Sea ice as an evaluation target for HEM modelling and inversion

Pfaffling, Andreas; Reid, James

doi:10.1016/j.jappgeo.2008.05.010

Cited by 15 publications

(13 citation statements)

References 25 publications

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“…A laser altimeter is used to determine the vertical distance between the EM coils and the snow or ice surface, thus allowing the combined snow and sea-ice thicknesses to be estimated. For a typical flight height of 10-15 m, the accuracy of the combined snow and ice thicknesses was 0.1 m (Pfaffling and Reid, 2009). Since we are primarily interested in sea-ice thickness, we need to independently determine snow thickness.…”

Section: Hem Sea-ice Thickness Determinationmentioning

confidence: 99%

“…The HEM instrument averaged the ice thickness within its footprint, which was approximately 70 m for the inphase signal of the AWI EM-Bird towed at a height of 15 m. Consequently, the instrument may have underestimated maximum thicknesses of ice ridges by up to 75 % (Pfaffling and Reid, 2009). However, since the footprint effect acts like a smoothing average filter along the transect, the mean thickness for a sufficiently long transect is within the specified 0.1 m accuracy (Hendricks, 2009).…”

Section: Hem Sea-ice Thickness Determinationmentioning

confidence: 99%

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A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

et al. 2013

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Abstract.A combined interpretation of synthetic aperture radar (SAR) satellite images and helicopter electromagnetic (HEM) sea-ice thickness data has provided an estimate of sea-ice volume formed in Laptev Sea polynyas during the winter of 2007/08. The evolution of the surveyed sea-ice areas, which were formed between late December 2007 and middle April 2008, was tracked using a series of SAR images with a sampling interval of 2-3 days. Approximately 160 km of HEM data recorded in April 2008 provided seaice thicknesses along profiles that transected sea ice varying in age from 1 to 116 days. For the volume estimates, thickness information along the HEM profiles was extrapolated to zones of the same age. The error of areal mean thickness information was estimated to be between 0.2 m for younger ice and up to 1.55 m for older ice, with the primary error source being the spatially limited HEM coverage. Our results have demonstrated that the modal thicknesses and mean thicknesses of level ice correlated with the sea-ice age, but that varying dynamic and thermodynamic sea-ice growth conditions resulted in a rather heterogeneous sea-ice thickness distribution on scales of tens of kilometers. Taking all uncertainties into account, total sea-ice area and volume produced within the entire surveyed area were 52 650 km 2 and 93.6 ± 26.6 km 3 . The surveyed polynya contributed 2.0 ± 0.5 % of the sea-ice produced throughout the Arctic during the 2007/08 winter. The SAR-HEM volume estimate compares well with the 112 km 3 ice production calculated with a high-resolution ocean sea-ice model. Measured modal and mean-level ice thicknesses correlate with calculated freezing-degree-day thicknesses with a factor of 0.87-0.89, which was too low to justify the assumption of homogeneous thermodynamic growth conditions in the area, or indicates a strong dynamic thickening of level ice by rafting of even thicker ice.

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Section: Hem Sea-ice Thickness Determinationmentioning

confidence: 99%

Section: Hem Sea-ice Thickness Determinationmentioning

confidence: 99%

A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

et al. 2013

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“…Single-frequency systems are usually optimized to the frequency that is least sensitive to the ice conductivity (typically 4 kHz) and derives reliable ice thickness without multilayer inversion. The 3D forward modeling revealed in detail that the sounding depth of a 4 kHz signal is insufficient to resolve deep, highly porous ridge structures (Hendricks, 2009) and inversion studies showed that several appropriately distributed frequencies (e.g., 30 and 60 kHz as used by DFO) are needed to resolve ice conductivity (Pfaffling and Reid, 2009).…”

Section: D Em Modelingmentioning

confidence: 99%

Progressing from 1D to 2D and 3D near-surface airborne electromagnetic mapping with a multisensor, airborne sea-ice explorer

2012

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The polar ocean's sea ice cover is an unconventional and challenging geophysical target. Helicopter-electromagnetic (HEM) sea-ice thickness mapping is currently limited to 1D interpretation due to traditional procedures and systems. These systems are mainly sensitive to layered structures, ideally set for the widespread flat (level) ice type. Because deformed sea ice (e.g., pressure ridges) is 3D and usually also heterogeneous, ice thickness errors up to 50% can be observed for pressure ridges using 1D approximations for the interpretation of HEM data. We researched a new generation multisensor, airborne sea ice explorer (MAiSIE) to overcome these limitations. Three-dimensional finite-element modeling enabled us to determine that more than one frequency is needed, ideally in the range 1-8 kHz, to improve thickness estimates of grounded sea-ice pressure ridges that are typical of 3D sea ice structures.With the MAiSIE system, we found a new electromagnetic concept based on one multifrequency transmitter loop and a 3C receiver coil triplet with active digital bucking. The relatively small weight of the EM components freed enough payload to include additional scientific sensors, including a cross-track lidar scanner and high-accuracy inertial-navigation system combined with dual-antenna differential GPS. Integrating the 3D ice-surface topography obtained from the lidar with the EM data at frequencies from 500 Hz to 8 kHz in x-, y-, and z-directions, significantly increased the accuracy of sea-ice pressure-ridge geometry derived from HEM data. Initial test flight results over open water showed the proof-of-concept with acceptable sensor drift and receiver sensitivity. Noise levels were relatively high (20-250 parts-per-million) due to unwanted interference, leaving room for optimization. The 20 ppm noise level at 4.1 kHz is sufficient to map level ice thickness with 10 cm precision for sensor altitudes below 13 m.

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“…The seawater conductivity is typically 2.5 -2.6 S/m, approximately two orders of magnitude larger than sea ice conductivity and at the relatively low frequencies used in frequency-domain AEM systems (typically 50 Hz to 100 kHz), the primary and induced secondary magnetic fields effectively "see through" the sea ice. The AEM system can therefore be used to measure sea ice thickness and also sub-ice bathymetry (Kovacs & Valleau, 1987;Pfaffling & Reid, 2009) in shallow waters. This same EM induction technique can also be applied using ship-borne sensors (Reid et al, 2003a;Reid et al, 2003b;Haas et al, 1997).…”

Section: Airborne Electromagnetic Bathymetry and Sea Ice Thickness Mementioning

confidence: 99%

Airborne Electromagnetic Bathymetry

Vrbancich¹

2012

Bathymetry and Its Applications

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Sea ice as an evaluation target for HEM modelling and inversion

Cited by 15 publications

References 25 publications

A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

Progressing from 1D to 2D and 3D near-surface airborne electromagnetic mapping with a multisensor, airborne sea-ice explorer

Airborne Electromagnetic Bathymetry

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