computer programs). ERDDAP has REST- and ROA-style links to make ERDDAP's services available to computer programs, so that other web applications and web services can be built on top of ERDDAP.