Airborne Electromagnetic Sensing of Sea Ice Thickness

• Main Authors: Becker, Alex, Liu, Guimin
• Other Authors: CALIFORNIA UNIV BERKELEY DEPT OF MATERIALS SCIENCE AND MINERAL ENGINEERING
• Format: Text
• Language: English
• Published: 1988
• Subjects: Snow; Ice and Permafrost; Computer Programming and Software; Electricity and Magnetism; *DEPTH FINDING; *SEA ICE; THICKNESS; FORWARD AREAS; COMPUTATIONS; DETECTION; COMPUTERS; AIRBORNE; SOLUTIONS(GENERAL); HELICOPTERS; FLIGHT; TABLES(DATA); INVERSION; ELECTROMAGNETISM; HEIGHT; NOMOGRAPHS; FREQUENCY; DATA PROCESSING; SEA ICE KEELS; ELECTROMAGNETIC DETECTION; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA214460; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA214460

A conventional frequency domain helicopter-borne electromagnetic (HEM) system can be used to map sea ice keels with a reasonable degree of accuracy. A preliminary interpretation of the acquired data can be made manually with the help of a nomogram or automated with the use of a table look-up routine on a small computer. Such data may also be more accurately interpreted with the use of an adaptation of Occam's inversion. This scheme allows for the practical non-uniqueness of the inverse solution but selects the smoothest keel shape that is consistent with the field data. The inversion method is much more computationally intensive than the table look-up technique. While the latter can be implemented on a small computer to form an interactive in-flight interpretation system, the inversion technique involves many forward computations and , for the present, is best reserved for past flight data analysis. It is possible that this difficulty can be resolved with the use of specialized computing equipment. In the strict sense both proposed interpretation techniques are only suitable for use on data acquired over two dimensional features whose strike length (measured in a direction perpendicular to the flight line) is much greater than the flight height. Examination of the anomalies for three-dimensional keels however, reveals that good data interpretation is possible whenever the keel strike length exceeds the system height by a factor of three.