Fixed-wing Airborne Research Articles

The Test Flight of iFTEM-I Fixed-Wing Airborne Time-Domain Electromagnetic System in Binxian, Heilongjiang Province, China

The fixed-wing time-domain airborne electromagnetic method (FTEM) has been widely used in metal mining exploration, groundwater mapping and other fields worldwide, and in recent decades, its use has gradually also become more prevalent in China. The first generation of the fixed-wing time-domain airborne electromagnetic system (iFTEM-I), researched and developed by the Institute of Geophysical and Geochemical Exploration (IGGE), has been demonstrated in recent years. In this article, we introduce the brief working principle and system parameters of iFTEM-I, and we show that the effective prospecting depth of iFTEM-I is up to 350 m, which is indicated by a comparison of the results between iFTEM-I and a ground TEM system (TEM-30B) carried out in Binxian.

Six-degrees-of-freedom simulation model for future multi-megawatt airborne wind energy systems

Currently developed airborne wind energy systems have reached sizes of up to several hundred kilowatts. This paper presents the high-level design and a six-degrees-of-freedom model of a future fixed-wing airborne wind energy system operated in pumping cycles. This framework is intended to be used as an open-source reference system. The fixed-wing aircraft has a span of 42.5 m and produces a nominal electrical power of 3 MW. The ground station is modelled as a winch with a rotational degree of freedom describing the reel-in and reel-out motion, constant drum diameter and drive train inertia. A quasi-static approach is used to model the relatively stiff tether. The tether is discretised by 16 segments with variable length to account for reeling. A tracking controller ensures the kite's flight path during the autonomous pumping cycle operation. The controller alternates between crosswind figure-of-eight manoeuvres while reeling out and gliding on an arc-shaped path towards the ground station during retraction. The operational and controller parameters are determined using a CMA-ES evolution algorithm to maximise the average cycle power of a specific kite design at different wind speeds and given operational constraints. The algorithm identifies optimised flight paths for a range of wind speeds up to 30 m s−1 leading to a power curve with a cut-in wind speed of 10 m s−1 at operating altitude.

Electrical Launch Catapult and Landing Decelerator for Fixed-Wing Airborne Wind Energy Systems

This paper presents a (pre)feasibility study of the rail-based ultra-short launch and landing system ElektRail for fixed-wing airborne wind energy systems, such as Ampyx Power. The ElektRail concept promises airborne mass reductions through the elimination of landing gear as well as decreased landing stresses and ground stability requirements, opening possibilities for improved aerodynamics through a single fuselage configuration. Initially designed for operating fixed-wing drones from open fields, the ElektRail concept had to be significantly shortened for application in an airborne wind energy (AWE) context. This shorter size is required due to the much more limited space available at AWE sites, especially on offshore platforms. Hence, a performance enhancement using the integration of a bungee launching and landing system (BLLS) was designed and a system dynamics model for the launch and landing was derived. The results demonstrated the possibility for the ElektRail to be shortened from 140 m to just 19.3 m for use with an optimised tethered aircraft with a mass of 317 kg. A system length below 20 m indicates that an enhanced ElektRail launch and landing concept could be viable for airborne wind energy operations, even with relatively low-tech bungee cord boosters. Linear motor drives with a long stator linear motor actuator could potentially shorten the system length further to just 15 m, as well as provide better control dynamics. An investigation into improved AWE net power outputs due to reduced airborne mass and aerodynamic improvements remains to be conducted.

Adjudicating Perspectives on Forest Structure: How Do Airborne, Terrestrial, and Mobile Lidar-Derived Estimates Compare?

Applications of lidar in ecosystem conservation and management continue to expand as technology has rapidly evolved. An accounting of relative accuracy and errors among lidar platforms within a range of forest types and structural configurations was needed. Within a ponderosa pine forest in northern Arizona, we compare vegetation attributes at the tree-, plot-, and stand-scales derived from three lidar platforms: fixed-wing airborne (ALS), fixed-location terrestrial (TLS), and hand-held mobile laser scanning (MLS). We present a methodology to segment individual trees from TLS and MLS datasets, incorporating eigen-value and density metrics to locate trees, then assigning point returns to trees using a graph-theory shortest-path approach. Overall, we found MLS consistently provided more accurate structural metrics at the tree- (e.g., mean absolute error for DBH in cm was 4.8, 5.0, and 9.1 for MLS, TLS and ALS, respectively) and plot-scale (e.g., R2 for field observed and lidar-derived basal area, m2 ha−1, was 0.986, 0.974, and 0.851 for MLS, TLS, and ALS, respectively) as compared to ALS and TLS. While TLS data produced estimates similar to MLS, attributes derived from TLS often underpredicted structural values due to occlusion. Additionally, ALS data provided accurate estimates of tree height for larger trees, yet consistently missed and underpredicted small trees (≤35 cm). MLS produced accurate estimates of canopy cover and landscape metrics up to 50 m from plot center. TLS tended to underpredict both canopy cover and patch metrics with constant bias due to occlusion. Taking full advantage of minimal occlusion effects, MLS data consistently provided the best individual tree and plot-based metrics, with ALS providing the best estimates for volume, biomass, and canopy cover. Overall, we found MLS data logistically simple, quickly acquirable, and accurate for small area inventories, assessments, and monitoring activities. We suggest further work exploring the active use of MLS for forest monitoring and inventory.

The Scientific Operations of Snow Eagle 601 in Antarctica in the Past Five Austral Seasons

The Antarctic ice sheet and the continent both play critical roles in global sea level rise and climate change but they remain poorly understood because data collection is greatly limited by the remote location and hostile conditions there. Airborne platforms have been extensively used in Antarctica due to their capabilities and flexibility and have contributed a great deal of knowledge to both the ice sheet and the continent. The Snow Eagle 601 fixed-wing airborne platform has been deployed by China for Antarctic expeditions since 2015. Scientific instruments on the airplane include an ice-penetrating radar, a gravimeter, a magnetometer, a laser altimeter, a camera and a Global Navigation Satellite System (GNSS). In the past five austral seasons, the airborne platform has been used to survey Princess Elizabeth Land, the largest data gap in Antarctica, as well as other critical areas. This paper reviews the scientific operations of Snow Eagle 601 including airborne and ground-based scientific instrumentation, aviation logistics, field data acquisition and processing and data quality control. We summarize the progress of airborne surveys to date, focusing on scientific motivations, data coverage and national and international collaborations. Finally, we discuss potential regions for applications of the airborne platform in Antarctica and developments of the airborne scientific system for future work.

Measuring gravity gradient in rugged terrain: HeliFalcon survey in Aso-Oguni, Japan

Since the first Falcon AGG survey in 1999 (van Leuwen et al., 2000), fixed-wing airborne gravity gradiometry (AGG) has proved to be a valuable tool for mining and oil and gas explora¬tion (Dransfield, 2007). The more compact digital Falcon AGG allowed the system to be installed in a helicopter and helicopter AGG surveys began in 2006 (Boggs et al., 2007). Compared with fixed-wing aircraft, the helicopter platform can fly surveys low and slow, offering superior spatial resolution as well as an improved signal-to-noise ratio (Dransfield, 2007). The superior spatial resolution and improved signal-to-noise ratio provided by helicopter AGG enhances its capability to detect smaller targets and better delineate subtler features. Dransfield and Christensen (2013) reported a HeliFalcon performance of 6 Eo RMS at 45 m resolution in vertical gravity gradient, by far the finest spatial resolution of any airborne AGG system. Another advantage afforded by helicopter AGG is its capa¬bility to follow terrains more closely especially in areas of high relief. Christensen and Hodges (2013) compared the vertical grav¬ity gradient from HeliFalcon with the simulated fixed-wing result over the Iron Range survey in the Canadian Rocky Mountains where the terrain variation reaches 1900 m. They showed that in this terrain, a fixed-wing survey would have to fly at ground clearances of more than 1000 m for much of the survey area. This high ground clearance would have greatly suppressed the signal at short wavelengths and degraded the spatial resolution. In this paper, we look at the HeliFalcon AGG survey conducted in the Aso-Oguni area exploring for geothermal fields, examin the technical challenges presented by the rugged terrains, describe some aspects of the data acquisition and processing, and present the survey results.

DEM sourcing guidelines for computing 1 Eö accurate terrain corrections for airborne gravity gradiometry

In this paper we investigate digital elevation model (DEM) sourcing requirements to compute gravity gradiometry terrain corrections accurate to 1Eötvös (Eö) at observation heights of 80m or more above ground. Such survey heights are typical in fixed-wing airborne surveying for resource exploration where the maximum signal-to-noise ratio is sought. We consider the accuracy of terrain corrections relevant for recent commercial airborne gravity gradiometry systems operating at the 10Eö noise level and for future systems with a target noise level of 1Eö. We focus on the requirements for the vertical gradient of the vertical component of gravity (Gdd) because this element of the gradient tensor is most commonly interpreted qualitatively and quantitatively.Terrain correction accuracy depends on the bare-earth DEM accuracy and spatial resolution. The bare-earth DEM accuracy and spatial resolution depends on its source. Two possible sources are considered: airborne LiDAR and Shuttle Radar Topography Mission (SRTM). The accuracy of an SRTM DEM is affected by vegetation height. The SRTM footprint is also larger and the DEM resolution is thus lower. However, resolution requirements relax as relief decreases. Publicly available LiDAR data and 1arc-second and 3arc-second SRTM data were selected over four study areas representing end member cases of vegetation cover and relief.The four study areas are presented as reference material for processing airborne gravity gradiometry data at the 1Eö noise level with 50m spatial resolution. From this investigation we find that to achieve 1Eö accuracy in the terrain correction at 80m height airborne LiDAR data are required even when terrain relief is a few tens of meters and the vegetation is sparse. However, as satellite ranging technologies progress bare-earth DEMs of sufficient accuracy and resolution may be sourced at lesser cost. We found that a bare-earth DEM of 10m resolution and 2m accuracy are sufficient for achieving 1Eö accuracy in the terrain correction independent of relief or vegetation cover. For AGG systems operating at greater noise levels the 3arc-second SRTM is adequate for areas having tens of meters of relief and sparse vegetation and even for areas of greater relief and sparse vegetation if a constant elevation survey is flown at 80m above terrain peak.

Using the in-line component for fixed-wing EM 1D inversion

Numerous authors have discussed the utility of multicomponent measurements. Generally speaking, for a vertical-oriented dipole source, the measured vertical component couples to horizontal planar bodies while the horizontal in-line component couples best to vertical planar targets. For layered-earth cases, helicopter EM systems have little or no in-line component response and as a result much of the in-line signal is due to receiver coil rotation and appears as noise. In contrast to this, the in-line component of a fixed-wing airborne electromagnetic (AEM) system with large transmitter–receiver offset can be substantial, exceeding the vertical component in conductive areas. This paper compares the in-line and vertical response of a fixed-wing airborne electromagnetic (AEM) system using a half-space model and calculates sensitivity functions. The a posteriori inversion model parameter uncertainty matrix is calculated for a bathymetry model (conductive layer over more resistive half-space) for two inversion cases; use of vertical component alone is compared to joint inversion of vertical and in-line components. The joint inversion is able to better resolve model parameters. An example is then provided using field data from a bathymetry survey to compare the joint inversion to vertical component only inversion. For each inversion set, the difference between the inverted water depth and ship-measured bathymetry is calculated. The result is in general agreement with that expected from the a posteriori inversion model parameter uncertainty calculation.

LiDAR-Derived Surface Roughness Texture Mapping: Application to Mount St. Helens Pumice Plain Deposit Analysis

Statistical measures of patterns (textures) in surface roughness are used to quantitatively differentiate volcanic deposit facies on the Pumice Plain, on the northern flank of Mount St. Helens (MSH). Surface roughness values are derived from a Light Detection and Ranging (LiDAR) point cloud collected in 2004 from a fixed-wing airborne platform. Patterns in surface roughness are characterized using co-occurrence texture statistics. Pristine-pyroclastic, reworked-pyroclastic, mudflow, boulder beds, eroded lava flows, braided streams, and other units within the Pumice Plain are all found to have significantly distinct roughness textures. The MSH deposits are reasonably accessible, and the textural variations have been verified in the field. Results of this work indicate that by affecting the distribution of large clasts and tens-of-meter scale landforms, modification of pyroclastic deposits by lahars alters the morphology of the surface in detectable quantifiable ways. When a lahar erodes a pyroclastic deposit, surface roughness increases, as does the randomness in the deposit surface. Conversely, when a lahar deposits material, the resulting landforms are less rough but more random than pristine pumice-rich pyroclastic deposits. By mapping these relationships and others, volcanic deposit facies can be differentiated. This new method of mapping, based on roughness texture, has the potential to aid mapping efforts in more remote regions, both on this planet and elsewhere in the solar system.

Design on the Time-domain Airborne Electromagnetic Weak Signal Data Acquisition System

According to principle of transient electromagnetic method as well as its signal characteristics, this paper designed and implemented a time-domain airborne electromagnetic weak signal data acquisition system. With the use of the floating-point amplification technology, the system amplifies the weak transient electromagnetic signal dynamically. CPLD and DSP were used as the decoding control circuit and the main controller for processing the sampled data, respectively. The transient electromagnetic signal acquisition system, which was designed with a dynamic range up to 144dB and a sampling rate up to 100 kHz, meets the requirements of the high sampling rate with high precision and it has been applied in the time-domain fixed-wing airborne electromagnetic mineral exploration. DOI : http://dx.doi.org/10.11591/telkomnika.v12i1.4144

Case histories illustrating the characteristics of the HeliGEOTEM system

The HeliGEOTEM system was introduced in 2005 to provide higher resolution data than fixed-wing electromagnetic (EM) systems. The characteristics of HeliGEOTEM are illustrated by comparing the system with other airborne EM systems. A comparison with previous versions of HeliGEOTEM shows that, since 2005, the early-time information has improved allowing rapidly decaying responses to be identified. An improvement in the signal-to-noise ratio means the system is able to detect bodies at greater depth. A height attenuation test over the Nighthawk conductive body indicates that the latest system could see that target if it were buried 380 m below surface. Another target that is difficult to detect (Caber) is clearly seen on the HeliGEOTEM data.A comparison of field data at the Maimon deposit indicates that the helicopter DIGHEM frequency-domain system and the HeliGEOTEM time-domain system both acquire data with similar spatial wavelengths. Data collected away from the main ore body and along strike indicate that the HeliGEOTEM sees a less attenuated response from a deeper part of the body. Also, the HeliGEOTEM is able to estimate the conductivity, whereas the DIGHEM system cannot discriminate the conductance, it can only indicate that the body is highly conductive. The DIGHEM data, however, is better able to resolve the near-surface conductivity, and the spatial form of the DIGHEM data is simpler. The data acquired with multiple transmitter-receiver coil pairs (DIGHEM and HeliGEOTEM) provides information superior to single-component data.Tools used to display fixed-wing airborne EM data have been modified to work with HeliGEOTEM data. These tools can image the structure in cases where the ground is assumed to be comprised of a) horizontal layers or b) discrete conductors.A comparison of HeliGEOTEM with the helicopter RESOLVE and fixed-wing GEOTEM systems shows that the HeliGEOTEM is able to map most of the shallow features seen on the RESOLVE and to image the resistivity to depths comparable to the GEOTEM (in a moderately conductive environment).A traverse line from Australia over what is considered a difficult target (the Nepean Mine) demonstrates that the HeliGEOTEM system provides good signal-to-noise ratios. Using the z- and x-component data does a better job of defining the geometry of the target than using the z-component data alone.

Footprints of airborne electromagnetic systems over onedimensional Earths

We have used an inductive-limit model to compare footprint sizes for a variety of common airborne electromagnetic survey geometries. The model incorporates the flight height and orientation of the transmitter, and accounts for electromagnetic coupling between the induced current system and the receiver. Horizontal magnetic dipole transmitters are shown to have a smaller footprint than vertical magnetic dipole sources. Given typical survey heights for helicopter and fixed wing airborne electromagnetic systems, the helicopter VCX geometry has the smallest inductive-limit footprint (40 m), and the fixed-wing, towed bird system the largest (550 m for a system measuring the vertical component of B-field). We also present preliminary calculations of frequency-domain airborne electromagnetic footprint sizes for the case of finite frequency or half-space conductivity. The original definition of the footprint is extended to be the side length of the cubic volume, centred below the transmitter, which contains the induced currents responsible for 90% of the secondary field measured at the receiver. Inphase footprint size for a horizontal coplanar helicopter frequency-domain system is shown to increase from around 3.7 times the flight height at the inductive limit to >9 times the flight height for induction numbers <0.7. The analysis also shows that the quadrature footprint is approximately two-thirds that of the inphase footprint, suggesting a higher spatial resolution for this component.

Time-Lapse Airborne EM Surveys Across a Municipal Landfill

In contrast to the majority of historical landfills, modern municipal landfills are highly engineered and follow a contain and seal strategy of leachate management. The purpose of the management system is to render the waste products inert and environmentally safe. A requirement for monitoring and assessment of the installation on the scale of decades is a consequence of the strategy. Data obtained from two repeated fixed-wing airborne electromagnetic surveys across an active, municipal solid waste landfill are considered here. The time interval between the surveys is [Formula: see text]. In theory such data may be used to both test the isolation performance of the installation and to monitor mass (leachate) transport behaviour within the landfill structure. Single frequency [Formula: see text] data obtained at a similar density ([Formula: see text] flight line spacing) over the [Formula: see text] span are presented and compared. These data have an expected mean depth of investigation of about [Formula: see text] within the landfill. Half-space conductivity models are determined from the survey data by an inversion procedure. Conductivities within the landfill are observed to be three orders of magnitude above background. From the initial survey data, a specific distribution of high conductivity material can be identified in three of the landfill cells (peak values of [Formula: see text]). Four years later, a considerable redistribution of material is apparent in the results obtained across two of the cells (peak values of [Formula: see text]). A third cell shows no change. A subtraction of the two time-lapse conductivity models allows the dynamic components of the conductivity distribution (all increases with time) to be mapped within individual cells. All larger conductivity increases [Formula: see text] are confined to the operational landfill.

Simplified Electrical Structure Models at AEM Scales, Lawlers, Western Australia

Fixed wing airborne electromagnetic (AEM) data in Australia commonly exhibit numerous local responses, most of which have been attributed to regolith inhomogeneities rather than the isolated conductive targets of sulphide exploration. To define the regolith structures causing local AEM responses several steps are needed. The first involves selecting a geological mapping scale matched to the scale of an AEM system. Sensitivity analysis indicates that an AEM system has a limited range, and is generally insensitive to any features located more than 200 to 300m from the system. Generally, any confined conductive target cannot be detected at a distance more than a few times its lateral dimensions. With a nominal transmitter altitude of 120m, this would set (say) a 30m or 40m minimum size on any structure likely to produce an anomaly. Long narrow features can however gather current and be detectable. A mapping scale was therefore indicated in the range between 1:10,000 and 1:100,000.In the Lawlers district of WA, the electrical structure could be resolved into at most 3 layers, specifically a thin (commonly 0 to 10m), moderately resistive layer of alluvium/colluvium overlying a thick (commonly 30 to 50m) conductive layer of saprolite/sediments, overlying a relatively resistive basement. One or both of the upper layers are absent in some areas.Seven important structures were identified at Lawlers at the scales suggested above. Drillhole data, ground and airborne EM, and ground resistivity were used to define vertical and lateral variations of importance within this overall layering scheme. The three common electrical structures were classified as 1) Layer (locations far from lateral inhomogeneity), 2) Contact, and 3) Wedge models. Four less common structures were the 4) Variable basement topography, 5) Variable surface topography, 6) Lateral inhomogeneity, and 7) Palaeochannel models. Geological and physical reasoning constrain the permissible geometry and dimensions of each of these structures.

Novel dual frequency fixed-wing airborne EM system of Geological Survey of Finland (GTK)

The Geological Survey of Finland (GTK) has upgraded its airborne geophysical system by developing a new dual frequency airborne EM system for its DHC Twin Otter aircraft. The coils are mounted on the wingtips and the configuration for both coil pairs is vertical-coplanar. The lower frequency is 3.1 kHz, and it is ideal for mapping good conductors like base metal ore deposits in Precambrian bedrock. The upper frequency of the system (14.4 kHz) is suitable for engineering and environmental applications where the conductivities of the targets are not very high. The two frequencies together provide more information for detailed interpretation of subsurface resistivity structure. Technical specifications of the new system are presented and compared to those of the predecessor. Careful calibration of the system is of crucial importance in quantitative interpretations of measured data. The calibration of the system is verified by flying at different altitudes over the sea, which can be regarded as a homogeneous and conductive half-space. An interpretation example is also given where the use of dual frequency data significantly improves the inversion of model parameters compared to the single frequency inversion.

Airborne electromagnetic systems - 50 years of development

The initial successful test flights of the Stanmac-McPhar fixed-wing airborne EM (AEM) system in Canada during the summer of 1948 can nominally be called the birth of this branch of exploration geophysics. The discovery of the Heath Steele deposit in New Brunswick, Canada in 1954, as a result of an AEM survey, proved to be the catalyst for the development of additional AEM systems and the eventual application of AEM surveys worldwide.

A helicopter time-domain EM system applied to mineral exploration: system and data

David Fountain, Richard Smith, Tom Payne, and Jean Lemieux (Fugro Airborne Surveys) describe recent progress in developing helicopter systems for time-domain airborne electromagnetic surveys, once the ‘domain’ of fixed-wing aircraft. The first operational fixed-wing airborne electromagnetic (AEM) system was introduced in 1948 and was followed by the first operational helicopter AEM system in 1955 (Fountain, 1998; Fountain and Smith, 2003). There has been parallel development of both fixedwing and helicopter AEM since that time and, up to the early 1960s, all these systems were frequency-domain. However, since the late 1970s, fixed-wing AEM systems have been primarily time-domain while the helicopter systems remained primarily frequency-domain. With the new millennium, and especially since 2002/ 2003, there has been significant development and introduction of helicopter time-domain AEM systems (Boyko, et al., 2001; Balch et al., 2003; Eaton et al., 2004; Sorenson and Auken, 2004; Vrbancich and Fullagar, 2004; Witherly et al., 2004). The pace of introduction has been such that, today, the number of time-domain systems in use is equal to the number of frequency-domain systems. Fugro Airborne Surveys and its predecessor companies have been leaders in the continuing development of fixedwing AEM systems, including the introduction of the GEOTEM, MEGATEM, and TEMPEST systems (Smith and Annan, 1997; Lane et al., 2000; Smith, Fountain and Allard, 2003). By the same token, Fugro has been involved in the continuing development of helicopter frequency-domain AEM systems including DIGHEM and RESOLVE. Based upon this combined experience and seeing the need for a broader band, high power helicopter time-domain AEM system, Fugro has introduced the HeliGEOTEM system in 2005. This system brings together the proven GEOTEM/ MEGATEM technology with the greater operational flexibility and improved lateral resolution of helicoptermounted AEM systems.