Bird orientation effects in quantitative airborne electromagnetic interpretation of pack ice thickness sounding

Changes in helicopter electromagnetic (HEM) bird orientation caused by bird swing occur continuously during normal surveying. These changes generate small, continuously varying errors in the measured HEM responses and in estimated bird altitude. These errors have been considered to be negligible in the past, and for small swings are certainly not critical to first-order interpretation. However, significant errors can occur during quantitative interpretation of HEM responses unless accurate estimates of bird attitude are recorded and used during interpretation. An example derived from a precision sea ice thickness survey illustrates two components of orientation-generated error. Fortunately, technological advances have simplified the acquisition of bird attitude data.