Field Estimates of Gravity Terrain Corrections and Y2K-Compatible Method to Convert from Gravity Readings with Multiple Base Stations to Tide- and Long-Term Drift-Corrected Observations.

摘要

FORTRAN computer programs to convert gravity readings to absolute values of observed gravity with minimum data entry and ample prompting are documented and released with this report. Inasmuch as gravity meter drift is linked for up to one calendar year of field data, the first line of the data input file only has the gravity meter name, the Y2K-compatible 4-digit year, the correction to Greenwich Mean Time (Coordinated Universal Time), and a code for the distance to which field terrain corrections are estimated. Only the 2-digit month and day are entered before each day of data. Each line of data has a 5-digit station name, local time, gravity meter reading, elevation, elevation units, an optional accuracy code, the estimated terrain correction, and an optional map code. Geographic locations and base station values are searched for and extracted from other files. Calibration tables in digital format are interactively created only for the needed span of gravity readings. Decisions for successively assigning absolute gravity values for gravity stations with more than one observation are based on printed summaries of least-square values computed in previous iterations and are confirmed by subsequent gravity meter drift plots. Field estimates of gravity terrain corrections utilize lists and graphs or entry of distances, heights, and angular slopes into a program based on models for thin vertical slabs.