Using High–Low Flight Gravity Data to Improve Geoid Model Precision: A Case Study in U.S. Virgin Islands (July 2021)

The Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project collected airborne gravity data over Puerto Rico (PR) and the U.S. Virgin Islands (VI). There was one large N-S/E-W survey at about 11-km altitude running from N17 to N21 latitude and E291 to E297 longitude. Considering the very limited surface gravity coverage on VI, only about 500 points, additional flights were conducted at lower altitudes (1.5–1.8 km). By adding these additional low altitude aerial gravity data, the geoid model precision is improved from 6.55 cm with no airborne data to 2.55 cm with both the high and low altitude data. Using only the high altitude flights achieves only 4.99-cm geoid model precision. The ~500 surface gravity data points in the target area do not improve the model precision significantly, which justifies the rationale of carrying out these lower altitude flights. Noticing the nearly three times geoid model precision improvements from the low flight data, we suggest to fly in low altitudes in future airborne gravimetric survey for geoid modeling in the areas that have limited surface gravity coverage and/or small topographic features like islands that are not well-sampled in high-altitude, wider-spaced data.