This data set was acquired with a ship-based Gravimeter and SeaBeam Classic Multibeam Sonar syste... more This data set was acquired with a ship-based Gravimeter and SeaBeam Classic Multibeam Sonar system during Robert D. Conrad expedition RC2601 conducted in 1985 (Chief Scientist: Dr. John Brozena). These data files are of MGD77 format and include Singlebeam Bathymetry and Gravity Field data that were processed after data collection. Funding was provided by NSF grant(s): N00014-84-C-2425.
: This report describes the results of a hardware design study for an airborne gravity measuremen... more : This report describes the results of a hardware design study for an airborne gravity measurement system. The system is intended for use aboard a fixed wing aircraft for measurements over oceanic areas including ice caps. Hardware for measurement of total vertical acceleration including gravity, aircraft vertical acceleration, and precise positioning is discussed; and example equipment types are specified. A data acquisition system capable of handling all measurements sources is also specified. Various aircraft operational requirements and parameters are considered.
These data are derived products from the 2015 field campaign of the "Sea State and Boundary ... more These data are derived products from the 2015 field campaign of the "Sea State and Boundary Layer Physics of the Emerging Arctic Ocean" program. The campaign occurred during autumn, when refreezing of the ocean surface was a dominant signal. These data include collections from the Research Vessel "Sikuliaq", as well as numerous autonomous buoys. The main results of the program are described in a special issue of the Journal of Geophysical Research - Oceans.Office of Naval Researc
The geoid is the gravity equipotential surface that approximates global mean sea-level (msl), and... more The geoid is the gravity equipotential surface that approximates global mean sea-level (msl), and if sufficiently accurate, can provide a reference surface useful for water level measurement systems in oceanography and hydrography. An accurate geoid can be used to connect the ellipsoid referenced positioning capabilities of GPS with sea-level referenced quantities. The US Naval Research Laboratory (NRL) and the Danish National Survey and Cadastre (KMS) have been developing capabilities in airborne gravity and altimetry that can simultaneously improve the geoid, provide precise water level profiles and transfer absolute vertical coordinates to tide-gages and bottom-moored inverted echo-sounder or pressure gage systems. Examples of high-precision geodesy and altimetry in the Gulf of Mexico demonstrate the general possibilities of the technique and its potential application to the Baltic. Recent airborne gravity surveys of the Baltic performed by KMS, when combined with regional historical terrestrial and marine gravity measurements and the new intermediate wavelength gravity data from the CHAMP and GRACE satellite gravity missions allow the production of a precise gravimetric geoid for the area. This msl reference can provide a unified vertical reference frame for water-level measurement systems and future advanced circulation models of water level and currents in the Baltic.
ABSTRACT The U.S. Naval Research Laboratory (NRL) has been collecting sea ice data in the Arctic,... more ABSTRACT The U.S. Naval Research Laboratory (NRL) has been collecting sea ice data in the Arctic, off the northern coast of Alaska, with an airborne system employing a radar altimeter, lidar, and a photogrammetric camera in an effort to obtain wide swaths of measurements coincident with CryoSat-2 track footprints. Because the satellite tracks traverse regions of moving pack ice, and the aircraft speed and measurement footprint are smaller than that of the satellite, it is necessary to know the local ice motion in order to plan and fly a full-coverage survey. With the advent of functional and real-time orthographic photogrammetric systems, we have developed a Real-Time Ice Motion Estimation (RTIME) system that permits the rapid determination of sea ice motion. RTIME enables tracking of specific patches of ice, allowing direct comparison of airborne data to satellite data on a point-by-point basis. This system should be of utility to other Arctic airborne science programs.
Abstract A new combined magnetic database and a magnetic-profile map are developed for the Eurasi... more Abstract A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes ...
Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenl... more Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin.
An airborne gravity study of the western Weddell Sea, east of the Antarctic Peninsula, has shown ... more An airborne gravity study of the western Weddell Sea, east of the Antarctic Peninsula, has shown that floating pack-ice provides a useful radar altimetric reference surface for altitude and vertical acceleration corrections to airborne gravimetry. Airborne gravimetry provides an important alternative to satellite altimetry for the sea-ice covered regions of the world since satellite altimeters are not designed or intended to provide accurate geoidal heights in areas where significant sea-ice is present within the radar footprint. Errors in radar corrected airborne gravimetry are primarily sensitive to the variations in the second derivative of the sea-ice reference surface in the frequency pass-band of interests. With the exception of imbedded icebergs the second derivative of the pack-ice surface closely approximates that of the mean sea-level surface at wavelengths>10-20 km. With the airborne method the percentage of ice coverage, the mixture of first and multi-year ice and the existence of leads and pressure ridges prove to be unimportant in determining gravity anomalies at scales of geophysical and geodetic interest, provided that the ice is floating and not grounded. In the Weddell study an analysis of 85 crosstrack miss-ties distributed over 25 data tracks yields an rms error of 2.2 mGals. Significant structural anomalies including the continental shelf and offsets and lineations interpreted as fracture zones recording the early spreading directions within the Weddell Sea are observed in the gravity map.
ABSTRACT The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean ... more ABSTRACT The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean sea level) aero-geophysical surveys over Afghanistan in 2006 (Rampant Lion I). The surveys were done in collaboration with the US Geological Survey and upon the request of Islamic Republic of Afghanistan Ministry of Mines. In this study, we show that a best fitting admittance between topography and airborne gravity in western Afghanistan can be used to predict airborne gravity for the no-data area of eastern Afghanistan where the mountains are too high to conduct airborne surveys, due to the threat of ground fire. The differences between the airborne and the predicted gravity along a tie-track through the no-data area were found to be within ±12 mGal range with rms difference 7.3 mGal, while those between the predicted gravity from a simple Airy model (with compensation depth of 32 km and crustal density of 2.67 g cm-3) and the airborne gravity were within ±22 mGal range with rms difference 10.3 mGal. A combined airborne free-air anomaly has been constructed by merging the predicted gravity with the airborne data. We also demonstrate that sediment thickness can be estimated for basin areas where surface topography and airborne free-air anomaly profiles do not show a correlation presumably because of thick sediments. In order to estimate sediment thickness, we first determine a simple linear relationship from a scatter plot of the airborne gravity points and the interpolated Shuttle Radar Topography Mission (SRTM) topography along the Rampant Lion I tracks, and computed corresponding quasi-topography tracks by multiplying the linear relationship with the airborne free-air anomalies. We then take the differences between the SRTM and quasi-topography as a first-order estimate of sediment thickness. A global gravity model (GOCO02S), upward continued to the same altitude (7 km above mean sea level) as the data collection, was compared with the low-pass filtered (with cutoff wavelength 132 km which is approximately equivalent to the reported safe degree and order 250 of GOCO02S at 34º N) combined airborne free-air anomalies. The rms difference between the two data sets was 12.4 mGal. The observed admittance in the western Afghanistan mountains appears to be best fit to a theoretical elastic plate compensation model (with an effective elastic thickness of 5 km and crustal thickness of 22 km) where the ratio between surface load and subsurface load is equal.
Between the Ascension and Bode Verde Fracture Zones, an ˜200 km length of the axis of the Mid-Atl... more Between the Ascension and Bode Verde Fracture Zones, an ˜200 km length of the axis of the Mid-Atlantic Ridge has a large positive residual depth anomaly and an axial high morphology that suggest a plume influence. New wide-angle seismic and gravity data from this area show that (1) the crustal thickness increases from 6 km at the propagating rift marking
Page 1. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic ri... more Page 1. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic rift system John С Behrendt US Geological Survey, MS 964, Federal Center, Denver, Colorado 80225 Donald D. Blankenship ...
This data set was acquired with a ship-based Gravimeter and SeaBeam Classic Multibeam Sonar syste... more This data set was acquired with a ship-based Gravimeter and SeaBeam Classic Multibeam Sonar system during Robert D. Conrad expedition RC2601 conducted in 1985 (Chief Scientist: Dr. John Brozena). These data files are of MGD77 format and include Singlebeam Bathymetry and Gravity Field data that were processed after data collection. Funding was provided by NSF grant(s): N00014-84-C-2425.
: This report describes the results of a hardware design study for an airborne gravity measuremen... more : This report describes the results of a hardware design study for an airborne gravity measurement system. The system is intended for use aboard a fixed wing aircraft for measurements over oceanic areas including ice caps. Hardware for measurement of total vertical acceleration including gravity, aircraft vertical acceleration, and precise positioning is discussed; and example equipment types are specified. A data acquisition system capable of handling all measurements sources is also specified. Various aircraft operational requirements and parameters are considered.
These data are derived products from the 2015 field campaign of the "Sea State and Boundary ... more These data are derived products from the 2015 field campaign of the "Sea State and Boundary Layer Physics of the Emerging Arctic Ocean" program. The campaign occurred during autumn, when refreezing of the ocean surface was a dominant signal. These data include collections from the Research Vessel "Sikuliaq", as well as numerous autonomous buoys. The main results of the program are described in a special issue of the Journal of Geophysical Research - Oceans.Office of Naval Researc
The geoid is the gravity equipotential surface that approximates global mean sea-level (msl), and... more The geoid is the gravity equipotential surface that approximates global mean sea-level (msl), and if sufficiently accurate, can provide a reference surface useful for water level measurement systems in oceanography and hydrography. An accurate geoid can be used to connect the ellipsoid referenced positioning capabilities of GPS with sea-level referenced quantities. The US Naval Research Laboratory (NRL) and the Danish National Survey and Cadastre (KMS) have been developing capabilities in airborne gravity and altimetry that can simultaneously improve the geoid, provide precise water level profiles and transfer absolute vertical coordinates to tide-gages and bottom-moored inverted echo-sounder or pressure gage systems. Examples of high-precision geodesy and altimetry in the Gulf of Mexico demonstrate the general possibilities of the technique and its potential application to the Baltic. Recent airborne gravity surveys of the Baltic performed by KMS, when combined with regional historical terrestrial and marine gravity measurements and the new intermediate wavelength gravity data from the CHAMP and GRACE satellite gravity missions allow the production of a precise gravimetric geoid for the area. This msl reference can provide a unified vertical reference frame for water-level measurement systems and future advanced circulation models of water level and currents in the Baltic.
ABSTRACT The U.S. Naval Research Laboratory (NRL) has been collecting sea ice data in the Arctic,... more ABSTRACT The U.S. Naval Research Laboratory (NRL) has been collecting sea ice data in the Arctic, off the northern coast of Alaska, with an airborne system employing a radar altimeter, lidar, and a photogrammetric camera in an effort to obtain wide swaths of measurements coincident with CryoSat-2 track footprints. Because the satellite tracks traverse regions of moving pack ice, and the aircraft speed and measurement footprint are smaller than that of the satellite, it is necessary to know the local ice motion in order to plan and fly a full-coverage survey. With the advent of functional and real-time orthographic photogrammetric systems, we have developed a Real-Time Ice Motion Estimation (RTIME) system that permits the rapid determination of sea ice motion. RTIME enables tracking of specific patches of ice, allowing direct comparison of airborne data to satellite data on a point-by-point basis. This system should be of utility to other Arctic airborne science programs.
Abstract A new combined magnetic database and a magnetic-profile map are developed for the Eurasi... more Abstract A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes ...
Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenl... more Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin.
An airborne gravity study of the western Weddell Sea, east of the Antarctic Peninsula, has shown ... more An airborne gravity study of the western Weddell Sea, east of the Antarctic Peninsula, has shown that floating pack-ice provides a useful radar altimetric reference surface for altitude and vertical acceleration corrections to airborne gravimetry. Airborne gravimetry provides an important alternative to satellite altimetry for the sea-ice covered regions of the world since satellite altimeters are not designed or intended to provide accurate geoidal heights in areas where significant sea-ice is present within the radar footprint. Errors in radar corrected airborne gravimetry are primarily sensitive to the variations in the second derivative of the sea-ice reference surface in the frequency pass-band of interests. With the exception of imbedded icebergs the second derivative of the pack-ice surface closely approximates that of the mean sea-level surface at wavelengths>10-20 km. With the airborne method the percentage of ice coverage, the mixture of first and multi-year ice and the existence of leads and pressure ridges prove to be unimportant in determining gravity anomalies at scales of geophysical and geodetic interest, provided that the ice is floating and not grounded. In the Weddell study an analysis of 85 crosstrack miss-ties distributed over 25 data tracks yields an rms error of 2.2 mGals. Significant structural anomalies including the continental shelf and offsets and lineations interpreted as fracture zones recording the early spreading directions within the Weddell Sea are observed in the gravity map.
ABSTRACT The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean ... more ABSTRACT The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean sea level) aero-geophysical surveys over Afghanistan in 2006 (Rampant Lion I). The surveys were done in collaboration with the US Geological Survey and upon the request of Islamic Republic of Afghanistan Ministry of Mines. In this study, we show that a best fitting admittance between topography and airborne gravity in western Afghanistan can be used to predict airborne gravity for the no-data area of eastern Afghanistan where the mountains are too high to conduct airborne surveys, due to the threat of ground fire. The differences between the airborne and the predicted gravity along a tie-track through the no-data area were found to be within ±12 mGal range with rms difference 7.3 mGal, while those between the predicted gravity from a simple Airy model (with compensation depth of 32 km and crustal density of 2.67 g cm-3) and the airborne gravity were within ±22 mGal range with rms difference 10.3 mGal. A combined airborne free-air anomaly has been constructed by merging the predicted gravity with the airborne data. We also demonstrate that sediment thickness can be estimated for basin areas where surface topography and airborne free-air anomaly profiles do not show a correlation presumably because of thick sediments. In order to estimate sediment thickness, we first determine a simple linear relationship from a scatter plot of the airborne gravity points and the interpolated Shuttle Radar Topography Mission (SRTM) topography along the Rampant Lion I tracks, and computed corresponding quasi-topography tracks by multiplying the linear relationship with the airborne free-air anomalies. We then take the differences between the SRTM and quasi-topography as a first-order estimate of sediment thickness. A global gravity model (GOCO02S), upward continued to the same altitude (7 km above mean sea level) as the data collection, was compared with the low-pass filtered (with cutoff wavelength 132 km which is approximately equivalent to the reported safe degree and order 250 of GOCO02S at 34º N) combined airborne free-air anomalies. The rms difference between the two data sets was 12.4 mGal. The observed admittance in the western Afghanistan mountains appears to be best fit to a theoretical elastic plate compensation model (with an effective elastic thickness of 5 km and crustal thickness of 22 km) where the ratio between surface load and subsurface load is equal.
Between the Ascension and Bode Verde Fracture Zones, an ˜200 km length of the axis of the Mid-Atl... more Between the Ascension and Bode Verde Fracture Zones, an ˜200 km length of the axis of the Mid-Atlantic Ridge has a large positive residual depth anomaly and an axial high morphology that suggest a plume influence. New wide-angle seismic and gravity data from this area show that (1) the crustal thickness increases from 6 km at the propagating rift marking
Page 1. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic ri... more Page 1. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic rift system John С Behrendt US Geological Survey, MS 964, Federal Center, Denver, Colorado 80225 Donald D. Blankenship ...
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