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A multi-sensor, multidisciplinary aerogeophysical survey over much of Afghanistan was recently conducted by investigators from NRL and the U.S. Geological Survey. The survey was flown aboard an NP-3D Orion aircraft operated by VXS-1. Sensor systems installed on the P-3 included dual gravimeters, scalar and vector magnetometers, a digital photogrammetric camera, a hyperspectral imager, and an L-band polarimetric synthetic aperture radar. Data from all sources was precisely co-registered to the ground by a combination of interferometric-mode Global Positioning System and inertial measurements. The data from this integrated mapping mission supports numerous efforts in Afghanistan: combat operations, economic exploration for oil, gas, and minerals, humanitarian missions, development of civil infrastructure, and agriculture resource management. This mission has also advanced the state of the art in integrated multi-sensor airborne remote sensing., Published in Naval Research Laboratory (NRL) Review, p107-115, 2007. Sponsored in part by the National Geospatial-intelligence Agency (NGA).

Shallow water (littoral) regions present unique challenges for Naval operations. Warfighter support in the littoral region is hampered by our inability to relate tide and ocean circulation models directly to nautical charts via an absolute vertical datum. Various water measurements of critical importance to the Navy (such as tide gauges, ocean bottom pressure/inverted echo sounders, satellite altimetry, and heights now easily measured by GPS) are made with respect to different vertical reference frames (tidal datums and ellipsoidal frames), and there is no mechanism for conversion from one frame to another. An accurate geoid can provide the vertical reference required to relate the various vertical reference frames. The geoid is the surface of equal gravitational potential that most closely approximates mean sea level (in a motionless ocean) located with respect to the ellipsoidal (GPS) reference frame. Historically, the gravity field had not been sufficiently determined to produce a geoid accurate enough to relate the reference frames. Since 2003, however, the Gravity Recovery and Climate Experiment (GRACE) satellite has revolutionized our ability to construct geoids by accurately resolving the long-wavelength component of the global gravity field to wavelengths as short as 350-400 km. NRL has been combining GRACE data with short-wavelength terrestrial, marine, and airborne gravity to create a geoid for the Gulf of Mexico accurate to 5 cm (as compared with tide gauge data located by GPS surveys). NRL's interest in accurate geoid determination dovetails closely with the mission of NOAA's National Geodetic Survey (NGS): to maintain and evolve a National Spatial Reference System based on the most accurate geoid possible for North America. NRL has recently partnered with NGS to conduct high-altitude airborne surveys at critical locations along the Gulf Coast., Published in NRL Review, p1-2, 2006.