Integrated Surface Database (ISD)
The Integrated Surface Database (ISD) consists of global hourly and synoptic observations compiled from numerous sources into a single common ASCII format and common data model. ISD was developed as a joint activity within Asheville's Federal Climate Complex. NCDC, with U.S. Air Force and Navy partners, began the effort in 1998 with the assistance of external funding from several sources. ISD integrates data from over 100 original data sources, including numerous data formats that were key-entered from paper forms during the 1950s–1970s time frame.
The database includes over 35,000 stations worldwide, with some having data as far back as 1901, though the data show a substantial increase in volume in the 1940s and again in the early 1970s. Currently, there are over 14,000 "active" stations updated daily in the database. The total uncompressed data volume is around 600 gigabytes; however, it continues to grow as more data are added. ISD includes numerous parameters such as wind speed and direction, wind gust, temperature, dew point, cloud data, sea level pressure, altimeter setting, station pressure, present weather, visibility, precipitation amounts for various time periods, snow depth, and various other elements as observed by each station.
ISD Version 1 was released in 2001, and Version 2 (additional quality control applied) in 2003. Since 2003, there have been continued incremental improvements in automated quality control (QC) software. The input sources used in ISD were previously processed through automated and some manual QC and then additional QC software was developed and applied to the entire ISD archive. This includes algorithms checking for proper data format for each field, extreme values and limits, consistency between parameters, and continuity between observations (e.g., for temperature). For more detailed information regarding the QC process, see The Quality Control of the Integrated Surface Hourly Database.
ISD is a global database, though the best spatial coverage is evident in North America, Europe, Australia, and parts of Asia. Coverage in the Northern Hemisphere is better than the Southern Hemisphere, and the overall period of record is currently 1901 to present. Some stations have over 50 years of continuous reporting during the latter half of that time period. However, many stations have "breaks" in the period of record (e.g., 40 years of data may be spread over a 70-year period).
Efforts are well underway to integrate additional data sources into ISD, which will provide for more U.S. data prior to 1950 and some data prior to 1900. Plans are also in place to gradually integrate datasets provided by various countries to increase data coverage and periods of record for some areas.