TOPOGRAPHIC AND TERRAIN CORRECTION FOR AIRBORNE GRAVITY

Geophysics ◽  
1974 ◽  
Vol 39 (4) ◽  
pp. 537-542 ◽  
Author(s):  
Sigmund Hammer
Keyword(s):  
Real Time ◽  
Simple Procedure ◽  
Airborne Gravity ◽  
Airborne Gravimetry ◽  
Terrain Effects ◽  
Order Of Magnitude ◽  
Time Correction ◽  
Simple Product ◽  
Irregular Topography ◽  
Product Series

A simple, convenient procedure is outlined for evaluating topographic and terrain effects in airborne gravimetry. The method assumes that continuous terrain data (flight elevation and terrain clearance) are available along a traverse. The terrain is taken to be uniform to infinity in both directions perpendicular to the flight line. The correction is easily calculated from a simple product series. The error tolerances are not serious. Nonperpendicular, irregular topography cannot be evaluated by this simple procedure, but order of magnitude considerations demonstrate that this problem ordinarily is not prohibitively important. In flight, real‐time correction for topographic and terrain effects is not a major obstacle in the development of airborne gravity exploration.

TOPOGRAHIC CORRECTIONS FOR GRADIENTS IN AIRBORNE GRAVIMETRY

Geophysics ◽  
1976 ◽  
Vol 41 (6) ◽  
pp. 1346-1352 ◽  
Author(s):  
Sigmund Hammer
Keyword(s):  
Real Time ◽  
Practical Method ◽  
Airborne Gravity ◽  
Airborne Gravimetry

Progress in airborne gradiometer instrumentation has advanced to the point that procedures for determining corrections for the variable effects of topography merit consideration. An approximate practical method, based on real‐time recording of flight elevation and variable terrain clearance as a function of position along the flight line, appears to be appropriate for the purpose. The procedure is similar to that for determing topographic corrections for airborne gravity published previously by the author in Geophysics (Hammer, 1974a).

VERTICAL ATTENUATION OF ANOMALIES IN AIRBORNE GRAVIMETRY

Geophysics ◽  
1971 ◽  
Vol 36 (5) ◽  
pp. 867-877 ◽  
Author(s):  
Sigmund Hammer
Keyword(s):  
Three Dimensional ◽  
Signal Strength ◽  
Airborne Gravity ◽  
Airborne Gravimetry ◽  
Anomaly Field ◽  
Different Types ◽  
Order Of Magnitude ◽  
The Difference ◽  
Minimum Points ◽  
Derivative Order

Analysis of components of the gravity anomaly field from basic one, two, and three‐dimensional masses demonstrates that all components of the same derivative order attenuate with flight elevation at the same rate for a given type of anomaly. Different types of anomalies attenuate with significantly different rates. The signal strength of an anomaly component is conveniently defined as the difference between values at adjacent maximum and minimum points along a profile. For a given type of anomaly, the signal strengths of all comparable components are roughly equal, within about half an order of magnitude. Relative attenuations of anticipated signal and terrain noise permit evaluation of favorable and unfavorable prospect areas for airborne gravity exploration. A corollary result is that the tolerance in flight elevation control is orders of magnitude less severe for gradiometer surveying than for airborne gravity surveying. The conclusions are relevant in the choice of the most advantageous component for possible development of airborne gravimetry.

High speed interferometric device for real-time correction of aero-optic effects

1995 ◽  
Author(s):  
Rod Clark ◽  
John Karpinsky ◽  
Gregg Borek ◽  
Eric Johnson
Keyword(s):  
Real Time ◽  
High Speed ◽  
Time Correction

scholarly journals Near-surface real-time seismic imaging using parsimonious interferometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sherif M. Hanafy ◽  
Hussein Hoteit ◽  
Jing Li ◽  
Gerard T. Schuster
Keyword(s):  
Fluid Flow ◽  
Real Time ◽  
Temporal Resolution ◽  
Seismic Imaging ◽  
Time Lapse ◽  
Rock Properties ◽  
Recording Time ◽  
Near Surface ◽  
Arrival Times ◽  
Order Of Magnitude

AbstractResults are presented for real-time seismic imaging of subsurface fluid flow by parsimonious refraction and surface-wave interferometry. Each subsurface velocity image inverted from time-lapse seismic data only requires several minutes of recording time, which is less than the time-scale of the fluid-induced changes in the rock properties. In this sense this is real-time imaging. The images are P-velocity tomograms inverted from the first-arrival times and the S-velocity tomograms inverted from dispersion curves. Compared to conventional seismic imaging, parsimonious interferometry reduces the recording time and increases the temporal resolution of time-lapse seismic images by more than an order-of-magnitude. In our seismic experiment, we recorded 90 sparse data sets over 4.5 h while injecting 12-tons of water into a sand dune. Results show that the percolation of water is mostly along layered boundaries down to a depth of a few meters, which is consistent with our 3D computational fluid flow simulations and laboratory experiments. The significance of parsimonious interferometry is that it provides more than an order-of-magnitude increase of temporal resolution in time-lapse seismic imaging. We believe that real-time seismic imaging will have important applications for non-destructive characterization in environmental, biomedical, and subsurface imaging.

scholarly journals Utilisation of CryoSat-2 SAR altimeter in operational ice charting

2016 ◽  
Vol 10 (1) ◽  
pp. 121-131 ◽  
Author(s):  
E. Rinne ◽  
M. Similä
Keyword(s):  
Synthetic Aperture Radar ◽  
Real Time ◽  
Training Data ◽  
Synthetic Aperture ◽  
First Year ◽  
Success Rates ◽  
Hit Rate ◽  
Snow Conditions ◽  
Simple Product ◽  
Barents And Kara Seas

Abstract. We present methods to utilise CryoSat-2 (CS-2) synthetic aperture radar (SAR) mode data in operational ice charting. We compare CS-2 data qualitatively to SAR mosaics over the Barents and Kara seas. Furthermore, we compare the CS-2 to archived operational ice charts. We present distributions of four CS-2 waveform parameters for different ice types as presented in the ice charts. We go on to present an automatic classification method for CS-2 data which, after training with operational ice charts, is capable of determining open ocean from ice with a hit rate of  >  90 %. The training data are dynamically updated every 5 days using the most recent 15 days of CS-2 data and operative ice charts. This helps the adaption of the classifier to the evolving ice/snow conditions throughout winter. The classifier is also capable of detecting three different ice classes (thin and thick first-year ice as well as old ice) with success rates good enough for the output to be usable to support operational ice charting. Finally, we present a near-real-time CS-2 product just plotting the waveform characteristics and conclude that even such a simple product is usable for some of the needs of ice charting.

scholarly journals Reliable real-time Polar Cap (PC) indices for space weather monitoring and forecasts

2018 ◽  
Vol 8 ◽  
pp. A49 ◽  
Author(s):  
Peter Stauning
Keyword(s):  
Real Time ◽  
Space Weather ◽  
International Association ◽  
Magnetic Activity ◽  
Magnetic Data ◽  
Polar Cap ◽  
International Scientific Community ◽  
Order Of Magnitude ◽  
General Basis ◽  
Index Calculation

The Polar Cap (PC) indices were approved by the International Association for Geomagnetism and Aeromony (IAGA) by Resolution No. 3 (2013) noting that “IAGA … recommends use of the PC index by the international scientific community in its near-real time and definitive forms”. PC indices were made available in 2014 at the web portal http://pcindex.org holding near-real time as well as final index values. The near-real time PC index values are not permanently available. However, analyses of indices on basis of occasional downloads have detected differences between near-real time and final PC indices of up to 3.65 mV/m (Stauning, 2018b, Ann Geophys, 36, 621–631). At such differences, one or the other index may indicate (or hide) strong geomagnetic activity without justification in the actual conditions. The present work has disclosed the cause of observed large differences between real-time and final PC index values in the IAGA-endorsed versions. In addition, anticipated differences are derived on a general basis from the available basic magnetic data by using the index calculation procedures and calibration constants provided by the PC index suppliers. It is shown that corresponding or even larger anomalies are expected to be common during moderate to strong magnetic activity where the near-real time PC indices might otherwise prove very useful for space weather monitoring, e.g., for power grid protection. An alternative real-time PC index derivation scheme described here reduces the excessive differences between real-time and final PC index values by an order of magnitude.

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