Airborne Gravity: NGS' Gravity Data for AS01 (2008)

Airborne gravity data for Alaska collected in 2008 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D) project initiated by NOAA's National Geodetic Survey to collect and monitor gravity data suitable for the re-definition of the vertical datum for at least the United States and territories. The data is available at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml in ASCII text format.

These data sets were collected and processed by NOAA's National Geodetic Survey (www.ngs.noaa.gov) as part of its GRAV-D effort to modernize the U.S. vertical datum. The purpose of these data is to provide accurate gravity data for geoid modeling for the U.S. and its territories. It was designed to provide medium wavelength gravity information (around 20-400 km) to connect satellite and ground gravity measurements.

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The ASCII text file provides a single processed observation per row with the following elements comma separated: year, month, day, hour, minutes, seconds, latitude (dd), longitude (dd), ellipsoid height (m), full field gravity at altitude (mGals), full field EGM08 gravity at altitude (mGal)

http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml

While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by any errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.

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Must read and fully comprehend the metadata prior to use, acknowledgment of the Originator when using the data set as a source, data should not be used beyond the limits of the source scale

The absolute accuracy of airborne gravity is difficult to quantify. The following measures are indicators of data quality, but are not definitive measures. The cross over precision is 0.60 mGals, which is a combination of differences between cross track and data track and may not be indicative of data quality. Adjacent data lines have an average cross-correlation of 98.55%. Low correlation between adjacent lines may indicate either poor quality on one of the two lines or rapidly changing features. More detailed information can be found at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml.

GPS horizontal positions are good to 0.053 meters average standard deviation. More detailed information can be found at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml.

GPS vertical positions are good to 0.043 meters average standard deviation. More detailed information can be found at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml.

Due to the altitude, speed of data collection, and track spacing of 10 kilometers the resolution of these data are limited to 20 kilometers. More detailed information can be found at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml.

Data processing is fully automated and output file is computer generated. All lines are checked by an analyst and any errors in production are corrected. More detailed information can be found at http://www.ngs.noaa.gov/GRAV-D/data_as01.shtml.