Helicopter-borne measurements of sea ice thickness, using a small and lightweight, digital EM system

Abstract

Sea ice is an important climate variable and is also an obstacle for marine operations in polar regions. We have developed a small and lightweight, digital frequency-domain electromagnetic-induction (EM) system, a so-called EM bird, dedicated for measurements of sea ice thickness. 3.5 m long and weighing only 105 kg, it can easily be shipped to remote places and can be operated from icebreakers and small helicopters. Here, we describe the technical design of the bird operating at two frequencies of f1 = 3.68 kHz and f2 = 112 kHz, and study its technical performance. On average, noise amounts to ±8.5 ppm and ±17.5 ppm for f1 and f2, respectively. Electrical drift amounts to 200 ppm/h and 2000 ppm/h for f1 and f2, during the first 0.5 h of operation. It is reduced by 75% after two hours. Calibration of the Inphase and Quadrature ppm signals varies by 2 to 3%. A sensitivity study shows that all these signal variations do affect the accuracy of the ice thickness retrieval, but that it remains better than ±0.1 m over level ice in most cases.This accuracy is also confirmed by means of comparisons of the helicopter EM data with other thickness measurements. The paper also presents the ice thickness retrieval from single component Sea ice is an important climate variable and is also an obstacle for marine operations 3 in polar regions. We have developed a small and lightweight, digital frequency-4 domain electromagnetic-induction (EM) system, a so-called EM bird, dedicated for 5 measurements of sea ice thickness. 3.5 m long and weighing only 105 kg, it can 6 easily be shipped to remote places and can be operated from icebreakers and small 7 helicopters. Here, we describe the technical design of the bird operating at two 8 frequencies of f1 = 3.68 kHz and f2 = 112 kHz, and study its technical performance. 9On average, noise amounts to ±8.5 ppm and ±17.5 ppm for f1 and f2, respectively. 10Electrical drift amounts to 200 ppm/h and 2000 ppm/h for f1 and f2, during the first 11 0.5 h of operation. It is reduced by 75% after two hours. Calibration of the Inphase 12and Quadrature ppm signals varies by 2 to 3%. A sensitivity study shows that all 13 these signal variations do affect the accuracy of the ice thickness retrieval, but that it 14 remains better than ±0.1 m over level ice in most cases. This accuracy is also 15 confirmed by means of comparisons of the helicopter EM data with other thickness 16 measurements. The paper also presents the ice thickness retrieval from single

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

“…Within the MIZ and PIZ, Terra-Synthetic Aperture Radar (TerraSAR) images and airborne electromagnetic (AEM)-measurements 40 were used to locate areas of thin, less-deformed and thick, highly deformed sea-ice habitats. The difference between the mean and the modal sea-ice thickness indicates the degree of seaice deformation: the larger the difference, the higher the deformation of sea ice.…”

SMOS-derived thin sea ice thickness: algorithm baseline, product specifications and initial verification

“…EM-Bird consists of a laser altimeter and an assembly of coils that transmit and receive low-frequency EM fields. Utilizing the contrast of electrical conductivity between sea water and ice, EM-Bird can determine the distance to the ice-water interface (Haas et al, 2009). The laser altimeter yields the distance to the uppermost reflecting surface.…”

The Spring-Time Boundary Layer in the Central Arctic Observed during PAMARCMiP 2009

“…The EM Bird's height above the surface of the snow, ice or water is measured with a laser altimeter. The difference between both measurements corresponds to the total (ice plus snow) thickness [38]. The thickness estimates have an accuracy of ±0.1 m over level ice [38].…”

“…The difference between both measurements corresponds to the total (ice plus snow) thickness [38]. The thickness estimates have an accuracy of ±0.1 m over level ice [38]. The ice thickness is averaged over the horizontal footprint of about 50 m. Measurements were performed at flying altitudes of approximately 100 m, with the EM bird operated 20 m above the ice surface using a 80 m long towing rope.…”