The voids occur in areas where the initial processing did not meet quality specifications. SRTM Void Filled (Digital Object Identifier (DOI) number: /10.5066/F7F76B1X ) elevation data are the result of additional processing to address areas of missing data or voids in the SRTM Non-Void Filled collection. Data for regions outside the United States were sampled at 3 arc-seconds (approximately 90 meters) using a cubic convolution resampling technique for open distribution. This version was then edited or finished by the NGA to delineate and flatten water bodies, better define coastlines, remove spikes and wells, and fill small voids. SRTM Non-Void Filled (Digital Object Identifier (DOI) number: /10.5066/F7K072R7) elevation data were processed from raw C-band radar signals spaced at intervals of 1 arc-second (approximately 30 meters) at NASA’s Jet Propulsion Laboratory (JPL). The level of processing and the resolution of the data will vary by SRTM data set. SRTM successfully collected radar data over 80% of the Earth's land surface between 60° north and 56° south latitude with data points posted every 1 arc-second (approximately 30 meters). Differences between the two signals allowed for the calculation of surface elevation.Įndeavour orbited Earth 16 times each day during the 11-day mission, completing 176 orbits. An antenna located on board the space shuttle collected one data set and the other data set was collected by an antenna located at the end of a 60-meter mast that extended from the shuttle. This mission used single-pass interferometry, which acquired two signals at the same time by using two different radar antennas. The technology was modified for the SRTM mission to collect interferometric radar, which compared two radar images or signals taken at slightly different angles.

The C-band Spaceborne Imaging Radar and the X-Band Synthetic Aperture Radar (X-SAR) hardware were used on board the space shuttle in April and October 1994 to gather data about Earth's environment. The radars used during the SRTM mission were actually developed and flown on two Endeavour missions in 1994. The National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA) participated in an international project to acquire radar data which were used to create the first near-global set of land elevations. The Shuttle Radar Topography Mission (SRTM) was flown aboard the space shuttle Endeavour February 11-22, 2000. Shuttle Radar Topography Mission (SRTM) 1 Arc Second over Tennessee-Virginia border(Public domain)

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