An inductive‐limit model has been used to determine footprint sizes for a variety of common airborne electromagnetic‐survey geometries. The model accounts both for variations in the height and orientation of the electromagnetic transmitter, and 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. We show that footprint sizes for the vertical coaxial and vertical coplanar geometries are essentially identical, provided the transmitter‐receiver separation is much less than the transmitter height. The inductive‐limit horizontal‐component footprint for a fixed‐wing horizontal‐loop transmitter with a towed‐bird receiver is shown to be two‐thirds of that for the vertical component.

A comparison of the inductive-limit footprints of airborne electromagnetic configurations

Preliminary results are presented from the first validation of geophysical data products (ice concentration, snow thickness on sea ice (h(sub s) and ice temperature (T(sub i))fr om the NASA EOS Aqua AMSR-E sensor, in East Antarctica (in September-October 2003). The challenge of collecting sufficient measurements with which to validate the coarse-resolution AMSR-E data products adequately was addressed by means of a hierarchical approach, using detailed in situ measurements, digital aerial photography and other satellite data. Initial results from a circumnavigation of the experimental site indicate that, at least under cold conditions with a dry snow cover, there is a reasonably close agreement between satellite- and aerial-photo-derived ice concentrations, i.e. 97.2+/-.6% for NT2 and 96.5+/-2.5% for BBA algorithms vs 94.3% for the aerial photos. In general, the AMSR-E concentration represents a slight overestimate of the actual concentration, with the largest discrepancies occurring in regions containing a relatively high proportion of thin ice. The AMSR-E concentrations from the NT2 and BBA algorithms are similar on average, although differences of up to 5% occur in places, again related to thin-ice distribution. The AMSR-E ice temperature (T(sub i)) product agrees with coincident surface measurements to approximately 0.5 C in the limited dataset analyzed. Regarding snow thickness, the AMSR h(sub s) retrieval is a significant underestimate compared to in situ measurements weighted by the percentage of thin ice (and open water) present. For the case study analyzed, the underestimate was 46% for the overall average, but 23% compared to smooth-ice measurements. The spatial distribution of the AMSR-E h(sub s) product follows an expected and consistent spatial pattern, suggesting that the observed difference may be an offset (at least under freezing conditions). Areas of discrepancy are identified, and the need for future work using the more extensive dataset is highlighted.

/pdf/arise-antarctic-remote-ice-sensing-experiment-in-the-east-3cu145ile4.pdf

ARISE (Antarctic Remote Ice Sensing Experiment) in the East 2003: validation of satellite-derived sea-ice data products

Sea ice as an evaluation target for HEM modelling and inversion

Helicopter electromagnetic sea ice thickness estimation : an induction method in the centimetre scale = Meereisdickenbestimmung mittels Hubschrauberelektromagnetik : ein Induktionsverfahren im Zentimeterbereich

Airborne, ship-borne and surface low-frequency electromagnetic (EM) methods have become widely applied to measure sea-ice thickness. EM responses measured over sea ice depend mainly on the sea-water conductivity and on the height of the sensor above the sea-ice-sea-water interface, but may be sensitive to the sea-ice conductivity at high excitation frequencies. We have conducted in situ measurements of direct-current conductivity of sea ice using standard geophysical geoelectrical methods. Sea-ice thickness estimated from the geoelectrical sounding data was found to be consistently underestimated due to the pronounced vertical-to-horizontal conductivity anisotropy present in level sea ice. At five sites, it was possible to determine the approximate horizontal and vertical conductivities from the sounding data. The average horizontal conductivity was found to be 0.017 S m -1 , and that in the vertical direction to be 9-12 times higher. EM measurements over level sea

/pdf/in-situ-measurements-of-the-direct-current-conductivity-of-3t1whtpxwt.pdf

In situ measurements of the direct-current conductivity of Antarctic Sea ice: implications for airborne electromagnetic Sounding of Sea-ice thickness

A new, extremely small helicopter-borne frequency-domain electromagnetic induction sensor (HEM bird) has been developed by Alfred-Wegener-Institute (AWI), Aerodata Systems GmbH, Ferra Dynamics Inc., and K.-P. Sengpiel for extensive surveys of sea-ice thickness. In the summer of 2001 it has been successfully operated for the first time from the German research icebreaker Polarstern over sea ice in the central Arctic. This paper describes the system and shows some results of the first deployment.

First operation of AWI HEM-bird for sea-ice thickness sounding

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First operation of AWI HEM-bird for sea-ice thickness sounding