Geoid determination from airborne gravity data using different filtering frequencies and DTM resolutions

Gravity disturbances obtained from an airborne system are low-pass filtered with a certain cut-off frequency to minimize the high frequency errors. To use the filtered disturbances in geoid determination, the gravity signal coming from the topography should also be filtered to the same frequency. The cut-off frequencies that are used here are: 1/30, 1/60, and 1/90 Hz. The first purpose of this study is to investigate whether all the filtering frequencies can be used for geoid determination. Although filtering is essential for consistent treatment of the data, our second objective is to study the effect of not filtering the topographic gravity signal in a way that it is consistent with the filtering of the gravity disturbances. The last goal will be to evaluate the DTM resolution needed for computing a precise geoid from airborne gravity. To study the above objectives, we worked with data obtained from a strapdown INS/GPS gravimeter in September 1996 over the Canadian Rocky Mountains. Different DTM resolutions were tested. Geoid solutions from the three filtering frequencies and the geoid solution without filtering of the topographic signal were Computed and intercompared. By comparing all solutions to an existing gravimetric geoid in the area, conclusions were drawn and recommendations were made on the appropriate use of filtering frequencies and DTM resolutions.