Helicopter-borne Survey Research Articles

A novel semiairborne frequency-domain controlled-source electromagnetic system: Three-dimensional inversion of semiairborne data from the flight experiment over an ancient mining area near Schleiz, Germany

We have developed a novel semiairborne frequency-domain electromagnetic (EM) system and successfully tested it within the DESMEX project. The semiairborne approach relies on the fact that part of the system is positioned on the ground and the rest is airborne. This allows us to take advantage of ground and airborne techniques. In particular, a high-moment transmitter can be installed on the earth’s surface, which enables us to inject and induce strong EM fields in the subsurface. Moreover, galvanic coupling is possible, which is an advantage if additional ground stations are deployed. The airborne receivers allow easier, significantly faster, and more uniform spatial coverage of the study area than the ground receivers. In our implementation, transmitters and electric field receivers are installed on the ground. Magnetic field sensors, such as commercially available fluxgate, total field magnetometers, and newly developed induction coils, are installed on a helicopter-towed bird. First, we describe the results of a semiairborne survey performed in a selected area with ancient mining located in the Saxothuringian zone near Schleiz, Germany. A 3D semiairborne inversion model represents several conductive anomalies, which agree well with the outcrop of alum shale formations at the surface. In addition, the shallow parts of the semiairborne model are compared with the result of an independent helicopter-borne survey, which consists of stepwise 1D models.

Pros and Cons in Helicopter-Borne GPR Data Acquisition on Rugged Mountainous Areas: Critical Analysis and Practical Guidelines

We critically discuss both advantages and limitations of helicopter-borne GPR surveys in rugged mountainous areas by analyzing a pseudo 3D data set acquired over the Marmolada Glacier, which constitutes the largest ice body in the Dolomites (Eastern Alps) and contains several peculiar features both in terms of the internal structures and the surrounding topography. In this paper we analyze several possible issues that can be encountered when performing airborne surveys in mountain regions, related to both the local conditions in the particular survey areas, and the general performance of the data acquisition equipment, which includes the GPR device, the GPS system, and the helicopter itself. Based on our analyses and observations, we propose a few guidelines and optimization strategies in order to address several issues, including the choice of various data acquisition parameters, interpretation problems related to curvilinear or irregular flight paths, and trace positioning errors caused by GPS malfunctioning or oscillating antennas. Such results have general validity and can be used for helicopter-borne survey planning, as well as for data analysis and interpretation.

Potential field continuation between arbitrary surfaces — Comparing methods

The continuation of potential field data from one irregular surface to another, not always horizontal, is often a necessary component within the data processing and interpretation stream. The most common requirement is to reduce field values (or some related component or derivative) to a horizontal plane, to facilitate further quantitative processing. Methods available to continue data comprise two main approaches. The first (source-based) involves calculating a source distribution that produces a fit to the data and can be used to calculate the field at any other point above. The second (field-based) requires no source determinations and deals with only fields but may involve calculating the field on some intermediate surface. Nine different continuation methods were compared (four source based and five field based) through synthetic tests and on real data from a helicopter-borne survey in Yukon, Canada. The preferred methods of Guspi and Hansen are those that do not involve any theoretical or geometric approximations and involve intermediate calculations on a plane or surface close to the observation surface. The Guspi approach is faster, based on using frequency-domain processing, but the Hansen method uses equivalent sources close enough to and consistently below the observation surface so that no low-pass filtering needs to be used.

Design and Validation of a Multimode Multifrequency VHF/UHF Airborne Radar

This letter deals with the design, realization, and validation of a multimode/multifrequency airborne radar designed for both surface and subsurface prospections. The system operates in the frequency band from very high frequency (VHF) to ultrahigh frequency (UHF) and works in two different modes: 1) a nadir-looking sounder in the VHF band (carrier frequency of 163 MHz); and 2) a side-looking imager (i.e., synthetic aperture radar) in the UHF band with two channels at 450 and 860 MHz, respectively. The system validation has been carried out for the “sounder” mode due to helicopter-borne surveys carried out over an area in the Campania region, Southern Italy. The surveys have provided a first proof of system capability in obtaining useful information about the surface and shallower subsurface layers over a large scale and in a relatively short time. In particular, the data collected by the sounder have been processed by means of a microwave tomographic reconstruction approach, and features consistent with tunnels buried at a depth of 15 m have been identified.

Spatial distribution and habitat selection of Barrow’s and Common goldeneyes wintering in the St. Lawrence marine system

Our study addresses winter spatial distribution of Barrow’s Goldeneyes ( Bucephala islandica (Gmelin, 1789)) and Common Goldeneyes ( Bucephala clangula (L., 1758)) at the scale of the St. Lawrence marine system (estuary and northwestern gulf), eastern Canada. Our objectives were (i) to identify and compare the physical factors that control their distributions, (ii) to quantify the level of sympatry between the two species, and (iii) to compare their distribution patterns. We analyzed large-scale synoptic views of winter distribution of both goldeneye species obtained through helicopter-borne surveys. Habitat description was obtained through spatial analyses and remote sensing. Both species showed strong preference for the tidal zone and river mouths. A multiscale analysis showed a decreasing level of sympatry as spatial resolution was refined. The distribution of the Barrow’s Goldeneye was more clustered compared with that of the Common Goldeneye, and Barrow’s Goldeneye was repeatedly observed in the same few areas. A use-availability analysis identified the northern coast of the St. Lawrence estuary as the main wintering ground for Barrow’s Goldeneye in eastern North America.

Aeromagnetic survey of the Somma-Vesuvius volcanic area

In this paper we present and discuss the results of a geophysical airborne survey carried out in the Somma-Vesuvius volcanic area, Southern Italy, in 1999. The helicopter-borne survey was aimed at giving new detailed insights into the distribution of the magnetization of the area and, therefore, into the volcanological characteristics of the region, enhancing the knowledge given by a previous low resolution survey carried out at a regional scale by Agip. The new survey was carried out by flying on a surface parallel to the topography of the area, along flight lines spaced 600 m apart. The obtained total field map is dominated by a large anomaly related to the Mt. Somma-Vesuvius complex itself and characterized by a roughly elliptical shape. High-frequency anomalies occur in the edifice and in the area east of it, partly produced by cultural noise due to the densely inhabited area. The compilation of the maps of the analytic signal and of the horizontal derivative of the field allowed the location of the lateral boundaries of the magnetic sources of the area and represents a first step toward the interpretation of the maps in terms of geological structures.

Estimation of landslide area by helicopter-borne survey

Estimation of landslide area by helicopter-borne survey

HELP ACEH – A post‐tsunami helicopter‐borne groundwater project along the coasts of Aceh, northern Sumatra

ABSTRACTAfter the earthquake and the tsunami event on December 26, 2004, the Indonesian and German governments set up a project dedicated to re‐installing the public life of the people in the coastal region of Aceh Province in northern Sumatra, Indonesia. As the tsunami waves caused large‐scale coastal salt‐water intrusions and destroyed thousands of shallow drinking‐waterwells, the focal point was water assessment along the shorelines of Aceh about nine months after the tsunami. The target areas were the city of Banda Aceh and the district of Aceh Besar on the north coast and the area on the west coast between the towns of Calang (district of Aceh Jaya) and Meulaboh (district of Aceh Barat). A helicopter‐borne survey including electromagnetics (HEM), magnetics and gamma‐ray spectrometry was conducted by the airborne group of the German Federal Institute for Geosciences and Natural Resources from August to October 2005. The HEM surveys revealed shallow coastal salt‐water occurrences caused by the tsunami, deep salt‐water occurrences up to several kilometres inland, and a number of potential freshwater resources. Numerous requests for information on the geological and hydrogeological situation at sites for planned water‐wells were successfully evaluated.

Risk management for the new tunnelling construction using other tunnel records and helicopter borne survey in accretionary complex

The accurate evaluation for geotechnical properties of underground is very important for process control and mitigation of geotechnical risk during the tunnel construction. In particular, more detailed surveys are required for areas with complicated geological structures such as accretionary complexes than normal areas. The authors examined the applicability and the effectiveness of magnetic prospecting in the helicopter borne surveys for the geological investigation of tunnel ground which was constructed in the accretionary complex area in Hokkaido, North Japan. As a result of comparisons with the construction records and magnetic intensity distribution, the final tunnel displacement differs depending on lithofacies and density of the fracture and shear zones. These results suggest that the state of rock distribution in this area could be determined based on relative differences in magnetic susceptibility or magnetic intensity distribution. (A) This paper was presented at Safety in the underground space – Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.

Mapping Groundwater in Regolith and Fractured Bedrock using Ground and Airborne Geophysics: Case studies from Malawi and Brazil

Water supply exploration in rural regions of eastern Malawi (Africa) and northeastern Brazil (South America) is complicated by the highly irregular nature of aquifers in weathered regolith and crystalline bedrock. Drilling success can be as low as 30%. Improvements in the success rate can be achieved by using simple geophysical investigations to target the thickest zones of weathering. Sophisticated geophysical surveys that image the full range in aquifer types can further improve the success rate to 70%. In Malawi, a total of 250 hand pumps were sited using a combination of borehole geophysics (natural gamma, conductivity and magnetic susceptibility), ground-based frequency-domain electromagnetics (Geonics EM34 and Apex Max-Min), and two-dimensional electrical resistivity imaging. In a similar terrain in northeastern Brazil, resistivity profiling and Very Low Frequency electromagnetic surveys are the mainstay of water exploration. A recent project introduced ground-based and airborne frequency-domain electromagnetics (Geonics EM34 and Aerodat helicopter electromagnetics) to improve the imaging of complex fracture zones and the detection of saline aquifers. Helicopter-borne surveys are a valuable tool in groundwater exploration because they cover large areas at high resolution. In both case studies, inversion of geophysical data integrated with remote sensing images and hydrogeology has increased the chances of drilling successful wells and finding potable water for rural communities.

Merging aeromagnetic data collected at different levels: the GEOMAUD survey

As part of the German GEOMAUD-expedition an aeromagnetic survey was carried out in Central Queen Maud Land. The helicopter-borne survey was designed in a conventional form of a regional survey with a spacing of profile-lines of 4.4 km. Due to terrain considerations - surveying from the coast across the mountain ranges to the high altitudes of the polar plateau - the survey was split into two sections flown at different constant levels. Over the coastal part survey elevation was 570 m (above sea level) while for the mountain section 2845 m was chosen. Both survey parts were processed separately. The low level section was upward continued before merging with the high level section. Though this leads to a homogeneous magnetic anomaly map, in some applications it may be more advantageous to present the anomalies of the magnetic field in original survey levels as a simple combined map because small scale features are preserved and can be used in recognizing magnetic units and patterns for geological/geophysical interpretation.